Performance of adaptive matched filter receivers over fading multipath channels
NASA Astrophysics Data System (ADS)
Pahlavan, Kaveh; Matthews, James W.
1990-12-01
A unified discrete channel model from the information source up to the sampler was developed for fading multipath channels. Different methods for adaptive channel measurement are studied. The performance of a discrete matched filter using different adaptation techniques and working over a troposcatter channel is predicted. It is shown that the effects of channel measurement noise are less damaging for the decision-directed adaptation technique as compared to any kind of reference-directed adaptation.
Utilizing space frequency COFDM on multipath fading channels
NASA Astrophysics Data System (ADS)
Kellerman, Fred C.
2007-04-01
This paper will investigate the use of an enhanced rate one Alamouti Space Frequency (SF) multiple antenna Orthogonal Frequency Division Multiplex (OFDM) radio communication system. A two transmit, single receive antenna system will be simulated to operate under conditions of multipath fading with noise. A simple modification to the standard coherent Alamouti receive combiner will be applied and shown to improve bit error rate (BER) performance on rapidly fading multipath HF channels. Orthogonal Frequency Division Multiplexing frequency domain techniques will be utilized to effectively eliminate the Inter-Symbol Interference (ISI) resulting from the effects of multipath. Numerically simulated results will be shown for several multipath fading High Frequency (HF) radio channels. Inner convolutional error correction coding will be applied in addition to the Alamouti coding and numerically simulated BER results presented. Various HF channel conditions will be simulated including the 2 ms, 10 Hz, 2 ms, 5 Hz, CCIR poor (2 ms, 1 Hz) and extra poor (2 ms, 2 Hz) channel conditions. Performance under conditions of correlated transmit antennas will also be investigated.
Multicarrier chaotic communications in multipath fading channels without channel estimation
Wang, Shilian Zhang, Zhili
2015-01-15
A multi-carrier chaotic shift keying(MC-CSK) communication scheme with low probability of interception(LPI) is proposed in this article. We apply chaotic spreading sequences in the frequency domain, mapping a different chip of a chaotic sequence to an individual orthogonal frequency division multiplexing(OFDM) subcarrier. In each block size of $M$ OFDM symbols, we use one pilot OFDM symbol inserted time-spaced in all-frequency to transmit the reference chaotic signal and use the other M-1 OFDM symbols to transmit the information-bearing signals each spreaded by the reference chaotic signal. At the receiver, we construct a differential detector after DFT and recover the information bits from the correlations between the pilot OFDM symbol and the other M-1 OFDM symbols in each block size of M. Performance analysis and computer simulations show that the MC-CSK outperforms differential chaos shift keying(DCSK) in AWGN channels with high bandwidth efficiency for the block size of M=2 and that the MC-CSK exploits effectively the frequent diversity of the multipath channel.
Design of a robust underwater acoustic communication system over multipath fading channels
NASA Astrophysics Data System (ADS)
Kim, Jangeun; Shim, Taebo
2012-11-01
Due to the surface and bottom constraints of the underwater acoustic channel (UAC) in shallow waters, multipath fading occurs and causes degradation of the signal for the UAC system. To overcome these problems, a robust underwater acoustic communication system was designed over multipath fading channels by employing both decision feedback equalization with the RLS algorithm and convolutional coding with interleaving+shuffling block data sequence. The dual use of these two methods simultaneously can reduce the intersymbol interference (ISI) and the adjacent bit and burst errors. The system will retransmit the same signal if the system fails to estimate the channel due to severe multipath fading. To verify the performance of the system, the transmission of an image was tested using a 524,288bit gray-scaled image through the multipath fading channel. The test results showed that the number of bit errors was reduced from 86,824 to 5,106 when the reference SNR was 12 dB.
Performance optimization of partially coherent CPM on multipath fading channel
NASA Astrophysics Data System (ADS)
Norris, James A.
2012-05-01
Constant Envelope, Continuous Phase Modulation (CPM) is highly desirable for low-power, battery-operated systems as well as for small-profile vehicular and aircraft systems where large amplifiers won't fit. In the past, CPM was noted for increased demodulator complexity (over simple PSK or FSK receivers) but with modern computational power it is possible to continue to improve the power efficiency of CPM modulation at the receiver. In the specific case of multipath, there are several known methods (Rake Receiver is one example) to resolve and correct for inter-symbol interference and phase distortion. This paper develops a standard CPM demodulation and compares the optimal coherent performance with a partially coherent receiver. Several methods are developed to compensate and correct for ISI due to various types of multipath and the power efficiency is compared to the original, coherent demodulation.
NASA Astrophysics Data System (ADS)
Elhakeem, Ahmed K.; Digirolamo, Rocco; Bdira, Ilyess B.; Talla, M.
1994-05-01
The new concepts of adaptive time hopping and variable frame Code Division (CDMA) Multiple Access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five Time Division (TDMA), Code Division, and Time Hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nonetheless, two CDMA systems outperform TDMA systems at low and medium input traffics.
A Differential MIMO SC-FDE Transceiver Design over Multipath Fast Fading Channels
NASA Astrophysics Data System (ADS)
Deng, Juinn-Horng; Hwang, Jeng-Kuang
In this paper, we propose a new differential MIMO single-carrier system with frequency-domain equalization (SC-FDE) aided by the insertion of cyclic prefix. This block transmission system not only inherits all the merits of the SISO SC-FDE system, but is also equipped with a differential space-time block coding (DSTBC) such as to combat the fast-changing frequency selective fading channels without the needs to estimate and then compensate the channel effects. Hence, for practical applications, it has the additional merits of decoding simplicity and robustness against high mobility transmission environments. Computer simulations show that the proposed system can provide diversity benefit as the non-differential system does, while greatly reducing the receiver complexity.
The Multipath and Fading Profile of the High Latitude Meteor Burst Communication Channel.
1986-10-01
APPROVED: j~ ~ e. c ALLAN C. SCHELL Chief, Electromagnetic Sciences Division FOR THE COMMANDER: [ JOHN A. RITZ - Plans and Programs Division *, If your...multipath measurement VHF propagation / 19 ABSTRACT (Continue on reverse ,f necessary and identify by block number) ------ ------ .. tion High...latitude propagation phenomenon such as scatter from the aurora and sporadic-E propagation can alter the communication characteristics of the high latitude
NASA Astrophysics Data System (ADS)
Djordjević, Nebojša; Jaksić, Branimir S.; Matović, Ana; Matović, Marija; Smilić, Marko
2015-11-01
A system with macrodiversity selection combining (SC) receiver and for microdiversity equal gain combining (EGC) receivers is considered. Received signal is subjected, simultaneously to multipath fading and shadowing, resulting in signal envelope and signal power variation. Closed form expressions for moments of macrodiversity SC receiver output signal envelope are calculated. Numerical expressions are plotted to present the influences of Gamma shadowing severity and Nakagami-m severity on moments of proposed system output signal.
Measurement of multipath delay profile in land mobile satellite channels
NASA Technical Reports Server (NTRS)
Ikegami, Tetsushi; Arakaki, Yoshiya; Wakana, Hiromitsu; Suzuki, Ryutaro
1993-01-01
Mobile satellite communication channel has been evaluated mainly with fading statistics of signal. When bandwidth of transmitting signal becomes wider, frequency selectivity of fading becomes a significant factor of the channel. Channel characteristics, not only signal variation but multipath delay spread should be evaluated. A multipath measurement system is proposed and developed for mobile satellite applications. With this system and ETS-V satellite, multipath delay profiles are measured in various environments including Tokyo metropolis and Sapporo city at 1.5 GHz. Results show that the maximum excess delay is within 1 microsec and the maximum delay spread is 0.2 microsecs at elevation angles of 40 to 47 degrees. In wideband signal transmission of about 1 MHz and more, designers should consider the effect of selective fading due to the multipath of land mobile satellite channel.
Antifade sonar employs acoustic field diversity to recover signals from multipath fading
Lubman, D.
1996-04-01
Co-located pressure and particle motion (PM) hydrophones together with four-channel diversity combiners may be used to recover signals from multipath fading. Multipath fading is important in both shallow and deep water propagation and can be an important source of signal loss. The acoustic field diversity concept arises from the notion of conservation of signal energy and the observation that in rooms at least, the total acoustic energy density is the sum of potential energy (scalar field-sound pressure) and kinetic energy (vector field-sound PM) portions. One pressure hydrophone determines acoustic potential energy density at a point. In principle, three PM sensors (displacement, velocity, or acceleration) directed along orthogonal axes describe the kinetic energy density at a point. For a single plane wave, the time-averaged potential and kinetic field energies are identical everywhere. In multipath interference, however, potential and kinetic field energies at a point are partitioned unequally, depending mainly on relative signal phases. Thus, when pressure signals are in deep fade, abundant kinetic field signal energy may be available at that location. Performance benefits require a degree of uncorrelated fading between channels. The expectation of nearly uncorrelated fading is motivated from room theory. Performance benefits for sonar limited by independent Rayleigh fading are suggested by analogy to antifade radio. Average SNR can be improved by several decibels, holding time on target is multiplied manifold, and the bit error rate for data communication is reduced substantially. {copyright} {ital 1996 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Beirouti, Patrick; Leib, Harry; Morgera, Salvatore D.
A recursive procedure for obtaining a (2 to the power n)-state extended Gilbert-Elliott fading channel model suitable for n-bit block codes is described. The extended model may be used for numerical assessment of the throughput of a variety of popular automatic repeat-request schemes used over fading channels such as those encountered in mobile communications systems. Computationally efficient lower and upper performance bounds are also developed for low memory fading channels. It is found that the throughput of the stop-and-wait protocol exhibits a maximum; therefore, there exists an optimum codeword length for this automatic repeat-request scheme.
Effectiveness of Convolutional Code in Multipath Underwater Acoustic Channel
NASA Astrophysics Data System (ADS)
Park, Jihyun; Seo, Chulwon; Park, Kyu-Chil; Yoon, Jong Rak
2013-07-01
The forward error correction (FEC) is achieved by increasing redundancy of information. Convolutional coding with Viterbi decoding is a typical FEC technique in channel corrupted by additive white gaussian noise. But the FEC effectiveness of convolutional code is questioned in multipath frequency selective fading channel. In this paper, how convolutional code works in multipath channel in underwater, is examined. Bit error rates (BER) with and without 1/2 convolutional code are analyzed based on channel bandwidth which is frequency selectivity parameter. It is found that convolution code performance is well matched in non selective channel and also effective in selective channel.
Argo, P.E.; Fitzgerald, T.J.
1991-12-31
This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.
Argo, Paul E.; Fitzgerald, T. Joseph
1993-01-01
Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.
Ultrasonic simulation of MSBLS multipath fading for orbiter landing configuration
NASA Technical Reports Server (NTRS)
Hayre, H. S.
1978-01-01
The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.
Eigenvalues and troposcatter multipath analysis
NASA Astrophysics Data System (ADS)
Matthews, James W.
1992-04-01
Performance predictions for troposcatter channels with multipath are developed using the eigenvalues in the Karhunen-Loeve representation of the tropo signal. Flat Rayleigh fading predictions, in the presence of jamming, are easily extended to multipath channels with this technique.
Hardware Emulation of Wireless Communication Fading Channels
2011-01-01
vol. 19, no. 6 , pp. 1009-1018, Jun. 2001. [9] B. E. Baddour and N. C. Beaulieu, “Accurate simulation of multiple cross- correlated Rician fading...Rayleigh fading waveforms,” IEEE Trans. Commun., vol. 6 , no. 6 , pp. 256-258, Nov. 2002. [18] Y. R. Zheng and C. Xiao, “ Simulation models with correct...waveforms in the baseband equivalent channel due to the bandlimited nature of wireless systems [ 6 ]. Software-based channel simulators usually employ
A tone-aided dual vestigial sideband system for digital communications on fading channels
NASA Technical Reports Server (NTRS)
Hladik, Stephen M.; Saulnier, Gary J.; Rafferty, William
1989-01-01
A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.
A tone-aided dual vestigial sideband system for digital communications on fading channels
NASA Technical Reports Server (NTRS)
Hladik, Stephen M.; Saulnier, Gary J.; Rafferty, William
1989-01-01
A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.
NASA Astrophysics Data System (ADS)
Djordjevic, Goran T.; Antic, Dragan
2013-12-01
In this paper, the outage performance of a dual-branch switch and stay combining (SSC) diversity receiver operating over composite multipath Nakagami-m fading/gamma shadowing channels in the presence of a co-channel interference is determined. For a single channel composite fading environment, we derive the new analytical expressions for the probability density function and cumulative distribution function of the instantaneous signal-to-interference (SIR) ratio that can be used as alternatives to the previously published results. In the case of non-identically distributed and power unbalanced SSC branches with arbitrary fading parameters, the outage performance is determined. The choice of optimal switching threshold in minimum outage probability sense is discussed. The results show the outage probability dependence on simultaneous effects of the SIR unbalancing, as well as multipath fading and shadowing severities. The analytical results are confirmed by Monte Carlo simulations.
Consensus Algorithms Over Fading Channels
2010-10-01
studying the effect of fading and collisions on the performance of wireless consensus gossiping and in comparing its cost (measured in terms of number of...not assumed to be symmetric under A2. III. RELATED WORK There has been a resurgence of interest in characterizing consen- sus and gossip algorithms...tree, and then distribute the consensus value, with a finite number of exchanges. The price paid is clearly that of finding the appropriate routing
Chip Discrimination for UWB Impulse Radio Networks in Multipath Channels
2005-08-01
IEEE, 92(2):295 – 311, Feb. 2004. [8] J. R. Foerster, M. Pendergrass, A. F. Molisch . A Channel Model for Ultrawideband Indoor Communication...Multipath Channels. In Proc. IRE, volume 46, pages 555 – 570, March 1958. [24] D. Cassioli, M. Z. Win, F. Vatalaro, A. F. Molisch . Performance of Low...M. Z. Win, F. Vatalaro, A. F. Molisch . Effects of Spreading Bandwidth on the Performance of UWB RAKE Receivers. IEEE International Conference on
Capacity Analysis of MIMO Rayleigh Channel with Spatial Fading Correlation
NASA Astrophysics Data System (ADS)
Trung, Ha Duyen; Benjapolakul, Watit; Araki, Kiyomichi
MIMO (Multiple Input Multiple Output) communications systems equipped with array antennas at both the transmitter and receiver sides are a promising scheme to realize higher rate and/or reliable data transmission. In this paper, capacity analysis of MIMO Rayleigh channel with spatial correlation at the receiver of multipath taken into account is presented. In general, a model configuration of local scattering around a mobile station in MIMO environment is carried out by simulation to examine spatial correlation coefficients. Based on statistical properties of the eigenvalues of correlated complex random Wishart matrices, the exact closed-form expressions of distribution of the eigenvalues are investigated. Then, the general closed-form evaluation of integral form is proposed based on Meijer's G-function. The results demonstrate that the ergodic capacities are improved by increasing the number of the antennas and the SNR's. Compared with i. i. d. (independent identically distributed) Rayleigh channel, the incremental improvement of correlated Rayleigh channel is reduced by spatial fading correlation. The analytical results validated by Monte-Carlo simulations show a good agreement.
Multipath fading analysis of telemetry signals power fluctuations from Universitetsky microsatellite
NASA Astrophysics Data System (ADS)
Shakhparonov, Vladimir; Millán Adán, Espinoza; Vicente Vivas, Esaú
2012-03-01
The article deals with the results of the fading fluctuations analysis for telemetry signals in the 2 m and 70 cm bands from the first Moscow State University microsatellite better known as "Universitetsky". Radio telemetry signals were received from the microsatellite for around 2 years, collecting and recording the power signal data of almost 7500 satellite overpasses. The received signals from about 2300 satellite overpasses had a very low signal to noise ratio (SNR) that caused high transmission losses. The rest of the signals had a SNR high enough to complete the transmission without losses. The main objective of this paper was to find the fading fluctuations caused both by diffusion and by the presence of Gaussian and non Gaussian noise in telemetry signal power data. The purpose was both to characterize the communication channel as well as to elaborate solutions both to improve the communication quality as well as to identify no homogeneous zones in the ionosphere environment. The signal power analysis was based in the observation of statistical characteristics from different power signal components, in particular the components influenced by diffusion and non Gaussian noise. The employed methodology follows the next steps: removing the power signal envelope; taking away the Gaussian noise; obtaining the statistical characteristics from non Gaussian noise, Gaussian noise and envelope; finally identifying the LOS and NLOS signal fading components. For this purpose, the wavelet technique was used to perform the signal decomposition. In particular, the discrete wavelet transform DWT was utilized to carry out the signal de-noising. Then, the results were statistically treated in order to obtain a diffusion index for Rician fading, which are associated with fading in atmosphere and ionosphere layers. In this way the communications channel among satellite and ground station was characterized and a BER parameter was obtained for every satellite overpass, which
A Reliability Study of RFID Technology in a Fading Channel
2007-06-01
systems. Bit and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best...performing schemes are identified for future employment. 15. NUMBER OF PAGES 69 14. SUBJECT TERMS RFID, Fading Channel, Nakagami , On-off...and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best performing
GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties
NASA Technical Reports Server (NTRS)
Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.
1996-01-01
In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.
GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties
NASA Technical Reports Server (NTRS)
Kavak, Adnan; Xu, Guanghan; Vogel, W. J.
1996-01-01
In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, global positioning system (GPS) receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.
GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties
NASA Technical Reports Server (NTRS)
Kavak, Adnan; Xu, Guanghan; Vogel, W. J.
1996-01-01
In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, global positioning system (GPS) receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.
GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties
NASA Technical Reports Server (NTRS)
Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.
1996-01-01
In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.
Digital Communications Over Non-Fading and Fading Channels
2008-09-01
quality of the demodulated bits entering the channel decoder as shown in Figure 1. Figure 1. Information bit...error and channel bit error relationship [4]. The probability of channel bit error, prior to the channel decoder , directly impacts the output...systems with convolutional coding and hard decision decoding for various commonly used code rates, the relationship between information bit error bP
Wireless Fading Channel Models: From Classical to Stochastic Differential Equations
Olama, Mohammed M; Djouadi, Seddik M; Charalambous, Prof. Charalambos
2010-01-01
The wireless communications channel constitutes the basic physical link between the transmitter and the receiver antennas. Its modeling has been and continues to be a tantalizing issue, while being one of the most fundamental components based on which transmitters and receivers are designed and optimized. The ultimate performance limits of any communication system are determined by the channel it operates in. Realistic channel models are thus of utmost importance for system design and testing. In addition to exponential power path-loss, wireless channels suffer from stochastic short term fading (STF) due to multipath, and stochastic long term fading (LTF) due to shadowing depending on the geographical area. STF corresponds to severe signal envelope fluctuations, and occurs in densely built-up areas filled with lots of objects like buildings, vehicles, etc. On the other hand, LTF corresponds to less severe mean signal envelope fluctuations, and occurs in sparsely populated or suburban areas. In general, LTF and STF are considered as superimposed and may be treated separately. Ossanna was the pioneer to characterize the statistical properties of the signal received by a mobile user, in terms of interference of incident and reflected waves. His model was better suited for describing fading occurring mainly in suburban areas (LTF environments). It is described by the average power loss due to distance and power loss due to reflection of signals from surfaces, which when measured in dB's give rise to normal distributions, and this implies that the channel attenuation coefficient is log-normally distributed. Furthermore, in mobile communications, the LTF channel models are also characterized by their special correlation characteristics which have been reported. Clarke introduced the first comprehensive scattering model describing STF occurring mainly in urban areas. An easy way to simulate Clarke's model using a computer simulation is described. This model was later
Performance of Digital Communications over Selective Fading Channels.
1983-09-01
J. G. Proakis , Digital Communications, McGraw-Hill, New York, 1983. ’ [45] R. D. Gitlin, E. Y. Ho and 3. E. Mazo, "Passband equalization of...7 D-A142 427 PERFORNANCE OF DIGITAL COMMUNICATIONS OVER SELECTIVE 1/2 FADING CHRNNELS(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB F D GARBER...PERIOD COVERED Technical Report PERFORMANCE OF DIGITAL COMMUNICATIONS OVER 6. PERFORMING ORG. REPORT NUMBER SELECTIVE FADING CHANNELS R-998; UILU-ENG
Trellis coded modulation for transmission over fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Simon, Marvin K. (Inventor); Divasalar, Dariush (Inventor)
1990-01-01
The combination of trellis coding and multiple phase-shift keyed (MPSK) signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel. For MPSK signaling, introducing nonuniformity in the phase spacing between signal points provides an improvement in performance over that achievable with trellis codes symmetric MPSK signaling, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Block interleaving may be used to reduce error and pilot tone(s) may be used for improving the error correction performance of the trellis decoder in the presence of channel fading.
The design of trellis codes for fading channels
NASA Technical Reports Server (NTRS)
Divsalar, Dariush; Simon, Marvin K.
1987-01-01
The appropriate criterion for optimum trellis coded modulation design on the additive white Gaussian noise channel is maximization of the free Euclidean distance. When trellis coded modulation is used on a Rician fading channel with interleaving/deinterleaving, the design of the code for optimum performance is guided by other factors, in particular the length of the shortest error event path, and the product of branch distances (possibly normalized by the Euclidean distance of the path) along that path. Although maximum free distance (d sub free) is still an important consideration, it plays a less significant role the more severe the fading is on the channel. These considerations lead to the definition of a new distance measure for optimization of trellis codes transmitted over Rician fading channels. If no interleaving/deinterleaving is used, then once again the design of the trellis code is guided by maximizing d sub free. It is also shown that allowing for multiple symbols per trellis branch, i.e., multiple trellis coded modulation (MTCM), provides an additional degree of freedom for designing a code to meet the above optimization criteria on the fading channel. It is here where the MTCM technique exploits its full potential.
New 16-PSK trellis codes for fading channels
NASA Technical Reports Server (NTRS)
Du, Jun; Vucetic, Branka; Zhang, Lin
1990-01-01
Growth in satellite mobile communications leads to increasing requirements for high data rate transmission that can be met by more efficient modulation schemes (M greater than 8). The 16-PSK trellis coded modulation technique is a very promising solution. A class of new 16-PSK trellis codes with improved error rate are designed based on the criteria on fading channels.
NASA Astrophysics Data System (ADS)
Geise, Robert; Neubauer, Bjoern; Zimmer, Georg
2015-11-01
The performance of navigation systems is always reduced by unwanted multipath propagation. This is especially of practical importance for airborne navigation systems like the instrument landing system (ILS) or the VHF omni directional radio range (VOR). Nevertheless, the quantitative analysis of corresponding, potentially harmful multipath propagation disturbances is very difficult due to the large parameter space. Experimentally difficulties arise due to very expensive, real scale measurement campaigns and numerical simulation techniques still have shortcomings which are briefly discussed. In this contribution a new universal approach is introduced on how to measure very flexibly multipath propagation effects for arbitrary navigation systems using a channel sounder architecture in a scaled measurement environment. Two relevant scenarios of multipath propagation and the impact on navigation signals are presented. The first describes disturbances of the ILS due to large taxiing aircraft. The other example shows the influence of rotating wind turbines on the VOR.
Communication performance over the TDRS multipath/interference channel
NASA Technical Reports Server (NTRS)
Jenny, J.; Gaushell, D.; Shaft, P.
1971-01-01
Previously developed models are used to predict communication system performance for two cases: and aircraft/TDRS and a weather satellite/TDRS relay. The magnitude of multipath, differential time delay, Doppler shift, time and Doppler spread, and interference expected to be encountered are reviewed and applied to the two cases of interest.
Convolutional fountain distribution over fading wireless channels
NASA Astrophysics Data System (ADS)
Usman, Mohammed
2012-08-01
Mobile broadband has opened the possibility of a rich variety of services to end users. Broadcast/multicast of multimedia data is one such service which can be used to deliver multimedia to multiple users economically. However, the radio channel poses serious challenges due to its time-varying properties, resulting in each user experiencing different channel characteristics, independent of other users. Conventional methods of achieving reliability in communication, such as automatic repeat request and forward error correction do not scale well in a broadcast/multicast scenario over radio channels. Fountain codes, being rateless and information additive, overcome these problems. Although the design of fountain codes makes it possible to generate an infinite sequence of encoded symbols, the erroneous nature of radio channels mandates the need for protecting the fountain-encoded symbols, so that the transmission is feasible. In this article, the performance of fountain codes in combination with convolutional codes, when used over radio channels, is presented. An investigation of various parameters, such as goodput, delay and buffer size requirements, pertaining to the performance of fountain codes in a multimedia broadcast/multicast environment is presented. Finally, a strategy for the use of 'convolutional fountain' over radio channels is also presented.
NASA Astrophysics Data System (ADS)
Kida, Yukihiro; Shimura, Takuya; Deguchi, Mitsuyasu; Watanabe, Yoshitaka; Ochi, Hiroshi; Meguro, Koji
2017-07-01
In this study, the performance of passive time reversal (PTR) communication techniques in multipath rich underwater acoustic environments is investigated. It is recognized empirically and qualitatively that a large number of multipath arrivals could generally raise the demodulation result of PTR. However, the relationship between multipath and the demodulation result is hardly evaluated quantitatively. In this study, the efficiency of the PTR acoustic communication techniques for multipath interference cancelation was investigated quantitatively by applying a PTR-DFE (decision feed-back filter) scheme to a synthetic dataset of a horizontal underwater acoustic channel. Mainly, in this study, we focused on the relationship between the signal-to-interference ratio (SIR) of datasets and the output signal-to-noise ratio (OSNR) of demodulation results by a parametric study approach. As a result, a proportional relation between SIR and OSNR is confirmed in low-SNR datasets. It was also found that PTR has a performance limitation, that is OSNR converges to a typical value depending on the number of receivers. In conclusion, results indicate that PTR could utilize the multipath efficiently and also withstand the negative effects of multipath interference at a given limitation.
Evaluations of SSC Diversity Receiver over EGK Fading Channels
NASA Astrophysics Data System (ADS)
Anastasov, Jelena A.; Djordjevic, Goran T.; Panic, Stefan R.; Stefanovic, Mihajlo C.
2014-09-01
In this paper, a detailed performance analysis of switch-and-stay combining receivers over non identical distributed extended generalized K fading channels is presented. The analysis has been performed in both noise and interference-limited environments (the level of interference or noise is ignored, respectively). The expressions for the output signal-to-noise (SNR) and signal-to-interference (SIR) probability density function and cumulative distribution function, in a form of Fox's H functions, are presented. Based on this, analytical expressions for evaluating the moments, outage probability, average bit error rate and average channel capacity are derived. The influence of fading and shadowing phenomena, as well as the influence of unbalanced input SNR/SIR on the most important performance metrics is obtained. Presented numerical results are confirmed by Monte Carlo simulations.
Approximate Minimum Bit Error Rate Equalization for Fading Channels
NASA Astrophysics Data System (ADS)
Kovacs, Lorant; Levendovszky, Janos; Olah, Andras; Treplan, Gergely
2010-12-01
A novel channel equalizer algorithm is introduced for wireless communication systems to combat channel distortions resulting from multipath propagation. The novel algorithm is based on minimizing the bit error rate (BER) using a fast approximation of its gradient with respect to the equalizer coefficients. This approximation is obtained by estimating the exponential summation in the gradient with only some carefully chosen dominant terms. The paper derives an algorithm to calculate these dominant terms in real-time. Summing only these dominant terms provides a highly accurate approximation of the true gradient. Combined with a fast adaptive channel state estimator, the new equalization algorithm yields better performance than the traditional zero forcing (ZF) or minimum mean square error (MMSE) equalizers. The performance of the new method is tested by simulations performed on standard wireless channels. From the performance analysis one can infer that the new equalizer is capable of efficient channel equalization and maintaining a relatively low bit error probability in the case of channels corrupted by frequency selectivity. Hence, the new algorithm can contribute to ensuring QoS communication over highly distorted channels.
Simulation of the TDRS multipath environment
NASA Technical Reports Server (NTRS)
Baghdady, E. J.; Ghais, A. F.; Wachsman, R. H.
1970-01-01
Design principles and implementation methods are discussed for simulating the propagation path between a tracking and data relay satellite and a mission spacecraft. The emphasis is on multipath and Doppler simulation but additive disturbances are also considered. The recommended form of the simulator is fed separately with the unmodulated carrier, the unmodulated subcarriers (or spread-spectrum components) and the data signals. The perturbations are also introduced separately; then successive modulation operations are performed. The simulator is segmented into elements that perform the various functions of direct and specular multipath, diffuse fading, Doppler shift and delay spread. Delay spreads are realized by discrete delays operating on baseband signals. Doppler simulation and ionospheric or diffuse multipath fading are applied to individual paths before or after modulation of the carrier by delayed baseband signals. Block diagrams are presented on how the different elements are combined to create a complete channel simulator.
Zhang, Guosong; Hovem, Jens M.; Dong, Hefeng
2012-01-01
Underwater communication channels are often complicated, and in particular multipath propagation may cause intersymbol interference (ISI). This paper addresses how to remove ISI, and evaluates the performance of three different receiver structures and their implementations. Using real data collected in a high-frequency (10–14 kHz) field experiment, the receiver structures are evaluated by off-line data processing. The three structures are multichannel decision feedback equalizer (DFE), passive time reversal receiver (passive-phase conjugation (PPC) with a single channel DFE), and the joint PPC with multichannel DFE. In sparse channels, dominant arrivals represent the channel information, and the matching pursuit (MP) algorithm which exploits the channel sparseness has been investigated for PPC processing. In the assessment, it is found that: (1) it is advantageous to obtain spatial gain using the adaptive multichannel combining scheme; and (2) the MP algorithm improves the performance of communications using PPC processing. PMID:22438755
Statistical Space-Time-Frequency Characterization of MIMO Shallow Water Acoustic Channels
2010-06-01
multiple - input multiple - output ( MIMO ) SWA communication systems. By taking into account...20375 USA Abstract—This paper proposes a geometry-based statistical model for multiple - input multiple - output shallow water acous- tic multipath fading...statistical model for multiple - input multiple - output shallow water acoustic multipath fading channels. From the reference model, the corresponding
Outage Probability of MRC for κ-μ Shadowed Fading Channels under Co-Channel Interference
Chen, Changfang; Shu, Minglei; Wang, Yinglong; Yang, Ming; Zhang, Chongqing
2016-01-01
In this paper, exact closed-form expressions are derived for the outage probability (OP) of the maximal ratio combining (MRC) scheme in the κ-μ shadowed fading channels, in which both the independent and correlated shadowing components are considered. The scenario assumes the received desired signals are corrupted by the independent Rayleigh-faded co-channel interference (CCI) and background white Gaussian noise. To this end, first, the probability density function (PDF) of the κ-μ shadowed fading distribution is obtained in the form of a power series. Then the incomplete generalized moment-generating function (IG-MGF) of the received signal-to-interference-plus-noise ratio (SINR) is derived in the closed form. By using the IG-MGF results, closed-form expressions for the OP of MRC scheme are obtained over the κ-μ shadowed fading channels. Simulation results are included to validate the correctness of the analytical derivations. These new statistical results can be applied to the modeling and analysis of several wireless communication systems, such as body centric communications. PMID:27851817
Multipath Separation-Direction of Arrival (MS-DOA) with Genetic Search Algorithm for HF channels
NASA Astrophysics Data System (ADS)
Arikan, Feza; Koroglu, Ozan; Fidan, Serdar; Arikan, Orhan; Guldogan, Mehmet B.
2009-09-01
Direction-of-Arrival (DOA) defines the estimation of arrival angles of an electromagnetic wave impinging on a set of sensors. For dispersive and time-varying HF channels, where the propagating wave also suffers from the multipath phenomena, estimation of DOA is a very challenging problem. Multipath Separation-Direction of Arrival (MS-DOA), that is developed to estimate both the arrival angles in elevation and azimuth and the incoming signals at the output of the reference antenna with very high accuracy, proves itself as a strong alternative in DOA estimation for HF channels. In MS-DOA, a linear system of equations is formed using the coefficients of the basis vector for the array output vector, the incoming signal vector and the array manifold. The angles of arrival in elevation and azimuth are obtained as the maximizers of the sum of the magnitude squares of the projection of the signal coefficients on the column space of the array manifold. In this study, alternative Genetic Search Algorithms (GA) for the maximizers of the projection sum are investigated using simulated and experimental ionospheric channel data. It is observed that GA combined with MS-DOA is a powerful alternative in online DOA estimation and can be further developed according to the channel characteristics of a specific HF link.
Outage Capacity Analysis of TAS/MRC Systems over Arbitrary Nakagami-m Fading Channels
NASA Astrophysics Data System (ADS)
Hung, Chia-Chun; Chiang, Ching-Tai; Lin, Shyh-Neng; Wu, Rong-Ching
A simple closed-form approximation for the outage capacity of Transmit Antenna Selection/Maximal-Ratio Combining (TAS/MRC) systems over independent and identically distributed (i.i.d) Nakagami-m fading channels is derived while the fading index is a positive integer. When the Nakagami-m fading index is not an integer, the approximate outage capacity is derived as a single infinite series of Gamma function. Computer simulations verify the accuracy of the approximate results.
Estimation of FBMC/OQAM fading channels using dual Kalman filters.
Aldababseh, Mahmoud; Jamoos, Ali
2014-01-01
We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method.
Estimation of FBMC/OQAM Fading Channels Using Dual Kalman Filters
Aldababseh, Mahmoud
2014-01-01
We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method. PMID:24701181
NASA Technical Reports Server (NTRS)
Takhar, G. S.; Gupta, S. C.
1976-01-01
The multipath channel for communication between an aerospace vehicle and a ground terminal is modeled by a multiplicative first-order Markov process. The multiplicative process is treated as a component of the message model and the discrete-time demodulation algorithms using the extended Kalman nonlinear estimation technique are developed for continuous-time angle-modulated signals. The equivalent baseband form of the demodulator structure is derived. Two examples of the message process are discussed for an FM system. The simulation results are presented for various values of the bandwidth expansion ratio and the additive SNR. The performance of the baseband algorithms is discussed.
A Serial Unequal Error Protection Codes System Using MMSE-FDE for Fading Channels
NASA Astrophysics Data System (ADS)
Yamazaki, Satoshi; Asano, David K.
In our previous research, to achieve unequal error protection (UEP), we proposed a scheme which encodes the data by randomly switching between several codes which use different signal constellations and showed the effectiveness in AWGN channels. In this letter, we propose our UEP system using MMSE-FDE for fast and selective fading by using the fact that importance levels are changed every few symbols, i.e., every block, in the proposed system. We confirmed the improvement in BER performance and the effectiveness of adaptive equalization for the proposed system in fading channels. Moreover, in fading channels we confirmed the validity of the theoretical tradeoff shown in static conditions.
A subspace-based parameter estimation algorithm for Nakagami-m fading channels
NASA Astrophysics Data System (ADS)
Dianat, Sohail; Rao, Raghuveer
2010-04-01
Estimation of channel fading parameters is an important task in the design of communication links such as maximum ratio combining (MRC). The MRC weights are directly related to the fading channel coefficients. In this paper, we propose a subspace based parameter estimation algorithm for the estimation of the parameters of Nakagami-m fading channels in the presence of additive white Gaussian noise. Comparisons of our proposed approach are made with other techniques available in the literature. The performance of the algorithm with respect to the Cramer-Rao bound (CRB) is investigated. Computer simulation results for different signal to noise ratios (SNR) are presented.
The performance of trellis coded multilevel DPSK on a fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Simon, Marvin K.; Divsalar, Dariush
1987-01-01
The performance of trellis coded multilevel differential phase-shift-keying (MDPSK) over Rician and Rayleigh fading channels is discussed. For operation at L-Band, this signalling technique leads to a more robust system than the coherent system with dual pilot tone calibration previously proposed for UHF. The results are obtained using a combination of analysis and simulation. The analysis shows that the design criterion for trellis codes to be operated on fading channels with interleaving/deinterleaving is no longer free Euclidean distance. The correct design criterion for optimizing bit error probability of trellis coded MDPSK over fading channels will be presented along with examples illustrating its application.
NASA Astrophysics Data System (ADS)
Li, Min
2014-07-01
In this paper, the performance of beamforming (BF) for a dual-hop amplify-and-forward (AF) relay network, where the source and destination are each equipped with multiple antennas, is investigated. It is assumed that the source-relay and relay-destination channels experience mixed fading distributions, namely, correlated Nakagami-m/Rician and correlated Rician/Nakagami-m, respectively. By considering fixed-gain relaying, analytical expressions for outage probability (OP) and average symbol error rate (ASER) are derived in closed-form. Numerical results are presented to demonstrate the efficacy of our performance analysis, also illustrate the impact of channel correlation, fading severity, Rician factor and antenna configuration on the performance of the system. It is shown that the correlated Nakagami-m/Rician fading channel can achieve better performance than the correlated Rician/Nakagami-m fading channel with the increase of fading severity parameter, and the correlated Rician/Nakagami-m fading channel may outperform the correlated Nakagami-m/Rician fading channel by enlarging the Rician factor.
2014-01-01
To make use of the sparsity property of broadband multipath wireless communication channels, we mathematically propose an lp-norm-constrained proportionate normalized least-mean-square (LP-PNLMS) sparse channel estimation algorithm. A general lp-norm is weighted by the gain matrix and is incorporated into the cost function of the proportionate normalized least-mean-square (PNLMS) algorithm. This integration is equivalent to adding a zero attractor to the iterations, by which the convergence speed and steady-state performance of the inactive taps are significantly improved. Our simulation results demonstrate that the proposed algorithm can effectively improve the estimation performance of the PNLMS-based algorithm for sparse channel estimation applications. PMID:24782663
Joint Symbol Timing and CFO Estimation for OFDM/OQAM Systems in Multipath Channels
NASA Astrophysics Data System (ADS)
Fusco, Tilde; Petrella, Angelo; Tanda, Mario
2009-12-01
The problem of data-aided synchronization for orthogonal frequency division multiplexing (OFDM) systems based on offset quadrature amplitude modulation (OQAM) in multipath channels is considered. In particular, the joint maximum-likelihood (ML) estimator for carrier-frequency offset (CFO), amplitudes, phases, and delays, exploiting a short known preamble, is derived. The ML estimators for phases and amplitudes are in closed form. Moreover, under the assumption that the CFO is sufficiently small, a closed form approximate ML (AML) CFO estimator is obtained. By exploiting the obtained closed form solutions a cost function whose peaks provide an estimate of the delays is derived. In particular, the symbol timing (i.e., the delay of the first multipath component) is obtained by considering the smallest estimated delay. The performance of the proposed joint AML estimator is assessed via computer simulations and compared with that achieved by the joint AML estimator designed for AWGN channel and that achieved by a previously derived joint estimator for OFDM systems.
Power and Rate Adaptation Based on Imperfect Channel Estimation over MIMO Fading Channels
NASA Astrophysics Data System (ADS)
Kobravi, Alireza; Shikh-Bahaei, Mohammad
We derive the optimum power and rate adaptation for maximizing the spectral efficiency of Multilevel Quadrature Amplitude Modulation (MQAM) over Multiple-Input Multiple-Output (MIMO) fading channels based on imperfect channel estimation. We use Pilot Symbol Assisted Modulation (PSAM)-based Minimum Mean Square Error (MMSE) channel estimator, and show that the optimum power adaptation on each sub-channel is a generalization of water-filling. We also show that the conventional water-filling (with bias) strategy for power adaptation is a suboptimum solution of the general optimization problem and it tends to the optimal solution as the correlation coefficients between eigenvalues of the true channel matrix and its estimate tend to one.
A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels
NASA Technical Reports Server (NTRS)
Leung, Patrick S. K.; Feher, Kamilo
1990-01-01
A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation.
A Low-Complexity Transceiver Design in Sparse Multipath Massive MIMO Channels
NASA Astrophysics Data System (ADS)
Yu, Yuehua; Wang, Peng; Chen, He; Li, Yonghui; Vucetic, Branka
2016-10-01
In this letter, we develop a low-complexity transceiver design, referred to as semi-random beam pairing (SRBP), for sparse multipath massive MIMO channels. By exploring a sparse representation of the MIMO channel in the virtual angular domain, we generate a set of transmit-receive beam pairs in a semi-random way to support the simultaneous transmission of multiple data streams. These data streams can be easily separated at the receiver via a successive interference cancelation (SIC) technique, and the power allocation among them are optimized based on the classical waterfilling principle. The achieved degree of freedom (DoF) and capacity of the proposed approach are analyzed. Simulation results show that, compared to the conventional singular value decomposition (SVD)-based method, the proposed transceiver design can achieve near-optimal DoF and capacity with a significantly lower computational complexity.
NASA Astrophysics Data System (ADS)
Yigit, Halil; Kavak, Adnan
2012-03-01
The capacity of multiple-input multiple-output (MIMO) wireless communication channels is affected by the multipath angle spread and relative multiple signal strength (RMSS) at both sides of the transmitter and the receiver. In this paper, we study analytically how these two factors emerge in the MIMO capacity equation when the channel state information (CSI) is unknown at the transmitter and perfectly known at the receiver. Mathematical expression for the channel capacity is carried out for
2011-04-12
will examine the performance of a frame synchronization algorithm suitable for the system shown in Fig. 1. Section II discusses the communications...provides the conclusions. II . CHANNEL MODEL A block diagram of the communication channels shown in Fig.l is provided in Fig. 2. These conununication...channel 10 -lsL---~~--~--~--~--~--~--~--~--- 0 :Z 3 4 5 6 7 II !I 10 Sample x10’ Figure 4: Channel Fading B. Summary of Channel Induced Framing Errors
Channel fading for mobile satellite communications using spread spectrum signaling and TDRSS
NASA Technical Reports Server (NTRS)
Jenkins, Jeffrey D.; Fan, Yiping; Osborne, William P.
1995-01-01
This paper will present some preliminary results from a propagation experiment which employed NASA's TDRSS and an 8 MHz chip rate spread spectrum signal. Channel fade statistics were measured and analyzed in 21 representative geographical locations covering urban/suburban, open plain, and forested areas. Cumulative distribution Functions (CDF's) of 12 individual locations are presented and classified based on location. Representative CDF's from each of these three types of terrain are summarized. These results are discussed, and the fade depths exceeded 10 percent of the time in three types of environments are tabulated. The spread spectrum fade statistics for tree-lined roads are compared with the Empirical Roadside Shadowing Model.
Fading losses on the LCRD free-space optical link due to channel turbulence
NASA Astrophysics Data System (ADS)
Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon
2013-03-01
The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Optical turbulence over the communication paths will cause random uctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by optical turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.
Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence
NASA Technical Reports Server (NTRS)
Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon
2013-01-01
The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.
Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence
NASA Technical Reports Server (NTRS)
Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon
2013-01-01
The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.
Performance of quasi-optimum digital FM demodulators for fading channels
NASA Technical Reports Server (NTRS)
Dharamsi, M. T.; Gupta, S. C.
1975-01-01
This paper deals with the problem of digital demodulation of FM signals transmitted over Rayleigh and Rician fading channels. The Rayleigh and Rician fading channels are represented by two quadrature multiplicative nonzero mean white Gaussian processes in addition to an additive zero-mean white Gaussian noise. Quasi-optimum digital baseband demodulation algorithms using various nonlinear estimation techniques are derived. The digital demodulator structures are then simulated on a digital computer for an FM system with first order message spectrum for various values of the parameters for Rayleigh and Rician channels.
2010-11-30
sight signals (DLOS) is very short. This form of multipath is difficult to detect and mitigate using traditional correlator -based methods. Our approach...direct line of sight signals (DLOS) is very short. This form of multipath is difficult to detect and mitigate using traditional correlator -based...Multipath reflector 0 m d MP Detection ANOVA Hypothesis Test DLOS & MP AOA Estimation Contractive Map & Alternating Projection Correlators 0
Communications by vocoder on a mobile satellite fading channel
NASA Astrophysics Data System (ADS)
dal Degan, N.; Perosino, F.; Rusina, F.
The performance of a LPC vocoder system is analyzed under various bit rate and fading errors. The error generation model developed to estimate error probability, and length of error bursts and distributions is described. Two algorithms that will improve burst are proposed. The evaluation of the spectral distance measures of the voice coding system is examined. The intelligibility, quality, and acceptability of the system are assessed using the mean opinion scores method.
Detection performance of cooperative spectrum sensing with hard decision fusion in fading channels
NASA Astrophysics Data System (ADS)
Nallagonda, S.; Chandra, A.; Roy, S. D.; Kundu, S.; Kukolev, P.; Prokes, A.
2016-02-01
In this paper, we investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-m and log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels.
Performance of convolutional codes on fading channels typical of planetary entry missions
NASA Technical Reports Server (NTRS)
Modestino, J. W.; Mui, S. Y.; Reale, T. J.
1974-01-01
The performance of convolutional codes in fading channels typical of the planetary entry channel is examined in detail. The signal fading is due primarily to turbulent atmospheric scattering of the RF signal transmitted from an entry probe through a planetary atmosphere. Short constraint length convolutional codes are considered in conjunction with binary phase-shift keyed modulation and Viterbi maximum likelihood decoding, and for longer constraint length codes sequential decoding utilizing both the Fano and Zigangirov-Jelinek (ZJ) algorithms are considered. Careful consideration is given to the modeling of the channel in terms of a few meaningful parameters which can be correlated closely with theoretical propagation studies. For short constraint length codes the bit error probability performance was investigated as a function of E sub b/N sub o parameterized by the fading channel parameters. For longer constraint length codes the effect was examined of the fading channel parameters on the computational requirements of both the Fano and ZJ algorithms. The effects of simple block interleaving in combatting the memory of the channel is explored, using the analytic approach or digital computer simulation.
Performance analysis of digital FM demodulators for fading channels in the threshold region
NASA Technical Reports Server (NTRS)
Dharamsi, M. T.; Gupta, S. C.
1976-01-01
The quasi-optimum digital FM demodulators for fading channels reported earlier (1975) reflected the system performance accurately under high signal to noise ratio conditions. In this paper, the prediction of the system performance for low SNR values is considered. A new set of error variance algorithms is developed from the filter algorithm assuming a Gaussian distribution for the state estimation errors and taking the effect of high frequency terms into consideration. Simulation analysis for an FM system with Rician fading channel shows that these algorithms predict the system performance accurately in the threshold region.
Trellis coded modulation for 4800-9600 bps transmission over a fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Divsalar, D.; Simon, M. K.
1986-01-01
The combination of trellis coding and multiple phase-shift-keyed (MPSK) signalling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.
Comparasion of Energy Detection in Cognitive Radio over different fading channels
NASA Astrophysics Data System (ADS)
Buttar, Simar
2012-07-01
With the advance of wireless communications, the problem of bandwidth scarcity has become more prominent. Cognitive radio technology has come out as a way to solve this problem by allowing the unlicensed users to use the licensed bands opportunistically. To sense the existence of licensed users, many spectrum sensing techniques have been devised. In this paper, energy detection and cyclic prefix is used for spectrum sensing.The comparison of ROC curves has been done for various wireless fading channels using squaring and cubingoperation,the improvement has gone as high as up to 0.6 times for AWGN channel and 0.4 times for Rayleigh channel as we go from squaring to cubing operation in an energy detector. Closed form expressions for Probability of detection for AWGN and Rayleigh channels are described.Nakagami fading channel shows worst results .
NASA Astrophysics Data System (ADS)
Yang, Chang-Yi; Chen, Bor-Sen
2010-12-01
A recursive maximum-likelihood (RML) algorithm for channel estimation under rapidly fading channel and colored noise in a multicarrier code-division multiple-access (MC-CDMA) system is proposed in this paper. A moving-average model with exogenous input (MAX) is given to describe the transmission channel and colored noise. Based on the pseudoregression method, the proposed RML algorithm can simultaneously estimate the parameters of channel and colored noise. Following the estimation results, these parameters can be used to enhance the minimum mean-square error (MMSE) equalizer. Considering high-speed mobile stations, a one-step linear trend predictor is added to improve symbol detection. Simulation results indicate that the proposed RML estimator can track the channel more precisely than the conventional estimator. Meanwhile, the performance of the proposed enhanced MMSE equalizer is robust to the rapidly Rayleigh fading channel under colored noise in the MC-CDMA systems.
Multipath propagation models for near line-of-sight conditions
NASA Astrophysics Data System (ADS)
Martens, Walter
This thesis analyzes the behaviour of a multipath channel for suburban and semi-rural areas in which line of sight (LOS) or near LOS exists between the transmitter and receiver. The thesis is divided into five major parts: a background and literature survey, a theoretical analysis, experimental measurements which validate the analysis, applications to practical communication channels and a study of the effects of such a channel on typical signal waveforms. It is found that the channel is either good or very bad. The latter usually occurs close to buildings where a single dominant reflection with a relative delay of less than a microsecond produces a periodic severe fading and distortion of the signal, often making a link unusable. A methodology is also outlined for determining which locations in a defined area will show the behaviour associated with a bad channel. Key words: Digital communication, propagation, multipath
A free-space optical terminal for fading channels
NASA Astrophysics Data System (ADS)
Williams, T.; Murphy, R. J.; Walther, F.; Volpicelli, A.; Wilcox, B.; Crucioli, D.
2009-08-01
This paper describes a lasercom terminal using spatial diversity to mitigate fading caused by atmospheric scintillation. Multiple receive apertures are separated sufficiently to capture statistically independent samples of the incoming beam. The received optical signals are tracked individually, photo-detected, and summed electrically, with measured diversity gain. The terminal consists of COTS components. It was used in successful demonstrations over a 5.4km ground-ground link from June through September 2008, during which it experienced a wide temperature range. Design overview and hardware realization are presented. This work was sponsored by the Department of Defense, RRCO DDR&E, under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Government.
Performance Improvement in Spatially Multiplexed MIMO Systems over Weibull-Gamma Fading Channel
NASA Astrophysics Data System (ADS)
Tiwari, Keerti; Saini, Davinder S.; Bhooshan, Sunil V.
2016-11-01
In multiple-input multiple-output (MIMO) systems, spatial demultiplexing at the receiver has its own significance. Thus, several detection techniques have been investigated. There is a tradeoff between computational complexity and optimal performance in most of the detection techniques. One of the detection techniques which gives improved performance and acceptable level of complexity is ordered successive interference cancellation (OSIC) with minimum mean square error (MMSE). However, optimal performance can be achieved by maximum likelihood (ML) detection but at a higher complexity level. Therefore, MMSE-OSIC with candidates (OSIC2) detection is recommended as a solution. In this paper, spatial multiplexed (SM) MIMO systems are considered to evaluate error performance with different detection techniques such as MMSE-OSIC, ML and MMSE-OSIC2 in a composite fading i. e. Weibull-gamma (WG) fading environment. In WG distribution, Weibull and gamma distribution represent multipath and shadowing effects, respectively. Simulation results illustrate that MMSE-OSIC2 detection technique gives the improved symbol error rate (SER) performance which is similar to ML performance and its complexity level approaches to MMSE-OSIC.
2005-09-01
is examined. The amplitude of the signal power 2ca is modeled as a random variable, and the channel is modeled as either Rayleigh fading or Ricean...Decoding, Soft Decision Decoding, FEC, Convolutional Code, Rayleigh Fading, Ricean Fading, Pulse-Noise Interference, Noise-Normalization 16. PRICE CODE...channel is modeled as either Rayleigh fading or Ricean fading, depending on the modulation under consideration
Demodulation of OFDM Signals in the Presence of Deep Fading Channels and Signal Clipping
2012-06-01
FFT) operation zero padded to twice the data length allows for the recovery of subcarriers located next to a deep faded (at low signal-to-noise ratio...signals transmitted over fading channels. We show that the use of a zero prefix (ZP) along with a fast Fourier transform (FFT) operation zero padded to...refer to two widely used standards: IEEE 802.11 for local area networks (LAN) and WiFi and IEEE 802.16 for wide area networks (WAN) and WiMax. The two
Receiver diversity combining using evolutionary algorithms in Rayleigh fading channel.
Akbari, Mohsen; Manesh, Mohsen Riahi; El-Saleh, Ayman A; Reza, Ahmed Wasif
2014-01-01
In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods.
Receiver Diversity Combining Using Evolutionary Algorithms in Rayleigh Fading Channel
Akbari, Mohsen; Manesh, Mohsen Riahi
2014-01-01
In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods. PMID:25045725
Fading probability density function of free-space optical communication channels with pointing error
NASA Astrophysics Data System (ADS)
Zhao, Zhijun; Liao, Rui
2011-06-01
The turbulent atmosphere causes wavefront distortion, beam wander, and beam broadening of a laser beam. These effects result in average power loss and instantaneous power fading at the receiver aperture and thus degrade performance of a free-space optical (FSO) communication system. In addition to the atmospheric turbulence, a FSO communication system may also suffer from laser beam pointing error. The pointing error causes excessive power loss and power fading. This paper proposes and studies an analytical method for calculating the FSO channel fading probability density function (pdf) induced by both atmospheric turbulence and pointing error. This method is based on the fast-tracked laser beam fading profile and the joint effects of beam wander and pointing error. In order to evaluate the proposed analytical method, large-scale numerical wave-optics simulations are conducted. Three types of pointing errors are studied , namely, the Gaussian random pointing error, the residual tracking error, and the sinusoidal sway pointing error. The FSO system employs a collimated Gaussian laser beam propagating along a horizontal path. The propagation distances range from 0.25 miles to 2.5 miles. The refractive index structure parameter is chosen to be Cn2 = 5×10-15m-2/3 and Cn2 = 5×10-13m-2/3. The studied cases cover from weak to strong fluctuations. The fading pdf curves of channels with pointing error calculated using the analytical method match accurately the corresponding pdf curves obtained directly from large-scale wave-optics simulations. They also give accurate average bit-error-rate (BER) curves and outage probabilities. Both the lognormal and the best-fit gamma-gamma fading pdf curves deviate from those of corresponding simulation curves, and they produce overoptimistic average BER curves and outage probabilities.
NASA Astrophysics Data System (ADS)
Milić, Dejan N.; Đorđević, Goran T.
2013-01-01
In this paper, we study the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch and stay combining receiver over Nakagami-m fading/gamma shadowing channels with arbitrary parameters. The average BER of quaternary phase shift keying is evaluated under the assumption that the reference carrier signal is extracted from the received modulated signal. We compute numerical results illustrating simultaneous influence of average signal-to-noise ratio per bit, fading severity, shadowing, phase-locked loop bandwidth-bit duration (BLTb) product, and switching threshold on BER performance. The effects of BLTb on receiver performance under different channel conditions are emphasized. Optimal switching threshold is determined which minimizes BER performance under given channel and receiver parameters.
Robustness of predictive sensor network routing in fading channels
NASA Astrophysics Data System (ADS)
Muraleedharan, Rajani; Osadciw, Lisa A.
2005-06-01
Sensors have varied constraints, which make the network challenging for communicating with peers. In this paper, an extension, to the physical layer of the previous predictive sensor network model using the ant system is proposed. The tiny and low-cost sensor nodes are made of RF wireless links, where the states of the nodes vary with respect to time and environment. The ant system is a learning algorithm, that can be used to solve any NP hard communication problem and possesses characteristics such as robustness and versatility. The ant system possesses unique features that keep the network functional by detecting weak links and re-routing the agents. The swarm agents are distributed along the network, where the agent communicates with its neighbors (agents) by means of pheromone deposition and tabu list. The transition probability in the ant system includes an objective function, which is influenced by the poset weights. The poset weights on each of the orthogonal communication parameters greatly affects the decisions made by ant system. The agents carry updated information of its previous nodes, which helps in monitoring the strength of the communication links. Through simulation, comparison between DSSS-BPSK and Bluetooth-GFSK signals are shown. This paper demonstrates the robustness of the model under slow/fast fading, and energy loss at node during transmission. Implementation of this algorithm should be able to handle hostile environmental conditions and human tampering of data. The performance of the network is evaluated based on accuracy and response time of the agents within the network.
Blind Equalization and Fading Channel Signal Recovery of OFDM Modulation
2011-03-01
of WiMAX. San Francisco, CA: Prentice Hall, 2007. [2] P. P. Vaidyanathan and B. Vrcelj, “A frequency domain approach for blind identification with...filter bank precoders,” in Proc. 2004 Int. Symp. Circuits and Systems, pp. III- 349–52, 2004. [3] P. P. Vaidyanathan and B. Su, “Remarks on certain...OBJECTIVES AND METHODOLOGY The goal of this thesis was to further investigate the method of blind channel equalization proposed by P. P. Vaidyanathan , et al
NASA Astrophysics Data System (ADS)
Metelev, S. A.; Lvov, A. V.
2016-09-01
We propose a method for estimating potential interference immunity of radio reception in the multipath radio-communication channels. Using this method for the modified Watterson model of the decameter radio channel, we study the achievable interference immunity of devices with spatial signal processing.
On the performance analysis of SSC diversity system over η-μ fading channels
NASA Astrophysics Data System (ADS)
Khatalin, Sari
2016-06-01
In this paper, we study key performance measures of dual-branch switch-and-stay combining (SSC) system operating in ? fading environment. Specifically, analytical expressions for the kth order moment, average signal-to-noise ratio, amount of fading and outage probability are obtained for an SSC system operating over ? fading channels. Expressions of the average bit error rate (BER) for coherent detection and non-coherent detection were also derived with SSC for various modulation schemes. The BER expressions for the coherent detection case were derived using the moment generating function-based approach. Some of the final expressions are presented in the form of infinite series. Therefore, those series are truncated and upper bounds are derived for truncation errors. Expressions to determine the optimum adaptive switching thresholds are also presented. Corresponding results for Nakagami-q and Nakagami-m fading are derived in this paper as special cases. Numerical results are provided to demonstrate the applications of the new results.
Multiple trellis coded modulation (MTCM) performance on a fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Simon, Marvin K.; Divsalar, Dariush
1987-01-01
The author recently introduced the notion of multiple trellis coding, in which more than one channel symbol per trellis branch is transmitted. He showed that on the ideal additive white Gaussian noise (AWGN) channel, the combination of multiple trellis coding with M-ary modulation yields a performance gain with symmetric signal sets comparable to and in some cases better than that previously achieved only with signal constellation asymmetry. The combination of conventional trellis coding with multiple phase-shift-keyed (MPSK) signaling has recently been shown by the author to be a well-suited modulation/coding scheme for transmission over the fading mobile satellite channel. In particular, a rate 2/3 coded 8-PSK scheme operating at 4800 b/s is currently under development for use in NASA's Mobile Satellite Experiment (MSAT-X). The author applies the multiple trellis-coded modulation technique in the same fading mobile satellite environment, extending the analysis results previously found for its performance over the AWGN channel to the MSAT-X channel.
NASA Astrophysics Data System (ADS)
Xu, D.; Li, Q.
2015-11-01
This paper investigates the capacity of the secondary user (SU) in a cognitive radio (CR) network in Rayleigh fading environments. Different from existing works where perfect channel state information (CSI) or channel distribution information (CDI) of the interference link from the SU to the primary user (PU) is assumed to be available, this paper assumes that only partial CDI is available. Specifically, we assume the distribution parameter is unknown and estimated from a set of channel gain samples. With such partial CDI, closed-form expressions for the ergodic and outage capacities of the SU are obtained under the transmit power and the interference outage constraints. It is shown that the capacity with partial CDI is not degraded compared to that with perfect CDI if the interference outage constraint is loose. It is also shown that the capacity can be significantly improved by increasing the number of channel gain samples.
Measurement of satellite PCS fading using GPS
NASA Astrophysics Data System (ADS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.
1995-08-01
A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.
Measurement of satellite PCS fading using GPS
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.
1995-01-01
A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.
Methods and Apparatuses for Signaling with Geometric Constellations in a Raleigh Fading Channel
NASA Technical Reports Server (NTRS)
Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)
2017-01-01
Communication systems are described that use signal constellations, which have unequally spaced (i.e. `geometrically` shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR, over the Raleigh fading channel. In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d.sub.min, are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.
NASA Astrophysics Data System (ADS)
Hajjarian, Zeinab; Kavehrad, Mohsen; Fadlullah, Jarir
2010-01-01
Free Space Optical (FSO) communications is the only practical candidate for realizing universal network coverage between ground and airborne nodes, satellites, and even moon and other nearby planets. When atmosphere (be it the earth or Mars) is a part of the optical channel, attributes of scattering and turbulence bring about amplitude attenuation, and scintillation, as well as beam wander and phase aberrations at the receiving aperture. Phase screens are usually used in order to simulate the atmospheric fading channel and phase fluctuations. In this paper, different methods of generating phase screens are compared based on their accuracy and computational complexity, as in most computer simulations, a large ensemble of phase screens are required for averaging purposes. To combat the focal plane intensity fading, caused by amplitude and phase variations in the received wave-front, it is possible to replace the Single Input-Single Output (SISO) communications system with its Multiple Input Multiple Output (MIMO) equivalent, which has the same total transmit power and receiving aperture area. Another alternative is to equip the receiver with a state of the art Adaptive Optics (AO) correction system. Using average Bit Error Rate (BER), as a performance metric, effectiveness of these two approaches are compared and it is shown that while a MIMO configuration outperforms a basic AO system capable of only tilt corrections, an ideal AO system, which is able to remove higher orders of Zernike modes can asymptotically perform as well as an equivalent MIMO configuration.
Upper and lower bounds for the ergodic capacity of MIMO Jacobi fading channels.
Nafkha, Amor; Bonnefoi, Rémi
2017-05-29
In multi-(core/mode) optical fiber communication, the transmission channel can be modeled as a complex sub-matrix of the Haar-distributed unitary matrix (complex Jacobi unitary ensemble). In this letter, we present new analytical expressions of the upper and lower bounds for the ergodic capacity of multiple-input multiple-output Jacobi-fading channels. Recent results on the determinant of the Jacobi unitary ensemble are employed to derive a tight lower bound on the ergodic capacity. We use Jensen's inequality to provide an analytical closed-form upper bound to the ergodic capacity at any signal-to-noise ratio (SNR). Closed-form expressions of the ergodic capacity, at low and high SNR regimes, are also derived. Simulation results are presented to validate the accuracy of the derived expressions.
Use of Bigaussian approximation to describe fading in scattering communications channel
NASA Astrophysics Data System (ADS)
Sushkova, L. T.; Marchenko, Y. Y.; Bryksin, V. V.
1985-01-01
An algorithm is presented for the analytical description of the statistical properties of fading in a scattering radio channel. Two Gaussian random processes W1 (x) and W2 (x) with parameters a1, delta 1, a2, delta 2, respectively where a1; delta 1- mathematical expectation, as the expression approximating the arbitrary probability density W*(x) of the composition are considered. A graph analytical method is proposed for estimating the parameters a sub 1, a sub 2, delta and lambda from the known estimates of the moments of the empirical distribution described. The proposed method is used to describe the real statistics of signal level variation in a troposcatter radio channel as an example.
NASA Astrophysics Data System (ADS)
Zhao, Zhijun; Liao, Rui
2011-03-01
Free-space optical (FSO) communication systems suffer from average power loss and instantaneous power fading due to the atmospheric turbulence. The channel fading probability density function (pdf) is of critical importance for FSO communication system design and evaluation. The performance and reliability of FSO communication systems can be greatly enhanced if fast-tacking devices are employed at the transmitter in order to compensate laser beam wander at the receiver aperture. The fast-tracking method is especially effective when communication distance is long. This paper studies the fading probability density functions of both fast-tracked and untracked FSO communication channels. Large-scale wave-optics simulations are conducted for both tracked and untracked lasers. In the simulations, the Kolmogorov spectrum is adopted, and it is assumed that the outer scale is infinitely large and the inner scale is negligibly small. The fading pdfs of both fast-tracked and untracked FSO channels are obtained from the simulations. Results show that the fast-tracked channel fading can be accurately modeled as gamma-distributed if receiver aperture size is smaller than the coherence radius. An analytical method is given for calculating the untracked fading pdfs of both point-like and finite-size receiver apertures from the fast-tracked fading pdf. For point-like apertures, the analytical method gives pdfs close to the well-known gamma-gamma pdfs if off-axis effects are omitted in the formulation. When off-axis effects are taken into consideration, the untracked pdfs obtained using the analytical method fit the simulation pdfs better than gamma-gamma distributions for point-like apertures, and closely fit the simulation pdfs for finite-size apertures where gamma-gamma pdfs deviate from those of the simulations significantly.
Javed, Umer; He, Di; Liu, Peilin
2016-01-01
The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes. PMID:27527182
Javed, Umer; He, Di; Liu, Peilin
2016-08-05
The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes.
NASA Astrophysics Data System (ADS)
Ahmad Ansari, Ejaz; Rajatheva, Nandana
Although the topic of multiple-input multiple-output (MIMO) based orthogonal frequency division multiplexing (OFDM) over different fading channels is well investigated, its closed form symbol error rate (SER) expressions and performance results employing orthogonal space time block codes (OSTBCs) over uncorrelated frequency-selective Nakagami-m fading channels are still not available. The closed form expressions are extremely useful for evaluating system's performance without carrying out time consuming simulations. Similarly, the performance results are also quite beneficial for determining the system's performance in the sense that many practical wireless standards extensively employ MIMO-OFDM systems in conjunction with M-ary quadrature amplitude modulation (M-QAM) constellation. This paper thus, derives exact closed form expressions for the SER of M-ary Gray-coded one and two dimensional constellations when an OSTBC is employed and Nt transmit antennas are selected for transmission over frequency-selective Nakagami-m fading channels. For this purpose, first an exact closed-form of average SER expression of OSTBC based MIMO-OFDM system for M-ary phase shift keying (M-PSK) using traditional probability density function (PDF) approach is derived. We then compute exact closed form average SER expressions for M-ary pulse amplitude modulation (M-PAM) and M-QAM schemes by utilizing this generalized result. These expressions are valid over both frequency-flat and frequency-selective Nakagami-m fading MIMO channels and can easily be evaluated without using any numerical integration methods. We also show that average SER of MIMO-OFDM system using OSTBC in case of frequency-selective Rayleigh fading channels remains independent to the number of taps, L of that fading channel and the performance of the same system for two-tap un-correlated Rayleigh and Nakagami-m fading channels is better than that of the correlated one. Moreover, Monte Carlo simulation of MIMO-OFDM system
2008-12-01
L-branch maximal-ratio combining with Rayleigh -fading signals, the resulting signal is Nakagami with m L= . It can be shown that when diversity L is...used and the channel is modeled as a Nakagami - m fading channel, the performance is identical to that obtained for a Rayleigh fading channel with...when 1m = the Nakagami - m pdf corresponds to the Rayleigh pdf since ( )1 !n nΓ + = . Generally speaking, for 1m < , the fading is more severe than
Trellis coded modulation for 4800-9600 bits/s transmission over a fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Divsalar, Dariush; Simon, Marvin K.
1987-01-01
The combination of trellis coding and multiple phase-shift-keyed (MPSK) signaling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.
Trellis coded modulation for 4800-9600 bits/s transmission over a fading mobile satellite channel
NASA Technical Reports Server (NTRS)
Divsalar, Dariush; Simon, Marvin K.
1987-01-01
The combination of trellis coding and multiple phase-shift-keyed (MPSK) signaling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.
NASA Astrophysics Data System (ADS)
Sithamparanathan, Kandeepan; Piesiewicz, Radoslaw
In this paper we study and present some results on the performances of frequency tracking for Ka-band satellite communications in rain fading channels. The carrier frequency is tracked using a 2nd order hyperbolic phase detector based digital-phase locked loop (D-PLL). The hyperbolic D-PLL has the capability of extending the tracking range compared to the other D-PLL and hence can be designed such that to achieve low phase jitter performance for improved carrier tracking. We present the design and analysis of the D-PLL and show some simulation results on the frequency tracking performance for Ka-band rain fading channel. The results are compared with the non-fading noise only case and comparative analyses are made.
NASA Astrophysics Data System (ADS)
Lee, Wooju; Yoon, Dongweon
Cooperative relay selection, in which one of multiple relays is selected to retransmit the source signal to the destination, has received considerable attention in recent years, because it is a simple way to obtain cooperative diversity in wireless networks. The exact expression of outage probability for a decode-and-forward cooperative relay selection with multiple source and destination antennas over Rayleigh fading channels was recently derived in [9]. In this letter, we derive the exact expressions of outage probability and diversity-multiplexing tradeoff over independent and non-identically distributed Nakagami-m fading channels as an extension of [9]. We then analyze the effects of various parameters such as fading conditions, number of relays, and number of source and destination antennas on the outage probability.
NASA Astrophysics Data System (ADS)
Bui, Huu Phu; Nishimoto, Hiroshi; Nishimura, Toshihiko; Ohgane, Takeo; Ogawa, Yasutaka
In time-varying fading environments, the performance of multiple-input multiple-output (MIMO) systems applying an eigenbeam-space division multiplexing (E-SDM) technique may be degraded due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed some channel prediction methods. Simulation results based on computer-generated channel data showed that better performance can be obtained when using the prediction methods in Rayleigh fading environments assuming the Jakes model with rich scatterers. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS case, scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antennas at both the transmitter and the receiver cannot be ignored as it affects the system performance in actual implementation. We conducted MIMO channel measurement campaigns at a 5.2GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. The results show that robust bit-error rate performance is obtained when using the channel prediction methods and that the methods can be used in both Rayleigh and Rician fading environments, and do not need to know the maximum Doppler frequency.
Acoustic echo cancellation for full-duplex voice transmission on fading channels
NASA Technical Reports Server (NTRS)
Park, Sangil; Messer, Dion D.
1990-01-01
This paper discusses the implementation of an adaptive acoustic echo canceler for a hands-free cellular phone operating on a fading channel. The adaptive lattice structure, which is particularly known for faster convergence relative to the conventional tapped-delay-line (TDL) structure, is used in the initialization stage. After convergence, the lattice coefficients are converted into the coefficients for the TDL structure which can accommodate a larger number of taps in real-time operation due to its computational simplicity. The conversion method of the TDL coefficients from the lattice coefficients is derived and the DSP56001 assembly code for the lattice and TDL structure is included, as well as simulation results and the schematic diagram for the hardware implementation.
NASA Astrophysics Data System (ADS)
Wang, Ping; Yang, Bensheng; Guo, Lixin; Shang, Tao
2015-11-01
In this work, the symbol error rate (SER) performance of the multiple pulse position modulation (MPPM) based free-space optical communication (FSO) system with three different decision thresholds, fixed decision threshold (FDT), optimized decision threshold (ODT) and dynamic decision threshold (DDT) over exponentiated Weibull (EW) fading channels has been investigated in detail. The effects of aperture averaging on each decision threshold under weak-to-strong turbulence conditions are further studied and compared. The closed-form SER expressions for three thresholds derived with the help of generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulations. This work is helpful for the design of receivers for FSO communication systems.
Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links.
Toyoshima, Morio; Takenaka, Hideki; Takayama, Yoshihisa
2011-08-15
The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime. © 2011 Optical Society of America
Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links
NASA Astrophysics Data System (ADS)
Toyoshima, Morio; Takenaka, Hideki; Takayama, Yoshihisa
2011-08-01
The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime.
NASA Astrophysics Data System (ADS)
Zhu, Shanying; Soh, Yeng Chai; Xie, Lihua
2016-02-01
In this paper, we consider a general distributed estimation problem in relay-assisted sensor networks by taking into account time-varying asymmetric communications, fading channels and intermittent measurements. Motivated by centralized filtering algorithms, we propose a distributed innovation-based estimation algorithm by combining the measurement innovation (assimilation of new measurement) and local data innovation (incorporation of neighboring data). Our algorithm is fully distributed which does not need a fusion center. We establish theoretical results regarding asymptotic unbiasedness and consistency of the proposed algorithm. Specifically, in order to cope with time-varying asymmetric communications, we utilize an ordering technique and the generalized Perron complement to manipulate the first and second moment analyses in a tractable framework. Furthermore, we present a performance-oriented design of the proposed algorithm for energy-constrained networks based on the theoretical results. Simulation results corroborate the theoretical findings, thus demonstrating the effectiveness of the proposed algorithm.
NASA Technical Reports Server (NTRS)
Lin, Shu; Rhee, Dojun
1996-01-01
This paper is concerned with construction of multilevel concatenated block modulation codes using a multi-level concatenation scheme for the frequency non-selective Rayleigh fading channel. In the construction of multilevel concatenated modulation code, block modulation codes are used as the inner codes. Various types of codes (block or convolutional, binary or nonbinary) are being considered as the outer codes. In particular, we focus on the special case for which Reed-Solomon (RS) codes are used as the outer codes. For this special case, a systematic algebraic technique for constructing q-level concatenated block modulation codes is proposed. Codes have been constructed for certain specific values of q and compared with the single-level concatenated block modulation codes using the same inner codes. A multilevel closest coset decoding scheme for these codes is proposed.
Ren, Peng; Qian, Jiansheng
2016-06-07
This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face.
Ren, Peng; Qian, Jiansheng
2016-01-01
This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face. PMID:27338380
Performance Analysis of Amplify-and-Forward Relaying over Shadowed Nakagami-
NASA Astrophysics Data System (ADS)
Cai, Chunxiao; Cai, Yueming; Yang, Weiwei
2011-11-01
In the paper, the closed-form approximation for outage probability and symbol error probability are presented for amplify-and-forward cooperative network over shadowed Nakagami-
2002-09-01
modeled as a random variable. Typical models are the Rayleigh , Ricean, and Nakagami - m distributions. In this thesis, two widely used models for...and [2], frequency-selective, Rayleigh fading channels [3], and frequency-selective, slow, Nakagami channels [4]. Unlike the above referenced work...signal component where i qM M M = × ; therefore, the probability of symbol error for rectangular QAM can be expressed as ( )error on error on . i q i
NASA Astrophysics Data System (ADS)
Miyatani, Tetsuhiko
This letter describes a new QR-decomposition maximum likelihood detector that is combined with frequency-domain equalization for single-carrier transmission based multiple-input multiple-output systems. By utilizing the equalized substreams to adjust the frequency selectivity in corresponding substreams in subsequent stages, the packet error rate performances of the proposed detector is superior to that of the minimum mean squared error receiver by a factor of the receive antenna diversity gain.
NASA Astrophysics Data System (ADS)
Liang, Bin; Gunawan, Erry; Law, Choi Look; Teh, Kah Chan
Analytical expressions based on the Gauss-Chebyshev quadrature (GCQ) rule technique are derived to evaluate the bit-error rate (BER) for the time-hopping pulse position modulation (TH-PPM) ultra-wide band (UWB) systems under a Nakagami-m fading channel. The analyses are validated by the simulation results and adopted to assess the accuracy of the commonly used Gaussian approximation (GA) method. The influence of the fading severity on the BER performance of TH-PPM UWB system is investigated.
Wide-band packet radio for multipath environments
NASA Astrophysics Data System (ADS)
Fischer, Jeffrey H.; Cafarella, John H.; Bouman, Charles A.; Flynn, Gerard T.; Dolat, Victor S.
1988-05-01
A direct-sequence spread-spectrum packet radio is described that has versatile signal-processing and local-control capabilities designed to support the functions required of a robust mobile communications network. Noteworthy capabilities include eleven selectable data rates with accurate range measurements in a fading multipath channel. The radio uses a hybrid analog/digital signal processor and nonrepeating spreading codes for suppression of intersymbol interference and jamming. It incorporates two sets of monolithic surface-acoustic-wave convolvers as programmable matched filters with time-bandwidth products of 64 and 2000. The analog matched filters are coupled with binary postprocessing for the functions of detection, RAKE demodulation, and ranging measurements over a wide multipath spread. The data rate can be varied in response to channel conditions from 1.45 Mb/s down to 44 b/s with an almost ideal tradeoff in signal-processing gain from 18 dB up to 61 dB prior to multipath combining.
NASA Astrophysics Data System (ADS)
Zhang, Zeyu; Zhu, Chengrui; He, Guangqiang
2015-08-01
Quantum key distribution can be used to share secret keys with information-theoretic security between two legitimate partners for secure communication. In the case of satellite communication, free-space channel is the only way to transmit information, thus research on its properties is of great significance to quantum cryptographic communication. In this paper, we thoroughly analyze the influence of free-space channel fading effects on continuous variable quantum key distribution and for the first time prove that random distribution (such as Rayleigh distribution, Rice distribution and et al.) of free-space channel fading coefficients can be used to increase secret information rates and improve system stability against excess noises. Our results offer academic reference for practical applications of ground-space and space-space quantum communication and global quantum communication network.
Xu, Yong; Lu, Renquan; Shi, Peng; Li, Hongyi; Xie, Shengli
2016-12-15
This paper considers finite-time distributed state estimation for discrete-time nonlinear systems over sensor networks. The Round-Robin protocol is introduced to overcome the channel capacity constraint among sensor nodes, and the multiplicative noise is employed to model the channel fading. In order to improve the performance of the estimator under the situation, where the transmission resources are limited, fading channels with different stochastic properties are used in each round by allocating the resources. Sufficient conditions of the average stochastic finite-time boundedness and the average stochastic finite-time stability for the estimation error system are derived on the basis of the periodic system analysis method and Lyapunov approach, respectively. According to the linear matrix inequality approach, the estimator gains are designed. Finally, the effectiveness of the developed results are illustrated by a numerical example.
Outage performance of MIMO FSO links over strong turbulence and misalignment fading channels.
García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2011-07-04
Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the performance over free-space optical (FSO) links. Additionally, since FSO systems are usually installed on high buildings, building sway causes vibrations in the transmitted beam, leading to an unsuitable alignment between transmitter and receiver and, hence, a greater deterioration in performance. In this paper, the outage probability as a performance measure for multiple-input/multiple-output (MIMO) FSO communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels with pointing errors is analyzed. Novel closed-form expressions for the outage probability as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam is susceptible to either strong turbulence conditions, following a negative exponential distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show that the diversity order is independent of the pointing error when the equivalent beam radius at the receiver is at least twice the value of the pointing error displacement standard deviation at the receiver. Simulation results are further demonstrated to confirm the analytical results. Additionally, since proper FSO transmission requires transmitters with accurate control of their beamwidth, asymptotic expressions here obtained for different diversity techniques are used to find the optimum beamwidth that minimizes the outage performance.
On the capacity of MISO FSO systems over gamma-gamma and misalignment fading channels.
Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Beatriz; Castillo-Vázquez, Carmen
2015-08-24
In this work, the ergodic capacity performance for multiple-input/single-output (MISO) free-space optical (FSO) communications system with equal gain combining (EGC) reception is analyzed over gamma-gamma and misalignment fading channels, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.). Novel and analytical closed-form ergodic capacity expression is obtained in terms of H-Fox function by using the well-known inequality between arithmetic and geometric mean of positive random variables (RV) in order to obtain an approximate closed-form expression of the distribution of the sum of M gamma-gamma with pointing errors variates. In addition, we present an asymptotic ergodic capacity expression at high signal-to-noise ratio (SNR) for the ergodic capacity of MISO FSO systems. It can be concluded that the use of MISO technique can significantly reduce the effect of the atmospheric turbulence as well as pointing errors and, hence, provide significant capacity gain over the direct path link (DL). The impact of pointing errors on the MISO FSO system is also analyzed, which only depends on the number of laser sources and pointing error parameters. Moreover, it can be also concluded that the ergodic capacity performance is dramatically reduced as a consequence of the severity of pointing error effects. Simulation results are further demonstrated to confirm the analytical results.
Improved GOB synchronization for robust transmission of H.263 video over slow-fading channels
NASA Astrophysics Data System (ADS)
Abrardo, Andrea; Barni, Mauro; Garzelli, Andrea
2001-10-01
Among the techniques to limit the effect of error propagation in low bitrate video coding, the best performance is achieved through the joint use of forward error correction (FEC) and automatic repeat request strategies. However, retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission bit rate. In this paper, a strategy is proposed which instead of protecting the whole H.263 video stream, uses all the redundancy to protect the most important parts of the bit stream, i.e., group-of-block (GOB) start codes. More specifically, the 22-bit long start code used in the H.263 standard is replaced with longer Gold sequences which ensure a higher protection against noise. A different sequence is used for each GOB so that additional information can be obtained which can be used to improve the quality of the decoded sequence. The new technique is derived by assuming a slow-fading channel such as those encountered in pedestrian applications. Simulation results prove the effectiveness of the proposed technique with respect to classical FEC schemes in terms of PSNR and overall bit rate.
NASA Technical Reports Server (NTRS)
Rajpal, Sandeep; Rhee, DoJun; Lin, Shu
1997-01-01
In this paper, we will use the construction technique proposed in to construct multidimensional trellis coded modulation (TCM) codes for both the additive white Gaussian noise (AWGN) and the fading channels. Analytical performance bounds and simulation results show that these codes perform very well and achieve significant coding gains over uncoded reference modulation systems. In addition, the proposed technique can be used to construct codes which have a performance/decoding complexity advantage over the codes listed in literature.
Hou, Nan; Dong, Hongli; Wang, Zidong; Ren, Weijian; Alsaadi, Fuad E
2017-05-01
In this paper, the H∞ state estimation problem is investigated for a class of uncertain discrete-time neural networks subject to infinitely distributed delays and fading channels. Randomly occurring uncertainties (ROUs) are introduced to reflect the random nature of the network condition fluctuations, and the channel fading phenomenon is considered to account for the possibly unreliable network medium on which the measurement signal is transmitted. A set of Bernoulli-distributed white sequences are employed to govern the ROUs and the L-th Rice fading model is utilized where channel coefficients are mutually independent random variables with certain probability density function on [0,1]. We aim to design a state estimator such that the dynamics of the estimation error is asymptotically stable while satisfying the prescribed H∞ performance constraint. By adopting the Lyapunov-Krasovskii functional and the stochastic analysis theory, sufficient conditions are established to ensure the existence of the desired state estimators and the explicit expression of such estimators is acquired. A simulation example is provided to verify the usefulness of the proposed approach. Copyright © 2016 Elsevier Ltd. All rights reserved.
QAM multi-path characterization due to ocean scattering
Petersen, T. L.; Bracht, R. R.; Pasquale, R. V.; Dimsdle, J.; Swanson, R.
2002-01-01
A series of RF channel flight characterization tests are to be run, in early March, to benchmark high speed, 16QAM multi-path performance over the ocean surface. The modulation format being tested is a 16 differential phase, absolute amplitude, two level polar quadrature amplitude modulation. The bit rate is 100 Megabits per second. This transmitted signal will be generated in a burst mode, being on for 40 microseconds once every 40 milliseconds. An aircraft will radiate the RF test signal at 5 different altitudes. The aircraft will make two inward flights at each altitude with vertical and horizontal polarization respectively. Receivers are to be placed in two different locations using circular antenna polarization. One receiver will be placed at an altitude of 230 feet above the ocean surface, and the other on a boat with the antenna placed just up off of the ocean surface. Data is to be collected over multiple wavelength changes in the difference between the line of sight and the reflected multi-path ray. The real time signal strength variation is to be recorded as well. Analysis of the resulting data will show flat fading and frequency selective fading effects. The test is run over two different days to provide for some variation in sea state conditions. This resulting information will help quantify the effectiveness of this novel modulation scheme for missile telemetry end event data applications.
NASA Astrophysics Data System (ADS)
Xu, Ding; Li, Qun
2017-01-01
This paper addresses the power allocation problem for cognitive radio (CR) based on hybrid-automatic-repeat-request (HARQ) with chase combining (CC) in Nakagamimslow fading channels. We assume that, instead of the perfect instantaneous channel state information (CSI), only the statistical CSI is available at the secondary user (SU) transmitter. The aim is to minimize the SU outage probability under the primary user (PU) interference outage constraint. Using the Lagrange multiplier method, an iterative and recursive algorithm is derived to obtain the optimal power allocation for each transmission round. Extensive numerical results are presented to illustrate the performance of the proposed algorithm.
NASA Astrophysics Data System (ADS)
Bochkov, G. N.; Gorokhov, K. V.; Kolobkov, A. V.
2013-08-01
New methods of symbol-timing and carrier-frequency blind synchronization of an OFDM-signal receiver are developed and studied. They generalize the well-known methods which use either the protection interval in time in the cyclic prefix form or the protection interval with respect to frequency in the form of virtual subcarriers, and are based on their joint application. To reduce the computational complexity, approximate algorithms which are based on the approximation of the optimal rules, but, according to the study results, have almost the same characteristics of parameter-estimation accuracy and the reception bit-error-rate performance are proposed. It is shown that in terms of the parameter-estimation accuracy and the reception bit-error-rate performance, the proposed methods are superior to the well-known methods of synchronization by the cyclic prefix and the virtual subcarriers in the two-path Rayleigh-fading channel. For incoherent systems with the differential phase shift keying variants, using such methods makes it possible to rule out the necessity of accurate synchronization and, due to insignificant redundancy of the system band and the cyclic prefix length, closely approach the reception bit-error-rate performance for perfect synchronization.
Ultrasonic Digital Communication System for a Steel Wall Multipath Channel: Methods and Results
Murphy, Timothy L.
2005-12-01
As of the development of this thesis, no commercially available products have been identified for the digital communication of instrumented data across a thick ({approx} 6 n.) steel wall using ultrasound. The specific goal of the current research is to investigate the application of methods for digital communication of instrumented data (i.e., temperature, voltage, etc.) across the wall of a steel pressure vessel. The acoustic transmission of data using ultrasonic transducers prevents the need to breach the wall of such a pressure vessel which could ultimately affect its safety or lifespan, or void the homogeneity of an experiment under test. Actual digital communication paradigms are introduced and implemented for the successful dissemination of data across such a wall utilizing solely an acoustic ultrasonic link. The first, dubbed the ''single-hop'' configuration, can communicate bursts of digital data one-way across the wall using the Differential Binary Phase-Shift Keying (DBPSK) modulation technique as fast as 500 bps. The second, dubbed the ''double-hop'' configuration, transmits a carrier into the vessel, modulates it, and retransmits it externally. Using a pulsed carrier with Pulse Amplitude Modulation (PAM), this technique can communicate digital data as fast as 500 bps. Using a CW carrier, Least Mean-Squared (LMS) adaptive interference suppression, and DBPSK, this method can communicate data as fast as 5 kbps. A third technique, dubbed the ''reflected-power'' configuration, communicates digital data by modulating a pulsed carrier by varying the acoustic impedance at the internal transducer-wall interface. The paradigms of the latter two configurations are believed to be unique. All modulation methods are based on the premise that the wall cannot be breached in any way and can therefore be viably implemented with power delivered wirelessly through the acoustic channel using ultrasound. Methods, results, and considerations for future research are discussed
Doppler-multipath tolerant voice communication
NASA Astrophysics Data System (ADS)
Harris, R. M.
Line of sight communication between high performance aircraft has been found to be subject to a peculiar form of multipath radio wave propagation - Doppler multipath. It degrades analogue voice reception on the standard fit ultrahigh frequency radio, producing low frequency random noise and warbling. Various modifications were carried out on the aircraft's communications system, but the problem remained. All the evidence points to a natural phenomenon. The reported observations are corroborated by theoretical studies and laboratory simulations of multipath radio wave propagation between two points moving relative to a diffusely scattering reflector. Theoretical predictions of Rician fading have explained the disruption of speech transmitted using conventional dsb(am) modulation. This also indicated suppressing the carrier as a radical cure. Double sideband suppressed carrier radios have been developed for airborne evaluation in comparison with standard dsb(am). The air to air flying trials proved the superior performance of the suppressed carrier system under conditions of Doppler multipath.
NASA Astrophysics Data System (ADS)
Ranjha, Bilal; Zhou, Zhou; Kavehrad, Mohsen
2014-08-01
We have compared the bit error rate (BER) performance of precoding-based asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and pulse amplitude modulated discrete multitone (PAM-DMT) optical wireless (OW) systems in additive white Gaussian noise (AWGN) and indoor multipath frequency selective channel. Simulation and analytical results show that precoding schemes such as discrete Fourier transform, discrete cosine transform, and Zadoff-Chu sequences do not affect the performance of the OW systems in the AWGN channel while they do reduce the peak-to-average power ratio (PAPR) of the OFDM output signal. However, in a multipath indoor channel, using zero forcing frequency domain equalization precoding-based systems give better BER performance than their conventional counterparts. With additional clipping to further reduce the PAPR, precoding-based systems also show better BER performance compared to nonprecoded systems when clipped relative to the peak of nonprecoded systems. Therefore, precoding-based ACO-OFDM and PAM-DMT systems offer better BER performance, zero signaling overhead, and low PAPR compared to conventional systems.
NASA Astrophysics Data System (ADS)
Garzelli, Andrea; Abrardo, Andrea; Barni, Mauro; Marotta, D.
2000-11-01
The objective of this work is to analyze and compare H.263 resilience techniques for H.223-based real-time video transmission over narrow-band slow-fading channels. These channel conditions, which are typical for pedestrian video communications, are very critical, because they require Forward Error Correction (FEC), since data retransmission is not feasible, due to high network delay, and they reduce the effectiveness of FEC techniques- due to the bursty nature of the channel. In this work, two different strategies for H.263 video protection against channel errors are considered and compared. The strategies are tested over a slow-fading wireless channel, over which the H.263 video streams, organized and multiplexed by the H.223 Multiplex Protocol, are transmitted. Both standard FEC techniques considered by the H.223 recommendation for equal error protection of the video stream, and unequal error protection (UEP) through GOB synchronization are tested. The experimental results of this comparative analysis prove the superiority of the UEP technique for H.223-based video transmission.
NASA Astrophysics Data System (ADS)
Panajotović, Aleksandra; Sekulović, Nikola; Drača, Dragan; Stefanović, Mihajlo; Stefanović, Časlav
2013-12-01
A dual selection combining (SC) receiver with correlated and unbalanced diversity branches operating in interference-limited Nakagami-m fading environment is considered in this paper. Actually, average fade duration (AFD) of SC system applying desired signal decision algorithm is obtained. Numerical results can be used to examine the effects of fading severity, input signal-to-interference ratio (SIR) unbalance and level of branch correlation on the AFD, as well as the correctness of proposed analytical formulation.
NASA Astrophysics Data System (ADS)
Xu, D.; Feng, Z.; Zhang, P.
2013-04-01
This paper considers a spectrum sharing cognitive radio (CR) network consisting of one secondary user (SU) and one primary user (PU) in Rayleigh fading environments. The channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is assumed to be imperfect. Particularly, this CSI is assumed to be not only having channel estimation errors but also outdated due to feedback delay, which is different from existing work. We derive the closed-form expression for the outage capacity of the SU with this imperfect CSI under the average interference power constraint at the PU. Analytical results confirmed by simulations are presented to show the effect of the imperfect CSI. Particularly, it is shown that the outage capacity of the SU is robust to the channel estimation errors and feedback delay for low outage probability and high channel estimation errors and feedback delay.
NASA Astrophysics Data System (ADS)
Schmidt, Barnet Michael
An optimal performance monitoring metric for a hybrid free space optical and radio-frequency (RF) wireless network, the Outage Capacity Objective Function, is analytically developed and studied. Current and traditional methods of performance monitoring of both optical and RF wireless networks are centered on measurement of physical layer parameters, the most common being signal-to-noise ratio, error rate, Q factor, and eye diagrams, occasionally combined with link-layer measurements such as data throughput, retransmission rate, and/or lost packet rate. Network management systems frequently attempt to predict or forestall network failures by observing degradations of these parameters and to attempt mitigation (such as offloading traffic, increasing transmitter power, reducing the data rate, or combinations thereof) prior to the failure. These methods are limited by the frequent low sensitivity of the physical layer parameters to the atmospheric optical conditions (measured by optical signal-to-noise ratio) and the radio frequency fading channel conditions (measured by signal-to-interference ratio). As a result of low sensitivity, measurements of this type frequently are unable to predict impending failures sufficiently in advance for the network management system to take corrective action prior to the failure. We derive and apply an optimal measure of hybrid network performance based on the outage capacity of the hybrid optical and RF channel, the outage capacity objective function. The objective function provides high sensitivity and reliable failure prediction, and considers both the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The radio frequency segment analysis considers the three most common RF channel fading statistics: Rayleigh, Ricean, and Nakagami-m. The novel application of information theory to the underlying physics of the
NASA Astrophysics Data System (ADS)
Giggenbach, Dirk; Wilkerson, Brandon L.; Henniger, Hennes; Perlot, Nicolas
2006-08-01
Mitigation of index of refraction turbulence (IRT) effects is crucial in long-range atmospheric communication links. Diversity-transmission is one favorable way for fading compensation. One of several different diversity concepts is the exploitation of the wavelength-dependent index of refraction of the atmosphere, which leads to ideal stochastically independent fading at different wavelengths, depending on the scenario. This concept is here named wavelength-diversity (WLD). Theoretical analysis and numerical simulation for the strength of this effect are given and verified by experimental tests.
NASA Astrophysics Data System (ADS)
Kim, Jung-Bin; Kim, Dongwoo
Combining relaying and multi-input multi-output (MIMO) transmission is a generic way to overcome the channel-fading impairments. Best antenna selection is a simple but efficient MIMO method that achieves the full diversity and also serves as a lower bound reference of MIMO performance. For a dual-hop MIMO system with an ideal amplify-and-forward (AF) relaying gain and best antenna selection, we provide a probability density function (PDF) of received signal-to-noise ratio (SNR) and an analytic BER equation when using M-ary PSK in Rayleigh fading channels. The analytic result is shown to exactly match with simulated one. Furthermore, the effect of link unbalance between the first hop and the second hop, due to differences in the number of antennas deployed in both hops as well as in the average power of channel coefficients, on the BER performance is numerically investigated and the results show that the links with better balance give better performance.
Bit error rate performance of pi/4-DQPSK in a frequency-selective fast Rayleigh fading channel
NASA Technical Reports Server (NTRS)
Liu, Chia-Liang; Feher, Kamilo
1991-01-01
The bit error rate (BER) performance of pi/4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For pi/4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) pi/4-DQPSK operated at a carrier frequency of 850 MHz and C/I less than 20 dB, the BER will be dominated by CCI if the vehicular speed is below 100 mi/h. In this derivation, frequency-selective fading is modeled by two independent Rayleigh signal paths. Only one co-channel is assumed in this derivation. The results obtained are also shown to be valid for discriminator detection of M-ary DPSK signals.
NASA Astrophysics Data System (ADS)
Lee, Jaeyoon; Yoon, Dongweon; Park, Sang Kyu
Recently, we provided closed-form expressions involving two-dimensional (2-D) joint Gaussian Q-function for the symbol error rate (SER) and bit error rate (BER) of an arbitrary 2-D signal with I/Q unbalances over an additive white Gaussian noise (AWGN) channel [1]. In this letter, we extend the expressions to Nakagami-m fading channels. Using Craig representation of the 2-D joint Gaussian Q-function, we derive an exact and general expression for the error probabilities of arbitrary 2-D signaling with I/Q phase and amplitude unbalances over Nakagami-m fading channels.
Cognitive Jointly Optimal Code-Division Channelization and Routing Over Cooperative Links
2014-04-01
Estimation . . . . . . . 47 Q. Experimental Testbed Setup . . . . . . . . . . . . . . . . . . . . . 50 R. USRP2 Receiver: Low-cost, Commercial SDRs ...we design and implement a wireless software defined radio ( SDR ) testbed for cognitive channelization in multipath fading environments. Pri- mary and...while at the same time maintains interference to primary users below a prespec- ified threshold. We deployed four commercial, low-cost SDR
System for Processing Coded OFDM Under Doppler and Fading
NASA Technical Reports Server (NTRS)
Tsou, Haiping; Darden, Scott; Lee, Dennis; Yan, Tsun-Yee
2005-01-01
An advanced communication system has been proposed for transmitting and receiving coded digital data conveyed as a form of quadrature amplitude modulation (QAM) on orthogonal frequency-division multiplexing (OFDM) signals in the presence of such adverse propagation-channel effects as large dynamic Doppler shifts and frequency-selective multipath fading. Such adverse channel effects are typical of data communications between mobile units or between mobile and stationary units (e.g., telemetric transmissions from aircraft to ground stations). The proposed system incorporates novel signal processing techniques intended to reduce the losses associated with adverse channel effects while maintaining compatibility with the high-speed physical layer specifications defined for wireless local area networks (LANs) as the standard 802.11a of the Institute of Electrical and Electronics Engineers (IEEE 802.11a). OFDM is a multi-carrier modulation technique that is widely used for wireless transmission of data in LANs and in metropolitan area networks (MANs). OFDM has been adopted in IEEE 802.11a and some other industry standards because it affords robust performance under frequency-selective fading. However, its intrinsic frequency-diversity feature is highly sensitive to synchronization errors; this sensitivity poses a challenge to preserve coherence between the component subcarriers of an OFDM system in order to avoid intercarrier interference in the presence of large dynamic Doppler shifts as well as frequency-selective fading. As a result, heretofore, the use of OFDM has been limited primarily to applications involving small or zero Doppler shifts. The proposed system includes a digital coherent OFDM communication system that would utilize enhanced 802.1la-compatible signal-processing algorithms to overcome effects of frequency-selective fading and large dynamic Doppler shifts. The overall transceiver design would implement a two-frequency-channel architecture (see figure
NASA Astrophysics Data System (ADS)
Landolsi, Taha; Elrefaie, Aly F.
2016-05-01
M-ary pulse position modulation (PPM) systems have been considered in free-space optical (FSO) communications, optical fiber links, and passive optical networks. In this paper, we study the error performance of direct-detection optically preamplified M-ary PPM systems over slowly fading FSO channels. The study considers the combined effects on the probability of bit error, Pb, of channel fading with a given scintillation index, σp2, the transmitter finite extinction ratio, r, and the preamplifier spontaneous emission (ASE) noise. We provide results for both single and dual-polarized systems with symbol sizes M ∈ { 2, 4, …, 1024 } at Pb =10-4 and Pb =10-9. The fading models considered in this study are the exponential, log-normal, and gamma-gamma channels. For single-polarized systems with infinite extinction ratios, we provide closed-form expressions for the bit error probabilities for the three channel models. For the dual-polarized systems we compute them numerically. The results indicate that gamma-gamma fading imposes a more severe penalty than the log-normal case. In this study, the power penalty at Pb =10-9 ranges between 1.8 and 14 dB for the log-normal channel, whereas it ranges between 2.2 and 30.7 dB for the gamma-gamma channel. The study also demonstrates that the power penalty due to the combined effects of transmitter finite r and channel fading is the sum of the penalty due to fading alone and the penalty due to a finite r alone, and that the power penalty for dual-polarized systems is about 0.4 dB larger than single-polarized ones.
NASA Astrophysics Data System (ADS)
Al-Hussaibi, Walid
2015-09-01
Chaos synchronization is one of the main challenging issues involved in the development of wireless chaos-based secure communication (CBSC) due its crucial influence on the error performance and system reliability. This paper is concerned with the effect of filtering chaotic signals on the synchronization and error performance of CBSC schemes due to the finite bandwidth of realistic fading channel and/or signal detection necessities. The double scroll chaotic attractor is employed at the transmit and receive terminals as in a drive-response configuration with identical synchronization and a low pass filter model is utilized in this investigation. The upper bound of bit error probability considering Rayleigh fading channel and synchronization mean squared error is derived and evaluated for different values of filter parameter. Theoretical analysis and simulation results show that as the filter cut-off frequency decreased lower than the chaotic signal bandwidth, the synchronization error is considerably increased due to high distortion in the normal geometrical configuration of the attractor. As a result, the average bit-error-rate performance is degraded significantly with high possibility of link failure. Therefore, careful system design should be made to mitigate the filtering effects and achieve the essential synchronization of promising CBSC systems.
Lee, In-Ho
2014-01-01
We propose enhanced spatial multiplexing codes (E-SMCs) to enable various encoding rates. The symbol error rate (SER) performance of the E-SMC is investigated when zero-forcing (ZF) and maximal-ratio combining (MRC) techniques are used at a receiver. The proposed E-SMC allows a transmitted symbol to be repeated over time to achieve further diversity gain at the cost of the encoding rate. With the spatial correlation between transmit antennas, SER equations for M-ary QAM and PSK constellations are derived by using a moment generating function (MGF) approximation of a signal-to-noise ratio (SNR), based on the assumption of independent zero-forced SNRs. Analytic and simulated results are compared for time-varying and spatially correlated Rayleigh fading channels that are modelled as first-order Markovian channels. Furthermore, we can find an optimal block length for the E-SMC that meets a required SER. PMID:25114969
Effects of fading and interference in narrowband land-mobile networks
NASA Astrophysics Data System (ADS)
Linnartz, Johan Paul Marie Gerard
1991-05-01
The performance of mobile radio systems with narrowband radio channels is studied. Several results of previous research are included. In particular, the effects of multipath and shadow 'fading' and of mutual 'interference' between mobile users is investigated. To this end, initially the relevant propagation mechanisms are addressed, focusing on statistical channel models. For the planning of real systems, the suitability of some propagation models using terrain data is empirically evaluated. The statistical channel description is used to compute the performance of mobile radio links. Expressions are given for the outage probability and for the average duration of fades, taking account of mutual interference between users. A simplified model for the bit error rate in digital transmission is proposed. Numerical results are given for mobile telephone networks.
Combined coding and delay-throughput analysis for fading channels of mobile satellite communications
NASA Technical Reports Server (NTRS)
Wang, C. C.; Yan, Tsun-Yee
1986-01-01
This paper presents the analysis of using the punctured convolutional code with Viterbi decoding to improve communications reliability. The punctured code rate is optimized so that the average delay is minimized. The coding gain in terms of the message delay is also defined. Since using punctured convolutional code with interleaving is still inadequate to combat the severe fading for short packets, the use of multiple copies of assignment and acknowledgment packets is suggested. The performance on the average end-to-end delay of this protocol is analyzed. It is shown that a replication of three copies for both assignment packets and acknowledgment packets is optimum for the cases considered.
NASA Astrophysics Data System (ADS)
El-Bahaie, Ebtehal H.; Al-Hussaini, Emad K.
2010-12-01
In this paper analytical and simulation results for the decentralized detection of unknown signals are introduced. Parallel sensor network scheme is assumed. Additive White Gaussian Noise (AWGN) and Nakagami fading are assumed in both links, that is, from the source to the decentralized local sensors and from the sensors to the fusion center. Furthermore, diversity employing Square Law Combining (SLC) or Square Law Selection (SLS) is considered at each sensor, for both independent and correlated branches. Appreciable improvements are obtained with the increase of the number of sensors and the diversity employment.
Performance Analysis of OFDM in Frequency Selective, Slowly Fading Nakagami Channels
2001-12-01
Rayleigh is a special case of the Nakagami - m distribution. 3...35 This is why we consider the Rayleigh distribution to be a special case of the Nakagami PDF. In Figure 11 the Nakagami - m PDF is illustrated...obtain ( )4 1 3 1 b b M qP Q Mq M γ− = − (3.29) 44 Once again, to obtain the BER in Nakagami fading, we must average the
NASA Technical Reports Server (NTRS)
Bell, David; Gevargiz, John; Vaisnys, Arvydas; Julian, David
1995-01-01
The DBS radio propagation environment is divided into three sub-environments, indoor, rural-suburban mobile and urban mobile. Indoor propagation effects are in a large part determined by construction material. Non-metallic materials afford direct, albeit attenuated penetration of the satellite signal with a minimum of multipath signal scattering. Signal penetration into structures using significant metallic materials is often indirect, through openings such as doors and windows and propagation will involve significant multipath components. Even so, delay spread in many situations is on the order of 10's of nanoseconds resulting in relatively flat fading. Thus frequency diversity techniques such as Orthogonal Frequency Division Multiplex (OFDM) and Code Division Multiple Access (CDMA) or equalization techniques do not realize their intended performance enhancement. Antenna diversity, directivity and placement are key mitigation techniques for the indoor environment. In the Rural-Suburban mobile environment with elevation angles greater than 20 deg, multipath components from the satellite signal are 15-20 dB below the line-of-sight signal level and often originate from nearby reflectors. Thus shadowing is the dominant signal impairment and fading effects are again found to be relatively flat for a large fading margin. Because receiver motion induces rapid variations in the signal level, temporal diversity techniques such as interleaving, channel coding and retransmission can be used to combat short intermittent fading events. Antenna diversity and directivity techniques are again useful in this environment. Finally, in the Urban mobile environment, slower vehicle speeds and blockage by buildings causes signal fades that are too long and too deep to combat with signal margin or time diversity. Land-based signal boosters are needed to fill in the coverage gaps of the satellite only broadcast scheme. On frequency boosters are suggested to conserve bandwidth yet these
Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2014-06-30
In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.
Analytic Nakagami fading parameter estimation in dependent noise channel using copula
NASA Astrophysics Data System (ADS)
Gholizadeh, Mohammad Hossein; Amindavar, Hamidreza; Ritcey, James A.
2013-12-01
In this paper, the probability density function (PDF) estimation is introduced in the framework of estimating the Nakagami fading parameter. This approach provides an analytic procedure for finding the fading parameter. Using the copula theory, an accurate PDF estimate is obtained even when the desired signal is corrupted in a noisy environment. In the real world, the noise samples could be highly dependent on the main signal. Copula-based models are a general set of statistical models defined for any multivariate random variable. Thus, they depict the statistical behavior of a received signal including two dependent terms, representative of the desired signal and noise. Previous works in the Nakagami parameter determination have mainly examined estimation based on either a noiseless sample model or an independent trivial noisy one. In this paper, we consider a more comprehensive situation about the noise destruction and our investigation is done in low signal-to-noise ratios. The parametric bootstrap method approves the accuracy of the analytically estimated PDF, and simulation results show that the new estimator has superior performance over conventional estimators.
Performance of concatenated Reed-Solomon trellis-coded modulation over Rician fading channels
NASA Technical Reports Server (NTRS)
Moher, Michael L.; Lodge, John H.
1990-01-01
A concatenated coding scheme for providing very reliable data over mobile-satellite channels at power levels similar to those used for vocoded speech is described. The outer code is a shorter Reed-Solomon code which provides error detection as well as error correction capabilities. The inner code is a 1-D 8-state trellis code applied independently to both the inphase and quadrature channels. To achieve the full error correction potential of this inner code, the code symbols are multiplexed with a pilot sequence which is used to provide dynamic channel estimation and coherent detection. The implementation structure of this scheme is discussed and its performance is estimated.
On Frequency Offset Estimation Using the iNET Preamble in Frequency Selective Fading Channels
2014-03-01
ASM fields; (bottom) the relationship between the indexes of the received samples r(n), the signal samples s(n), the preamble samples p (n) and the short...frequency offset estimators for SOQPSK-TG equipped with the iNET preamble and operating in ISI channels. Four of the five estimators exam - ined here are...sync marker ( ASM ), and data bits (an LDPC codeword). The availability of a preamble introduces the possibility of data-aided synchro- nization in
NASA Astrophysics Data System (ADS)
Le, Minh Hung; Liyana-Pathirana, Ranjith
2003-06-01
The unequal error protection (UEP) codes with wavelet-based algorithm for video compression over wide-band code division multiple access (W-CDMA), additive white Gaussian noise (AWGN) and Rayleigh fading channels are analysed. The utilization of Wavelets has come out to be a powerful method for compress video sequence. The wavelet transform compression technique has shown to be more appropriate to high quality video applications, producing better quality output for the compressed frames of video. A spatially scalable video coding framework of MPEG2 in which motion correspondences between successive video frames are exploited in the wavelet transform domain. The basic motivation for our coder is that motion fields are typically smooth that can be efficiently captured through a multiresolutional framework. Wavelet decomposition is applied to video frames and the coefficients at each level are predicted from the coarser level through backward motion compensation. The proposed algorithms of the embedded zero-tree wavelet (EZW) coder and the 2-D wavelet packet transform (2-D WPT) are investigated.
NASA Astrophysics Data System (ADS)
Yu, Xiangbin; Dong, Tao; Xu, Dazhuan; Bi, Guangguo
2010-09-01
By introducing an orthogonal space-time coding scheme, multiuser code division multiple access (CDMA) systems with different space time codes are given, and corresponding system performance is investigated over a Nakagami-m fading channel. A low-complexity multiuser receiver scheme is developed for space-time block coded CDMA (STBC-CDMA) systems. The scheme can make full use of the complex orthogonality of space-time block coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, the average bit error rate (BER) of the system is derived in detail for integer m and non-integer m, respectively. As a result, a tight closed-form BER expression is obtained for STBC-CDMA with an orthogonal spreading code, and an approximate closed-form BER expression is attained for STBC-CDMA with a quasi-orthogonal spreading code. Simulation results show that the proposed scheme can achieve almost the same performance as the existing scheme with low complexity. Moreover, the simulation results for average BER are consistent with the theoretical analysis.
Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku
2016-02-26
In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source's radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks.
García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz
2014-01-01
A novel bit-detect-and-forward (BDF) relaying scheme based on repetition coding with the relay is proposed, significantly improving the robustness to impairments proper to free-space optical (FSO) communications such as unsuitable alignment between transmitter and receiver as well as fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence. Closed-form asymptotic bit-error-rate (BER) expressions are derived for a 3-way FSO communication setup. Fully exploiting the potential time-diversity available in the relay turbulent channel, a relevant better performance is achieved, showing a greater robustness to the relay location since a high diversity gain is provided regardless of the source-destination link distance. PMID:24587711
NASA Astrophysics Data System (ADS)
Jeon, Cha-Eul; Hwang, Seung-Hoon
For automatic repeat request (ARQ)-aided TSTD (Time Switched Transmit Diversity) system, a receiver sends the acknowledgement signal (ACK or NACK) to a transmitter in order to predict the condition of the channel. In this paper, two antenna switching schemes, in which the NACK trigger the transmit antenna switching in the proposed antenna switching patterns, are proposed for the TSTD with the ARQ in WCDMA LCR-TDD systems. In addition, the system performances are investigated. Simulation results demonstrate that the performances of the TSTD systems can be improved by applying the ARQ scheme. Furthermore, the performances of ARQ-aided TSTD systems may be significantly improved by applying the proposed antenna switching schemes, especially when the mobile's speed is low.
Characterization of time delayed diversity to mitigate fading in atmospheric turbulence channels
NASA Astrophysics Data System (ADS)
Trisno, Sugianto; Smolyaninov, Igor I.; Milner, Stuart D.; Davis, Christopher C.
2005-08-01
Atmospheric turbulence is caused by inhomogeneities in the temperature and pressure of the atmosphere, resulting in random variations of the refractive index. A laser beam propagating through such turbulences experiences random amplitude and phase fluctuations, which can severely degrade the performance of free space optical (FSO) communication systems. In our time delayed diversity (TDD) technique, we transmit twice and take advantage of the fact that propagation along an atmospheric path is statistically uncorrelated with an earlier-time path for a time interval greater than the atmospheric turbulence correlation time. Communications performance is improved because the joint probability of error is less than the probability of error from individual channels. In this paper, we describe the theoretical and experimental analyses of FSO systems implementing this novel scheme in various performance scenarios. Theoretical models and performance of TDD systems are derived and characterized. The experimental performance results obtained under weak turbulence conditions are shown to be in good agreement with the theory. Related system design and implementation issues, such as: atmospheric turbulence statistics, laser beam depolarization, and diversity receiver architecture are also discussed.
2005-03-01
Wright-Patterson AFB OH, March 2004. AFIT/GE/ENG/04-20. 7. Papoulis, Athanasios and S. Unnikrishna Pillai . Probability, Random Variables, and...Upper Saddle River, New Jersey 07458, 2001. 129 13. Swackhammer, Patrick J. Design and Simulation of a Multiple Access Trans- form Domain Communication
Fade durations in satellite-path mobile radio propagation
NASA Technical Reports Server (NTRS)
Schmier, Robert G.; Bostian, Charles W.
1986-01-01
Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.
Performance of filter bank-based spreading codes for multipath/multiuser interference
NASA Astrophysics Data System (ADS)
Hetling, Kenneth J.; Saulnier, Gary J.; Das, Pankaj K.
1996-03-01
Spread spectrum communications is a technique in which the transmission bandwidth is much larger than that normally required to transmit at the given data rate. The use of this excess bandwidth provides the system with advantages in the areas of anti-jam communications, high resolution ranging, resistance to multipath fading, and low probability of intercept/detection of the transmissions. The traditional spreading sequences used in spread spectrum communications are the maximal length sequences, due to their good randomness properties as well as their ease of generation. Recently a new class of spreading codes has been developed based upon the time-frequency duality of multirate filter bank structures. Unlike the maximal length sequences, these new codes are not limited to being binary valued. Instead, the elements of the sequences are determined by an optimization process which emphasizes certain desirable code properties. In this paper, spreading codes based upon multirate filter banks are developed for use in a channel characterized by both multiuser and multipath interference. Several sets of codes are designed for various channel conditions and analytical bit error rate results are generated. These results are then compared to those for conventional maximal length sequences.
NASA Technical Reports Server (NTRS)
Ashman, Ben; Veldman, Jeanette; Axelrad, Penina; Garrison, James; Winternitz, Luke
2016-01-01
In the rendezvous and docking of spacecraft, GNSS signals can reflect off the target vehicle and cause prohibitively large errors in the chaser vehicle receiver at ranges below 200 meters. It has been proposed that the additional ray paths, or multipath, be used as a source of information about the state of the target relative to the receiver. With Hubble Servicing Mission 4 as a case study, electromagnetic ray tracing has been used to construct a model of reflected signals from known geometry. Oscillations in the prompt correlator power due to multipath, known as multipath fading, are studied as a means of model validation. Agreement between the measured and simulated multipath fading serves to confirm the presence of signals reflected off the target spacecraft that might be used for relative navigation.
NASA Technical Reports Server (NTRS)
Ashman, B. W.; Veldman, J. L.; Axelrad, P.; Garrison, J. L.; Winternitz, L. B.
2016-01-01
In the rendezvous and docking of spacecraft, GNSS signals can reflect off the target vehicle and cause large errors in the chaser vehicle receiver at ranges below a few hundred meters. It has been proposed that the additional ray paths, or multipath, be used as a source of information about the state of the target relative to the receiver. With Hubble Servicing Mission 4 as a case study, electromagnetic ray tracing has been used to construct a model of reflected signals from known geometry. Oscillations in the prompt correlator power due to multipath, known as multipath fading, are studied as a means of model validation. Agreement between the measured and simulated multipath fading serves to confirm the presence of signals reflected off the target spacecraft that might be used for relative navigation.
Fan, Xiaozheng; Wang, Yan; Hu, Manfeng
2016-01-01
In this paper, the fuzzy [Formula: see text] output-feedback control problem is investigated for a class of discrete-time T-S fuzzy systems with channel fadings, sector nonlinearities, randomly occurring interval delays (ROIDs) and randomly occurring nonlinearities (RONs). A series of variables of the randomly occurring phenomena obeying the Bernoulli distribution is used to govern ROIDs and RONs. Meanwhile, the measurement outputs are subject to the sector nonlinearities (i.e. the sensor saturations) and we assume the system output is [Formula: see text], [Formula: see text]. The Lth-order Rice model is utilized to describe the phenomenon of channel fadings by setting different values of the channel coefficients. The aim of this work is to deal with the problem of designing a full-order dynamic fuzzy [Formula: see text] output-feedback controller such that the fuzzy closed-loop system is exponentially mean-square stable and the [Formula: see text] performance constraint is satisfied, by means of a combination of Lyapunov stability theory and stochastic analysis along with LMI methods. The proposed fuzzy controller parameters are derived by solving a convex optimization problem via the semidefinite programming technique. Finally, a numerical simulation is given to illustrate the feasibility and effectiveness of the proposed design technique.
NASA Astrophysics Data System (ADS)
Epple, Bernhard; Henniger, Hennes; Serrano Solsona, Clara
2008-02-01
This paper presents an extensive insight into error protection techniques for free space optical links, focusing in particular in aeronautic stratospherically applications. The long distances present in these scenarios along with challenging atmospherically conditions present significant obstacles that degrade link performance. Thus it is imperative to apply highly efficient error protection scheme to avoid unacceptably high loss rates. The goal was to design a point-to-point data link layer error protection protocol that allows user-transparent bridging of Fast Ethernet data transmission over the optical fading channel in an high altitude inter platform link environment.
2006-06-01
subchannel and (b) an OFDM signal......................7 Figure 3. The Nakagami - m PDF...diffractions, and scattering processes and, at the same time, achieve high data rates. The Nakagami - m distribution was used to model different fading...is the Nakagami distribution, where the amplitude of the received signal cα is modeled as a Nakagami - m random variable. 11 The probability
Channel Estimation in DCT-Based OFDM
Wang, Yulin; Zhang, Gengxin; Xie, Zhidong; Hu, Jing
2014-01-01
This paper derives the channel estimation of a discrete cosine transform- (DCT-) based orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective multipath fading channel. Channel estimation has been proved to improve system throughput and performance by allowing for coherent demodulation. Pilot-aided methods are traditionally used to learn the channel response. Least square (LS) and mean square error estimators (MMSE) are investigated. We also study a compressed sensing (CS) based channel estimation, which takes the sparse property of wireless channel into account. Simulation results have shown that the CS based channel estimation is expected to have better performance than LS. However MMSE can achieve optimal performance because of prior knowledge of the channel statistic. PMID:24757439
Efficient Multipath Diversity Receiver for STBC Block Transmission System
NASA Astrophysics Data System (ADS)
Wang, Jieling; Yang, Hong; Yi, Kechu
A space-time and multipath diversity combining algorithm is presented for STBC single carrier block transmission system with two transmit and one receive antennas. The initial solution is achieved by an STBC-based frequency domain equalizer, and the multipath components in the received signal are decoupled by this initial solution and channel state information. Finally, STBC combining is carried out on each decoupled multipath component separately, and then the single carrier output branches are combined further using the maximal ratio combining (MRC) algorithm.
NASA Astrophysics Data System (ADS)
Xu, Kui; Sun, Xiaoli; Zhang, Dongmei
2016-10-01
This paper investigates the spectral and energy efficiencies of a multi-pair two-way amplify-and-forward (AF) relay system over Ricean fading channels, where multiple user-pairs exchange information within pair through a relay with very large number of antennas, while each user equipped with a single antenna. Firstly, beamforming matrixe of zero-forcing reception/zero-forcing transmission (ZFR/ZFT) with imperfect channel state information (CSI) at the relay is given. Then, the unified asymptotic signal-to-interference-plus-noise ratio (SINR) expressions with imperfect CSI are obtained analytically. Finally, two power scaling schemes are proposed and the asymptotic spectral and energy efficiencies based on the proposed power scaling schemes are derived and verified by the Monte-Carlo simulations. Theoretical analyses and simulation results show that with imperfect CSI, if the number of relay antennas grows asymptotically large, we need cut down the transmit power of each user and relay to different proportion when the Ricean K-factor is non-zero and zero (Rayleigh fading) in order to maintain a desirable rate.
ERIC Educational Resources Information Center
Sio, Betsy Menson
2009-01-01
A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…
ERIC Educational Resources Information Center
Nader, Karim; Wang, Szu-Han
2006-01-01
Patient H.M. can form new memories and maintain them for a few seconds before they fade away. From a neurobiological perspective, this amnesia is usually attributed to the absence of memory consolidation, that is, memory storage. An alternative view holds that this impairment reflects that the memory is present but cannot be retrieved. This debate…
ERIC Educational Resources Information Center
Sio, Betsy Menson
2009-01-01
A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…
ERIC Educational Resources Information Center
Nader, Karim; Wang, Szu-Han
2006-01-01
Patient H.M. can form new memories and maintain them for a few seconds before they fade away. From a neurobiological perspective, this amnesia is usually attributed to the absence of memory consolidation, that is, memory storage. An alternative view holds that this impairment reflects that the memory is present but cannot be retrieved. This debate…
Error Probability of MRC in Frequency Selective Nakagami Fading in the Presence of CCI and ACI
NASA Astrophysics Data System (ADS)
Rahman, Mohammad Azizur; Sum, Chin-Sean; Funada, Ryuhei; Sasaki, Shigenobu; Baykas, Tuncer; Wang, Junyi; Harada, Hiroshi; Kato, Shuzo
An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.
NASA Astrophysics Data System (ADS)
Bouidene, A.; Vandamme, P.
1984-10-01
A channel simulator for line-of-sight digital radio systems is presented. The basic principle is to reproduce channel transfer functions measured in the field during multipath propagation activity, by driving a complex linear transversal filter with precomputed data. The criterion used for calculating the values of the filter taps for each transfer function is the minimum mean square error criterion. It is shown that a thirteen-taps complex transversal filter with a period of 70 MHz in the frequency domain leads to accurate simulations of selective fading transfer functions in a 50 MHz bandwidth. Technological features are investigated. Effects of the accuracy in the delays implementation and of the tap-weight quantification are particularly analyzed.
Multipath signal model development
NASA Technical Reports Server (NTRS)
Ghais, A. F.; Wachsman, R. H.
1970-01-01
The development and use of mathematical models of signals received through the multipath environmental of a TDRS-to-user spacecraft link and vice versa are discussed. The TDRS (tracking and data relay satellite) will be in synchronous orbit. The user spacecraft will be in a low altitude orbit between 200 and 4000 km.
Statistical analysis on the optical fading in free space optical channel for RoFSO link design
NASA Astrophysics Data System (ADS)
Kim, Kyung-Hwan; Higashino, Takeshi; Tsukamoto, Katsutoshi; Komaki, Shozo; Kazaura, Kamugisha; Matsumoto, Mitsuji
2010-01-01
This paper presents empirical probability density functions (p.d.fs) of variance and fluctuation speed of scintillation, through analyzing a number of experimental data measured in Japan by a statistical model. The model enables us to treat scintillation speed by one parameter of cut-off frequency in the power spectral density (PDS). By using the model and based on the two p.d.fs, we also present simulation results on the level crossing rate (LCR) and average fade duration (AFD). Combined the two results, an outage probabilities corresponding to a threshold optical intensity can be derived.
Gao, Zhengguang; Liu, Hongzhan; Ma, Xiaoping; Lu, Wei
2016-11-10
Multi-hop parallel relaying is considered in a free-space optical (FSO) communication system deploying binary phase-shift keying (BPSK) modulation under the combined effects of a gamma-gamma (GG) distribution and misalignment fading. Based on the best path selection criterion, the cumulative distribution function (CDF) of this cooperative random variable is derived. Then the performance of this optical mesh network is analyzed in detail. A Monte Carlo simulation is also conducted to demonstrate the effectiveness of the results for the average bit error rate (ABER) and outage probability. The numerical result proves that it needs a smaller average transmitted optical power to achieve the same ABER and outage probability when using the multi-hop parallel network in FSO links. Furthermore, the system use of more number of hops and cooperative paths can improve the quality of the communication.
Multipath analysis diffraction calculations
NASA Technical Reports Server (NTRS)
Statham, Richard B.
1996-01-01
This report describes extensions of the Kirchhoff diffraction equation to higher edge terms and discusses their suitability to model diffraction multipath effects of a small satellite structure. When receiving signals, at a satellite, from the Global Positioning System (GPS), reflected signals from the satellite structure result in multipath errors in the determination of the satellite position. Multipath error can be caused by diffraction of the reflected signals and a method of calculating this diffraction is required when using a facet model of the satellite. Several aspects of the Kirchhoff equation are discussed and numerical examples, in the near and far fields, are shown. The vector form of the extended Kirchhoff equation, by adding the Larmor-Tedone and Kottler edge terms, is given as a mathematical model in an appendix. The Kirchhoff equation was investigated as being easily implemented and of good accuracy in the basic form, especially in phase determination. The basic Kirchhoff can be extended for higher accuracy if desired. A brief discussion of the method of moments and the geometric theory of diffraction is included, but seems to offer no clear advantage in implementation over the Kirchhoff for facet models.
NASA Astrophysics Data System (ADS)
Van Torre, Patrick; Vallozzi, Luigi; Rogier, Hendrik; Moeneclaey, Marc; Verhaevert, Jo
2010-12-01
In the 2.45 GHz band, indoor wireless off-body data communication by a moving person can be problematic due to time-variant signal fading and the consequent variation in channel parameters. Off-body communication specifically suffers from the combined effects of fading, shadowing, and path loss due to time-variant multipath propagation in combination with shadowing by the human body. Measurements are performed to analyze the autocorrelation, coherence time, and power spectral density for a person equipped with a wearable receive system moving at different speeds for different configurations and antenna positions. Diversity reception with multiple textile antennas integrated in the clothing provides a means of improving the reliability of the link. For the dynamic channel estimation, a scheme using hard decision feedback after MRC with adaptive low-pass filtering is demonstrated to be successful in providing robust data detection for long data bursts, in the presence of dramatic channel variation.
NASA Technical Reports Server (NTRS)
Kwa, S. C.; Vanderaar, Mark J.; Kim, Junghwan; Stevens, Grady H.
1991-01-01
The performance of the land mobile satellite system (LMSS) was evaluated by using two trellis coded modulation (TCM) schemes under multipath fading and interference. The results were also compared with uncoded QPSK. The trellis coding formats included a trellis code designed for optimum performance on the fading channel that typifies satellite to mobile communications, as well as one designed for optimum performance in the additive white Gaussian noise (AWGN) channel. The results show that, in Rayleigh fading, the TCM code designed for optimum performance in such an environment performs 4 dB better than the TCM code designed for optimum performance in AWGN, and 10 dB better than the uncoded format, at a bit error rate (BER) of 10 exp -4. Additional results on the performance degradation due to the nonlinearities in the satellite transponder and the adjacent and cochannel interference show that the TCM system is more sensitive than the uncoded system to the phase distortion caused by these impairments.
NASA Technical Reports Server (NTRS)
Kwa, S. C.; Vanderaar, Mark J.; Kim, Junghwan; Stevens, Grady H.
1991-01-01
The performance of the land mobile satellite system (LMSS) was evaluated by using two trellis coded modulation (TCM) schemes under multipath fading and interference. The results were also compared with uncoded QPSK. The trellis coding formats included a trellis code designed for optimum performance on the fading channel that typifies satellite to mobile communications, as well as one designed for optimum performance in the additive white Gaussian noise (AWGN) channel. The results show that, in Rayleigh fading, the TCM code designed for optimum performance in such an environment performs 4 dB better than the TCM code designed for optimum performance in AWGN, and 10 dB better than the uncoded format, at a bit error rate (BER) of 10 exp -4. Additional results on the performance degradation due to the nonlinearities in the satellite transponder and the adjacent and cochannel interference show that the TCM system is more sensitive than the uncoded system to the phase distortion caused by these impairments.
GPS antenna multipath rejection performance
NASA Astrophysics Data System (ADS)
Dinius, A. M.
1995-08-01
A GPS antenna multipath rejection performance evaluation was conducted. Ground reference station antennas and aviation patches were tested for their ability to reject a multipath signal. Different types of ground plane structures were used such as choke rings, ground planes, and mock sections of fuselage. Frequencies transmitted were L1 (1575 MHz), L2 (1227 MHz), and the median GLONASS frequency (1609 MHz). Receive amplitude and phase were measured on each antenna. Subsequently, these data were converted to absolute gain for a right hand and left hand circularly polarized signal as a function of satellite elevation angle. Two types of multipath signals were considered: ground bounce multipath and building or structure bounce multipath. Ground bounce multipath typically occurs at low satellite elevation angles while structure bounce multipath can occur at any satellite elevation angle. Separate analysis methods were used to assess an antenna's ability to reject either type of multipath. This report describes the data collection methods, data reduction and analysis, and the results.
NASA Technical Reports Server (NTRS)
Manning, Robert M.
2004-01-01
The systems engineering description of a wideband communications channel is provided which is based upon the fundamental propagation aspects of the problem. In particular, the well known time variant description of a channel is formulated from the basic multiple scattering processes that occur in a random propagation medium. Such a connection is required if optimal processing methods are to be applied to mitigate the deleterious random fading and multipathing of the channel. An example is given which demonstrates how the effective bandwidth of the channel is diminished due to atmospheric propagation impairments.
Multipath calibration in GPS pseudorange measurements
NASA Technical Reports Server (NTRS)
Kee, Changdon (Inventor); Parkinson, Bradford W. (Inventor)
1998-01-01
Novel techniques are disclosed for eliminating multipath errors, including mean bias errors, in pseudorange measurements made by conventional global positioning system receivers. By correlating the multipath signals of different satellites at their cross-over points in the sky, multipath mean bias errors are effectively eliminated. By then taking advantage of the geometrical dependence of multipath, a linear combination of spherical harmonics are fit to the satellite multipath data to create a hemispherical model of the multipath. This calibration model can then be used to compensate for multipath in subsequent measurements and thereby obtain GPS positioning to centimeter accuracy.
NASA Technical Reports Server (NTRS)
Coney, Thom A.
1996-01-01
Performance status of the Adaptive Rain Fade Compensation includes: (1) The rain fade protocol is functional detecting fades, providing an additional 10 dB of margin and seamless transitions to and from coded operation; (2) The stabilization of the link margins and the optimization of rain fade decision thresholds has resulted in improved BER performance; (3) Characterization of the fade compensation algorithm is ongoing.
NASA Technical Reports Server (NTRS)
Coney, Thom A.
1996-01-01
Performance status of the Adaptive Rain Fade Compensation includes: (1) The rain fade protocol is functional detecting fades, providing an additional 10 dB of margin and seamless transitions to and from coded operation; (2) The stabilization of the link margins and the optimization of rain fade decision thresholds has resulted in improved BER performance; (3) Characterization of the fade compensation algorithm is ongoing.
GPS Multipath in Urban Environments
NASA Astrophysics Data System (ADS)
Bilich, A.; Sella, G.
2008-12-01
Multipath, where a GNSS signal arrives by more than one path, is considered one of the last unmodeled errors remaining in GNSS. Multipath is of great concern because the additional path length traveled by the incoming signal biases the satellite-receiver range and therefore determination of position. Siting a GNSS station in an urban area, in the immediate vicinity of large reflecting objects such as rooftops, buildings, asphalt and concrete parking lots, grassy fields, and chainlink fences, is both a multipath nightmare and a necessary evil. We note that continuously-operating GNSS stations are becoming increasingly common in urban areas, which makes sense as these stations are often installed in support of civil infrastructure (e.g. departments of transportation, strong motion monitoring of buildings in earthquake-prone areas, surveying networks). Urban stations are well represented in geodetic networks such as the CORS (United States) and GeoNet (Japan) networks, with more stations likely to be installed in the coming years. What sources and types of urban multipath are the most detrimental to geodetic GPS positioning? Which reflecting objects are assumed to be a major source of multipath error, but the GPS data show otherwise? Are certain reflecting environments worse for specific applications, i.e. kinematic vs. static positioning? If forced to install a GNSS station in a highly reflective environment, is it possible to rank objects for their multipath severity? To answer these questions, we provide multipath examples taken from continuously- operating GNSS stations sited in urban environments. We concentrate on some of the most common obstacles and reflecting objects for urban sites - rooftops, parking lots, and fences. We analyze the multipath signature of these objects as manifested in the GPS phase, pseudorange, and signal-to-noise ratio (SNR) observables, and also examine multipath impacts on the precision and accuracy of GPS-derived positions.
Wang, Ping; Liu, Xiaoxia; Cao, Tian; Fu, Huihua; Wang, Ranran; Guo, Lixin
2016-09-20
The impact of nonzero boresight pointing errors on the system performance of decode-and-forward protocol-based multihop parallel optical wireless communication systems is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by an exponentiated Weibull model, and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a nonidentically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances, and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions.
Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku
2016-01-01
In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source’s radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks. PMID:26927119
NASA Astrophysics Data System (ADS)
Wunderlich, S.; Welpot, M.; Gaspard, I.
2014-11-01
The markets for smart home products and services are expected to grow over the next years, driven by the increasing demands of homeowners considering energy monitoring, management, environmental controls and security. Many of these new systems will be installed in existing homes and offices and therefore using radio based systems for cost reduction. A drawback of radio based systems in indoor environments are fading effects which lead to a high variance of the received signal strength and thereby to a difficult predictability of the encountered path loss of the various communication links. For that reason it is necessary to derive a statistical path loss model which can be used to plan a reliable and cost effective radio network. This paper presents the results of a measurement campaign, which was performed in six buildings to deduce realistic radio channel models for a high variety of indoor radio propagation scenarios in the short range devices (SRD) band at 868 MHz. Furthermore, a potential concept to reduce the variance of the received signal strength using a circular polarized (CP) patch antenna in combination with a linear polarized antenna in an one-to-one communication link is presented.
NASA Technical Reports Server (NTRS)
Liu, Jian; Kim, Junghwan; Kwatra, S. C.; Stevens, Grady H.
1991-01-01
Aspects of error performance of various power and bandwidth efficient modulations for the land mobile satellite systems (LMSS) were investigated under multipath fading and interferences by using Monte-Carlo simulation. A differential detection for 16QAM (quadrature amplitude modulation) was proposed to cope with Ricean fading and Doppler shift. Computer simulation results show that the performance of 16QAM with differential detection is as good as that of 16PSK with coherent detection and 3 dB better than that of 16PSK with differential detection, although it degrades by about 4.5 dB as compared to 16QAM with coherent detection under an additive white Gaussian noise (AWGN) channel. For the nonlinear channels, 16QAM with modified signal constellations is introduced and analyzed. The simulation results show that the modified 16QAM exhibits a gain of 2.5 dB over 16PSK under traveling-wave tube nonlinearity, and about 4 dB gain over 16PSK at the bit error rate of 10 exp -5 under AWGN. Computer simulation results for modified 16 QAM under cochannel interference and adjacent-channel interference are also presented.
A study of land mobile satellite service multipath effects using SATLAB software
NASA Technical Reports Server (NTRS)
Campbell, Richard L.
1991-01-01
A software package is proposed that uses the known properties of signals received in multipath environments along with the mathematical relationships between signal characteristics to explore the effects of antenna pattern, vehicle velocity, shadowing of the direct wave, distributions of scatters around the moving vehicle and levels of scattered signals on the received complex envelope, fade rates and fade duration, Doppler spectrum, signal arrival angle spectrum, and spatial correlation. The data base may be either actual measured received signals entered as ASCII flat files or data synthesized using a built in model. An example illustrates the effect of using different antennas to receive signals in the same environment.
Multipath Binomial Congestion Control Algorithms
NASA Astrophysics Data System (ADS)
Le, Tuan Anh; Hong, Choong Seon; Lee, Sungwon
Nowadays portable devices with multiple wireless interfaces and using multimedia services are becoming more popular on the Internet. This paper describes a family of multipath binomial congestion control algorithms for audio/video streaming, where a low variant of transmission rate is important. We extend the fluid model of binomial algorithms for single-path transmission to support the concurrent transmission of packets across multiple paths. We focus on the extension of two particular algorithms, SQRT and IIAD, for multiple paths, called MPSQRT and MPIIAD, respectively. Additionally, we apply the design technique (using the multipath fluid model) for multipath TCP (MPTCP) into the extension of SQRT and IIAD, called fbMPSQRT and fbMPIIAD, respectively. Both two approaches ensure that multipath binomial congestion control algorithms achieve load-balancing, throughput improvement, and fairness to single-path binomial algorithms at shared bottlenecks. Through the simulations and comparison with the uncoordinated protocols MPSQRT/MPIIAD, fbMPSQRT/fbMPIIAD and MPTCP, we find that our extended multipath transport protocols can preserve lower latency and transmission rate variance than MPTCP, fairly share with single-path SQRT/IIAD, MPTCP and TCP, and also can achieve throughput improvements and load-balancing equivalent to those of MPTCP under various scenarios and network conditions.
Chaos-based wireless communication resisting multipath effects
NASA Astrophysics Data System (ADS)
Yao, Jun-Liang; Li, Chen; Ren, Hai-Peng; Grebogi, Celso
2017-09-01
In additive white Gaussian noise channel, chaos has been shown to be the optimal coherent communication waveform in the sense of using a very simple matched filter to maximize the signal-to-noise ratio. Recently, Lyapunov exponent spectrum of the chaotic signals after being transmitted through a wireless channel has been shown to be unaltered, paving the way for wireless communication using chaos. In wireless communication systems, inter-symbol interference caused by multipath propagation is one of the main obstacles to achieve high bit transmission rate and low bit-error rate (BER). How to resist the multipath effect is a fundamental problem in a chaos-based wireless communication system (CWCS). In this paper, a CWCS is built to transmit chaotic signals generated by a hybrid dynamical system and then to filter the received signals by using the corresponding matched filter to decrease the noise effect and to detect the binary information. We find that the multipath effect can be effectively resisted by regrouping the return map of the received signal and by setting the corresponding threshold based on the available information. We show that the optimal threshold is a function of the channel parameters and of the information symbols. Practically, the channel parameters are time-variant, and the future information symbols are unavailable. In this case, a suboptimal threshold is proposed, and the BER using the suboptimal threshold is derived analytically. Simulation results show that the CWCS achieves a remarkable competitive performance even under inaccurate channel parameters.
Digital Communications Over Fading Channels
2007-11-02
46 22 Exact and approximate performance of BPSK with continuous narrowband...1) M−1∑ n=1 (−1)n+1 n + 1 ( M − 1 n ) exp (−nγs n+ 1 ) ( 46 ) Substituting (14) and ( 46 ) into (10), we obtain Pb = M 2(M − 1) ∫ ∞ 0 M−1∑ n=1 (−1)n+1 n...average transmitted power is the same whether coded or uncoded bits are transmitted: EbcRbc = EbRb (60) Hence, Ebc = rEb (61) Since r < 1, the average
Long-Range Atlantic Acoustic Multipath Identification.
NASA Astrophysics Data System (ADS)
Legters, George Richard
Multipath data from three long-range (900 kilometers) transmissions are examined. Two of the transmissions follow similar tracks, but are separated by the Gulf Stream at the receiving end. The third, which is substantially free of Gulf Stream influence, has been intensively studied Spiesberger et al. (J. Acoust. Soc. Am. 67, 2011-7 (1980)). A package of computer algorithms based on the geometrical optics approximation was developed to model and analyze the acoustic transmission. Path identification with ray calculations was attempted for the two transmission channels exhibiting stable multipath with success for the major features of the path structures. Excessive smoothing of the sound speed profile which eliminates the influence of the Atlantic eighteen-degree celsius water mass in the upper layers is shown to degrade the identification of early arrivals. The slight curvature of the ocean sound speed profile around four kilometers of depth also was critical to early arrival identification. The effect of weak range dependence was small while the effect of a gradual sloping bottom near one receiver was significant.
Space Station GPS Multipath Analysis and Validation
NASA Technical Reports Server (NTRS)
Hwu, Shian U.; Loh, Y. C.
1999-01-01
To investigate the multipath effects on the International Space Station (ISS) Global Positioning System (GPS) measurement accuracy, experimental and computational investigations were performed to estimate the carrier phase errors due to multipath. A new modeling approach is used to reduce the required computing time by separating the dynamic structure elements from the static structure elements in the multipath computations. This study confirmed that the multipath is a major error source to the ISS GPS performance and can possibly degrade the attitude determination solution. It is demonstrated that the GPS antenna carrier phase errors due to multipath can be analyzed using the electromagnetic modeling technique such as the Uniform Geometrical Theory of Diffraction (UTD).
A review of atmospheric multipath measurements and digital system performance
NASA Astrophysics Data System (ADS)
Hubbard, R. W.
1984-10-01
The effects of multipath propagation on digital communication systems are discussed. Recent literature and experiments are reviewed for information that either describes or defines the phenomenon in terms of the propagation media itself. A morphology is presented which is intended to produce better understanding and improved performance of digital radio systems. The technical posture for the digital troposcatter channel up to the 1980s is summarized.
Multipath noise reduction spread spectrum signals
NASA Technical Reports Server (NTRS)
Meehan, Thomas K. (Inventor)
1994-01-01
The concepts of early-prompt delay tracking, multipath correction of early-prompt delay tracking from correlation shape, and carrier phase multipath correction are addressed. In early-prompt delay tracking, since multipath is always delayed with respect to the direct signals, the system derives phase and pseudorange observables from earlier correlation lags. In multipath correction of early-prompt delay tracking from correlation shape, the system looks for relative variations of amplitude across the code correlation function that do not match the predicted multipath-free code cross-correlation shape. The system then uses deviations from the multipath-free shape to infer the magnitude of multipath, and to generate corrections pseudorange observables. In carrier phase multipath correction, the system looks for variations of phase among plural early and prompt lags. The system uses the measured phase variations, along with the general principle that the multipath errors are larger for later lags, to infer the presence of multipath, and to generate corrections for carrier-phase observables.
An optimized node-disjoint multipath routing scheme in mobile ad hoc
NASA Astrophysics Data System (ADS)
Yu, Yang; Liang, Mangui; Liu, Zhiyu
2016-02-01
In mobile ad hoc networks (MANETs), link failures are caused frequently because of node’s mobility and use of unreliable wireless channels for data transmission. Multipath routing strategy can cope with the problem of the traffic overloads while balancing the network resource consumption. In the paper, an optimized node-disjoint multipath routing (ONMR) protocol based on ad hoc on-demand vector (AODV) is proposed to establish effective multipath to enhance the network reliability and robustness. The scheme combines the characteristics of reverse AODV (R-AODV) strategy and on-demand node-disjoint multipath routing protocol to determine available node-disjoint routes with minimum routing control overhead. Meanwhile, it adds the backup routing strategy to make the process of data salvation more efficient in case of link failure. The results obtained through various simulations show the effectiveness of the proposed scheme in terms of route availability, control overhead and packet delivery ratio.
Fade measurements at L-band and UHF in mountainous terrain for land mobile satellite systems
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Goldhirsh, Julius
1988-01-01
Fading results related to land mobile satellite communications at L-band (1502 MHz) and UHF (870 MHz) are described. These results were derived from an experiment performed in a series of canyon passes in the Boulder, Colorado region of the US. The experimental configuration involved a helicopter as the source platform, which maintained a relatively fixed geometry with a mobile van containing the receiver and data-acquisition system. An unobstructed line of sight between the radiating sources and the receiving van was, for the most part, also maintained. In this configuration, the dominant mechanism causing signal fading (or enhancement) is a result of multipath. The resulting fade distributions demonstrated that at the 1 percent and 5 percent levels, 5.5- and 2.6-dB fades were on the average exceeded at L-band and 4.8- and 2.4-dB at UHF, respectively, for a path elevation angle of 45 deg. The canyon results as compared with previous roadside-tree-shadowing results demonstrate that the deciding factor dictating fade margin for future land mobile satellite systems is tree shadowing rather than fades caused by multipath.
Statistics of Sampled Rician Fading
1993-02-01
Equation 2.3. When R is zero, corresponding to full Rayleigh fading, i; il uces to the well-known form. 1 (PsE.) = 2( 1 + "y (Rayleigha Channel...t+ T)) = 20T2 p(r) Il where Eo = r cos +ir sin . There are two limiting forms for the correlation function p(,,). Under strongly disturbed scattering...f*1 , " I I Il I 1 I I’ I "i I I 1 1 I 1 I I I ’ 0 5 10.5.0.5.3.3.4 where ro, the decorrelation time of the electric field, is defined as the e
Multipath ultrasonic flow meters for gas measurement
Saunders, M.P.
1995-11-01
This paper gives an introduction to the practical application of ultrasonic gas flow meters. A general outline of the theory and methods applied using multipath flow meters. The multi-path type meter provides state of the art gas flow measurements and its accuracy and reliability satisfy the requirements for custody transfer. A typical multi-path device can achieve accuracies better than 0.2%.
Toward a multi-path approach for SETI
NASA Astrophysics Data System (ADS)
Papagiannis, Michael D.
1989-11-01
Conceptualizations of plausible SETI modes of communication have evolved in parallel with the whole range of communications technologies; it is accordingly suggested that a 'multipath' approach to SETI may constitute the most astute strategy. A major project illustrative of this approach is the 8 million-channel NASA Multi-Channel Spectrum-Analyzer (MCSA), currently under construction; while the 'Targeted Search' component of CMSA examines 800-1000 sun-like stars with very high sensitivity and spectral resolution in the 1.2-2.0 GHz, 'water hole', its 'Sky Survey' will search the sky over the entire, 1-10 GHz microwave window of the earth's atmosphere.
Time-Frequency Based Channel Estimation for High-Mobility OFDM Systems-Part I: MIMO Case
NASA Astrophysics Data System (ADS)
Önen, Erol; Akan, Aydın; Chaparro, LuisF
2010-12-01
Multiple-input multiple-output (MIMO) systems hold the potential to drastically improve the spectral efficiency and link reliability in future wireless communications systems. A particularly promising candidate for next-generation fixed and mobile wireless systems is the combination of MIMO technology with Orthogonal Frequency Division Multiplexing (OFDM). OFDM has become the standard method because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. Doppler frequency shifts are expected in fast-moving environments, causing the channel to vary in time, that degrades the performance of OFDM systems. In this paper, we present a time-varying channel modeling and estimation method based on the Discrete Evolutionary Transform to obtain a complete characterization of MIMO-OFDM channels. Performance of the proposed method is evaluated and compared on different levels of channel noise and Doppler frequency shifts.
Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels
Olama, Mohammed M.; Djouadi, Seddik M.; Li, Yanyan; ...
2013-01-01
Stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean-square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and nonresolvable multipath received signals are considered and represented as small-scaled Nakagami fading. Themore » proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method’s viability and the results are presented.« less
Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels
Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan; Fathy, Aly
2013-01-01
In this paper, stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and non-resolvable multipath received signals are considered and represented as small-scaled Nakagami fading. The proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method s viability and the results are presented.
NASA Astrophysics Data System (ADS)
Cote, Owen R.; Morrissey, James F.; Izumi, Yutaka
1987-11-01
Results from recent USAF field testing of digital radio line-of-sight (LOS) and troposcatter (TROPO) radio path performance, in which concurrent fine vertical resolution refractivity profiles were also made, show that multipath effects on LOS and TROPO complement each other both performancewise and weatherwise. Maximum multipath delay is a clear propagation path related event in LOS and a heavy rain/thunderstorm related event in TROPO. Because radio holes and multipath zones occur concurrently, being produced by the same refractive ducting layer, LOS paths can be designed to minimize the occurrence of frequency selective fading at the possible expense of some increase in non-frequency selective fading under strong ducting conditions. Path length is less important in affecting path performance than are duct layer strength and geometry. The rule that maximum multipath delay goes as the third power of path length is not confirmed by these measurements. Measured maximum multipath delay on an LOS is better represented by a half-power dependence on path length.
Studies on an Iterative Frequency Domain Channel Estimation Technique for MIMO-UWB Communications
NASA Astrophysics Data System (ADS)
Takanashi, Masaki; Ogawa, Yasutaka; Nishimura, Toshihiko; Ohgane, Takeo
MIMO (Multiple-Input Multiple-Output) technologies have attracted much interest for high-rate and high-capacity wireless communications. MIMO technologies under frequency-selective fading environments (wideband MIMO technologies) have also been studied. A wideband MIMO system is affected by ISI (Inter Symbol Interference) and CCI (Co-Channel Interference). Hence, we need a MIMO signal detection technique that simultaneously suppresses ISI and CCI. The OFDM system and SC-FDE (Single Carrier-Frequency Domain Equalization) techniques are often used for suppressing ISI. By employing these techniques with the ZF (Zero Forcing) or the MMSE (Minimum Mean Square Error) spatial filtering technique, we can cancel both ISI and CCI. To use ZF or MMSE, we need channel state information for calculating the receive weights. Although an LS (Least Square) channel estimation technique has been proposed for MIMO-OFDM systems, it needs a large estimation matrix at the receiver side to obtain sufficient estimation performance in heavy multipath environments. However, the use of a large matrix increases computational complexity and the circuit size. We use frequency domain channel estimation to solve these problems and propose an iterative method for achieving better estimation performance. In this paper, we assume the use of a MIMO-UWB system that employs a UWB-IR (Ultra-Wideband Impulse Radio) scheme with the FDE technique as the wideband wireless transmission scheme for heavy multipath environments, and we evaluate the iterative frequency domain channel estimation through computer simulations and computational complexity calculations.
Codeless GPS Applications to Multi-Path: CGAMP
NASA Technical Reports Server (NTRS)
Macdoran, P. F.; Miller, R. B.; Jenkins, D.; Lemmon, J.; Gold, K.; Schreiner, W.; Snyder, G.
1990-01-01
Cordless Global Positioning System (GPS) Applications to Multi-Path (CGAMP) is meeting the challenge of exploiting the L-band signals from the Global Positioning System (GPS) satellites for the measurement of the impulse response of radio transmission channels over space-Earth paths. This approach was originally suggested by E. K. Smith and has been pursued by J. Lemmon, without an affordable implementation being identifiable. In addition to the high cost of a suitable P code correlating GPS receiver, there is also the major impediment of the often announced Department of Defense policy of selective availability/anti-spoof (SA/AS) that clouds reliable access to the wideband (20 MHz) P channel of the GPS signals without cryptographic access. A technique proposed by MacDoran utilizes codeless methods for exploiting the P channel signals implemented by the use of a pair of antennas and cross correlation signal detection.
NASA Astrophysics Data System (ADS)
Fu, Hui-hua; Wang, Ping; Wang, Ran-ran; Liu, Xiao-xia; Guo, Li-xin; Yang, Yin-tang
2016-07-01
The average bit error rate ( ABER) performance of a decode-and-forward (DF) based relay-assisted free-space optical (FSO) communication system over gamma-gamma distribution channels considering the pointing errors is studied. With the help of Meijer's G-function, the probability density function (PDF) and cumulative distribution function (CDF) of the aggregated channel model are derived on the basis of the best path selection scheme. The analytical ABER expression is achieved and the system performance is then investigated with the influence of pointing errors, turbulence strengths and structure parameters. Monte Carlo (MC) simulation is also provided to confirm the analytical ABER expression.
Reduction of Kinematic Short Baseline Multipath Effects Based on Multipath Hemispherical Map
Cai, Miaomiao; Chen, Wen; Dong, Danan; Song, Le; Wang, Minghua; Wang, Zhiren; Zhou, Feng; Zheng, Zhengqi; Yu, Chao
2016-01-01
Multipath hemispherical map (MHM) is a kind of multipath mitigation approach that takes advantage of the spatial repeatability of the multipath effect under an unchanged environment. This approach is not only suitable for static environments, but also for some kinematic platforms, such as a moving ship and airplane, where the dominant multipath effects come from the platform itself and the multipath effects from the surrounding environment are considered minor or negligible. Previous studies have verified the feasibility of the MHM approach in static environments. In this study, we expanded the MHM approach to a kinematic shipborne environment. Both static and kinematic tests were carried out to demonstrate the feasibility of the MHM approach. The results indicate that, after MHM multipath mitigation, the root mean square (RMS) of baseline length deviations are reduced by 10.47% and 10.57%, and the RMS of residual values are reduced by 39.89% and 21.91% for the static and kinematic tests, respectively. Power spectrum analysis has shown that the MHM approach is more effective in mitigating multipath in low-frequency bands; the high-frequency multipath effects still exist, and are indistinguishable from observation noise. Taking the observation noise into account, the residual reductions increase to 41.68% and 24.51% in static and kinematic tests, respectively. To further improve the performance of MHM for kinematic platforms, we also analyzed the influence of spatial coverage and resolution on residual reduction. PMID:27754322
BOC(n,n) signal multipath mitigation using MEDLL technology
NASA Astrophysics Data System (ADS)
Su, Xuan; Zhang, Yanmei; Su, Lianqing; Guo, Haichao
2015-11-01
For satellite navigation and positioning receivers are susceptible to the influence of the multipath, this paper used multipath estimating delay lock loop (MEDLL) technology for BOC (n, n) multipath signal tracking. Through the analysis of multipath signal model, it is concluded that all the multipath signal can be expressed by its amplitude, phase and delay. Then in odor to get the accurate direct signal, this paper applied MEDLL algorithm to estimate the received signal. Finally, the simulation show that this algorithm can realize multipath signal track demodulation and accurate data demodulation under a low signal noise ratio environment (SNR= -20db).
Channel measurement decoding for troposcatter communications
NASA Astrophysics Data System (ADS)
Chase, D.
1981-02-01
The object of this program is to theoretically investigate and experimentally verify the performance improvement possible by the use of channel-measurement (soft-decision) information when decoding an interleaved (24,12) Golay code. The experimental results obtained during this effort indicate that under certain conditions, such as pulse jamming, significant gains can be achieved by the use of channel measurement decoding. For typical multipath profiles, coding gains in the 5 to 10 dB range have been achieved by fairly simple binary decoding techniques. Unfortunately, the predicted theoretical gains due to the use of channel measurement decoding have not been achieved by the experimental results. While channel measurement decoding did offer a 3-dB gain over binary decoding for flat fading, this gain is well below the theoretical prediction of 7.2 dB. The discrepancy between the theoretical and experimental results is still an open question which may be resolved by future work in this area. Nevertheless, in the presence of pulse jamming, channel measurement decoding doubled the effective pulse duration that can be handled by the Golay code. This result is in agreement with theory and a strong indication of the importance of optimum decoding techniques in an ECCM environment.
Channel Deviation-Based Power Control in Body Area Networks.
Dinh Van, Son; Cotton, Simon L; Smith, David B
2017-08-18
Internet enabled body area networks (BANs) will form a core part of future remote health monitoring and Ambient Assisted Living (AAL) technology. In BAN applications, due to the dynamic nature of human activity, the off-body BAN channel can be prone to deep fading caused by body shadowing and multipath fading. Using this knowledge, we present some novel practical adaptive power control protocols based on the channel deviation to simultaneously prolong the lifetime of wearable devices and reduce outage probability. The proposed schemes are both flexible and relatively simple to implement on hardware platforms with constrained resources making them inherently suitable for BAN applications. We present the key algorithm parameters used to dynamically respond to the channel variation. This allows the algorithms to achieve a better energy efficiency and signal reliability in everyday usage scenarios such as those in which a normal person undertakes many different activities (e.g. sitting, walking, standing, etc). We also profile their performance against traditional, optimal and other existing schemes for which it is demonstrated that not only does the outage probability reduce significantly, but the proposed algorithms also save up to 35% average transmit power compared to the competing schemes.
NASA Astrophysics Data System (ADS)
Seo, Jiwon; Walter, Todd; Chiou, Tsung-Yu; Enge, Per
2009-02-01
Deep and frequent fading of Global Positioning System (GPS) signals caused by ionospheric scintillation is a major concern for aircraft navigation using GPS in the equatorial region during solar maximum. Aviation receivers use both code and carrier measurements to calculate position solutions. Deep signal fading can break a receiver's carrier tracking lock to a satellite channel. The lost channel cannot be used for position calculation until the receiver reacquires the channel and reestablishes tracking. A solar maximum data set analyzed in this paper demonstrates frequent deep signal fading of almost all satellites in view. This could significantly reduce the number of simultaneous tracked satellites and consequently decrease navigation availability. Forty-five minutes of strong scintillation, which was the worst scintillation period of a 9 day campaign at Ascension Island in 2001, are analyzed in this paper. The importance of short reacquisition time of the receiver is described. In order to design an aviation receiver with short reacquisition time under frequent deep signal fading, the characteristics of signal fading should be well understood. Fading duration and the time between deep fades are two important characteristics for GPS navigation. This paper presents a fading duration model based on real scintillation data. The time between deep fades observed in this data shows very frequent deep fades which can significantly reduce benefit of carrier smoothing filters of aviation receivers.
NASA Astrophysics Data System (ADS)
Karasawa, Yoshio; Vanmany, Changarkame
In order to evaluate the effect of Nakagami-Rice fading on Orthogonal Frequency Division Multiplex (OFDM) signal transmission when the delay profile exceeds the guard interval, a simple prediction model is developed by extending the Equivalent Transmission-Path (ETP) model for Rayleigh fading. The validity of the model is demonstrated by comparing the calculated values of BER to those obtained by computer simulation. Using the newly developed ETP-OFDM model, digital transmission characteristics of the OFDM signal in a multipath environment when the delay profile exceeds the guard interval are shown as a function of K factor, delay spread, guard interval and OFDM symbol period.
Yan, Yan; Li, Long; Xie, Guodong; Bao, Changjing; Liao, Peicheng; Huang, Hao; Ren, Yongxiong; Ahmed, Nisar; Zhao, Zhe; Wang, Zhe; Ashrafi, Nima; Ashrafi, Solyman; Talwar, Shilpa; Sajuyigbe, Soji; Tur, Moshe; Molisch, Andreas F; Willner, Alan E
2016-09-23
Electromagnetic waves carrying orbital angular momentum (OAM) have been used for mode division multiplexing in free-space communication systems to increase both the capacity and the spectral efficiency. In the case of conventional wireless communication links using non-OAM beams, multipath effects caused by beam spreading and reflection from the surrounding objects affect the system performance. This paper presents the results of analysis, simulations, and measurements of multipath effects in a millimetre-wave communication link using OAM multiplexing at 28 GHz. Multipath-induced intra- and inter-channel crosstalk, which are caused by specular reflection from a plane parallel to the propagation path, are analysed and measured. Both the simulation and the experimental results show that an OAM channel with a high OAM number ℓ tends to suffer from both strong intra-channel crosstalk and strong inter-channel crosstalk with other OAM channels. Results of the analysis show that this observation can be explained on the basis of both the properties of OAM beam divergence and the filtering effect at the receiver, which is associated with the spiral wavefront of OAM beams.
Yan, Yan; Li, Long; Xie, Guodong; Bao, Changjing; Liao, Peicheng; Huang, Hao; Ren, Yongxiong; Ahmed, Nisar; Zhao, Zhe; Wang, Zhe; Ashrafi, Nima; Ashrafi, Solyman; Talwar, Shilpa; Sajuyigbe, Soji; Tur, Moshe; Molisch, Andreas F.; Willner, Alan E.
2016-01-01
Electromagnetic waves carrying orbital angular momentum (OAM) have been used for mode division multiplexing in free-space communication systems to increase both the capacity and the spectral efficiency. In the case of conventional wireless communication links using non-OAM beams, multipath effects caused by beam spreading and reflection from the surrounding objects affect the system performance. This paper presents the results of analysis, simulations, and measurements of multipath effects in a millimetre-wave communication link using OAM multiplexing at 28 GHz. Multipath-induced intra- and inter-channel crosstalk, which are caused by specular reflection from a plane parallel to the propagation path, are analysed and measured. Both the simulation and the experimental results show that an OAM channel with a high OAM number ℓ tends to suffer from both strong intra-channel crosstalk and strong inter-channel crosstalk with other OAM channels. Results of the analysis show that this observation can be explained on the basis of both the properties of OAM beam divergence and the filtering effect at the receiver, which is associated with the spiral wavefront of OAM beams. PMID:27658443
NASA Astrophysics Data System (ADS)
Yan, Yan; Li, Long; Xie, Guodong; Bao, Changjing; Liao, Peicheng; Huang, Hao; Ren, Yongxiong; Ahmed, Nisar; Zhao, Zhe; Wang, Zhe; Ashrafi, Nima; Ashrafi, Solyman; Talwar, Shilpa; Sajuyigbe, Soji; Tur, Moshe; Molisch, Andreas F.; Willner, Alan E.
2016-09-01
Electromagnetic waves carrying orbital angular momentum (OAM) have been used for mode division multiplexing in free-space communication systems to increase both the capacity and the spectral efficiency. In the case of conventional wireless communication links using non-OAM beams, multipath effects caused by beam spreading and reflection from the surrounding objects affect the system performance. This paper presents the results of analysis, simulations, and measurements of multipath effects in a millimetre-wave communication link using OAM multiplexing at 28 GHz. Multipath-induced intra- and inter-channel crosstalk, which are caused by specular reflection from a plane parallel to the propagation path, are analysed and measured. Both the simulation and the experimental results show that an OAM channel with a high OAM number ℓ tends to suffer from both strong intra-channel crosstalk and strong inter-channel crosstalk with other OAM channels. Results of the analysis show that this observation can be explained on the basis of both the properties of OAM beam divergence and the filtering effect at the receiver, which is associated with the spiral wavefront of OAM beams.
NASA Astrophysics Data System (ADS)
Paulson, Kevin S.; Basarudin, Hafiz
2011-08-01
Several research groups in Europe are developing joint channel simulators for arbitrarily complex networks of terrestrial and slant path, microwave telecommunications links. Currently, the Hull Rain Fade Network Simulator (HRFNS) developed at University of Hull can simulate rain fade on arbitrary terrestrial networks in the southern United Kingdom, producing joint rain fade time series with a 10 s integration time. This paper reports on work to broaden the function of the existing HRFNS to include slant paths such as Earth-space links and communications to high altitude platforms and unmanned airborne systems. The area of application of the new simulation tool is being extended to the whole of Europe, and other fade mechanisms are being included. Nimrod/OPERA has been chosen as the input meteorological data sets for the new system to simulate rain fade. Zero-degree isotherm heights taken from NCEP/NCAR Reanalysis Data are used in conjunction with the Eden-Bacon sleet (wet snow) model to introduce melting layer effects. Other fading mechanisms, including cloud fade, scintillation and absorption losses by atmospheric gasses, can be added to the simulator. The simulator is tested against ITU-R models for rain fade distribution experienced by terrestrial and Earth-space links in the southern United Kingdom. Statistics of fade dynamics, i.e., fade slope and fade duration, for a simulated Earth-space link are compared to International Telecommunication Union models.
Optimization of MLS receivers for multipath environments
NASA Technical Reports Server (NTRS)
Mcalpine, G. A.; Highfill, J. H., III
1976-01-01
The design of a microwave landing system (MLS) aircraft receiver, capable of optimal performance in multipath environments found in air terminal areas, is reported. Special attention was given to the angle tracking problem of the receiver and includes tracking system design considerations, study and application of locally optimum estimation involving multipath adaptive reception and then envelope processing, and microcomputer system design. Results show processing is competitive in this application with i-f signal processing performance-wise and is much more simple and cheaper. A summary of the signal model is given.
NASA Astrophysics Data System (ADS)
Kaddouri, Samar
The underwater channel poses numerous challenges for acoustic communication. Acoustic waves suffer long propagation delay, multipath, fading, and potentially high spatial and temporal variability. In addition, there is no typical underwater acoustic channel; every body of water exhibits quantifiably different properties. Underwater acoustic modems are traditionally operated at low frequencies. However, the use of broadband, high frequency communication is a good alternative because of the lower background noise compared to low-frequencies, considerably larger bandwidth and better source transducer efficiency. One of the biggest problems in the underwater acoustic communications at high frequencies is time-selective fading, resulting in the Doppler spread. While many Doppler detection, estimation and compensation techniques can be found in literature, the applications are limited to systems operating at low frequencies contained within frequencies ranging from a few hundred Hertz to around 30 kHz. This dissertation proposes two robust channel estimation techniques for simultaneous transmissions using multiple sources and multiple receivers (MIMO) that closely follows the rapidly time-varying nature of the underwater channel. The first method is a trended least square (LS) estimation that combines the traditional LS method with an empirical modal decomposition (EMD) based trend extraction algorithm. This method allows separating the slow fading modes in the MIMO channels from the fast-fading ones and thus achieves a close tracking of the channel impulse response time fluctuations. This dissertation also outlines a time-varying underwater channel estimation method based on the channel sparsity characteristic. The sparsity of the underwater communication channel is exploited by using the MIMO P-iterative greedy orthogonal matching pursuit (MIMO-OMP) algorithm for the channel estimation. Both techniques are demonstrated in a fully controlled environment, using simulated
An Adaptive Multipath Mitigation Filter for GNSS Applications
NASA Astrophysics Data System (ADS)
Chang, Chung-Liang; Juang, Jyh-Ching
2008-12-01
Global navigation satellite system (GNSS) is designed to serve both civilian and military applications. However, the GNSS performance suffers from several errors, such as ionosphere delay, troposphere delay, ephemeris error, and receiver noise and multipath. Among these errors, the multipath is one of the most unpredictable error sources in high-accuracy navigation. This paper applies a modified adaptive filter to reduce code and carrier multipath errors in GPS. The filter employs a tap-delay line with an Adaline network to estimate the direction and the delayed-signal parameters. Then, the multipath effect is mitigated by subtracting the estimated multipath effects from the processed correlation function. The hardware complexity of the method is also compared with other existing methods. Simulation results show that the proposed method using field data has a significant reduction in multipath error especially in short-delay multipath scenarios.
Optimization of MLS receivers for multipath environments
NASA Technical Reports Server (NTRS)
Mcalpine, G. A.; Highfill, J. H., III; Tzeng, C. P. J.; Koleyni, G.
1978-01-01
Reduced order receiver (suboptimal receiver) analysis in multipath environments is presented. The origin and objective of MLS is described briefly. Signal modeling in MLS the optimum receiver is also included and a description of a computer oriented technique which was used in the simulation study of the suboptimal receiver is provided. Results and conclusion obtained from the research for the suboptimal receiver are reported.
Optimization of MLS receivers for multipath environments
NASA Technical Reports Server (NTRS)
Mcalpine, G. A.; Highfill, J. H., III; Irwin, S. H.; Padgett, J. E.
1975-01-01
A receiver is designed for aircraft (A/C), which, as a component of the proposed Microwave Landing System (MLS), is capable of optimal performance in the multipath environments found in air terminal areas. Topics discussed include: the angle-tracking problem of the MLS receiver; signal modeling; preliminary approaches to optimal design; suboptimal design; and simulation study.
Multipath and Doppler observations during transatlantic digital HF propagation experiments
NASA Astrophysics Data System (ADS)
Reinisch, B. W.; Bibl, K.; Ahmed, M.; Soicher, H.; Gorman, F.; Jodogne, J. C.
1984-10-01
Digital HF transatlantic propagation experiments between two nodes at Dourbes, Belgium, and Needham, MA, using identical digisonde 256 systems became operational in October 1983. Adaptive two way sounding and real time channel evaluation studies are to be conducted among the network's nodes. Presently, the Dourbes station is transmitting 10 kW pulses using a horizontal rhombic antenna while the Needham station uses a long-periodic antenna for both transmission and reception. Amplitude and Doppler shifts of different multipath modes were measured during magnetically quiescent and disturbed periods for the first month of operation. The pulse modulation enables clear separation and identification of the multihop paths. Real time discrete Fourier transforms determine the Doppler shifts imposed by height changes of the reflecting ionospheric layers. A comparison of the observed MUF's of the dominant 2F mode with the MUF's predicted by the IONCAP model show the latter to be about 20 to 30% higher.
Modeling of Doppler frequency shift in multipath radiochannels
NASA Astrophysics Data System (ADS)
Penzin, Maksim; Iyin, Nikolay
2016-06-01
We discuss the modeling of propagation of a quasi-monochromatic radio signal, represented by a coherent pulse sequence, in a non-stationary multipath radio channel. In such a channel, signal propagation results in the observed frequency shift for each ray (Doppler effect). The modeling is based on the assumption that during propagation of a single pulse a channel can be considered stationary. A phase change in the channel transfer function is shown to cause the observed frequency shift in the received signal. Thus, instead of measuring the Doppler frequency shift, we can measure the rate of change in the mean phase of one pulse relative to another. The modeling is carried out within the framework of the method of normal waves. The method enables us to model the dynamics of the electromagnetic field at a given point with the required accuracy. The modeling reveals that a local change in ionospheric conditions more severely affects the rays whose reflection region is in the area where the changes occur.
Performance analysis of a finite radon transform in OFDM system under different channel models
Dawood, Sameer A.; Anuar, M. S.; Fayadh, Rashid A.; Malek, F.; Abdullah, Farrah Salwani
2015-05-15
In this paper, a class of discrete Radon transforms namely Finite Radon Transform (FRAT) was proposed as a modulation technique in the realization of Orthogonal Frequency Division Multiplexing (OFDM). The proposed FRAT operates as a data mapper in the OFDM transceiver instead of the conventional phase shift mapping and quadrature amplitude mapping that are usually used with the standard OFDM based on Fast Fourier Transform (FFT), by the way that ensure increasing the orthogonality of the system. The Fourier domain approach was found here to be the more suitable way for obtaining the forward and inverse FRAT. This structure resulted in a more suitable realization of conventional FFT- OFDM. It was shown that this application increases the orthogonality significantly in this case due to the use of Inverse Fast Fourier Transform (IFFT) twice, namely, in the data mapping and in the sub-carrier modulation also due to the use of an efficient algorithm in determining the FRAT coefficients called the optimal ordering method. The proposed approach was tested and compared with conventional OFDM, for additive white Gaussian noise (AWGN) channel, flat fading channel, and multi-path frequency selective fading channel. The obtained results showed that the proposed system has improved the bit error rate (BER) performance by reducing inter-symbol interference (ISI) and inter-carrier interference (ICI), comparing with conventional OFDM system.
Digital Communications in Fading Channels: COMLINK Validation
2000-09-01
U.S. Customary to metric (SI) units of measurement MULTIPLY "- BY D- TOGET TOGET N-o BY -- DIVIDE angstrom 1.000000 x E -10 meters (m) atmosphere...normal) 1.01325 x E +2 kilo pascal (kPa) bar 1.000000 x E +2 kilo pascal (kPa) barn 1.000000 x E -28 meter2 (m2 ) British thermal unit (thermochemical...1.054350 x E +3 joule (J) calorie (thermochemical) 4.184000 joule (J) cal (thermochemical) /cm2’ 4.184000 x E -2 mega joule/m2 (MJ/m 2) curie 3.700000
Multipath Propagation over Snow at Millimeter Wavelengths,
1980-02-01
Propagation Branch Electromagnetic Sciences Division APPROVED: ALLAN C. SCHELL , Chief Electromagnetic Sciences Division FOR THE COMANDER: JOHN P...type of snow cover. A computer program was developed in order to model the reflection as a specular process, with the underlying terrain represented...data. 2,B’ 3II Contents 1. INTRODUCTION 9 2. ANALYSIS OF MULTIPATH PROPAGATION 10 2. 1 Propagation Mechanisms 12 2.2 Model Calculations for Flat Terrain
Global Positioning System Multipath Reduction with Correlator Beamforming
2014-03-14
GPS MULTIPATH REDUCTION WITH CORRELATOR BEAMFORMING THESIS Jason M. Barhorst, Captain, USAF AFIT-ENG-14-M-10 DEPARTMENT OF THE AIR FORCE AIR...in the United States. AFIT-ENG-14-M-10 GPS MULTIPATH REDUCTION WITH CORRELATOR BEAMFORMING THESIS Presented to the Faculty Department of Electrical...March 2014 DISTRIBUTION STATEMENT A APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT-ENG-14-M-10 GPS MULTIPATH REDUCTION WITH CORRELATOR
A New Synthetic Aperture Sonar Design with Multipath Mitigation
NASA Astrophysics Data System (ADS)
Pinto, Marc; Bellettini, Andrea; Wang, Lian Sheng; Munk, Peter; Myers, Vincent; Pautet, Lucie
2004-11-01
Sonar performance in shallow water is severely degraded by multipath which reduces image contrast and degrades the performance of interferometric processing. This is an important limitation for high resolution applications such as minehunting, where target recognition exploits chiefly the shape and size of the target shadow. Experimental data showing the nature and importance of the multipath is presented together with a new sonar design, optimized to achieve a high level of multipath rejection at large range to water depth ratio.
Control of Multipath TCP and Optimization of Multipath Routing in the Internet
NASA Astrophysics Data System (ADS)
Wischik, Damon; Handley, Mark; Raiciu, Costin
There are moves in the Internet architecture community to add multipath capabilities to TCP, so that end-systems will be able to shift their traffic away from congested parts of the network. We study two problems relating to the design of multipath TCP. (i) We investigate stochastic packet-level behaviour of some proposed multipath congestion control algorithms, and find that they do not behave how we might expect from fluid modeling: they tend to flap randomly between their available paths. We explain why, and propose a congestion control algorithm that does not flap. (ii) We consider how the path choice offered by the network affects the ability of end-systems to shift their traffic between a pool of resources. We define a 'resource poolability' metric, which measures for each resource how easy it is for traffic to be shifted away from that resource e.g. in the event of a traffic surge or link failure.
Freeman, Simon E; Emokpae, Lloyd; Nicholas, Michael; Edelmann, Geoffrey F
2015-08-01
This paper presents a transducer design of the hollow cylinder type designed to minimize transmission multipath and the need for channel equalization over short acoustic communication distances in shallow water. Operating at 750 kHz, the half-maximum envelope of the main lobe is approximately 3°. The transducer was incorporated into a low-complexity modem system in which it acted as both transmitter and receiver. At-sea testing indicated that the system is capable of operating over horizontal distances of 5 m without evidence of multipath distortion. The system was also found to be effective as an omnidirectional transmitter/receiver in the 10-60 kHz band.
Earth-Space Links and Fade-Duration Statistics
NASA Technical Reports Server (NTRS)
Davarian, Faramaz
1996-01-01
In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.
Earth-space links and fade-duration statistics
NASA Technical Reports Server (NTRS)
Davarian, Faramaz
1995-01-01
In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.
Phase and frequency coherency in fading environment in tracking and data relay satellites
NASA Astrophysics Data System (ADS)
Varanasi, S.; Gupta, S. C.
Communication systems employing relay satellites require strict maintaining of frequency and phase coherence. In this paper, the tracking performance of a Digital Fading Phase Locked Loop (DFPLL) is presented considering that the transmitted signal passes through a Rician fading communication channel and also an Additive White Gaussian Noise (AWGN) channel. The stochastic difference equations governing the loop operation considering both phase-step and frequency-step inputs for a first order DFPLL is derived and also mathematical modeling of the Rician fading communication channel. Approximate analytic expressions for the steady state phase error process probability density function (pdf) and phase error variance, which characterize the tracking performance of the loop are presented by solving the corresponding Chapman-Kolmogorov (C-K) equations for both types of inputs considered. Numerical and simulation results are provided that confirm the analytical results for various signal to noise ratios and for various values of the fading parameter.
Performance of FH/BFSK with generalized fading in worst case partial-band Gaussian interference
NASA Astrophysics Data System (ADS)
Crepeau, Paul J.
1990-06-01
For frequency-hopped (noncoherent) binary frequency shift keying (FH/BFSK) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases where the signal is either nonfading or Rayleigh fading. In this work, the region between these extremes is filled in by considering the general Nakagami-m fading model. The worst-case partial-band Gaussian interference results are given by a one-parameter family which for m goes to infinity gives the Viterbi-Jacobs nonfading result, and for m = 1 gives the Rayleigh fading result. In the latter case, a broadband interference strategy is optimal. Thus, the Nakagami-m results provide a smooth one-parameter bridge between the Viterbi-Jacobs channel and the Rayleigh fading channel. The results show that the worst-case interference fraction rho increases as the fading variance increases, up to Rayleigh fading. Any fading less severe than Rayleigh, however slight the departure from Rayleigh, requires a partial-band strategy for sufficiently large Eb/NI.
Analysis of Multipath Pixels in SAR Images
NASA Astrophysics Data System (ADS)
Zhao, J. W.; Wu, J. C.; Ding, X. L.; Zhang, L.; Hu, F. M.
2016-06-01
As the received radar signal is the sum of signal contributions overlaid in one single pixel regardless of the travel path, the multipath effect should be seriously tackled as the multiple bounce returns are added to direct scatter echoes which leads to ghost scatters. Most of the existing solution towards the multipath is to recover the signal propagation path. To facilitate the signal propagation simulation process, plenty of aspects such as sensor parameters, the geometry of the objects (shape, location, orientation, mutual position between adjacent buildings) and the physical parameters of the surface (roughness, correlation length, permittivity)which determine the strength of radar signal backscattered to the SAR sensor should be given in previous. However, it's not practical to obtain the highly detailed object model in unfamiliar area by field survey as it's a laborious work and time-consuming. In this paper, SAR imaging simulation based on RaySAR is conducted at first aiming at basic understanding of multipath effects and for further comparison. Besides of the pre-imaging simulation, the product of the after-imaging, which refers to radar images is also taken into consideration. Both Cosmo-SkyMed ascending and descending SAR images of Lupu Bridge in Shanghai are used for the experiment. As a result, the reflectivity map and signal distribution map of different bounce level are simulated and validated by 3D real model. The statistic indexes such as the phase stability, mean amplitude, amplitude dispersion, coherence and mean-sigma ratio in case of layover are analyzed with combination of the RaySAR output.
Multipath Effects on High-Frequency Coherent Acoustic Communications in Shallow Water
NASA Astrophysics Data System (ADS)
Son, Su-Uk; Kim, Hyeonsu; Joo, Jongmin; Choi, Jee Woong
2013-07-01
Shallow-water acoustic communication channel, referred to as a multipath-limited channel, produces inter-symbol interference that poses a significant obstacle to reliable communication. Accordingly, signal-to-multipath ratio (SMR), rather than signal-to-noise ratio (SNR), becomes an important factor affecting communication performance. However, it is difficult to estimate SMR from measured communication data, especially at higher frequency (>10 kHz) because many arrivals scattered from rough ocean boundaries produce a significant intrapath time spreading, which acts as random noise in communication. In this paper, the energy fraction of the channel impulse response existing in one symbol duration is proposed as a parameter for estimating the quality of shallow-water communication channels. This parameter is compared with the bit-error-rate performance for data acquired in shallow water off the south coast of Korea, where the water depth is 45 m and the bottom consists of sandy clay sediment. The results imply that the energy fraction in one symbol duration may be used as a parameter for describing shallow-water communication channels and applied to the quick decision of a symbol or bit rate in a shallow-water field for reliable underwater communication.
GPS integrity monitoring and multipath error distributions
NASA Technical Reports Server (NTRS)
Skidmore, Trent A.; Vangraas, Frank
1995-01-01
The ability to perform integrity monitoring of a differential Global Positioning System (DGPS) precision approach system is dependent upon the form of monitor used and the various noise sources acting on the reference station, the monitor, and the approaching aircraft. This paper focuses on how multipath and assumptions about its probability density function (pdf) affect the availability of the integrity monitoring function. Also discussed is a technique specified as code/carrier integrity monitoring which can be used to greatly improve integrity monitoring availability over methods employing conventional C/A-code operations.
Optimization of MLS receivers for multipath environments
NASA Technical Reports Server (NTRS)
Mcalpine, G. A.; Highfill, J. H., III
1979-01-01
The angle tracking problems in microwave landing system receivers along with a receiver design capable of optimal performance in the multipath environments found in air terminal areas were studied. Included were various theoretical and evaluative studies like: (1) signal model development; (2) derivation of optimal receiver structures; and (3) development and use of computer simulations for receiver algorithm evaluation. The development of an experimental receiver for flight testing is presented. An overview of the work and summary of principal results and conclusions are reported.
Mitigation of multipath in DGPS ground reference stations
NASA Technical Reports Server (NTRS)
Braasch, Michael S.; Van Graas, Frank
1992-01-01
Multipath represents one of the most serious threats to accuracy in Differential GPS (DGPS). The theoretical foundations of multipath are presented and several multipath mitigation techniques are reviewed. Special emphasis is placed on signal diffraction methods. Reflections enter peaks and nulls in the distorted antenna pattern in a random manner. This, coupled with the oscillations in relative phase (with respect to the direct signal), results in a multipath error signature which is noise-like. Since it is noise-like, it may be significantly reduced by averaging the code phase measurements against the more stable carrier-phase measurements. Exploitation of this effect to reduce multipath error represents a significant increase in accuracy for real time DGPS. Experiments have been performed which verify these conclusions.
A review of fade detection techniques
NASA Technical Reports Server (NTRS)
Pergal, F. J.
1990-01-01
Several proposed propagation fade detection techniques are reviewed in light of general requirements presented for beacon fade characterization. The discussion includes an analysis of phase lock versus frequency lock beacon tracking loops and of excess noise injection type radiometers. The Advanced Communications Technology Satellite (ACTS) beacon fade detection schemes proposed by the Communications Satellite Corporation and the Jet Propulsion Laboratory are examined along with the fade detection technique used by Harris in the Advanced Communications Technology Satellite (ACTS) low burst rate (LBR) terminal.
Perceptual Fading without Retinal Adaptation
ERIC Educational Resources Information Center
Hsieh, Po-Jang; Colas, Jaron T.
2012-01-01
A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…
Perceptual Fading without Retinal Adaptation
ERIC Educational Resources Information Center
Hsieh, Po-Jang; Colas, Jaron T.
2012-01-01
A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…
Ultrasonic Multipath and Beamforming Clutter Reduction: A Chirp Model Approach
Byram, Brett; Jakovljevic, Marko
2014-01-01
In vivo ultrasonic imaging with transducer arrays suffers from image degradation due to beamforming limitations, which includes diffraction limited beamforming as well as beamforming degradation due to tissue inhomogeneity. Additionally, based on recent studies, multipath scattering also causes significant image degradation. To reduce degradation from both sources, we propose a model-based, signal decomposition scheme. The proposed algorithm identifies spatial frequency signatures to decompose received wavefronts into their most significant scattering sources. Scattering sources originating from a region of interest are used to reconstruct decluttered wavefronts, which are beamformed into decluttered radio frequency (RF) scan lines or A-lines. To test the algorithm, ultrasound system channel data were acquired during liver scans from 8 patients. Multiple data sets were acquired from each patient, with 55 total data sets, 43 of which had identifiable hypoechoic regions on normal B-mode images. The data sets with identifiable hypoechoic regions were analyzed. The results show the decluttered B-mode images have an average improvement in contrast over normal images of 7.3±4.6 dB. The CNR changed little on average between normal and decluttered B-mode, −0.4±5.9 dB. The in vivo speckle SNR decreased; the change was −0.65±0.28. Phantom speckle SNR also decreased but only by −0.40±0.03. PMID:24569248
Ultrasonic multipath and beamforming clutter reduction: a chirp model approach.
Byram, Brett; Jakovljevic, Marko
2014-03-01
In vivo ultrasonic imaging with transducer arrays suffers from image degradation resulting from beamforming limitations, including diffraction-limited beamforming and beamforming degradation caused by tissue inhomogeneity. Additionally, based on recent studies, multipath scattering also causes significant image degradation. To reduce degradation from both sources, we propose a model-based signal decomposition scheme. The proposed algorithm identifies spatial frequency signatures to decompose received wavefronts into their most significant scattering sources. Scattering sources originating from a region of interest are used to reconstruct decluttered wavefronts, which are beamformed into decluttered RF scan lines or A-lines. To test the algorithm, ultrasound system channel data were acquired during liver scans from 8 patients. Multiple data sets were acquired from each patient, with 55 total data sets, 43 of which had identifiable hypoechoic regions on normal B-mode images. The data sets with identifiable hypoechoic regions were analyzed. The results show the decluttered B-mode images have an average improvement in contrast over normal images of 7.3 ± 4.6 dB. The contrast-to-noise ratio (CNR) changed little on average between normal and decluttered Bmode, -0.4 ± 5.9 dB. The in vivo speckle SNR decreased; the change was -0.65 ± 0.28. Phantom speckle SNR also decreased, but only by -0.40 ± 0.03.
Fading testbed for free-space optical communications
NASA Astrophysics Data System (ADS)
Shrestha, Amita; Giggenbach, Dirk; Mustafa, Ahmad; Pacheco-Labrador, Jorge; Ramirez, Julio; Rein, Fabian
2016-10-01
Free-space optical (FSO) communication is a very attractive technology offering very high throughput without spectral regulation constraints, yet allowing small antennas (telescopes) and tap-proof communication. However, the transmitted signal has to travel through the atmosphere where it gets influenced by atmospheric turbulence, causing scintillation of the received signal. In addition, climatic effects like fogs, clouds and rain also affect the signal significantly. Moreover, FSO being a line of sight communication requires precise pointing and tracking of the telescopes, which otherwise also causes fading. To achieve error-free transmission, various mitigation techniques like aperture averaging, adaptive optics, transmitter diversity, sophisticated coding and modulation schemes are being investigated and implemented. Evaluating the performance of such systems under controlled conditions is very difficult in field trials since the atmospheric situation constantly changes, and the target scenario (e.g. on aircraft or satellites) is not easily accessible for test purposes. Therefore, with the motivation to be able to test and verify a system under laboratory conditions, DLR has developed a fading testbed that can emulate most realistic channel conditions. The main principle of the fading testbed is to control the input current of a variable optical attenuator such that it attenuates the incoming signal according to the loaded power vector. The sampling frequency and mean power of the vector can be optionally changed according to requirements. This paper provides a brief introduction to software and hardware development of the fading testbed and measurement results showing its accuracy and application scenarios.
Coded Modulations for Mobile Satellite Communication Channels
NASA Astrophysics Data System (ADS)
Rhee, Dojun
1995-01-01
The mobile satellite (MSAT) channel is subject to multipath fading, shadowing, Doppler frequency shift, and adjacent channel interference (ACI). Therefore, transmitted signals face severe amplitude and phase distortions. This dissertation investigates various high performance and low decoding complexity coded modulation schemes for reliable voice and data transmissions over the shadowed mobile satellite channel and the Rayleigh fading channel. The dissertation consists of four parts. The first part presents a systematic technique for constructing MPSK trellis coded modulation (TCM) codes for voice transmission over the MSAT channel. The multilevel coding method is used for constructing TCM codes using convolutional codes with good free branch distances as the component codes or using both convolutional and block codes as the component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform existing TCM codes with the same decoding complexity. In the second part, using the multilevel coding method, multilevel block coded modulation (BCM) codes are constructed for voice transmission over the MSAT channel. Even though BCM is generally less power efficient than TCM for AWGN channels, BCM has a great potential to compete with TCM in the MSAT channel because of its shorter decoding depth and hence more effective interleaving. Binary Reed -Muller (RM) codes of length up to 32 are used as component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform TCM codes with the same decoding complexity. In the third part, a simple and systematic technique for constructing multilevel concatenated BCM schemes for data transmission over the shadowed MSAT channel and the Rayleigh fading channel is presented. These schemes are designed to achieve high-performance or large coding gain with reduced decoding complexity. Construction is based on a
Limitations on Ku-band communications due to multipath
NASA Technical Reports Server (NTRS)
Lindsey, J. F.; Rudnicki, J. F.
1977-01-01
The earth and orbiter body reflections involving the Tracking Data Relay Satellite (TDRS)/orbiter communications link are evaluated. Recommendations address operational conditions in order to avoid critical multipath impacts, modulation preferences during acquisition, and preferred scan limit implementation.
Multipath Propagation for Helicopter-to-Ground MIMO Links
2011-06-02
AFFTC-PA-11118 Multipath Propagation for Helicopter-to-Ground MIMO Links Michael Rice, Michael Jensen AIR FORCE FLIGHT TEST CENTER...EDWARDS AFB, CA June 2, 2011 A F F T C m Approved for public release; distribution is unlimited. AIR FORCE FLIGHT TEST CENTER...TITLE AND SUBTITLE Multipath Propagation for Helicopter-to-Ground MIMO Links 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM
Methods and Apparatus for Reducing Multipath Signal Error Using Deconvolution
NASA Technical Reports Server (NTRS)
Kumar, Rajendra (Inventor); Lau, Kenneth H. (Inventor)
1999-01-01
A deconvolution approach to adaptive signal processing has been applied to the elimination of signal multipath errors as embodied in one preferred embodiment in a global positioning system receiver. The method and receiver of the present invention estimates then compensates for multipath effects in a comprehensive manner. Application of deconvolution, along with other adaptive identification and estimation techniques, results in completely novel GPS (Global Positioning System) receiver architecture.
On the technology of aerospace communication in multipath.
NASA Technical Reports Server (NTRS)
Painter, J. H.; Gupta, S. C.; Wilson, L. R.
1972-01-01
The mechanism, effects, and modelling of multipath propagation, caused by rough earth reflection, are examined for aerospace communication. Emphasis is on binary digital signalling for aircraft and hybrid vehicles, such as Shuttle. The cases of direct Air-Ground and satellite relay (Aerosat) are treated. The recursive, adaptive, coherent Bayes detector for binary phase-shift-keying in nonselective multipath is presented. The derivation for the frequency-shift-keying detector is indicated.
2014-04-29
Two channels are visible in this image from NASA 2001 Mars Odyssey spacecraft . The smaller one near the bottom did not carve as deeply as the larger channel at the top. The channel near the top of the image is near the origin of Mamers Valles.
An Energy-Efficient and Robust Multipath Routing Protocol for Cognitive Radio Ad Hoc Networks.
Singh, Kishor; Moh, Sangman
2017-09-04
Routing in cognitive radio ad hoc networks (CRAHNs) is a daunting task owing to dynamic topology, intermittent connectivity, spectrum heterogeneity, and energy constraints. Other prominent aspects such as channel stability, path reliability, and route discovery frequency should also be exploited. Several routing protocols have been proposed for CRAHNs in the literature. By stressing on one of the aspects more than any other, however, they do not satisfy all requirements of throughput, energy efficiency, and robustness. In this paper, we propose an energy-efficient and robust multipath routing (ERMR) protocol for CRAHNs by considering all prominent aspects including residual energy and channel stability in design. Even when the current routing path fails, the alternative routing path is immediately utilized. In establishing primary and alternative routing paths, both residual energy and channel stability are exploited simultaneously. Our simulation study shows that the proposed ERMR outperforms the conventional protocol in terms of network throughput, packet delivery ratio, energy consumption, and end-to-end delay.
Crystal Diagnostics MultiPath System™.
Stumpf, Curtis H; Zhao, Weidong; Bullard, Brian; Ammons, Christine; Devlin, Karl I; Niehaus, Gary D
2014-01-01
The Crystal Diagnostics MultiPath System™ provides rapid detection of Escherichia coli O157 in fresh raw ground beef, raw beeftrim, and spinach. The Crystal Diagnostics system combines patented Liquid Crystal technology with antibody-coated paramagnetic microspheres to selectively capture and detect E. coli O157 in food matrixes. This is the only liquid crystal-based biosensor commercially available for the detection of pathogens. The Crystal Diagnostics system expeditiously provides the sensitivity and accuracy of the U.S. Department of Agriculture Food Safety Inspection Service (USDA-FSIS) and the U.S. Food and Drug Administration Bacteriological Analytical Manual (FDA-BAM) methods for detecting as low as one CFU of E. coli O157 per 375 g of raw ground beef and raw beef trim, or 200 g of raw spinach. An internal inclusivity validation demonstrated detection of all 50 tested strains of . coli O157. The internal and independent laboratory tests demonstrate that the method is rapid and sensitive for detecting of E. coli O157 in fresh raw ground beef, beef trim, and spinach.
Geoacoustic inversion using multipath pulse shape.
Prior, Mark K; Harrison, Chris H; Nielsen, Peter L
2007-12-01
Experimental data, measured in a shallow water region of the Mediterranean Sea, are used to show that the variation of received intensity with time is well described by existing expressions [Harrison and Nielsen, J. Acoust. Soc. Am. 121, 1362-1373 (2007)]. These expressions indicate that the effect of the sea-water sound speed profile can be neglected for times greater than the peak intensity arrival. Beyond this time, intensity is shown to decay at a rate determined by the seabed acoustic properties in a manner very similar to that for an isovelocity water column. It is shown that a method of determining seabed acoustic properties, previously restricted to isovelocity water columns [Prior and Harrison, J. Acoust. Soc. Am. 116, 1341-1344 (2004)], can consequently be used in the presence of a sound-speed profile. The method relates the decay rate of smeared multipath arrivals to the angular derivative of seabed reflection loss. Two datasets are studied and the method is used to describe average seabed properties and to detect changes in seabed type. The seabed descriptions thus derived are used to predict total received intensity as a function of source-receiver separation. Agreement between the propagation measurements and predictions is shown to be within measurement uncertainties.
NASA Technical Reports Server (NTRS)
Mukai, Ryan (Inventor); Vilnrotter, Victor A. (Inventor)
2011-01-01
An Advanced Focal Plane Array ("AFPA") for parabolic dish antennas that exploits spatial diversity to achieve better channel equalization performance in the presence of multipath (better than temporal equalization alone), and which is capable of receiving from two or more sources within a field-of-view in the presence of multipath. The AFPA uses a focal plane array of receiving elements plus a spatio-temporal filter that keeps information on the adaptive FIR filter weights, relative amplitudes and phases of the incoming signals, and which employs an Interference Cancelling Constant Modulus Algorithm (IC-CMA) that resolves multiple telemetry streams simultaneously from the respective aero-nautical platforms. This data is sent to an angle estimator to calculate the target's angular position, and then on to Kalman filters FOR smoothing and time series prediction. The resulting velocity and acceleration estimates from the time series data are sent to an antenna control unit (ACU) to be used for pointing control.
Multipath routing in wireless sensor networks: survey and research challenges.
Radi, Marjan; Dezfouli, Behnam; Abu Bakar, Kamalrulnizam; Lee, Malrey
2012-01-01
A wireless sensor network is a large collection of sensor nodes with limited power supply and constrained computational capability. Due to the restricted communication range and high density of sensor nodes, packet forwarding in sensor networks is usually performed through multi-hop data transmission. Therefore, routing in wireless sensor networks has been considered an important field of research over the past decade. Nowadays, multipath routing approach is widely used in wireless sensor networks to improve network performance through efficient utilization of available network resources. Accordingly, the main aim of this survey is to present the concept of the multipath routing approach and its fundamental challenges, as well as the basic motivations for utilizing this technique in wireless sensor networks. In addition, we present a comprehensive taxonomy on the existing multipath routing protocols, which are especially designed for wireless sensor networks. We highlight the primary motivation behind the development of each protocol category and explain the operation of different protocols in detail, with emphasis on their advantages and disadvantages. Furthermore, this paper compares and summarizes the state-of-the-art multipath routing techniques from the network application point of view. Finally, we identify open issues for further research in the development of multipath routing protocols for wireless sensor networks.
Multipath Routing in Wireless Sensor Networks: Survey and Research Challenges
Radi, Marjan; Dezfouli, Behnam; Bakar, Kamalrulnizam Abu; Lee, Malrey
2012-01-01
A wireless sensor network is a large collection of sensor nodes with limited power supply and constrained computational capability. Due to the restricted communication range and high density of sensor nodes, packet forwarding in sensor networks is usually performed through multi-hop data transmission. Therefore, routing in wireless sensor networks has been considered an important field of research over the past decade. Nowadays, multipath routing approach is widely used in wireless sensor networks to improve network performance through efficient utilization of available network resources. Accordingly, the main aim of this survey is to present the concept of the multipath routing approach and its fundamental challenges, as well as the basic motivations for utilizing this technique in wireless sensor networks. In addition, we present a comprehensive taxonomy on the existing multipath routing protocols, which are especially designed for wireless sensor networks. We highlight the primary motivation behind the development of each protocol category and explain the operation of different protocols in detail, with emphasis on their advantages and disadvantages. Furthermore, this paper compares and summarizes the state-of-the-art multipath routing techniques from the network application point of view. Finally, we identify open issues for further research in the development of multipath routing protocols for wireless sensor networks. PMID:22368490
Pseudorage Multipath Estimation and Analysis at the GPS Rgna Network
NASA Astrophysics Data System (ADS)
Vazquez, G. E.; Barron, M. A.
2010-12-01
A research study was conducted to evaluate the amount of pseudorange multipath at GPS sites in the National Active Geodetic Network (RGNA) that is administrated by the National Institute of Statistics, Geography and Informatics (INEGI) of México, which supports three dimensional positioning for public users. The RGNA Network consists of 20 GPS stations located throughout México, where double difference geodetic-grade receivers collect GPS data continuously the 365 days of the year. It is well known that, despite carefully selected locations, the GPS stations are to some extent, affected by the presence of multipath. Furthermore, it is very feasible that for RGNA users that relied on precise measurements of pseudorange observables, the existence of pseudorange multipath could affect any type of related application for a short period of time. Thus, in order to identify the most and the least affected stations, the pseudorange multipath (MP1 and MP2) and the daily root mean square (rms-MP1 and rms-MP2) variations were estimated and analyzed at each GPS site of the RGNA Network. The GPS data processing was performed using the public software TEQC (Test of Quality Check) by UNAVCO and the pseudorange multipath analysis is presented at each site over a year basis (in terms of time-series) considering the data span from year 2005 (doy 265) to year 2010 (doy 300).
Estimating Effects of Multipath Propagation on GPS Signals
NASA Technical Reports Server (NTRS)
Byun, Sung; Hajj, George; Young, Lawrence
2005-01-01
Multipath Simulator Taking into Account Reflection and Diffraction (MUSTARD) is a computer program that simulates effects of multipath propagation on received Global Positioning System (GPS) signals. MUSTARD is a very efficient means of estimating multipath-induced position and phase errors as functions of time, given the positions and orientations of GPS satellites, the GPS receiver, and any structures near the receiver as functions of time. MUSTARD traces each signal from a GPS satellite to the receiver, accounting for all possible paths the signal can take, including all paths that include reflection and/or diffraction from surfaces of structures near the receiver and on the satellite. Reflection and diffraction are modeled by use of the geometrical theory of diffraction. The multipath signals are added to the direct signal after accounting for the gain of the receiving antenna. Then, in a simulation of a delay-lock tracking loop in the receiver, the multipath-induced range and phase errors as measured by the receiver are estimated. All of these computations are performed for both right circular polarization and left circular polarization of both the L1 (1.57542-GHz) and L2 (1.2276-GHz) GPS signals.
When Does Fading Enhance Perceptual Category Learning?
ERIC Educational Resources Information Center
Pashler, Harold; Mozer, Michael C.
2013-01-01
Training that uses exaggerated versions of a stimulus discrimination (fading) has sometimes been found to enhance category learning, mostly in studies involving animals and impaired populations. However, little is known about whether and when fading facilitates learning for typical individuals. This issue was explored in 7 experiments. In…
When Does Fading Enhance Perceptual Category Learning?
ERIC Educational Resources Information Center
Pashler, Harold; Mozer, Michael C.
2013-01-01
Training that uses exaggerated versions of a stimulus discrimination (fading) has sometimes been found to enhance category learning, mostly in studies involving animals and impaired populations. However, little is known about whether and when fading facilitates learning for typical individuals. This issue was explored in 7 experiments. In…
NASA Astrophysics Data System (ADS)
Skoro Kaskarovska, Violeta
High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining. The second configuration implements a form of turbo equalization to evaluate the individual receivers using the feedback parameters as decision symbols. The improved signals from individual receivers are used in the next iteration of selective combining. Multiple iterations are used to achieve optimal estimate of the received signal. The multilevel adaptive configuration is evaluated on experimental and simulated data using SIMO system with three, four and five receivers. The simulation channel model developed for this research is based on experimental channel and Rician fading channel model. The performance of the channel is evaluated in terms of Bit Error Rate (BER) and Signal-to-Noise-and-Interference Ratio (SNIR). Using experimental data with non-zero BER, multilevel adaptive spatial diversity can achieve BER of 0 % and SNIR gain of 3 dB. The simulation results show that the average BER and SNIR after multilevel combining improve dramatically compared to the single receiver, even in case of extremely high BER of individual received signals. The results demonstrate the
Glistening-region model for multipath studies
NASA Astrophysics Data System (ADS)
Groves, Gordon W.; Chow, Winston C.
1998-07-01
The goal is to achieve a model of radar sea reflection with improved fidelity that is amenable to practical implementation. The geometry of reflection from a wavy surface is formulated. The sea surface is divided into two components: the smooth `chop' consisting of the longer wavelengths, and the `roughness' of the short wavelengths. Ordinary geometric reflection from the chop surface is broadened by the roughness. This same representation serves both for forward scatter and backscatter (sea clutter). The `Road-to-Happiness' approximation, in which the mean sea surface is assumed cylindrical, simplifies the reflection geometry for low-elevation targets. The effect of surface roughness is assumed to make the sea reflection coefficient depending on the `Deviation Angle' between the specular and the scattering directions. The `specular' direction is that into which energy would be reflected by a perfectly smooth facet. Assuming that the ocean waves are linear and random allows use of Gaussian statistics, greatly simplifying the formulation by allowing representation of the sea chop by three parameters. An approximation of `low waves' and retention of the sea-chop slope components only through second order provides further simplification. The simplifying assumptions make it possible to take the predicted 2D ocean wave spectrum into account in the calculation of sea-surface radar reflectivity, to provide algorithms for support of an operational system for dealing with target tracking in the presence of multipath. The product will be of use in simulated studies to evaluate different trade-offs in alternative tracking schemes, and will form the basis of a tactical system for ship defense against low flyers.
A multipath self-routing switch
Henrion, M.A.; Eilenberger, G.J.; Petit, G.H.; Parmentier, P.H.
1993-04-01
The multipath, self-routing technique associated with a multislot cell transfer mode reduces the switching element complexity and allows for realization of all its functions in a single-chip ISE of relatively large size. The described design work demonstrates the feasibility of the switching technology fully supporting the MPSR switching architecture with its first implementation based on the ISE 16 x 16 VLSI and switch module 64 x 64 the board at the leading edge of advanced technology. The MPSR switch fabric is upward compatible with the target ISE 32 x 32 and SM128 switching technology. Two levels of distributed control resources have been incorporated in the MPSR transport equipment. The OBC per individual PBA (switch module or link termination board), together with the MTR, controls and monitors all transport functions of the on-board VLSI circuits, and provides high-speed control communication capabilities with other RCC/OBC controllers via the switch fabric. The RCC in each rack controls and supervises the OBCs of boards equipped in that rack, autonomously performs configuration management, maintenance, traffic monitoring, and internal connection control functions closely related to the ATM transport equipment. It provides a loose coupling interface with CSs in charge of communication services and global OAM functions. The expandable MPSR switch fabric supported by its embedded distributed controllers exhibit high throughput/delay performance. We have presented results on the ISE buffer size engineering for 10[sup [minus]10] overall through-switch cell loss ratio based on analytical methods verified by extensive simulations, on the derived total cell transfer delay (79/246 [mu]s for average/maximum delay), and on the engineering of the output buffer capacity. 4 refs., 6 figs.
Fast sparsity adaptive multipath matching pursuit for compressed sensing problems
NASA Astrophysics Data System (ADS)
Zhang, Xiaofang; Du, Hongwei; Qiu, Bensheng; Chen, Shanshan
2017-05-01
The high computational complexity of tree-based multipath search approaches makes putting them into practical use difficult. However, reselection of candidate atoms could make the search path more accurate and efficient. We propose a multipath greedy approach called fast sparsity adaptive multipath matching pursuit (fast SAMMP), which performs a sparsity adaptive tree search to find the sparsest solution with better performances. Each tree branch acquires K atoms, and fast SAMMP reselects the best K atoms among 2K atoms. Fast SAMMP adopts sparsity adaptive techniques that allow more practical applications for the algorithm. We demonstrated the reconstruction performances of the proposed fast scheme on both synthetically generated one-dimensional signals and two-dimensional images using Gaussian observation matrices. The experimental results indicate that fast SAMMP achieves less reconstruction time and a much higher exact recovery ratio compared with conventional algorithms.
Fade-resistant forward error correction method for free-space optical communications systems
Johnson, Gary W.; Dowla, Farid U.; Ruggiero, Anthony J.
2007-10-02
Free-space optical (FSO) laser communication systems offer exceptionally wide-bandwidth, secure connections between platforms that cannot other wise be connected via physical means such as optical fiber or cable. However, FSO links are subject to strong channel fading due to atmospheric turbulence and beam pointing errors, limiting practical performance and reliability. We have developed a fade-tolerant architecture based on forward error correcting codes (FECs) combined with delayed, redundant, sub-channels. This redundancy is made feasible though dense wavelength division multiplexing (WDM) and/or high-order M-ary modulation. Experiments and simulations show that error-free communications is feasible even when faced with fades that are tens of milliseconds long. We describe plans for practical implementation of a complete system operating at 2.5 Gbps.
Outage Probability for ARQ Decode-and-Forward Relaying under Packet-Rate Fading
NASA Astrophysics Data System (ADS)
Lee, Sangkook; Su, Weifeng; Batalama, Stella; Matyjas, John D.
In this paper, a new analytical approach is developed for the evaluation of the outage probability of decode-and-forward (DF) automatic-repeat-request (ARQ) relaying under packet-rate fading (fast fading) channels. Based on this approach, a closed-form asymptotically tight (as SNR → ∞) approximation of the outage probability is derived, and the diversity order of the DF cooperative ARQ relay scheme is shown to be equal to 2L - 1, where L is the maximum number of ARQ retransmissions. The closed-form expression clearly shows that the achieved diversity is partially due to the DF cooperative relaying and partially due to the fast fading nature of the channels (temporal diversity). Numerical and simulation studies illustrate the theoretical developments.
Multi-carrier Communications over Time-varying Acoustic Channels
NASA Astrophysics Data System (ADS)
Aval, Yashar M.
Acoustic communication is an enabling technology for many autonomous undersea systems, such as those used for ocean monitoring, offshore oil and gas industry, aquaculture, or port security. There are three main challenges in achieving reliable high-rate underwater communication: the bandwidth of acoustic channels is extremely limited, the propagation delays are long, and the Doppler distortions are more pronounced than those found in wireless radio channels. In this dissertation we focus on assessing the fundamental limitations of acoustic communication, and designing efficient signal processing methods that cam overcome these limitations. We address the fundamental question of acoustic channel capacity (achievable rate) for single-input-multi-output (SIMO) acoustic channels using a per-path Rician fading model, and focusing on two scenarios: narrowband channels where the channel statistics can be approximated as frequency- independent, and wideband channels where the nominal path loss is frequency-dependent. In each scenario, we compare several candidate power allocation techniques, and show that assigning uniform power across all frequencies for the first scenario, and assigning uniform power across a selected frequency-band for the second scenario, are the best practical choices in most cases, because the long propagation delay renders the feedback information outdated for power allocation based on the estimated channel response. We quantify our results using the channel information extracted form the 2010 Mobile Acoustic Communications Experiment (MACE'10). Next, we focus on achieving reliable high-rate communication over underwater acoustic channels. Specifically, we investigate orthogonal frequency division multiplexing (OFDM) as the state-of-the-art technique for dealing with frequency-selective multipath channels, and propose a class of methods that compensate for the time-variation of the underwater acoustic channel. These methods are based on multiple
Multipath Metropolis simulation: An application to the classical Heisenberg model
NASA Astrophysics Data System (ADS)
Rakić, Predrag S.; Radošević, Slobodan M.; Mali, Petar M.; Stričević, Lazar M.; Petrić, Tara D.
2016-01-01
This study explores the Multipath Metropolis simulation of the classical Heisenberg model. Unlike the standard single-path algorithm, the Metropolis algorithm applied to multiple random-walk paths becomes an embarrassingly parallel algorithm in which many processor cores can be easily utilized. This is important since processor cores are progressively becoming less expensive and thus more accessible. The most obvious advantage of the multipath approach is in employing independent random-walk paths to produce an uncorrelated simulation output with a normal distribution allowing for straightforward and rigorous statistical analysis.
K/Ka-band channel characterization for mobile satellite systems
NASA Technical Reports Server (NTRS)
Pinck, Deborah S.; Rice, Michael D.
1995-01-01
Mobile satellite systems allow truly ubiquitous wireless communications to users anywhere and anytime. NASA's Advanced Communications Technology Satellite (ACTS) provides an ideal space-based platform for the measurement of K/Ka band propagation characteristics in a land mobile satellite application. Field tests conducted in Southern California during the first seven months of 1994 using JPL's ACTS Mobile Terminal (AMT) provided channel characterization data for the K/Ka-band link. A pilot tone was transmitted from a fixed station in Cleveland, Ohio through the satellite and downlinked at 20 GHz in the Southern California spot beam. The AMT was equipped with a narrow beam, high gain antenna which tracked the satellite in azimuth for a fixed elevation angle (46 degrees for this case). The field tests were conducted in three basic environments: clear line-of-sight (LOS) highways, lightly shadowed suburban, and heavily shadowed suburban. Preliminary results of these field tests indicate very little multipath for rural environments and for clear LOS links (as expected with a narrow beam antenna). Deep fades were experienced in shadowed areas, especially those where tree canopies covered the road.
Differential reinforcement with and without instructional fading.
Ringdahl, Joel E; Kitsukawa, Kana; Andelman, Marc S; Call, Nathan; Winborn, Lisa; Barretto, Anjali; Reed, Gregory K
2002-01-01
We evaluated a differential-reinforcement-based treatment package for the reduction of problem behavior during instructional situations. Differential reinforcement of alternative behavior (DRA; compliance) was implemented across two conditions. During one condition, instructions were presented approximately once every other minute. This condition was considered the terminal goal for treatment. During the second condition, the rate of instructions was gradually increased (beginning at zero and ending when instruction rate was similar to the first condition). Results indicated that DRA with instructional fading resulted in less problem behavior than DRA without instructional fading. These results are similar to previous studies regarding the utility of instructional fading. PMID:12365743
Multipath diffusion: A general numerical model
NASA Astrophysics Data System (ADS)
Lee, J. K. W.; Aldama, A. A.
1992-06-01
The effect of high-diffusivity pathways on bulk diffusion of a solute in a material has been modeled previously for simple geometries such as those in tracer diffusion experiments, but not for the geometries and boundary conditions appropriate for experiments involving bulk exchange. Using a coupled system of equations for simultaneous diffusion of a solute through two families of diffusion pathways with differing diffusivities, a general 1-D finite difference model written in FORTRAN has been developed which can be used to examine the effect of high-diffusivity paths on partial and total concentration profiles within a homogeneous isotropic sphere, infinite cylinder, and infinite slab. The partial differential equations are discretized using the θ-method/central-difference scheme, and an iterative procedure analogous to the Gauss-Seidel method is employed to solve the two systems of coupled equations. Using Fourier convergence analysis, the procedure is shown to be unconditionally convergent. Computer simulations demonstrate that a multipath diffusion mechanism can enhance significantly the bulk diffusivity of a diffusing solute species through a material. The amount of solute escaping from a material is dependent strongly on the exchange coefficients, which govern the transfer of solute from the crystal lattice to the high-diffusivity paths and vice versa. In addition, the exchange coefficients ( ϰ1, and ϰ2) seem to control not only the amount of solute that is lost, but also the shape of the concentration profile. If | K1| < | K2|, concentration profiles generally are non-Fickian in shape, typically having shallow concentration gradients near the center (radius r = 0) and steep gradients towards the outer boundary of the material ( r = R). When | K1| ⩾ | K2| a concentration profile is generated which resembles a Fickian (volume) diffusion profile with an apparent bulk diffusivity between that of the crystal lattice and that of the high-diffusivity pathways
2015-11-20
Today's VIS image shows a number of unnamed channels located on the northeastern margin of Terra Sabaea. Orbit Number: 61049 Latitude: 33.5036 Longitude: 58.6967 Instrument: VIS Captured: 2015-09-18 12:54 http://photojournal.jpl.nasa.gov/catalog/PIA20097
Bayesian sparse channel estimation
NASA Astrophysics Data System (ADS)
Chen, Chulong; Zoltowski, Michael D.
2012-05-01
In Orthogonal Frequency Division Multiplexing (OFDM) systems, the technique used to estimate and track the time-varying multipath channel is critical to ensure reliable, high data rate communications. It is recognized that wireless channels often exhibit a sparse structure, especially for wideband and ultra-wideband systems. In order to exploit this sparse structure to reduce the number of pilot tones and increase the channel estimation quality, the application of compressed sensing to channel estimation is proposed. In this article, to make the compressed channel estimation more feasible for practical applications, it is investigated from a perspective of Bayesian learning. Under the Bayesian learning framework, the large-scale compressed sensing problem, as well as large time delay for the estimation of the doubly selective channel over multiple consecutive OFDM symbols, can be avoided. Simulation studies show a significant improvement in channel estimation MSE and less computing time compared to the conventional compressed channel estimation techniques.
Multipath exploitation in through-wall radar imaging via point spread functions.
Setlur, Pawan; Alli, Giovanni; Nuzzo, Luigia
2013-12-01
Due to several sources of multipath in through-wall radar sensing, such as walls, floors, and ceilings, there could exist multipath ghosts associated with a few genuine targets in the synthetic aperture beamformed image. The multipath ghosts are false positives and therefore confusable with genuine targets. Here, we develop a multipath exploitation technique using point spread functions, which associate and map back the multipath ghosts to their genuine targets, thereby increasing the effective signal-to-clutter ratio (SCR) at the genuine target locations. To do so, we first develop a multipath model advocating the Householder transformation, which permits modeling multiple reflections at multiple walls, and also allows for unconventional room/building geometries. Second, closed-form solutions of the multipath ghost locations assuming free space propagation are derived. Third, a nonlinear least squares optimization is formulated and initialized with these free space solutions to localize the multipath ghosts in through-wall radar sensing. The exploitation approach is general and does not require a priori assumptions on the number of targets. The free space multipath ghost locations and exploitation technique derived here may be used as is for multipath exploitation in urban canyons via synthetic aperture radar. Analytical expressions quantifying the SCR gain after multipath exploitation are derived. The analysis is validated with experimental EM results using finite-difference time-domain simulations.
NASA Technical Reports Server (NTRS)
Toda, M.; Brown, S. C.; Burrous, C. N.
1976-01-01
The simulated response is described of a STOL aircraft to Microwave Landing System (MLS) multipath errors during final approach and touchdown. The MLS azimuth, elevation, and DME multipath errors were computed for a relatively severe multipath environment at Crissy Field California, utilizing an MLS multipath simulation at MIT Lincoln Laboratory. A NASA/Ames six-degree-of-freedom simulation of an automatically-controlled deHavilland C-8A STOL aircraft was used to determine the response to these errors. The results show that the aircraft response to all of the Crissy Field MLS multipath errors was small. The small MLS azimuth and elevation multipath errors did not result in any discernible aircraft motion, and the aircraft response to the relatively large (200-ft (61-m) peak) DME multipath was noticeable but small.
Effects and mitigation of multipath on GPS/Galileo
NASA Astrophysics Data System (ADS)
Zhao, Yi; Wang, Qing; Pan, Shuguo; He, Jun
2007-11-01
A conventional method to mitigate multipath errors in GNSS receivers is the strobe correlator, which achieves discriminator function shaping by combining two different narrow-correlator discriminators [1] [2]. The method performs a good performance when the difference in delays of direct and reflected signal is biggish in GPS scenario. Nevertheless, the performance of the method is not so good for Galileo scenario. The advent of the European navigation system Galileo has made it an exigent requirement to develop the receiver that can track Galileo signals as well as GPS signals. So, a better way should be groped for to mitigate both GPS and Galileo multipath errors. In the paper, a novel multipath mitigation scheme, named Early-Late Strobe Correlator (ELSC), was presented for both GPS and Galileo signals. By the Matlab simulation to the method, multipath errors could be mitigated effectively by using ELSC, especially to Galileo signals. The experiment results show that more excellent performances can be obtained by adopting ELSC presented in the paper with respected to the strobe correlator, although this will result in a more complex structure of discriminators.
Ultrasonic imaging of material flaws exploiting multipath information
NASA Astrophysics Data System (ADS)
Shen, Xizhong; Zhang, Yimin D.; Demirli, Ramazan; Amin, Moeness G.
2011-05-01
In this paper, we consider ultrasonic imaging for the visualization of flaws in a material. Ultrasonic imaging is a powerful nondestructive testing (NDT) tool which assesses material conditions via the detection, localization, and classification of flaws inside a structure. Multipath exploitations provide extended virtual array apertures and, in turn, enhance imaging capability beyond the limitation of traditional multisensor approaches. We utilize reflections of ultrasonic signals which occur when encountering different media and interior discontinuities. The waveforms observed at the physical as well as virtual sensors yield additional measurements corresponding to different aspect angles. Exploitation of multipath information addresses unique issues observed in ultrasonic imaging. (1) Utilization of physical and virtual sensors significantly extends the array aperture for image enhancement. (2) Multipath signals extend the angle of view of the narrow beamwidth of the ultrasound transducers, allowing improved visibility and array design flexibility. (3) Ultrasonic signals experience difficulty in penetrating a flaw, thus the aspect angle of the observation is limited unless access to other sides is available. The significant extension of the aperture makes it possible to yield flaw observation from multiple aspect angles. We show that data fusion of physical and virtual sensor data significantly improves the detection and localization performance. The effectiveness of the proposed multipath exploitation approach is demonstrated through experimental studies.
Fade-durations derived from land-mobile-satellite measurements in Australia
NASA Technical Reports Server (NTRS)
Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius
1991-01-01
Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.
Fade-durations derived from land-mobile-satellite measurements in Australia
NASA Technical Reports Server (NTRS)
Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius
1991-01-01
Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.
NASA Technical Reports Server (NTRS)
Parks, M. A. N.; Butt, G.; Evans, Barry G.; Richharia, M.
1993-01-01
Signal propagation in the land mobile satellite (LMS) service is an important consideration due to its critical impact on the overall economic and commercial viability of the system. At frequencies allocated for LMS systems, shadowing of the line-of-sight (LOS) signal as well as multipath propagation phenomena can severely impair the link availability. In particular, as most of the studies have shown, the shadowing of LOS signal causes long and deep fades in a variety of mobile environments due to the inherent nature of the channel between the satellite and a mobile. Roadside obstacles, such as buildings, trees, utility poles etc., in the immediate vicinity of a mobile and the surrounding terrain are major sources of signal shadowing in LMS links. Therefore, a proper knowledge of link degradation is essential for cost-effective planning of a satellite based mobile communication system. The results of a propagation campaign undertaken to characterize the fading nature of LMS channel at high elevation angles is presented. It was envisaged that one of the most important physical variables contributing to the amount of LOS signal shadowing is the elevation angle of the satellite. At higher elevation angles to the satellite, less obstructions in the direct satellite-to-mobile path would therefore amount to statistically better link availability. Narrowband channel measurements were carried out at three RF frequencies corresponding to L (1.3 GHz), S (2.32/2.45 GHz), and Ku (10.4 GHz) bands. The campaign itself was divided into two phases to observe the effects of seasonal variation of foliage on the roadside trees. Phase measurements were carried out in September 1991 and in April 1992. Some important aspects from the statistical analysis of the propagation data are presented.
NASA Technical Reports Server (NTRS)
Goldhirsh, Julius; Vogel, Wolfhard J.
1989-01-01
Field tests related to planned mobile satellite systems were performed, and results that add to the existing database of propagation measurements at L-band (1.5 GHz) are described. They are considered particularly useful in that propagation effects were studied systematically, with repeated and controlled runs pertaining to different path elevation angles, road types, and path geometries defining shadowing and line-of-sight modes. In addition, simultaneous L-band and UHF measurements were performed for the purpose of establishing scaling factors applicable to previous UHF (870 MHz) results. The control of the experimental parameters was made possible by using a helicopter as the source platform and a mobile van to house the receiver.
Xie, Lin; Cui, Xiaowei; Zhao, Sihao; Lu, Mingquan
2017-02-13
It is well known that multipath effect remains a dominant error source that affects the positioning accuracy of Global Navigation Satellite System (GNSS) receivers. Significant efforts have been made by researchers and receiver manufacturers to mitigate multipath error in the past decades. Recently, a multipath mitigation technique using dual-polarization antennas has become a research hotspot for it provides another degree of freedom to distinguish the line-of-sight (LOS) signal from the LOS and multipath composite signal without extensively increasing the complexity of the receiver. Numbers of multipath mitigation techniques using dual-polarization antennas have been proposed and all of them report performance improvement over the single-polarization methods. However, due to the unpredictability of multipath, multipath mitigation techniques based on dual-polarization are not always effective while few studies discuss the condition under which the multipath mitigation using a dual-polarization antenna can outperform that using a single-polarization antenna, which is a fundamental question for dual-polarization multipath mitigation (DPMM) and the design of multipath mitigation algorithms. In this paper we analyze the characteristics of the signal received by a dual-polarization antenna and use the maximum likelihood estimation (MLE) to assess the theoretical performance of DPMM in different received signal cases. Based on the assessment we answer this fundamental question and find the dual-polarization antenna's capability in mitigating short delay multipath-the most challenging one among all types of multipath for the majority of the multipath mitigation techniques. Considering these effective conditions, we propose a dual-polarization sequential iterative maximum likelihood estimation (DP-SIMLE) algorithm for DPMM. The simulation results verify our theory and show superior performance of the proposed DP-SIMLE algorithm over the traditional one using only an RHCP
Long GPS coordinate time series: multipath and geometry effects
NASA Astrophysics Data System (ADS)
King, M. A.; Watson, C. S.
2009-04-01
Within analyses of Global Positioning System (GPS) observations, unmodelled sub-daily signals are known to propagate into long-period signals via a number of different mechanisms. In this paper, we investigate the effects of time-variable satellite geometry and the propagation of an unmodelled multipath signal that is analogous to a change in the elevation dependant phase centre of the receiving antenna. Multipath reflectors at H=0.1 m, 0.2 m and 1.5 m below the antenna are modeled and their effects on GPS coordinate time series are examined. Simulated time series at 20 global IGS sites for 2000-2008 were derived using the satellite geometry as defined by daily broadcast orbits, in addition to that defined using a perfectly repeating synthetic orbit. For the simulations generated using the broadcast orbits with a perfectly clear horizon, we observe the introduction of a time variable bias in the time series of up to several centimeters. Considerable site to site variability of the frequency and magnitude of the signal is observed, in addition to variation as a function of multipath source. When adopting realistic GPS observation geometries obtained from real data (e.g., those that include the effects of tracking outages, local obstructions, etc.), we observe concerning levels of temporal coordinate variation in the presence of the multipath signals. In these cases, we observe spurious signals across the frequency domain, in addition to what appears as offsets and secular trends. Velocity biases of more than 1mm/yr are evident at some few sites. The propagated signal in the vertical component is consistent with a noise model with a spectral index marginally above flicker noise (mean index -1.4), with some sites exhibiting power law magnitudes at comparable levels to actual height time series generated in GIPSY. The propagated signal also shows clear spectral peaks across all coordinate components at harmonics of the draconitic year for a GPS satellite (351.4 days
Long GPS coordinate time series: multipath and geometry effects
NASA Astrophysics Data System (ADS)
King, M.; Watson, C. S.
2009-12-01
Within analyses of Global Positioning System (GPS) observations, unmodelled sub-daily signals are known to propagate into long-period signals via a number of different mechanisms. We report on the effects of time-variable satellite geometry and the propagation of an unmodelled multipath signal. Multipath reflectors at H=0.1 m, 0.2 m and 1.5 m below the antenna are modeled and their effects on GPS coordinate time series are examined. Simulated time series at 20 global IGS sites for 2000-2008 were derived using the satellite geometry as defined by daily broadcast orbits, in addition to that defined using a perfectly repeating synthetic orbit. For the simulations generated using the broadcast orbits with a perfectly clear horizon, we observe the introduction of a time variable bias in the time series of up to several centimeters. Considerable site to site variability of the frequency and magnitude of the signal is observed, in addition to variation as a function of multipath source. When adopting realistic GPS observation geometries obtained from real data (e.g., those that include the effects of tracking outages, local obstructions, etc.), we observe concerning levels of temporal coordinate variation in the presence of the multipath signals. In these cases, we observe spurious signals across the frequency domain, in addition to what appears as offsets and secular trends. Velocity biases of more than 1mm/yr are evident at some few sites. The propagated signal in the vertical component is consistent with a noise model with a spectral index marginally above flicker noise (mean index -1.4), with some sites exhibiting power law magnitudes at comparable levels to actual height time series generated in GIPSY. The propagated signal also shows clear spectral peaks across all coordinate components at harmonics of the draconitic year for a GPS satellite (351.2 days). When a perfectly repeating synthetic GPS constellation is used, the simulations show near-negligible power law
NASA Astrophysics Data System (ADS)
Haeggman, S. G.
1991-06-01
Seven scientific papers published during 1978 to 1990 are reviewed. The papers constitute the basis for a PhD. The titles of the 7 papers are as follows: Time domain observation of microwave multipath propagation and estimation of channel model parameters; Microwave channel model parameters from pulse propagation measurements; The use of simple channel models in the analysis of 16 QAM radio links; Multipath outage probability for QAM systems with interference; Planning of propagation measurements for characterization of digital radio link channels; Measurement and statistical characterization of two 40 MHz line of sight radio channels at 6.2 GHz; and Effects on bandwidth on microwave line of sight channel modeling and digital radio performance prediction.
Modeling and characterization of multipath in global navigation satellite system ranging signals
NASA Astrophysics Data System (ADS)
Weiss, Jan Peter
The Global Positioning System (GPS) provides position, velocity, and time information to users in anywhere near the earth in real-time and regardless of weather conditions. Since the system became operational, improvements in many areas have reduced systematic errors affecting GPS measurements such that multipath, defined as any signal taking a path other than the direct, has become a significant, if not dominant, error source for many applications. This dissertation utilizes several approaches to characterize and model multipath errors in GPS measurements. Multipath errors in GPS ranging signals are characterized for several receiver systems and environments. Experimental P(Y) code multipath data are analyzed for ground stations with multipath levels ranging from minimal to severe, a C-12 turboprop, an F-18 jet, and an aircraft carrier. Comparisons between receivers utilizing single patch antennas and multi-element arrays are also made. In general, the results show significant reductions in multipath with antenna array processing, although large errors can occur even with this kind of equipment. Analysis of airborne platform multipath shows that the errors tend to be small in magnitude because the size of the aircraft limits the geometric delay of multipath signals, and high in frequency because aircraft dynamics cause rapid variations in geometric delay. A comprehensive multipath model is developed and validated. The model integrates 3D structure models, satellite ephemerides, electromagnetic ray-tracing algorithms, and detailed antenna and receiver models to predict multipath errors. Validation is performed by comparing experimental and simulated multipath via overall error statistics, per satellite time histories, and frequency content analysis. The validation environments include two urban buildings, an F-18, an aircraft carrier, and a rural area where terrain multipath dominates. The validated models are used to identify multipath sources, characterize signal
Multipath Effects on Phase Measurements with Continuous Terahertz Waves
NASA Astrophysics Data System (ADS)
Cordes, A. H.; Albarracin, M. G.; Thomas, D. H.; von der Weid, J. P.
2016-05-01
We evaluate the effect of multipath waves on terahertz phase measurements due to multiple reflections between the transmitter antenna and the sample. We show that the phase shift introduced by the sample will be biased by a value which depends on the sample position in the terahertz path. We show how to remove the bias and use the technique in the measurement of the index of refraction of Mylar at 194.4 GHz.
Measurements and predictions of multipath dispersion for troposcatter links
NASA Astrophysics Data System (ADS)
Larsen, R.
1984-10-01
Multipath dispersion measurements made on several 4.5 GHz paths in the United Kingdom are presented. Beamwidth and scatter angle dependence and several features of dispersion in angle and space diversity are discussed. These measurements and other from the literature are compared with predictions of dispersion. The predictions considerably underestimated the measured dispersion, but the inclusion of a beam broadening factor in the calculations gave a significant improvement in accuracy.
Modeling the effects of Multi-path propagation and scintillation on GPS signals
NASA Astrophysics Data System (ADS)
Habash Krause, L.; Wilson, S. J.
2014-12-01
GPS signals traveling through the earth's ionosphere are affected by charged particles that often disrupt the signal and the information it carries due to "scintillation", which resembles an extra noise source on the signal. These signals are also affected by weather changes, tropospheric scattering, and absorption from objects due to multi-path propagation of the signal. These obstacles cause distortion within information and fading of the signal, which ultimately results in phase locking errors and noise in messages. In this work, we attempted to replicate the distortion that occurs in GPS signals using a signal processing simulation model. We wanted to be able to create and identify scintillated signals so we could better understand the environment that caused it to become scintillated. Then, under controlled conditions, we simulated the receiver's ability to suppress scintillation in a signal. We developed a code in MATLAB that was programmed to: 1. Create a carrier wave and then plant noise (four different frequencies) on the carrier wave, 2. Compute a Fourier transform on the four different frequencies to find the frequency content of a signal, 3. Use a filter and apply it to the Fourier transform of the four frequencies and then compute a Signal-to-noise ratio to evaluate the power (in Decibels) of the filtered signal, and 4.Plot each of these components into graphs. To test the code's validity, we used user input and data from an AM transmitter. We determined that the amplitude modulated signal or AM signal would be the best type of signal to test the accuracy of the MATLAB code due to its simplicity. This code is basic to give students the ability to change and use it to determine the environment and effects of noise on different AM signals and their carrier waves. Overall, we were able to manipulate a scenario of a noisy signal and interpret its behavior and change due to its noisy components: amplitude, frequency, and phase shift.
Multipath Routing Algorithm Applied to Cloud Data Center Services
NASA Astrophysics Data System (ADS)
Matsuura, Hiroshi
Cloud data center services, such as video on demand (VoD) and sensor data monitoring, have become popular. The quality of service (QoS) between a client and a cloud data center should be assured by satisfying each service's required bandwidth and delay. Multipath traffic engineering is effective for dispersing traffic flows on a network; therefore, an improved k-shortest paths first (k-SPF) algorithm is applied to these cloud data center services to satisfy their required QoS. k-SPF can create a set of multipaths between a cloud data center and all edge routers, to which client nodes are connected, within one algorithm process. Thus, k-SPF can produce k shortest simple paths between a cloud data center and every access router faster than with conventional Yen's algorithm. By using a parameter in the algorithm, k-SPF can also impartially use links on a network and shorten the average hop-count and number of necessary MPLS labels for multiple paths that comprise a multipath.
Computing Path Tables for Quickest Multipaths In Computer Networks
Grimmell, W.C.
2004-12-21
We consider the transmission of a message from a source node to a terminal node in a network with n nodes and m links where the message is divided into parts and each part is transmitted over a different path in a set of paths from the source node to the terminal node. Here each link is characterized by a bandwidth and delay. The set of paths together with their transmission rates used for the message is referred to as a multipath. We present two algorithms that produce a minimum-end-to-end message delay multipath path table that, for every message length, specifies a multipath that will achieve the minimum end-to-end delay. The algorithms also generate a function that maps the minimum end-to-end message delay to the message length. The time complexities of the algorithms are O(n{sup 2}((n{sup 2}/logn) + m)min(D{sub max}, C{sub max})) and O(nm(C{sub max} + nmin(D{sub max}, C{sub max}))) when the link delays and bandwidths are non-negative integers. Here D{sub max} and C{sub max} are respectively the maximum link delay and maximum link bandwidth and C{sub max} and D{sub max} are greater than zero.
A Multipath Calculation of Surface-Generated Underwater Acoustic Ambient Vertical Directivity
1988-11-18
nth Eigenray I Homogeneous Source Intensity Density g( Source Directivity dA = r dr dO 0 Azimuthal Position of Source Relative to Receiver * 2...Directional-Frequency Spectra - Multipath Expansion ( Eigenray ) Approach 5 TD 8431 SLIDE 3 Although the calculations were done with a specific location in...Frequency Spectra - Multipath Expansion ( Eigenray ) Approach 0 0 13 0 TD 8431 Multipath Calculation of the Acoustic Vertical Directional Spectra RESULTS e
Xie, Lin; Cui, Xiaowei; Zhao, Sihao; Lu, Mingquan
2017-01-01
It is well known that multipath effect remains a dominant error source that affects the positioning accuracy of Global Navigation Satellite System (GNSS) receivers. Significant efforts have been made by researchers and receiver manufacturers to mitigate multipath error in the past decades. Recently, a multipath mitigation technique using dual-polarization antennas has become a research hotspot for it provides another degree of freedom to distinguish the line-of-sight (LOS) signal from the LOS and multipath composite signal without extensively increasing the complexity of the receiver. Numbers of multipath mitigation techniques using dual-polarization antennas have been proposed and all of them report performance improvement over the single-polarization methods. However, due to the unpredictability of multipath, multipath mitigation techniques based on dual-polarization are not always effective while few studies discuss the condition under which the multipath mitigation using a dual-polarization antenna can outperform that using a single-polarization antenna, which is a fundamental question for dual-polarization multipath mitigation (DPMM) and the design of multipath mitigation algorithms. In this paper we analyze the characteristics of the signal received by a dual-polarization antenna and use the maximum likelihood estimation (MLE) to assess the theoretical performance of DPMM in different received signal cases. Based on the assessment we answer this fundamental question and find the dual-polarization antenna’s capability in mitigating short delay multipath—the most challenging one among all types of multipath for the majority of the multipath mitigation techniques. Considering these effective conditions, we propose a dual-polarization sequential iterative maximum likelihood estimation (DP-SIMLE) algorithm for DPMM. The simulation results verify our theory and show superior performance of the proposed DP-SIMLE algorithm over the traditional one using only an
Multipath exploited Bayesian and Cramér-Rao bounds for single-sensor target localization
NASA Astrophysics Data System (ADS)
Setlur, Pawan; Devroye, Natasha
2013-12-01
In urban scenarios, radar returns consist of a direct path return along with multipath returns from signal reflections off surfaces such as building walls or floors. When multipath is resolvable, and given the knowledge of the geometry of the reflecting surfaces, it has recently been demonstrated that multipath returns create additional "virtual" radar sensors, thereby permitting target localization with a single radar sensor. The goal of this article is to determine theoretical variance lower bounds on how well a single-sensor system is able to localize a target in the presence of exploitable multipath and discuss several practical issues that arise in this context, including the multipath association problem, clutter, and the impact of wall roughness. Exploiting multipath, rather than viewing it strictly as a hindrance, is an emerging topic in the radar community whose potential is not yet fully understood. Towards this goal, we first derive the Cramér-Rao and the Bayesian Cramér-Rao bounds on target localization using a single-sensor which exploits resolvable multipath. For a wide class of radar-target geometries, functions termed multipath preservers are derived which indicate when multipath is physically observable in the radar returns; these functions assist in evaluating the potential of multipath exploitation in urban sensing. Given a reflecting geometry, the obtained lower bounds allow the radar operator to anticipate blind spots, place confidence levels on the localization results, and permit sensor positioning to optimally aid in exploiting multipath for target localization. It is shown that variance bounds on the location parameters improve with richer resolvable multipath generating mechanisms.
An Energy-Efficient and Robust Multipath Routing Protocol for Cognitive Radio Ad Hoc Networks
Singh, Kishor
2017-01-01
Routing in cognitive radio ad hoc networks (CRAHNs) is a daunting task owing to dynamic topology, intermittent connectivity, spectrum heterogeneity, and energy constraints. Other prominent aspects such as channel stability, path reliability, and route discovery frequency should also be exploited. Several routing protocols have been proposed for CRAHNs in the literature. By stressing on one of the aspects more than any other, however, they do not satisfy all requirements of throughput, energy efficiency, and robustness. In this paper, we propose an energy-efficient and robust multipath routing (ERMR) protocol for CRAHNs by considering all prominent aspects including residual energy and channel stability in design. Even when the current routing path fails, the alternative routing path is immediately utilized. In establishing primary and alternative routing paths, both residual energy and channel stability are exploited simultaneously. Our simulation study shows that the proposed ERMR outperforms the conventional protocol in terms of network throughput, packet delivery ratio, energy consumption, and end-to-end delay. PMID:28869551
Dai, Wujiao; Shi, Qiang; Cai, Changsheng
2017-01-01
The carrier phase multipath effect is one of the most significant error sources in the precise positioning of BeiDou Navigation Satellite System (BDS). We analyzed the characteristics of BDS multipath, and found the multipath errors of geostationary earth orbit (GEO) satellite signals are systematic, whereas those of inclined geosynchronous orbit (IGSO) or medium earth orbit (MEO) satellites are both systematic and random. The modified multipath mitigation methods, including sidereal filtering algorithm and multipath hemispherical map (MHM) model, were used to improve BDS dynamic deformation monitoring. The results indicate that the sidereal filtering methods can reduce the root mean square (RMS) of positioning errors in the east, north and vertical coordinate directions by 15%, 37%, 25% and 18%, 51%, 27% in the coordinate and observation domains, respectively. By contrast, the MHM method can reduce the RMS by 22%, 52% and 27% on average. In addition, the BDS multipath errors in static baseline solutions are a few centimeters in multipath-rich environments, which is different from that of Global Positioning System (GPS) multipath. Therefore, we add a parameter representing the GEO multipath error in observation equation to the adjustment model to improve the precision of BDS static baseline solutions. And the results show that the modified model can achieve an average precision improvement of 82%, 54% and 68% in the east, north and up coordinate directions, respectively. PMID:28387744
Isolating the multipath component in GNSS signal-to-noise data and locating reflecting objects
NASA Astrophysics Data System (ADS)
Benton, C. J.; Mitchell, C. N.
2011-12-01
A filter to separate the effect of multipath in Global Navigation Satellite System (GNSS) signal-to-noise ratio (SNR) data is presented. The filter removes multipath cleanly, and affects neither slowly varying trends (such as tropospheric absorption or variation in satellite range) nor high frequency components (such as ionospheric scintillation), and so is potentially useful in space-weather research. Similarly, the multipath data removed from the input data is minimally distorted, and contains useful information as to the multipath geometry. A method to locate reflecting objects using a form of spectral analysis is described.
Dai, Wujiao; Shi, Qiang; Cai, Changsheng
2017-04-07
The carrier phase multipath effect is one of the most significant error sources in the precise positioning of BeiDou Navigation Satellite System (BDS). We analyzed the characteristics of BDS multipath, and found the multipath errors of geostationary earth orbit (GEO) satellite signals are systematic, whereas those of inclined geosynchronous orbit (IGSO) or medium earth orbit (MEO) satellites are both systematic and random. The modified multipath mitigation methods, including sidereal filtering algorithm and multipath hemispherical map (MHM) model, were used to improve BDS dynamic deformation monitoring. The results indicate that the sidereal filtering methods can reduce the root mean square (RMS) of positioning errors in the east, north and vertical coordinate directions by 15%, 37%, 25% and 18%, 51%, 27% in the coordinate and observation domains, respectively. By contrast, the MHM method can reduce the RMS by 22%, 52% and 27% on average. In addition, the BDS multipath errors in static baseline solutions are a few centimeters in multipath-rich environments, which is different from that of Global Positioning System (GPS) multipath. Therefore, we add a parameter representing the GEO multipath error in observation equation to the adjustment model to improve the precision of BDS static baseline solutions. And the results show that the modified model can achieve an average precision improvement of 82%, 54% and 68% in the east, north and up coordinate directions, respectively.
Evaluating Pseudorange Multipath at CGPS Stations Spanning Mexico
NASA Astrophysics Data System (ADS)
Vazquez, G.; Bennett, R. A.; Spinler, J. C.
2013-12-01
A research study was conducted in order to quantify and analyze the amount of pseudorange multipath at continuous Global Positioning System (CGPS) stations spanning Mexico. These CGPS stations are administered by a variety of organizations, including government agencies and public universities, and thus serve a wide range of positioning needs. Despite the diversity of the networks and their intended audiences, a core function of all of the networks is to provide a stable framework for high-precision positioning in support of diverse commercial and scientific applications. CGPS data from a large number of publicly available networks located in Mexico were studied. These include the RGNA (National Active Geodetic Network) administered by INEGI (National Institute of Statistics and Geography), the PBO network (Plate Boundary Observatory) funded by the National Science Foundation (NSF) and operated by UNAVCO (University NAVstar Consortium), the Southern California Integrated GPS Network (SCIGN), which is a collaboration effort of the United States Geological Survey (USGS), Scripps Institution of Oceanography and the Jet Propulsion Laboratory (JPL), the UNAM network, operated by the National Seismological System (SSN) and the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), the Suominet Geodetic Network (SNG) and the CORS (Continuously Operating Reference Station) network, operated by the Federal Aviation Administration (FAA). A total of 54 CGPS stations were evaluated, where dual-frequency geodetic-grade receivers collected GPS data continuously during the period from 1994 to 2013. It is usually assumed that despite carefully selected locations, all CGPS stations are to some extent, affected by the presence of signal multipath. In addition, the geographic distribution of stations provides a nation-wide access to the International Terrestrial Reference Frame (ITRF). For real-time kinematic (RTK) and rapid static applications that depend on
Distortion outage minimization in Nakagami fading using limited feedback
NASA Astrophysics Data System (ADS)
Wang, Chih-Hong; Dey, Subhrakanti
2011-12-01
We focus on a decentralized estimation problem via a clustered wireless sensor network measuring a random Gaussian source where the clusterheads amplify and forward their received signals (from the intra-cluster sensors) over orthogonal independent stationary Nakagami fading channels to a remote fusion center that reconstructs an estimate of the original source. The objective of this paper is to design clusterhead transmit power allocation policies to minimize the distortion outage probability at the fusion center, subject to an expected sum transmit power constraint. In the case when full channel state information (CSI) is available at the clusterhead transmitters, the optimization problem can be shown to be convex and is solved exactly. When only rate-limited channel feedback is available, we design a number of computationally efficient sub-optimal power allocation algorithms to solve the associated non-convex optimization problem. We also derive an approximation for the diversity order of the distortion outage probability in the limit when the average transmission power goes to infinity. Numerical results illustrate that the sub-optimal power allocation algorithms perform very well and can close the outage probability gap between the constant power allocation (no CSI) and full CSI-based optimal power allocation with only 3-4 bits of channel feedback.
"Concreteness Fading" Promotes Transfer of Mathematical Knowledge
ERIC Educational Resources Information Center
McNeil, Nicole M.; Fyfe, Emily R.
2012-01-01
Recent studies have suggested that educators should avoid concrete instantiations when the goal is to promote transfer. However, concrete instantiations may benefit transfer in the long run, particularly if they are "faded" into more abstract instantiations. Undergraduates were randomly assigned to learn a mathematical concept in one of three…
"Concreteness Fading" Promotes Transfer of Mathematical Knowledge
ERIC Educational Resources Information Center
McNeil, Nicole M.; Fyfe, Emily R.
2012-01-01
Recent studies have suggested that educators should avoid concrete instantiations when the goal is to promote transfer. However, concrete instantiations may benefit transfer in the long run, particularly if they are "faded" into more abstract instantiations. Undergraduates were randomly assigned to learn a mathematical concept in one of three…
NASA Astrophysics Data System (ADS)
Zhang, Lu; Wu, Zhiyong; Zhang, Yaoyu; Detian, Huang
2013-01-01
To mitigate the impact of the error between the estimated channel fading coefficient and the perfect fading coefficient on the bit error rate (BER), a priori conditional probability density function averaging the estimation error is proposed. Then, an improved maximum-likelihood (ML) symbol-by-symbol detection is derived for the free-space optical communication systems, which implement pilot symbol assisted modulation. To reduce complexity, a closed-form suboptimal improved ML detection is deduced using distribution approximation. Numerical results confirm that BER performance improvement can be reached by the improved ML detection, and that its suboptimal version performs as well as it does. Therefore, they both outperform classical ML detection, which doses not consider channel estimation error.
New Time and Multipath Augmentations for the Global Positioning System
NASA Astrophysics Data System (ADS)
Pratt, John A.
Although developed with a narrow focus in mind, use of GPS has expanded into dozens of fields in industry, science, and military applications. The purpose of the research detailed in this dissertation is an increase in the utility of GPS by improving primary applications of the constellation and expand the practicality of some secondary applications. The first portion of this disseration focuses on the development of clock estimation algorithms for a GPS aiding system called iGPS which has been designed to improve the performance of the system in challenging environments. Central to the functioning of iGPS are the Iridium communication satellites. This dissertation describes a Kalman filter for estimating Iridium satellite clock biases from GPS-like measurements at an interval of 10 s. Typical results show the current filter to be accurate to within 200 ns while always meeting the initial system specification of half a microsecond. The following chapter examines the expediency of increasing the number of terms used to represent the clock bias in the broadcast message and it is shown that the current broadcast message is sufficient. The second half of the dissertation deals with the use of GPS multipath as an environmental measurement. It is shown that reflections of GPS signals from the ground can be used to estimate several important phenological indicators relative to the vegetation surrounding the GPS antenna. Methods are developed for refining the reflected signal and preparing it for use as a vegetation index. Finally, the effect of temperature and multipath supression algorithms on the GPS multipath data is examined relative to its viability for use as previously described. It is shown that these effects are minor in the majority of the GPS sites used in this study and that the data can be adjusted to avoid temperature difficulties.
Signal Classification in Fading Channels Using Cyclic Spectral Analysis
2009-07-01
efficient algorithms to detect and classify an OFDM signal based on its cyclic prefix through the use of a simple autocorrelation procedure [21–23...we focus on the case of an OFDM signal transmitted with no cyclic prefix. Therefore, an intermediate stage is needed between the SOF- based ...classifications and the HOCS- based classifications. A simple yet effective method to distinguish OFDM signals from the single carrier signals in question is
Performance Analysis of Pilot-Aided Forward CDMA Cellular Channel
2001-09-01
in the DS- CDMA cellular systems. For example, performance analysis in a Nakagami or a Ricean instead of a Rayleigh fading channel could be done...operating in a Rayleigh -fading, Lognormal-shadowing environment. We develop an upper bound on the probability of bit error, including all the participating...Wireless, Performance Analysis, Rayleigh Fading, Lognormal Shadowing, Hata Model, Convolutional Code, Narrowband Filtering, Pilot Tone, Power
In search of multipath interference using large molecules.
Cotter, Joseph P; Brand, Christian; Knobloch, Christian; Lilach, Yigal; Cheshnovsky, Ori; Arndt, Markus
2017-08-01
The superposition principle is fundamental to the quantum description of both light and matter. Recently, a number of experiments have sought to directly test this principle using coherent light, single photons, and nuclear spin states. We extend these experiments to massive particles for the first time. We compare the interference patterns arising from a beam of large dye molecules diffracting at single, double, and triple slit material masks to place limits on any high-order, or multipath, contributions. We observe an upper bound of less than one particle in a hundred deviating from the expectations of quantum mechanics over a broad range of transverse momenta and de Broglie wavelength.
Multipath effects in a Global Positioning Satellite system receiver
NASA Technical Reports Server (NTRS)
Mcdonald, Malcolm W.
1992-01-01
This study, as a part of a large continuing investigation being conducted by the Communications Systems Branch of the Information and Electronic Systems Laboratory at the Marshall Space Flight Center, was undertaken to explore the multipath response characteristics of a particular Global Positioning Satellite (GPS) receiver which was available in the laboratory at the beginning and throughout the entirety of the study, and to develop a suitable regime of experimental procedure which can be applied to other state-of-the-art GPS receivers in the larger investigation.
Forward and Inverse Modeling of GPS Multipath for Snow Monitoring
NASA Astrophysics Data System (ADS)
Nievinski, Felipe Geremia
Snowpacks provide reservoirs of freshwater, storing solid precipitation and delaying runoff to be released later in the spring and summer when it is most needed. The goal of this dissertation is to develop the technique of GPS multipath reflectometry (GPS-MR) for ground-based measurement of snow depth. The phenomenon of multipath in GPS constitutes the reception of reflected signals in conjunction with the direct signal from a satellite. As these coherent direct and reflected signals go in and out of phase, signal-to-noise ratio (SNR) exhibits peaks and troughs that can be related to land surface characteristics. In contrast to other GPS reflectometry modes, in GPS-MR the poorly separated composite signal is collected utilizing a single antenna and correlated against a single replica. SNR observations derived from the newer L2-frequency civilian GPS signal (L2C) are used, as recorded by commercial off-the-shelf receivers and geodetic-quality antennas in existing GPS sites. I developed a forward/inverse approach for modeling GPS multipath present in SNR observations. The model here is unique in that it capitalizes on known information about the antenna response and the physics of surface scattering to aid in retrieving the unknown snow conditions in the antenna surroundings. This physically-based forward model is utilized to simulate the surface and antenna coupling. The statistically-rigorous inverse model is considered in two parts. Part I (theory) explains how the snow characteristics are parameterized; the observation/parameter sensitivity; inversion errors; and parameter uncertainty, which serves to indicate the sensing footprint where the reflection originates. Part II (practice) applies the multipath model to SNR observations and validates the resulting GPS retrievals against independent in situ measurements during a 1-3 year period in three different environments---grasslands, alpine, and forested. The assessment yields a correlation of 0.98 and an RMS error
Multi-path transportation futures study: Results from Phase 1
Patterson, Phil; Singh, Margaret; Plotkin, Steve; Moore, Jim
2007-03-09
This PowerPoint briefing provides documentation and details for Phase 1 of the Multi-Path Transportation Futures Study, which compares alternative ways to make significant reductions in oil use and carbon emissions from U.S. light vehicles to 2050. Phase I, completed in 2006, was a scoping study, aimed at identifying key analytic issues and constructing a study design. The Phase 1 analysis included an evaluation of several pathways and scenarios; however, these analyses were limited in number and scope and were designed to be preliminary.
In search of multipath interference using large molecules
Cotter, Joseph P.; Brand, Christian; Knobloch, Christian; Lilach, Yigal; Cheshnovsky, Ori; Arndt, Markus
2017-01-01
The superposition principle is fundamental to the quantum description of both light and matter. Recently, a number of experiments have sought to directly test this principle using coherent light, single photons, and nuclear spin states. We extend these experiments to massive particles for the first time. We compare the interference patterns arising from a beam of large dye molecules diffracting at single, double, and triple slit material masks to place limits on any high-order, or multipath, contributions. We observe an upper bound of less than one particle in a hundred deviating from the expectations of quantum mechanics over a broad range of transverse momenta and de Broglie wavelength. PMID:28819641
Optical scintillations and fade statistics for a satellite-communication system.
Andrews, L C; Phillips, R L; Yu, P T
1995-11-20
Estimates of the scintillation index, fractional fade time, expected number of fades, and mean duration of fade time associated with a propagating Gaussian-beam wave are developed for uplink and downlink laser satellite-communication channels. Estimates for the spot size of the beam at the satellite or the ground or airborne receiver are also provided. Weak-fluctuation theory based on the log-normal model is applicable for intensity fluctuations near the optical axis of the beam provided that the zenith angle is not too large, generally not exceeding 60°. However, there is an increase in scintillations that occurs with increasing pointing error at any zenith angle, particularly for uplink channels. Large off-axis scintillations are of particular significance because they imply that small pointing errors can cause serious degradation in the communication-channel reliability. Off-axis scintillations increase more rapidly for larger-diameter beams and, in some cases, can lead to a radial saturation effect for pointing errors less than 1 µrad off the optical beam axis.
Multipath estimation in urban environments from joint GNSS receivers and LiDAR sensors.
Ali, Khurram; Chen, Xin; Dovis, Fabio; De Castro, David; Fernández, Antonio J
2012-10-30
In this paper, multipath error on Global Navigation Satellite System (GNSS) signals in urban environments is characterized with the help of Light Detection and Ranging (LiDAR) measurements. For this purpose, LiDAR equipment and Global Positioning System (GPS) receiver implementing a multipath estimating architecture were used to collect data in an urban environment. This paper demonstrates how GPS and LiDAR measurements can be jointly used to model the environment and obtain robust receivers. Multipath amplitude and delay are estimated by means of LiDAR feature extraction and multipath mitigation architecture. The results show the feasibility of integrating the information provided by LiDAR sensors and GNSS receivers for multipath mitigation.
Multipath Estimation in Urban Environments from Joint GNSS Receivers and LiDAR Sensors
Ali, Khurram; Chen, Xin; Dovis, Fabio; De Castro, David; Fernández, Antonio J.
2012-01-01
In this paper, multipath error on Global Navigation Satellite System (GNSS) signals in urban environments is characterized with the help of Light Detection and Ranging (LiDAR) measurements. For this purpose, LiDAR equipment and Global Positioning System (GPS) receiver implementing a multipath estimating architecture were used to collect data in an urban environment. This paper demonstrates how GPS and LiDAR measurements can be jointly used to model the environment and obtain robust receivers. Multipath amplitude and delay are estimated by means of LiDAR feature extraction and multipath mitigation architecture. The results show the feasibility of integrating the information provided by LiDAR sensors and GNSS receivers for multipath mitigation. PMID:23202177
Monocular depth effects on perceptual fading.
Hsu, Li-Chuan; Kramer, Peter; Yeh, Su-Ling
2010-08-06
After prolonged viewing, a static target among moving non-targets is perceived to repeatedly disappear and reappear. An uncrossed stereoscopic disparity of the target facilitates this Motion-Induced Blindness (MIB). Here we test whether monocular depth cues can affect MIB too, and whether they can also affect perceptual fading in static displays. Experiment 1 reveals an effect of interposition: more MIB when the target appears partially covered by, than when it appears to cover, its surroundings. Experiment 2 shows that the effect is indeed due to interposition and not to the target's contours. Experiment 3 induces depth with the watercolor illusion and replicates Experiment 1. Experiments 4 and 5 replicate Experiments 1 and 3 without the use of motion. Since almost any stimulus contains a monocular depth cue, we conclude that perceived depth affects perceptual fading in almost any stimulus, whether dynamic or static. Copyright 2010 Elsevier Ltd. All rights reserved.
Observations of auroral fading before breakup
NASA Technical Reports Server (NTRS)
Pellinen, R. J.; Heikkila, W. J.
1978-01-01
The onset of auroral breakup was studied by using a variety of instruments with time resolution of some tens of second. Rapid sequences of all-sky photographs, and fast meridian scans by photometers, show that breakup is usually preceded by moderate brightening, followed by fading of the auroral brightness lasting one or two minutes, before the actual breakup itself. This optical activity is closely correlated with the development of auroral radar echoes. Data from a magnetometer network provide some indication of a correlated response by the local auroral and ionospheric currents. Riometer recordings show a slow decrease in ionspheric radio wave absorption over a period of about ten minutes prior to breakup, with the largest decrease essentially to quiet-time values in the region of auroral fading and subsequent breakup.
Backwards Fading to Speed Task Learning
2013-09-01
Schaefer: 14. ABSTRACT (Maximum 200 words): In Backwards Fading (BF), a learner is provided with an initial, complete demonstration of a multi ...promise for effective/efficient training, but the utility of BF in Army settings and with Army tasks needs to be empirically evaluated. To that end...accelerated BF resulted in poorer performance than gradual BF (Experiment 2). Recommendations for utilizing BF in Army settings are provided. 15
Back-propagation imaging by exploiting multipath from point scatterers
NASA Astrophysics Data System (ADS)
Solimene, Raffaele; Cuccaro, Antonio
2017-10-01
An inverse scattering problem under the linearised Born approximation is considered for a non-homogeneous background medium. An ensemble of pointlike scatterers is oppositely deployed in the scattering scene in order to introduce multipath and to gain an advantage in the reconstruction procedure. It is well known that inverse scattering can benefit from multipath, but at the same time it can produce artefacts in the reconstructions. This is confirmed once again in this study. Indeed, we show that some artefacts, which have been discarded in some previous works, are actually the cause of resolution improvement. To this end, standard stationary phase arguments are employed along with an adjoint inversion method (backpropagation). Theoretical results succeeds in predicting the reconstruction’s leading order terms. However, spurious artefacts due to high order terms become relevant, because more than one point scatterer is used. A simple way to mitigate such artefacts without renouncing the gain in resolution is introduced for the case where the unknown scatterers are small compared to the wavelength.
Target time smearing with short transmissions and multipath propagation.
Harrison, Chris H
2011-09-01
In active sonar the target echo level is often estimated with a propagation model that adds all multipath arrivals. If the (post-correlator) transmitted pulse is short compared to the multipath time spread then there is effectively an extra loss (which may be substantial) since only a few of the paths contribute to the target echo at any one instant. This well known "time-smearing" loss is treated in a self-consistent manner with previous calculations of reverberation [Harrison, J. Acoust. Soc. Am. 114, 2744-2756 (2003)] to estimate the target response and the signal-to-reverberation-ratio. Again isovelocity water, Lambert's law, and reflection loss proportional to angle are assumed. In this important short pulse regime the target response becomes independent of boundary reflection properties but proportional to transmitted pulse length. Thus the signal-to-reverberation-ratio becomes independent of pulse length. The effect on signal-to-ambient-noise is also investigated and the resulting formulas presented in a table. © 2011 Acoustical Society of America
Analysis of the Bias on the Beidou GEO Multipath Combinations
Ning, Yafei; Yuan, Yunbin; Chai, Yanju; Huang, Yong
2016-01-01
The Beidou navigation satellite system is a very important sensor for positioning in the Asia-Pacific region. The Beidou inclined geosynchronous orbit (IGSO) and medium Earth orbit (MEO) satellites have been analysed in some studies previously conducted by other researchers; this paper seeks to gain more insight regarding the geostationary earth orbit (GEO) satellites. Employing correlation analysis, Fourier transformation and wavelet decomposition, we validate whether there is a systematic bias in their multipath combinations. These biases can be observed clearly in satellites C01, C02 and C04 and have a great correlation with time series instead of elevation, being significantly different from those of the Beidou IGSO and MEO satellites. We propose a correction model to mitigate this bias based on its daily periodicity characteristic. After the model has been applied, the performance of the positioning estimations of the eight stations distributed in the Asia-Pacific region is evaluated and compared. The results show that residuals of multipath series behaves random noise; for the single point positioning (SPP) and precise point positioning (PPP) approaches, the positioning accuracy in the upward direction can be improved by 8 cm and 6 mm, respectively, and by 2 cm and 4 mm, respectively, for the horizontal component. PMID:27509503
Surface Wave Multipath Signals in Near-Field Microwave Imaging
Meaney, Paul M.; Shubitidze, Fridon; Fanning, Margaret W.; Kmiec, Maciej; Epstein, Neil R.; Paulsen, Keith D.
2012-01-01
Microwave imaging techniques are prone to signal corruption from unwanted multipath signals. Near-field systems are especially vulnerable because signals can scatter and reflect from structural objects within or on the boundary of the imaging zone. These issues are further exacerbated when surface waves are generated with the potential of propagating along the transmitting and receiving antenna feed lines and other low-loss paths. In this paper, we analyze the contributions of multi-path signals arising from surface wave effects. Specifically, experiments were conducted with a near-field microwave imaging array positioned at variable heights from the floor of a coupling fluid tank. Antenna arrays with different feed line lengths in the fluid were also evaluated. The results show that surface waves corrupt the received signals over the longest transmission distances across the measurement array. However, the surface wave effects can be eliminated provided the feed line lengths are sufficiently long independently of the distance of the transmitting/receiving antenna tips from the imaging tank floor. Theoretical predictions confirm the experimental observations. PMID:22566992
Analysis of the Bias on the Beidou GEO Multipath Combinations.
Ning, Yafei; Yuan, Yunbin; Chai, Yanju; Huang, Yong
2016-08-08
The Beidou navigation satellite system is a very important sensor for positioning in the Asia-Pacific region. The Beidou inclined geosynchronous orbit (IGSO) and medium Earth orbit (MEO) satellites have been analysed in some studies previously conducted by other researchers; this paper seeks to gain more insight regarding the geostationary earth orbit (GEO) satellites. Employing correlation analysis, Fourier transformation and wavelet decomposition, we validate whether there is a systematic bias in their multipath combinations. These biases can be observed clearly in satellites C01, C02 and C04 and have a great correlation with time series instead of elevation, being significantly different from those of the Beidou IGSO and MEO satellites. We propose a correction model to mitigate this bias based on its daily periodicity characteristic. After the model has been applied, the performance of the positioning estimations of the eight stations distributed in the Asia-Pacific region is evaluated and compared. The results show that residuals of multipath series behaves random noise; for the single point positioning (SPP) and precise point positioning (PPP) approaches, the positioning accuracy in the upward direction can be improved by 8 cm and 6 mm, respectively, and by 2 cm and 4 mm, respectively, for the horizontal component.
Proposal for automated transformations on single-photon multipath qudits
NASA Astrophysics Data System (ADS)
Baldijão, R. D.; Borges, G. F.; Marques, B.; Solís-Prosser, M. A.; Neves, L.; Pádua, S.
2017-09-01
We propose a method for implementing automated state transformations on single-photon multipath qudits encoded in a one-dimensional transverse spatial domain. It relies on transferring the encoding from this domain to the orthogonal one by applying a spatial phase modulation with diffraction gratings, merging all the initial propagation paths by using a stable interferometric network, and filtering out the unwanted diffraction orders. The automation feature is attained by utilizing a programmable phase-only spatial light modulator (SLM) where properly designed diffraction gratings displayed on its screen will implement the desired transformations, including, among others, projections, permutations, and random operations. We discuss the losses in the process which is, in general, inherently nonunitary. Some examples of transformations are presented and, considering a realistic scenario, we analyze how they will be affected by the pixelated structure of the SLM screen. The method proposed here enables one to implement much more general transformations on multipath qudits than is possible with a SLM alone operating in the diagonal basis of which-path states. Therefore, it will extend the range of applicability for this encoding in high-dimensional quantum information and computing protocols as well as fundamental studies in quantum theory.
2011-07-01
in Hybrid- ARQ Rayleigh Fading Links 5a. CONTRACT NUMBER FA8750-08-1-0063 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT NUMBER N/A 6. AUTHOR(S...sequence for hybrid automatic-repeat- request (H- ARQ ) communications over quasistatic Rayleigh fading channels. For any targeted H- ARQ link outage...reveals that conventional equal-power H- ARQ assignment is far from optimal. For example, for targeted outage probability of 10e−3 with a maximum of two
Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading
NASA Astrophysics Data System (ADS)
Eng, Thomas; Milstein, Laurence B.
1994-06-01
A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signaling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal.
NASA Astrophysics Data System (ADS)
Moore, J. H.
1987-09-01
The Countisbury UHF relay station serves the localities of Lynmouth and Lynton in North Devon. For some time, the problems of co-channel interference and tidal fading have on occasion been evident . Results obtained utilizing a new Rebroadcast LINK (RBL) antenna array are given. The RBL has improved considerably the quality of signals received at this relay station. Details are also given of apparatus which enables sampled television picture sequences to be recorded on a VHS video cassette recorder. The channel identification, date and time are derived from the teletext signal and superimposed at the top of the picture.
Outage Probability of SINR for Underlay Cognitive Radio Systems in Nakagami Fading
NASA Astrophysics Data System (ADS)
Jarrouj, Jiana; Blagojevic, Vesna; Ivanis, Predrag
2014-11-01
In this paper underlay cognitive radio system is analyzed in Nakagami fading environment, for the case when the available channel state information (CSI) of the link from the secondary transmitter to the primary receiver is outdated. We considered the case when both interference and transmit power constraints are applied. The impact of the co-channel interference that originates from the primary user is analyzed in details. The exact closed-form expressions for probability density function, outage probability, and the moments of signal-to-interference and noise ratio (SINR) at the secondary user's receiver are derived. The analytical expressions are verified by using independent Monte Carlo simulation method.
Capacity fade of Sony 18650 cells cycled at elevated temperatures. Part II. Capacity fade analysis
NASA Astrophysics Data System (ADS)
Ramadass, P.; Haran, Bala; White, Ralph; Popov, Branko N.
A complete capacity fade analysis was carried out for Sony 18650 cells cycled at elevated temperatures. The major causes of capacity loss were identified and a complete capacity fade balance was carried out to account for the total capacity loss of Li-ion battery as a function of cycle number and temperature. The three most significant parameters that cause capacity loss were loss of secondary active material (LiCoO 2/carbon) and primary active material (Li +) and the rate capability losses. Intrinsic capacity measurements for both positive and negative electrode has been used to estimate the capacity loss due to secondary active material and a charge balance gives the capacity lost due to primary active material (Li +). Capacity fade has been quantified with secondary active material loss dominating the other losses.
Capacity fade in nickel cadmium and nickel hydrogen cells
NASA Technical Reports Server (NTRS)
Edgar, Tim; Hayden, Jeff; Pickett, David F.; Abrams-Blakemore, Bruce; Liptak, ED
1993-01-01
Research and operational experience with capacity fade in nickel cadmium and nickel hydrogen cells are summarized in outline form. The theoretical causes of capacity fade are reviewed and the role of cell storage, positive electrodes, and cobalt additives are addressed. Three examples of observed capacity fade are discussed: INTELSAT 5, INTELSAT 6, and an Explorer platform. Finally, prevention and recovery methods are addressed and the current status of Eagle Picher/Hughes research is discussed.
Design of an anti-Rician-fading modem for mobile satellite communication systems
NASA Technical Reports Server (NTRS)
Kojima, Toshiharu; Ishizu, Fumio; Miyake, Makoto; Murakami, Keishi; Fujino, Tadashi
1995-01-01
To design a demodulator applicable to mobile satellite communication systems using differential phase shift keying modulation, we have developed key technologies including an anti-Rician-fading demodulation scheme, an initial acquisition scheme, automatic gain control (AGC), automatic frequency control (AFC), and bit timing recovery (BTR). Using these technologies, we have developed one-chip digital signal processor (DSP) modem for mobile terminal, which is compact, of light weight, and of low power consumption. Results of performance test show that the developed DSP modem achieves good performance in terms of bit error ratio in mobile satellite communication environment, i.e., Rician fading channel. It is also shown that the initial acquisition scheme acquires received signal rapidly even if the carrier-to-noise power ratio (CNR) of the received signal is considerably low.
Design of an anti-Rician-fading modem for mobile satellite communication systems
NASA Technical Reports Server (NTRS)
Kojima, Toshiharu; Ishizu, Fumio; Miyake, Makoto; Murakami, Keishi; Fujino, Tadashi
1995-01-01
To design a demodulator applicable to mobile satellite communication systems using differential phase shift keying modulation, we have developed key technologies including an anti-Rician-fading demodulation scheme, an initial acquisition scheme, automatic gain control (AGC), automatic frequency control (AFC), and bit timing recovery (BTR). Using these technologies, we have developed one-chip digital signal processor (DSP) modem for mobile terminal, which is compact, of light weight, and of low power consumption. Results of performance test show that the developed DSP modem achieves good performance in terms of bit error ratio in mobile satellite communication environment, i.e., Rician fading channel. It is also shown that the initial acquisition scheme acquires received signal rapidly even if the carrier-to-noise power ratio (CNR) of the received signal is considerably low.
NASA Astrophysics Data System (ADS)
Yang, G.; Khalighi, M. A.; Bourennane, S.; Ghassemlooy, Z.
2014-03-01
This paper investigates fading correlation in space-diversity free-space optical (FSO) communication systems and its effect on the link performance. We firstly evaluate the fading correlation in multiple-aperture FSO systems using wave-optics simulations. The influence of different system parameters including the link distance and aperture spacing is illustrated under realistic beam propagation conditions. In particular, we show that, at relatively large link distances where the scattering disk is much larger than the receiver aperture size, the fading correlation coefficient is almost independent of the apertures’ diameter and depends only on the apertures’ edge separation. To investigate the impact of fading correlation on the system’s performance, we propose an analytical approach to evaluate the performance of the space-diversity FSO system over a correlated Gamma-Gamma (ΓΓ) fading channel. Our approach is based on approximating the sum of arbitrarily correlated ΓΓ random variables by an α-μ distribution. To validate the accuracy of this method, we evaluate the average bit-error-rate (BER) performance for the case of a multiple-aperture FSO system and compare it with the BER results obtained via Monte Carlo simulations.
Downie, John D; Hurley, Jason; DePedro, Hector; Garner, Steven; Blaker, Jeremy; Zakharian, Aramais; Ten, Sergey; Mills, Greg
2017-04-17
Transmission below the cable cut-off wavelength may be a concern in some systems, especially for an optical supervisory channel (OSC) operating below the signal transmission band in systems built with G.654 fiber. In this work, we constructed a cabled span of G.654-compliant fiber and measured the multipath interference (MPI) generated during propagation through the span at a range of wavelengths below the cable cut-offs of the constituent fibers. Measurements were made under a range of conditions including different splice losses and the presence or absence of higher order mode filters placed around the splices. MPI levels were found to be sufficiently low at wavelengths far below the average cable cut-off such that OSC transmission was penalty-free. We compare the experimental results to modeling predictions and find very good agreement.
Multi-Path Transportation Futures Study. Results from Phase 1
Phil Patterson, Phil; Singh, Margaret; Plotkin, Steve; Moore, Jim
2007-03-09
Presentation reporting Phase 1 results, 3/9/2007. Projecting the future role of advanced drivetrains and fuels in the light vehicle market is inherently difficult, given the uncertainty (and likely volatility) of future oil prices, inadequate understanding of likely consumer response to new technologies, the relative infancy of several important new technologies with inevitable future changes in their performance and costs, and the importance — and uncertainty — of future government marketplace interventions (e.g., new regulatory standards or vehicle purchase incentives). The Multi-Path Transportation Futures (MP) Study has attempted to improve our understanding of this future role by examining several scenarios of vehicle costs, fuel prices, government subsidies, and other key factors. These are projections, not forecasts, in that they try to answer a series of “what if” questions without assigning probabilities to most of the basic assumptions.
Multipath effect suppression for instrument landing system based on MUSIC
NASA Astrophysics Data System (ADS)
Zhao, Xiubin; Wang, Yongsheng; Jiang, Hengle; Dai, Chuanjin
2005-11-01
The Decimeter-wavelength Instrument Landing System is designed to assure an exact and timely flight arrival on many airports. But its signal can often be distorted by reflections and scattering caused by objects which are illuminated by the radiating antennas, sometimes referred to be "multipath", which pose a great threat to the system's operation. In this paper, an improved receiver based on spatial spectrum estimation concepts is proposed for safer automatic landing procedures. The new approach is based on Direction of Arrival (DOA) estimation performed by the MUSIC algorithm and signal filter performed by beamforming algorithm. The superior performance of the proposed system with respect to currently employed techniques in the presence of unwanted interferences has been tested in extensive computer simulations.
Teaching braille line tracking using stimulus fading.
Scheithauer, Mindy C; Tiger, Jeffrey H
2014-01-01
Line tracking is a prerequisite skill for braille literacy that involves moving one's finger horizontally across a line of braille text and identifying when a line ends so the reader may reset his or her finger on the subsequent line. Current procedures for teaching line tracking are incomplete, because they focus on tracking lines with only small gaps between characters. The current study extended previous line-tracking instruction using stimulus fading to teach tracking across larger gaps. After instruction, all participants showed improvement in line tracking, and 2 of 3 participants met mastery criteria for tracking across extended spaces.
NASA Technical Reports Server (NTRS)
Birch, J. N.; French, R. H.
1972-01-01
An investigation was made to define experiments for collection of RFI and multipath data for application to a synchronous relay satellite/low orbiting satellite configuration. A survey of analytical models of the multipath signal was conducted. Data has been gathered concerning the existing RFI and other noise sources in various bands at VHF and UHF. Additionally, designs are presented for equipment to combat the effects of RFI and multipath: an adaptive delta mod voice system, a forward error control coder/decoder, a PN transmission system, and a wideband FM system. The performance of these systems was then evaluated. Techniques are discussed for measuring multipath and RFI. Finally, recommended data collection experiments are presented. An extensive tabulation is included of theoretical predictions of the amount of signal reflected from a rough, spherical earth.
2007-06-01
are less or more severe than the Rayleigh model since, for m =1, the Nakagami PDF is a Rayleigh PDF. For small m (1/ 2 1) m , fading is very severe...flat, slowly fading Nakagami channel with m =1/2 in AWGN. ................................................... 36 Figure 19. Magnified performance of 8...PSK and r=2/3 convolutionally encoded bits with HDD for different numbers of memory elements and a flat, slowly fading Nakagami channel with m =1/2
Channel simulation for optical communication systems
NASA Technical Reports Server (NTRS)
Tycz, M.; Fitzmaurice, M. W.
1974-01-01
A technique is reported for simulating the signal fading that will be experienced by typical optical communication systems. The desired irradiance or amplitude fading statistics can be simulated by incorporating a linearized optical modulator subsystem between the transmitter and receiver. This technique has been implemented in the design and construction of a laboratory channel simulator. The design of the processing electronics is discussed along with the results of tests performed for each mode of operation.
Why does consciousness fade in early sleep?
Tononi, Giulio; Massimini, Marcello
2008-01-01
Consciousness fades during deep nonrapid eye movement (NREM) sleep early in the night, yet cortical neurons remain active, keep receiving sensory inputs, and can display patterns of synchronous activity. Why then does consciousness fade? According to the integrated information theory of consciousness, what is critical for consciousness is not firing rates, sensory input, or synchronization per se, but rather the ability of a system to integrate information. If consciousness is the capacity to integrate information, then the brain should be able to generate consciousness to the extent that it has a large repertoire of available states (information), yet it cannot be decomposed into a collection of causally independent subsystems (integration). A key prediction stemming from this hypothesis is that such ability should be greatly reduced in deep NREM sleep; the dreamless brain either breaks down into causally independent modules, shrinks its repertoire of possible responses, or both. In this article, we report the results of a series of experiments in which we employed a combination of transcranial magnetic stimulation and high-density electroencephalography (TMS/hd-EEG) to directly test this prediction in humans. Altogether, TMS/hdEEG measurements suggest that the sleeping brain, despite being active and reactive, loses its ability of entering states that are both integrated and differentiated; it either breaks down in causally independent modules, responding to TMS with a short and local activation, or it bursts into an explosive and aspecific response, producing a full-fledged slow wave.
T1 VSAT Fade Compensation Statistical Results
NASA Technical Reports Server (NTRS)
Johnson, Sandra K.; Acosta, Roberto; Ugweje, Oke
2000-01-01
New satellite communication systems are steadily seeking to use higher frequency bands to accommodate the requirements for additional capacity. At these higher frequencies, propagation impairments that did not significantly affect the signal at lower frequencies begin to have considerable impact. In Ka-band. the next logical commercial frequency band to be used for satellite communication, attenuation of the signal due to rain is a primary concern. An experimental satellite built by NASA, the Advanced Communication Technology Satellite (ACTS). launched in September 1993, is the first U.S. communication satellite operating in the Ka-band. In addition to higher carrier frequencies, a number of other new technologies, including on-board baseband processing. multiple beam antennas, and rain fade detection and compensation techniques, were designed into the ACTS. Verification experiments have been conducted since the launch to characterize the new technologies. The focus of this paper is to characterize the method used by the ACTS TI Very Small Aperture Terminal (TI VSAT) ground stations in detecting the presence of fade in the communication signal and to adaptively compensate for it by the addition of burst rate reduction and forward error correction. Measured data obtained from the ACTS program was used to validate the compensation technique. A software process was developed and demonstrated to statistically characterize the increased availability achieved by the compensation techniques in terms of the bit error rate time enhancement factor. Several improvements to the ACTS technique are discussed and possible implementations for future Ka band system are offered.
MLS Multipath Studies. Phase 3. Volume 3. Application of Models to MLS Assessment Issues. Part 2.
1981-06-08
time evidently were such as to suggest a suboptimum ap- proach based on the small signal suppression properties of a multiple baseline * ,interferometer...features of the proposed implementation signifi- cantly degraded the azimuth multipath performance. The proposed acquisition algorithm utilizing multiple ... baseline interfer- ometry could fail with out of beam multipath at lower levels than those re- quired for failure with DMLS or TRSB. These problems
Restoration Of Faded Color Photographs By Digital Image Processing
NASA Astrophysics Data System (ADS)
Gschwind, Rudolf
1989-10-01
Color photographs possess a poor stability towards light, chemicals heat and humidity. As a consequence, the colors of photographs deteriorate with time. Because of the complexity of processes that cause the dyes to fade, it is impossible to restore the images by chemical means. It is therefore attempted to restore faded color films by means of digital image processing.
Fading characteristics of panchromatic radar backscatter from selected agricultural targets
NASA Technical Reports Server (NTRS)
Bush, T. F.; Ulaby, F. T.
1973-01-01
An experiment was performed to empirically determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and results of the data are analyzed. Comparison with theory shows adequate agreement with the experimental results, provided of course, the targets are modeled in a correct manner.
Autonomous detection of ISO fade point with color laser printers
NASA Astrophysics Data System (ADS)
Yan, Ni; Maggard, Eric; Fothergill, Roberta; Jessome, Renee J.; Allebach, Jan P.
2015-01-01
Image quality assessment is a very important field in image processing. Human observation is slow and subjective, it also requires strict environment setup for the psychological test 1. Thus developing algorithms to match desired human experiments is always in need. Many studies have focused on detecting the fading phenomenon after the materials are printed, that is to monitor the persistence of the color ink 2-4. However, fading is also a common artifact produced by printing systems when the cartridges run low. We want to develop an automatic system to monitor cartridge life and report fading defects when they appear. In this paper, we first describe a psychological experiment that studies the human perspective on printed fading pages. Then we propose an algorithm based on Color Space Projection and K-means clustering to predict the visibility of fading defects. At last, we integrate the psychological experiment result with our algorithm to give a machine learning tool that monitors cartridge life.
Beam-tracking in FSO links impaired by correlated fading
NASA Astrophysics Data System (ADS)
Kiasaleh, Kamran
2006-08-01
In this paper, the performance of quad-APD spatial tracking loop (STL)in the presence of scintillation is studied for a frozen atmosphere turbulent model for free-space communications (FSO). The atmospheric turbulence responsible for the beam scintillation is assumed to follow the weak turbulence model, described by Rytov approximation, which in turn suggests log-normal statistics for the received optical signal intensity. It is assumed that pointing error in large part is due to atmospheric wander and that the correlation time of the beam wander is comparable to the correlation time of the amplitude variations due to amplitude scintillation. Provided recently reported estimation strategies, a new model for spatial tracking is proposed where estimates of channel coefficient are used to adjust the gain of the tracking loop, enabling an adaptive bandwidth adjustment in the presence of correlated fading. The performance of the proposed loop as well as that of the standard tracking loop are assessed and compared via simulation in terms of the mean square tracking error (MSTE).
NASA Technical Reports Server (NTRS)
Svoboda, James S.; Kachmar, Brian A.
1993-01-01
The design and performance of a rain fade simulation/counteraction system on a laboratory simulated 30/20 GHz, time division multiple access (TDMA) satellite communications testbed is evaluated. Severe rain attenuation of electromagnetic radiation at 30/20 GHz occurs due to the carrier wavelength approaching the water droplet size. Rain in the downlink path lowers the signal power present at the receiver, resulting in a higher number of bit errors induced in the digital ground terminal. The laboratory simulation performed at NASA Lewis Research Center uses a programmable PIN diode attenuator to simulate 20 GHz satellite downlink geographic rain fade profiles. A computer based network control system monitors the downlink power and informs the network of any power threshold violations, which then prompts the network to issue commands that temporarily increase the gain of the satellite based traveling wave tube (TWT) amplifier. After the rain subsides, the network returns the TWT to the normal energy conserving power mode. Bit error rate (BER) data taken at the receiving ground terminal serves as a measure of the severity of rain degradation, and also evaluates the extent to which the network can improve the faded channel.
The multipath and SNR Quality in civil code L2
NASA Astrophysics Data System (ADS)
Polezel, W. G.; Souza, E. M.; Monico, J. F.
2007-12-01
The new generation of GPS satellites, with the addition of the new L2C civil code, may provide to the users better positioning capabilities. The new code in the L2 may increase the signal robustness, improve resistance to interference, reduce tracking noise and consequently, improve accuracy and provide better positioning inside buildings and in wooded areas. The second civil frequency code will eliminate the need of using fragile semi- codeless tracking techniques currently used in connection with L2. The L2C has a different structure that allows civil and military share the same code. L2C owns two codes of different length: moderate code (CM) and long code (CL). The CM was chosen to have 10.230 chips repeated to every 20 millisecond. The CL was chosen to have 767250 chips with period of 1.5 second. The main reasons for these choices were due to excellent correlation properties. Furthermore, L2C enhances performance by having no data modulation on CL code, which improves, among others, the threshold tracking performance. Comparing the L2C acquisition with the C/A, the CM code is ten times longer than the C/A and the two components have half the total power. This is an important feature for many low-power applications. Although this signal has several advantages, some investigations about its performance are necessary, mainly about the provided accuracy under some effects, for example, multipath. Thus, this paper aims to analyze the L2C signal, as well as its quality using some parameters, such as Signal to Noise Ratio (SNR) and multipath level (MP). The experiment was realized at Sao Paulo State University UNESP in Presidente Prudente, Brazil. The data were collected by two receivers of different brands, both able to collect the L2C signal, and connected to the same antenna, thought the use of a splitter. The results showed that the MP and SNR values were better for the modernized satellites. Furthermore, the SNR values of the two receivers were similar while the
Nekoogar, F
2003-06-12
In this paper, the performance of a two user UWB multiple access (UWB-MA) system based on multiple-pulse multiple-delay (MPMD) modulation scheme in an indoor wireless channel is evaluated by computer simulations. The indoor multipath propagation channel model used in this study is based on the modified statistical Saleh-Valenzuela model proposed by Foerester and Li from Intel. The simulation results indicate that the multipath performance of MPMD modulated signals in a multiple access system outperforms the nonmultipath case as the number of autocorrelation function (ACF) sampling points increases for each user. This is an unusual but important result, since MPMD receiver exploits multipath phenomenon in indoor wireless channels to increase the BER performance, hence the transmission rate in a UWB-MA system.
Adaptive tracking of narrowband HF channel response
NASA Astrophysics Data System (ADS)
Arikan, F.; Arikan, O.
2003-12-01
Estimation of channel impulse response constitutes a first step in computation of scattering function, channel equalization, elimination of multipath, and optimum detection and identification of transmitted signals through the HF channel. Due to spatial and temporal variations, HF channel impulse response has to be estimated adaptively. Based on developed state-space and measurement models, an adaptive Kalman filter is proposed to track the HF channel variation in time. Robust methods of initialization and adaptively adjusting the noise covariance in the system dynamics are proposed. In simulated examples under good, moderate and poor ionospheric conditions, it is observed that the adaptive Kalman filter based channel estimator provides reliable channel estimates and can track the variation of the channel in time with high accuracy.
Multipathing Via Three Parameter Common Image Gathers (CIGs) From Reverse Time Migration
NASA Astrophysics Data System (ADS)
Ostadhassan, M.; Zhang, X.
2015-12-01
A noteworthy problem for seismic exploration is effects of multipathing (both wanted or unwanted) caused by subsurface complex structures. We show that reverse time migration (RTM) combined with a unified, systematic three parameter framework that flexibly handles multipathing can be accomplished by adding one more dimension (image time) to the angle domain common image gather (ADCIG) data. RTM is widely used to generate prestack depth migration images. When using the cross-correlation image condition in 2D prestack migration in RTM, the usual practice is to sum over all the migration time steps. Thus all possible wave types and paths automatically contribute to the resulting image, including destructive wave interferences, phase shifts, and other distortions. One reason is that multipath (prismatic wave) contributions are not properly sorted and mapped in the ADCIGs. Also, multipath arrivals usually have different instantaneous attributes (amplitude, phase and frequency), and if not separated, the amplitudes and phases in the final prestack image will not stack coherently across sources. A prismatic path satisfies an image time for it's unique path; Cavalca and Lailly (2005) show that RTM images with multipaths can provide more complete target information in complex geology, as multipaths usually have different incident angles and amplitudes compared to primary reflections. If the image time slices within a cross-correlation common-source migration are saved for each image time, this three-parameter (incident angle, depth, image time) volume can be post-processed to generate separate, or composite, images of any desired subset of the migrated data. Images can by displayed for primary contributions, any combination of primary and multipath contributions (with or without artifacts), or various projections, including the conventional ADCIG (angle vs depth) plane. Examples show that signal from the true structure can be separated from artifacts caused by multiple
A Secure Cluster-Based Multipath Routing Protocol for WMSNs
Almalkawi, Islam T.; Zapata, Manel Guerrero; Al-Karaki, Jamal N.
2011-01-01
The new characteristics of Wireless Multimedia Sensor Network (WMSN) and its design issues brought by handling different traffic classes of multimedia content (video streams, audio, and still images) as well as scalar data over the network, make the proposed routing protocols for typical WSNs not directly applicable for WMSNs. Handling real-time multimedia data requires both energy efficiency and QoS assurance in order to ensure efficient utility of different capabilities of sensor resources and correct delivery of collected information. In this paper, we propose a Secure Cluster-based Multipath Routing protocol for WMSNs, SCMR, to satisfy the requirements of delivering different data types and support high data rate multimedia traffic. SCMR exploits the hierarchical structure of powerful cluster heads and the optimized multiple paths to support timeliness and reliable high data rate multimedia communication with minimum energy dissipation. Also, we present a light-weight distributed security mechanism of key management in order to secure the communication between sensor nodes and protect the network against different types of attacks. Performance evaluation from simulation results demonstrates a significant performance improvement comparing with existing protocols (which do not even provide any kind of security feature) in terms of average end-to-end delay, network throughput, packet delivery ratio, and energy consumption. PMID:22163854
Millimeter-wave multipath measurements on snow cover
NASA Astrophysics Data System (ADS)
Lammers, Uve H. W.; Hayes, Dallas T.; Marr, Richard A.
1988-05-01
Multipath data were obtained at frequencies of 35.1, 98.1, and 140.1 GHz over a pathlength of 179.5 m by measuring height-gain patterns between 0.2 and 4.0 m with a vertically moving receiving antenna. Grazing angles from this geometry range between 0.5 and 2 deg measured interference patterns between direct and snow-reflected rays were generally coherent in appearance and on occassion exhibited cancellation depths greater than 20 dB. A computer program models the reflection as a coherent process, with the underlying snow surface represented by a series of linear sloping segments derived from actual terrain heights. The reflection coefficient near a 2-deg grazing angle ranged from 0.53 to 0.20 over matted grass, from 0.66 to 0.34 over freshly fallen snow, and from 0.85 to 0.71 over old snow. The higher numbers correspond to 35.1 GHz, the lower numbers correspond to 140.1 GHz.
Modeling Infrared Signal Reflections to Characterize Indoor Multipath Propagation
De-La-Llana-Calvo, Álvaro; Lázaro-Galilea, José Luis; Gardel-Vicente, Alfredo; Rodríguez-Navarro, David; Bravo-Muñoz, Ignacio; Tsirigotis, Georgios; Iglesias-Miguel, Juan
2017-01-01
In this paper, we propose a model to characterize Infrared (IR) signal reflections on any kind of surface material, together with a simplified procedure to compute the model parameters. The model works within the framework of Local Positioning Systems (LPS) based on IR signals (IR-LPS) to evaluate the behavior of transmitted signal Multipaths (MP), which are the main cause of error in IR-LPS, and makes several contributions to mitigation methods. Current methods are based on physics, optics, geometry and empirical methods, but these do not meet our requirements because of the need to apply several different restrictions and employ complex tools. We propose a simplified model based on only two reflection components, together with a method for determining the model parameters based on 12 empirical measurements that are easily performed in the real environment where the IR-LPS is being applied. Our experimental results show that the model provides a comprehensive solution to the real behavior of IR MP, yielding small errors when comparing real and modeled data (the mean error ranges from 1% to 4% depending on the environment surface materials). Other state-of-the-art methods yielded mean errors ranging from 15% to 40% in test measurements. PMID:28406436
A secure cluster-based multipath routing protocol for WMSNs.
Almalkawi, Islam T; Zapata, Manel Guerrero; Al-Karaki, Jamal N
2011-01-01
The new characteristics of Wireless Multimedia Sensor Network (WMSN) and its design issues brought by handling different traffic classes of multimedia content (video streams, audio, and still images) as well as scalar data over the network, make the proposed routing protocols for typical WSNs not directly applicable for WMSNs. Handling real-time multimedia data requires both energy efficiency and QoS assurance in order to ensure efficient utility of different capabilities of sensor resources and correct delivery of collected information. In this paper, we propose a Secure Cluster-based Multipath Routing protocol for WMSNs, SCMR, to satisfy the requirements of delivering different data types and support high data rate multimedia traffic. SCMR exploits the hierarchical structure of powerful cluster heads and the optimized multiple paths to support timeliness and reliable high data rate multimedia communication with minimum energy dissipation. Also, we present a light-weight distributed security mechanism of key management in order to secure the communication between sensor nodes and protect the network against different types of attacks. Performance evaluation from simulation results demonstrates a significant performance improvement comparing with existing protocols (which do not even provide any kind of security feature) in terms of average end-to-end delay, network throughput, packet delivery ratio, and energy consumption.
NASA Astrophysics Data System (ADS)
Queiroz, Wamberto J. L.; Lopes, Waslon T. A.; Madeiro, Francisco; Alencar, Marcelo S.
2010-12-01
This paper presents an alternative method for determining exact expressions for the bit error probability (BEP) of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In this method, the Nakagami-[InlineEquation not available: see fulltext.] fading channel is seen as an additive noise channel whose noise is modeled as the ratio between Gaussian and Nakagami-[InlineEquation not available: see fulltext.] random variables. The method consists of using the cumulative density function of the resulting noise to obtain closed-form expressions for the BEP of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In particular, the proposed method is used to obtain closed-form expressions for the BEP of [InlineEquation not available: see fulltext.]-ary quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM), [InlineEquation not available: see fulltext.]-ary pulse amplitude modulation ([InlineEquation not available: see fulltext.]-PAM), and rectangular quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM) under Nakagami-[InlineEquation not available: see fulltext.] fading. The main contribution of this paper is to show that this alternative method can be used to reduce the computational complexity for detecting signals in the presence of fading.
On the Fading of the STIS Ultraviolet Calibration Lamps
NASA Astrophysics Data System (ADS)
Peeples, Molly S.
2017-09-01
The Space Telescope Imaging Spectrograph (STIS) has been in orbit for over 20 years, so its calibration lamps are fading, risking the precision of future science opportunities. The report documents analysis on the fading of these lamps in the ultraviolet and suggests possible mitigation strategies. A discussion of the strategy of alternating years to obtain deep NUV and FUV flats appears to have slowed the fading of these lamps, but the modes in which the flat fields are taken may have to be changed again in future cycles to obtain enough counts for robust flat fields.
Fade detector for the FODA-TDMA access scheme
NASA Astrophysics Data System (ADS)
Celandroni, Nedo; Ferro, Erina; Marzoli, Antonio
1989-05-01
The First in first out Ordered Demand Assignment-Time Division Multiple Access (FODA-TDMA) satellite access scheme designed for simultaneous transmissions of real time data, like packetized voice and slow-scan images (stream traffic) and data coming from standard EDP applications, such as bulk data tansfer, interactive computer access, mailing, data base enquiry and updating (datagram traffic) is described. When deep fades are experienced due to rain attenuation, the system is able to counter the fade. Techniques to detect the fade are presented.
NASA Astrophysics Data System (ADS)
Moradi, Hassan; Refai, Hazem H.; LoPresti, Peter G.; Atiquzzaman, Mohammed
2010-02-01
Incoherent receivers of Free Space Optical (FSO) signals have no knowledge of instantaneous channel state. Thus, the receiver requires some information about the noise and fading statistics for a maximum likelihood (ML)-based optimal detection. Using pilot-aided symbols, we develop a simple multi slot averaging (MSA) estimation technique to approximate the values of parameters required at the incoherent detector. No channel state information (CSI) is available at the receiver side and this work will not be also trying to estimate it. But the estimation of noise and fading statistics will be practically investigated. We evaluate the bit error rate (BER) performance of FSO links with MSA estimation over both Gaussian and lognormal atmospheric turbulence fading (scintillation) channels. Numerical simulation will be completed to evaluate the estimation error of the MSA estimator. We will see that at signal to noise ratio (SNR)=13dB, the performance loss of the Gaussian estimator improves from 3dB to 0.4dB when we increase the number of pilot symbols from 16 to 64. This paper also presents the hardware design of the estimator using Xilinx system generator.
NASA Astrophysics Data System (ADS)
Le, Tuan Anh; Haw, Rim; Hong, Choong Seon; Lee, Sungwon
Cubic TCP, one of transport protocols designed for high bandwidth-delay product (BDP) networks, has successfully been deployed in the Internet. Multi-homed computers with multiple interfaces to access the Internet via high speed links will become more popular. In this work, we introduce an extended version of Cubic TCP for multiple paths, called MPCubic. The extension process is approached from an analysis model of Cubic by using coordinated congestion control between paths. MPCubic can spread its traffic across paths in load-balancing manner, while preserving fair sharing with regular TCP, Cubic, and MPTCP at common bottlenecks. Moreover, to improve resilience to link failure, we propose a multipath fast recovery algorithm. The algorithm can significantly reduce the recovery time of data rate after restoration of failed links. These techniques can be useful for resilient high-bandwidth applications (for example, tele-health conference) in disaster-affected areas. Our simulation results show that MPCubic can achieve stability, throughput improvement, fairness, load-balancing, and quick data rate recovery from link failure under a variety of network conditions.
Global Navigation Satellite System Multipath Mitigation Using a Wave-Absorbing Shield.
Yang, Haiyan; Yang, Xuhai; Sun, Baoqi; Su, Hang
2016-08-22
Code multipath is an unmanaged error source in precise global navigation satellite system (GNSS) observation processing that limits GNSS positioning accuracy. A new technique for mitigating multipath by installing a wave-absorbing shield is presented in this paper. The wave-absorbing shield was designed according to a GNSS requirement of received signals and collected measurements to achieve good performance. The wave-absorbing shield was installed at the KUN1 and SHA1 sites of the international GNSS Monitoring and Assessment System (iGMAS). Code and carrier phase measurements of three constellations were collected on the dates of the respective installations plus and minus one week. Experiments were performed in which the multipath of the measurements obtained at different elevations was mitigated to different extents after applying the wave-absorbing shield. The results of an analysis and comparison show that the multipath was mitigated by approximately 17%-36% on all available frequencies of BeiDou Navigation Satellite System (BDS), Global Positioning System (GPS), and Global Navigation Satellite System (GLONASS) satellites. The three-dimensional accuracies of BDS, GPS, and GLONASS single-point positioning (SPP) were, respectively, improved by 1.07, 0.63 and 0.49 m for the KUN1 site, and by 0.72, 0.79 and 0.73 m for the SHA1 site. Results indicate that the multipath of the original observations was mitigated by using the wave-absorbing shield.
Global Navigation Satellite System Multipath Mitigation Using a Wave-Absorbing Shield
Yang, Haiyan; Yang, Xuhai; Sun, Baoqi; Su, Hang
2016-01-01
Code multipath is an unmanaged error source in precise global navigation satellite system (GNSS) observation processing that limits GNSS positioning accuracy. A new technique for mitigating multipath by installing a wave-absorbing shield is presented in this paper. The wave-absorbing shield was designed according to a GNSS requirement of received signals and collected measurements to achieve good performance. The wave-absorbing shield was installed at the KUN1 and SHA1 sites of the international GNSS Monitoring and Assessment System (iGMAS). Code and carrier phase measurements of three constellations were collected on the dates of the respective installations plus and minus one week. Experiments were performed in which the multipath of the measurements obtained at different elevations was mitigated to different extents after applying the wave-absorbing shield. The results of an analysis and comparison show that the multipath was mitigated by approximately 17%–36% on all available frequencies of BeiDou Navigation Satellite System (BDS), Global Positioning System (GPS), and Global Navigation Satellite System (GLONASS) satellites. The three-dimensional accuracies of BDS, GPS, and GLONASS single-point positioning (SPP) were, respectively, improved by 1.07, 0.63 and 0.49 m for the KUN1 site, and by 0.72, 0.79 and 0.73 m for the SHA1 site. Results indicate that the multipath of the original observations was mitigated by using the wave-absorbing shield. PMID:27556466
BDS relative static positioning over long baseline improved by GEO multipath mitigation
NASA Astrophysics Data System (ADS)
Wang, Min; Chai, Hongzhou; Liu, Jun; Zeng, Anmin
2016-02-01
Due to the satellite and constellation deployment design, the variation pattern of multipath effect in BeiDou Navigation Satellite System (BDS) code observation is different from GPS. The amplitude of systematic multipath variation (SMV) exists in multipath combination series may exceed 0.5 m for some geostationary earth orbit (GEO) satellites, which is larger than the normal noise level of GPS code observation. After characterization of the variation pattern of BDS multipath series for BDS GEO satellites, we propose to improve the performance of relative positioning over long baseline by mitigating the SMV effect of GEO satellite. The proposed method uses the SMV extracted from multipath (MP) combination series with adaptive wavelet transform as correction for current day observation in post-processing use or as following day correction in real-time use. In addition, the Double Station Observation Processing (DSOP) method that directly uses undifferenced observation is applied for relative static positioning. Experiment results show improvement in convergence speed for both BDS only and BDS/GPS combined solution.
A novel communication mechanism based on node potential multi-path routing
NASA Astrophysics Data System (ADS)
Bu, Youjun; Zhang, Chuanhao; Jiang, YiMing; Zhang, Zhen
2016-10-01
With the network scales rapidly and new network applications emerge frequently, bandwidth supply for today's Internet could not catch up with the rapid increasing requirements. Unfortunately, irrational using of network sources makes things worse. Actual network deploys single-next-hop optimization paths for data transmission, but such "best effort" model leads to the imbalance use of network resources and usually leads to local congestion. On the other hand Multi-path routing can use the aggregation bandwidth of multi paths efficiently and improve the robustness of network, security, load balancing and quality of service. As a result, multi-path has attracted much attention in the routing and switching research fields and many important ideas and solutions have been proposed. This paper focuses on implementing the parallel transmission of multi next-hop data, balancing the network traffic and reducing the congestion. It aimed at exploring the key technologies of the multi-path communication network, which could provide a feasible academic support for subsequent applications of multi-path communication networking. It proposed a novel multi-path algorithm based on node potential in the network. And the algorithm can fully use of the network link resource and effectively balance network link resource utilization.
NASA Technical Reports Server (NTRS)
Goldhirsh, J.
1982-01-01
The first absolute rain fade distribution method described establishes absolute fade statistics at a given site by means of a sampled radar data base. The second method extrapolates absolute fade statistics from one location to another, given simultaneously measured fade and rain rate statistics at the former. Both methods employ similar conditional fade statistic concepts and long term rain rate distributions. Probability deviations in the 2-19% range, with an 11% average, were obtained upon comparison of measured and predicted levels at given attenuations. The extrapolation of fade distributions to other locations at 28 GHz showed very good agreement with measured data at three sites located in the continental temperate region.
NiH2 capacity fade during early cycling
NASA Technical Reports Server (NTRS)
Zagrodnik, Jeffrey P.
1993-01-01
Tests were conducted on nickel hydrogen batteries to determine the charge efficiency of the nickel electrode as a function of rate and temperature, cell discharge capacity, and capacity fade. Test procedures and results are presented in outline and graphic form.
An examination of ham colour fading using optical fibre methods
NASA Astrophysics Data System (ADS)
Sheridan, Cormac; O'Farrell, Marion; Lewis, Elfed; Flanagan, Colin; Kerry, John F.; Jackman, Nick
2006-10-01
Sliced ham products undergo significant discolouration and fading when placed in retail display cabinets. This is due to factors such as illumination of the display cabinet, packaging, i.e. low OTR (Oxygen Transmission Rate) or very low OTR packaging, product to headspace ratio and percentage of residual oxygen. This paper presents initial investigations into the development of a sensor to measure rate of colour fading in cured ham, in order to predict an optimum colour sell-by-date. An investigation has been carried out that shows that spectral reflections offer more reproducibility than CIE L*a*b* readings, which are, at present, most often used to measure meat colour. Self-Organising Maps were then used to classify the data into five colour fading stages, from very pink to grey. The results presented here show that this classifier could prove an effective system for determining the rate of colour fading in ham.
Kinetics of the Fading of Phenolphthalein in Alkaline Solution.
ERIC Educational Resources Information Center
Nicholson, Lois
1989-01-01
Described is an experiment which illustrates pseudo-first-order kinetics in the fading of a common indicator in an alkaline solution. Included are background information, details of materials used, laboratory procedures, and sample results. (CW)
Motion fading is driven by perceived, not actual angular velocity.
Kohler, P J; Caplovitz, G P; Hsieh, P-J; Sun, J; Tse, P U
2010-06-01
After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here we examine the relationship between such 'motion fading' and perceived angular velocity. Using several different dot patterns that generate emergent virtual contours, we demonstrate that whenever there is a difference in the perceived angular velocity of two patterns of dots that are in fact rotating at the same angular velocity, there is also a difference in the time to undergo motion fading for those two patterns. Conversely, whenever two patterns show no difference in perceived angular velocity, even if in fact rotating at different angular velocities, we find no difference in the time to undergo motion fading. Thus, motion fading is driven by the perceived rather than actual angular velocity of a rotating stimulus.
OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTHNORTHEAST ...
OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTH-NORTHEAST - Shoshone Falls Hydroelectric Project, Reservoir and Dam Complex, North Bank of Snake River, extreme Eastern end of the Shoshone Falls Hydroelectric Project, Tipperary Corner, Jerome County, ID
Fading of Jupiter's South Equatorial Belt
NASA Technical Reports Server (NTRS)
Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma
2011-01-01
One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.
Fading of Jupiter's South Equatorial Belt
NASA Technical Reports Server (NTRS)
Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma
2011-01-01
One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.
Optically derived elevation angle dependence of fading for satellite PCS
NASA Technical Reports Server (NTRS)
Akturan, R.; Vogel, Wolf J.
1995-01-01
Images of urban Japan taken vertically through a 180 deg fisheye lens were analyzed to derive, as a function of elevation the fraction of sky that is clear, shadowed by trees, or blocked by buildings. At 32 deg elevation, results match those derived from satellite measurements fit to a 3-state fade model. Using the same model, for the first time the elevation angle dependence of mobile satellite fading is predicted.
Duan, Li; Zhang, Peng; Tang, Ming; Wang, Ruoxu; Zhao, Zhiyong; Fu, Songnian; Gan, Lin; Zhu, Benpeng; Tong, Weijun; Liu, Deming; Shum, Perry Ping
2016-09-05
A compact high temperature sensor utilizing a multipath Michelson interferometer (MI) structure based on weak coupling multicore fiber (MCF) is proposed and experimentally demonstrated. The device is fabricated by program-controlled tapering the spliced region between single mode fiber (SMF) and a segment of MCF. After that, a spherical reflective structure is formed by arc-fusion splicing the end face of MCF. Theoretical analysis has been implemented for this specific multipath MI structure; beam propagation method based simulation and corresponding experiments were performed to investigate the effect of taper and spherical end face on system's performance. Benefiting from the multipath interferences and heterogeneous structure between the center core and surrounding cores of the all-solid MCF, an enhanced temperature sensitivity of 165 pm/°C up to 900°C and a high-quality interference spectrum with 25 dB fringe visibility were achieved.
Analysis and exploitation of multipath ghosts in radar target image classification.
Smith, Graeme E; Mobasseri, Bijan G
2014-04-01
An analysis of the relationship between multipath ghosts and the direct target image for radar imaging is presented. A multipath point spread function (PSF) is defined that allows for specular reflections in the local environment and can allow the ghost images to be localized. Analysis of the multipath PSF shows that certain ghosts can only be focused for the far field synthetic aperture radar case and not the full array case. Importantly, the ghosts are shown to be equivalent to direct target images taken from different observation angles. This equivalence suggests that exploiting the ghosts would improve target classification performance, and this improvement is demonstrated using experimental data and a naïve Bayesian classifer. The maximum performance gain achieved is 32%.
NASA Technical Reports Server (NTRS)
Gomez, Susan F.; Hood, Laura; Panneton, Robert J.; Saunders, Penny E.; Adkins, Antha; Hwu, Shian U.; Lu, Ba P.
1996-01-01
Two computational techniques are used to calculate differential phase errors on Global Positioning System (GPS) carrier war phase measurements due to certain multipath-producing objects. The two computational techniques are a rigorous computati electromagnetics technique called Geometric Theory of Diffraction (GTD) and the other is a simple ray tracing method. The GTD technique has been used successfully to predict microwave propagation characteristics by taking into account the dominant multipath components due to reflections and diffractions from scattering structures. The ray tracing technique only solves for reflected signals. The results from the two techniques are compared to GPS differential carrier phase ns taken on the ground using a GPS receiver in the presence of typical International Space Station (ISS) interference structures. The calculations produced using the GTD code compared to the measured results better than the ray tracing technique. The agreement was good, demonstrating that the phase errors due to multipath can be modeled and characterized using the GTD technique and characterized to a lesser fidelity using the DECAT technique. However, some discrepancies were observed. Most of the discrepancies occurred at lower devations and were either due to phase center deviations of the antenna, the background multipath environment, or the receiver itself. Selected measured and predicted differential carrier phase error results are presented and compared. Results indicate that reflections and diffractions caused by the multipath producers, located near the GPS antennas, can produce phase shifts of greater than 10 mm, and as high as 95 mm. It should be noted tl the field test configuration was meant to simulate typical ISS structures, but the two environments are not identical. The GZ and DECAT techniques have been used to calculate phase errors due to multipath o the ISS configuration to quantify the expected attitude determination errors.
A Forward GPS Multipath Simulator Based on the Vegetation Radiative Transfer Equation Model.
Wu, Xuerui; Jin, Shuanggen; Xia, Junming
2017-06-05
Global Navigation Satellite Systems (GNSS) have been widely used in navigation, positioning and timing. Nowadays, the multipath errors may be re-utilized for the remote sensing of geophysical parameters (soil moisture, vegetation and snow depth), i.e., GPS-Multipath Reflectometry (GPS-MR). However, bistatic scattering properties and the relation between GPS observables and geophysical parameters are not clear, e.g., vegetation. In this paper, a new element on bistatic scattering properties of vegetation is incorporated into the traditional GPS-MR model. This new element is the first-order radiative transfer equation model. The new forward GPS multipath simulator is able to explicitly link the vegetation parameters with GPS multipath observables (signal-to-noise-ratio (SNR), code pseudorange and carrier phase observables). The trunk layer and its corresponding scattering mechanisms are ignored since GPS-MR is not suitable for high forest monitoring due to the coherence of direct and reflected signals. Based on this new model, the developed simulator can present how the GPS signals (L1 and L2 carrier frequencies, C/A, P(Y) and L2C modulations) are transmitted (scattered and absorbed) through vegetation medium and received by GPS receivers. Simulation results show that the wheat will decrease the amplitudes of GPS multipath observables (SNR, phase and code), if we increase the vegetation moisture contents or the scatters sizes (stem or leaf). Although the Specular-Ground component dominates the total specular scattering, vegetation covered ground soil moisture has almost no effects on the final multipath signatures. Our simulated results are consistent with previous results for environmental parameter detections by GPS-MR.
A Forward GPS Multipath Simulator Based on the Vegetation Radiative Transfer Equation Model
Wu, Xuerui; Jin, Shuanggen; Xia, Junming
2017-01-01
Global Navigation Satellite Systems (GNSS) have been widely used in navigation, positioning and timing. Nowadays, the multipath errors may be re-utilized for the remote sensing of geophysical parameters (soil moisture, vegetation and snow depth), i.e., GPS-Multipath Reflectometry (GPS-MR). However, bistatic scattering properties and the relation between GPS observables and geophysical parameters are not clear, e.g., vegetation. In this paper, a new element on bistatic scattering properties of vegetation is incorporated into the traditional GPS-MR model. This new element is the first-order radiative transfer equation model. The new forward GPS multipath simulator is able to explicitly link the vegetation parameters with GPS multipath observables (signal-to-noise-ratio (SNR), code pseudorange and carrier phase observables). The trunk layer and its corresponding scattering mechanisms are ignored since GPS-MR is not suitable for high forest monitoring due to the coherence of direct and reflected signals. Based on this new model, the developed simulator can present how the GPS signals (L1 and L2 carrier frequencies, C/A, P(Y) and L2C modulations) are transmitted (scattered and absorbed) through vegetation medium and received by GPS receivers. Simulation results show that the wheat will decrease the amplitudes of GPS multipath observables (SNR, phase and code), if we increase the vegetation moisture contents or the scatters sizes (stem or leaf). Although the Specular-Ground component dominates the total specular scattering, vegetation covered ground soil moisture has almost no effects on the final multipath signatures. Our simulated results are consistent with previous results for environmental parameter detections by GPS-MR. PMID:28587255
Localization of a noisy broadband surface target using time differences of multipath arrivals.
Gebbie, John; Siderius, Martin; McCargar, Reid; Allen, John S; Pusey, Grant
2013-07-01
Previous studies [Tiemann et al., J. Acoust. Soc. Am. 120, 2355-2365 (2006)] have reported the localization of marine mammals in 3-D from their clicks using multipath arrivals. Bathymetric variations were advantageously used to predict multipath arrival times with a raytracer. These arrivals are directly discernible from the time series for impulsive sources, such as whale clicks, but extension of the method to continuous broadband sources presents additional complications. By pulse compressing noise emitted from a small boat using two hydrophones, the hyperbolic direct-arrival ambiguity can be refined in both range and bearing. Acoustic-derived results are validated with target GPS measurements.
SVD Approaches in Multisource, Multipath Passive Array Processing.
NASA Astrophysics Data System (ADS)
Lo, Chien-Kuo
Several system identification techniques have been proposed to treat high resolution directional finding problems in passive sonar, radar, and communication systems. In this dissertation, we present a new covariance approximation approach. The covariance matrices of source signals, in stationary environments often have a special form known as Toeplitz matrix. Our approach is based on what is known as the Toeplitz approximation method (TAM) via Singular Value Decomposition (SVD) in stochastic realization theory, which can deal with the color noise environment and the correlated sources. One of such practical situations is the multipath situation. To reduce the effect of rounding errors incurred in spectrum estimation algorithm, a SVD state space modeling is suggested. It offers the important advantage of low sensitivity to the perturbation of parameter estimation. Using the TAM approach we can first obtain source bearing information, and then cancel undesired signals. For cancellation, we introduce a Least-Square beamformer to form an adaptive spatial filter network. The weighting vector of our spatial filter is derived using a Gram-Schmidt partial orthogonalization procedure which leads to an adaptive scheme, allowing computational savings. This recursive algorithm enjoys another important feature in that it may be implemented in a compact VLSI array processor, such as wavefront/systolic array processors. This implementation aspect is critical for real-time processing applications. Another problem discussed in the dissertation is that of determining desired or undesired path directions from target source under the hypothesis of given correlation coefficients. For that we first formulate the path identification criterion. The decision criterion is based upon the probability density function for estimated path correlation coefficients. The performance of such criterion is also discussed. Extensive simulations have been conducted and the simulation results indicate
Digital data communications over microwave radio channels
NASA Astrophysics Data System (ADS)
Salz, J.
1984-10-01
A major contribution to system outage in a terrestrial digital radio channel is deep fading of the frequency transfer characteristic, which in addition to causing a precipitous drop in received signal-to-noise ratio also causes signal dispersion that can result in severe intersymbol interference. Because the temporal variation of the channel is slow compared to the signaling rate, the information theoretic channel capacity and the efficiency index in bits/cycle can be viewed as random processes. Based on an established mathematical model for fading channels, the probability distribution of channel capacity and the distribution of efficiency indices for different communications techniques are estimated. A crucial obstacle to achieving these rates is the nonlinear distortion introduced by power amplifiers. A method for coping with this nonlinear distortion is also described.
2010-02-01
JCR (τ̂ ) = T 2π ∫ ∞ −∞ ω2 SNR(ω) dω, (8) where SNR(ω) is defined as SNR(ω) = (S(ω)/N1(ω)) (S(ω)/N2(ω)) 1 + (S(ω)/N1(ω)) + (S(ω)/N2(ω)) (9) and the...expression with a linear array is given in (9). 5 and the Fisher information in equation 8 evaluates to JCR (τ̂ ) = 2ω 2 c ( TB 2π )[ 1 + 1 12 ( B ωc )2] SNR
A Tone-Aided/Dual Vestigial Sideband (TA/DVSB) system for mobile satellite channels
NASA Technical Reports Server (NTRS)
Saulnier, Gary J.; Millar, Gilbert M.; Depaolo, Anthony D.
1990-01-01
Tone-aided modulation is one way of combatting the effects of multipath fading and Doppler frequency shifts. A new tone-aided modulation format for M-ary phase-shift keyed signals (MPSK) is discussed. A spectral null for the placement of the tone is created in the center of the MPSK signal by translating the upper sideband upwards in frequency by the same amount. The key element of the system is the algorithm for recombining the data sidebands in the receiver, a function that is performed by a specialized phase-locked loop (PLL). The system structure is discussed and simulation results showing the PLL acquisition performance are presented.
Signal Detection and Jammer Localization in Multipath Channels for Frequency Hopping Communications
2005-10-30
possible. 2. SFH with M-ary PSK or M-ary QAM modulation : During one hop dwell, frequency is constant, but the complex amplitudes are different from symbol...from frequency change. Hence symbol rate and hop rate are distinguishable from the result of DP. 3. SFH with GMSK modulation : A GMSK signal is not a...have essentially the same hop timing and frequency sequence. Similar results have been obtained for GMSK modulated signals [16]. Figure 5 plots the
Multipath study for a low altitude satellite utilizing a data relay satellite system
NASA Technical Reports Server (NTRS)
Eggert, D.
1970-01-01
Technical considerations associated with a low altitude satellite operating in conjuction with a data relay satellite system are reported. Emphasis was placed on the quantitative characterization of multipath phenomenon and determination of power received via both the direct and earth reflection paths. Attempts were made to develop a means for estimating the magnitude and nature of the reflected power.
Broadband Microwave Wireless Power Transfer for Weak-Signal and Multipath Environments
NASA Technical Reports Server (NTRS)
Barton, Richard J.
2014-01-01
In this paper, we study the potential benefits of using relatively broadband wireless power transmission WPT strategies in both weak-signal and multipath environments where traditional narrowband strategies can be very inefficient. The paper is primarily a theoretical and analytical treatment of the problem that attempts to derive results that are widely applicable to many different WPT applications, including space solar power SSP.
Multipath errors in range rate measurement by a TDRS/VHF - GRARR
NASA Technical Reports Server (NTRS)
Sohn, S. J.
1970-01-01
Range rate errors due to multipath reflection are calculated for a tracking and data relay satellite system using the VHF Goddard range and range rate (GRARR) system. At VHF the reflection is primarily specular, and the strength of the multipath relative to the direct path can be modeled in terms of the geometry and the surface characteristics, specifically the root-mean-square (rms) ocean wave height. The uplink and downlink multipath introduces phase jitter on the GRARR carrier and subcarrier. The derivation of these effects is reviewed leading to an expression for the rms range rate error. The derivation assumed the worst-case orbital configurations in which there was very little relative specular Doppler. This means that the specular multipath interference was not attenuated by the carrier and subcarrier PLL transfer functions. Curves of range rate error are presented as a function of grazing angle with wave height 0.3 to 0.7 meters and spacecraft altitude 100 to 700 miles as parameters.
NASA Astrophysics Data System (ADS)
Yang, Hui; Cheng, Lei; Yuan, Jian; Zhang, Jie; Zhao, Yongli; Lee, Young
2015-06-01
With the rapid growth of data center services, the elastic optical network is a very promising networking architecture to interconnect data centers because it can elastically allocate spectrum tailored for various bandwidth requirements. In case of a link failure, to ensure a high-level quality of service (QoS) for user request after the failure becomes a research focus. In light of it, in this paper, we propose and experimentally demonstrate multipath protection for data center services in OpenFlow-based software defined elastic optical network testbed aiming at improving network reliability. We first propose an OpenFlow-based software defined elastic optical network architecture for data center service protection. Then, based on the proposed architecture, multipath protection scheme is figured based on the importance level of the service. To implement the proposed scheme in the architecture, OpenFlow protocol is extended to support multipath protection in elastic optical network. The performance of our proposed multipath protection scheme is evaluated by means of experiment on our OpenFlow-based testbed. The feasibility of our proposed scheme is also demonstrated in software defined elastic optical networks.
Field Test of a Remote Multi-Path CLaDS Methane Sensor
Plant, Genevieve; Nikodem, Michal; Mulhall, Phil; Varner, Ruth K.; Sonnenfroh, David; Wysocki, Gerard
2015-01-01
Existing technologies for quantifying methane emissions are often limited to single point sensors, making large area environmental observations challenging. We demonstrate the operation of a remote, multi-path system using Chirped Laser Dispersion Spectroscopy (CLaDS) for quantification of atmospheric methane concentrations over extended areas, a technology that shows potential for monitoring emissions from wetlands. PMID:26343670
Autonomous detection of text fade point with color laser printers
NASA Astrophysics Data System (ADS)
Ju, Yanling; Maggard, Eric; Jessome, Renee; Allebach, Jan
2015-01-01
Fading is one of the issues of most critical concern for print quality degradation with color laser electro- photographic printers. Fading occurs when the cartridge is depleted. ISO/IEC 19798:2007(E) specifies a process for determining the cartridge page yield for a given color electro-photographic printer model. It is based on repeatedly printing a suite of test pages, followed by visual examination of the sequence of printed diagnostic pages. But this method is a very costly process since it involves visual examination of a large number of pages. And also the final decision is based on the visual examination of a specially designed diagnostic page, which is different than typical office document pages, since it consists of color bars, and contains no text. In this paper, we propose a new method to autonomously detect the text fading in prints from home or office color printers using a typical office document page instead of a specially designed diagnostic page. In our method, we scan and analyze the printed pages to predict where expert observers would judge fading to have occurred in the print sequence. Our approach is based on a machine-learning framework in which features derived from image analysis are mapped to a fade point prediction.
Rain Fade Compensation for Ka-Band Communications Satellites
NASA Technical Reports Server (NTRS)
Mitchell, W. Carl; Nguyen, Lan; Dissanayake, Asoka; Markey, Brian; Le, Anh
1997-01-01
This report provides a review and evaluation of rain fade measurement and compensation techniques for Ka-band satellite systems. This report includes a description of and cost estimates for performing three rain fade measurement and compensation experiments. The first experiment deals with rain fade measurement techniques while the second one covers the rain fade compensation techniques. The third experiment addresses a feedback flow control technique for the ABR service (for ATM-based traffic). The following conclusions were observed in this report; a sufficient system signal margin should be allocated for all carriers in a network, that is a fixed clear-sky margin should be typically in the range of 4-5 dB and should be more like 15 dB in the up link for moderate and heavy rain zones; to obtain a higher system margin it is desirable to combine the uplink power control technique with the technique that implements the source information rate and FEC code rate changes resulting in a 4-5 dB increase in the dynamic part of the system margin. The experiments would assess the feasibility of the fade measurements and compensation techniques, and ABR feedback control technique.
NASA Astrophysics Data System (ADS)
Gao, Tao; Li, Xin; Guo, Bingli; Yin, Shan; Li, Wenzhe; Huang, Shanguo
2017-07-01
Multipath provisioning is a survivable and resource efficient solution against increasing link failures caused by natural or man-made disasters in elastic optical datacenter networks (EODNs). Nevertheless, the conventional multipath provisioning scheme is designed only for connecting a specific node pair. Also, it is obvious that the number of node-disjoint paths between any two nodes is restricted to network connectivity, which has a fixed value for a given topology. Recently, the concept of content connectivity in EODNs has been proposed, which guarantees that a user can be served by any datacenter hosting the required content regardless of where it is located. From this new perspective, we propose a survivable multipath provisioning with content connectivity (MPCC) scheme, which is expected to improve the spectrum efficiency and the whole system survivability. We formulate the MPCC scheme with Integer Linear Program (ILP) in static traffic scenario and a heuristic approach is proposed for dynamic traffic scenario. Furthermore, to adapt MPCC to the variation of network state in dynamic traffic scenario, we propose a dynamic content placement (DCP) strategy in the MPCC scheme for detecting the variation of the distribution of user requests and adjusting the content location dynamically. Simulation results indicate that the MPCC scheme can reduce over 20% spectrum consumption than conventional multipath provisioning scheme in static traffic scenario. And in dynamic traffic scenario, the MPCC scheme can reduce over 20% spectrum consumption and over 50% blocking probability than conventional multipath provisioning scheme. Meanwhile, benefiting from the DCP strategy, the MPCC scheme has a good adaption to the variation of the distribution of user requests.
NASA Astrophysics Data System (ADS)
Atilaw, Tsige Y.; Cilliers, Pierre; Martinez, Peter
2017-06-01
Physical structures found in the vicinity of GNSS receivers can introduce multipath interference effects when a signal arrives at the receiver by different routes. Multipath effects are well recognized as one of the most significant sources of error that degrade the accuracy of GNSS signals for navigation and positioning applications. These effects also reduce the quality of GNSS data used for ionospheric studies. The principal cause of multipath effects is proximity of the antenna to reflecting structures and it is more pronounced when the signal comes from a satellite with low elevation. Typically, conservative fixed-elevation thresholds of 20-40° are used to filter out signals from low elevation angles, but this leads to the exclusion of a significant quantity of useable data. In this paper we present a series of azimuth-dependent elevation thresholds that were developed by characterizing the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Mauritius (20.14°S and 57°E), Marion Island (46.87 ° S and 37.86 ° E) and SANAE IV in Antarctica (71.73 ° S and 2.2 ° W). The threshold masks were developed from azimuth-elevation maps of the S4 index, σϕ index, the Code-Carrier Divergence Standard Deviation (CC-STDDEV) and the L1 Carrier-to-Noise Density (L1 CNo) from 1-min scintillation data taken over a period of 10-12 months at each location to identify signals that are distorted by multipath effects. Using the azimuth-dependent elevation threshold (ADET) mask typically gives 22-28% more useful data than using a fixed-elevation threshold at the sites studied in this paper.
Stochastic Wireless Channel Modeling, Estimation and Identification from Measurements
Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan
2008-07-01
This paper is concerned with stochastic modeling of wireless fading channels, parameter estimation, and system identification from measurement data. Wireless channels are represented by stochastic state-space form, whose parameters and state variables are estimated using the expectation maximization algorithm and Kalman filtering, respectively. The latter are carried out solely from received signal measurements. These algorithms estimate the channel inphase and quadrature components and identify the channel parameters recursively. The proposed algorithm is tested using measurement data, and the results are presented.
An Analysis of Vocal Stereotypy and Therapist Fading
Athens, Elizabeth S; Vollmer, Timothy R; Sloman, Kimberly N; St. Peter Pipkin, Claire
2008-01-01
A functional analysis for a boy with Down syndrome and autism suggested that vocal stereotypy was maintained by automatic reinforcement. The analysis also showed that instructions and noncontingent attention suppressed vocal stereotypy. A treatment package consisting of noncontingent attention, contingent demands, and response cost effectively reduced vocal stereotypy. The treatment package remained effective even when noncontingent attention was removed, making the procedure easier to implement. Also, the presence of the therapist in the room with the participant was faded systematically. After completion of fading, vocal stereotypy remained low during conditions similar to the no-consequence phase of the functional analysis. PMID:18595296
Fast Faraday fading of long range satellite signals.
NASA Technical Reports Server (NTRS)
Heron, M. L.
1972-01-01
20 MHz radio signals have been received during the day from satellite Beacon-B when it was below the optical horizon by using a bank of narrow filters to improve the signal to noise ratio. The Faraday fading rate becomes constant, under these conditions, at a level determined by the plasma frequency just below the F-layer peak. Variations in the Faraday fading rate reveal fluctuations in the electron density near the peak, while the rate of attaining the constant level depends on the shape of the electron density profile.
An analysis of vocal stereotypy and therapist fading.
Athens, Elizabeth S; Vollmer, Timothy R; Sloman, Kimberly N; St Peter Pipkin, Claire
2008-01-01
A functional analysis for a boy with Down syndrome and autism suggested that vocal stereotypy was maintained by automatic reinforcement. The analysis also showed that instructions and noncontingent attention suppressed vocal stereotypy. A treatment package consisting of noncontingent attention, contingent demands, and response cost effectively reduced vocal stereotypy. The treatment package remained effective even when noncontingent attention was removed, making the procedure easier to implement. Also, the presence of the therapist in the room with the participant was faded systematically. After completion of fading, vocal stereotypy remained low during conditions similar to the no-consequence phase of the functional analysis.
Different fixational eye movements mediate the prevention and the reversal of visual fading
McCamy, Michael B; Macknik, Stephen L; Martinez-Conde, Susana
2014-01-01
Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long-standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation. PMID:25128571
Transmission over EHF mobile satellite channels
NASA Technical Reports Server (NTRS)
Zhuang, W.; Chouinard, J.-Y.; Yongacoglu, A.
1993-01-01
Land mobile satellite communications at Ka-band (30/20 GHz) are attracting an increasing interest among researchers because of the frequency band availability and the possibility of small earth station designs. However, communications at the Ka-band pose significant challenges in the system designs due to severe channel impairments. Because only very limited experimental data for mobile applications at Ka-band is available, this paper studies the channel characteristics based on experimental data at L-band (1.6/1.5 GHz) and the use of frequency scaling. The land mobile satellite communication channel at Ka-band is modelled as log-normal Rayleigh fading channel. The first and second-order statistics of the fading channel are studied. The performance of a coherent BPSK system over the fading channel at L-band and K-band is evaluated theoretically and validated by computer simulations. Conclusions on the communication channel characteristics and system performance at L-band and Ka-band are presented.
Meana-Pañeda, Rubén; Fernández-Ramos, Antonio
2014-05-07
This work reports a detailed theoretical study of the hydrogen abstraction reactions from ethanol by atomic hydrogen. The calculated thermal rate constants take into account torsional anharmonicity and conformational flexibility, in addition to the variational and tunneling effects. Specifically, the kinetics calculations were performed by using multi-path canonical variational transition state theory with least-action path tunneling corrections, to which we have added the two-dimensional non-separable method to take into account torsional anharmonicity. The multi-path thermal rate constant is expressed as a sum over conformational reaction channels. Each of these channels includes all the transition states that can be reached by internal rotations. The results show that, in the interval of temperatures between 250 and 2500 K, the account for multiple paths leads to higher thermal rate constants with respect to the single path approach, mainly at low and at high temperatures. In addition, torsional anharmonicity enhances the slope of the Arrhenius plot in this range of temperatures. Finally, we show that the incorporation of tunneling into the hydrogen abstraction reactions substantially changes the contribution of each of the transition states to the conformational reaction channel.
Combining Stimulus Fading, Reinforcement, and Extinction To Treat Food Refusal.
ERIC Educational Resources Information Center
Freeman, Kurt A.; Piazza, Cathleen C.
1998-01-01
The food refusal of a 6-year-old girl with autism and destructive behavior was treated using stimulus fading, reinforcement, and escape extinction. Intake increased, and compliance with prompting procedures remained relatively stable despite the increased consumption requirement. (Author/CR)
The Landmark Decision that Faded into Historical Obscurity
ERIC Educational Resources Information Center
Nance, Molly
2007-01-01
This article takes a look at the Mendez v. Westminster School District, a landmark case that faded into historical obscurity. In the 1940s, Gonzalo and Felicita Mendez wanted their three children to attend the school nearest their farm, which was the 17th Street Elementary School in Westminster. But in the Westminster, Orange County, El Medina,…
Fade Measurements into Buildings from 500 to 3000 MHz
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.
1996-01-01
Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2% of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heatshield, respectively. The median decorrelation distance was from 0.5 to 1.1 m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 dB/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8% of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2% of frequency.
Fade Measurements into Buildings from 500 to 3000 MHz
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.
1996-01-01
Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2 percent of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heat shield, respectively. The median decorrelation distance was from 0.5 to 1.1. m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 db/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8 percent of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2 percent of frequency.
Use of Texture Fading in the Treatment of Food Selectivity.
ERIC Educational Resources Information Center
Shore, Bridget A.; Babbitt, Roberta L.; Williams, Keith E.; Coe, David A.; Snyder, Angela
1998-01-01
A study investigated the efficacy of texture fading in the treatment of food selectivity displayed by four children (ages 2-5). Successful treatment involved the gradual addition of higher textures based on results of periodic probes. Food acceptance and swallowing were reinforced, while food refusal and expulsion were placed on extinction.…
Treating Total Liquid Refusal with Backward Chaining and Fading.
ERIC Educational Resources Information Center
Hagopian, Louis P.; And Others
1996-01-01
In this study of a 12-year-old boy with autism, mental retardation, and a history of severe gastrointestinal problems, who refused liquids and food, backward chaining was used to shape drinking from a cup and a fading procedure was used to increase the water he was required to drink. (Author/CR)
77 FR 22381 - Odorant Fade in Railroad Tank Cars
Federal Register 2010, 2011, 2012, 2013, 2014
2012-04-13
... Federal Railroad Administration Odorant Fade in Railroad Tank Cars AGENCY: Federal Railroad Administration... Safety Advisory 2012-01 to remind shippers and consignees of railroad tank cars containing odorized... United States by railroad tank car is from bulk suppliers to either industrial end-users or to...
A Probe Intermix Procedure for Fading Response Prompts.
ERIC Educational Resources Information Center
Billingsley, Felix F.
1987-01-01
A prompt fading method was employed to teach an eight-year-old student with severe behavior disorders the self-paced use of a functional behavior (requesting rather than grabbing food items). Initial pairing of prompts and natural cues was followed by a mix of prompted and probe (unprompted) trials. (Author/JW)
A Probe Intermix Procedure for Fading Response Prompts.
ERIC Educational Resources Information Center
Billingsley, Felix F.
1987-01-01
A prompt fading method was employed to teach an eight-year-old student with severe behavior disorders the self-paced use of a functional behavior (requesting rather than grabbing food items). Initial pairing of prompts and natural cues was followed by a mix of prompted and probe (unprompted) trials. (Author/JW)
The Landmark Decision that Faded into Historical Obscurity
ERIC Educational Resources Information Center
Nance, Molly
2007-01-01
This article takes a look at the Mendez v. Westminster School District, a landmark case that faded into historical obscurity. In the 1940s, Gonzalo and Felicita Mendez wanted their three children to attend the school nearest their farm, which was the 17th Street Elementary School in Westminster. But in the Westminster, Orange County, El Medina,…
Enuresis Control through Fading, Escape, and Avoidance Training.
ERIC Educational Resources Information Center
Hansen, Gordon D.
1979-01-01
A twin signal device that provides both escape and avoidance conditioning in enuresis control was documented with case studies of two enuretic children (eight and nine years old). In addition, a technique of fading as an adjunct to the process was utilized with one subject. (Author/SBH)
A new fading event is underway in FO Aqr
NASA Astrophysics Data System (ADS)
Littlefield, Colin; Myers, Gordon; Sabo, Richard; Garnavich, Peter; Kennedy, Mark
2017-09-01
The intermediate polar FO Aqr, which in 2016 underwent the first low state in its observational history (Littlefield et al. 2016, ApJ, 833, 93), has faded by nearly 0.7 mag since 2017 August 10, implying a decrease in the system's accretion rate.
NASA Astrophysics Data System (ADS)
Wright, R. B.; Christophersen, J. P.; Motloch, C. G.; Belt, J. R.; Ho, C. D.; Battaglia, V. S.; Barnes, J. A.; Duong, T. Q.; Sutula, R. A.
This paper presents the test results and analysis of the power and capacity fade resulting from the cycle-life testing using PNGV (now referred to as FreedomCAR) test protocols at 25 and 45 °C of 18650-size Li-ion batteries developed by the US Department of Energy sponsored Advanced Technology Development (ATD) Program. Two cell chemistries were studied, a Baseline chemistry that had a cathode composition of LiNi 0.8Co 0.15Al 0.05O 2 with binders, that was cycle-life tested at 25 and 45 °C, and a Variant C chemistry with a cathode composition of LiNi 0.8Co 0.10Al 0.10O 2 with binders, that was tested only at 45 °C. The 300 Wh power, and % power fade were determined as a function of test time, i.e. the number of test cycles for up to 44 weeks (369,600 test cycles) for the Baseline cells, and for 24 weeks (201,600 test cycles) for the Variant C cells. The C/1 and C/25 discharge capacity and capacity fade were also determined during the course of these studies. The results of this study indicate that the 300 Wh power for the Baseline cells tested at 25 °C (up to 44 weeks of testing) decreased as a linear function of test time. The % power fade for these cells increased as a linear function of test time. The Baseline cells tested at 45 °C (up to 44 weeks of testing) displayed a decrease in their power proportional to the square root of the test time, with a faster rate of decrease of the power occurring at ˜28 weeks of testing. The % power fade for these cells also increased as the square root of the test time, and exhibited an increase in the % power fade rate at ˜28 weeks of testing. The 45 °C tested Baseline cells' power decreased, and their % power fade increased at a greater rate than the 25 °C tested Baseline cells. The power fade was greater for the Variant C cells. The power of the Variant C cells (tested at 45 °C) decreased as the square root of the test time, and their % power fade was also found to be a function of the square root of the test time
Intelligibility Performance of the LPC-10 and APC/SQ Speech Algorithms in a Fading Environment.
1985-02-26
Conditions ----------------------------- 26 3 INTELLIGIBILITY TEST RESULTS --------------------- 29 3.1 Overview ------------------------------------ 29 3.2...ideal conditions , this study needed to use a new approach to more characteristically describe the algorithms’ performance in a fading environment. As...evaluating the performance in fading environments. 3. Conducting a series of intelligibility tests in a variety of noise and fading conditions . For LPC-10
Clock Synchronization Through Time-Variant Underwater Acoustic Channels
2012-09-01
stage, we analyze a series of chirp responses to identify the least time -varying multipath present in the channel between the two nodes. Based on the... based on the detected arrivals and determines the most stable one based on the correlation coefficient of a model fit to the time -of-arrival estimates...short periods of time . Nevertheless, signal fluctuations can occur due to transceiver motion or inherent changes within the propagation medium
A study of GPS measurement errors due to noise and multipath interference for CGADS
NASA Technical Reports Server (NTRS)
Axelrad, Penina; MacDoran, Peter F.; Comp, Christopher J.
1996-01-01
This report describes a study performed by the Colorado Center for Astrodynamics Research (CCAR) on GPS measurement errors in the Codeless GPS Attitude Determination System (CGADS) due to noise and multipath interference. Preliminary simulation models fo the CGADS receiver and orbital multipath are described. The standard FFT algorithms for processing the codeless data is described and two alternative algorithms - an auto-regressive/least squares (AR-LS) method, and a combined adaptive notch filter/least squares (ANF-ALS) method, are also presented. Effects of system noise, quantization, baseband frequency selection, and Doppler rates on the accuracy of phase estimates with each of the processing methods are shown. Typical electrical phase errors for the AR-LS method are 0.2 degrees, compared to 0.3 and 0.5 degrees for the FFT and ANF-ALS algorithms, respectively. Doppler rate was found to have the largest effect on the performance.
Multipath error in range rate measurement by PLL-transponder/GRARR/TDRS
NASA Technical Reports Server (NTRS)
Sohn, S. J.
1970-01-01
Range rate errors due to specular and diffuse multipath are calculated for a tracking and data relay satellite (TDRS) using an S band Goddard range and range rate (GRARR) system modified with a phase-locked loop transponder. Carrier signal processing in the coherent turn-around transponder and the GRARR reciever is taken into account. The root-mean-square (rms) range rate error was computed for the GRARR Doppler extractor and N-cycle count range rate measurement. Curves of worst-case range rate error are presented as a function of grazing angle at the reflection point. At very low grazing angles specular scattering predominates over diffuse scattering as expected, whereas for grazing angles greater than approximately 15 deg, the diffuse multipath predominates. The range rate errors at different low orbit altutudes peaked between 5 and 10 deg grazing angles.
Multipath performance of a TDRS system employing wideband FM VHF signals
NASA Technical Reports Server (NTRS)
Sohn, S. J.; Ghais, A. F.
1969-01-01
An approximate theoretical analysis is presented for the effects of specular reflection multipath on the performance of a one-way tracking and data relay satellite-to-user link. The analysis pertains to the wideband FM system employing a sinusoidal subcarrier to achieve spectrum spreading. Bounds on multipath effects are derived for receivers with and without limiters and for data modulated on the carrier or the subcarrier. For data modulation, performance is evaluated in terms of an additive lowpass signal at the data detection filter. Doppler and range tracking performance is evaluated in terms of root-mean-square (RMS) error of carrier frequency in a carrier PLL and rms phase jitter in a subcarrier PLL.
Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves.
Badiey, Mohsen; Katsnelson, Boris G; Lin, Ying-Tsong; Lynch, James F
2011-04-01
Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd's mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.
1979-04-25
future landing guidance system . Thus, to aid in the system selection, optimization, and standardization process, there was need for realistic multipath...sponding system can be plotted. Plots of the means, standard deviations, and peak errors can be obtained if perturbation smoothing was used. The...Landing System , DLS," as proposed by the Federal Republic of Germany developed by Standard Elektrik Lorenz AG. and Siemens, AG. (Sept. 1975). 7
Time-Frequency Analysis of Multipath Doppler Signatures of Maneuvering Targets
2012-03-01
images . 14. ABSTRACT Multipath signals arise in many active sensing modalities, such as radar and sonar. Moving targets cause Doppler effects that...for the estimation of the target’s maneuvering behavior. REFERENCES [1] V. Chen and H. Ling, Time-Frequency Transforms for Radar Imaging and...analysis for SAR and ISAR imaging ,” in R. de Amicis, R. Stojanovic, and G. Conti (eds), GeoSpatial Visual Analytics, Springer, pp. 113-127, 2009. 3400
Signal Processing Equipment and Techniques for Use in Measuring Ocean Acoustic Multipath Structures
1983-12-01
effort and look forward to participating in the Pacific Gyre work. Working with John Spiesberger has also been a rewarding experience. I look...Knox, ill K. Metzger, W. Munk, J. L. Spiesberger , R. Spindel, D. Webb, P. Worcester, and C. Wunch, "A demonstration of ocean acoustic tomography...California, 1982. 4. J. L. Spiesberger , R. Spindel, and K. Metzger, "Stability and Identification of Ocean Acoustic Multipaths," The Journal of
Least-Squares Time-Delay Estimation for Transient Signals in a Multipath Environment
1992-07-01
characterized by a thin sediment In order to obtain unbiased estimates, we need to go layer over a highly reflecting basalt as shown in Fig. 6. The...surface and the basalt . The model Transient data were gathered in the Atlantic Ocean on a ocean impulse response is shown in Fig. 8 with the four paths...Senamato and D. G. Childers , "Signal resolution via digital inverse Multipath Environment." in Proc. Oceans , Washington. DC, pp filtering." [EEE Trans
Multipath propagation study for L-band, over-ocean, satellite-aircraft communication link
NASA Technical Reports Server (NTRS)
Deal, J. H.
1972-01-01
The results are presented of a study of multipath propagation between an aeronautical relay satellite in synchronous earth orbit and an aircraft flying over the ocean. An analytical model for the reflected power is developed and the results of a computer solution are compared with an approximate solution obtained through integration by the method of steepest descent. The computer solution is shown to differ considerably from the approximate solution. Both methods are compared with the limited experimental results available.
Quasicontinuous-Variable Quantum Computation with Collective Spins in Multipath Interferometers
NASA Astrophysics Data System (ADS)
Opatrný, Tomáš
2017-07-01
Collective spins of large atomic samples trapped inside optical resonators can carry quantum information that can be processed in a way similar to quantum computation with continuous variables. It is shown here that by combining the resonators in multipath interferometers one can realize coupling between different samples, and that polynomial Hamiltonians can be constructed by repeated spin rotations and twisting induced by dispersive interaction of the atoms with light. Application can be expected in the efficient simulation of quantum systems.
WEAMR — A Weighted Energy Aware Multipath Reliable Routing Mechanism for Hotline-Based WSNs
Tufail, Ali; Qamar, Arslan; Khan, Adil Mehmood; Baig, Waleed Akram; Kim, Ki-Hyung
2013-01-01
Reliable source to sink communication is the most important factor for an efficient routing protocol especially in domains of military, healthcare and disaster recovery applications. We present weighted energy aware multipath reliable routing (WEAMR), a novel energy aware multipath routing protocol which utilizes hotline-assisted routing to meet such requirements for mission critical applications. The protocol reduces the number of average hops from source to destination and provides unmatched reliability as compared to well known reactive ad hoc protocols i.e., AODV and AOMDV. Our protocol makes efficient use of network paths based on weighted cost calculation and intelligently selects the best possible paths for data transmissions. The path cost calculation considers end to end number of hops, latency and minimum energy node value in the path. In case of path failure path recalculation is done efficiently with minimum latency and control packets overhead. Our evaluation shows that our proposal provides better end-to-end delivery with less routing overhead and higher packet delivery success ratio compared to AODV and AOMDV. The use of multipath also increases overall life time of WSN network using optimum energy available paths between sender and receiver in WDNs. PMID:23669714
Receiver-Based Ad Hoc On Demand Multipath Routing Protocol for Mobile Ad Hoc Networks
Al-Nahari, Abdulaziz; Mohamad, Mohd Murtadha
2016-01-01
Decreasing the route rediscovery time process in reactive routing protocols is challenging in mobile ad hoc networks. Links between nodes are continuously established and broken because of the characteristics of the network. Finding multiple routes to increase the reliability is also important but requires a fast update, especially in high traffic load and high mobility where paths can be broken as well. The sender node keeps re-establishing path discovery to find new paths, which makes for long time delay. In this paper we propose an improved multipath routing protocol, called Receiver-based ad hoc on demand multipath routing protocol (RB-AOMDV), which takes advantage of the reliability of the state of the art ad hoc on demand multipath distance vector (AOMDV) protocol with less re-established discovery time. The receiver node assumes the role of discovering paths when finding data packets that have not been received after a period of time. Simulation results show the delay and delivery ratio performances are improved compared with AOMDV. PMID:27258013
Fair resource allocation and stability for communication networks with multipath routing
NASA Astrophysics Data System (ADS)
Li, Shiyong; Sun, Wei; Hua, Changchun
2014-11-01
Multipath networks allow that each source-destination pair can have several different paths for data transmission, thus they improve the performance of increasingly bandwidth-hungry applications and well cater for traffic load balancing and bandwidth usage efficiency. This paper investigates fair resource allocation for users in multipath networks and formulates it as a multipath network utility maximisation problem with several fairness concepts. By applying the Lagrangian method, sub-problems for users and paths are derived from the resource allocation model and interpreted from an economic point of view. In order to solve the model, a novel rate-based flow control algorithm is proposed for achieving optimal resource allocation, which depends only on local information. In the presence of round-trip delays, sufficient conditions are obtained for local stability of the delayed algorithm. As for the end-to-end implementation in Internet, a window-based flow control mechanism is presented since it is more convenient to implement than rate-based flow control.
Zhang, Hongjun; Zhang, Rui; Li, Yong; Zhang, Xuliang
2014-01-01
Service oriented modeling and simulation are hot issues in the field of modeling and simulation, and there is need to call service resources when simulation task workflow is running. How to optimize the service resource allocation to ensure that the task is complete effectively is an important issue in this area. In military modeling and simulation field, it is important to improve the probability of success and timeliness in simulation task workflow. Therefore, this paper proposes an optimization algorithm for multipath service resource parallel allocation, in which multipath service resource parallel allocation model is built and multiple chains coding scheme quantum optimization algorithm is used for optimization and solution. The multiple chains coding scheme quantum optimization algorithm is to extend parallel search space to improve search efficiency. Through the simulation experiment, this paper investigates the effect for the probability of success in simulation task workflow from different optimization algorithm, service allocation strategy, and path number, and the simulation result shows that the optimization algorithm for multipath service resource parallel allocation is an effective method to improve the probability of success and timeliness in simulation task workflow. PMID:24963506
Wang, Zhiteng; Zhang, Hongjun; Zhang, Rui; Li, Yong; Zhang, Xuliang
2014-01-01
Service oriented modeling and simulation are hot issues in the field of modeling and simulation, and there is need to call service resources when simulation task workflow is running. How to optimize the service resource allocation to ensure that the task is complete effectively is an important issue in this area. In military modeling and simulation field, it is important to improve the probability of success and timeliness in simulation task workflow. Therefore, this paper proposes an optimization algorithm for multipath service resource parallel allocation, in which multipath service resource parallel allocation model is built and multiple chains coding scheme quantum optimization algorithm is used for optimization and solution. The multiple chains coding scheme quantum optimization algorithm is to extend parallel search space to improve search efficiency. Through the simulation experiment, this paper investigates the effect for the probability of success in simulation task workflow from different optimization algorithm, service allocation strategy, and path number, and the simulation result shows that the optimization algorithm for multipath service resource parallel allocation is an effective method to improve the probability of success and timeliness in simulation task workflow.
A novel multi-path combination matching Michelson interferometer for straindeformation sensing
NASA Astrophysics Data System (ADS)
Jiang, Haili; Yuan, Yonggui; Yang, Jun; Yuan, Libo
2010-11-01
Based on low-coherence white light interferometric technology, a novel multi-path combination matching Michelson interferometer system has been proposed and demonstrated. The multi-path combination Michelson interferometer is configured by a series 2x2 fiber optic coupler connected each other. One end of the coupler array is connected with SLD light source in one port, the other port is linked with a photodiode detector. The other end of the 3dB fiber coupler array is with a coated reflective mirror in one port, the other port is terminated with a fiber collimator, and a reflective scanning mirror mounted on a translation stage and perpendicular to the fiber collimator. The scanning mirror is moving back and forth to match each optical path of the combination Michelson interferometer. In this multi-path combination Michelson interferometer, each fiber arm could be used as strain or deformation sensor. By using optical path tracking and recording technique, the quasi-distributed strain of each fiber arm can be calculated. The sensing system can be used to measure distribution strain or temperature. It has the potential in the applications of large scale smart structures health monitoring.
NASA Astrophysics Data System (ADS)
Fang, Kun; Rugini, Luca; Leus, Geert
2010-12-01
Modern wireless communication systems require high transmission rates, giving rise to frequency selectivity due to multipath propagation. In addition, high-mobility terminals and scatterers induce Doppler shifts that introduce time selectivity. Therefore, advanced techniques are needed to accurately model the time- and frequency-selective (i.e., doubly selective) channels and to counteract the related performance degradation. In this paper, we develop new receivers for orthogonal frequency-division multiplexing (OFDM) systems and single-carrier (SC) systems in doubly selective channels by embedding the channel estimation task within low-complexity block turbo equalizers. Linear minimum mean-squared error (MMSE) pilot-assisted channel estimators are presented, and the soft data estimates from the turbo equalizers are used to improve the quality of the channel estimates.
NASA Astrophysics Data System (ADS)
Yin, Zhendong; Zong, Zhiyuan; Sun, Hongjian; Wu, Zhilu; Yang, Zhutian
2012-12-01
In this article, an efficient multiuser detector based on the artificial fish swarm algorithm (AFSA-MUD) is proposed and investigated for direct-sequence ultrawideband systems under different channels: the additive white Gaussian noise channel and the IEEE 802.15.3a multipath channel. From the literature review, the issues that the computational complexity of classical optimum multiuser detection (OMD) rises exponentially with the number of users and the bit error rate (BER) performance of other sub-optimal multiuser detectors is not satisfactory, still need to be solved. This proposed method can make a good tradeoff between complexity and performance through the various behaviors of artificial fishes in the simplified Euclidean solution space, which is constructed by the solutions of some sub-optimal multiuser detectors. Here, these sub-optimal detectors are minimum mean square error detector, decorrelating detector, and successive interference cancellation detector. As a result of this novel scheme, the convergence speed of AFSA-MUD is greatly accelerated and the number of iterations is also significantly reduced. The experimental results demonstrate that the BER performance and the near-far effect resistance of this proposed algorithm are quite close to those of OMD, while its computational complexity is much lower than the traditional OMD. Moreover, as the number of active users increases, the BER performance of AFSA-MUD is almost the same as that of OMD.
NASA Astrophysics Data System (ADS)
Du, Jie; Deng, Honggui; Qian, Xuewen; Zhang, Chaoyang
2016-11-01
In order to mitigate bandwidth attenuation of diffusion link visible light communication systems caused by multipath effects, we present an optical orthogonal frequency division multiplexing channel estimation scheme based on compressed sensing (CS) and estimation of signal parameters via rotational invariance techniques (ESPRIT). First, we derived a parametric channel model. Then, we used ESPRIT to obtain multipath channel parameters. After that, we built a dynamic over-complete dictionary that can be used in CS processing. Finally, we reconstructed the channel response by using a basis pursuit denoising algorithm to equalize the received signal in frequency domain. Compared with traditional schemes, the proposed scheme can improve channel estimation accuracy without increasing dictionary size. A set of computer simulations demonstrated the effectiveness of the proposed scheme.
Spoon distance fading with and without escape extinction as treatment for food refusal.
Rivas, Kristi D; Piazza, Cathleen C; Patel, Meeta R; Bachmeyer, Melanie H
2010-01-01
Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and without escape extinction (EE), and compared fading plus EE to EE alone. Initially, inappropriate mealtime behavior decreased during fading, but this effect was not maintained as fading progressed. Inappropriate mealtime behavior was lower initially when we combined fading and EE relative to EE alone, but acceptance increased more rapidly with EE than with fading plus EE. These results suggest that a number of mealtime characteristics might function as MOs for escape behavior and that analyses of MOs may be useful for developing treatments for food refusal.
1989-04-28
coherent BPSK and for coherent offset quaternary PSK ( OQPSK ). The different curves in these figures show the effect of different channel decorrelation...77=-- --- - - 7 ~ To/Tcb - TO/Tcb =10 05101202303 1012 7 _ 7---7 7-77 COHERENT OQPSK -BLTcb)= V30 RAYLEIGH FADING f-4 FADING SpECTRUM - roTcb =30
Use of texture fading in the treatment of food selectivity.
Shore, B A; Babbitt, R L; Williams, K E; Coe, D A; Snyder, A
1998-01-01
Children with feeding disorders often display severe food selectivity. For many of these children, consuming highly textured foods may be aversive or potentially dangerous because of frequent gagging. The purpose of this study was to demonstrate the efficacy of texture fading in the treatment of food selectivity displayed by 4 children. Treatment involved the gradual addition of higher textures based on the results of periodic probes. In addition, food acceptance and swallowing were reinforced, while food refusal and food expulsion were placed on extinction. Results showed that all participants successfully advanced to consumption of age-appropriate texture and volume. The results suggest that texture fading with intermittent probes at higher textures may be an effective method for the treatment of food selectivity by texture.
Motor learning with fading and growing haptic guidance.
Heuer, Herbert; Lüttgen, Jenna
2014-07-01
Haptic guidance has been shown to have both facilitatory and interfering effects on motor learning. Interfering effects have been hypothesized to result from the particular dynamic environment, which supports a passive role of the learner, and they should be attenuated by fading guidance. Facilitatory effects, in particular for dynamic movement characteristics, have been hypothesized to result from the high-quality information provided by haptic demonstration. If haptic demonstration provides particularly precise information about target movements, the motor system's need for such information should more likely increase in the course of motor learning, in which case growing guidance should be more beneficial for learning. We contrasted fading and growing guidance in the course of learning a spatio-temporal motor pattern. To stimulate an active role of the learner, practice trials consisted of three phases, a visual demonstration of the target movement, a guided reproduction, and a reproduction without haptic guidance. Performance was assessed in terms of variable duration errors, relative-timing errors, variable path-length errors, and shape errors. Motor learning with growing and fading guidance turned out to be largely equivalent, so that the notion of an increasing optimal precision of haptic demonstrations, which matches a demand of increasingly precise information on the target movement, found no support. Duration errors declined only with fading, but not with growing guidance. Relative timing revealed a benefit of immediately preceding haptic demonstration, but learning was not different between the two practice protocols. This contrast between absolute and relative timing adds to other evidence according to which acquisition of these two aspects of motor timing involves different learning mechanisms. Whereas relative timing gained from immediately preceding haptic demonstration, but revealed no practice-related improvement in the presence of haptic guidance
Optical communication system performance with tracking error induced signal fading.
NASA Technical Reports Server (NTRS)
Tycz, M.; Fitzmaurice, M. W.; Premo, D. A.
1973-01-01
System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming (1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and (2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2- to 3-dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.
On the nature of rapidly fading Type II supernovae
NASA Astrophysics Data System (ADS)
Moriya, Takashi J.; Pruzhinskaya, Maria V.; Ergon, Mattias; Blinnikov, Sergei I.
2016-01-01
It has been suggested that Type II supernovae with rapidly fading light curves (a.k.a. Type IIL supernovae) are explosions of progenitors with low-mass hydrogen-rich envelopes which are of the order of 1 M⊙. We investigate light-curve properties of supernovae from such progenitors. We confirm that such progenitors lead to rapidly fading Type II supernovae. We find that the luminosity of supernovae from such progenitors with the canonical explosion energy of 1051 erg and 56Ni mass of 0.05 M⊙ can increase temporarily shortly before all the hydrogen in the envelope recombines. As a result, a bump appears in their light curves. The bump appears because the heating from the nuclear decay of 56Ni can keep the bottom of hydrogen-rich layers in the ejecta ionized, and thus the photosphere can stay there for a while. We find that the light-curve bump becomes less significant when we make explosion energy larger (≳2 × 1051 erg), 56Ni mass smaller (≲0.01 M⊙), 56Ni mixed in the ejecta, or the progenitor radius larger. Helium mixing in hydrogen-rich layers makes the light-curve decline rates large but does not help reducing the light-curve bump. Because the light-curve bump we found in our light-curve models has not been observed in rapidly fading Type II supernovae, they may be characterized by not only low-mass hydrogen-rich envelopes but also higher explosion energy, larger degrees of 56Ni mixing, and/or larger progenitor radii than slowly fading Type II supernovae, so that the light-curve bump does not become significant.
Optical communication system performance with tracking error induced signal fading.
NASA Technical Reports Server (NTRS)
Tycz, M.; Fitzmaurice, M. W.; Premo, D. A.
1973-01-01
System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming (1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and (2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2- to 3-dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.
Land-mobile-satellite fade measurements in Australia
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Goldhirsh, Julius; Hase, Yoshihiro
1992-01-01
Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.
Rain Fade Compensation Alternatives for Ka Band Communication Satellites
NASA Technical Reports Server (NTRS)
Acosta, Roberto J.
1997-01-01
Future satellite communications systems operating in Ka-band frequency band are subject to degradation produced by the troposphere which is much more severe than those found at lower frequency bands. These impairments include signal absorption by rain, clouds and gases, and amplitude scintillation's arising from refractive index irregularities. For example, rain attenuation at 20 GHz is almost three times that at 11 GHz. Although some of these impairments can be overcome by oversizing the ground station antennas and high power amplifiers, the current trend is using small (less than 20 inches apertures), low-cost ground stations (less than $1000) that can be easily deployed at user premises. As a consequence, most Ka-band systems are expected to employ different forms of fade mitigation that can be implemented relatively easily and at modest cost. The rain fade mitigation approaches are defined by three types of Ka-band communications systems - a low service rate (less than 1.5 Mb/s), a moderate service rate (1.5 to 6 Mb/s) system and a high service rate (greater than 43 Mb/s) system. The ACTS VSAT network, which includes an adaptive rain fade technique, is an example of a moderate service rate.
DISK-RELATED BURSTS AND FADES IN YOUNG STARS
Findeisen, Krzysztof; Hillenbrand, Lynne; Levitan, David; Sesar, Branimir; Ofek, Eran; Laher, Russ; Surace, Jason E-mail: lah@astro.caltech.edu
2013-05-01
We present first results from a new, multiyear, time domain survey of young stars in the North America Nebula complex using the Palomar Transient Factory. Our survey is providing an unprecedented view of aperiodic variability in young stars on timescales of days to years. The analyzed sample covers R{sub PTF} Almost-Equal-To 13.5-18 and spans a range of mid-infrared color, with larger-amplitude optical variables (exceeding 0.4 mag root mean squared) more likely to have mid-infrared evidence for circumstellar material. This paper characterizes infrared excess stars with distinct bursts above or fades below a baseline of lower-level variability, identifying 41 examples. The light curves exhibit a remarkable diversity of amplitudes, timescales, and morphologies, with a continuum of behaviors that cannot be classified into distinct groups. Among the bursters, we identify three particularly promising sources that may represent theoretically predicted short-timescale accretion instabilities. Finally, we find that fading behavior is approximately twice as common as bursting behavior on timescales of days to years, although the bursting and fading duty cycle for individual objects often varies from year to year.
Land-mobile-satellite fade measurements in Australia
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Goldhirsh, Julius; Hase, Yoshihiro
1992-01-01
Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.
Into building fading at L- and S-band for satellite PCS
NASA Technical Reports Server (NTRS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.; Lin, Hsin Piao'
1995-01-01
Selected results from L- and S-Band slant-path fade measurements into six different buildings employing a tower-mounted transmitter and dual-frequency receiver are presented. The objective of the measurements was to provide information for personal communications satellite design on the correlation of fading inside buildings between frequencies near 1620 and 2500 MHz. Fades were measured along horizontal directions with 5 cm spacing. Fade differences between L- and S-Band exhibited a normal distribution with means usually near 0 dB and standard deviations from 7.2 to 8.2 dB. After spatial averaging over a few wavelengths, the correlation between L- and S-Band was significantly improved. Simultaneous swept measurements over 160 MHz spans showed that the standard deviation of the power levels as function of frequency increased linearly with average fade depth from a minimum of about 1.3 dB and increased by .2 dB per 1 dB of fade. Fade slopes were also a function of fade level, with LMSS-Band averages in the range of 1 to 2 dB/MHz for 10 dB fades and increasing to about 3 to 4 dB/MHz at a 30 dB fade.
Into building fading at L- and S-band for satellite PCS
NASA Astrophysics Data System (ADS)
Vogel, Wolfhard J.; Torrence, Geoffrey W.; Lin, Hsin Piao'
1995-08-01
Selected results from L- and S-Band slant-path fade measurements into six different buildings employing a tower-mounted transmitter and dual-frequency receiver are presented. The objective of the measurements was to provide information for personal communications satellite design on the correlation of fading inside buildings between frequencies near 1620 and 2500 MHz. Fades were measured along horizontal directions with 5 cm spacing. Fade differences between L- and S-Band exhibited a normal distribution with means usually near 0 dB and standard deviations from 7.2 to 8.2 dB. After spatial averaging over a few wavelengths, the correlation between L- and S-Band was significantly improved. Simultaneous swept measurements over 160 MHz spans showed that the standard deviation of the power levels as function of frequency increased linearly with average fade depth from a minimum of about 1.3 dB and increased by .2 dB per 1 dB of fade. Fade slopes were also a function of fade level, with LMSS-Band averages in the range of 1 to 2 dB/MHz for 10 dB fades and increasing to about 3 to 4 dB/MHz at a 30 dB fade.
Different fixational eye movements mediate the prevention and the reversal of visual fading.
McCamy, Michael B; Macknik, Stephen L; Martinez-Conde, Susana
2014-10-01
Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long-standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation. © 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.
NASA Astrophysics Data System (ADS)
Zhang, Zongsheng; Pi, Xurong
2014-09-01
In this paper, we investigate the outage performance of decode-and-forward cognitive relay networks for Nakagami-m fading channels, with considering both best relay selection and interference constraints. Focusing on the relay selection and making use of the underlay cognitive approach, an exact closed-form outage probability expression is derived in an independent, non-identical distributed Nakagami-m environment. The closed-form outage probability provides an efficient means to evaluate the effects of the maximum allowable interference power, number of cognitive relays, and channel conditions between the primary user and cognitive users. Finally, we present numerical results to validate the theory analysis. Moreover, from the simulation results, we obtain that the system can obtain the full diversity.
Time reversal communication over doubly spread channels.
Zeng, Wen-Jun; Jiang, Xue
2012-11-01
Conventional time reversal can mitigate multipath delay dispersion by temporal focusing. But it is not applicable to time-varying channels with a Doppler spread. Although recently time reversal communication has been adapted to time-variant channels, the modified technique requires frequent channel updates to track channel variations and cannot handle large Doppler spread, which means that it cannot achieve frequency focusing. In this paper, two time reversal receivers for underwater acoustic communications over doubly spread channels are proposed. The proposed approach, which can be interpreted as time-frequency channel matching, is based on the channel spreading function rather than impulse response adopted by the existing techniques; this leads to much less frequent channel updates. Unlike existing methods that only correct a single Doppler shift, the proposed approach uses a rake-like structure to compensate for multiple Doppler shifts and hence can eliminate severe Doppler spread induced by temporal channel variations. Simulation results verify the effectiveness of the proposed approach, indicating that it can simultaneously counteract delay and Doppler spreads, achieving both temporal and frequency focusing.
Mid-Latitude Mobile Wideband HF- NVIS Channel Analysis: Part 1
2017-09-14
response and thereby limits the rate of digital transmission In 1989, Wagner -Goldstein-Meyers-Bello measured HF channels using 1-MHz bandwidths in the...Multipath Channels,” Radio Science 32(5):2083–2090. 81. Wagner , L. S., J. A. Goldstein, W. D. Meyers, and P. A. Bello. 1989. “The HF Skywave Channel...Military Communications Conference 198 (pp. 48.2.1–48.2.10). October 15–18, Boston, MA. 82. Wagner , L. S. and J. A. Goldstein. 1995. “Channel Spread
Node localization via analyzing multi-path signals in ultrasonic sensor networks
NASA Astrophysics Data System (ADS)
Tomlinson, W. J.; Dong, B.; Lorenz, S.; Biswas, S.
2014-05-01
This paper proposes a novel signal analysis based node localization strategy for sensor networks used in structural health monitoring (SHM) applications. The key idea is to analyze location-dependent multipath signal patterns in inter-node ultrasonic signals, and use machine-learning mechanisms to detect such patterns for accurate node localization on metal substrates on target structures. Majority of the traditional mechanisms rely on radio based Time Delay of Arrival (TDOA), coupled with multilateration, and multiple reference nodes. The proposed mechanism attempts to solve the localization problem in an ultrasonic sensor network (USN), avoiding the use of multiple reference beacon nodes. Instead, it relies on signal analysis and multipath signature classification from a single reference node that periodically transmits ultrasonic localization beacons. The approach relies on a key observation that the ultrasonic signal received at any point on the structure from the reference node, is a superposition of the signals received on the direct path and through all possible multi-paths. It is hypothesized that if the location of the reference node and the substrate properties are known a-priori, it should be possible to train a receiver (source node), to identify its own location by observing the exact signature of the received signal. To validate this hypothesis, steps were taken to develop a TI MSP-430 based module for implementing a run-time system from a proposed architecture. Through extensive experimentation within an USN on the 2024 Aluminum substrate, it was demonstrated that localization accuracies up to 92% were achieved in the presence of varying spatial resolutions.
NASA Astrophysics Data System (ADS)
Ashman, Benjamin W.
Automated rendezvous and docking (AR&D;) operations are important for many future space missions, such as the resupply of space stations, repair and refueling of large satellites, and active removal of orbital debris. These operations depend critically on accurate, real-time knowledge of the relative position and velocity between two space vehicles. Unfortunately, Global Navigation Satellite System (GNSS) capabilities remain severely limited in close proximity to large space structures due to significant multipath effects and signal blockage. Although GNSS is used for the initial stages of approach, other instruments such as laser, radar and vision-based systems, are required to augment GNSS during AR&D; over the last few hundred meters. This dissertation evaluates the feasibility of GNSS multipath-based relative space navigation. Methods for separating and interpreting reflected signals are demonstrated using GNSS data collected during Hubble Servicing Mission 4 (HSM4), a model of the mission geometry, electromagnetic (EM) ray tracing, and a custom GNSS software receiver. EM ray tracing is used to show that a number of signals sufficient for ranging are reflected by the Hubble Space Telescope (HST) during HSM4, and the properties of these reflections are used to generate simulated GNSS data. The impact of reflected signals on code correlation shape, code tracking error, and pseudorange measurement is demonstrated using the simulated and experimental data. Relative navigation is demonstrated using simulated reflected signal measurements and the dependence of relative navigation on the reflecting object's scattering properties is illustrated. From the tracking of data from two oppositely polarized antennas, both simulated and experimental, it is determined that multipath measurements are limited by system properties such as antenna polarization quality and front end bandwidth. Design considerations involved in optimizing a receiver to measure reflected signals are
NASA Astrophysics Data System (ADS)
Liu, Xu; Guang, Liang; Yang, Longxiang; Zhu, Hongbo
2012-12-01
A novel joint angle and delay estimation (JADE) algorithm for multipath signals, based on the PARAllel profiles with LINear Dependencies (PARALIND) model, is proposed. Capitalizing on the structure property of Vandermonde matrices, PARALIND model is proved to be unique. Angle and delay of multiple rays of sources can be estimated by PARALIND decomposition and an ESPRIT-like shift-invariance technique. Simulation results show that the proposed algorithm outperforms the traditional JADE algorithm. It can automatically distinguish the estimated parameters between sources, and still be available when the number of rays is larger than the number of receiving antennae.
Multi-path light extinction approach for high efficiency filtered oil particle measurement
NASA Astrophysics Data System (ADS)
Pengfei, Yin; Jun, Chen; Huinan, Yang; Lili, Liu; Xiaoshu, Cai
2014-04-01
This work present a multi-pathlight extinction approach to determine the oil mist filter efficiency based on measuring the concentration and size distribution of oil particles. Light extinction spectrum(LES) technique was used to retrieve the oil particle size distribution and concentration. The multi-path measuring cell was designed to measure low concentration and fine particles after filtering. The path-length of the measuring cell calibrated as 200 cm. The results of oil particle size with oil mist filtering were obtained as D32 = 0.9μm. Cv=1.6×10-8.
L-Band DME Multipath Environment in the Microwave Landing System (MLS) Approach and Landing Region.
1982-04-13
present hope is that an L-band DME which is fully compatible with current VOR/DME navigation and/or RNAV requirements can provide range guidance which is...adequate for all the MLS needs (e.g., RNAV to MLS transition, complex terminal maneuvers for curved approach, flare initiation and the flare maneu...NTERROGATOR ANTENA 4r 1 X1ro 2 ANTENNA I - T V1- - - - - - - - - h RUNWAYI’ M~ Fig 3-. Cnfi~raionused to determine multipath parameters due to scatterinlg
Rain-fade simulation and power augmentation for satellite communication systems
NASA Technical Reports Server (NTRS)
Shalkhauser, Kurt A.; Nagy, Lawrence A.; Svoboda, James S.
1990-01-01
The design and implementation of an automated rain-fade simulation and power augmentation system is presented. The system experimentally simulates and measures the effects of radiofrequency power fade on a 20 GHz communication link using a multimode travelling wave tube amplifier for loss compensation. Precision, computer-controlled attenuators are used in the fade simulation. Test plans for analog and digital testing are discussed.
NASA Astrophysics Data System (ADS)
Mathis, R. F.; Pawula, R. F.
1980-10-01
The performance of a spread spectrum system which incorporates frequency hopping, sequentially balanced modulation, phase-comparison tone ranging, and pseudoorthogonal block coding of BPSK data with maximum likelihood of soft decision decoding, is evaluated in jamming environments and multipath. The jamming models considered include partial-band noise jamming, comb-type partial-band noise jamming, multitone jamming, and comb-type multitone jamming. Specular multipath with broad-band noise are shown to be the most serious form of interference. Bit-error probability and ranging accuracy curves are presented.
A recursive solution for a fading memory filter derived from Kalman filter theory
NASA Technical Reports Server (NTRS)
Statman, J. I.
1986-01-01
A simple recursive solution for a class of fading memory tracking filters is presented. A fading memory filter provides estimates of filter states based on past measurements, similar to a traditional Kalman filter. Unlike a Kalman filter, an exponentially decaying weight is applied to older measurements, discounting their effect on present state estimates. It is shown that Kalman filters and fading memory filters are closely related solutions to a general least squares estimator problem. Closed form filter transfer functions are derived for a time invariant, steady state, fading memory filter. These can be applied in loop filter implementation of the Deep Space Network (DSN) Advanced Receiver carrier phase locked loop (PLL).
Dye fading test for mission control operator console displays
NASA Technical Reports Server (NTRS)
Lockwood, H. E.
1975-01-01
A dye fading test of 40 days duration was conducted to determine the effect of mission control operator console and ambient lighting effects on a series of photographic products under consideration for use in mission console operator consoles. Six different display samples, each containing 36 windows of several different colors, were prepared and placed in the mission control consoles for testing. No significant changes were recorded during the testing period. All changes were attributed to a mechanical problem with the densitometer. Detailed results are given in graphs.
Modeling capacity fade in lithium-ion cells.
Liaw, Bor Yann; Doughty, Daniel Harvey; Nagasubramanian, Ganesan; Jungst, Rudolph George
2003-09-01
Battery life is an important, yet technically challenging, issue for battery development and application. Adequately estimating battery life requires a significant amount of testing and modeling effort to validate the results. Integrated battery testing and modeling is quite feasible today to simulate battery performance, and therefore applicable to predict its life. A relatively simple equivalent-circuit model (ECM) is used in this work to show that such an integrated approach can actually lead to a high-fidelity simulation of a lithium-ion cell's performance and life. The methodology to model the cell's capacity fade during thermal aging is described to illustrate its applicability to battery calendar life prediction.
Fade duration statistics for Ku-band satellite links
NASA Astrophysics Data System (ADS)
Mandeep, J. S.
2013-08-01
Fade duration database was built to enhance the study of propagation characterises in the Equatorial region. The data was measured via a beacon receiver Ku-band whereby the antenna was directed to a SUPERBIRD-C2 satellite at 12.255 GHz. The performance of the measured data has been compared with ITU-R model, Kormanyos et al. and Paulson-Gibbins. The results show that the Paulson-Gibbins fits well with measured data with a low RMS error of 0.2 dB. The number of statistics available for the equatorial is small and the periods of measurement are short compared to those for temperate regions.
Channel simulation for direct-detection optical communication systems
NASA Technical Reports Server (NTRS)
Tycz, M.; Fitzmaurice, M. W.
1974-01-01
A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct-detection optical communication system. The system is capable of providing signal fading statistics which obey log-normal, beta, Rayleigh, Ricean, or chi-square density functions. Experimental tests of the performance of the channel simulator are presented.
Channel simulation for direct detection optical communication systems
NASA Technical Reports Server (NTRS)
Tycz, M.; Fitzmaurice, M. W.
1974-01-01
A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct detection optical communication system. The system is capable of providing signal fading statistics which obey log normal, beta, Rayleigh, Ricean or chi-squared density functions. Experimental tests of the performance of the Channel Simulator are presented.
Reliability of a jammed binary transmission over a Nakagami channel
NASA Astrophysics Data System (ADS)
Zenon, Syroka
2014-05-01
This study presents a mathematic and numerical analysis of the probability of error in a binary transmission over a fading radio channel described by Nakagami-m distribution and its special cases. The transmission is jammed by a signal occupying the entire (or comparable) band before detection.
Zhang, Tao; Shi, Hongfei; Chen, Liping; Li, Yao; Tong, Jinwu
2016-03-11
This paper researches an AUV (Autonomous Underwater Vehicle) positioning method based on SINS (Strapdown Inertial Navigation System)/LBL (Long Base Line) tightly coupled algorithm. This algorithm mainly includes SINS-assisted searching method of optimum slant-range of underwater acoustic propagation multipath, SINS/LBL tightly coupled model and multi-sensor information fusion algorithm. Fuzzy correlation peak problem of underwater LBL acoustic propagation multipath could be solved based on SINS positional information, thus improving LBL positional accuracy. Moreover, introduction of SINS-centered LBL locating information could compensate accumulative AUV position error effectively and regularly. Compared to loosely coupled algorithm, this tightly coupled algorithm can still provide accurate location information when there are fewer than four available hydrophones (or within the signal receiving range). Therefore, effective positional calibration area of tightly coupled system based on LBL array is wider and has higher reliability and fault tolerance than loosely coupled. It is more applicable to AUV positioning based on SINS/LBL.
Energy-Aware Multipath Routing Scheme Based on Particle Swarm Optimization in Mobile Ad Hoc Networks
Robinson, Y. Harold; Rajaram, M.
2015-01-01
Mobile ad hoc network (MANET) is a collection of autonomous mobile nodes forming an ad hoc network without fixed infrastructure. Dynamic topology property of MANET may degrade the performance of the network. However, multipath selection is a great challenging task to improve the network lifetime. We proposed an energy-aware multipath routing scheme based on particle swarm optimization (EMPSO) that uses continuous time recurrent neural network (CTRNN) to solve optimization problems. CTRNN finds the optimal loop-free paths to solve link disjoint paths in a MANET. The CTRNN is used as an optimum path selection technique that produces a set of optimal paths between source and destination. In CTRNN, particle swarm optimization (PSO) method is primly used for training the RNN. The proposed scheme uses the reliability measures such as transmission cost, energy factor, and the optimal traffic ratio between source and destination to increase routing performance. In this scheme, optimal loop-free paths can be found using PSO to seek better link quality nodes in route discovery phase. PSO optimizes a problem by iteratively trying to get a better solution with regard to a measure of quality. The proposed scheme discovers multiple loop-free paths by using PSO technique. PMID:26819966
Advanced Launch System Multi-Path Redundant Avionics Architecture Analysis and Characterization
NASA Technical Reports Server (NTRS)
Baker, Robert L.
1993-01-01
The objective of the Multi-Path Redundant Avionics Suite (MPRAS) program is the development of a set of avionic architectural modules which will be applicable to the family of launch vehicles required to support the Advanced Launch System (ALS). To enable ALS cost/performance requirements to be met, the MPRAS must support autonomy, maintenance, and testability capabilities which exceed those present in conventional launch vehicles. The multi-path redundant or fault tolerance characteristics of the MPRAS are necessary to offset a reduction in avionics reliability due to the increased complexity needed to support these new cost reduction and performance capabilities and to meet avionics reliability requirements which will provide cost-effective reductions in overall ALS recurring costs. A complex, real-time distributed computing system is needed to meet the ALS avionics system requirements. General Dynamics, Boeing Aerospace, and C.S. Draper Laboratory have proposed system architectures as candidates for the ALS MPRAS. The purpose of this document is to report the results of independent performance and reliability characterization and assessment analyses of each proposed candidate architecture and qualitative assessments of testability, maintainability, and fault tolerance mechanisms. These independent analyses were conducted as part of the MPRAS Part 2 program and were carried under NASA Langley Research Contract NAS1-17964, Task Assignment 28.
Lize, Yannick K; Christen, Louis; Nazarathy, Moshe; Nuccio, Scott; Wu, Xiaoxia; Willner, Alan E; Kashyap, Raman
2007-05-28
We present an optical multipath error correction technique for differentially encoded modulation formats such as differential-phase-shift-keying (DPSK) and differential polarization shift keying (DPolSK) for fiber-based and free-space communication. This multipath error correction method combines optical and electronic logic gates. The scheme can easily be implemented using commercially available interferometers and high speed logic gates and does not require any data overhead therefore does not affect the effective bandwidth of the transmitted data. It is not merely compatible but also complementary to error correction codes commonly used in optical transmission systems such as forward-error-correction (FEC). The technique consists of separating the demodulation at the receiver in multiple paths. Each path consists of a Mach-Zehnder interferometer with a different integer bit delay used in each path. Some basic logic operations follow and the three paths are compared using a simple majority vote algorithm. Experimental results show that the scheme improves receiver sensitivity by 1.5 dB at BER of 10(-3),in back-to-back configuration. Numerical results indicate a 1.6 dB improvement in the presence of Chromatic Dispersion for a 25% increase in tolerance for a 3dB penalty from +/-1220 ps/nm to +/-1520 ps/nm. and a 0.35 dB improvement for back-to-back operation.
Multi-GNSS and Multi-frequency SNR Multipath Reflectometry of Snow Depth
NASA Astrophysics Data System (ADS)
Tabibi, S.; Geremia-Nievinski, F.; van Dam, T. M.
2015-12-01
Global Navigation Satellite System multipath reflectometry (GNSS-MR) uses ground-based signals of opportunity to retrieve snow depth at an intermediate space scale. This technique is based on the signal-to-noise ratio (SNR) of the simultaneously received direct (line-of-sight) and coherently ground reflected signals. In this contribution, forward and inverse modeling of SNR observations is presented for GLONASS-MR, extending GPS-MR to multiple GNSS. The coupling of the surface and antenna responses from short-delay near-grazing incidence multipath from CDMA and FDMA satellite navigation systems are simulated using an electromagnetic forward model. The inverse model is used to estimate parameter corrections responsible for observation residuals to estimate snow depth. The correlation between snow depth retrievals using GPS L2C signal and GLONASS R2-C/A signal is excellent, with r2 value of 0.990. In a related approach, dual-frequency SNR-based GNSS-MR, which is based on linear combination of SNR observables, is used to estimate snow depth. This ionospheric delay free method synthesizes longer carrier wavelengths ("widelaning" or delta-k) to isolate the direct power contribution in environmental retrievals.
Multipath colourimetric assay for copper(II) ions utilizing MarR functionalized gold nanoparticles
Wang, Yulong; Wang, Limin; Su, Zhenhe; Xue, Juanjuan; Dong, Jinbo; Zhang, Cunzheng; Hua, Xiude; Wang, Minghua; Liu, Fengquan
2017-01-01
We use the multiple antibiotic resistance regulator (MarR), as a highly selective biorecognition elements in a multipath colourimetric sensing strategy for the fast detection of Cu2+ in water samples. The colourimetric assay is based on the aggregation of MarR-coated gold nanoparticles in the presence of Cu2+ ions, which induces a red-to-purple colour change of the solution. The colour variation in the gold nanoparticle aggregation process can be used for qualitative and quantitative detection of Cu2+ by the naked eye, and with UV–vis and smartphone-based approaches. The three analysis techniques used in the multipath colourimetric assay complement each other and provide greater flexibility for differing requirements and conditions, making the assay highly applicable for Cu2+ detection. Under optimal conditions, the Cu2+ concentration was quantified in less than 5 min with limits of detection for the naked eye, UV–vis and smartphone-based approaches of 1 μM, 405 nM and 61 nM, respectively. Moreover, the sensing system exhibited excellent selectivity and practical application for Cu2+ detection in real water samples. Thus, our strategy has great potential for application in on-site monitoring of Cu2+, and the unique response of MarR towards copper ions may provide a new approach to Cu2+ sensing. PMID:28155905
Multipath colourimetric assay for copper(II) ions utilizing MarR functionalized gold nanoparticles
NASA Astrophysics Data System (ADS)
Wang, Yulong; Wang, Limin; Su, Zhenhe; Xue, Juanjuan; Dong, Jinbo; Zhang, Cunzheng; Hua, Xiude; Wang, Minghua; Liu, Fengquan
2017-02-01
We use the multiple antibiotic resistance regulator (MarR), as a highly selective biorecognition elements in a multipath colourimetric sensing strategy for the fast detection of Cu2+ in water samples. The colourimetric assay is based on the aggregation of MarR-coated gold nanoparticles in the presence of Cu2+ ions, which induces a red-to-purple colour change of the solution. The colour variation in the gold nanoparticle aggregation process can be used for qualitative and quantitative detection of Cu2+ by the naked eye, and with UV-vis and smartphone-based approaches. The three analysis techniques used in the multipath colourimetric assay complement each other and provide greater flexibility for differing requirements and conditions, making the assay highly applicable for Cu2+ detection. Under optimal conditions, the Cu2+ concentration was quantified in less than 5 min with limits of detection for the naked eye, UV-vis and smartphone-based approaches of 1 μM, 405 nM and 61 nM, respectively. Moreover, the sensing system exhibited excellent selectivity and practical application for Cu2+ detection in real water samples. Thus, our strategy has great potential for application in on-site monitoring of Cu2+, and the unique response of MarR towards copper ions may provide a new approach to Cu2+ sensing.
Nonlinear elastic multi-path reciprocal method for damage localisation in composite materials.
Boccardi, S; Callá, D B; Ciampa, F; Meo, M
2017-09-05
Nonlinear ultrasonic techniques rely on the measurement of nonlinear elastic effects caused by the interaction of ultrasonic waves with the material damage, and have shown high sensitivity to detect micro-cracks and defects in the early stages. This paper presents a nonlinear ultrasonic technique, here named nonlinear elastic multi-path reciprocal method, for the identification and localisation of micro-damage in composite laminates. In the proposed methodology, a sparse array of surface bonded ultrasonic transducers is used to measure the second harmonic elastic response associated with the material flaw. A reciprocal relationship of nonlinear elastic parameters evaluated from multiple transmitter-receiver pairs is then applied to locate the micro-damage. Experimental results on a damaged composite panel revealed that an accurate damage localisation was obtained using the normalised second order nonlinear parameter with a high signal-to-noise-ratio (∼11.2dB), whilst the use of bicoherence coefficient provided high localisation accuracy with a lower signal-to-noise-ratio (∼1.8dB). The maximum error between the calculated and the real damage location was nearly 13mm. Unlike traditional linear ultrasonic techniques, the proposed nonlinear elastic multi-path reciprocal method allows detecting material damage on composite materials without a priori knowledge of the ultrasonic wave velocity nor a baseline with the undamaged component. Copyright © 2017. Published by Elsevier B.V.
Energy-Efficient Channel Coding Strategy for Underwater Acoustic Networks.
Barreto, Grasielli; Simão, Daniel H; Pellenz, Marcelo E; Souza, Richard D; Jamhour, Edgard; Penna, Manoel C; Brante, Glauber; Chang, Bruno S
2017-03-31
Underwater acoustic networks (UAN) allow for efficiently exploiting and monitoring the sub-aquatic environment. These networks are characterized by long propagation delays, error-prone channels and half-duplex communication. In this paper, we address the problem of energy-efficient communication through the use of optimized channel coding parameters. We consider a two-layer encoding scheme employing forward error correction (FEC) codes and fountain codes (FC) for UAN scenarios without feedback channels. We model and evaluate the energy consumption of different channel coding schemes for a K-distributed multipath channel. The parameters of the FEC encoding layer are optimized by selecting the optimal error correction capability and the code block size. The results show the best parameter choice as a function of the link distance and received signal-to-noise ratio.
Color transplant for reverse ageing of faded artworks
NASA Astrophysics Data System (ADS)
Del Mastio, A.; Piva, A.; Barni, M.; Cappellini, V.; Stefanini, L.
2008-02-01
Nowadays, photographs are one of the most used media for communication. Images are used for the representation of documents, Cultural goods, and so on: they are used to pass on a wedge of historical memory of the society. Since its origin, the photographic technique has got several improvements; nevertheless, photos are liable to several damages, both concerning the physical support and concerning the colors and figures which are depicted in it: for example, think about scratches or rips happened to a photo, or think about the fading or red (or yellow) toning concerning the colors of a photo. In this paper, we propose a novel method which is able to assess the original beauty of digital reproductions of aged photos, as well as digital reproductions of faded goods. The method is based on the comparison of the degraded image with a not-degraded one showing similar contents; thus, the colors of the not-degraded image can be transplanted in the degraded one. The key idea is a dualism between the analytical mechanics and the color theory: for each of the degraded and not-degraded images we compute first a scatter plot of the x and y normalized coordinates of their colors; these scatter diagrams can be regarded as a system of point masses, thus provided of inertia axes and an inertia ellipsoid. Moving the scatter diagram of the degraded image over the one belonging to the not-degraded image, the colors of the degraded image can be restored.
Fading AGN Candidates: AGN Histories and Outflow Signatures
NASA Astrophysics Data System (ADS)
Keel, William C.; Lintott, Chris J.; Maksym, W. Peter; Bennert, Vardha N.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Sartori, Lia F.; Urry, C. Megan; Pancoast, Anna; Schirmer, Mischa; Scott, Bryan; Showley, Charles; Flatland, Kelsi
2017-02-01
We consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of ≈50,000 yr. We explore the use of minimum ionizing luminosity Qion derived from photoionization balance in the brightest pixels in Hα at each projected radius. Tests using presumably constant Palomar-Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Qion values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈2 × 104 yr before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission
ERIC Educational Resources Information Center
Steif, Paul S.; Fu, Luoting; Kara, Levent Burak
2016-01-01
Problems faced by engineering students involve multiple pathways to solution. Students rarely receive effective formative feedback on handwritten homework. This paper examines the potential for computer-based formative assessment of student solutions to multipath engineering problems. In particular, an intelligent tutor approach is adopted and…
ERIC Educational Resources Information Center
Steif, Paul S.; Fu, Luoting; Kara, Levent Burak
2016-01-01
Problems faced by engineering students involve multiple pathways to solution. Students rarely receive effective formative feedback on handwritten homework. This paper examines the potential for computer-based formative assessment of student solutions to multipath engineering problems. In particular, an intelligent tutor approach is adopted and…
Borg, Matthew K; Lockerby, Duncan A; Reese, Jason M
2014-02-21
The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually "fades-in" (inserts) or "fades-out" (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C60 Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.
Examining the Impact of Adaptively Faded Worked Examples on Student Learning Outcomes
ERIC Educational Resources Information Center
Flores, Raymond; Inan, Fethi
2014-01-01
The purpose of this study was to explore effective ways to design guided practices within a web-based mathematics problem solving tutorial. Specifically, this study examined student learning outcome differences between two support designs (e.g. adaptively faded and fixed). In the adaptively faded design, students were presented with problems in…
ERIC Educational Resources Information Center
Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven
2014-01-01
The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…
ERIC Educational Resources Information Center
Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven
2014-01-01
The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…
Beam evolutions of solitons in strongly nonlocal media with fading optical lattices
NASA Astrophysics Data System (ADS)
Dai, Zhi-Ping; Lu, Shi-Zhuan; You, Kai-Ming
2013-01-01
We address the impact of imprinted fading optical lattices on the beam evolution of solitons in strongly nonlocal nonlinear media. The results show that the width of the soliton experiences a change with the increasing propagation distance, the critical power for the soliton varies with the lattice fading away, and the soliton breathing is affected by the initial lattice depth and the nonlocality degree.
ERIC Educational Resources Information Center
Wu, Pei-Fang; Cannella-Malone, Helen I.; Wheaton, Joe E.; Tullis, Chris A.
2016-01-01
Two students with developmental disabilities were taught two daily living skills using video prompting with error correction presented on an iPod Touch, and two different fading procedures were implemented. In one fading procedure, individual video clips were merged into multiple larger clips following acquisition of the entire skill. In the…
Borg, Matthew K.; Lockerby, Duncan A.; Reese, Jason M.
2014-02-21
The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C{sub 60} Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.
Spoon Distance Fading with and without Escape Extinction as Treatment for Food Refusal
ERIC Educational Resources Information Center
Rivas, Kristi D.; Piazza, Cathleen C.; Patel, Meeta R.; Bachmeyer, Melanie H.
2010-01-01
Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and…
ERIC Educational Resources Information Center
Bishop, Michele R.; Kenzer, Amy L.; Coffman, Christine M.; Tarbox, Courtney M.; Tarbox, Jonathan; Lanagan, Taira M.
2013-01-01
Routine toothbrushing is an essential part of good oral hygiene. This study investigated the use of stimulus fading without escape extinction to increase compliance with toothbrushing with three children with autism spectrum disorder (ASD). A 30-step stimulus fading hierarchy was implemented; gradually increasing the proximity of the toothbrush to…
ERIC Educational Resources Information Center
Brown, John L.; Krantz, Patricia J.; McClannahan, Lynn E.; Poulson, Claire L.
2008-01-01
Script fading was used to teach three youths with autism to initiate and sustain verbal interactions under stimulus control consistent with the natural environment. The youths learned to engage in verbal interactions during simulated shopping trips and during visits to community stores. The effectiveness of script fading was examined using a…
Grouping Inhibits Motion Fading by Giving Rise to Virtual Trackable Features
ERIC Educational Resources Information Center
Hsieh, P. -J.; Tse, P. U.
2007-01-01
After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. The authors show that grouping can slow down the process of "motion fading," suggesting that cortical configural form analysis interacts with the computation of motion signals during motion fading. The…
ERIC Educational Resources Information Center
Wu, Pei-Fang; Cannella-Malone, Helen I.; Wheaton, Joe E.; Tullis, Chris A.
2016-01-01
Two students with developmental disabilities were taught two daily living skills using video prompting with error correction presented on an iPod Touch, and two different fading procedures were implemented. In one fading procedure, individual video clips were merged into multiple larger clips following acquisition of the entire skill. In the…
ERIC Educational Resources Information Center
Bishop, Michele R.; Kenzer, Amy L.; Coffman, Christine M.; Tarbox, Courtney M.; Tarbox, Jonathan; Lanagan, Taira M.
2013-01-01
Routine toothbrushing is an essential part of good oral hygiene. This study investigated the use of stimulus fading without escape extinction to increase compliance with toothbrushing with three children with autism spectrum disorder (ASD). A 30-step stimulus fading hierarchy was implemented; gradually increasing the proximity of the toothbrush to…