Showing papers on "Multipath propagation published in 1990"
TL;DR: It is shown that the extended Kalman filter (EKF) can be used to obtain joint estimates of time-of-arrival and multipath coefficients for deterministic signals when the channel can be modeled as a tapped-delay line.
Abstract: The problem of delay estimation in the presence of multipath is considered. It is shown that the extended Kalman filter (EKF) can be used to obtain joint estimates of time-of-arrival and multipath coefficients for deterministic signals when the channel can be modeled as a tapped-delay line. Simulation results are presented for the EKF joint estimator used for synchronization in a direct-sequence spread-spectrum system operating over a frequency-selective fading channel. A simplified model of the EKF joint estimator is considered for analysis purposes. The evolution in time of the tracking error probability density function and the nonlinear tracking error variance are examined through numerical solution of the Chapman-Kolmogorov equation. The nonlinear tracking error variance is compared to both the linear error variance estimate directly provided by the EKF and the Cramer-Rao lower bound. >
234 citations
TL;DR: A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied.
Abstract: A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied. This model is named a Rician/Rayleigh fading environment. Expressions of outage probabilities are presented for the mobile radio system in the Rician/Rayleigh fading environment.
193 citations
TL;DR: In this paper, the results of multipath power delay profile measurements of 900-MHz mobile radio channels in Washington, DC, Greenbelt, MD, Oakland, CA, and San Francisco, CA are presented.
Abstract: The results of multipath power delay profile measurements of 900-MHz mobile radio channels in Washington, DC, Greenbelt, MD, Oakland, CA, and San Francisco, CA, are presented. The measurements have focused on acquiring worst-case profiles for typical operating locations. The data reveal that at over 98% of the measured locations, root mean square (RMS) delay spreads are less than 12 mu s. Urban areas typically have RMS delay spreads on the order of 2-3 mu s and continuous multipath power out to excess delays of 5 mu s. In hilly residential areas and in open areas within a city, RMS delay spreads are slightly larger, typically having values of 5-7 mu s. In very rare instances, reflections from city skylines and mountains can cause RMS delay spreads in excess of 20 mu s. The worst-case profiles show resolvable diffuse multipath components at excess delays of 100 mu s and amplitudes 18 dB below that of the first arriving signal. >
187 citations
TL;DR: A five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception and experimental results of the CDMA system are presented, showing the behavior in a multipath environment.
Abstract: A microcellular local area network (LAN) for indoor communications is proposed using code-division multiple access (CDMA) and differential phase-shift keying (DPSK) for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment. >
90 citations
TL;DR: In this article, the authors derived the maximum likelihood estimator of the angle of arrival of sources having diverse polarization via the simulated annealing optimization technique, which is applicable equally well to the case of coherent signals appearing, for example, in multipath propagation problems.
Abstract: The maximum likelihood estimator of the angle-of-arrival of sources having diverse polarization is derived and computed via the simulated annealing optimization technique. The estimator is applicable equally well to the case of coherent signals appearing, for example, in multipath propagation problems and to the case of a single snapshot. Simulation results that demonstrate the performance of the algorithm are included. >
88 citations
TL;DR: It is shown that M-ary signaling improves the bandwidth efficiency significantly when compared to binary signaling.
Abstract: Direct-sequence spread spectrum, with its inherent resistance to multipath, is a promising technique for indoor wireless communication. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. The bandwidth efficiency of M-ary CDMA systems in fading multipath indoor radio channels is analyzed. It is shown that M-ary signaling improves the bandwidth efficiency significantly when compared to binary signaling. >
72 citations
TL;DR: A centralized, integrated voice/data radio network for fading multipath indoor radio channels is proposed and analyzed and a simple relationship between the number of voice terminals and the throughput of the data traffic are derived for an upper bound of 10-ms delay for the data packets.
Abstract: A centralized, integrated voice/data radio network for fading multipath indoor radio channels is proposed and analyzed. The packets of voice and data are integrated through a movable boundary method. The uplink channel access uses a framed-polling protocol whereas the downlink uses a time-division multiple-access (TDMA) scheme. This system dynamically switches between two transmission rates and uses multiple antennas to maximize the throughput in the fading multipath indoor environment. Throughput and delay characteristics of the system are analyzed using four different techniques. The results are compared with those of Monte Carlo computer simulations. A simple relationship between the number of voice terminals and the throughput of the data traffic are derived for an upper bound of 10-ms delay for the data packets. >
65 citations
03 Jun 1990
TL;DR: Diversity coding can be extended to provide protection from short-duration environmental disruptions, such as multipath fading in radio networks and polarization dispersion in fiber-optic networks, or, in conjunction with previous error detection schemes, to provide forward error correction for random and burst errors.
Abstract: An error-control-based approach, called diversity coding, that provides nearly instantaneous self-healing digital communication networks is presented. This is achieved by constructing an error-correcting code across logically independent channels and by treating link failures within the framework of an erasure channel model. Diversity coding is more efficient than previous approaches to self-healing communication networks since it is nearly instantaneous, is transparent to the end user, minimizes the required extra capacity, and does not need rerouting, resynchronization, or a feedback channel. It is applicable to both circuit-switched and packet-switched networks and to a wide variety of network topologies. Diversity coding can be extended to provide protection from short-duration environmental disruptions, such as multipath fading in radio networks and polarization dispersion in fiber-optic networks, or, in conjunction with previous error detection schemes, to provide forward error correction for random and burst errors. >
61 citations
Patent•
27 Jul 1990TL;DR: In this article, the authors proposed a demodulation scheme for the receiving circuit of a mobile telephone apparatus, where the incoming baseband signals are demodulated and equalized so as to compensate for the deficiencies of the radio medium between base station and mobile telephone devices.
Abstract: In a receiving circuit of a mobile telephone apparatus the incoming baseband signals are demodulated and equalized so as to compensate for deficiencies (multipath propagation) of the radio medium between base station and mobile telephone apparatus. It is not, however, always necessary to equalize the demodulated signals, for instance at low symbol rates or in the case of monopath propagation. According to the invention, time dispersion of the received signals is estimated prior to demodulation, and demodulation with equalization (3a) is effected when the time dispersion is established to be higher than a given value, whereas demodulation without equalization (3b) is effected when the time dispersion is lower than this value. This will enable the power consumed by the receiving circuit to be reduced, particularly in the listening mode of the apparatus.
46 citations
TL;DR: An instrument capable of simulating the multipath fading associated with VHF/UHF mobile radio channels is described and level crossing rate and probability distribution function measurements over a wide range of Doppler frequencies indicate good agreement with theoretical results.
Abstract: An instrument capable of simulating the multipath fading associated with VHF/UHF mobile radio channels is described. The implementation is simple, flexible, economical, and allows the fading waveforms to be repeated exactly. The control section, the quadrature modulator, and the method by which the simulator was tested are described. Level crossing rate and probability distribution function measurements over a wide range of Doppler frequencies indicate good agreement with theoretical results. >
42 citations
TL;DR: It is expected that this type of system will lead to better performance than currently used transparent-tone-in-band and other techniques used in multipath fading environments, which are especially problematic in mobile broadcast and communication applications.
Abstract: A technique that has been verified experimentally to improve the synchronization efficiency of digital communication systems over present systems without sacrificing reliability is presented. This technique is called the spread-spectrum system pilot technique (SSPT). Incorporated into this technique are elements of tone-calibrated techniques (TCT) and spread-spectrum systems. In the SSPT system, the desired pilot tone is modulated by a pseudorandom binary sequence (PRBS) generator of finite duration and then linearly added to the source (customer) data that is actually being sent. At the receiver, the same finite PRBS sequence is used to decode the received signal. The system works because it provides an accurate version of the actual data carrier to be used in demodulation of the received signal. Based on the research presented, it is expected that this type of system will lead to better performance than currently used transparent-tone-in-band and other techniques used in multipath fading environments, which are especially problematic in mobile broadcast and communication applications. >
03 Apr 1990
TL;DR: An algorithm that combines the signal selectivity of cyclic MUSIC with the ability to function well in the presence of fully correlated multipath is presented and implicitly obtains maximum signal-to-interference-plus-noise ratio (SINR) estimates of those signals.
Abstract: An algorithm that combines the signal selectivity of cyclic MUSIC with the ability to function well in the presence of fully correlated multipath is presented. Analytical results and computer simulations are presented to support the claims, which include the ability to estimate directions of arrival of desired signals in the presence of multipath and arbitrary numbers of arbitrarily closely spaced interfering signals. Furthermore, the algorithm can estimate the number of spectrally correlated signals with any particular cycle frequency, and it implicitly obtains maximum signal-to-interference-plus-noise ratio (SINR) estimates of those signals. >
Patent•
29 Jun 1990TL;DR: In this article, a deghosting scheme for eliminating multipath signal components in a received transmitted television signal incorporates a training signal which is a finite duration sequence of repetitions of a 2n-1 pseudorandom sequence.
Abstract: 2103925 9200646 PCTABS00010 Deghosting apparatus for eliminating multipath signal components in a received transmitted television signal incorporates a training signal which is a finite duration sequence of repetitions of a 2n-1 pseudorandom sequence The 2n-1 pseudorandom sequences (12) are mapped into 2r sample intervals at either the transmitter (13) or the receiver (28) to facilitate fast Fourier transform processing Power spectra of the received and mapped training signal (30) and a stored version (44) of the training signal are deconvolved (36) with the deconvolution coefficients produced in logarithmic form The logarithms (32, 34) are inverse Fourier transformed (38) to produce (40) delay coefficients related to the time of occurrence of the multipath signals, which coefficients are utilized to program variable delay circuitry in an adaptive filter (42) to cancel the multipath components
Patent•
13 Jun 1990
TL;DR: In this article, a single receiver in a multipath environment or a plurality of receivers receive the signal from the source having different propagation delays along different paths are used to generate a locus line, either explicitly or implicitly.
Abstract: A passive surveillance system provides ranging and location capability of a signal source. A single receiver in a multipath environment or alternatively a plurality of receivers receive the signal from the source having different propagation delays along different paths. Selection of corresponding frequency components from different paths and mixing of the corresponding selected frequency components from each of the paths generates complex pseudo-noise signals that are suitable for correlation processing. Correlation processing of the mixed signals yields the time difference between the multiple paths. The maximum time difference parameters for each path are used to generate a locus line, either explicitly or implicitly. Range and location processing of the locus information identifies range and location of the signal source.
01 Aug 1990
TL;DR: In this article, the importance of phase derivatives with respect to space and frequency is emphasised and it is shown that the group delay follows a Student's t-distribution, delay spread as the determining parameter, and does not depend on the details of the power delay profile.
Abstract: The classical multipath model of mobile communications is reviewed and the importance of phase derivatives with respect to space and frequency is emphasised. Using an analogy it is shown that the group delay follows a Student's t-distribution, delay spread as the determining parameter, and does not depend on the details of the power delay profile. The delay spread is the second central moment of the average power delay profile. The distribution is important for frequency selective effects of datacommunication over a narrowband channel.
Patent•
28 Sep 1990
TL;DR: In this paper, the frequency hop digital phase shift keying and convolutional coding were used to achieve high frequency (HF) modem communications. But the performance of the modem was not limited by the multimode multipath characteristics of the HF path.
Abstract: Methods and apparatus for achieving high frequency (HF) modem communications. A predetermined plurality of frequency hopped, digital phase shift keying modulated tones are generated at a predetermined number of pseudo-randomly generated frequencies during a successive plurality of time frames. The phase of the tone at each frequency during a particular time frame is differentially modulated to one of a predetermined number of new phases using the phase of the tone at the same frequency in the previous frame as a reference. The tones are transmitted in the high frequency (HF) band, and then received and converted into digital signals. The digital signals are processed to determine the phase of the tone at each transmitted frequency. This may be accomplished by means of a Fourier transform filter. Finally the phase of each tone is compared to the phase of the tone received at the same frequency in the previous frame to decode the received signals, and hence accomplish the desired communications. The present invention provides for communications methods and apparatus which achieves HF skywave communications at high data rates with low bit error rate performance. The invention employs the use of frequency hopped digital phase shift keying and the convolutional coding that overcomes the dispersive nature of the HF channel and achieves the high data rate without resorting to channel equalization techniques. The performance of the modem of the present invention is not limited by the multimode multipath characteristics of the HF path. This is due to selection of a frequency dwell time that is significantly less than the multipath differential times of arrival, and a frame time of the waveform that is longer than the maximum multipath differential times of arrival.
TL;DR: Consideration is given to the performance of a binary phase-shift-keyed direct-sequence spread-spectrum (DS/SS) communication system in a fading dispersive channel with the direct or specular component of the signal present.
Abstract: Consideration is given to the performance of a binary phase-shift-keyed (BPSK) direct-sequence spread-spectrum (DS/SS) communication system in a fading dispersive channel with the direct or specular component of the signal present. Two types of multipath intensity profiles are analyzed. Large values of the multipath spread (larger than a symbol duration) are considered, and a useful approximation to the symbol error probability, based on random spreading sequences, is derived. The effect of pulsed jamming on the performance is analyzed. Both the uncoded and the coded case are considered. In the coded case, hard- and soft-decision decoding metrics, with and without jammer-state information (JSI), are analyzed and discussed. >
TL;DR: Frequency-division multiple access appears in general to be the more capable system, because CDMA can better absorb Doppler and multipath effects and permits higher rate coding.
Abstract: A comparison between frequency-division multiple access (FDMA) and code-division multiple access (CDMA) when both methods operate in the mobile satellite communication environment is presented. The mobile satellites under consideration use multiple beams or scan beam antennas and employ frequency reuse of the allocated L-band frequency spectrum. Because CDMA can better absorb Doppler and multipath effects and permits higher rate coding, it appears in general, with practical considerations set aside, to be the more capable system. >
TL;DR: The effects of local traffic around a transmitter and receiver and local movements of an antenna are studied by collecting and analysing multipath profiles at 910 MHz.
Abstract: The effects of local traffic around a transmitter and receiver and local movements of an antenna are studied by collecting and analysing multipath profiles at 910 MHz. The statistics of RMS delay spread and the received power in the multipath profiles are computed and compared for these experiments.
TL;DR: The results of a campaign to measure multipath effects on pseudorange measurements of stationary receivers are presented, which include steep earth embankments, overhead wires, fresh-and saltwater horizons, and railway right-of-way.
Abstract: The results of a campaign to measure multipath effects on pseudorange measurements of stationary receivers are presented. The multipath scenarios, which were intentionally selected, include steep earth embankments, overhead wires, fresh and saltwater horizons, and railway right-of-way. An absorber screen was tested for its effectiveness in shielding antennas from low-angle multipath, and its performance is reported in each multipath situation. A convenient classification of multipath effects is presented based on the periodicity of the multipath interference and the nature of the interfering surface or object. An estimate of the pseudorange multipath error is presented in each case.
TL;DR: In this paper, the power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers.
Abstract: Power penalties due to multipath interference (MPI) have been measured for 1.7-Gb/s lightwave systems that use single-frequency (SF) or multifrequency (MF) lasers. Systems that use SF lasers potentially exhibit worse degradation than those using MF lasers. Bit-error-rate (BER) floors occur only under the worse-case conditions of poor receiver margin and large multiple reflections. The use of optical isolation to reduce laser feedback is ineffective in reducing multipath interference, and in many cases may worsen the penalty. It is shown that for a typical transmission system, these degradations are reduced if optical interconnection reflections are maintained below -20.5 dB. The experimental study is in good agreement with theoretical predictions using an analytic expression of the MPI noise power spectral density and with computer simulations using multimode laser rate equations. >
05 Jun 1990
TL;DR: In this article, a compact telemetry system for digital data telemetry at rates up to 10 kb/s over 1 to 10 km is presented for worst-case ocean acoustic channel conditions, and operates in the presence of source/receiver motion, fading and multiple transmission paths.
Abstract: A compact telemetry system for digital data telemetry at rates up to 10 kb/s over 1 to 10 km is presented. The system is designed for worst-case ocean acoustic channel conditions, and operates in the presence of source/receiver motion, fading, and multiple transmission paths. In addition, the system incorporates spatial diversity by utilizing multiple hydrophones and data processing subsystems. This allows much more reliable operation under realistic circumstances where noise events and transducer masking are unavoidable. The result is a system specifically geared toward use at sea with a remotely operated vehicle (ROV). Preliminary dockside test results are presented to demonstrate the effectiveness of this multichannel system. >
TL;DR: A finite population Markov model is used to obtain the throughput of a multiantenna and multireceiver slotted ALOHA system and results indicate that substantial gains are possible with the use of several antennas and receivers.
Abstract: The problem of data transmission in a mobile packet radio system with one central base station and a number of mobile terminals is addressed. A method using multiple directional antennas and receivers at the base station to improve the efficiency of transmission on the inbound channel (from the terminals to the base station) is proposed. A number of channel models are considered, including flat terrestrial propagation loss, Rayleigh fading, and noise. A finite population Markov model is used to obtain the throughput of a multiantenna and multireceiver slotted ALOHA system. Numerical results indicate that substantial gains are possible with the use of several antennas and receivers. The dynamic behavior of the system is also improved. >
06 May 1990
TL;DR: An adaptive phase equalizer structure using decision-directed phase tracking which does not require the multiplication operations required in most conventional equalization algorithms is proposed and computer simulations confirm the feasibility of the proposed receiver structure.
Abstract: A low-complexity equalization technique for improving the reliability of portable radio links in the presence of multipath time delay spread is described. A technique that operates on hard-limited received signals, with only the phase information available, is presented. The use of passband hard-limiters in radio front end circuits reduces the complexity of portable radio receivers. An adaptive phase equalizer structure using decision-directed phase tracking which does not require the multiplication operations required in most conventional equalization algorithms is proposed. A receiver that includes a time-reversal structure and a joint estimator for optimum timing recovery and equalizer training is described. The time-reversal structure plays a crucial role in maximizing the compensation capability of the phase equalizer. The combined use of phase equalization and diversity reception is also considered. Computer simulations confirm the feasibility of the proposed receiver structure. >
03 Sep 1990
TL;DR: A combined MLSE (maximum likelihood sequence estimation) equalizer and decoder with D-diversity reception is analyzed for slowly time-varying frequency-selective Rayleigh fading channels and an upper bound on the (decoded) bit error probability is derived.
Abstract: A combined MLSE (maximum likelihood sequence estimation) equalizer and decoder with D-diversity reception is analyzed for slowly time-varying frequency-selective Rayleigh fading channels. An upper bound on the (decoded) bit error probability is derived. This bound is tight for high signal-to-noise ratios or when diversity reception is employed. A method based on a one-directional stack algorithm is proposed for calculating the bound that efficiently uses computer memory. Two systems have been analyzed using this procedure and compared with computer simulations: BPSK (binary phase shift keying) with a three-tap channel and coded quadrature PSK with a two-tap channel. >
TL;DR: In this article, a large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed.
Abstract: Multipath fading data obtained from 47 terrestrial microwave line-of-sight links in France and the United Kingdom are analyzed to derive narrowband prediction equations for the deep fading range of the cumulative distribution for the average worst month. A large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed. The improvement is achieved by increasing the number of prediction variables, using the most statistically significant variables, introducing a zonally varying geoclimatic factor, and employing more accurate analysis techniques. A reasonable choice of variables for system design includes path length, radio frequency, path inclination, and the grazing angle of specular reflection from the average terrain profile. A physical interpretation of the results suggests that a large amount of multipath fading is caused by ground reflection in combination with fading of the direct wave through the atmosphere. >
16 Apr 1990
TL;DR: Measured multipath profiles from five different indoor areas are used for the performance analysis of a binary phase-shift-keying modem, with and without a decision feedback equalizer, and it was observed that data rates are obtainable with a DFE having three forward and three feedback taps.
Abstract: Measured multipath profiles from five different indoor areas are used for the performance analysis of a binary phase-shift-keying modem, with and without a decision feedback equalizer. Both the average bit error rate and outage probability are calculated as the performance criteria. The average probability of error from the measured multipath profiles is compared with the performance predictions based on theoretical and computer-simulated channel models. For all five areas, it was observed that data rates on the order of 10 Mb/s are obtainable with a DFE having three forward and three feedback taps. Equivalent performance without equalization requires data rates of less than 1 Mb/s. >
06 May 1990
TL;DR: Using standard propagation models, it is shown that excess delays greater than 100 mu s may be encountered in scenarios with a line-of-sight path to large scatterers and an obstructed direct path.
Abstract: 900 MHz multipath intensity profiles (impulse response estimates) which may be expected in mountainous terrain are described. Using standard propagation models, it is shown that excess delays greater than 100 mu s may be encountered in scenarios with a line-of-sight path to large scatterers and an obstructed direct path. Possible scenarios in which large excess delays may occur are presented, and two models are proposed. These models are used to predict the channel impulse response that may be expected. Calculated results are presented, and a comparison with measured results in the literature is given. The measurement equipment is briefly described. Such long excess delays are consistent with measured results. >
TL;DR: Results are presented of experimental measurements of the angle of arrival and amplitude of the individual rays in a multipath microwave propagation situation, and a sampling interval of 1 s appears to be sufficient to capture the variations in the individual paths.
Abstract: Results are presented of experimental measurements of the angle of arrival and amplitude of the individual rays in a multipath microwave propagation situation. On the basis of extensive data collected on a 31.5-km path, statistical distributions that are expected to be of assistance in the design of diversity, especially angle-diversity, microwave systems are presented. In the application of the technique, a sampling interval of 1 s appears to be sufficient to capture the variations in the individual paths, and the range in angle of arrival (1.4 degrees ), determined by the element spacing, appears to be sufficiently wide to avoid aliasing problems. >
TL;DR: In this article, a modified pseudorandom noise (PN) sequence and a properly designed correlator are used to track changing ghosts at a weak signal level (low signal-to-noise ratio).
Abstract: The problem of multipath propagation in television terrestrial broadcasting can be solved by channel equalization. Such equalization is needed for an enhanced NTSC system and is particularly critical in most HDTV (high-definition television) proposals. Techniques for precisely characterizing a multipath channel are proposed. These characterizations can be used to reduce hardware complexity and to speed up equalizer convergence. In particular, an approach that provides an opportunity to track changing ghosts at a weak signal level (low signal-to-noise ratio) is proposed. A modified pseudorandom noise (PN) sequence and a properly designed correlator are used. The correlator, matched to a modified PN sequence, provides noise rejection that is 24 dB better than that obtained from the use of a single pulse. No long-term averaging is needed to improve the signal-to-noise ratio. Therefore, it has better system convergence speed and makes it possible to track changing ghosts, or it can tradeoff the speed of convergence against the use of vertical blanking interval by sending the ghost cancellation reference signal less frequently. >