Showing papers on "Multipath propagation published in 1989"
TL;DR: In this paper, a wideband multipath measurements at 1300 MHz were made in five factory buildings in Indiana and the average factory path loss was found to be a function of distance to the 2.2 power.
Abstract: Wideband multipath measurements at 1300 MHz were made in five factory buildings in Indiana. Root-mean-square delay spread ( sigma ) values were found to range between 30 and 300 ns. Median sigma values were 96 ns for line-of-sight paths along aisleways and 105 ns for obstructed paths across aisles. Worst-case sigma or 300 ns was measured in a modern open-plan metal-working factory. Delay spreads were not correlated with transmitter-receiver separation or factory topography but were affected by factory inventory, building construction materials, and wall locations. Wideband path loss measurements consistently agreed with continuous-wave measurements made at identical locations. It is shown that such empirical data suggest independent and identical uniform distributions on the phases of resolvable multipath signal components. Average factory path loss was found to be a function of distance to the 2.2 power. >
429 citations
TL;DR: Radio wave propagation experiments at 1300 MHz, which were conducted by the author in five operational factories, are described, and studies of multipath propagation are discussed, and techniques for overcoming it are considered.
Abstract: The need for reliable, real-time communication for automated factories is discussed. The ability of narrowband digital radio systems to meet that need is examined. The major problems encountered in multipath propagation, resulted from multiple reflections of the transmitted signal from the building structure and surrounding inventory. Radio wave propagation experiments at 1300 MHz, which were conducted by the author in five operational factories, are described. Other studies of multipath propagation are discussed, and techniques for overcoming it are considered. Research on multiple-access networking is summarized. >
187 citations
TL;DR: The authors present a simulation study of an adaptive receiver, based on the concept of maximum-likelihood sequence estimation (MLSE), which compensates for the heavy selective distortions caused by multipath propagation.
Abstract: The authors present a simulation study of an adaptive receiver, based on the concept of maximum-likelihood sequence estimation (MLSE), which compensates for the heavy selective distortions caused by multipath propagation. The receiver includes a matched filter and a modified Viterbi processor and is suitable for implementation in a digital form. It operates adaptively, in a training mode at the beginning of each burst, as well as in a tracking mode during message detection. This makes the receiver robust both to fast Doppler shifts and to a large frequency offset. Simulation results are presented which show the performance in different multipath environments, with echo delay in excess of 20 mu s and vehicle speed up to 250 km/h. >
139 citations
Patent•
30 Mar 1989
TL;DR: In this article, a multipath rejection scheme was proposed to combine transponder placements with pseudonoise coding for robust and secure data transmission in an intra-office communication system.
Abstract: Described is an intraoffice communication system as the final communication link of a broadband, baseband, or fiber optic LAN. Each user or workstation is a node on the network and can transmit at high data rates with bit error rates of ≦10-9 in packets through the LAN. Message relaying transponders are placed on the ceiling and walls communicating by electromagnetic waves to individual workstations by broadcast. A novel multipath rejection scheme is combining transponder placements with pseudonoise coding for robust and secure data transmission. For the present state of the art if infrared is used, we estimate a minimum light collecting aperture (receive antenna) of 1 cm2 for transmission rates of 30 to 100 Mb/s.
103 citations
TL;DR: Field tests related to planned mobile satellite systems (MSS) were performed, and results that add to the existing database of propagation measurements at L-band (1.5 GHz) are described.
Abstract: Field tests related to planned mobile satellite systems (MSS) 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 which housed the receiver. >
94 citations
TL;DR: The Prony algorithm's ability to resolve delays to better than half the Fourier limit is shown, and its tendency to yield biased estimates is studied.
Abstract: This study is concerned with using modern spectral analysis techniques to derive estimates of multipath ray parameters (delays and amplitudes) from measurements of selective fading over a wide band at microwave frequencies. The applicability of the general category of autoregressive methods is addressed, and the specific method adopted, the Prony algorithm, is described. An illustrative example in which this is applied to a typical field measurement is followed by an investigation into the capabilities and limitations of the algorithm. A statistical analysis of the method has been carried out using a database of laboratory measurements. The Prony algorithm's ability to resolve delays to better than half the Fourier limit is shown, and its tendency to yield biased estimates is studied. >
88 citations
27 Nov 1989
TL;DR: The results of multipath power delay profile measurements of 900-MHz mobile radio channels in Washington, DC, Greenbelt, MD, Oakland, CA, and San Francisco, California, are presented, revealing that at over 98% of the measured locations, RMS delay spreads are less than 12 mu s.
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, RMS (root mean square) delay spreads are less than 12 mu s. Urban areas typically have RMS delay spreads on the order of 2 to 3 mu s and have 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 to 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 components at excess delays of 100 mu s which are 15 dB down from the first arriving signal. Depending on the precise symbol duration, unequalized 40-kb/s TDMA (time division multiple access) channels will be harmed by multipath at less than 1% to 4% of vehicle locations. >
72 citations
TL;DR: A novel discrete-time method is proposed for estimating the impulse response of a frequency-selective digitally modulated communication channel and its low sensitivity to observation noise, and its improved performance in terms of probability of error or the reconstructed transmitted sequence.
Abstract: A novel discrete-time method is proposed for estimating the impulse response of a frequency-selective digitally modulated communication channel. The received signal is first demodulated and sampled and then the fourth-order cumulants of the resulting discrete-time sequence are estimated. The method estimates the channel impulse response from the complex cepstrum of the aforementioned fourth-order cumulants (i.e. tricepstrum). The method depends only on the second- and fourth-order statistics of the transmitted sequence and is capable of reconstructing nonminimum-phase impulse responses. Monte Carlo simulation results demonstrate the effectiveness of the method, its low sensitivity to observation noise, and its improved performance in terms of probability of error or the reconstructed transmitted sequence. >
72 citations
TL;DR: In this article, the propagation and time delay spread at 910 MHz on several different manufacturing floors were measured and the statistics of RMS multipath delay spread and the values of the distance/power law gradient were computed and compared for these experimental sites.
Abstract: Measurements of propagation and time delay spread at 910 MHz on several different manufacturing floors are presented. The statistics of RMS multipath delay spread and the values of the distance/power law gradient are computed and compared for these experimental sites.
65 citations
27 Nov 1989
TL;DR: Multipath profiles obtained from propagation measurements done on several manufacturing floors and college campus laboratories at 910 MHz are analyzed and a suitable model for the distribution of the gain coefficients is found to be the log-normal distribution.
Abstract: Multipath profiles obtained from propagation measurements done on several manufacturing floors and college campus laboratories at 910 MHz are analyzed to model the arrival of the paths, the respective amplitudes of the paths, and the received power. The discrepancies between the empirical distribution of the arriving paths and Poisson arrivals are discovered. The modified Poisson process is shown to fit the arriving paths closely. Rayleigh, Weibull, Nakagami, log-normal, and Suzuki distributions are considered as potential models for the amplitude of the arriving paths. The path amplitudes are shown to closely follow a log-normal rather than a Rayleigh distribution. The delay power spectrum is shown to fit an exponential function closely. The statistics of RMS multipath delay spread and the values of the distance/power law gradient are also computed and compared for these experimental sites. The interarrival times of the signals were modeled by the Weibull distribution. A model for the distribution of the number of signals was presented using the modified Beta distribution. Finally, for the data with no threshold at the receiver a suitable model for the distribution of the gain coefficients is found to be the log-normal distribution. >
54 citations
TL;DR: This paper reviews the various experimental techniques used to investigate the multipath microwave channel, their successes, and their limitations, and concludes by stressing the directions in which progress has to be made.
Abstract: It is very difficult to relate the behavior of a multipath microwave channel to its physical description. Much information, however, can be gained from radioelectrical probing of the channel, and models can be built independent of the complex underlying physical situation. In this paper we review the various experimental techniques used to investigate the channel, their successes, and their limitations. We conclude by stressing the directions in which progress has to be made.
TL;DR: In this paper, computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel, and it is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel.
Abstract: Computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel. Unfiltered 2-, 4-, and 8-PSK and 16-QAM with a rectangular signaling pulse are compared first, followed by 4- and 16-QAM with a raised-cosine Nyquist pulse. The bit error rate performances averaged over fading samples under the influence of the intersymbol interference caused by delay spread are compared for modulations of different levels. It is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel. Both the spectral and the power efficiencies can be enhanced using Nyquist signaling pulses. >
29 Sep 1989
TL;DR: In this paper, the problem of recovering the initial baseline, i.e., the initial coordinate differences between the shore-based monitor station and the vessel is discussed, using code measurements.
Abstract: The operational constraints of DGPS in the marine environment are reviewed In particular the problem of recovering the initial baseline, ie, the initial coordinate differences between the shore-based monitor station and the vessel is discussed The recovery of this initial baseline requires the use of code measurements However, the relative position changes of the vessel are best determined using the relatively more accurate carrier phase measurements A procedure to combine both code and carrier phase measurements to achieve the above goal in an operationally acceptable manner is discussed An external accuracy of <5 m (95% confidence level) can generally be obtained with this method However, code measurements can be affected significantly by multipath, which can decrease the reliability of the above method to an unacceptably low level Examples of code multipath obtained under field conditions show systematic effects with peak to peak amplitudes of 20 m and periods of several minutes Two multipath counter-measures are discussed and tested, namely the use of a RF absorbent ground plane made of carbon impregnated foam at the monitor station and the use of parallel filters at both the monitor and mobile stations These methods reduce the effect of code multipath to a level sufficiently low to maintain the accuracy quoted above in a high multipath environment
TL;DR: The author considers the problem of demodulating a direct-sequence spread-spectrum signal in the presence of narrowband interference and multipath using the generalized likelihood-ratio test (GLRT), in which the interferer is modeled as an Nth-order circular Gaussian autoregressive process and the multipath channel is represented by a tapped-delay line.
Abstract: The author considers the problem of demodulating a direct-sequence (DS) spread-spectrum signal in the presence of narrowband interference and multipath. A receiver is considered that is based on the generalized likelihood-ratio test (GLRT), in which the interferer is modeled as an Nth-order circular Gaussian autoregressive (AR) process and the multipath channel is represented by a tapped-delay line. The maximum-likelihood joint estimator for the channel coefficients and interferer AR parameters is then derived. Analytical expressions for bit-error rate are presented for GLRT receiver, under the assumption of perfect estimates of the channel and interferer parameters. The performance of the GLRT receiver is compared to that of a DS receiver using a transversal equalizer. It is shown that the GLRT receiver consistently outperforms the equalizer-based receiver by 2-3 dB. The performance of an adaptive GLRT receiver is evaluated where the recursive least-squares algorithm is used to jointly estimate the interferer and channel parameters. >
TL;DR: In this paper, the authors studied the discrepancies between the empirical distribution of the arriving paths and Poisson arrivals and discovered the modified Poisson process is shown to fit the arriving path closely.
Abstract: Arrival of the paths in fading multipath channels obtained from several manufacturing floors and college campus laboratories at 910 MHz are studied. The discrepancies between the empirical distribution of the arriving paths and Poisson arrivals are discovered. The modified Poisson process is shown to fit the arriving paths closely.
01 May 1989
TL;DR: 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) date that are actually being sent.
Abstract: A technique is presented that has been verified experimentally to improve the synchronization efficiency of digital communication systems over present systems without sacrificing any reliability. This technique is called the spread-spectrum pilot technique (SSPT). Incorporated into this technique are elements of both tone-calibrated techniques 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) date that are 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. It is strongly believed that this type of system will enable better performance in multipath fading environments that are especially problematic in mobile-radio applications. >
09 Apr 1989
TL;DR: A technique for determining receiver threshold for channel impulse response measurements is analyzed and applied to show that the interpretation of measured results is critically dependent on the value of receiver threshold used.
Abstract: Mathematical models which estimate the number and amplitude of multipath signals in a typical factory environment, and the probability that a multipath component is likely to occur for a given excess delay interval are presented. A technique for determining receiver threshold for channel impulse response measurements is analyzed and applied to show that the interpretation of measured results is critically dependent on the value of receiver threshold used. Models for the number of paths, the likelihood of multipath components, and the strength of the multipath components are given as functions of topography and transmitter-receiver separation. It was shown that a Rayleigh distribution for the amplitude of multipath components is a very good model. The likelihood of multipath was shown to fall off exponentially with excess delay at high threshold values and linearly at lower threshold values. Using a pulse resolution of 7.8 ns, the number of multipath components are shown to fit either a Poisson distribution or a uniform distribution, depending on the received power threshold of the receiver. >
01 May 1989
TL;DR: It is shown that the log-normal distribution describes the fading of multipath components over local areas for particular excess delays as well as the distributions of received power within a particular excess delay interval.
Abstract: The secondary statistics for an indoor radio impulse response model in the factory environment are investigated. Under the assumption that multipath signal amplitudes are jointly log-normally distributed over local areas and excess delay, the application of second-order statistics (correlation) is presented. In addition, the distributions of received power within a particular excess delay interval are found for both global and local areas. It is shown that the log-normal distribution describes the fading of multipath components over local areas for particular excess delays. Moreover, individual multipath signal strengths are log-normal about a mean power law of the form d/sup n/. The log-normal distribution is attractive for modeling the impulse response amplitudes because correlation data are easily incorporated. Conditional probabilities of path occupancy are presented which show the effect power control will have on indoor radio systems. >
Patent•
31 Jan 1989
TL;DR: In this article, a high frequency (HF) communications buoy that employs HF surface wave and sky wave, communication and spread spectrum modulation to suppress multipath fading and to decrease the undesired detectability of transmitted signals is presented.
Abstract: A high frequency (HF) communications buoy that employs HF surface wave, and sky wave, communication and spread spectrum modulation to suppress multipath fading and to decrease the undesired detectability of transmitted signals. The buoy comprises a water-tight floatable enclosure that may be deployed from a flying vehicle or a submerged vessel. An HF communications transceiver is disposed within the enclosure that is capable of transmitting and receiving signals employing high frequency (HF) band surface wave and sky wave propagation. The transceiver further comprises spread spectrum modulation and demodulation circuitry for modulating transmitted signals utilizing spread spectrum modulation and for demodulating received signals encoded by means of spread spectrum modulation. The spread spectrum modulation and demodulation circuitry is provided to suppress multipath fading and decrease the probability of detection of transmitted signals. An antenna is coupled to the transceiver and supports the transmission and reception of the high frequency (HF) spread spectrum modulated signals. The use of HF surface wave communications in conjunction with the spread spectrum modulation of the transmitted signals provides for networking of a plurality of buoys. The use of HF spread spectrum communications also reduces the probability of exposing the presence and location of the transmitting terminal and eliminates multipath interference between ground wave and sky wave transmissions, or transmissions reflected from different sky wave layers. In addition, utilization of the underwater communication circuitry permits a submerged vehicle to take advantage of the relatively secure communications link provided by the present invention.
01 May 1989
TL;DR: In this paper, a statistical model based on experimental data is presented to characterize the multipath propagation medium in typical manufacturing environments, which includes the statistics of multipath propagations characteristics for cases of light and heavy clutter in a factory where there is a direct path from transmitter to receiver.
Abstract: A statistical model, based on experimental data, is presented to characterize the multipath propagation medium in typical manufacturing environments. This model includes the statistics of multipath propagation characteristics for cases of light and heavy clutter in a factory where there is a direct path from transmitter to receiver. The dynamic behavior of the medium is described by a time-varying impulse response which includes the distribution of the parameters of the channel such as the gain, the interarrival time, and the number of paths. The peaks and the inflections of a number of experimentally measured pulse responses of channels were used to estimate the channel statistics. >
11 Jun 1989
TL;DR: The use of a computer simulation of a time division multiple access (TDMA) digital mobile radio link demonstrates that the M-algorithm can be substituted for the optimum Viterbi algorithm in adaptive MLSE equalizers for frequency-selective fading mobile radio channels.
Abstract: The performance loss of an adaptive M-algorithm maximum likelihood sequence estimation (MLSE) equalizer system is presented for frequency-selective fading mobile ratio channels, assuming a two-ray and a six-ray multipath fading model. The use of a computer simulation of a time division multiple access (TDMA) digital mobile radio link demonstrates that the M-algorithm can be substituted for the optimum Viterbi algorithm in adaptive MLSE equalizers for frequency-selective fading mobile radio channels. For a two-ray channel model, the degradation due to the use of the M-algorithm is less than 1 dB if the number M of evolved paths is 2 or larger. For channels with a heavy multipath propagation, such as the six-ray channel, the M-algorithm MLSE equalizer suffers from a considerable degradation. >
Patent•
23 Jan 1989
TL;DR: In this paper, the signal format has a block structure with a fixed pattern preceding and following the data portion of each block and synchronization is obtained by trial using the detected pattern with the known pattern.
Abstract: Methods for detection or, or equivalently, demodulation of phase-and-amplitude-shift-keyed communication signals that may be received via multipath propagation or dispersion in a noisy channel are disclosed. The signal format has a block structure with a fixed pattern preceding and following the data portion of each block. Implementation is accomplished in real-time by obtaining samples of the complex-envelope of the received waveform, processing at the symbol rate mainly in the frequency domain, then returning to the time domain with a coagulated signal where ordinary detection of the symbols is completed according to the modulation in use. The signal format and computation in the frequency domain permit the estimation of the multipath-structure of the channel, which in turn permits the estimation of the data using a reasonable amount of processing. Performance of the basic method is substantially improved by generating a metric and searching for alterations of the data that reduce the metric. The search can be controlled by an indicant vector that identifies those symbols of a block that are likely to be in error. Synchronization is obtained by trial using the basic method to compare the detected pattern with the known pattern.
TL;DR: The guard time effect, is used in multipath spread channels, is evaluated for frequency-selective channels, and the optimal combination of signaling rate, code rate, and guard time is presented.
Abstract: The generalized cutoff rate of time- and frequency-selective fading channels is evaluated for M-ary frequency-shift keying (MFSK) and M-ary differential phase-shift keying (MDPSK) modulation with soft decoding. The optimal signaling rate and code rate for dispersive channels are evaluated. The guard time effect, is used in multipath spread channels, is evaluated for frequency-selective channels, and the optimal combination of signaling rate, code rate, and guard time is presented. Special attention is given to CCIR (International Radio Consultative Committee) HF channel models. >
TL;DR: The performance of binary frequency-shift-keyed communications over frequency-selective wide-sense-stationary uncorrelated-scattering Rayleigh fading channels is discussed and a technique for obtaining bounds on the average error probability for FSK in terms of one or two parameters obtainable from multipath spread or frequency correlation functions channel measurements is described.
Abstract: The performance of binary frequency-shift-keyed communications over frequency-selective wide-sense-stationary uncorrelated-scattering Rayleigh fading channels is discussed. Previous analyses of FSK communications over frequency-selective channels have considered the average probability of error for specific models for the fading channel and typically assume that the two FSK signals are orthogonal. A technique for obtaining bounds on the average error probability for FSK in terms of one or two parameters obtainable from multipath spread or frequency correlation functions channel measurements is described. >
TL;DR: In this paper, the authors describe multipath power delay profile measurements of 900 MHz mobile radio channels in four US cities and show that reflections from city skylines and mountains can cause RMS delay spreads which exceed 20 μs and excess delays which exceed 100 μs.
Abstract: This letter describes multipath power delay profile measurements of 900 MHz mobile radio channels in four US cities. Preliminary data show that for over 98% of the measured locations, RMS delay spreads are less than 12 μs. In very rare instances, reflections from city skylines and mountains can cause RMS delay spreads which exceed 20 μs and excess delays which exceed 100 μs. Such large excess delays have not been previously reported in the literature.
11 Dec 1989
TL;DR: These measurements show that the multipath time delay spread profile often contains significant discrete components, and the direction of arrival measurements with the frequency response measurements and the derived timedelay spread profiles made previously are compared.
Abstract: In land mobile radio systems the signal at a mobile receiver is usually the sum of a number of multipath components. The time delay spread of the multipath signal has been measured in many situations. These measurements show that the multipath time delay spread profile often contains significant discrete components. The paper compares the direction of arrival measurements (at 870 Mhz) with the frequency response measurements and the derived time delay spread profiles made previously.
Patent•
03 Feb 1989TL;DR: In this paper, a GMSK radio receiver for operation in the presence of strong multipath interference is presented, comprising a baseband frequency converter which operates so as to produce I and Q baseband signals, which are correlated with a plurality of different possible signals to afford in respect of each correlation a probability signal, the probability signals being processed to determine the significance of the signal received.
Abstract: A GMSK radio receiver for operation in the presence of strong multipath interference, comprising a baseband frequency converter which operates so as to produce I and Q baseband GMSK signals, which will be distorted by any multipath interference present, which are correlated with a plurality of different possible signals to afford in respect of each correlation a probability signal, the probability signals being processed to determine the significance of the signal received, whereby the transmitted data is determined in the presence of multipath interference.
27 Nov 1989
TL;DR: Computer simulation using a six-ray propagation model confirms that waveform distortion and adjacent channel interference distortion can be removed simultaneously using the proposed approach.
Abstract: In order to properly utilize NB-TDMA (narrow-band time division multiple access) digital mobile radio, it is necessary to remove both frequency-selective fading distortion caused by multipath propagation on the radio path and adjacent channel interference distortion from burst signals. It is suggested that an equalization system which combines a fractional interval equalizer and a decision feedback equalizer can solve this problem. Computer simulation using a six-ray propagation model confirms that waveform distortion and adjacent channel interference distortion can be removed simultaneously using the proposed approach. >