Showing papers on "Fading published in 1988"
TL;DR: The definition of a new distance measure of optimization of trellis codes transmitted over Rician fading channels, guided by maximizing d/sub free, is proposed.
Abstract: It has been well established that the appropriate criterion for optimum trellis-coded modulation design on the additive white Gaussian noise channel is maximization of the free Euclidean distance. It is shown that when the trellis-coded modulation is used on a Rician fading channel with interleaving/deinterleaving, the design of the code of 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 the 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 of 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/. >
613 citations
TL;DR: In this paper, the results of measurements made to determine propagation characteristics on urban mobile radio channels with low-base-station antennas and line-of-sight between the base and mobile units are reported.
Abstract: To mitigate fading and reduce time dispersion on urban mobile radio channels, it has been proposed that future systems be configured with many small cells having low-powered base stations with street-lamp-level antennas. The results of measurements made to determine propagation characteristics on urban mobile radio channels with low-base-station antennas and line-of-sight between the base and mobile units are reported. Cumulative distribution functions for envelope fading as well as delay spread and frequency correlation statistics are presented. Comparisons are made with similar statistics for conventional channels. Results show that multipath propagation conditions would be significantly less severe if small-celled systems were implemented. Root mean square delay spread averages are reduced by a factor of approximately four in comparison with those typical in conventional systems. In addition, microcellular-type channels have Rician, rather than Rayleigh, envelope fading characteristics, and correspondingly different frequency correlation statistics, which offers further advantages. >
232 citations
TL;DR: It is demonstrated that allowing for multiple symbols per trellis branch provides an additional degree of freedom for designing a code to meet the optimization on the fading channel.
Abstract: A previous work on criteria for designing trellis-coded MPSK modulation to achieve minimum error probability performance on the Rician fading channel (see ibid., vol.36, no.9, p.1004-1012, Sep. 1988) is extended. It is demonstrated 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 optimization on the fading channel. Diversities larger than those achievable with conventional trellis codes having the same number of trellis states are now attainable, it is under these conditions that MTCM achieves its full potential. >
196 citations
Patent•
15 Sep 1988
TL;DR: In this article, the combination of trellis coding and MPSK signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel.
Abstract: The combination of trellis coding and 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.
154 citations
TL;DR: The performance of a trellis-coded multilevel differential phase-shift keying (DPSK) modulation over a mobile satellite channel characterized by additive white Gaussian noise (AWGN) and slow Rician fading is presented.
Abstract: The performance of a trellis-coded multilevel differential phase-shift keying (DPSK) modulation over a mobile satellite channel characterized by additive white Gaussian noise (AWGN) and slow Rician fading is presented. Both the optimum and Gaussian (suboptimum) decoding metrics are considered, with performance results given only for the latter. Analytical results (upper bounds on bit error rate) are obtained wherever possible and illustrated by several numerical examples. Also given are simulation results which are more indicative of the exact system performance. Comparisons with results previously obtained for coherent detection of the same coded modulations are presented. >
99 citations
01 Jun 1988
TL;DR: In this paper, the outage probability for multiple uncorrelated interferers in a Rayleigh fading environment is presented and the effect of several co-channel Rayleigh interferers on the service area of a cellular base station is examined.
Abstract: The calculation of outage probability is discussed in relation to cochannel interference problems inherent in mature cellular radio systems. Outage probability equations for coverage only and for single cochannel interferer situations are reviewed briefly, and examples of the application of these results to the estimation of the service area of a typical cellular base station are given. An analytical technique for multiple uncorrelated interferers in a Rayleigh fading environment is presented and the effect of several cochannel Rayleigh interferers on the service area of a cellular base station is examined.
84 citations
Patent•
18 Mar 1988TL;DR: In this article, a transmitter has an adaptive interleaver that sets an interleaving interval in accordance with the fading characteristic of a channel and transmits in another channel and the intereleaver duration is indicated by a synchronization signal and typically is 3 to 10 times the mean time between fades.
Abstract: A transmitter has an interleaver that sets an interleaving interval in accordance with the fading characteristic of a channel and transmits in another channel. The inteleaver duration is indicated by a synchronization signal and typically is 3 to 10 times the mean time between fades (decorrelation time). If the two channels substantially differ in frequency, a scaling factor can be used. A receiver has an adaptive deinterleaver that has a deinterleaving time in accordance with the synchronization signal occurring at the interleaving interval.
83 citations
TL;DR: A survey of techniques for measuring selective fading on line-of-sight (LOS) microwave links, particularly over a wide band, is presented, with the aim of assisting an experimenter in the choice of technique in a given experimental context.
Abstract: A survey is presented of techniques for measuring selective fading on line-of-sight (LOS) microwave links, particularly over a wide band. Classical pulse methods, including pulse compression, as well as the much used frequency-sweep approach are covered. Methods utilizing both frequency-hopping and direct-sequence spread-spectrum transmissions are also discussed. An analysis of this latter method (used by the US National Bureau of Standards and by the authors) is included and a relationship is established between the true channel transmittance and that estimated by this approach. The advantages and disadvantages of the various schemes are outlined with the aim of assisting an experimenter in the choice of technique in a given experimental context. >
78 citations
TL;DR: The performance of 8-PSK and 8-DPSK trellis codes is presented for a class of fast fading, land mobile satellite communication channels and optimality is found to be dependent on the presence of lognormal shadowing.
Abstract: The performance of 8-PSK and 8-DPSK trellis codes is presented for a class of fast fading, land mobile satellite communication channels. The fading model is Rician but, in addition, the line-of-sight path is subjected to a fast lognormal attenuation that represents tree shadowing. The fading parameters used in this study represent the degree of shadowing and are based on measured data. The primary application considered is for digital speech transmission and thus, bit error probabilities in the order of 10/sup -3/ are emphasized. Sensitivity of the bit error probability to amplitude fading, amplitude and phase fading, and decoding delay is presented. Performance is determined via digital computer simulation. Optimal four- and eight-state codes are determined and optimality is found to be dependent on the presence of lognormal shadowing. >
78 citations
TL;DR: In this paper, the applicability of the Rayleigh fading model for characterizing radar scattering from terrain is examined at 35 GHz for both backscattering and bistatic scattering.
Abstract: The applicability of the Rayleigh fading model for characterizing radar scattering from terrain is examined at 35 GHz for both backscattering and bistatic scattering. The model is found to be in excellent agreement with experimental observations for single-frequency observations of uniform targets such as asphalt and snow-covered ground. The use of frequency averaging to reduce signal fading variations was examined experimentally by sweeping the radar signal from 34-36 GHz in 401 steps. The results show that the formulation based on the Rayleigh model relating the reduction in signal fluctuation to the bandwidth used provides a reasonable estimate for the improvement provided by frequency averaging. >
72 citations
28 Nov 1988
TL;DR: The properties of a TDMA/TDD ( time-division multiple-access/time-division duplex) pico cellular cordless telephone system using decentralized dynamic channel allocation and handover are presented.
Abstract: The properties of a TDMA/TDD (time-division multiple-access/time-division duplex) pico cellular cordless telephone system using decentralized dynamic channel allocation and handover are presented. The system has 16 time-division time-duplex channels (slots) per carrier, each occupying 2 MHz. The TDMA frame is 16-ms long, and each slot has bits for synchronization, signaling and data. The data speed is suited for 32-kb/s speech codecs. Procedures have been developed for efficient and quick dynamic channel allocation and handover, using the fact that one single radio can simultaneously monitor or communicate on all 16 channels. Simulations for a specific six-storeyed building indicate that 16 channels can provide wireless communication for up to 30% of the telephones, and 32 channels for up to 100% of the telephones. Tests show that no time dispersion equalizers are needed, and that antenna diversity is effective against fading dips and time dispersion. >
Patent•
03 Nov 1988
TL;DR: In this paper, the authors proposed a method for producing time-varying trellis-coded phase-shift-keying modulations to facilitate carrier phase recovery when the signal has been exposed to extraneous phase variations and noise.
Abstract: TIME-VARYING TRELLIS-CODED MODULATION FORMATS WHICH ARE ROBUST IN CHANNELS WITH PHASE VARIATIONS Abstract There are described apparatus and methods for producing time-varying of trellis-coded modulations, specifically, time-varying trellis-coded phase-shift-keying, to facilitate carrier phase recovery when the signal has been exposed to extraneous phase variations and noise. Typically, eight-phase-shift-keying (8-PSK), with rate 2/3 convolutional coding, is followed on a repetitive basis by one or two formats of four-phase-shift-keying (4-PSK), which formats are chosen to ease phase synchronization and to conserve the use of bandwidth and not to worsen the bit error probability while reducing the probability of synchronization loss and the length of error bursts or "random walks". The variation of the modulation formats could be:1) 8-PSK (rate 2/3) followed by 4-PSK, 2) 8-PSK (rate 2/3) followed by 4-PSK (preferred format) and then 4-PSK (secondary format) or, 3) any of many other periodic formats of 8-PSK and 4-PSK sections.The use of this improved type of modulation is contemplated, for example, mobile radio links, particularly to counteract fading, or for optical fiber links to counteract other causes of signal degradation.
TL;DR: In this article, the authors demonstrate the usefulness of macroscopic selection diversity in combatting shadow fading produced by buildings and other large geographic features in the portable radio communication environment by analyzing 816 MHz residential propagation data.
Abstract: Analysis of 816 MHz residential propagation data is presented, demonstrating the usefulness of macroscopic selection diversity in combatting shadow fading produced by buildings and other large geographic features in the portable radio communication environment. Macroscopic diversity can reduce the link margin needed for 99% reliability by 10 dB. The analysis of these data indicates that log-normal shadow fading is partially correlated on the paths between a portable user and several surrounding ports. A two-component shadow-fading model duplicates this behavior. One log-normal term is identical for all paths from a given location and characterizes the propagation losses associated with the location. A second log-normal component is independent for each path and characterizes the remainder of the path to the port. The model fits the propagation data as well. A standard deviation of 8 dB for the path-specific term fits subsets of the available data well and is consistent with the standard deviation of shadow fading in the mobile (vehicular) communication environment. >
TL;DR: In this article, a single-scatterer multipath model was introduced to duplicate some of the measured data and to show the dependence of power variations on satellite elevation angle, and the maximum fade was found to increase by the logarithm of the number of branches.
Abstract: A propagation experiment is described in which a stratospheric balloon served as a transmitter platform at 870 and 1502 MHz in simulation of a land mobile satellite. A vehicle followed the drifting balloon along roads of western Texas and New Mexico, collecting at L-band amplitude and phase, and at UHF amplitude information only for elevation angles between 25 degrees and 45 degrees . The data obtained has been analyzed and is presented along with results from modeling of multipath scattering and roadside tree attenuation. The signal, with variations caused by multipath propagation and tree shadowing, was reduced by 3 dB at L-band and 2 dB at UHF for one percent of all locations. A median ratio of 3.9 was found between peak-to-peak phase (degrees) and power (dB) fluctuations. The ratio between L-band and UHF dB attenuation averages varied from 1.3 to 1.0 at fade levels from 6 to 23 dB. Optical sky brightness was measured and used to predict fade distribution with great accuracy. A single-scatterer multipath model is introduced. It is used to duplicate some of the measured data and to show the dependence of power variations on satellite elevation angle. Using Fresnel diffraction theory, the attenuation caused by a model tree was calculated to be near 10 dB and the maximum fade was found to increase by the logarithm of the number of branches. >
01 Feb 1988
TL;DR: In this paper, general expressions for the level crossing rate (LCR) and average fade duration (AFD) are obtained for several diversity combining schemes employing two-branch predetection reception of correlated Rayleigh fading signals.
Abstract: General expressions for the level crossing rate (LCR) and average fade duration (AFD) are obtained for several diversity combining schemes employing two-branch predetection reception of correlated Rayleigh fading signals. These expressions are obtained from joint and conditional probability density functions (PDFs) of the received signals, and lead to a unified treatment. This simplified method contrasts with the characteristic function approach used in previous investigations. Numerical results are presented for a space-diversity system using horizontally spaced antennas at a mobile station. It is shown that while the angle between the antenna axis and the direction of vehicle motion does not appear in the cumulative distribution function (CDF) of the combined output signal envelopes, it affects the LCR and AFD when the two fading signals are correlated. When the two antennas parallel with the direction of vehicle motion are used, the LCR can be reduced below the value obtainable from signals which fade independently. When the two antennas are perpendicular to the direction of vehicle motion, the AFD is loosely dependent on the antenna spacing and, provided the antenna spacing is not too small, is approximately half that for the no-diversity case.
TL;DR: A method of approximating the performance of systems using various data-pulse shapes and systems where it is difficult to obtain a complete channel characterization is developed, and examples of the most interesting cases are given.
Abstract: The performance of binary differential phase-shift keyed (DPSK) communications over frequency-selective wide-sense-stationary uncorrelated-scattering fading channels is considered. A technique is described for obtaining bounds on the average error probability for DPSK in terms of one or two parameters obtained from multipath spread or frequency-correlation-function channel measurements. A method of approximating the performance of systems using various data-pulse shapes and systems where it is difficult to obtain a complete channel characterization is developed. Numerical examples and comparisons of the most interesting cases are given. >
TL;DR: M-ary phase-shift keying and differential phase- shift keying (DPSK) on a slow fading Rayleigh channel without diversity is investigated and expressions for the distribution of the phase angle are obtained.
Abstract: M-ary phase-shift keying and differential phase-shift keying (DPSK) on a slow fading Rayleigh channel without diversity is investigated. Expressions for the distribution of the phase angle between a vector with Rayleigh amplitude distribution and a noiseless reference, and between two vectors both with Rayleigh amplitude distribution perturbed by Gaussian noise are obtained. >
15 Jun 1988
TL;DR: Wideband mobile radio channel characteristics were measured in mountainous terrain in Switzerland to define parameter settings for a frequency-selective fading simulator with which the performance of adaptive equalizers for the Pan-European digital land mobile radio system is to be tested.
Abstract: Wideband mobile radio channel characteristics were measured in mountainous terrain in Switzerland. Based on more than 76000 impulse responses, measured with two different experimental set-ups, statistical results were evaluated for mean excess delay, delay spread, delay interval, and correlation distance. This data was used to define parameter settings for a frequency-selective fading simulator with which the performance of adaptive equalizers for the Pan-European digital land mobile radio system is to be tested. >
TL;DR: The coding gain of a constraint-length-three, rate one-half convolutional code over a long clear-air atmospheric direct-detection optical communication channel using binary pulse-position modulation signalling is directly measured as a function of interleaving delay for both hard- and soft-decision Viterbi decoding.
Abstract: The coding gain of a constraint-length-three, rate one-half convolutional code over a long clear-air atmospheric direct-detection optical communication channel using binary pulse-position modulation signalling is directly measured as a function of interleaving delay for both hard- and soft-decision Viterbi decoding. Maximum coding gains theoretically possible for this code with perfect interleaving and physically unrealizable perfect-measurement decoding were about 7 dB under conditions of weak clear-air turbulence, and 11 dB at moderate turbulence levels. The time scale of the fading (memory) of the channel was directly measured to be tens to hundreds of milliseconds, depending on turbulence levels. Interleaving delays of 5 ms between transmission of the first and second channel bits output by the encoder yield coding gains within 1.5 dB of theoretical limits with soft-decision Viterbi decoding. Coding gains of 4-5 dB were observed with only 100 mu s of interleaving delay. Soft-decision Viterbi decoding always yielded 1-2 dB more coding gain than hard-decision Viterbi decoding. >
TL;DR: In this paper, propagation loss measurements taken in the Ottawa region in the 900-MHz frequency band are reported and discussed, and significant statistical parameters for a mobile radio channel, such as the mean, the standard deviation of the signals, the level crossing rates and the fading distance, are presented.
Abstract: Propagation loss measurements taken in the Ottawa region in the 900-MHz frequency band are reported and discussed. Significant statistical parameters for a mobile radio channel, such as the mean, the standard deviation of the signals, the level crossing rates and the fading distance, are presented. The signal is first transformed from a time scale to a distance scale; it is then separated into slow and rapid variation components, a low-pass filter with a cutoff point corresponding to 0.125 cycle per wavelength being used to estimate the slow variation component. The statistical analysis of the rapid variation is related to the Rice probability law and to a direct-component-to-multipath-component ratio. For the medium-density urban area under consideration, this ratio is shown to change from around 5 dB to around 9 dB as one moves from medium-density urban to the surrounding open areas. >
01 Jan 1988-Canadian Journal of Electrical and Computer Engineering-revue Canadienne De Genie Electrique Et Informatique
TL;DR: In this paper, the authors investigated block adaptation techniques by computer simulation for decision feedback equalization on a rapidly fading dispersive channel and found that block adaptation supplemented by linear interpolation of coefficients is an attractive alternative to more complex continuously adapting recursive least squares adaption algorithms.
Abstract: Block adaptation techniques are investigated by computer simulation for decision feedback equalization on a rapidly fading dispersive channel. Trade-offs between training sequence length and block length are found. Block adaptation supplemented by linear interpolation of coefficients is found to be an attractive alternative to more complex continuously-adapting recursive least squares adaption algorithms.
TL;DR: In this paper, the results of a series of canyon passes in the Boulder, Colorado region of the USA were derived from an experiment performed by a helicopter as the source platform with a mobile van containing the receiver and data-acquisition system.
Abstract: 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 USA. 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% and 5% 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 degrees . 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. >
01 Jun 1988
TL;DR: In this paper, the bit-error-rate (BER) performance of premodulation Gaussian filtered MSK using frequency detection (FD) in conjunction with 1-bit decision feedback equalisation (DFE) is theoretically investigated.
Abstract: The bit-error-rate (BER) performance of premodulation Gaussian filtered MSK (GMSK) using frequency detection (FD) in conjunction with 1 bit decision feedback equalisation (DFE) is theoretically investigated. The introduction of the premodulation filter causes severe intersymbol interference (ISI) in the waveform of the input to the FM modulator. DFE is used for reducing the ISI effect and therefore improving the BER performance. Applying the analysis to additive white Gaussian noise (AWGN) channels (no fading) shows that a 1-bit DFE attains about 8.5 dB Eb/N0 improvement at BER = 10−3for the premodulation filter bandwidth-time product BbT = 0.25 (typical for mobile radio applications) when the receiver predetection bandpass filter bandwidth-time product BT is optimised. It is shown that the effect of error propagation due to DFE is negligible and the exact BER can be well approximated by the BER that is obtained assuming the decision 1-bit prior is correct. The analysis is then extended to the case of Rayleigh fading channels. Both predetection and postdetection diversity reception are considered. When two-branch predetection maximal-ratio combining (MRC) is used, the 1-bit DFE attains about 6.3 dB Eb/N0 improvement at BER = 10−3for BbT = 0.25.
15 Jun 1988
TL;DR: A 9600-b/s 16-QAM data system is used together with the transparent tone-in-band (TTIB) reference processing technique and excellent performance under both static and fading conditions is observed.
Abstract: The transmission of high-speed data to and from a mobile terminal is considered to be far from simple. Practical results for one solution to the problem, namely reference-base channel sounding, are presented. A 9600-b/s 16-QAM data system is used together with the transparent tone-in-band (TTIB) reference processing technique. Excellent performance under both static and fading conditions is observed. >
15 Jun 1988
TL;DR: In this paper, the propagation and bit error rate (BER) measurements have been conducted within buildings using phase-locked oscillators at 60 GHz for both LOS (line-of-sight) and non-LOS conditions.
Abstract: The authors report propagation and bit error rate (BER) measurements that have been conducted within buildings using phase-locked oscillators at 60 GHz. The propagation measurements were conducted to study the envelope distribution, the power law with distance for different environments, the signal coverage, the received power spectrum, and edge diffraction effects. Measurements were also conducted to determine the BER performance in fading for FSK (frequency-shift keyed) modulation at 240 and 480 kb/s for both LOS (line-of-sight) and non-LOS conditions. >
01 Jan 1988-International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements
TL;DR: In this paper, the effect of fading corrections on the quality of dating plateaux is discussed. But the authors do not consider the long-term effects of short-term fading on the dating results.
TL;DR: A summary is presented of a series of critical experiments that led to recent discoveries of large improvement factors for digital radio performance by antenna pattern diversity, antenna angle diversity, frequency diversity, and space diversity that are larger than those predicted by the existing analog radio model.
Abstract: A summary is presented of a series of critical experiments that led to recent discoveries of large improvement factors for digital radio performance by antenna pattern diversity, antenna angle diversity, frequency diversity, and space diversity. The measured diversity improvement factors for digital radio against multipath dispersive fading are larger than those predicted by the existing analog radio model by at least one order of magnitude. Applications of these findings will lead to substantial savings in the cost for diversity protections for digital radio routes. These discoveries stimulated the development of new models of diversity improvement factors for digital radio and the development of the DRDIV computer program for engineering digital radio routes. Background information is given on multipath fading and diversity concepts, and a glossary of terms is included. >
TL;DR: In this article, the authors show that polarisation-induced signal fading, caused by random polarisation fluctuations in an interferometric sensor, can be overcome by interrogating the sensor at three pre-defined input SOPs.
Abstract: Results of theoretical and experimental studies are presented, which show that polarisation-induced signal fading, caused by random polarisation fluctuations in an interferometric sensor, can be overcome by interrogating the sensor at three pre-defined input SOPs.
01 Jan 1988-International Journal of Radiation Applications and Instrumentation. Part D. Nuclear Tracks and Radiation Measurements
TL;DR: In this paper, Hasan et al. showed that anomalous fading is only exhibited by those samples in which the feldspar is in the low-temperature form and further suggested that the fading proceeded via tunnelling.
TL;DR: Large and rapid timing fluctuations of eye pattern due to severe delay distortion of the multipath channel was found to be the most dominant source of error.
Abstract: The so-called irreducible error due to frequency-selective fading is known to have a serious effect on mobile radio communication systems. Thus, the analysis of such errors is a prerequisite for making high-speed digital signal transmission over a fading channel feasible. The authors attempted to elucidate the physical mechanisms causing such errors using laboratory measurements of microscopic bit error rate. The results clarified some sources of burst errors in a multipath fading channel. In particular, large and rapid timing fluctuations of eye pattern due to severe delay distortion of the multipath channel was found to be the most dominant source of error. >