Showing papers on "Fading distribution published in 1989"

Bandwidth efficient coding for fading channels: code construction and performance analysis

Abstract: The authors apply a general method of bounding the event error probability of TCM (trellis-coded modulation) schemes to fading channels and use the effective length and the minimum-squared-product distance to replace the minimum-free-squared-Euclidean distance as code design parameters for Rayleigh and Rician fading channels with a substantial multipath component. They present 8-PSK (phase-shift-keying) trellis codes specifically constructed for fading channels that outperform equivalent codes designed for the AWGN (additive white Gaussian noise) channel when v>or=5. For quasiregular trellis codes there exists an efficient algorithm for evaluating event error probability, and numerical results which demonstrate the importance of the effective length as a code design parameter for fading channels with or without side information have been obtained. This is consistent with the case for binary signaling, where the Hamming distance remains the best code design parameter for fading channels. The authors show that the use of Reed-Solomon block codes with expanded signal sets becomes interesting only for large value of E/sub s//N/sub 0/, where they begin to outperform trellis codes. >

TCMP-a modulation and coding strategy for Rician fading channels

Abstract: The authors describe TCMP, a novel modulation strategy for Rician fading channels that multiplexes a time domain pilot sequence with trellis-coded data to permit coherent detection. This technique is shown to provide remarkably robust performance in the presence of fading. It is also shown that, when choosing trellis codes for fading channels, time diversity is of greater important than asymptotic coding gain. The motivation for studying this strategy is to find signaling schemes for transmitting data at a 4.8 kb/s rate over a mobile satellite channel with 5-kHz channel spacing. >

Rayleigh fading compensation method for 16QAM in digital land mobile radio channels

Abstract: The authors propose a novel Rayleigh fading compensation method for 16 quadrature amplitude modulation (16QAM). The optimum parameters for 16QAM with a transmission rate of 16 k symbol/s, the BER (bit error rate) performance, and the interference performance are determined by computer simulation. It is shown that second-order interpolation is suitable for the fading compensation method. In the case of 16 k-symbol/s transmission, the optimum frame length is 16 symbols. The degradation due to the proposed fading compensation method is about 2 dB. The BER performance under Rayleigh fading environments at f/sub d/ >

Performance of trellis coded MDPSK on fast fading channels

Abstract: The performance of trellis-coded multiple differential phase-shift keying (MDPSK) over fast fading channels characteristic of a mobile environment with high vehicle speeds is presented. The envelope of the fading process is modeled as a Rician distribution, with parameter K denoting the ratio of power in the specular plus direct components to that in the diffuse component. On the basis of this model, upper bounds on the bit error probability are derived, and the sensitivity of the performance to an increase in the speed of the mobile vehicle is demonstrated as a function of K. In particular, it has been observed that as K decreases, the performance degradation due to the phase variation increases. All of the results are obtained from a combination of analysis and computer simulation, the latter being used to verify the former. >

Slotted ALOHA radio networks with PSK modulation in Rayleigh fading channels

Abstract: The throughput of a local slotted ALOHA radio network using PSK modulation over Raylcigh fading channels is analysed. The capture effect is related to the modulation technique, signal/noise ratio of the received signal, distribution of terminals in the area and the length of the transmitted packets. Owing to the capture effect a maximum throughput of 0.75, rather than 0.36 with no capture, is predicted. This improved performance is observed in the slow fading channels with a very high signal/noise ratio.

Performance of binary FSK communications over frequency-selective Rayleigh fading channels

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. >

Measured performance of 4-QAM with 2-branch selection diversity in frequency-selective fading using only one receiver

Abstract: The authors present the measured performance of a 500 kb/s 4-QAM (quadrature amplitude modulation) radio link with two-branch selection diversity using only one receiver subjected to hardware-simulated slow frequency-selective Rayleigh fading. The single coherent receiver input is switched between two uncorrelated Rayleigh-fading signals and the one with higher power is selected. The experimental radio link uses time-division multiplexing with a coherent receiver. Since the down-link transmitter is always on the received signal measurements and selection can be performed just before the reception of the user's data burst. The measured performance compares favorably with computer simulation. The effect of delay between measurement/selection and the actual data burst demodulation is also presented. It is found from both experiment and computer simulation that selection diversity is effective in reducing the bit-error-rate floor caused by frequency-selective fading. As a result, a higher data rate can be supported by a multipath fading channel without using adaptive equalization. Thus, a low-complexity hardware design incorporating selection diversity is feasible for a portable radio communication system. >

Equal gain diversity improvement in fast frequency hopping spread spectrum multiple-access (FFH-SSMA) communications over Rayleigh fading channels

Abstract: The authors present the performance analysis of an FFH-SSMA system with a binary frequency-shift keying modulation scheme and noncoherent demodulation, operating in a combined environment of Rayleigh selective fading, other users interference, and additive white Gaussian noise. Improvement due to the use of equal gain diversity (EGD) is studied in terms of bit-error rate (BER). Expressions of the BER are evaluated when a maximum-likelihood decision criterion is used to show the advantages of the use of frequency hopping selective Rayleigh fading channels. Results show the equivalence between frequency hopping and direct-sequence (DS) modulation in combating multipath fading. The performance, in terms of irreducible error probability, of the system under study and that of the DS-CPSK when using EGD are not significantly different. >

Effects of Rayleigh fading on packet radio channels with shadowing

Abstract: The combined effect of Rayleigh fading and log-normal shadowing on slotted-Aloha data communications in the mobile radio channel is studied. The joint presence of these two propagation effects is shown to yield higher channel throughput than with either effect alone. The results are useful for packet radio systems with contention-limited performance. >

Analytical performance bounds on average bit error probability for trellis coded PSK transmitted over fading channels

Abstract: Analytical performance bounds are presented for trellis coded phase-shift keying (PSK) transmitted over general fading channels. In particular, log-normal shadowing of the received signal over a mobile satellite channel is considered, and analytical performance bounds for encoder structures with four and eight states are provided. previously published results for Rayleigh and Rician fading environments are extended to encoder structures with four states, and in the limiting case of Rayleigh fading, analytical lower performance bounds are included. Line-of-sight shadowing, a situation that occurs in mobile satellite applications, is included in the Rician case. Monte-Carlo simulation results are also presented and indicate that the generalized transfer function bounding techniques are somewhat weak for general fading environments. >

Analysis of a modified Suzuki fading channel model

Abstract: Suzuki processes can be considered to be models for the random fluctuations of the envelope of the received signal in land-mobile radio systems. The Suzuki processes are obtained by combining stationary normal random processes assumed to be statistically independent. Often the assumption of statistical independence does not meet the real conditions in multipath wave propagation. Therefore, modified Suzuki processes with cross-correlation between the normal processes of the Rayleigh part have been introduced. In this study modified Suzuki processes have been investigated by computer simulation. In particular, the distribution of the fading time-intervals of the modified Suzuki processes has been analyzed. Typical results are presented in normalized form. >

Dispersive microwave fading and lower atmospheric structure: An observational study

Abstract: Simultaneous measurements of microwave fading and lower atmospheric conditions were carried out in Georgia in 1986 as a part of the continuing effort to study the line-of-sight digital radio performance. Acoustic sounding was a principal means of exploring the mechanism that causes dispersive fading. It was found that dispersive multipath fading occurs during nights with strong radiation inversion accompanied by a subsiding air mass. Subsidence inversion causes dispersion, and the origin of the air mass affects the mean received power level under multipath propagation conditions. When the height of the nocturnal boundary layer coincides with the height of the ground-based radiation inversion layer and is at 100–150 m, fading is heavy, active, and dispersive for a 57-km path with both transmitting and receiving antennae at 60 m above grade. Case studies of the significant episodes are presented, and the statistics of the different types of fading associated with the types of meteorological conditions are summarized for the 5-month study period.

Trellis-coded DPSK for mobile fading channels

Abstract: The error performances of the trellis-coded 8DPSK signals in Rayleigh fading channels are presented. The interrelationships between the bit error rate, the fade rate, the interleaving depth, and the decision depth of the decoder are examined. It is found that for fade rates between 0.01 and 0.03, one can safely choose an interleaving depth of 20 symbols and an interleaving span of 10 symbols to achieve about 10-dB fade margin at a 10/sup -3/ bit error rate. It is also found that the differential detection of PSK breaks down for fade rates greater than or equal to 0.06, due to the severe differential phase jitter introduced by the fading process. >

High bit-rate digital mobile radio transmission with a decision feedback equalizer

Abstract: High bit-rate digital mobile radio transmission performance in a selective fading environment is discussed. Analysis and computer simulation show the amount of performance improvement by utilizing a preset-type decision feedback equalizer. The equalizer adopts the recursive least-squares (RLS) algorithm for tap coefficient determination. The performance is approximately analyzed by using the zero-forcing criterion. This criterion is separately applied to the minimum and nonminimum phase conditions of the two-wave selective fading model. The improved performance is almost equivalent to that of two-branch selection diversity reception. Finally, hardware implementations of a dynamic selective fading simulator and a decision feedback equalizer are demonstrated. >

Performance of M-ary QAM schemes in a

Abstract: A simple, statistical model to evaluate the performance of M-ary QAM schemes in a line-of-sight multipath fading channel is proposed. The model is based on assumptions about the channel which are often encountered in practice. It leads to the postulation of an exponential-type probability density describing the effects of multipath fading on M-ary QAM schemes, whereby closed-form expressions for the average error probability can be derived. Illustrative results for 16-, 64-, and 256-QAM signals are presented. >

Performance of optimum threshold incoherent diversity in non-Gaussian noise and fading

Abstract: The optimum diversity receiver in arbitrary non-Gaussian noise and Rayleigh fading statistics is derived for binary narrowband correlated symmetric incoherent signalling in the threshold regime, i.e. for small signals and independent noise samples. Its performance is obtained in terms of the error probability Pe for various values of a specific signal crosscorrelation coefficient ρ and multichannel order, when fading in the channel is assumed to be slow, nonselective Rician or Rayleigh. This expression for Pe is shown to be a generalisation of a recent performance result in optimum threshold detection of incoherent narrowband signals in narrowband non-Gaussian noise. It is graphically demonstrated that the best signalling in Rayleigh fading is orthogonal (ρ = 0) and that performance significantly improves as the diversity order increases for fixed sample size N(≥≥ 1) and second-order noise statistic L(2)(≥ 1). A novel by-product of the analysis is the error probability expression of the single-channel threshold incoherent receiver with Rician fading, which is used to graphically demonstrate that the signalling scheme which optimises, i.e. gives the minimum possible value of, Pe is also orthogonal.

A connection between Rayleigh fading and worst-case partial band interference

Abstract: For FH/BFSK (frequency hopping/binary frequency-shift keying) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases in which the signal is either nonfading or Rayleigh fading In the present work the author fills in the region between these extremes by considering the general Nakagami-m fading model Here the worst-case partial-band Gaussian interference results are given by a one-parameter family, which for m to infinity gives the Viterbi-Jacobs (1975) nonfading result and for m=1 gives the Rayleigh fading result In the latter case a broadband interference strategy is optimal Thus the Nakagami-m solutions provide a smooth one-parameter bridge between the Viterbi-Jacobs channel and the Rayleigh fading channel The results show that the worst-case interference fraction rho increases as the fading variance increases, up to Rayleigh fading Any fading less severe than Rayleigh, however slight the departure from Rayleigh, requires a partial-band strategy for sufficiently large E/sub b//N/sub I/ >

Transparent tone-in-band (TTIB) aided GMSK/MSK modem systems

Abstract: The authors propose a scheme which employs BBC (binary block code) coding to allow carrier pilot insertion in GMSK/MSK (Gaussian minimum-shift keying/minimum-shift keying) modems for tone calibration and coherent detection. They analyze the performance of the BBC-coded GMSK/MSK modem and derive a closed-form expression for its performance under Rayleigh fading. The effect of carrier phase noise on the modem's performance in a nonfading channel is investigated. it is found that, in the absence of fading, GMSK signalling with small bandwidth-time product (BT) value is more sensitive to carrier phase jitter than that with larger BT. The authors also investigated the performance of a BBC-coded GMSK modem with tone calibration over a Rayleigh fading channel. It is found that the modem is capable of delivering good performance in a Rayleigh fading environment where the more conventional coherent detection would cease to be practical due to its relatively high error floor. >

A tone-aided dual vestigial sideband system for digital communications on fading channels

Abstract: A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application. >

Performance of m-ary qam schemes in a line-of-sight multipath fading channel

Abstract: A simple, statistical model to evaluate th? performance of M-ary QAM schemes in a line-of-sight multipath fading channel is proposed. The model is based upon assumptions about the channel which are often encountered in practice. It leads to the postulation of an exponential-type probability density describing the effects of multipath fading on M-ary QAM schemes, whereby closed form expressions for the average error probability can be derived. Illustrative results for 16-, 64-, and 256-QAM signals are presented.

Trellis code modulation on a Rayleigh fading channel

Abstract: The performance of trellis codes on a Rayleigh fading channel is presented. Performance of good Gaussian channel codes is assessed by means of a simulation. Two four-state trellis-coded modulated (TCM) codes for Rayleigh fading channels, which perform significantly better than the best additive white Gaussian noise (AWGN) channel codes previously published, are presented. The best four-state code achieves a 5.8-dB gain at an error rate of 10/sup -2/ as opposed to the 3.7-dB gain achieved by the Gaussian channel code. >

Space diversity improvement factors for overwater path in New Zealand

Abstract: Space diversity improvement factors for an overwater path in New Zealand are derived from field trial data and compared with predicted results. Improvement factors of about 50 were measured for single frequency fading, and those of about 30 were achieved for dispersive fading.

The effect of fading in mobile ALOHA radio communications

Abstract: The application of unslotted ALOHA to mobile communication systems is studied. In such systems, the terminal-to-base channel can undergo various types of fade such as shadowing (log-normal fading) or unshadowed multipath reflections with a direct component (Rician fading), or the near/far effect. It is shown that fading may give rise to a capture effect that improves the ALOHA throughput. >

Packet communications in a multipath fading mobile radio network

Abstract: The authors present ARQ (automatic repeat request) strategies for packet communications in a fading mobile radio network. A queuing-theory approach is used to analyze various data-link-control protocols between a mobile node and a base station. Three fading models are considered for the mobile channel, namely, the slow Rayleigh fading model, the Rayleigh/Rayleigh fading model, and the threshold model. Numerical results are also presented for the queuing delay of packets. >

Performance analysis of non-orthogonal MT-FSK systems with degraded branch statistics

Abstract: The authors analyze the performance degradation of a MT-FSK (multiple-tone frequency-shift keying) scheme based on Steiner designs on a Rayleigh fading channel with degraded branches Two cases are shown, a fading channel with correlated branches and a fading channel with unequal average signal-to-noise ratio per branch These two impairments are shown to decrease the effective diversity; however, improvements are still observed over conventional MFSK >

Theoretical analysis of error sequence characteristics in digital land mobile radio channels

Abstract: It is important to clarify error sequence characteristics in digital land mobile radio channels with memory for accurate performance evaluation of error control schemes such as error correction coding. This research deals with the theoretical analysis of error sequence characteristics in digital land mobile radio channels with very slow Rayleigh fading. First, the digital channel model is studied on the basis of the error generation mechanism in digital land mobile radio channels and the analytical model is simplified, assuming that the envelope fading effect is dominant and fading rate is very small. The quasi-static approximation method is applied to simplify analysis. Numerical expressions of gap probability and joint gap probability, which are important in making the mathematical model of error process, are derived for binary PSK under the Rayleigh fading environment. The calculated result from the anlytical model and the experimental measured result from the laboratory experiment are shown to agree well when the effect of fading variation is small.

Estimating service reliability in multiple interferer mobile radio systems

Abstract: Outage probability calculations are discussed as a method for estimating the reliability of reception in multiple interferer mobile radio systems in which the received signals suffer both 'Rayleigh fading' and 'lognormal shadowing'. Such calculations are particularly relevant to the design of cellular mobile radio systems. The use of selection diversity to improve the service reliability is also considered.

Statistical characteristics of channel parameter for HF communication circuit

Abstract: The design optimization of digital communication systems, using selective fading channels (such as HF and troposcatter), requires some knowledge of the statistics of the fading parameters of these media. The test results are presented of the phase jitter, signal-to-noise ratio, multipath spread and Doppler spread measurements on several approximate 8000 km HF digital communication circuits from 1975 to 1978, using the continuous wave and Bello's real-envelope methods respectively. From these test results, two real-time channel evaluation techniques, the multitone envelope method and multitone complex envelope method, for real-time frequency selection systems of ionospheric radio circuits are presented.< >

Combined frequency/phase modulation with multiple trellis coding

Abstract: The concept of multiple trellis-coded modulation (MTCM) is extended to frequency- and phase-modulated (FPM) signal sets. A significant improvement is observed in the performance for AWGN and fading channels when compared to MTCM of MPSK signal sets. For values of the fading parameter used, the performance on the fading channel is guided by the length and distance of the shortest error event path. >