Showing papers on "Fading distribution published in 1988"
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: 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. >
52 citations
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.
39 citations
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. >
38 citations
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. >
27 citations
28 Nov 1988
TL;DR: The authors present the measured average bit error and block error ratio performance of a coherent burst time-division multiple-access radio link in a simulated flat Rayleigh fading environment using a unique technique for implementing two-branch selection diversity.
Abstract: The authors present the measured average bit error and block error ratio performance of a coherent burst time-division multiple-access radio link in a simulated flat Rayleigh fading environment using a unique technique for implementing two-branch selection diversity The link consists of a 500-kb/s quadrature amplitude modulation burst transmitter and a coherent receiver with a fast carrier recovery circuit The receiver is switched between two signals which are corrupted by uncorrelated Rayleigh fading If the transmitter is on before the actual data burst, received signal measurement and selection can be performed just before the reception of a data burst This way, when data is to be demodulated, the receiver is already switched to the branch with the higher power With this technique, the performance of selection diversity is achieved with only one receiver chain Experimental results are presented showing link performance as functions of Rayleigh fading rate and the time delay between signal measurement/diversity selection and the actual data burst >
24 citations
15 Jun 1988
TL;DR: An instrument which can be used to simulate 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 which can be used to simulate the multipath fading associated with VHF/UHF mobile radio channels is described. The implementation is considered simple, flexible, and economical and allows the fading waveforms to be repeated exactly. Level crossing rate and probability distribution function measurements over a wide range of Doppler frequencies indicate good agreement with theoretical results. >
23 citations
DOI•
01 Feb 1988TL;DR: In this article, a modified two-level scheme for coarse code acquisition of spread-spectrum signals in a fading environment is considered, where the passive correlators are matched to short sync prefixes, which areinterspersed in the incoming signal.
Abstract: A modified two-level scheme for coarse code acquisition of spread-spectrum signals in a fading environment is considered. The scheme uses a bank of passive correlators followed by a bank of active correlators. The passive correlators are matched to short sync prefixes, which areinterspersed in the incoming signal. The passive devices correlate over sliding windows (in time), providing a rapid search capability. Threshold exceedances of the passive correlators areused to initiate active correlation over longer time intervals so that high reliability of decision is obtained. The multiple sync prefixes reduce the probability of missing the signal in a fading environment. An analytical model based on queueing and detection theory results is developed, and optimisation of the scheme is treated. A Gilbert model is used to characterise the signal fading on the channel. The performance in the presence of background noise with noisejamming is analysed. Theoretical performance curves and a discussion of the results are also presented.
18 citations
TL;DR: In this paper, the effect of fading on antijam (AJ) performance was considered when the envelopes of both the desired signal and the jamming signal fade with a Nakagami distribution.
Abstract: The effect of fading on antijam (AJ) performance is considered when the envelopes of both the desired signal and the jamming signal fade with a Nakagami distribution. Two cases are analysed for conventional systems. In the first case, the fading is assumed to be slow compared with the duration of the message. In the second case, the fading is assumed to be slow compared with the symbol duration but fast compared with the message duration. For both cases numerical results are also included.
14 citations
12 Jun 1988
TL;DR: It is found that coherent detection is superior to differential detection by at least 2.4 dB, which converts to about 30% improvement of spectral efficiency in a two-dimensional frequency reuse system with a fourth-power propagation exponent.
Abstract: The advantage of coherent detection over differential detection for both BPSK (binary phase-shift keying), and QPSK (quaternary phase-shift keying) in a multipath radio channel with either frequency-flat or frequency-selective fading is evaluated. The difference in receiver sensitivity is compared on the basis of three criteria: (1) bit-error rate (VER) averaged over fading samples, (2) BER distribution, and (3) distribution of block error rate. For a quasistatic fading channel, (2) and (3) provide a more meaningful comparison. Both analytical expressions and simulation are used in the comparison. The difference between differential detection of 2- and 4-level PSK is taken into consideration, as is the difference between pure coherent detection and coherent detection that uses differential encoding to resolve phase ambiguity. Both selection diversity and channel coding are considered as techniques for mitigating fading effects. It is found that coherent detection is superior to differential detection by at least 2.4 dB, which converts to about 30% improvement of spectral efficiency in a two-dimensional frequency reuse system with a fourth-power propagation exponent. >
9 citations
TL;DR: A multipath fading simulator with a number of narrowband channels with controllable mutual correlation is described, which is possible to test the influence of joint fading statistics of mutually correlated channels on a mobile data communication link with frequency diversity.
Abstract: A multipath fading simulator with a number of narrowband channels with controllable mutual correlation is described. With this simulator it is possible to test the influence of joint fading statistics of mutually correlated channels on a mobile data communication link with frequency diversity.
12 Jun 1988
TL;DR: For the Rayleigh fading model, it is found that, when the automatic gain control of the receiver is off, the received signal fades as in real-life transmission, as expected.
Abstract: Several fading models, including the general fading model, the Rayleigh fading model, and the simple three-path fading model are simulated to study the effect of fading in radio communication links. These models are implemented in hardware using computer control. The effect of fading is demonstrated using speech as the test signal. For the Rayleigh fading model, it is found that, when the automatic gain control (AGC) of the receiver is off, the received signal fades as in real-life transmission. When the AGC is on, the effect of fading is not noticeable most of the times but the noise level goes up when fading occurs, as expected. When the fading is severe, it is found that AGC cannot totally compensate for the fading; this is also expected. Other models are tested in a similar manner and yield expected results. >
TL;DR: A frequency-hopped multilevel frequency-shift-keying (FH-MFSK) system has been proposed for digital mobile radio communications and the performance of the system is evaluated by studying average probability of error caused by transmission impairments.
Abstract: A frequency-hopped multilevel frequency-shift-keying (FH-MFSK) system has been proposed for digital mobile radio communications. The performance of the system is evaluated by studying average probability of error caused by transmission impairments. The degradation in performance due to Rayleigh fading and log-normal shadowing environments is determined. With perfect transmission, where the degradation in the system performance is due to mutual interference between users only, the system can accommodate up to 209 simultaneous users at an average bit error rate of 10/sup -3/. The system capacity decreases to 110 users as a result of additive white Gaussian noise (AWGN), mutual interference, frequency-selective Rayleigh fading, and log-normal shadowing with normalized area mean of 20 dB and standard deviation of 6 dB. >
12 Jun 1988
TL;DR: A digital carrier recovery structure which allows coherent detection on frequency-nonselective fading channels is presented and it is shown that the structure is superior to a phase-locked loop and well suited for a fully digital realization.
Abstract: A digital carrier recovery structure which allows coherent detection on frequency-nonselective fading channels is presented. The synchronizer estimates the multiplicative distortion introduced by the channel. It is shown that the structure is superior to a phase-locked loop and is well suited for a fully digital realization. A detailed synchronizer design and simulation results are presented for a land-mobile radio channel. This includes a novel scheme for a fully digital frequency offset estimation and correction. >
15 Jun 1988
TL;DR: The performance of an adaptive multipath diversity receiver, operating in a quasi-static frequency selective Rayleigh fading channel, is considered and probability-of-error expressions are presented for channels with uniform and nonuniform delay cross power spectra.
Abstract: The performance of an adaptive multipath diversity receiver, operating in a quasi-static frequency selective Rayleigh fading channel, is considered. Phase coded direct sequence spread spectrum signaling is used. The receiver formulation is presented as an extension of a previously derived result by the authors (1988). Probability-of-error expressions are presented for channels with uniform and nonuniform delay cross power spectra. The performance with multiuser interference is considered by invoking the Gaussian assumption. The validity of this assumption is verified through simulation. >
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TL;DR: The authors investigate the throughput of unslotted ALOHA with power-capture capability and finds the distribution of the maximum number of interfacing packets can be found from a set of appropriate binary numbers.
Abstract: The authors investigate the throughput of unslotted ALOHA with power-capture capability. Two types of capture effects are considered, namely created capture and natural capture. The capture probability of a tagged packet is a function of the maximum number of interfering packets that form a stochastic process during the transmission time of a tagged packet. The distribution of the maximum number of interfacing packets can be found from a set of appropriate binary numbers. Four cases are analyzed: ALOHA with two random power levels, ALOHA in a uniform Rayleigh fading channel, ALOHA with two random power levels in a uniform Rayleigh fading channel, and ALOHA-CDMA in a uniform Rayleigh fading channel. >
12 Jun 1988
TL;DR: A simulation technique for evaluating the degradation in performance due to the cochannel in interference and adjacent channel interference over Rayleigh fading channels is introduced and the improvement in performance that can be obtained by using space diversity with different numbers of branches is introduced.
Abstract: Coherent detection of signals transmitted over a slow Rayleigh fading channel with additive white Gaussian noise with interference is considered. A simulation technique for evaluating the degradation in performance due to the cochannel in interference and adjacent channel interference over Rayleigh fading channels is introduced and the improvement in performance that can be obtained by using space diversity with different numbers of branches. The use of maximum ratio diversity combiner as an alternative to improve the error probability is also considered using a modified Monte Carlo simulation technique. >
11 Apr 1988
TL;DR: The authors deal with the simulation and the analysis of a Suzuki process, which can be considered to be a model for the random fluctuations of the envelope of the received signal in land mobile radio transmission systems.
Abstract: The authors deal with the simulation and the analysis of a Suzuki process. This stochastic process can be considered to be a model for the random fluctuations of the envelope of the received signal in land mobile radio transmission systems. Digital speech transmission over such a channel is disturbed by these random fluctuations, in particular during the fading periods. Therefore, the knowledge of the frequency of the fades and the distribution of their duration is of special interest. The simulation system is used to determine these quantities experimentally. Recent results are presented, and the average number of fades is derived theoretically. >
23 Oct 1988
TL;DR: An algorithm based on the modification of the recursive modified Gram-Schmidt algorithm is presented, which utilizes the low-rank property of the input autocorrection matrix to reduce the misadjustment error of fractionally spaced equalizers (FSEs), and thus, equivalently, improve the tracking.
Abstract: The authors investigate various techniques for improving the performance of fractionally spaced decision-feedback equalizers (FSDFEs) when they are applied to HF fading channels. Because of the time-varying characteristics of these channels, a rapid tracking capability of the equalizer is essential. The authors focus on various techniques which reduce the misadjustment error of fractionally spaced equalizers (FSEs), and thus, equivalently, improve the tracking. An algorithm based on the modification of the recursive modified Gram-Schmidt algorithm is presented, which utilizes the low-rank property of the input autocorrection matrix to reduce the misadjustment error by about 2.5 dB when an optimum sampling phase is used. FSEs with smaller sampling rates also prove to be beneficial in improving the performance if the transmitted signal has a smaller excess bandwidth. The results are then extended to the FSDFE. >
28 Nov 1988
TL;DR: A model of space diversity improvement for line-of-sight microwave radio against outage during multipath fading caused by thermal noise is proposed and predicts the existence of an optimum vertical separation to achieve the maximum DIF.
Abstract: Proposes a model of space diversity improvement for line-of-sight microwave radio against outage during multipath fading caused by thermal noise. The diversity improvement factor (DIF) predicted by this three-day model agrees very well with the data measured from the 26-mile Atlanta-Palmetto path. The model predicts the existence of an optimum vertical separation to achieve the maximum DIF, in agreement with the measured field data. The DIF is calculated for the 4-, 6-, and 11-GHz frequency bands. >
15 Jun 1988
TL;DR: It is shown that energy receivers are a good alternative to optimum receivers for channels with high speed factor and further gain can be obtained by passing channel erasure information to the decoder.
Abstract: Performances of energy receivers on mobile channels that are modeled as fading dispersive are investigated. It is shown that energy receivers are a good alternative to optimum receivers for channels with high speed factor. Improvement using Reed-Solomon codes is examined. Further gain, especially at low SNR, can be obtained by passing channel erasure information to the decoder. >
28 Nov 1988
TL;DR: The authors present the results of a 16-QAM (quadrature amplitude modulation) cochannel field trial on a 51-km path in the UK using a reference channel, two cofrequency cross-polarized channels together with two adjacent channels 40 MHz apart, and the results do not indicate any major problems with 16- QAM co-channel operation.
Abstract: The authors present the results of a 16-QAM (quadrature amplitude modulation) cochannel field trial on a 51-km path in the UK using a reference channel, two cofrequency cross-polarized channels together with two adjacent channels 40 MHz apart. The measured transmission quality compares well with the results of the performances prediction model DRUMBEAT, which takes into account fading, interference, and the system signature. An opportunity to study cochannel operation under conditions of severe obstruction occurred in a long-lasting event of unusual subrefraction (k varying down to 0.5). Statistical evaluations of the degrading effects (e.g. cross-polar discrimination) are given. During the six-month measurement period, the results do not indicate any major problems with 16-QAM co-channel operation. >
28 Nov 1988
TL;DR: In this paper, the transmission of 8-bit mu-law PCM (pulse-code-modulated) signals using M-level weighted quadrature amplitude modulation (WQAM) over Gaussian and Rayleigh fading channels is examined.
Abstract: Transmission of 8-bit mu -law PCM (pulse-code-modulated) signals using M-level weighted quadrature amplitude modulation (WQAM), M=16, 64 and 256, over Gaussian and Rayleigh fading channels is examined. The weighting process modifies the positions of the QAM constellation points so that the overall average distortion in the recovered information-bearing source signal is reduced. The PCM bits are mapped onto the WQAM points so that the most significant bits have a lower probability of being in error than the least significant bits. The WQAM systems have been optimized both for the same average and peak signal energy per transmitted symbol as for unweighted QAM. Theoretical and simulation results using speech indicate that 16-level and 256-level WQAM have gains of up to 3 and 5 dB, respectively, over unweighted QAM for the Gaussian channel. The gains due to weighting for 16-level QAM operating over an ideal slow Rayleigh fading channel are up to 5 dB. >
23 Oct 1988
TL;DR: The author presents an approximate formula for MFSK (M-ary frequency shift-keying) symbol error probability in nonfrequency selective fast Rayleigh fading, referring to channel decorrelation times on the order of a symbol duration.
Abstract: The author presents an approximate formula for MFSK (M-ary frequency shift-keying) symbol error probability in nonfrequency selective fast Rayleigh fading. Here, fast fading refers to channel decorrelation times on the order of a symbol duration. At the receiver, fast fading produces attenuation in the output of the filter matched to the transmitted signal and 'crosstalk' in the other filter outputs. These effects are studied quantitatively and lead to approximations which enable a simple formula for symbol error probability to be derived. The accuracy of this formula is determined by computer simulation. >
Proceedings Article•
01 Jan 1988
28 Nov 1988
TL;DR: The impact of the near-far problem on power differentials is studied, and improvements due to the use of soft-limiters at the receiver are shown as functions of the many parameters involved.
Abstract: An exact analysis is performed to find the probability of bit error for a multiple-access system using frequency-hopping multilevel frequency-shift-keying signals (FH/MFSK) in Rayleigh fading Inherent frequency diversity is utilized at the receiver The impact of the near-far problem on power differentials is studied, and improvements due to the use of soft-limiters at the receiver are shown as functions of the many parameters involved >
12 Jun 1988
TL;DR: Experimental results are presented for the multipath channel characterization of a 40 MHz wide RF channel in the 4 GHz band and the effects of bandwidth on in-band power-difference are described.
Abstract: Experimental results are presented for the multipath channel characterization of a 40 MHz wide RF channel in the 4 GHz band. The 40 MHz wide test signal is transmitted over a 52 km hop. The space diversity receiver combines the test signal using a continuous phase maximum power technique. Channel responses are measured on the main antenna, the diversity antenna, and the combined channel. The effects of bandwidth on in-band power-difference are also described. >
28 Nov 1988
TL;DR: The results show that with enough protection, such as frequency diversity and space diversity at the appropriate places, the 64-QAM digital radio system will meet the multipath fading outage requirements on virtually all hops for a 6-GHz short-haul network.
Abstract: A statistical model to evaluate the feasibility of installing high-capacity digital radios in the 6-GHz short-haul microwave network is presented. Improvement in network performance due to installation of high-capacity radios can be determined by estimating the number of acceptable hops that meet system requirements for multipath fading outage. Cases with and without interference are examined. The results show that with enough protection, such as frequency diversity and space diversity at the appropriate places, the 64-QAM (quadrature amplitude modulation) digital radio system will meet the multipath fading outage requirements on virtually all hops for a 6-GHz short-haul network. >
TL;DR: The results show that the FM signal with a modulation index of 1 or greater, outperforms an AM signal under identical fading conditions.
Abstract: A simple formula for the baseband signal-to-noise ratio of an FM signal under Rayleigh fading is derived. The formula automatically includes the noise component due to modulation. Calculated values of the average signal-to-noise ratio for FM and AM signals under Rayleigh fading are given. The results show that the FM signal with a modulation index of one or greater, outperforms an AM signal under identical fading conditions. >
28 Nov 1988
TL;DR: It is found that the FUB method, which is based on linear amplitude dispersion, is the most accurate for modeling the effects of selective multipath fading.
Abstract: The outage probabilities for two different digital radio systems (11 GHz, 140 Mbps) under test have been computed using three methods, in order to evaluate the accuracy of the models for predicting outage due to selective fading. The outage times obtained are independent of the multipath fading occurrence factor, P/sub 0/. The results are tabulated and compared with experimental values. It is found that the FUB method, which is based on linear amplitude dispersion, is the most accurate for modeling the effects of selective multipath fading. >