Showing papers on "Fading distribution published in 1990"
TL;DR: In this article, the authors derived the channel capacity in a Rayleigh fading environment and showed that channel capacity is always lower than that in a Gaussian-noise environment and that diversity schemes can improve channel capacity.
Abstract: The channel capacity in a Rayleigh fading environment is derived. The result shows that the channel capacity in a Rayleigh fading environment is always lower than that in a Gaussian-noise environment. When operating a digital transmission in a mobile radio environment that has Rayleigh fading statistics, it is very important to know the degradations in channel capacity due to Rayleigh fading, and also to what degree the diversity schemes can raise the channel capacity in a Rayleigh fading environment. The curves are generated to show the degradation of channel capacity in a Rayleigh fading environment and its improvement by diversity schemes. >
371 citations
TL;DR: A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied.
Abstract: A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied. This model is named a Rician/Rayleigh fading environment. Expressions of outage probabilities are presented for the mobile radio system in the Rician/Rayleigh fading environment.
193 citations
TL;DR: It is found that an ALOHA system under fast fading conditions also benefits from the capture results in higher throughput, and the superimposed Rayleigh fading, log-normal shadowing, and spatial distribution can further enhance the capture effect, resulting in a ALOha system with higher throughput.
Abstract: The influence of receiver capture on the performance of the ALOHA protocol in the presence of shadowing is investigated. The combined effect of Rayleigh fading, log-normal shadowing, and spatial distribution of mobile users is also studied. It is shown that shadowing is similar to fading and near/far phenomena, in that it makes the capture effect possible and provides ALOHA systems with substantial improvements in throughput. It is also confirmed that the superimposed Rayleigh fading, log-normal shadowing, and spatial distribution can further enhance the capture effect, resulting in a ALOHA system with higher throughput. The fast fading effect in ALOHA systems is explored. A very fast fading case is examined which may be considered to be equivalent to interleaving in slow fading. It is found that an ALOHA system under fast fading conditions also benefits from the capture results in higher throughput. >
98 citations
TL;DR: Go-back-N (GBN) and selective repeat (SR) protocols for automatic repeat request (ARQ) protocols are compared in a frequency-nonselective Rayleigh fading channel to investigate quantitatively whether data communications combining detection-only coding, diversity, and basic ARQ protocols can offer reasonable throughput in a fading channel.
Abstract: Go-back-N (GBN) and selective repeat (SR) protocols for automatic repeat request (ARQ) are compared in a frequency-nonselective Rayleigh fading channel. Protocols implemented in software are used in a computer-simulated fading channel to study the throughput of these protocols as a function of fading parameters, such as the mean signal-to-noise ratio (SNR), maximum Doppler frequency number of diversity branches, time-out period and round-trip delay. The purpose is to complement well-documented theoretical work in (1) providing some design considerations and (2) investigating quantitatively whether data communications combining detection-only coding, diversity, and basic ARQ protocols can offer reasonable throughput in a fading channel. Although based on a set of assumptions, the following conclusions remain valid: (1) SR is significantly superior to GBN when the fading rate is high; this advantage decreases as fading becomes slower; and (2) error detection combined with ARQ and diversity selection can provide reliable data communications in a Rayleigh fading channel. >
44 citations
TL;DR: Error rates for a narrowband digital FM system with discriminator detection in a land mobile radio channel characterized by fading and Doppler frequency shift are obtained using a new analytical method.
Abstract: Error rates for a narrowband digital FM system with discriminator detection in a land mobile radio channel characterized by fading and Doppler frequency shift are obtained using a new analytical method. The fading rate is assumed to be much slower than the bit rate so that signal distortion through a narrow bandpass filter can be analyzed via a quasistatic approach. An experiment was conducted using a Rayleigh fading simulator, and the error rate measurements are shown to agree well with the calculated results, except at high SNR (signal-to-noise ratio) where an irreducible error rate was observed. >
28 citations
TL;DR: These analyses demonstrate the frequency hopping benefits in selective channels by derived for the bit error rate in the context of selective Rayleigh and selective Rician fading channels, as a function of channel and system parameters.
Abstract: The performance of noncoherent reception in fast frequency hopped spread-spectrum (FFH-SS) communication systems operating through noisy, fading multipath channels is investigated. Systems operating with binary frequency-shift keying (BFSK) modulation and noncoherent demodulation are examined under the assumption of very slow fading. These analyses demonstrate the frequency hopping benefits in selective channels. Expressions are derived for the bit error rate in the context of selective Rayleigh and selective Rician fading channels, as a function of channel and system parameters. >
26 citations
TL;DR: Close-form expressions for the symbol error rate are presented and the coherent PSK signals are 3 dB stronger than the differentialPSK signals at high SNR for given M in a Rayleigh fading environment.
Abstract: The error rate performance of M-ary coherent phase shift keyed signals and M-ary differential phase shift keyed signals in slow Rayleigh fading channels is analysed. Closed-form expressions for the symbol error rate are presented. The coherent PSK signals are 3 dB stronger than the differential PSK signals at high SNR for given M in a Rayleigh fading environment. >
24 citations
TL;DR: In this article, a large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed.
Abstract: Multipath fading data obtained from 47 terrestrial microwave line-of-sight links in France and the United Kingdom are analyzed to derive narrowband prediction equations for the deep fading range of the cumulative distribution for the average worst month. A large number of possible predictor variables based on typical radio link parameters are investigated, and equations which reduce the standard error of prediction to less than half that of previous techniques for this part of Europe are developed. The improvement is achieved by increasing the number of prediction variables, using the most statistically significant variables, introducing a zonally varying geoclimatic factor, and employing more accurate analysis techniques. A reasonable choice of variables for system design includes path length, radio frequency, path inclination, and the grazing angle of specular reflection from the average terrain profile. A physical interpretation of the results suggests that a large amount of multipath fading is caused by ground reflection in combination with fading of the direct wave through the atmosphere. >
20 citations
TL;DR: It is seen as a result that the fading distortion can be compensated with high accuracy, making 16QAM applicable to land mobile communications.
Abstract: To cope with the increasing demands for the land mobile communication with a limited frequency band, it is necessary to improve the spectral efficiency beyond the present state. QAM (quadrature amplitude modulation) is one of the effective means for this purpose. When QAM is applied to land mobile communication, however, a great distortion is produced in the envelope and the phase due to fading fluctuation. Because of this property, few discussions have been made on the application of QAM to land mobile communication. This paper proposes the following system for such an application. The fading distortion is measured from the periodically inserted known frame symbol. By interpolating the obtained time-series, the fading distortion for all symbols is estimated. Then the distortion is compensated. The performance when the proposed method is applied to 16QAM is examined by computer simulation. It is seen as a result that the fading distortion can be compensated with high accuracy, making 16QAM applicable to land mobile communications.
18 citations
06 May 1990
TL;DR: It is shown that for fast-fading channels simple forward-error correction is sufficient for acceptable system performance, however, other techniques such as selection diversity are required.
Abstract: Packet reservation multiple access (PRMA) allows a group of spatially dispersed terminals to transmit packet voice and data over a common channel. A means to model and evaluate the effects of packet transmission errors on PRMA is developed. PRMA is considered in the context of a cellular system, and the effects of fading on the performance of PRMA are studied. PRMA performance is assessed in terms of system capacity, outage, and cellular efficiency when the transmission channel is subject to slow and fast fading. It is shown that for fast-fading channels simple forward-error correction is sufficient for acceptable system performance. In slow-fading channels, however, other techniques such as selection diversity are required. >
16 citations
Dissertation•
01 Sep 1990
TL;DR: Results indicate that such a receiver will reduce the receiver error floor two orders of magnitude at typical channel signal-to-noise ratios.
Abstract: The purpose of this thesis is to develop a practical receiver for Rayleigh fadin?; channels. which does not exhibit the error floor found for conventional receivers in this channel. .-\ model of a general time and frequency-selective channel is developed, and the opt.imal receiver structure for a time-selective channel is derived for general signalling. The theoretical performance of a standard and maximum likelihood receiver is analyzed for the case of f\I-ary differential phase shift keying. A recursive, channel adaptive version of the optimal receiver is derived, and through simulation, its performance is compared to theoretical expectations . Results indicate that such a receiver will reduce the receiver error floor severnl orders of magnitude at typical channel signal-to-noise ratios. I wish to thank Dr. Taylor for allowing me the opportunity to work on this thesis; his insights and suggestions were invaluable in its conception and completion. I would also like to thank the students and staff of the CRL for the many discussions that helped bring this work together. Thanks to my parents and family, who have given me their steady support and encouragement throughout. And finally to Pamela, of course, for everything.
02 Dec 1990
TL;DR: The nonlinear digital carrier synchronizer is proposed for phase estimation on the fading channel and a method of evaluating the BEP of a digital quadrature PSK in the presence of a noisy phase reference and Rician fading is presented.
Abstract: The nonlinear digital carrier synchronizer is proposed for phase estimation on the fading channel. This architecture's noncausal structure, efficient digital implementation, hangup-free operation, and near-optimum performance at low signal-to-noise ratio (SNR) are postulated to produce near-ideal bit error probability (BEP) performance in fading channels. A method of evaluating the BEP of a digital quadrature PSK. (QPSK) demodulator in the presence of a noisy phase reference and Rician fading is presented. This result is used to obtain accurate performance approximations for the nonlinear digital carrier synchronization architecture. >
TL;DR: In this article, the worst-case partial-band Gaussian interference results are given by a one-parameter family which for m to infinity gives the Viterbi-Jacobs nonfading result, and for m=1 gives the Rayleigh fading result.
Abstract: For frequency-hopped (noncoherent) binary frequency shift keying (FH/BFSK) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases where the signal is either nonfading or Rayleigh fading. In this work, the region between these extremes is filled in by considering the general Nakagami-m fading model. The worst-case partial-band Gaussian interference results are given by a one-parameter family which for m to infinity gives the Viterbi-Jacobs 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 results 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/. >
02 Dec 1990
TL;DR: The author investigates the use of smearing/desmearing filters in combination with linear modulation to achieve time diversity without bandwidth expansion in digital mobile radio systems and describes a low-complexity receiver structure for smeared data transmission in time-selective fading.
Abstract: The author investigates the use of smearing/desmearing filters in combination with linear modulation to achieve time diversity without bandwidth expansion in digital mobile radio systems. A low-complexity receiver structure for smeared data transmission in time-selective fading is described. The receiver is analyzed for perfect and noisy channel estimation and perfect interleaving. Results on the bit error performance show that the proposed data transmission system is very robust to Rayleigh fading and noisy channel estimation. In the proposed system, time-selective fading merely introduces an additional stationary Gaussian noise component. This makes the combination with coding straightforward. The first results on the performance of smeared data transmission with trellis-coded 8-PSK (phase-shift keying) are given. >
TL;DR: It is shown that the effective code length (ECL) of a short ECL block modulation code (BCM) is the dominant factor in its performance over a Rayleigh fading channel.
Abstract: It is shown that the effective code length (ECL) of a short ECL block modulation code (BCM) is the dominant factor in its performance over a Rayleigh fading channel. To demonstrate this, three new BCM codes are presented as examples. Their performances are evaluated and compared on both Gaussian and fading channels.
30 Sep 1990
TL;DR: The mean acquisition time performance of a straight, serial-search direct-sequence spread spectrum (DS-SS) acquisition system, operating in nonselective and frequency-selective Rician fading channels is analyzed.
Abstract: The mean acquisition time performance of a straight, serial-search direct-sequence spread spectrum (DS-SS) acquisition system, operating in nonselective and frequency-selective Rician fading channels is analyzed. The system was proposed by Polydoros and Weber (1984), and its performance is analyzed for a nonfading channel, at which all the cells that fall under hypothesis H/sub o/ are statically identical. This is not the case for the Rician fading channel. A signal flow graph for which the H/sub o/ cells are not identical is used to derive an expression for the mean acquisition time in terms of the probabilities of detection and false alarm. These probabilities are then derived for the nonselective and frequency selective Rician fading channels. The results show the effect of the channel and system parameters on the mean acquisition time performance. >
19 Mar 1990
TL;DR: In this article, differential encoding, and a circular star constellation rather than the conventional square one are employed at the transmitter, while oversampling techniques combined with the prediction of the received signal envelope are used at the receiver.
Abstract: Techniques to improve the BER performance of 16-level QAM transmissions over Rayleigh fading channels are presented. Differential encoding, and a circular star constellation rather than the conventional square one is employed at the transmitter, while oversampling techniques combined with the prediction of the received signal envelope are used at the receiver. These procedures considerably enhance the BER performance. Whereas the BER of conventional 16-level QAM has a residual BER of 7*10/sup -2/, the enhancement procedures yield BERs of 2*10/sup -2/, 3*10/sup -3/ and 6*10/sup -4/ at channel SNRs of 15, 25 and 35 dB, respectively. >
TL;DR: An antenna pattern diversity reception system was constructed experimentally as a means to cope with multipath fading in mobile communication, where the four-direction antenna is used as the diversity branches, which themselves have the fading reduction effect as discussed by the authors.
Abstract: An antenna pattern diversity reception system was constructed experimentally as a means to cope with multipath fading in mobile communication, where the four-direction antenna is used as the diversity branches, which themselves have the fading reduction effect. The variable threshold switching method is employed as the output scheme from the diversity branches. The switching algorithm for the four-branch multithreshold reception is discussed. From the computer simulation based on the actually measured fading data, the optimal values for the parameters of the branch switching control algorithm are determined.
A field experiment is made using the experimental system, and it is verified that the short-term fading is improved in the actual multipath environment with the value close to the theoretical value, for the selection switching by four receivers using uncorrelated branches with Rayleigh distribution.
TL;DR: A novel sequential receiver structure is derived that uses a detection algorithm which identifies the most probable transmitted sequence in the maximum-likelihood detection sense and substantial bit error rate (BER) improvements of more than three orders of magnitude over conventionally detected schemes are obtained.
Abstract: An approach for reducing the effects of multiplicative noise, such as fading, on the performance of mobile broadcasting transmission systems is introduced. The proposed method is based on a noise prediction/cancellation technique and is applied to phase-shift keyed (PSK) signals. By exploiting the statistical characteristics of the multipath fading signal and its strong correlation properties, a novel sequential receiver structure is derived that uses a detection algorithm which identifies the most probable transmitted sequence in the maximum-likelihood detection sense. The algorithm has been obtained for both Rayleigh and Rician fading channels. The proposed detection technique has been evaluated for various QPSK schemes operated in channels corrupted by a combination of additive white Gaussian noise (AWGN) and fading. The computer simulation results obtained show that by using a relatively simple receiver with a prediction algorithm of second order, considerable error floor reductions are achieved by the proposed receivers. As a direct result of these error floor reductions substantial bit error rate (BER) improvements of more than three orders of magnitude over conventionally detected schemes are obtained. >
02 Dec 1990
TL;DR: It is shown that this method can be applied to dispersive fades with in-band notches and that noise in the received signal is a major cause of identification errors.
Abstract: The use of an adaptive transversal equalizer at the receiver end of a digital radio receiver as a tool for identifying the phase of dispersive fading events is discussed. The identification is based on the online comparison of the equalizer precursor and postcursor taps and can be used without service disruption. It is shown that this method can be applied to dispersive fades with in-band notches and that noise in the received signal is a major cause of identification errors. The method used to compute the equalizer taps is described. >
26 Jan 1990
TL;DR: In this paper, closed-form analytical solutions were determined for the performance of M-branch microscopic selection diversity when the signal is subjected to both Rayleigh and log-normal fading.
Abstract: It is well known that mobile radio signals generally exhibit both fast (Rayleigh) and slow (log-normal) fading. This will severely affect the performance of digital transmissions by reducing the signal-to-noise ratio as well as the carrier-to-interference ratio. In this paper, closed form analytical solutions are determined for the performance of M-branch microscopic selection diversity when the signal is subjected to both Rayleigh and log-normal fading. It is shown that, although microscopic (antennas separated by small distances, so only the fast fading components become uncorrelated) diversity is a superb technique to mitigate the effects of fast fading, it is certainly, ineffective against the slow fading. The microscopic diversity improvement is related to the standard deviation of the log-normal (slow) fading. When the standard deviation increases the improvement decreases. Although the authors still believe that diversity is the most important technique to minimise the effect of fading, the conclusion drawn from this paper is that it is advantageous, whenever possible, to separate the receiver antennas by a distance large enough to ensure some degree of decorrelation between the slow fading components. One possibility is base station diversity.
16 Apr 1990
TL;DR: The throughput for a system using Go-Back-N or selective repeat protocols with Rayleigh fading in both directions of transmission is approximated by using fade- and interfade-duration statistics of a multipath channel.
Abstract: The throughput for a system using Go-Back-N or selective repeat protocols with Rayleigh fading in both directions of transmission is approximated by using fade- and interfade-duration statistics of a multipath channel. The retransmission for Go-Back-N is based on a time-out concept; for selective repeat it is based on either time-out or negative acknowledge. The estimated results on throughput agree well with simulation results. It is found that, for a slow fading channel (e.g. fading rate=1.34 Hz, encountered by a user at 1 mile/hr walking speed and 900-MHz carrier frequency), the throughput of Go-Back-N is only slightly inferior. This comparatively equal performance results from the burstiness of the channel bit errors. On the other hand, for a fast fading channel (e.g. fading rate=80 Hz), the throughput using selective repeat is significantly superior. >
12 Sep 1990
TL;DR: A channel estimator for extracting the discrete-time channel coefficients (“tap-gains”) of a time-varying frequency-selective channel is investigated and the performance curves are shown to be superior to that of the conventional LMS estimator, and are close to the theoretical lower bounds.
Abstract: A channel estimator for extracting the discrete-time channel coefficients (“tap-gains”) of a time-varying frequency-selective channel is investigated. A Kalman filter is integrated into a least mean squares (LMS) estimator such that a-priori knowledge about the statistics of the channel is taken into account. Assuming a state-space model of the channel is given, parameter settings and the stationary error variance of each single tap-gain are analytically derived for Rayleigh-fading channels. The performance curves of the modified algorithm are shown to be superior to that of the conventional LMS estimator, and are close to the theoretical lower bounds which are also investigated.
06 May 1990
TL;DR: In this paper, an empirical propagation model and the performance of a two-branch macroscopic diversity configuration for indoor microcells are presented, based on measurements made in three different cell types classified according to the indoor environment.
Abstract: An empirical propagation model and the performance of a two-branch macroscopic diversity configuration for indoor microcells are presented. The model is based on measurements made in three different cell types classified according to the indoor environment. Analysis of measured signal strength levels has shown that macroscopic diversity techniques can be used to reduce the link margin for the required 99% area coverage in each cell type. The reduction is dependent of the fading distribution and the maximum achievable rate at which the best path can be selected. The gain with selective macroscopic diversity varies from 4 dB in a cell with high overall propagation attenuation to 10 dB in an open area cell type with lower propagation attenuation. This reduction is obtained when the selections between base stations are made at intervals shorter than 25 cm and the short-fading component is eliminated. The gain can be as high as 12 dB, if all fading is taken into account and the selections are made at intervals shorter than 4 cm. >
16 Apr 1990
TL;DR: An infinite series for the complementary probability distribution function of the signal-to-noise ratio at the output of L-branch equal-gain diversity combiners in Nakagami fading channels is derived and it is shown that, even with -20 dB gain unbalance between the branches of a dual combiner, there is still a considerable improvement over the nondiversity instance for the generalized fading model.
Abstract: An infinite series for the complementary probability distribution function of the signal-to-noise ratio at the output of L-branch equal-gain diversity combiners in Nakagami fading channels is derived. The bit error rate for a matched-filter receiver is analyzed for the combiner and different fading parameters. Both coherent phase-shift keying and differential coherent phase-shift keying are considered. The effects of gain unbalance between branches on the probability distribution of the SNR and on the bit error rates are investigated. Bit-error-rate results are also obtained for coherent and noncoherent reception of frequency-shift keying. The effects of gain unbalances on FSK modulations are also investigated. It is shown that, even with -20 dB (k=0.01) gain unbalance between the branches of a dual combiner, there is still a considerable improvement over the nondiversity instance for the generalized fading model (m=1). >
01 Feb 1990
TL;DR: In this article, first-order intensity statistics under multipath scintillation conditions which are not sufficiently severe to lead to fully developed Rayleigh fading were examined and it was shown that neither Rice nor Nakagami-m statistics are accurate in general.
Abstract: : This report examines first-order intensity statistics under multipath scintillation conditions which are not sufficiently severe to lead to fully developed Rayleigh fading It is shown that neither Rice nor Nakagami-m statistics are accurate in general Actual signal intensity statistics can be systematically characterized in terms of the refractive index spatial power spectrum and the signal Fresnel length Numerous calculated results are provided for signal intensity distributions and channel symbols bit error rates in non- Rayleigh fading Keywords: Scintillation effects, Propagation effects, Satellite communications, Satellite links, Ionospheric scattering
02 Dec 1990
TL;DR: A multi-Rician fading model for radio communication systems in which the received signal consists of a finite number of specular components in addition to a diffuse component is presented and it is shown that, in some cases, the multi- Rician distribution gives fading which is deeper than Rayleigh fading.
Abstract: A multi-Rician fading model for radio communication systems in which the received signal consists of a finite number of specular components in addition to a diffuse component is presented. The probability density function of the envelope of the received signal is obtained from basic principles, and it is shown that, in some cases, the multi-Rician distribution gives fading which is deeper than Rayleigh fading. It is also shown that this general model includes the Rayleigh and Rician fading distributions as special cases. The use of spatial selection diversity is considered to combat the effects of fading, and the performance of two types of selection diversity receivers in the presence of multi-Rician fading is obtained for various cases of practical interest. >
01 Jan 1990
TL;DR: A concatenated coding scheme for providing very reliable data over mobile-satellite channels at power levels similar to those used for vocoded speech is described, which provides error detection as well as error correction capabilities.
Abstract: A concatenated coding scheme for providing very reliable data over mobile-satellite channels at power levels similar to those used for vocoded speech is described The outer code is a shorter Reed-Solomon code which provides error detection as well as error correction capabilities The inner code is a 1-D 8-state trellis code applied independently to both the inphase and quadrature channels To achieve the full error correction potential of this inner code, the code symbols are multiplexed with a pilot sequence which is used to provide dynamic channel estimation and coherent detection The implementation structure of this scheme is discussed and its performance is estimated
03 Sep 1990
TL;DR: In this article, a method was presented in which a computer was used to randomly simulate the statistical distributions of frequency selective fading over the Pacem 2 experimental path (a distance of 100 km, operating in the 11.123 GHz to 11.187 GHz range).
Abstract: A method is presented in which a computer is used to randomly simulate the statistical distributions of frequency selective fading. Relationships between the in-band frequency correlation coefficient and antenna height, the ground reflection coefficient, and the frequency bandwidth are randomly simulated. Using this method, frequency selective fading was randomly simulated over the Pacem 2 experimental path (a distance of 100 km, operating in the 11.123 GHz to 11.187 GHz range) from Bouffry to Viabon for the total fading period of 1985. >