Showing papers on "Fading distribution published in 1997"
TL;DR: The Shannon capacity of a fading channel with channel side information at the transmitter and receiver, and at the receiver alone is obtained, analogous to water-pouring in frequency for time-invariant frequency-selective fading channels.
Abstract: We obtain the Shannon capacity of a fading channel with channel side information at the transmitter and receiver, and at the receiver alone. The optimal power adaptation in the former case is "water-pouring" in time, analogous to water-pouring in frequency for time-invariant frequency-selective fading channels. Inverting the channel results in a large capacity penalty in severe fading.
2,163 citations
Book•
01 Oct 1997
TL;DR: The focus on these increasingly important topics, the systematic approach to algorithm development, and the linked algorithm-architecture methodology in digital receiver design are unique features of this book.
Abstract: From the Publisher:
Digital Communication Receivers offers a complete treatment on the theoretical and practical aspects of synchronization and channel estimation from the standpoint of digital signal processing. The focus on these increasingly important topics, the systematic approach to algorithm development, and the linked algorithm-architecture methodology in digital receiver design are unique features of this book. The material is structured according to different classes of transmission channels. In Part C, baseband transmission over wire or optical fiber is addressed. Part D covers passband transmission over satellite or terrestrial wireless channels. Part E deals with transmission over fading channels. Designed for the practicing communication engineer and the graduate student, the book places considerable emphasis on helpful examples, summaries, illustrations, and bibliographies. Contents include basic material, baseband communications, passband transmission, receiver structure for PAM signals, synthesis of synchronization algorithms, performance analysis of synchronizers, bit error degradation caused by random tracking errors, frequency estimation, timing adjustment by interpolation, DSP system implementation, characterization, modeling, and simulation of linear fading channels, detection and parameter synchronization on fading channels, receiver structures for fading channels, parameter synchronization for flat fading channels, and parameter synchronization for selective fading channels.
1,136 citations
29 Jun 1997
TL;DR: A broadcast transmission strategy for the single-user slowly fading Gaussian channel where the channel state is assumed to be known at the receiver end only is investigated, enabling one to simultaneously implement a continuum of capacity versus outage values rather than a single pair as is the case in the more standard approach.
Abstract: We investigate a broadcast transmission strategy for the single-user slowly fading Gaussian channel where the channel state is assumed to be known at the receiver end only. This strategy facilitates one to adapt the transmission rate to the actual channel conditions without having any feedback link to the transmitter. In essence this strategy enables one to simultaneously implement a continuum of capacity versus outage values rather than a single pair as is the case in the more standard approach.
210 citations
TL;DR: This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal.
Abstract: This paper proposes a bandwidth-efficient fading-resistant transmission scheme which implements transmitter diversity using L antennas at the base station. When the antennas are spaced sufficiently far apart, the transmission from each antenna undergoes a different degree of fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading.
146 citations
04 May 1997
TL;DR: The results show that optimal power and rate adaptation yields a small increase in capacity over just optimal rate adaptation with constant power, and this small increase diminishes as the average received carrier-to-noise ratio, m parameter, and/or number of diversity branches increase.
Abstract: We study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF channel capacity (with and without diversity) for each power and rate adaptation strategy, and compare them with the additive white Gaussian noise (AWGN) channel capacity. The capacity of a NMF channel is always smaller than the capacity of an AWGN channel. Moreover, the capacities converge to the AWGN channel capacity as the Nakagami fading parameter m tends to infinity, as expected. Our results also show that optimal power and rate adaptation yields a small increase in capacity over just optimal rate adaptation with constant power, and this small increase in capacity diminishes as the average received carrier-to-noise ratio, m parameter, and/or number of diversity branches increase. Finally, fixed rate transmission with channel inversion suffers the largest capacity penalty. However, this penalty diminishes as the amount of fading decreases.
134 citations
TL;DR: A supremum to the Shannon capacity of a Rayleigh fading channel without side information is computed using variational methods and is shown to be asymptotically achievable for signal-to-noise ratios (SNRs) approaching either zero or infinity.
Abstract: A supremum to the Shannon capacity of a Rayleigh fading channel without side information (SI) is computed using variational methods and is shown to be asymptotically achievable for signal-to-noise ratios (SNRs) approaching either zero or infinity. A lower bound is obtained from the mutual information corresponding to a specific discrete input distribution.
102 citations
TL;DR: Borders on the bit-error probability of a system with coded modulation and diversity for space- and time-correlated Rician flat fading are presented and a new method is derived which allows evaluation of the pairwise error probability extremely easily, as well as accurately and computationally fast.
Abstract: We address the problem of designing and analyzing the performance of a coded modulation scheme for the fading channel when space diversity is used. Under fairly general conditions, a channel affected by fading can be turned into an additive white Gaussian noise (AWGN) channel by increasing the number of diversity branches. Consequently, it can be expected (and is indeed verified by our analyses and simulations) that a coded modulation scheme designed to be optimal for the AWGN channel also will perform asymptotically well on a fading channel with diversity. This paper presents bounds on the bit-error probability of a system with coded modulation and diversity for space- and time-correlated Rician flat fading. Specifically, we derive a new method which allows evaluation of the pairwise error probability extremely easily, as well as accurately and computationally fast. The accuracy achieved improves considerably on the widely used, but rather loose Chernoff bound. Starting from this analysis, we study the asymptotic behavior of the fading channel with diversity as the number of diversity branches increases, and we address the effects of diversity on coded modulation performance and design criteria, including the effect on interleaver depth (which affects the total delay of the system).
99 citations
TL;DR: A new expression for the bit error rate (BER) of an asynchronous direct-sequence code-division multiple-access (DS-CDMA) system with coherent BPSK demodulation in a multipath Nakagami (1960) fading channel is derived and shows that in such systems, the effect of nonidentical fading on system performance cannot be ignored.
Abstract: A new expression for the bit error rate (BER) of an asynchronous direct-sequence code-division multiple-access (DS-CDMA) system with coherent BPSK demodulation in a multipath Nakagami (1960) fading channel is derived. The analysis assumes an arbitrary number of independent, but nonidentical resolvable paths combined by the RAKE receiver. The results obtained show that in such systems, the effect of nonidentical fading on system performance cannot be ignored.
96 citations
TL;DR: This work found that proper selections of the intentional frequency offset and interleaving depth can lead to good performance with traditional coded modulations (if enough antennas are used) using essentially the same simple demodulation structure as used in the traditional single-antenna PSAM.
Abstract: Coded modulation (usually with interleaving) is used in fading channel communications to achieve a good error performance. The major benefit from using coded modulation in fading channels is achieved if each code symbol of a codeword (or coded sequence) suffers statistically different fading (preferably independent fading). However, in many applications of mobile communications (e.g., in a metropolitan environment), a low vehicle speed (and hence, a small Doppler spread, f/sub D/) is very common. With a small Doppler spread, ideal or close-to-ideal interleaving is no longer feasible and all code symbols of a codeword would suffer highly correlated fading especially in stationary fading (f/sub D//spl ap/0). Coded modulations will thus suffer seriously degraded performance. Previous performance analyses based on ideal interleaving are not accurate when a small Doppler spread is encountered and the much used union bound error probability analysis is loose for small Doppler spreads. To rectify this situation, this paper presents an improved performance analysis of coded modulations with correlated fading and pilot-symbol-assisted modulation (PSAM). Transmitter diversity can generate the necessary time-varying fading to maintain the effectiveness of a coded signaling scheme which this paper examines in detail using an intentional frequency offset between antennas. This work found that proper selections of the intentional frequency offset and interleaving depth can lead to good performance with traditional coded modulations (if enough antennas are used) using essentially the same simple demodulation structure as used in the traditional single-antenna PSAM.
84 citations
01 Jan 1997
TL;DR: It is shown that the FIR detectors can be made near-far resistant under a given ratio between maximum and minimum received power of users by selecting an appropriate memory-length, and the iterative detectors are also shown to be applicable for parallel implementation.
Abstract: Multiuser demodulation algorithms for centralized receivers of asynchronous direct-sequence (DS) spread-spectrum code-division multiple-access (CDMA) systems in frequency-selective fading channels are studied. Both DS-CDMA systems with short (one symbol interval) and long (several symbol intervals) spreading sequences are considered. Linear multiuser receivers process ideally the complete received data block. The approximation of ideal infinite memory-length (IIR) linear multiuser detectors by finite memory-length (FIR) detectors is studied. It is shown that the FIR detectors can be made near-far resistant under a given ratio between maximum and minimum received power of users by selecting an appropriate memory-length. Numerical examples demonstrate the fact that moderate memory-lengths of the FIR detectors are sufficient to achieve the performance of the ideal IIR detectors even under severe near-far conditions. Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection receiver and suboptimal receivers are considered. The parallel interference cancellation (PIC) receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. Choice of channel estimation filters is shown to be crucial if low BER is required. Data-aided channel estimation is shown to be more robust than decision-directed channel estimation, which may suffer from BER saturation caused by hang-ups at high signal-to-noise ratios. Multiuser receivers for dynamic CDMA systems are studied. Algorithms for ideal linear detector computation are derived and their complexity is analyzed. The complexity of the linear detector computation is a cubic function of KL, where K and L are the number of users and multipath components, respectively. Iterative steepest descent, conjugate gradient, and preconditioned conjugate gradient algorithms are proposed to reduce the complexity. The computational requirements for one iteration are a quadratic function of KL. The iterative detectors are also shown to be applicable for parallel implementation. Simulation results demonstrate that a moderate number of iterations yields the performance of the corresponding ideal linear detectors. A quantitative analysis shows that the PIC receivers are significantly simpler to implement than the linear receivers and only moderately more complex than the conventional matched filter bank receiver.
75 citations
04 May 1997
TL;DR: In this article, the effect of correlation and fading parameter on the performance of an N-order conventional selection diversity system is studied. But the authors focus on the non-coherent case and do not consider the coherent case.
Abstract: This paper studies the effect of correlation and fading parameter on the performance of an N-order conventional selection diversity system. A Nakagami fading channel with identical but nonindependent fading on the diversity branches is assumed. The joint distribution of the output of the combiner is expressed in terms of the Laguerre polynomials. This analysis can be applied to both coherent and noncoherent demodulation schemes and an arbitrary number of diversity branches. Numerical results are presented showing the effect of correlation and the degree of fading on the system performance for the dual diversity case.
TL;DR: It is shown that block detection with diversity may or may not generate a better coding channel than usual differential detection, according to the code selected and the combination of values of M and N.
Abstract: For pt. I see ibid., vol.45, no.6, p.563-572, 1997. We study coded modulation with block differential detection in an arbitrarily correlated Rician fading channel with space diversity. Coded differential q-PSK is included in our analysis as a special case. A metric is chosen that is optimum for perfect interleaving, slow fading, and independent diversity branches. For slow fading, we compare the the cutoff rates of the channels resulting from different choices of block length N and diversity index M. Specifically, we show that block detection with diversity may or may not generate a better coding channel than usual differential detection, according to the code selected and the combination of values of M and N. In particular, for low-diversity orders (M=1,2) and for low-to-medium code rates, differential detection is still an optimal or near-optimal solution, while for high-diversity orders (M/spl ges/2) and medium-to-high code rates (up to uncoded modulation) block detection with N>2 can provide a significant gain. An error floor always exists when fading is fast. It decreases exponentially with the product of code diversity and space diversity, so that the latter emerges as a very effective technique for lowering the error floor of a system affected by fast fading. Performance examples based on actual coding schemes are also shown.
12 Oct 1997
TL;DR: In this paper, a performance comparison between maximal-ratio combining (MRC) and equal-gain combining (EGC) RAKE receivers is considered for coherent binary CDMA systems operating over frequency-selective Nakagami fading channels.
Abstract: We study coherent binary direct-sequence code division multiple access (DS-CDMA) systems operating over frequency-selective Nakagami fading channels. In particular a performance comparison between maximal-ratio combining (MRC) and equal-gain combining (EGC) RAKE receivers is considered. For interference limited systems, perfect MRC RAKE receivers can accommodate about 5m/(5m-1) more users than EGC RAKE receivers, where m is the Nakagami fading parameter. MRC has a higher rate of improvement than EGC as the number of combined paths increases. However, imperfect or inaccurate channel fading estimation leads to serious degradation in the performance of MRC receivers and in that case EGC becomes superior to MRC.
TL;DR: Results for both wide area and local SFN show that the coverage properties depends on the correlation in the shadow fading, which will affect the planning process since strong correlation, due to the structure of the terrain, yields better coverage for high transmitter powers (interference limited systems) and worse coverage for low transmitter power (noise limited systems).
Abstract: All transmitters in a single frequency network (SFN) simultaneously transmit the same information within the same frequency block. Simulcasting provides a diversity gain which has been shown to yield good coverage. In traditional analysis uncorrelated shadow fading is used. In some cases this assumption does not capture the behaviour of the shadow fading, e.g., when several transmitters are shadowed by a large obstacle. We investigate the changes in coverage due to correlation among the received signals field strength from different transmitters. A spatial shadow fading correlation model is proposed and validated using the Blomquist-Ladell (1974) prediction method on a digital terrain data base. Results for both wide area and local SFN show that the coverage properties depends on the correlation in the shadow fading. This will affect the planning process since strong correlation, due to the structure of the terrain, yields better coverage for high transmitter powers (interference limited systems) and worse coverage for low transmitter powers (noise limited systems).
02 Nov 1997
TL;DR: A new deterministic approach to the estimation and prediction of the fading channel by exploiting the physical nature of the flat fading signal will potentially result in the ability to anticipate and avoid "deep fades" which severely limit the performance of wireless communications systems and will aid in the development of low power mobile radio systems.
Abstract: We investigated a new deterministic approach to the estimation and prediction of the fading channel by exploiting the physical nature of the flat fading signal. Since the direct signal and the reflected signals form an interference pattern, the received signal is given by a sum of several scattered components. These are distinguished by their Doppler shifts at the mobile. The slowly varying parameters associated with these components are determined and tracked, and the composite fading signal is predicted. This approach will potentially result in the ability to anticipate and avoid "deep fades" which severely limit the performance of wireless communications systems and will aid in the development of low power mobile radio systems.
TL;DR: The capture probabilities, C/sub n/, defined as the probability that any of the n, contending packets are correctly received, are found with reference to a random-access mobile radio communications system in the presence or fading, shadowing, and near-far effect.
Abstract: The capture probabilities, C/sub n/, defined as the probability that any of the n, contending packets are correctly received, are found with reference to a random-access mobile radio communications system in the presence or fading, shadowing, and near-far effect. A Rician model for fading that is more general than the well-studied Rayleigh fading is considered. The capture probabilities are computed, and their dependence on the system parameters and, in particular, on the Rice factor, K, is investigated. As an example of application, a slotted ALOHA system is considered, and the performance of a simple control strategy is studied. Also, some analytical results are given as to the value of C/sub /spl alpha//=lim/sub n-/spl alpha//C/sub n/, which is relevant to the study of the system stability.
TL;DR: An analysis of the bit-error probability for receivers in which the diversity branches are correlated finds that Rician fading can be worse than Rayleigh fading in correlated diversity environments, a situation quite different from the independent diversity case.
Abstract: Due to the interest in wireless personal communications, there has been a lot of research on the performance of receivers with diversity. Most analyses assume the diversity branches are independent. This paper presents an analysis of the bit-error probability for receivers in which the diversity branches are correlated. Noncoherent orthogonal digital modulation (NCODM) with Rician and Rayleigh slow, nonselective fading models are assumed. Through the use of the diagonalization of quadratic forms, most of the calculations of the bit-error probability can be reduced to a two-dimensional numerical integration. For some cases for dual diversity, a closed-form expression for the error probability is given. A number of diversity combining laws, including square law and maximum likelihood, are considered. We find that Rician fading can be worse than Rayleigh fading in correlated diversity environments, a situation quite different from the independent diversity case. Also, for the Rayleigh fading model with correlated branch diversity, we find that an equal-weight, square-law combiner usually has the same error performance as the more complex maximum-likelihood combiner. However, this is not the case for a Rician fading model with the same correlation environment. Simple diagonalization methods that compensate for the lossy effect of correlation are specified and found to be effective when the dominant noise and interference have almost the same correlation distribution as the fading signals.
TL;DR: The structure of the optimal noncoherent FSK detector is derived and a novel analytical technique is proposed to compute the error performance of noncoherence FSK detectors in fast fading.
Abstract: Linearly time-varying fading models are used to investigate noncoherent detection of frequency shift keying (FSK) signals transmitted over frequency-flat fading channels. The structure of the optimal noncoherent FSK detector is derived and a novel analytical technique is proposed to compute the error performance of noncoherent FSK detectors in fast fading. Error performance results obtained by computer simulation are in excellent agreement with the analytical predictions.
TL;DR: The fast fading characteristics in an indoor environment are studied through a new statistical model established under the assumption of a finite number of scatterers and based on the modified Student's t distribution that reflects (better than the conventional Rayleigh model) the conditions that are met inside buildings and are described well by a small number of easily identifiable parameters.
Abstract: The fast fading characteristics in an indoor environment are studied through a new statistical model established under the assumption of a finite number of scatterers and based on the modified Student's t distribution. The use of this model in the indoor environment reflects (better than the conventional Rayleigh model) the conditions that are met inside buildings and are described well by a small number of easily identifiable parameters. An analytical expression for this so-called Polydorou Capsalis (POCA) distribution is developed assuming a finite number of scatterers, and its statistical characteristics are analyzed. Then, this distribution is used in order to describe the fast fading characteristics in an indoor environment. For this purpose, measurements in the 900-MHz-frequency band have been done in an office environment. The performance of the POCA distribution is compared to the conventional Rayleigh distribution, and it is found that the fast fading characteristics are better described by this distribution.
29 Jun 1997
TL;DR: An algorithm is developed for computing capacity and the corresponding optimal distribution of a discrete-time Rayleigh fading channel, in which successive symbols face independent fading, and where neither the transmitter nor the receiver has channel state information.
Abstract: We consider transmission over a discrete-time Rayleigh fading channel, in which successive symbols face independent fading, and where neither the transmitter nor the receiver has channel state information. Subject to an average power constraint, we study the capacity-achieving distribution of this channel and prove it to be discrete with a finite number of mass points, one of them located at the origin. We develop an algorithm for computing capacity and the corresponding optimal distribution.
29 Jun 1997
TL;DR: Here the authors look at a particularly simple model of the fading channel, but the methodology appears to be extendable to more general models.
Abstract: The issue of bandwidth scaling has always caused some confusion for channels subject to additive white Gaussian noise plus multipath fading On the one hand, there is an old result saying that the capacity of the channel (under a power constraint but no bandwidth constraint) is the same as the infinite bandwidth capacity of the non-fading additive noise channel with the same average received power as the fading channel On the other hand, it appears intuitively that when a CDMA system is spread too widely in bandwidth, it becomes increasingly difficult for a RAKE receiver to measure the channel and correspondingly difficult for detection to take place Here the authors look at a particularly simple model of the fading channel, but the methodology appears to be extendable to more general models
01 Jan 1997
TL;DR: This paper presents a time-frequency view of wireless communication over multipath channels that facilitates diversity signaling by exploiting multipath and Doppler shifts and illustrates the utility of the time- frequencies via novel signaling and receiver structures, and multiuser acquisition and interference-suppression algorithms.
Abstract: Dynamics of multipath fading have a major effect on the performance of mobile wireless communication systems. The inherently time-varying nature of the mobile wireless channel makes nonstationary signal processing techniques particularly attractive for system design. Time-frequency representations are powerful tools for time-varying signal processing, and in this paper, we present a time-frequency view of wireless communication over multipath channels. Our discussion is anchored on a fundamental finite-dimensional time-frequency representation of the wireless channel that facilitates diversity signaling by exploiting multipath and Doppler shifts. The substantially higher level of diversity afforded by time-frequency processing over conventional techniques translates into significant gains in virtually all aspects of system performance. We illustrate the utility of the time-frequency framework via novel signaling and receiver structures, and multiuser acquisition and interference-suppression algorithms.
04 May 1997
TL;DR: It is shown that in a comparative curve fitting of slow fading, Nakagami distribution also fits the fading data, and it is argued that radio link performance calculation based on the segregation of slow and fast fading are therefore unnecessary for Rice/lognormal or Nakag Japanese fading models and may be avoided in order to simplify complex analyses.
Abstract: Our investigations in understanding the physical mechanism of the LOS microcellular channel reveal that the principle source of slow fading is the random interference pattern of a few strong contributing paths which causes what we term as deceptive shadowing. It is shown that in a comparative curve fitting of slow fading, Nakagami distribution also fits the fading data. Also in non-zero mean complex Gaussian channels, the segregation of slow and fast fading using moving mean normalization is illusionary as the fading parameters in both cases remain the same. We argue that radio link performance calculation based on the segregation of slow and fast fading are therefore unnecessary for Rice/lognormal or Nakagami/lognormal fading models and may be avoided in order to simplify complex analyses.
04 May 1997
TL;DR: An adaptive suboptimum detector for signal detection during every bit period is proposed for an asynchronous DS-CDMA system in which the receiver has knowledge of the signature waveform of all the users.
Abstract: Direct sequence code division multiple access (DS-CDMA) is the muitiplexing method used for the next generation of wireless digital standards. This paper deals with an asynchronous DS-CDMA system in which the receiver has knowledge of the signature waveform of all the users. In the presence of white Gaussian noise and channel fading, we propose an adaptive suboptimum detector for signal detection during every bit period. The performance of this detector has been compared to the one shot detector under Gaussian noise and channel fading condition.
TL;DR: In this article, the matched filter bound for square quadrature amplitude modulation in time-discrete multipath Rayleigh fading channels is derived using GSM typical urban and hilly terrain channel models.
Abstract: The matched filter bound for square quadrature amplitude modulation is derived in time-discrete multipath Rayleigh fading channels. An example is given using the GSM typical urban and hilly terrain channel models.
08 Jun 1997
TL;DR: The effects of imperfect average power measurements on adaptive MQAM modulation, where the transmit power and data rate are varied relative to the received signal power, are considered.
Abstract: We consider the effects of imperfect average power measurements on adaptive MQAM modulation, where the transmit power and data rate are varied relative to the received signal power. The channel varies with both fast Rayleigh fading and slow log-normal shadowing. We assume that the fast fading is estimated perfectly, and that the estimation error of the shadowing is log-normally distributed. This estimation error leads to a change in the average transmit power and rate of the adaptive modulation. We characterize these changes for two adaptive modulation schemes: variable-rate variable-power MQAM, where the average data rate is maximized, and fixed-rate MQAM, where the transmit power is adapted to invert the signal fading. The shadowing estimation error affects these two modulation techniques in opposite ways: the data rate and dB power changes resulting from the error are positive for variable-rate variable-power MQAM, and negative for fixed-rate MQAM. In both cases, however, the changes are very small.
03 Nov 1997
TL;DR: The obtained results show considerable performance improvement compared to the conventional orthogonal frequency division multiplexing (OFDM) scheme and MC-CDMA schemes that use non-quadrature spreading.
Abstract: Multicarrier CDMA (MC-CDMA) schemes resolve the frequency selectivity in multipath fading channels and have good spectral properties. Spreading the information over many subcarriers adds flexibility to the system and a redundancy between subcarriers that can be combined with the derived frequency diversity from the fading channel. The performance of an MC-CDMA scheme over frequency selective, slowly fading channels is studied analytically and by computer simulations. The MC-CDMA system uses a BPSK modulation, quadrature (complex) spreading codes, and a simple correlator receiver. Quadrature spreading codes are used to reduce the effect of the multipath fading channel and restore some of the orthogonality losses between users. The obtained results show considerable performance improvement compared to the conventional orthogonal frequency division multiplexing (OFDM) scheme and MC-CDMA schemes that use non-quadrature spreading. The effect of frequency offsets on the system performance is also addressed.
TL;DR: The results show that, when perfect CSI is available, diversity is able to turn asymptotically the channel into a CCI-free additive white Gaussian noise (AWGN) channel with the same signal-to-noise ratio (SNR) as the channel is affected by co-channel interference.
Abstract: For pt.II see ibid., vol.45, no.6, p.55-67, 1997. In previous work, we have studied the impact of diversity on coded digital communication systems operating over fading channels. In particular, we have shown that diversity may be thought of as a way of making the channel more similar to a Gaussian one. The present paper extends this analysis to fading channels affected by co-channel interference (CCI). Three receiver models are examined, namely, with coherent detection and perfect channel-state information (CSI), with differential; and with pilot-tone detection. We study the effect of diversity on the irreducible error floor caused by CCI and fading, and the asymptotic behavior of the channel as the diversity order increases. Our results show that, when perfect CSI is available, diversity is able to turn asymptotically the channel into a CCI-free additive white Gaussian noise (AWGN) channel with the same signal-to-noise ratio (SNR). On the other hand, differential and pilot-tone detection do not remove interference in the limit. Nevertheless, also with these detection schemes, diversity achieves significant gains when the SNR is large enough. Calculation of the channel cutoff rate provides guidelines for the design of coded systems with CCI in fading environments. A wide range of examples, validated by computer simulation, illustrates our conclusions.
TL;DR: An IS stochastic technique for the efficient simulation of adaptive systems which employ diversity in the presence of frequency nonselective slow Rayleigh fading and additive, white, Gaussian noise is presented.
Abstract: We present an IS stochastic technique for the efficient simulation of adaptive systems which employ diversity in the presence of frequency nonselective slow Rayleigh fading and additive, white, Gaussian noise. The computational efficiency is achieved using techniques based on importance sampling (IS). We utilize a stochastic gradient descent (SGD) algorithm to determine the near-optimal IS parameters that characterize the dominant fading process. After accounting for the overhead of the optimization algorithm, average speed-up factors of up to six orders of magnitude [over conventional Monte Carlo (MC)] were attained for error probabilities as low as 10/sup -11/ for a fourth-order diversity model.
12 Oct 1997
TL;DR: This work evaluates the capacity of a direct sequence CDMA system (DS/CDMA) assuming low mobility users and taking into account the increase in the other-cell interference due to perfect tracking of multipath fading, and investigates the effect of the number of fading resolvable paths on system capacity.
Abstract: In a cellular system, low mobility users' transmitted power can be very accurately controlled by a fixed step power control algorithm. This results in lowering the signal to noise ratio necessary to achieve a given frame error rate (FER). However, accurate tracking of multipath fading has the negative effect of increasing the other-cell interference level during periods of deep fades. In this work, we evaluate the capacity of a direct sequence CDMA system (DS/CDMA) assuming low mobility users and taking into account the increase in the other-cell interference due to perfect tracking of multipath fading. The effect of the number of fading resolvable paths on system capacity is determined and the increase in the capacity due to soft handoff is found for different soft handoff thresholds. Finally we investigate the effect of limiting the maximum transmitted power to compensate for multipath fading and find that a limit of 10 dB results in maximizing the system capacity.