Showing papers on "Fading distribution published in 2004"

Digital Communications Over Fading Channels

Abstract: : In this report, the probabilities of bit error for the most commonly used digital modulation techniques are analyzed. Analytic solutions are developed for the probability of bit error when the signal is affected by the most commonly encountered impairment to system performance for a wireless channel, the transmission of the signal over a fading channel. In this report, the effect of a slow, flat Ricean fading channel on communications systems performance is examined. Since channel fading significantly degrades the performance of a communication system, the performance of digital communication systems that also use forward error correction channel coding is analyzed for hard decision decoding and, where appropriate, for soft decision decoding. Diversity, another technique to mitigate the effect of fading channels on digital communication systems performance, is also discussed. Also included is a discussion of the effect of narrowband noise interference, both continuous and pulsed, on digital communication systems. We then discuss the analysis of the probability of bit error for the combination of error correction coding and diversity. Following this, we briefly discuss spread spectrum systems. Next, we examine the link budget analysis and various models for channel loss. Finally, we examine in detail the second generation digital wireless standard Global System for Mobile (GSM).

Error Rates in Generalized Shadowed Fading Channels

Abstract: Most of the existing models to describe the shadowed fading channels use either the Suzuki or Nakagami-lognormal probability density function (pdf), both based on lognormal shadowing. However, these two density functions do not lead to closed form solutions for the received signal power, making the computations of error rates and outages very cumbersome. A generalized or compound fading model which takes into account both fading and shadowing in wireless systems, is presented here. Starting with the Nakagami model for fading, shadowing is incorporated using a gamma distribution for the average power in the Nakagami fading model. This compound pdf developed here based on a gamma-gamma distribution is analytically simpler than the two pdfs based on lognormal shadowing and is general enough to incorporate most of the fading and shadowing observed in wireless channels. The performance of coherent BPSK is evaluated using this compound fading model.

Distribution functions of selection combiner output in equally correlated Rayleigh, Rician, and Nakagami-m fading channels

Abstract: We develop a novel approach to derive the cumulative distribution functions (cdfs) of the selection-combining (SC) output signal-to-noise ratio (SNR) in equally correlated Rayleigh, Ricean, and Nakagami-m fading channels. We show that a set of equally correlated channel gains can be transformed into a set of conditionally independent channel gains. Single-fold integral expressions are, therefore, derived for the cdfs of the SC output SNR. Infinite series representations of the output cdfs are also provided. New expressions are applied to analyze the average error rate, the outage probability, and the output statistics of SC. Numerical and simulation results that illustrate the effect of fading correlation on the performance of L-branch SC in equally correlated fading channels are provided.

Opportunistic splitting algorithms for wireless networks

Abstract: In this paper, we develop medium access control protocols to enable users in a wireless network to opportunistically transmit when they have favorable channel conditions, without requiring a centralized scheduler. We consider approaches that use splitting algorithms to resolve collisions over a sequence of minislots, and determine the user with the best channel. First, we present a basic algorithm for a system with i.i.d. block fading and a fixed number of backlogged users. We give an analysis of the throughput of this system and show that the average number of minislots required to find the user with the best channel is less than 2.5 independent of the number of users or the fading distribution. We then extend this algorithm to a channel with memory and also develop a reservation based scheme that offers improved performance as the channel memory increases. Finally we consider a model with random arrivals and propose a modified algorithm for this case. Simulation results are given to illustrate the performance in each of these settings

Indoor channel measurements and characterization at 60 GHz for wireless local area network applications

Abstract: This work presents propagation measurement results at 60 GHz in order to determine the characteristics of indoor radio channels between fixed terminals. Path loss measurements are reported for line-of-sight (LoS) and non-line-of-sight (NLoS) cases, fading statistics in a physically stationary environment are extracted and a detailed investigation of the people movement effect on the temporal fading envelope is performed. Models that presented to predict path loss provide excellent fitting with errors of 1.13 and 3.84 dB for LoS and NLoS topographies, respectively. The dynamic range of fading in a quiescent environment is 8.8 dB and increased to 35 dB when a person moves between the fixed terminals with the channel becoming extremely nonstationary. Temporal variations induced by the moving people depend on the speed, the number of individuals the body sizes and the environment. Slow fading is observed as well as a quasi-wide-sense stationary (QWSS) behavior of the fading, but up to 50 ms of time.

Channel capacity and second-order statistics in Weibull fading

Abstract: The second-order statistics and the channel capacity of the Weibull fading channel are studied. Exact closed-form expressions are derived for the average level crossing rate, the average fade duration, as well as the average Shannon's channel capacity of the Weibull fading process. Numerical results are presented to illustrate the proposed mathematical analysis and to examine the effects of the fading severity on the concerned quantities.

Performance analysis of dual selection diversity in correlated Weibull fading channels

Abstract: Ascertaining the importance of the dual selection combining (SC) receivers and the suitability of the Weibull model to describe mobile fading channels, we study the performance of a dual SC receiver over correlated Weibull fading channels with arbitrary parameters. Exact closed-form expressions are derived for the probability density function, the cumulative distribution function, and the moments of the output signal-to-noise ratio (SNR). Important performance criteria, such as average output SNR, amount of fading, outage probability, and average bit-error probability for several modulation schemes are studied. Furthermore, for these performance criteria, novel closed-form analytical expressions are derived. The proposed analysis is complemented by various performance evaluation results, including the effects of the input SNR's unbalancing, fading severity, and fading correlation on the overall system's performance. Computer simulation results have verified the validity and accuracy of the proposed analysis.

Modulation classification in fading channels using antenna arrays

Abstract: Blind modulation classification (MC) is an intermediate step between signal detection and demodulation, and plays a key role in various civilian and military applications. In this paper, first we provide an overview of decision-theoretic MC approaches. Then we derive the average likelihood ratio (ALR) based classifier for linear and nonlinear modulations, in noisy channels with unknown carrier phase, offset and also in Rayleigh fading channels. Since these ALR-based classifiers are complex to implement, we then develop a quasi hybrid likelihood ratio (QHLR) based classifier, where the unknown parameters are estimated using low-complexity techniques. This QHLR-based classifier is much simpler to implement and is also applicable to any fading distribution, including Rayleigh and Rice. Afterwards, we propose a generic multi-antenna classifier for linear and nonlinear modulations, using an antenna array at the receiver. This classifier has the potential to improve the performance of traditional single-antenna classifiers, including the proposed QHLR-based algorithm, via spatial diversity. Simulation results are provided to show the performance enhancement offered by the new QHLR-based multi-antenna classifier, in a variety of channel and fading conditions.

Precise error-rate analysis of bandwidth-efficient BPSK in Nakagami fading and cochannel interference

Abstract: The bit-error rate (BER) of bandlimited binary phase-shift keying in a fading and cochannel interference (CCI) environment is derived for the case of perfect coherent detection. The fading-and-interference model assumed is general and of interest for microcellular system studies. The model allows both desired signal and interfering signals to experience arbitrary amounts of fading severity. A precise BER expression is derived using a characteristic function method. Using this accurate analytical result, the impact of the interfering users' fading severity on the desired user-error rate is examined. The BERs obtained under perfect coherent detection are also valid as lower performance bounds for practical realizable receivers where ideal coherent detection is difficult to implement. The error-rate performance of a novel bandwidth-efficient pulse shape is determined for the general fading and CCI environment. Analysis and numerical results show that the new pulse can provide better BER performance than the widely used raised-cosine pulse.

Gaussian codes and weighted nearest neighbor decoding in fading multiple-antenna channels

Abstract: We investigate the fading multiple-antenna channel. The decoder is assumed to possess imperfect channel fading information. A modified nearest neighbor decoder with an innovative weighting factor is introduced and an expression for the generalized mutual information (GMI), the achievable rate, is obtained. We show that under certain conditions the achievable rate is equivalent to that of a fading multiple-antenna Gaussian channel where fading is known to the receiver and is equal to the channel estimation, and where noise is due to both the channel noise and the channel estimation error. We show that for our communication scheme, the minimum mean square error (MMSE) channel estimator is optimal in the sense that it achieves the highest value of GMI, and hence the highest communication rate. Additionally, a training based multiple-input multiple-output (MIMO) scheme in a block-fading channel is investigated and it is shown that the number of degrees of freedom depends on the signal-to-noise ratio (SNR).

Noncoherent MIMO communication: Grassmannian constellations and efficient detection

Abstract: We propose a greedy algorithm for designing Grassmannian constellations that mimic the distribution that achieves the high SNR capacity of a noncoherent MIMO fading channel. We also introduce a reduced complexity suboptimum detector whose performance is comparable to that of the optimal detector.

Markov chains and performance comparison of switched diversity systems

Abstract: Switch-and-stay combining (SSC) diversity systems have the advantage of offering one of the least complex solutions to mitigating the effect of fading. In this paper, we present a Markov chain-based analytical framework for the performance analysis of various switching strategies used in conjunction with SSC systems. The resulting expressions are quite general, and are applicable to dual-branch diversity systems operating over a variety of correlated and/or unbalanced fading channels. The mathematical formalism is illustrated by some selected numerical examples, along with their discussion and interpretation. As a result, this paper presents a thorough comparison and highlights the main differences and tradeoffs between the various SSC switching strategies.

Accurate Simulation of multiple cross-correlated Rician fading channels

Abstract: The computer generation of multiple cross-correlated Rician fading channels is investigated. We prove that the output sequences of existing multichannel fading simulators are restricted to have cross-correlation statistics that have the same functional form as the component autocorrelation functions. To overcome this limitation, vector autoregressive stochastic models are proposed for the generation of multiple Rician fading processes with specified realizable autocorrelation and cross-correlation statistics. This capability is desirable, for example, to permit realistic performance assessments of space-time modem designs by enabling the simulation of space-time-selective wireless channel models. The utility of the simulation approach is demonstrated by the accurate synthesis of some bandlimited multichannel Rayleigh and Rician processes.

MIMO capacity with channel state information at the transmitter

Abstract: This paper presents analytical expressions for the capacity of single-user multi-antenna channels, known instantaneously by both transmitter and receiver, at moderate and high signal-to-noise ratios. Fading channels with both uncorrelated and correlated antennas are encompassed. The characterization is conducted primarily in the limit of large numbers of antennas, with accompanying examples that illustrate the validity of the results for even small numbers thereof. In the absence of correlation, the capacity is also tightly bounded for fixed numbers of antennas with compact closed-form expressions.

BER performance of dual predetection EGC in correlative Nakagami-m fading

Abstract: In this letter, an approach to the evaluation of the error performance in dual predetection equal-gain combining (EGC) systems over correlated Nakagami-m fading channels is presented. Deriving an infinite series representation for the characteristic function of the sum of two correlated Nakagami-m variables, a closed-form formula is extracted for binary phase-shift keying and coherent binary frequency-shift keying, while several other modulation schemes are studied, capitalizing on a Parsevals's theorem-based approach, previously published. Numerical results and simulations are also presented to illustrate the proposed mathematical analysis and to point out the effect of the input signal-to-noise ratio unbalancing, the fading severity, and the fading correlation on the system's error performance.

Simulation of Nakagami fading channels with arbitrary cross-correlation and fading parameters

Abstract: Nakagami fading model is widely used in modeling wireless communication systems. In this paper, we present methods to generate Nakagami fading signals with arbitrary cross-correlation and fading parameters by taking the square root of correlated Gamma random variables (RVs) with the corresponding shape parameters. To generate correlated Gamma RVs with different noninteger values of m-parameters, two methods, namely the decomposition method and Sim's method, are proposed. The former is more flexible and efficient. The latter is mathematically exact but carries constraints on the permissible simulation parameters. Simulations show that both methods produce outputs that match well with the specifications.

Turbo code design for block fading channels

Abstract: Shannon capacity approaching codes have been extensively studied during the last decade for ergodic channels. We propose and analyze new channel multiplexing/interleaving techniques for parallel turbo codes over non-ergodic block fading channels. We reveal word error probability performance at less than 1dB from outage capacity. The achieved word error probability is almost insensitive to the code length. The race to the outage capacity limit on block fading channels is declared open.

Performance analysis of L-branch equal gain combiners in equally correlated Rayleigh fading channels

Abstract: Theoretical performance results for L-branch (L/spl ges/3) coherent equal-gain combining (EGC) in correlated fading channels are not known. This letter develops a novel approach for performance analysis of L-branch EGC in equally correlated Rayleigh fading channels. Such channel gains can be transformed into a set of conditionally independent channel gains. The cumulative distribution function (cdf) of the EGC output signal-to-noise ratio (SNR) is, therefore, derived. The symbol error rate (SER) of different modulation schemes with EGC in equally correlated Rayleigh fading channels is evaluated. Numerical results that illustrate the effects of equally correlated fading on the SER performance of EGC are also provided.

Unified theory on wireless communication fading statistics based on SIRP

Abstract: Under various outdoor/indoor narrowband flat fading scenarios, a variety of statistical models of envelope distributions, such as Rayleigh, Rician, exponential, Nakagami-m, Weibull, lognormal, Kv etc., have been proposed. We show that spherically-invariant random processes (SIRP) and Fox H-functions can be used to provide a unified theory to model these fading channel statistics. Various performance measures of fading communication systems, such as error probability and "amount of fading," can be evaluated using the SIRP statistical characterization.

On the average output SNR in selection combining with three correlated branches over Nakagami-m fading channels

Abstract: An exact and rapidly converging infinite series for the average output signal-to-noise ratio in a triple selection diversity system, over correlated Nakagami-m fading channels, is presented. Numerical results are presented to illustrate the proposed approach and to point out the effect of the fading correlation to the performance of the combiner, as well as the improvement achieved by the triple selection combining compared to the dual diversity case.

Effect of power control imperfections on the reverse link of cellular CDMA networks under multipath fading

Abstract: In this paper, we present an analytical approach for the evaluation of the impact of power control errors on the reverse link of a multicell direct sequence code-division multiple access (CDMA) system with fast power control under multipath fading. Unlike many previous papers, the joint effect of multipath fading and fast power control on interference statistics is explicitly accounted for and mobiles are assumed to connect to a base station according to a minimum attenuation criterion. Both the average bit error rate (BER) and the outage probabilities that a user experiences are estimated. The results have been used to evaluate the system capacity from two points of view. First, the maximum capacity supported by the system in order to maintain an average BER below a prescribed level has been calculated. Second, the maximum capacity possible to ensure that the outage probability does not exceed a set limit is analyzed. Capacity is shown to be significantly affected by the imperfections of power control. Our results can be used to quantify the relative capacity loss due to fast power control errors in a cellular CDMA network affected by slow fading, multipath fading, and cochannel interference.

Comparison of space-time water-filling and spatial water-filling for MIMO fading channels

Abstract: We compare the capacities achieved by space-time water-filling and spatial water-filling for MIMO fading channels Both the effects of fast fading and shadowing are considered It is found that for Rayleigh fast fading MIMO channels, the spectral efficiency per antenna achieved by one-dimensional spatial water-filling is close to two-dimensional space-time water-filling However, with log-normal shadowing, space-time water-filling achieves significantly higher capacity per antenna than spatial water-filling at low to moderate SNR regimes Furthermore, space-time water-filling has lower computational complexity than spatial water-filling It is also shown that space-time water-filling requires a priori knowledge of the channel gain distribution, and for Rayleigh channels with log-normal shadowing, the spectral efficiency advantage over spatial water-filling comes with an increased channel outage probability

Performance of FM-DCSK communication system over a multipath fading channel with delay spread

Abstract: Multipath performance is an important consideration for chaos-based communication systems. In this paper the performance of the FM-DCSK communication system over a two-ray independent Rayleigh fading channel is evaluated by computer simulations. The low-pass equivalent model of the FM-DCSK system is considered. Based on this model, we analyze the bit error performance and the effects of system parameters on the bit-error performance.

Near maximum likelihood detection schemes for wireless MIMO systems

Abstract: In this letter, we propose two near maximum-likelihood detection (MLD) schemes for multiple input-multiple output antenna systems over flat fading channels. The schemes are based on utilizing an initial estimate of the received symbol and improving it by selectively updating various bits within the symbol. Simulation results show that the performance of the proposed schemes can approach that of MLD but with a significant reduction in complexity.

Maximum likelihood estimation of statistical properties of composite gamma-lognormal fading channels

Abstract: We propose maximum likelihood (ML) methods for estimating the parameters of composite gamma-lognormal fading channels. Newton-Raphson and expectation-maximization (EM) algorithms are developed to compute the ML estimates of the mean and variance of the shadowing component, and the Nakagami-m parameter of the fading component. We also derive Crame/spl acute/r-Rao bounds (CRBs) for the unknown parameters. Numerical simulations demonstrate the performance of the proposed method.

Experimental assessment of the UWB channel variability in a dynamic indoor environment

Abstract: Comprehensive modelling of the ultra-wide band (UWB) radio channel necessitates a good knowledge of its fading statistics. To evaluate the fluctuations of the UWB channel, a propagation experiment has been conducted in the 3.1 - 11 GHz frequency band, involving different antenna locations and moving people. The presented results emphasize the difference between the spatial and temporal channel variability, and provide a practical assessment of the UWB signal fading distribution in the case of a dynamic environment.

Statistical properties of the EGC output SNR over correlated Nakagami-m fading channels

Abstract: Previous studies have addressed with the performance analysis of L-branch equal gain combining (EGC) systems over independent Rayleigh- or Nakagami-m fading channels. In this paper, important statistical parameters, such as the /spl kappa/-moment, the /spl kappa/-central moment, the skewness, and the kurtosis of the output signal-to-noise ratio (SNR), in predetection EGC systems operating over correlated Nakagami-m fading channels are studied. Simple closed-form expressions for the mean and variance of the output SNR are presented and it is shown that our general results reduce to the specific noncorrelative fading case previously published. Moreover, significant performance criteria such as the amount of fading and the spectral efficiency in the low power regime, are investigated. Numerical results and simulations are presented to check the validity of the proposed mathematical analysis and to point out the impact of the fading correlation, the input SNRs unbalancing as well as the fading severity, on the EGC performance.

Bluetooth: channel coding considerations

Abstract: We have noted that several papers that address the performance of Bluetooth (BT) over a fading channel implicitly assume a perfectly interleaved channel and neglect the bursty nature of a fading channel. The paper analyzes the effects of this incorrect assumption on BT's performance over a frequency-flat Rayleigh block fading channel. Despite the simplicity of the analysis, we obtain interesting results not previously published. We show that neglecting the burst nature of the channel leads to overly-pessimistic conclusions about the performance of Bluetooth in the low SNR region and, thus, that many reported results on the coexistence of Bluetooth and 802.11 are overly-pessimistic. Moreover, we also conclude that the coding strategy used in Bluetooth has little or no effect on a frequency-flat Rayleigh block fading channel.

Signal-strength based localization in wireless fading channels

Abstract: We develop maximum likelihood (ML) methods for location estimation using spatio-temporal received-signal-strength (RSS) measurements in wireless fading channels. Fading and composite fading-shadowing scenarios with completely unknown and partially known source signals are considered. We adopt gamma (Nakagami-m) and lognormal models to describe fading and shadowing effects, respectively. We also derive Cramer-Rao bounds (CRBs) for the location parameters and discuss initialization of the proposed algorithms. Numerical simulations demonstrate the performance of our estimators.

Diversity analysis of space-time modulation over time-correlated Rayleigh-fading channels

Abstract: Most space-time codes in the literature were proposed based on two ideal channel conditions: either quasistatic or rapid fading. However, these codes may suffer performance degradation due to temporal correlation caused by the movement of the mobile terminal or imperfect interleaving. In this correspondence, we provide a novel analytical framework for the diversity analysis of space-time modulation in time-correlated fading environment. We show that the space-time signals of square size achieving full diversity in quasistatic fading channels also achieve full diversity in time-correlated fading channels, independently of the time correlation matrix. Consequently, various classes of space-time signals designed for quasistatic fading channels can also be used for full-diversity transmission over time-correlated fading channels. Moreover, we show that if the time correlation matrix is of full rank, the design criteria for time-correlated fading channels are the same as those for rapid fading channels. To illustrate the theoretical results, some simulations were also performed under various temporal fading conditions.