Lognormal Fading Channels Research Articles

Capacity of multiuser multiple input multiple output-orthogonal frequency division multiplexing systems with doubly correlated channels for various fading distributions

In this article, the capacity of multiuser multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system is analysed under Rayleigh, Rician, Lognormal and Weibull fading channels, and compared with each other under both semi- and doubly correlated channels. The distribution of the complex Wishart matrix is utilised to derive closed-form expressions of ergodic capacity of MIMO-OFDM systems under doubly correlated channels when the transmitter has no channel state information (CSI) and the receiver has perfect CSI. The capacity of MIMO-OFDM systems is plotted for various fading channels under different system specifications, such as number of transmit and receive antennas, number of subcarriers and different power levels. The obtained results are used to study the impact of channel correlation on capacity.

Capacity of single user MIMO-OFDM systems with doubly-correlated channels under various fading distributions

In this paper, the capacity of Single User (SU) Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system is analyzed under Rayleigh, Rician, Lognormal and Weibull fading channels, and compared with each other under both singly- and doubly-correlated channel conditions. The distribution of the complex Wishart matrix is utilized to derive closed form expressions of ergodic capacity of MIMO-OFDM systems under doubly-correlated channels when the transmitter has no Channel State Information (CSI) and the receiver has perfect CSI. The capacity of MIMO-OFDM systems is plotted for various channels under different system specifications, such as, number of transmit and receive antennas, number of subcarriers, and different power levels. The obtained results are used to study the impact of channel correlation on capacity.

New Results on the Statistics and the Capacity of Dual-Branch MRC and EGC Diversity in Correlated Lognormal Channels

This letter addresses the performance analysis of dual diversity reception systems in correlated lognormal fading channels with not-necessarily-identical parameters. More specifically, novel results on the probability density function (PDF) and the ergodic capacity of dual-branch maximal ratio combining (MRC) and equal gain combining (EGC) diversity receivers are presented. The proposed expressions find application in cost-sensitive diversity receiver implementations and handover designs.

Performance analysis of downlink W-CDMA systems in Weibull, Lognormal and Nakagami fading channels

Wideband Code Division Multiple Access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds to mobile and portable wireless devices than those which are commonly offered in todayʼs market. In W-CDMA systems transmitting over multipath channels, both Inter Symbol Interference (ISI) as a result of Inter Chip interference (ICI) and Multiple Access Interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired usersʼ signature waveform. Torlak and Xu proposed a blind estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiuser channels (Torlak and Xu, 1997 [1]). In our work, we study a similar blind channel estimation scheme for downlink W-CDMA systems that provides estimates of the multiuser channels by exploiting the structural information of the data output. In particular, we show that the subspace of the (data + noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellations. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for the Weibull and Lognormal fading channels. Estimated signal constellations under the Weibull, Lognormal and Nakagami fading channels are also plotted.

Performance of a Binary PPM Ultra-Wideband Communication System with Direct Sequence Spreading for Multiple Access

In this paper, we present an analysis of the BER performance of an ultra-wideband (UWB) system with pulse position modulation (PPM) for data modulation and direct sequence (DS) spreading for multiple access over indoor lognormal fading channels. A rake receiver is used to combine a subset of the resolvable multipath components using the maximal ratio combining technique. Inter-path and multiple-access interferences are modeled and incorporated into the bit-error-rate expressions. The analytical and simulation results allow one to quantify many critical aspects of a DS-PPM UWB system such as the gain of the optimally spaced signaling scheme over the orthogonal signaling scheme, the potential error floor given a specific channel multipath delay spread and the number of interfering users, tolerance of the system to timing jitter, and impact of user codes.

Error performance of PAM systems using energy detection with optimal and suboptimal decision thresholds

In this paper, we consider the error probability for multilevel pulse amplitude modulated (PAM) signals, which are used with a multipath diversity combiner based on energy detection (ED). A distinctive feature of ED combined with nonconstant envelope signals is that the symbol decision thresholds need to be determined from a non-Gaussian distributed decision variable. We first present a novel theoretical analysis framework which provides a basis to predict the error performance of ED-PAM systems with optimal maximum likelihood decision thresholds in general multipath fading channels with arbitrary number of degrees of freedom. We then use frequency-selective lognormal fading channels as a case example and evaluate simple approximations for the error probability. Moreover, the analysis is extended to include the joint effect of systematic and random threshold deviation on the error probability with suboptimal but practical data-aided threshold estimation.

Multiuser Detection Employing a Novel Genetic Algorithm for UWB Communications

In this paper, a differential multiuser detection (MUD) method using a novel genetic algorithm (GA) based on complementary error function mutation (CEFM) is employed for ultra-wideband (UWB) systems. The proposed MUD method, which combines a novel GA based on CEFM, is termed CEFM-GA for short. We describe the schemes of the CEFM-GA, analyze their algorithms and compare their computational complexity with other MUDs. Simulation results show a significant bit error rate (BER) performance gain can be achieved by employing the proposed CEFM-GA compared with successive interference cancellation (SIC), parallel interference cancellation (PIC) and conventional GA for UWB systems in lognormal fading channel.

Outage Performance Analysis of a Dual-Hop Radio Relay System Operating at Frequencies above 10GHz

The ever increasing demand for multimedia services has led to the extensive use of fixed wireless outdoor networks, where the transmitted information signals arrive to the final destination through a relay node, creating a dual-hop transmission. Due to the increased demand for bandwidth and the spectral congestion at low frequencies, operation at frequencies above 10GHz satisfying the Line-Of-Sight condition is required. At this frequency range, the dominant fading mechanism exposing spatial and temporal stochastic properties is rain attenuation, typically modeled as a lognormal flat fading channel when expressed in dB (log-lognormal in linear scale). In this paper, the outage performance of a dual hop system using several radio relay types is presented and physical prediction models with analytical formulas are proposed, employing spatially correlated lognormal fading channels. Extended numerical results investigate the impact of various operational, geometrical and geographical radio relay parameters, as well as the impact of the employment of a relay channel estimator, on the end-to-end performance.

Performance of Receive Diversity UWB Systems with Pulse Amplitude and Position Modulation

In this paper, we extend ultra-wideband (UWB) single input single output (SISO) systems with a hybrid pulse amplitude and position modulation (PAPM) to single input multiple output (SIMO) systems using receive antenna diversity. The performance of a rake receive diversity combining scheme for UWB SIMO systems with a PAPM is examined in a log-normal multipath fading channel and also compared with that of a time-switched transmit diversity (TSTD) multiple input single output (MISO) system. It is seen that as the number of receive antennas increases, the receive diversity combining system improves the error performance. It is shown that the TSTD UWB MISO systems offer the performance equivalent to the receive diversity combining scheme for SIMO systems.

On the Achievable Diversity Orders over Non-Severely Faded Lognormal Channels

We propose to approximate the distribution of the sum of identically-distributed lognormal random variables by an Erlang distribution. The advantage of the proposed approximation over the lognormal and non-lognormal approximations proposed in the literature resides mainly in the fact that it results in simple closed-form expressions of the average bit-error-rate (BER) thus offering clear insights on the performance of diversity combining techniques over correlated and uncorrelated lognormal fading channels. For instance, the proposed approach shows that, for typical values of the BER, the diversity order in the case of non-severe lognormal fading can be accurately approximated by the order of the approximating Erlang distribution.

A comprehensive framework for performance analysis of cooperative multi-hop wireless systems over log-normal fading channels

In this paper, we propose a comprehensive framework for performance analysis of multi-hop multi-branch wireless communication systems over log-normal fading channels. The framework allows to estimate the performance of amplify and forward (AF) relay methods for both channel state information (CSI-) assisted relays, and fixed-gain relays. In particular, the contribution of this paper is twofold: i) first of all, by relying on the Gauss quadrature rule (GQR) representation of the moment generation function (MGF) for a log-normal distribution, we develop accurate formulas for important performance indexes whose accuracy can be estimated a priori and just depends on GQR numerical integration errors; ii) then, in order to simplify the computational burden of the former framework for some system setups, we propose various approximations, which are based on the Improved Schwartz-Yeh (I-SY) method. We show with numerical and simulation results that the proposed approximations provide a good trade-off between accuracy and complexity for both Selection Combining (SC) and Maximal Ratio Combining (MRC) cooperative diversity methods.

Error Performance of Prerake Diversity Combining-Based UWB Spatial Multiplexing MIMO Systems over Indoor Wireless Channels

In this letter, we consider a novel ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) structure, which consists of prerake diversity combiners in the transmitter and a zero forcing (ZF) detector in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and L resolvable multipath components, it is shown that the proposed prerake combining-based MIMO detection scheme has the diversity order of (LN - M + 1) and its BER performance is analytically presented in a log-normal fading channel and also compared with that of a rake combining-based ZF scheme.

The Weibull–Lognormal Fading Channel: Analysis, Simulation, and Validation

In frequency-nonselective fading channels, the partial waves arriving at the mobile receiver cannot explicitly be of homogeneous nature due to nonuniform scattering caused by objects of specific reflective nature. Moreover, shadowing influences the received signal level by causing slow variations to its local mean. In this paper, we investigate a mixture stochastic process accounting for both inhomogeneous scattering and shadow fading by multiplying a Weibull process with a lognormal process. The first process models the possible scattering nonuniformities of the channel, whereas the second process accounts for the slow-term variations of the local mean due to shadowing. An exact solution for the composite probability density function (pdf) will be given, together with approximate solutions for the second-order statistics, i.e., the level crossing rate (LCR) and the average duration of fades (ADF). The approximate solutions come from the assumption of a slowly time-varying lognormal process compared with the Weibull process, the validity of which will be tested via an efficient deterministic simulation scheme that implements the analytical model on a digital computer. Finally, a curve fitting of the LCR to real-world data drawn from channel measurements will demonstrate the flexibility and usefulness of the proposed model.

An Ordered Successive Interference Cancellation Scheme in UWB MIMO Systems

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple-input multiple-output (MIMO) detection in ultra- wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log-normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining. Performance of the ZF detector is known to be similar to that of the MMSE receiver at high signal-to-noise ratios (SNRs). This work focuses on the analysis of a ZF related scheme. In this letter, we present the error performance of a ZF scheme with an ordered successive interference cancellation (OSIC) for UWB SM MIMO detection in a log-normal fading channel. We analytically investigate the theoretic bit error rate (BER) performance of the ZF-OSIC architecture followed by RAKE combining, called a ZF-OSIC-RAKE, in an UWB SM MIMO receiver. The diversity order that the ZF-OSIC-RAKE offers for detecting the n-th transmitted data stream is obtained for UWB MIMO systems. It is also seen that the ZF-OSIC-RAKE scheme outperforms the ZF-RAKE.

Guest Editorial - Limitations and Growth of Wireless Communication

Growth of cellular communication and wireless Internet continues to provoke further studies that focus at evaluating the performance of wireless system under various limitations, developing new schemes and technologies to overcome limitations and meeting the growing demand of communication capacity and quality. The current Special Issue of the Journal of Communication presents research works on the channel characterizations, modulations schemes, and equalization techniques for wireless communication systems. The Special Issue presents selected papers from the IEEE International Conference on Computer and Information Technology held on December 25-27, 2008. From more than 100 papers presented at the conference in the broad topic of communication, only 11 best papers were considered by the Editors, and their authors were then invited to enhance their papers significantly and submit the same to the Special Issue. Through an extensive peer review process, only 6 papers from among these enhanced papers were finally selected by the Guest Editors for publication in this Special Issue. These authors represent academic and/or research institutions from Australia, Bangladesh, Italy, Japan, and Malaysia. In the first paper, M.Z. Alam, C.S. Islam, and M.A. Sobhan investigate the bit error performance of a quadrature amplitude modulation based wireless communication system using log-likelihood ratio. The theoretical and simulation results compare different diversity techniques for Rayleigh fading channel and recommend the maximal ratio combiner to be the most suitable scheme for wireless communication. The second paper is contributed by M.R.H. Mandal and S.P. Majumder, which evaluates the bit error performance of an orthogonal frequency division multiplexed wireless communication system including the impact of time selective fading, timing jitter and additive white Gaussian noise. Different modulation schemes, namely differential phase shift keying, quaternary phase shift keying, differential quaternary phase shift keying, are investigated and compared for Rayleigh and Rician fading channels. In the next paper M.L.R. Khan, M.H. Wondimagegenehu, and T. Shimamura propose an amplitude banded technique with least mean square error on Godard and Sato algorithms for equalization of wireless channels. From mean square error and bit error rate investigations, the nonlinear features of amplitude banded technique are found to yield improved equalization performance and that the Sato algorithm performs better than the Godard technique. Then, V. Soluk, B.N. Ali, S. Khatun, K.D. Wong and M.A. Mahdi present a new access router discovery method and improved link layer mechanism to enhance seamless vertical handoffs in wireless communication. Analytical and simulation studies are presented in terms of latency and packet loss. The fifth paper is coauthored by M.T. Hossain, S. Kandeepan, and D. Smith, which investigates the performance of a non-data aided near maximum likelihood estimator for symbol timing recovery in wireless communication system incorporating Rayleigh, Weibull and log-normal fading channels. The bit error rate and error variance performance are evaluated and compared with Cramer Rao bound algorithms. In the last paper, W. Nasrin and M.M.I. Rajib present analytical and simulation studies on intelligent underlay overlay scheme in enhancing the capacity of global system for mobile communication system. Practical limitations from co-channels, super area coverage, traffic distribution, ratio and speed of moving vehicles, and blocking probability are taken into consideration in the performance evaluation; it shows a 41.42% capacity enhancement over normal cells. Finally, the Guest Editors would like to express their sincere gratitude to the many reviewers, who have been given immensely to this process. They have responded to the Guest Editors in the shortest possible time and dedicated their valuable time to ensure that the Special Issue contains high-quality papers with significant novelty and contributions. Last but not the least the Guest Editors would extend their appreciation to the Associate Editor-in-Chief, Dr. Haohong Wang for providing them with this opportunity and facilitating preparation of an excellent journal special issue.

Evaluation of Call Performance in Cellular Networks With Generalized Cell Dwell Time and Call-Holding Time Distributions in the Presence of Channel Fading

Call-completion probability, call-dropping probability, and handoff rate are important performance measures of wireless networks. In this paper, we study the joint effect of channel fading and handover failure on these performance measures. For the case of Rayleigh and lognormal fading channels and for generalized distributions of the cell dwell time and the call-holding time, we derive simple closed-form expressions that closely approximate these performance metrics. The results are given in terms of the moment-generating function (MGF) of the distribution for the call-holding time and may be useful in the cross-layer design and the optimization of wireless networks.

Performance of collaborative spectrum sensing for cognitive radio in the presence of gaussian channel estimation errors

The performance of collaborative spectrum sensing for cognitive radio in a lognormal shadowing and Rayleigh fading channel is investigated. Unlike previous works that assume perfect knowledge of the average channel signal-to-noise ratio, this paper considers the realistic case where estimation of the average channel signal-to-noise ratio has error. Furthermore, while previous works have designed and examined estimators based on assuming that the channel samples used in the average signal-to-noise ratio estimators are noiseless, the present work assumes that the channel samples are noisy, as is the case in practical systems. Numerical results show that the probability of missed opportunity decreases as the estimation error decreases, as expected. Perhaps unexpectedly, the results also show that in the presence of noise, there exists a threshold phenomenon for the noise level. Below a particular threshold, the probability of missed opportunity increases as the noise level increases. Yet above this threshold, the probability of missed opportunity decreases as the noise level increases.

A tight closed-form approximation of the log-normal fading channel capacity

The log-normal probability distribution has been commonly used in wireless communications to model the shadowing and, recently, the small-scale fading for indoor ultrawideband (UWB) communications. In this paper, a tight closed-form approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacities of communication systems operating over log-normal fading channels. We also utilize this expression to show that the capacity of a multi-antennas UWB system operating over the IEEE 802.15.3a channel can be improved mainly through receive diversity.

On the capacity of log-normal fading channels

In this letter we provide an analytical expression for the moments of the capacity for the log-normal fading channel. Since the developed expression involves infinite series, we show that the error that results from the truncation of these series is insignificant. We also analyze in more details the ergodic capacity by giving a simpler expression for the remainder of the truncated series. Relying on the fact that the sum of log-normal random variables (RV) is well approximated by another lognormal RV, we further utilize the obtained results to approximate the capacity of diversity combining techniques in correlated lognormal fading channels. The results that we provide in this letter are an important tool for measuring the performance of communication links in a log-normal environment.

Long-term fading channel estimation from sample covariances

The power attenuation dynamics for long-term log-normal fading channels in wireless communication systems is modeled by a stochastic differential equation. Estimators for the model parameters based on sample covariances from data corrupted by discrete-time measurement noise are given. It is shown that the estimators are consistent, and variance expressions are derived and compared numerically to the Cramér–Rao bound. The estimation of the model parameters allows for the design of power control algorithms.