Petros S. Bithas

On the performance analysis of digital communications over generalized-K fading channels

The performance of digital communication systems over generalized-K (K/sub G/) fading channels is analyzed and evaluated. Novel closed form expressions for the SNR statistics, the average Shannons channel capacity and the bit error rate (BER) are derived. These expressions are used to study important performance criteria such as the outage performance, the average capacity and the BER for a great variety of modulation formats in K/sub G/ fading channels. The proposed mathematical analysis is accompanied with various performance evaluation results, which demonstrate the usefulness of the proposed approach.

The bivariate generalized-Κ (Κ G ) distribution and its application to diversity receivers

The correlated bivariate generalized-K (KG) distribution, with not necessarily identical shaping and scaling parameters, is introduced and studied. This composite distribution is convenient for modeling multipath/shadowing correlated fading environments when the correlations between the signal envelopes and their powers are different. Generic infinite series expressions are derived for the probability density function (PDF), the cumulative distribution function (CDF) and the joint moments. Assuming identical shaping parameters, simpler expressions for the PDF, CDF and the characteristic function (CF) are provided, while the joint moments are derived in closed form. Furthermore, the PDFs of the product and ratio of two correlated KG random variables are obtained. Capitalizing on these theoretical expressions for the statistical characteristics of the correlated KG distribution, the performance analysis of various diversity reception techniques, such as maximal ratio combining (MRC), equal gain combining (EGC) and selection diversity (SD), over bivariate KG fading channels is presented. For the SD, the outage probability is studied, while for the MRC and EGC the average bit error probability is obtained. The proposed analysis is accompanied by numerical results, clearly demonstrating the usefulness of the theoretical approach as well as the appropriateness of the KG distribution to model multipath/shadowing fading channels.

GSC diversity receivers over generalized-gamma fading channels

A detailed performance analysis of generalized-selection combining GSC(2,L) receivers operating over generalized-gamma fading channels is presented. For this class of receivers, a novel closed-form expression for the moments output signal-to-noise ratio is derived. Furthermore, infinite series representations for the moments-generating and the cumulative distribution functions are obtained. The proposed mathematical analysis is accompanied by various performance evaluation results. These theoretical results are complemented by equivalent computer simulated results, which validate the accuracy of the proposed analysis.

On the correlated weibull fading model and its applications

Ascertaining on the suitability of the Weibull model to describe fading channels, a theoretical framework for the multivariate Weibull distribution, generated from correlated Gaussian elements, is presented. Concerning the bivariate Weibull model with arbitrary average fading powers, novel closed-form expressions for the joint probability density function (pdf), moments-generating function, cumulative distribution function (cdf), product moments, and the correlation coefficient are presented. Moreover, useful analytical formulae for the pdf and cdf of the multivariate Weibull distribution, with identical average fading powers and exponential correlation, are obtained. The derived theoretical results are applied to analytically evaluate the outage probability of selection diversity receivers, operating over correlated Weibull fading channels.

Switched Diversity Receivers over Correlated Weibull Fading Channels

The problem of analyzing the performance of switch and stay combing (SSC) diversity receivers, operating over correlated and not necessarily identical distributed Weibull fading channels is considered in this paper. By means of a convenient expression for the bivariate Weibull distribution, the probability density function (PDF) of the SSC output signal-to-noise ratio (SNR) is derived in terms of the first order Marcums Q-function. The moments of the output SNR and the corresponding cumulative distribution function (CDF) are also obtained in closed form and are utilized to derive expressions for the average output SNR, amount of fading and outage probability. By using a rapidly convergent infinite series representation for the bivariate Weibull distribution, an analytical expression for the moments generating function (MGF) is derived. The MGF can be efficiently used to evaluate the average bit error probability (ABEP) for several modulation schemes. The proposed mathematical analysis is complimented by various numerical evaluated results, which evaluate the effects of fading severity and correlation on the overall system performance

Dual-branch diversity receivers over correlated rician fading channels

In this paper the performance of dual-branch diver- sity receivers operating over correlated Rician fading channels is analyzed and novel performance evaluation results are presented. By representing the bivariate Rician probability density function of the signal-to-noise ratio (SNR) as a rapidly converging infi- nite sum, useful analytical expressions for the performance of dual-branch selection combining and maximal ratio combining receivers are derived. Capitalizing on these infinite series repre- sentations, novel analytical formulae for the average bit-error and outage probability are obtained. The proposed analysis is used to obtain various novel performance evaluation results having as parameters of interest fading severity, average SNR and Rician correlation coefficient. The series convergence rate is also studied verifying the fast convergence of the analytical expressions. The accuracy of most of the theoretical results have been verified by means of computer simulation.

Partitioning of Distributed MIMO Systems Based on Overhead Considerations

Distributed-Multiple Input Multiple Output (D-MIMO) networks is a promising enabler to address the challenges of high traffic demand in future wireless networks. A limiting factor that is directly related to the performance of these systems is the overhead signaling required for distributing data and control information among the network elements. In this paper, the concept of orthogonal partitioning is extended to D-MIMO networks employing joint multi-user beamforming, aiming to maximize the effective sum-rate, i.e., the actual transmitted information data. Furthermore, in order to comply with practical requirements, the overhead subframe size is considered to be constrained. In this context, a novel formulation of constrained orthogonal partitioning is introduced as an elegant Knapsack optimization problem, which allows the derivation of quick and accurate solutions. Several numerical results give insight into the capabilities of D-MIMO networks and the actual sum-rate scaling under overhead constraints.

An Improved Threshold-Based Channel Selection Scheme for Wireless Communication Systems

In several wireless communication systems, low complexity channel selection schemes are required, as power efficient mechanisms to improve performance. In this context, the best selection scheme, in terms of performance, comes at the cost of increased complexity, since it necessitates a continuous monitoring of all available channels. In this paper, a new threshold-based channel selection strategy is proposed, which decreases the system complexity, without considerably affecting the system performance. Assuming independent but nonidentically distributed channel conditions, a generic analytical framework is first presented, based on the Markov chain theory. Then, the proposed selection scheme is applied to three specific communication scenarios, namely multichannel reception, transmit antenna selection with diversity reception, and cooperative relay selection. In all three cases, closed-form results are obtained and used to analyze the performance of the systems under consideration. It is shown that based on the proposed scheme, computational complexity is reduced and thus important energy savings can be achieved, without a significant loss in performance.

On the Distribution of the Sum of Generalized Gamma Variates and Applications to Satellite Digital Communications

A versatile envelope distribution which may be useful for both terrestrial and satellite fading channel modelling is the generalized Gamma (GG) distribution. By considering the product of N GG random variables (RV)s, useful expressions for its moments-generating and cumulative distribution functions are obtained in closed-form. These expressions are used to derive closed-form union upper-bound for the distribution of the sum of GG distributed RVs. The proposed bound turns out to be an extremely convenient analytical tool for studying the performance of N-branch equal-gain combining receivers operating over GG fading channels. For such receivers, novel union upper-bounds for the outage and the average bit error probability are derived and evaluated in terms of the Meijers G-function. The tightness of the proposed bounds is verified by performing comparisons between numerical evaluation and computer simulations results

Digital Communications over Generalized-K Fading Channels

In this work, a flexible distribution, called as generalized-K, is used for fading channel modeling. Starting from its probability density function (PDF), useful closed-form expressions for the cumulative distribution function, moments-generating function, moments, and average Shannons channel capacity are derived. These expressions are used to study important performance criteria such as the capacity, amount of fading, outage performance, and bit error probability for a great variety of modulation formats. The proposed mathematical analysis is accompanied with various performance evaluation results, which demonstrate the usefulness and flexibility of the proposed model