This work presents accurate closed-form approximations for the probability density function (PDF) of the sum of independent and identically distributed (i.i.d.) fading envelopes and square fading envelopes, experienced by indoor and outdoor channels operating in the D-band. In order to provide a simple yet accurate analytical expression for these PDFs, we propose the use of the Pearson family of distributions, which are mainly characterized by their skewness and kurtosis. Our analysis has demonstrated that among the seven types of Pearson distributions, the type I Pearson distribution provides the most accurate fit to the exact PDF of envelopes and squared envelopes, for a diverse range of indoor and outdoor wireless propagation scenarios. The distribution parameters are estimated using moments-matching techniques, while the requisite moments are obtained through a measurement campaign conducted in indoor as well as outdoor environments. Specifically, with regard to the indoor scenarios, the following locations have been considered: A mall, an airport, and an entrance hall. With regard to the outdoor scenarios, the following locations have been selected: A university campus, a residential area, and a city center. Our results are further applied to analyze the average bit error rate performance and the ergodic capacity of equal-gain combining (EGC) and maximal-ratio combining (MRC) receivers, the sum rate of rate splitting multiple access (RSMA) systems with EGC diversity reception, as well as the coverage probability of wireless systems employing intelligent reflecting surfaces (IRS). Our analysis is supported by extensive numerical results and Monte Carlo simulations.

The authors consider a low earth orbit (LEO) mobile satellite system (MSS) that accepts new and handover calls of multirate service‐classes. New calls arrive in the system as batches, following the batched Poisson process. A batch has a generally distributed number of calls. Each call is treated separately from the others and its acceptance is decided according to the availability of the requested number of channels. Handover calls follow also a batched Poisson process. All calls compete for the available channels under the complete sharing policy. By considering the LEO‐MSS as a multirate loss system with ‘satellite‐fixed’ cells, it can be analysed via a multi‐dimensional Markov chain, which yields to a product form solution (PFS) for the steady‐state distribution. Based on the PFS, they propose a recursive and yet efficient formula for the determination of the channel occupancy distribution, and consequently, for the calculation of various performance measures including call blocking and handover failure probabilities. The latter are much higher compared to the corresponding probabilities in the case of the classical (and less bursty) Poisson process. Simulation results verify the accuracy of the proposed formulas. Furthermore, they discuss the applicability of the proposed model in software‐defined LEO‐MSS.

Secrecy capacity is a fundamental information-theoretic performance metric to predict the maximum data rate of reliable communication, while the intended message is not revealed to the eavesdropper. Motivated by this consideration in this paper, a unified communication-theoretic framework for the analysis of the probability of nonzero secrecy capacity, the secrecy outage probability, and the secrecy capacity of multiple-antenna systems over fading channels is proposed. Specifically, a powerful frequency-domain approach is first developed in which the integrals involved in the evaluation of the probability of nonzero secrecy capacity and secrecy outage probability are transformed into the frequency domain, by employing Parseval's theorem. A generic approach for the evaluation of the asymptotic secrecy outage probability at high signal-to-noise ratio (SNR) region is also introduced, thus providing useful insight as to the parameters affecting the secrecy performance. Finally, a unified numerical approach for computing the average secrecy capacity of multiple-antenna systems under arbitrary fading environments is developed. The proposed framework is general enough to accommodate any well-known multiantenna transmission technique and fading model. Finally, the secrecy performance of several multiple-antenna system setups is assessed, in the presence of generalized fading conditions and arbitrary antenna correlation, while various numerical and computer simulation results are shown and compared to substantiate the proposed mathematical analysis.

We present an analytical framework for estimating the benefits that arise from the utilization of semiconductor optical amplifiers (SOA)s at fade impaired outdoor optical wireless systems. We first investigate the impact of fading on both the signal optical power and the amplified spontaneous emission, and derive analytical relations that accurately associate the system bit-error-rate (BER) with the channel state. We then utilize the analytical relations to assess the performance of the amplified optical signal under moderate-to-strong fading and demonstrate that the sensitivity improvement, which is expected by the amplification process, improves the first- and second-order signal-to-noise ratio statistics at the electronic receiver. Our results show that the average BER and average fade duration can all be drastically reduced by the incorporation of the SOA, provided that the link length remains within reasonable limits that are dictated by the channel statistics.

We present an analytical framework for estimating the benefits that arise from the utilization of semiconductor optical amplifiers at the receiver of fade impaired outdoor optical wireless systems. We first investigate the impact of fading on both the signal optical power and the amplified spontaneous emission, and derive analytical relations that accurately associate the system bit-error-rate with the channel state. We then utilize the analytical relations to assess the performance of the amplified system under moderate-to-strong (γ - γ) fading in terms of first and second order signal statistics. Our results show that the receiver sensitivity improvement, which is imparted by the amplification process, can drastically reduce the average bit-error-rate, link outage probability and average fade duration, provided that the link length remains within certain limits that are determined by the turbulence intensity scenario under consideration.

We develop an analytical framework for the end-to-end (e2e) asymptotic performance of pilot-symbol assisted Mary phase-shift keying (M-PSK) dual-hop relaying communication networks. The relays use the selective-decode-and-forward protocol and are equipped with multiple receive antennas. Channel estimation per antenna branch is done based on the least-squares estimation technique by means of pilot symbols. Also, maximal-ratio combining and coherent detection are performed at the receiving end. Simple approximate average symbol error probability (ASEP) expressions are obtained for high signal-to-noise ratio (SNR) when M ≥2. Our analysis is generic enough to account for any frequency-flat, time-selective, and/or arbitrarily correlated fading channel model per hop. As a case study, we provide e2e M-PSK ASEP expressions considering arbitrarily correlated Nakagami fading channels. Moreover, the optimal power allocation is studied, while the cooperation-gain and diversity-order are extracted. Numerical results are finally presented to verify the accuracy of our asymptotic expressions.

We present a novel fade mitigation technique that is applicable on outdoor optical wireless systems. Our key idea is to utilize the nonlinear power-dependent gain properties of a semiconductor optical amplifier (SOA) to provide unbalanced amplification between faded and non-faded instances of the optical wireless signal. We analytically demonstrate that this power equalization process smoothes out fade-induced power fluctuations and drastically reduces the probability of the system being in a fade state. In medium to strong turbulence governed by gamma-gamma statistics, our results predict that the fade probability can be reduced by over 80% when the SOA is introduced at the optical wireless receiver. We also show that the duration of remaining fades is reduced by a sizeable percentage, and a percentile reduction of the average fade duration of over 85% can be achieved at the SOA output.

We develop an analytical framework for the end-to-end (e2e) average symbol error probability (ASEP) of dual-hop relaying networks with pilot-symbol assisted M-ary phase-shift keying (M-PSK) modulation. The relays use the selective decode-and-forward protocol and are equipped with multiple receive antennas. The channels are estimated per antenna branch based on the least-squares estimation (LSE) technique by means of pilot symbols. Also, maximal-ratio combining and coherent detection are performed per receiving end. Exact e2e analytical ASEP expressions are derived for binary and quadrature phase-shift keying (BPSK and QPSK), while simple approximate expressions and bounds are obtained for high signal-to-noise ratio (SNR) when M ≥ 2. Our analysis is generic enough to account for any frequency-flat, time-selective, and/or arbitrarily correlated fading channel model per hop. As a case study, we further provide e2e ASEP expressions considering arbitrarily correlated Nakagami fading channels. For high SNR, closed-form expressions are derived, while the cooperation-gain and diversity-order are also extracted. In addition, two power allocation strategies are investigated and analytical solutions are provided. Comparisons between numerical and computer simulation results are finally presented to verify the validity of the proposed approach and the accuracy of the high-SNR approximate expressions.

ABSTRACT In this paper, a study on the end‐to‐end performance of multi‐hop non‐regenerative relaying networks over independent generalized‐gamma (GG) fading channels is presented. Using an upper bound for the end‐to‐end signal‐to‐noise ratio (SNR), novel closed‐form expressions for the probability density function, the moments, and the moments‐generating function of the end‐to‐end SNR are presented. Based on these derived formulas, lower bounds for the outage and the average bit error probability (ABEP) are derived in closed form. Special attention is given to the low‐ and high‐SNR regions having practical interest as well as to the Nakagami fading scenario. Moreover, the performance of the considered system when employing adaptive square‐quadrature amplitude modulation is further analyzed in terms of the average spectral efficiency, the bit error outage, and the ABEP. Computer simulation results verify the tightness and the accuracy of the proposed bounds. Copyright © 2011 John Wiley & Sons, Ltd.

The authors study the performance of a dual-hop plus a direct link multiple-input multiple-output (MIMO) wireless communication system using orthogonal space–time block codes. The system under consideration is based on the decode-and-forward relaying protocol and operates over spatially correlated Nakagami-m fading channels. The proposed analysis is generic enough to account for any MIMO correlation model either from measurements or having theoretical and analytical justification. Analytical expressions for the system end-to-end outage and average symbol error probability are obtained, while critical parameters of the MIMO channel are taken into consideration such as the angle of arrival, the antenna array configuration, the wavelength and non-isotropic scattering conditions. Various numerical and computer simulation results demonstrate the proposed mathematical analysis and the impact of the above parameters to the system performance.

In this paper we study the statistics of the sum of not necessarily identically distributed kappa, that is, K, random variables (RV)s. Assuming half-integer values for the shaping parameters, novel closed-form expressions for the probability density function (PDF) of the sum of independent K RVs are obtained, while for arbitrary values of the shaping parameters, a corresponding PDF expression is derived in terms of fast converging infinite series. Furthermore, an infinite series representation for the PDF of the sum of two arbitrarily correlated K RVs is derived. The proposed analysis is employed to the performance analysis of equal-gain combining (EGC) receivers operating over composite fading/shadowing channels modeled by the K distribution. More specifically, the outage and the average bit error probabilities, as well as the average channel capacity of EGC receivers operating over such composite environment are studied. Considering different channel fading/shadowing conditions and correlation effects, various numerical performance evaluation results are presented. These results are complemented by equivalent computer simulated ones that validate the accuracy of the proposed analysis.

Let X and Y be two independent L x 1 complex Gaussian random vectors distributed as CN (m×, σ2× IL) and CN (mY, σY2IL), respectively, where I_L denotes the L x L identity matrix. The joint characteristic function (c.f.) of the real and imaginary parts of the inner product YHX is derived in closed form, with (·)Hdenoting the conjugate transpose. Based on this joint c.f., a unified analytical framework for the derivation of the average symbol error probability (ASEP) of a multibranch diversity reception system over flat correlated fading using M-ary phase-shift keying is developed. The receiver employs maximal-ratio combining with least squares channel estimation by means of pilot symbols. The optimal average pilot-to-noise power ratio is obtained in closed form, and the analytical framework is applied to Nakagami and Rice fading. For Nakagami fading, closed form ASEP expressions are obtained for the cases of high signal-to-noise (SNR) and binary phase-shift keying, while for Rice fading, high SNR approximate expressions are obtained in terms of a single integral under the constant correlation model and for independent and identically distributed channels. Both analytical and computer simulation results are presented and compared in order to verify the validity of the proposed analysis.

The spectral efficiency of L-branch selection diversity (SD) receiver with different adaptive transmission techniques operating over generalised-Gamma (GG) fading channels is studied. Novel expressions for important adaptive transmission techniques are obtained, namely optimal power and rate adaptation, optimal rate adaptation, channel inversion with fixed rate (CIFR) and truncated CIFR. Furthermore, simplified expressions for the capacities are obtained for SD reception in Nakagami-m as well as Weibull fading channels. The derived closed-from expressions extend previously published results to the GG fading model. Numerical results are given to demonstrate the usefulness of the theoretical approach.

In this paper, coherent detection for multilevel correlated signaling sets in additive white Gaussian noise is addressed. The contribution is twofold. Firstly, correlation structures that minimize the symbol error probability (SEP) of M-ary frequency-shift keying as well as of arbitrarily correlated signaling sets are investigated, while secondly, a general and analytical expression for the SEP is derived in the form of a single integral. The structure of the associated correlation matrix is generic and includes various known signaling sets as special cases. Specific correlation structures that minimize the SEP are also studied. Based on eigendecomposition or LU decomposition, generic methods for constructing a correlated signaling set for any correlation matrix under consideration are also provided.

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 KGrandom variables are obtained. Capitalizing on these theoretical expressions for the statistical characteristics of the correlated KGdistribution, the performance analysis of various diversity reception techniques, such as maximal ratio combining (MRC), equal gain combining (EGC) and selection diversity (SD), over bivariate KGfading 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 KGdistribution to model multipath/shadowing fading channels.

The statistical characteristics of the trivariate and quadrivariate Weibull fading distribution with arbitrary correlation, non-identical fading parameters and average powers are analytically studied. Novel expressions for important joint statistics are derived using the Weibull power transformation. These expressions are used to evaluate the performance of selection combining (SC) and maximal ratio combining (MRC) diversity receivers in the presence of such fading channels.

This paper deals with a trivariate Nakagami-m distribution derived from the diagonal elements of a Wishart matrix. For this distribution, infinite series representations for its probability density and cumulative distribution functions are derived having an arbitrary covariance matrix and integer-order fading parameters. Moreover, upper bounds on the error resulting from truncating the infinite series are obtained. Based on the derived formulas, the performance of triple-branch generalized selection combining (GSC) receivers is analyzed. For this type of receivers, the outage and the average bit error probability for a variety of modulation schemes are analytically obtained. The performance of GSC receivers is compared to that of conventional selection and maximal-ratio diversity schemes. In order to check the accuracy and convergence of the derived formulas, various performance evaluation results are presented and compared to equivalent simulation ones.

New results for the multichannel Nakagami-m fading model with an arbitrary correlation matrix are presented in this paper. By using an efficient tridiagonalization method based on Householder matrices, the inverse of the Gaussian correlation matrix is transformed to tridiagonal, managing to derive a closed-form union upper bound for the joint Nakagami-m probability density function and an exact analytical expression for the moment generating function of the sum of identically distributed gamma random variables. Our analysis considers an arbitrary correlation structure, which includes as special cases the exponential, constant, circular, and linear correlation ones. Based on the proposed mathematical analysis, we obtain a tight union upper bound for the outage probability of multibranch selection diversity receivers as well as exact analytical expressions for the outage and the average error probability of multibranch maximal-ratio diversity receivers. Our analysis is verified by comparing numerically evaluated with extensive computer simulation performance evaluation results, showing the usefulness of the proposed approach.

Abstract In this paper, an efficient cross‐layer design that performs joint adaptation of the physical (PHY) and application layers of a mobile WiMAX network is proposed. The design takes into account channel state and performance information from the PHY and medium access control (MAC) layers, respectively. It uses a decision algorithm to evaluate this information, specify unfavorable conditions regarding low channel quality and increased congestion, and take measures by coordinating modulation order, transmission power, and media encoding rate, toward improved overall quality of service (QoS) offered to the user. Extensive simulation results show that the proposed design achieves considerably reduced packet loss and power consumption, combined with increased throughput as compared to a typical mobile WiMAX system. Copyright © 2008 John Wiley & Sons, Ltd.

In this paper, coherent detection for multilevel correlated signaling sets in additive white Gaussian noise is addressed. From the decision rule, a general analytical expression for the symbol error probability (SEP) is derived, which is in the form of a single integral. Our new result is not only in agreement with a known equivalent expression, but it also has a much simpler analytical form. The structure of the correlation matrix under consideration of the signaling set is quite generic, including various known signaling sets as special cases. Hence the derived SEP expression is useful for analyzing the performance of various coherent modulation schemes such as multilevel phase-shift and frequency-shift keying. Specific correlation structures which minimize the SEP are also studied. Based on eigendecomposition or LU decomposition, generic methods for constructing a correlated signaling set for any correlation matrix under consideration are also provided.

The performance of dual-branch equal-gain combining (EGC) and maximal-ratio combining receivers operating over a composite correlated fading environment, modelled by the generalised Gamma (GG) distribution, is analysed. The moments of the output signal-to-noise ratio are derived in closed form for both types of receivers, and by employing the Padé approximants method, the average bit error probability is studied for a great variety of modulation schemes. Furthermore, based on the statistic of the product of two correlated GG random variables, a tight union upper bound for the outage probability of the EGC is obtained, whereas for the special case of Weibull fading a simpler bound is derived in closed form. The proposed mathematical analysis is complemented by various, numericaly evaluated performance results, whereas simulations verify the correctness of the proposed analysis.

The correlated bivariate K-distribution with arbitrary and not necessarily identical parameters is introduced and analyzed. Novel infinite series expressions for the joint probability density function and moments are derived for the general case where the associated bivariate distributions, i.e., Rayleigh and gamma, are both arbitrary correlated. These expressions generalize previously known analytical results obtained for identical parameter cases. Furthermore, considering independent gamma distributions, the cumulative distribution and characteristic functions are analytically obtained. Although the derived expressions can be used in a wide range of applications, this letter focuses on the performance analysis of dual branch diversity receivers. Specifically, the outage performance of dual selection diversity receivers operating over correlated K fading/shadowing channels is analytically evaluated. Moreover, for low normalized outage threshold values, closed-form expressions are obtained.

In this letter, closed-form outage probability expressions are presented for an -relays dual-hop plus a direct link network, in which the decode-and-forward relaying protocol is employed. Our analysis significantly extends previous results on Rayleigh fading, considering a Nakagami- fading environment with either equal or distinct second hops fading parameters to average power ratios. Various numerical examples illustrate the proposed analysis.

New results for the multichannel Nakagami-m fading model with an arbitrary correlation matrix are presented. By using an efficient tridiagonalization method based on Householder matrices, a union upper bound for the joint Nakagami-m probability density function and an infinite series representation for the moment generating function of the sum of gamma random variables are derived. Based on the proposed mathematical analysis, a tight union upper bound for the outage probability of multibranch selection diversity, as well as, exact analytical expressions for the outage and average error probability of multibranch maximal-ratio diversity receivers operating over identically distributed and arbitrarily correlated Nakagami-m fading channels are obtained. Our analysis is verified by comparisons of numerically evaluated results with extensive computer simulation ones.

In this paper, new results for the multivariate Rayleigh distribution with an arbitrary correlation matrix are presented. By using an efficient tridiagonalization method based on Householder matrices, closed-form union upper bounds for its joint probability density and cumulative density functions are derived. Based on the proposed mathematical analysis, a tight union upper bound and an analytical approximation for the outage probability of multibranch selection diversity receivers operating over identically distributed and arbitrarily correlated Rayleigh fading channels are obtained. Our analysis is verified by comparing numerically evaluated results with extensive computer simulation ones.

An infinite series representation for the moment generating function of the sum of squared arbitrarily correlated Rayleigh random variables is presented. Based on the derived formula, corresponding analytical expressions for the probability density and cumulative distribution functions are extracted. As an application for the aforementioned sum, exact analytical expressions for the outage and the average error probability, as well as, the channel average spectral efficiency of multibranch maximal-ratio diversity receivers operating over identically distributed and arbitrarily correlated Rayleigh fading channels are obtained. Our analysis is verified by comparing numerically evaluated results with extensive computer simulation ones.

In this paper, for an L-relays dual-hop plus a direct link wireless network, in which the decode-and-forward relaying protocol is employed, closed-form expressions for the end-end outage probability are presented. Our analysis considers a Nakagami-m fading environment with either equal or distinct second hops fading parameter to average power ratios. Various numerical examples illustrate the proposed analysis.

A generic and novel distribution, referred to as Nakagami, constructed as the product ofNstatistically independent, but not necessarily identically distributed, Nakagami-mrandom variables (RVs), is introduced and analyzed. The proposed distribution turns out to be a very convenient tool for modelling cascaded Nakagami-mfading channels and analyzing the performance of digital communications systems operating over such channels. The moments-generating, probability density, cumulative distribution, and moments functions of theN*Nakagami distribution are developed in closed form using the Meijer's G -function. Using these formulas, generic closed-form expressions for the outage probability, amount of fading, and average error probabilities for several binary and multilevel modulation signals of digital communication systems operating over theN*Nakagami fading and the additive white Gaussian noise channel are presented. Complementary numerical and computer simulation performance evaluation results verify the correctness of the proposed formulation. The suitability of theN*Nakagami fading distribution to approximate the lognormal distribution is also being investigated. Using Kolmogorov--Smirnov tests, the rate of convergence of the central limit theorem as pertaining to the multiplication of Nakagami-mRVs is quantified.

In this paper, we study the performance of multihop free-space optical (FSO) wireless systems over turbulence-induced fading channels. The analysis is carried out for systems employing amplify-and-forward (AF) or decode-and-forward (DF) relays and for turbulence channels which can be modeled by the Gamma-Gamma distribution. An exact analytical expression for the end-to-end outage probability of AF systems is obtained, while a closed-form expression of DF systems is derived. The average bit-error probability of a dual-hop FSO system employing a DF relay is studied as a special case. Numerical examples are also presented to illustrate the proposed analysis and to further investigate the effects of the turbulence severity on the multihop FSO systems' performance.

We present closed-form expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the sum of non-identical squared Nakagami-m random variables (RVs) with integer-order fading parameters. As it is shown, they can be written as a weighted sum of Erlang PDFs and CDFs, respectively, while the analysis includes both independent and correlated sums of RVs. The proposed formulation significantly improves previously published results, which are either in the form of infinite sums or higher order derivatives of the fading parameter m. The obtained formulas can be applied to the performance analysis of diversity combining receivers operating over Nakagami-m fading channels

A versatile envelope distribution which generalizes many commonly used models for multipath and shadow fading is the so-called generalized Gamma (GG) distribution. By considering the product of N GG random variables (RV)s, novel expressions for its moments-generating, probability density, and cumulative distribution functions are obtained in closed form. These expressions are used to derive a 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 TV-branch equal-gain combining receivers operating over GG fading channels. For such receivers, first the moments of the signal-to-noise (SNR) at the output, including average SNR and amount of fading, are obtained in closed form. Furthermore, novel union upper bounds for the outage and the average bit error probability are derived and evaluated in terms of Meijer's G-functions. The tightness of the proposed bounds is verified by performing comparisons between numerical evaluation and computer simulations results

We present closed-form bounds for the performance of multihop transmissions with non-regenerative relays over Nakagami-m fading channels. The end-to-end signal-to-noise ratio (SNR) is formulated and upper bounded by using the inequality between harmonic and geometric mean of positive random variables (RVs). Novel closed-form expressions are derived for the moment generating function, the probability density function, and the cumulative distribution function of the product of arbitrary powers of statistically independent Gamma RVs in terms of the Meijer's G-function. Using these theoretical results, closed-form lower bounds are obtained for the outage and average bit error probability of phase or frequency modulated signallings, while simple asymptotic expressions are also given for the bounds at high SNRs. Numerical results are compared to computer simulations, to show the tightness of the proposed bounds.

Ascertaining on the suitability of the Weibull distribution to model fading channels, a theoretical framework for a class of multivariate Weibull distributions, originated from Gaussian random processes, is introduced and analyzed. Novel analytical expressions for the joint probability density function (pdf), moment-generating function (mgf), and cumulative distribution function (cdf) are derived for the bivariate distribution of this class with not necessarily identical fading parameters and average powers. Two specific distributions with arbitrary number of correlated variates are considered and studied: with exponential and with constant correlation where their pdfs are introduced. Both cases assume equal average fading powers, but not necessarily identical fading parameters. For the multivariate Weibull distribution with exponential correlation, useful corresponding formulas, as for the bivariate case, are derived. The presented theoretical results are applied to analyze the performance of several diversity receivers employed with selection, equal-gain, and maximal-ratio combining (MRC) techniques operating over correlated Weibull fading channels. For these diversity receivers, several useful performance criteria such as the moments of the output signal-to-noise ratio (SNR) (including average output SNR and amount of fading) and outage probability are analytically derived. Moreover, the average symbol error probability for several coherent and noncoherent modulation schemes is studied using the mgf approach. The proposed mathematical analysis is complemented by various evaluation results, showing the effects of the fading severity as well as the fading correlation on the diversity receivers performance.

We study the performance of L-branch equal-gain combining (EGC) and maximal-ratio combining (MRC) receivers operating over nonidentical Weibull-fading channels. Closed-form expressions are derived for the moments of the signal-to-noise ratio (SNR) at the output of the combiner and significant performance criteria, for both independent and correlative fading, such as average output SNR, amount of fading and spectral efficiency at the low power regime, are studied. We also evaluate the outage and the average symbol error probability (ASEP) for several coherent and noncoherent modulation schemes, using a closed-form expression for the moment-generating function (mgf) of the output SNR for MRC receivers and the Pade/spl acute/ approximation to the mgf for EGC receivers. The ASEP of dual-branch EGC and MRC receivers is also obtained in correlative fading. The proposed mathematical analysis is complimented by various numerical results, which point out the effects of fading severity and correlation on the overall system performance. Computer simulations are also performed to verify the validity and the accuracy of the proposed theoretical approach.

In mobile radio systems, antenna diversity is used to combat fading and reduce the impact of cochannel interference. In this paper, we analyze the performance of L-branch equal-gain combining receivers over correlated nonidentically distributed Nakagami-m fading channels, in the presence of multiple identical cochannel interferers and additive white Gaussian noise. The performance criterion considered is the average output signal-to-interference-plus-noise ratio, which is obtained in closed form for both independent and correlative fading. Due to the simple form of the derived expressions, they readily allow numerical evaluation for cases of practical interest.

Efficient performance bounds for multihop wireless communications systems with non-regenerative fixed-gain relays operating over non-identical generalized fading channels, are presented. More specifically, the end-to-end signal-to-noise ratio (SNR) is formulated and upper bounded by using the well-known inequality between harmonic and geometric mean of positive random variables. Based on this bound, the moments of the end-to-end SNR for Rayleigh, Nakagami-m, and Rice fading channels, are obtained in simple closed-forms. Furthermore, the outage performance and the average error probability for coherent and non-coherent modulation schemes are also studied using the moment-generating function (MGF) approach. The proposed method for the evaluation of the MGF is based on the Pade approximants theory. Moreover, new expressions are derived for the gain of previously proposed "semi-blind" relays. These expressions are used in numerical and computer simulations examples, to verify the accuracy and to show the tightness of the proposed bounds.

Motivated by the suitability of the Weibull distribution to model multipath fading channels, the performance of L-branch selection combining (SC) receivers, with non-identical statistics, is presented. Deriving a useful expression for the probability density function of the SC output signal-to-noise ratio (SNR), important performance metrics are studied. More specifically, a closed-form expression is derived for the moments of the combiner output SNR, which is used to study the average output SNR and the amount of fading. The average symbol error probability for several coherent and non-coherent, binary and multilevel modulation schemes is also obtained in closed-form.

The performance of dual-branch SC receivers over correlated Weibull fading channels is studied in this paper. Exact closed-form expressions are derived for the probability/cumulative density functions and the moments of the output signal-to-noise ratio (SNR). Important performance criteria, such as average output SNR, amount of fading (AoF), outage probability and average bit error probability (ABEP) for several modulation schemes, are studied and novel closed-form analytical expressions are derived. The proposed analysis is complemented by various performance evaluation results, including the effects of input SNRs unbalancing, fading severity and fading correlation on the overall system performance. Computer simulations results verify the validity and the accuracy of the proposed analysis.

Motivated by the suitability of the Weibull distribution to model multipath fading channels, the second order statistics and the spectral efficiency (SE) of L-branch SC receivers are studied. Deriving a novel closed-form expression for the probability density function (pdf) of the SC output SNR, the average level crossing rate (LCR), the average fade duration (AFD) and the Shannon's average SE, at the output of the SC, are derived in closed-forms. Our results are sufficiently general to handle arbitrary fading parameter and dissimilar branch powers.

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.