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This paper studies the multivariate Ricean distribution, which is the most important distribution for modeling the magnitude of the received signal when line-of-sight propagation conditions exist. In this paper, assuming different mean values for the Ricean distributed random variables, generic expressions for the multivariate Ricean probability density function, cumulative distribution function, and the joint moments are derived in terms of integral representations. As an application example, these results have been used to analyze the performance of a multi-branch selection diversity receiver, operating in spatially correlated Ricean fading environment. Moreover, an asymptotic closed-form expression has been also provided, which approximates quite well to the exact one, and has been used to study various performance metrics. Finally, a complexity analysis has been performed and simulation results have been also presented. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of an underlay cognitive two-way relay system with direct link using time division broadcast protocol in the presence of primary user's interference. Herein, relying on the practicability and low complexity of statistical channel state information, the secondary transmissions are in compliance with the fading-averaged interference constraints imposed by the primary receiver. For this setup, we study an adaptive link utilization scheme (ALUS) that can exploit both direct and relay links with appropriate diversity combining methods to improve the performance of secondary users. Based on ALUS, we evaluate and compare the performance of two decode-and-forward based relaying strategies viz., fixed relaying and incremental relaying. We derive the tight closed-form expressions of outage probability of the secondary communications for both the strategies over Nakagami-mfading channels. We further conduct asymptotic high signal-to-interference-plus-noise ratio analysis to examine the achievable diversity order of the considered system. In addition, we quantify the expected spectral efficiency and average transmission time for both relaying strategies. Our results illustrate that the incremental relaying strategy can significantly improve the system performance in comparison with fixed relaying. Numerical and simulation results are provided to attest our theoretical studies. [ABSTRACT FROM AUTHOR]

Important statistical properties of the double-generalized Gamma (dGG) distribution are studied in this paper. The dGG distribution is suitable for modeling non-homogeneous double-scattering radio propagation fading conditions, which can be frequently observed in vehicle-to-vehicle (V2V) communications. In this context, important statistical metrics for the bivariate dGG distribution, such as the joint probability density function, cumulative distribution function, and the moments, are derived for the first time, while simplified expressions for the corresponding marginal statistical metrics are presented. Moreover, the second-order statistics of this distribution are also analytically studied. The derived analytical framework has been employed to analyze the performance of a transmit antenna selection system operating in V2V communication channels modeled by the dGG distribution. In this scenario, the impact of outdated channel state information (CSI) to the system’s performance is investigated in terms of various metrics, including the level crossing rate and the average fade duration. Furthermore, simplified asymptotic closed-form expressions for the outage probability have been derived to examine the achievable diversity and coding gains. Based on our analysis, insightful discussions are provided. It is shown that the diversity gain is independent from the number of transmit antennas when the available CSI becomes outdated. [ABSTRACT FROM PUBLISHER]

The performance of a molecular signal detector relies on selected value of the detection threshold. In fact, arbitrary choice of detection threshold would increase either the probability of miss detection or the probability of false alarm. Thereby, an appropriate value of detection threshold is required in order to optimize the error performance of a realistic diffusion-based molecular communication (DbMC) system. For this, we come up with a new approach that yields optimal value for convex optimization problem in DbMC using logarithmic barrier followed by modified Karush–Kuhn–Tucker conditions, Newton Raphson method, and finally rounding the solution to the nearest integer value. Previous works on threshold optimization in DbMC either give suboptimal solution or optimal one whereof the convergence depends on choosing the smallest interval that contains the optimal value. Numerical and simulation results reveal that our proposed methodology can provide optimal solution with utmost accuracy in few iterations. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the performance of an overlay multiuser two-way relay network with $N$ th-user selection by employing a three-phase cooperative spectrum sharing (3PCSS) scheme. Hereby, a one-end primary user (PU) communicates with the arbitrary (which may be the $N$ th best) selected other-end PUs with the cooperation of a secondary user (SU) in three transmission phases. By splitting up its available power, the SU assists in bidirectional primary transmissions and accesses the spectrum for its own transmission, based on satisfying the primary system outage constraint. Considering the involved $N$ th-order statistics with correlation, we derive the outage probability expressions for both primary and secondary systems over general fading channels. Based on these expressions, we compute the total system throughput of the 3PCSS scheme and compare it with other competitive schemes. We illustrate that the 3PCSS scheme can effectively realize spectrum sharing by harnessing additional cooperative diversity and achieving spectral efficiency at par with the primary two-phase direct transmission system. Numerical and simulation results substantiate our theoretical findings. [ABSTRACT FROM PUBLISHER]

This letter presents a unified framework for the outage performance analysis of cognitive opportunistic amplify-and-forward relay networks with a direct link using maximum ratio combining (MRC) and selection combining (SC) schemes in the presence of multiple primary receivers. Specifically, we derive unified closed-form expressions of outage probability and asymptotic outage behavior for both the schemes under Nakagami- $m$ fading. We manifest analytically that the primary network affects only the coding gains of these schemes, and not the diversity gains that are found to be same in both cases. Moreover, we provide an analytical high signal-to-noise ratio (SNR) gap expression between the two schemes, which is shown to be independent of the primary network parameters. Numerical and simulation results validate our theoretical analysis. [ABSTRACT FROM PUBLISHER]

We investigate the performance of a cognitive spectrum sharing system where a best selected secondary user (SU) assists two-way communication between two primary users (PUs) by employing time division broadcast over Rayleigh channels. We derive tight lower-bound expressions for the overall outage probability (OOP) of both the primary and secondary systems of the considered scheme. We also provide valuable insights into the achievable diversity order, cell coverage, and optimal power allocation factor to ensure spectrum sharing. Numerical and simulation results corroborate the theoretical analysis and illustrate the effectiveness of the considered scheme. [ABSTRACT FROM PUBLISHER]