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This paper considers non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) system, where the base station (BS) directly communicates with the nearby users while it requires the help of a dedicated relay to communicate with the cell-edge users. We derive exact closed form expression for the outage probabilities experienced by the downlink users and the system outage probability of the considered CDRT network with full-duplex relaying (FDR) technique. Further, we derive approximate closed form expressions for the ergodic rates achieved by the users. The channel of all the links experience Nakagami fading distribution and the analysis takes into account the residual interference generated due to the imperfect successive interference cancelation (I-SIC) technique. We provide numerical and simulation results to identify the impact of key system parameters on the outage and ergodic rate performance of the users and the system outage performance. The outage and ergodic rate performance of users in the considered FDR-based NOMA-CDRT system has been observed to be significantly improved compared to a FDR-based OMA (orthogonal multiple access)-CDRT system. It is observed that random selection of NOMA power allocation coefficients at the BS leads to higher outage for the near users compared to the far users. We determine numerical results for the NOMA power allocation coefficient that leads to equal outage performance for both the users. Finally, we derive analytical expression for the optimal power allocation (OPA) coefficient at the BS that minimizes the system outage probability. Through extensive numerical and simulation studies, we establish that OPA can lead to significant reduction of system outage probability compared to random selection of power allocation coefficients at the BS. [ABSTRACT FROM AUTHOR]

An approximation of the symbol error probability (SEP) of the cross QAM (XQAM) signal in a single-input multiple-output system over dual correlated Rayleigh, Nakagami-m, Nakagami-n (Rice) and Nakagami-q (Hoyt) fading channels is derived. The maximal-ratio combining is considered as the diversity technique, and the average SEP is obtained by using the moment generating function (MGF). Arbitrarily tight approximations for the Gaussian Q-function and the generalized Gaussian Q-function are obtained from the numerical analysis technique; the trapezoidal rule. The resulting expressions consist of a finite sum of MGF's which are easily evaluated and accurate enough. In addition, a transformation technique is used to derive independent channels from the correlated channels which are then used in the analysis. The simulation results show excellent agreement with the derived approximation expressions. [ABSTRACT FROM AUTHOR]

In this paper, we derive the error probability of multi-hop networks employing code-division multiple access transmission in a multiuser environment. The standard Gaussian approximation is used to model the multiple access interference in the network. We consider multi-hop networks employing serial, parallel, and selection relaying using the decode-and-forward technique. For the selection relaying, we consider two schemes; namely, the threshold-based relay selection and the maximum relay selection. In addition, we investigate the effect of different system parameters on the error performance of the system, such as the spreading gain, the number of interfering users, and the path loss exponent. Results show that as the number of users increases, the improvement coming from the relaying decreases. [ABSTRACT FROM AUTHOR]

We investigate the performance of the best-worse relay selection strategy in a two way cooperative non-regenerative relay network, where the relay is selected to maximize the worst Signal to Noise Ratio (SNR) of two links. In contrast to existing work, we aim to provide a theoretical performance analysis for this scheme under the more practical Nakagami channel. Closed-form expression of the probability density function for the SNRs of both two links is derived, based on which the outage probability of the best-worse relay selection is obtained. It is shown that the best-worse relay selection scheme achieves full diversity gain. Furthermore, the asymptotic packet error ratio with SNR increasing is also analyzed through rigorous derivations. The accuracy of our derivation is validated by computer simulations. [ABSTRACT FROM AUTHOR]

A unified analysis of statistical models for describing fading, shadowing, and shadowed fading channels is presented from a pedagogical viewpoint. The different probability density functions such the Rayleigh, Nakagami, gamma, generalized gamma, Weibull, lognormal, Nakagami-lognormal, K distribution, generalized K distribution, and Nakagami inverse Gaussian distribution are presented and the relationships among them are detailed. These density functions are compared in terms of two quantitative measures, namely the amount of fading and outage probability. A general approach to fading and shadowed fading channels using a cluster based approach is also presented to link several of the distributions. It is expected that this overview will be very helpful to students and educators who are engaged in the study of wireless systems and the adverse impact of fading and shadowing in wireless data transmission. [ABSTRACT FROM AUTHOR]

Block fading is a popular channel model that approximates the behavior of different wireless communication systems. Automatic-repeat request (ARQ) protocols are used to provide reliable communication in wireless networks. In this paper the throughput of the basic selective-repeat (SR) ARQ in block fading environments is derived. Single-antenna ARQ systems employing both coherent BPSK and QPSK and noncoherent orthogonal BFSK are analyzed over block fading channels characterized by Rician and Nakagami fading distributions. Moreover, the performance of multi-input multi-output (MIMO) ARQ systems employing space-time block codes (STBCs) is derived. The effect of antenna correlation in MIMO ARQ systems is investigated analytically. Results show that longer block lengths improve the performance of basic ARQ protocols. Furthermore, the throughput gain obtained by increasing the block length is a decreasing function of the block length. As the fading severity of the channel increases, the performance improvement resulting from increasing the block length increases. [ABSTRACT FROM AUTHOR]

In this paper, estimators of the Nakagami-lognormal (NL) distribution based on the method of log-moments have been derived and thoroughly analyzed. Unlike maximum likelihood (ML) estimators, the log-moment estimators of the NL distribution are obtained using straightforward equations with a unique solution. Also, their performance has been evaluated using the sample mean, confidence regions and normalized mean square error (NMSE). The NL distribution has been extensively used to model composite small-scale fading and shadowing in wireless communication channels. This distribution is of interest in scenarios where the small-scale fading and the shadowing processes cannot be easily separated such as the vehicular environment. [ABSTRACT FROM AUTHOR]