Browsing by Author "Nasri, A."

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Enhanced MRC for decode-and-forward cooperative diversity systems
(IEEE, 2012-10) Nasri, A.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this letter, we propose a novel enhanced maximal-ratio combining (E-MRC) scheme for multi-branch decode-and-forward (DF) cooperative diversity systems consisting of a source, a destination, and multiple relays. This scheme employs adjustable parameters at the relays and the destination which enable this scheme to appropriately adapt to variations in the source-relay and relay-destination channel gains. For the proposed E-MRC scheme, we analyze the asymptotic error rate performance for high signal-to-noise ratios and Rayleigh fading. Based on the obtained analytical expressions, we find the optimal parameters that lead to minimization of the asymptotic error rate. Furthermore, we compare the error rate performance as well as the feedback overhead of E-MRC with those of important DF schemes, namely, cooperative MRC (C-MRC) and two DF schemes based on the link adaptive regeneration (LAR) concept, namely, LAR-αinst and LAR-α. We show that although the feedback requirements of E-MRC are similar to those of LAR-α, E-MRC achieves a performance similar to that of LAR-αinst, which has a substantially higher feedback overhead.
Open Access
Performance and optimization of network-coded cooperative diversity systems
(IEEE, 2013-03) Nasri, A.; Schober, R.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we study network–coded cooperative diversity (NCCD) systems comprising multiple sources, one relay, and one destination, where the relay detects the packets received from all sources and performs Galois ﬁeld (GF) network coding over GF(2m) before forwarding a single packet to the destination. Assuming independent Rayleigh fading for all links of the network, we derive simple and accurate closed–formapproximations for the asymptotic symbol and bit error rates of NCCD systems. The derived error rate expressions are valid for arbitrary numbers of sources, arbitrary modulation schemes, and arbitrary constellation mappings and provide signiﬁcantinsight into the impact of various system and channel parameters on performance. Moreover, these expressions can be exploited for optimization of the constellation mapping as well as for formulation of various NCCD system optimization problemsincluding optimal power allocation, relay selection, and relay placement.