This paper presents closed-form expressions for the end-to-end performance of wireless dual-hop systems with multiple amplify-and-forward relays and multiple users over Rayleigh flat fading channels. These results are based on the statistics of the harmonic mean of two random variables related to exponential distribution. Two generalized scheduling policies are considered in the systems for selection diversity from multirelay and multiuser: the centralized scheduling (CS) and the distributed scheduling (DS). Numerical results show that the performance of DS can be degraded when large number of relays are used relative to the number of users. Additionally, it is shown that DS is quite competitive with CS at small number of relays that can be considered to be desirable.
An asymmetric pilot subcarrier allocation scheme (APSA) is proposed for orthogonal frequency division multiple access (OFDMA) systems which use regenerative relays. To achieve the best performance of regenerative relay systems, the performance of each hop should be balanced. When there is a direct link between the source and destination, APSA allocates pilot subcarriers asymmetrically to each hop to balance the performance. We show that APSA can improve the performance of the system based on the symbol error rate (SER) analysis and simulation results.
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