Design and Analysis of Multi-Relay Selection for Cooperative Spatial Multiplexing

This paper considers the relay selection problem for the cooperative spatial multiplexing scheme in wireless systems with M relay nodes. We consider half-duplex relays in which the relay nodes cannot transmit and receive simultaneously on the same frequency. To improve the transmission reliability, traditional approaches employ cooperative spatial diversity (such as distributed space-time coding) during the cooperative phase when relay and source both transmit to the destination. Most of the relay selection schemes considered in the literature deal with selecting one relay only. However, when we consider wireless systems with multi-antenna destination, we may have opportunities to transmit extra data through cooperative spatial multiplexing by selecting multiple relays to participate in the cooperative phase. In this paper, we shall propose a low complexity multi- relay selection algorithm for the cooperative spatial multiplexing using decode-and-forward (DF) protocol. We have also analyzed the asymptotic performance as well as the diversity-multiplexing tradeoff (DMT) of the proposed system. We found that the proposed cooperative spatial multiplexing scheme with multi- relay selection achieves a much better DMT tradeoff than the traditional cooperative diversity schemes.