Outage probability and SER of cooperative selection diversity in nonregenerative MIMO relaying

Cooperative diversity is a promising solution in wireless distributed networks where integrating multiple antennas onto small mobile devices is practically impossible due to size and cost constraints. As such, we consider a cooperative diversity network where the source and the destination user-pair are equipped with single antennas while the relay is a wireless access point equipped with N antennas. For such networks, we focus on cooperative selection diversity (CSD) to select a single link with the highest instantaneous received signal-to-noise ratio (SNR) between the direct link and the multiple-input multiple-output (MIMO) relay link. We present new closed-form expressions for the exact outage probability and the exact symbol error rate (SER) based on the cumulative distribution function (cdf) of the instantaneous received SNR. Our expressions are valid for arbitrary N antennas and apply to general operating scenarios with distinct average received SNRs in each link. Furthermore, we present a high SNR analysis of the outage probability and SER to explicitly characterize the diversity order and array gain. We show that the diversity order increases with the number of antennas according to N + 1.