Outage probability in distributed transmission based on best relay pair selection

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays and thereby mitigate the deleterious effect of fading channels in transmission. In an environment where multiple relays are available, selection of a subset of such relays may be required as, for example, in distributed space-time coding. In this study, the authors therefore use local measurements of the instantaneous channel conditions to select the best relay pair from a set of N available relays, which both come from the same cluster or different clusters, and then use these best relays for cooperation between the source and the destination. The authors also show that the best relay pair selection scheme has robustness against feedback error and outperforms a scheme based on selecting only the best single relay. The authors obtain analytical expressions for the probability density function, cumulative density function and the moment generating function of the received signal-to-noise ratio to derive closed-form expressions for outage probability over Rayleigh frequency flat-fading channels. The analytical results are supported by simulation studies.