Performance analysis of four relays selection scheme for cooperative networks

Cooperative diversity has been recently proposed as an approach 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 maybe required as, for example, in distributed space-time block coding (DSTBC). In this paper, we therefore select the best four relays from a set of N available relays, by using local measurements of the instantaneous channel conditions, and then use these best relays for cooperative transmission between the source and the destination. We also show that the best four relays selection scheme has robustness against feedback error and outperforms a scheme based on selecting only the best single relay. We use the joint distribution of the four largest values and multi-dimensional integration to derive closed form expressions for outage probability over Rayleigh frequency flat fading channels. The analytical results are supported by simulation studies.