En masse relay selection for decode-and-forward relaying in multiple source-destination systems

Opportunistic relay selection in a multiple source-destination (MSD) cooperative system involves allocating to each source-destination (SD) pair a relay based on its channel gains. Since each node in the system knows only its local channel gains, a relay selection algorithm is required to quickly identify and assign the best relay to each SD pair. For an MSD system in which the SD pairs communicate in a time-orthogonal manner, we propose two new relay selection algorithms, namely, contention-free en masse assignment (CFEA) and contention-based en masse assignment (CBEA). En masse assignment exploits the fact that in an MSD system a relay can often aid not one but multiple SD pairs, and, therefore, can be assigned multiple SD pairs en masse. We show that CFEA and CBEA require much less time to allocate an SD pair than in single SD systems, and achieve a higher net throughput in several regimes of interest when compared with other selection algorithms proposed in the literature. We also identify the regimes in which CFEA is better than CBEA and vice versa.