Order-statistics-based relay selection for uplink cellular networks

In this paper, we address the relay assignment in cooperative networks based on order statistics. We consider a network comprising a cluster of transmitting sources, a cluster of relay nodes and a single destination. This is motivated by the fact that the existing relay assignment schemes don´t achieve diversity for the network configuration under consideration. We assume that the cooperation is in the amplify-and-forward (AF) mode, but proposed scheme is applicable to the decode-and-forward (DF) mode. In the relay assignment process, the source nodes that have weaker source-destination links, have higher priority in relay selection. We analyze the probability density function (PDF) and the average bit error rate (BER) for the proposed scheme where we invoke important results that we first derive for simple two-hop networks. Specifically, we calculate the exact expression for the PDF of the end-to-end signal-to-noise ratio (SNR). Compared to other relay assignment schemes (like maximizing sum of SNR values or maximizing the minimum selected SNR), the proposed scheme has the advantages of simplicity, higher diversity order and fairness.