Fair relay selection in decode-and-forward cooperation based on outage priority

The opportunistic cooperation schemes, where only the “best” relay is selected to forward the message, have been widely investigated recently for their good performance in terms of outage probability. However, the unfair selections of relays may cause unbalance power consumptions among relays, which reduces the lifetime of energy constrained networks. In this paper, we introduce a novel concept of outage priority based fairness (OPF), aiming at improving the selection fairness among relays appropriately without outage performance deterioration. Then, a cooperation scheme is proposed to meet this concept, and corresponding theoretical analysis is also provided. Afterward, based on OPF, the achievable upper bound of the fairness is derived, and an optimal cross-layer designed scheme is also provided to achieve the bound. Numerical simulations are carried out finally, which not only validate the theoretical analysis, but also show that taking advantages of the proposed schemes, the fairness among all relays, as well as the network lifetime, can be greatly improved without any loss of outage performance, especially in high SNR regime.