Power allocation for three-stage cooperative relaying in wireless networks

In the conventional dual-hop cooperative communications, the relays with imbalanced channels to the source and the destination become the bottleneck of the overall cooperation. In this paper, a Three-Stage Relaying (TSR) scheme is presented to extend the dual-hop cooperation to three stages by dividing relays into two groups. The relay-to-relay cooperation is introduced with which the bottleneck link between the relay and the source (or the destination) can be efficiently broken. We focus on the power allocation based on this framework, with the objective of minimizing the outage probability at the destination under the total power constraint. To address the computational complexity, the problem is decomposed into two subproblems, one deals with the power allocation of the source and the first-hop relays, the other deals with the power allocation of the second-hop relays. We design the algorithms for each subproblems by exploiting the special structure of the problems, and develop a master procedure to handle the power allocation across these subproblems. The performance of the proposed scheme is evaluated through simulation study, which shows that the TSR framework achieves significant improvement on the outage probability compared with the dual-hop protocol, and the power consumption is more balanced across relays.