A dynamic relay selection scheme for mobile users in wireless relay networks

Cooperative communication has attracted dramatic attention in the last few years due to its advantage in mitigating channel fading. Despite much effort that has been made in theoretical analysis of the performance gain, cooperative relay selection, which is one of the fundamental issues in cooperative communications, is still left as an open problem. In this paper, the tradeoff between improvement and corresponding cost of cooperative communication, focusing on relay selection is addressed. We consider a challenging scenario which takes user mobility into consideration. Based on user mobility pattern, a dynamic relay selection scheme aiming at minimizing the long-term average cost while satisfying the QoS requirement is proposed. For relay selection to achieve maximal performance, an optimization model based on the constrained Markov decision process (CMDP) is formulated and solved by applying the linear programming (LP) technique. Comprehensive analysis and comparison with several other relay selection schemes are presented. Through extensive simulations, our scheme shows its high effectiveness and flexibility in balancing the cost and QoS performance.