Energy-efficient joint relay selection and power control for reliable cooperative communications

The energy efficiency of cooperative communications has attracted tremendous attentions recently. Considering that the energy consumption of a cooperative communication includes the transmit and receive energy in the relay nodes, we study an opportunistic decode-and-forward relaying with the best relay. In addition, we note that the retransmissions controlled by the high layer schemes like automatic repeat-request (ARQ) also require extra energy consumption. To this end, we propose a joint relay selection and power control scheme for reliable cooperative communications with retransmissions. Based on the analysis on energy efficiency of the reliable cooperative communications in terms of successfully delivered bits per Joule which tradeoffs the system throughput and energy consumption, we further propose two iterative algorithms based on discrete stochastic approximation, which do not require exact channel state information and their iterations are in accordance with the process of obtaining the channel state information. Simulation results show that the proposed algorithms converge fast to the optimum achievable energy efficiency.