Transmit Power Minimization for Two-Way Amplify-and-Forward Relaying With Asymmetric Traffic Requirements

This paper addresses the power minimization problem subject to a target quality-of-service (QoS) constraint of two-way relay systems with asymmetric traffic requirements using an amplify-and-forward (AF) relaying mode. By transforming the power minimization problem into a two-stage problem and by using the traffic information together with the short-term channel knowledge, an optimum power control (OPC) technique is first proposed, leading to closed-form solutions for individual transmit power at the relay and the sources. Then, by making use of the available diversity of the multiple-relay channel, the joint design of OPC and relay selection (RS) is investigated, eventually resulting in a joint power control and RS (JPCRS) algorithm with two decentralized RS policies for transmit power minimization. Simulation results are provided to validate the derived expressions and confirm the efficiency of the proposed strategies. It is shown that our proposed strategies can significantly reduce the system transmit power, while ensuring the target QoS of the system, and that the proposed RS algorithm is superior to the conventional max-min and max-sum methods in any traffic and/or channel conditions in terms of energy saving.