QoS-Aware Power Control Methods for Two-Way Amplify-and- Forward Relay Systems

We consider power control methods for two-way amplify-and-forward (AF) relay systems. Traffics with different quality-of-service (QoS) requirements are exchanged between two transmit nodes where one of the traffics is a rate-constrained (RC) traffic and the other is a best-effort (BE) traffic. Based on the QoS feasibility of RC traffic, we propose two types of power control methods to maximize the transmission rate of BE traffic. In case QoS requirement of RC traffic is satisfied, we derive a power control method that maximizes the transmission rate of BE traffic. On the contrary, when QoS requirement of RC traffic is not feasible, we propose a power control method to maximize the transmission rate of BE traffic considering the automaticrepeat-request (ARQ) protocols. Through the analysis and numerical results, we verify the performance improvement of the proposed method. Compared with the equal power allocation method, the overall transmission rate of the BE traffic is increased up to 30 % depending on the relay location and the QoS requirement of the RC traffic. Key-Words: Amplify-and-Forward, quality of service, power control, relay, outage.