A Cooperative Three-Time-Slot Transmission in Asymmetric Two-Way Relay Channels

In a two-way relay system where two nodes exchange information via a half-duplex relay, the achievable data rates of both directions are limited by the weaker link. When the two-way channel is asymmetric due to relay positioning or channel fading, the sum rate of the two-way relay system will suffer from severe degradation. In this paper, we propose a novel three time-slot cooperative transmission strategy in order to transmit at the maximum rate of each link, and therefore, to improve the sum rate of the two-way relay system. We obtain capacity region for the new strategy and derive an achievable rate region. Time slot allocation and power allocation at the relay are optimized to achieve the maximum sum rate. Simulation results show that the proposed strategy significantly outperforms existing transmission strategies under asymmetric channel conditions both in AWGN and Rayleigh fading channels.