Performance Analysis of Interference-Limited Three-Phase Two-Way Relaying with Direct Channel

Abstract: This paper investigates the performance of interference-limited three-phase two-way relaying with direct channel between two terminals in Rayleigh fading channels. The outage probability, sum bit error rate (BER) and ergodic sum rate are analyzed for a general model that both terminals and relay are corrupted by co-channel interference. We first derive the closed-form expressions of cumulative distribution function (CDF) for received signal-to-interference-plus-noise ratio (SINR) at the terminal. Based on the results for CDF, the lower bounds, approximate expressions as well as the asymptotic expressions for outage probability and sum BER are derived in closed-form with different computational complexities and accuracies. The approximate expression for ergodic sum rate is also presented. With the theoretic results, we consider the optimal power allocation at the relay and optimal relay location problems that aiming to minimize the outage and sum BER performances of the protocol. It is shown that jointly optimization of power and relay location can provide the best performance. Simulation results are presented to study the effect of system parameters while verify the theoretic analysis. The results show that three-phase TWR protocol can outperform two-phase TWR protocol in ergodic sum rate when the interference power at the relay is much larger than that at the terminals. This is in sharp contrast with the conclusion in interference free scenario. Moreover, we show that an estimation error on the interference channel will not affect the system performance significantly, while a very small estimation error on the desired channels can degrade the performance considerably.