Beamforming in Traffic-Aware Two-Way Relay Systems With Channel Estimation Error and Feedback Delay

This paper presents a comprehensive performance analysis of a multi-antenna-based traffic-aware two-way relay system with unavoidable imperfections in channel state information (CSI) under Nakagami-m fading. Herein, we employ transmit/receive beamforming at source nodes and analog network coding (ANC) at the relay node in the presence of CSI imperfections due to channel estimation errors (CEE) and feedback delay. With such a practical setup, we first deduce the pertinent instantaneous end-to-end signal-to-noise ratios (SNRs) after performing partial self-interference cancellation. Then, by imposing asymmetric traffic requirements in two opposite directions, we conduct an accurate analysis of overall outage probability (OOP) of the considered system. We further derive a tight lower bound on OOP that has a simple and compact closed-form representation. Moreover, based on the asymptotic OOP expression at high SNR, we examine the achievable diversity order of the system. In addition, we acquire an upper bound expression of ergodic sum-rate (ESR) and simplify it further in useful compact form for high SNR regime. Besides, we investigate the optimization problems of relay position to minimize the OOP and to maximize the ESR. Numerical and simulation results validate our theoretical analysis and highlight the impact of CEE and feedback delay under various traffic patterns on the overall system performance.