On the Performance of MIMO Full-Duplex Relaying in the Presence of Co-Channel Interference

This paper studies the deployment of multiple- input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment, where a multi-antenna amplify-and-forward (AF) FD relay station serves multiple half-duplex (HD) multi-antenna users. The fundamental challenges of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when incorporating FD relaying in cellular systems are addressed. Due to the higher frequency reuse in FD relaying compared to its HD relaying counterpart, the number of CCI is expected to double as the FD relay station simultaneously schedule uplink and downlink transmission on the same channel. In this paper, the optimal design of transmit/receive precoding/decoding weight vectors which maximizes the overall signal-to- interefernce-plus-noise ratio (SINR) is formulated by a proper optimization problem, then a closed-form sub-optimal solution is proposed. The proposed hop-by-hop zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination. To this end, new exact expressions for the outage probability and ergodic capacity are derived in closed-form. Numerical results sustained by Monte-Carlo simulations show the exactness of the proposed analytical expressions. In addition, our results show that while multi- antenna terminals improve the system performance, the detrimental effect of the number of interferers on FD relaying is clearly seen. Furthermore, our findings reveal that MIMO FD relaying could substantially boost the system performance compared to its conventional MIMO HD relaying counterpart.