Performance Analysis of Massive MIMO Two-Way Relay Networks With Pilot Contamination, Imperfect CSI, and Antenna Correlation

We consider a multicell two-way relay network consisting of single-antenna user nodes and amplify-and-forward relay nodes having very large antenna arrays. We investigate the combined impact of co-channel interference (CCI), imperfect channel state information (CSI), pilot contamination, and the antenna correlation at the massive multiple-input multiple-output (MIMO) node. By using a large number of antennas at the relay, we can completely mitigate the effect of CCI. However, the effects of imperfect CSI and pilot contamination degrade the performance even with a large antenna array. Yet, the use of massive MIMO allows power scaling at the user nodes and relay, and thus, even with channel imperfections, the benefits of employing a massive-MIMO-enabled relay on transmit power savings are significant. Furthermore, we derive closed-form approximations for the sum rate when CCI and pilot contamination are absent and CSI is perfect. This result helps to decide the required number of relay antennas to obtain a certain percentage of the asymptotic sum rate. Also, our analysis of antenna correlation shows that it can be mitigated by using a large antenna array. We also find the optimal pilot sequence length to maximize the sum rate of the system.