Relay Selection for Cognitive Massive MIMO Two-Way Relay Networks

We analyze relay selection for an underlay cognitive radio (CR) two-way relay network (TWRN) with zero-forcing (ZF) transmission and receiving. The source and the destination nodes are massive multiple-input multiple-output (MIMO) enabled. Relays will perform amplify and forwarding (AF) while the destination and source nodes perform self interference cancellation. We first obtain asymptotic signal-to-interference-plus-noise ratio (SINR) values under the power scaling at the relay and end nodes. Then, we derive optimal power allocation schemes for the end nodes to satisfy the interference constraints at the primary user (PU). Based on these optimal values, we analyze the effect of relay selection on the sum rate. With the use of massive MIMO, the SINR and the sum rate will only depend on the pathloss coefficients of the channels and average noise levels. Thus, the relay selection can be done at the deployment stages of the system and most of the time it simplifies to selection of the relay with the highest number of antennas. Our simulation results validate the analytical asymptotic results and qualify CR massive MIMO TWRNs as a possible candidate for future wireless systems.