Opportunistic Multiuser Two-Way Amplify-and-Forward Relaying With a Multiantenna Relay

We consider the opportunistic multiuser diversity in the multiuser two-way amplify-and-forward (AF) relay channel. The relay, which is equipped with multiple antennas and a simple zero-forcing beamforming (ZFBF) scheme, selects a set of two way relaying user pairs to enhance the degree of freedom (DoF) and, consequently, the sum throughput of the system. The proposed channel-aligned pair scheduling (CAPS) algorithm reduces the interpair interference and keeps the signal-to-interference-plus-noise-power ratio (SINR) of user pairs that are interference-free when the number of user pairs becomes very large. When the number of user pairs grows fast enough with the system signal-to-noise ratio (SNR), a DoF equal to the number of relay antennas can be achieved. For a realistic number of user pairs, we propose an adaptive CAPS and an adaptive semi-orthogonal CAPS (SCAPS) to improve performance. Simulation results show that adaptive CAPS and adaptive SCAPS provide throughput gain in the low-to-mid SNR region.This work was supported by the National Research Foundation of Korea funded by the Korean Ministry of Science, ICT, and Future Planning under Grant 2014R1A5A1011478. The review of this paper was coordinated by Dr. M. Elkashlan