Cooperative inter-beam nulling: A side-channel strategy for managing inter-beam interference

Conjugate beamforming is a practical method of enabling simultaneous downlink to multiple users, but it suffers from inter-beam interference. We propose to utilize side-channels so that users can amplify-and-forward their received signals to other users. The amplified-and-forwarded signals are used with a decorrelating receiver to null interference in a strategy called cooperative inter-beam nulling (CIBN). We derive, simulate, and analyze the achievable rate of CIBN. Our results show that CIBN provides significant rate gains with a sufficient number of base station antennas (>10) and received side-channel SNR (> 5 dB), and that rich scattering environments provide the most rate gains.