Impact of reduced antenna spacing on the post-processing SINR of interference rejection combining in cellular downlink receivers

The user equipments (UEs) in fourth-generation cellular networks employ multiple receive antennas for improved performance and reliability. In this scenario, interference rejection combining (IRC) has become a receiver of choice for its desirable properties such as interference mitigation and reduced complexity. Interference covariance matrix (ICM) inversion is a key step in obtaining the combiner weights in such a receiver. In this work, we study the impact of reduced antenna spacing on the post-processing signal-to-interference-plus-noise ratio (SINR) that is achievable in a UE performing IRC. We also investigate the invertibility and condition number of the ICM and its effects on the post-processing SINR. Finally, we study the impact of reduced antenna spacing on the post-processing SINR when there are channel estimation errors.