Hybrid Channel Pre-Inversion and Interference Alignment Strategies

Abstract—In this paper we consider strategies for MIMO interference channels which combine the notions of interference alignment and channel pre-inversion. For symmetric MIMO channels, we consider a variant on interference alignment wherein groups of users collaborate to share their data, and can thereby eliminate some of the interference by pre-inverting their channel matrices. For every possible grouping of K = 4 users each with N = 5 antennas, we completely classify the degrees of freedom available to each user, and construct explicit interference alignment strategies which maximize the sum capacity. To improve the capacity of our schemes at finite SNR, we propose that the groups of users invert their subchannel using a regularized Tikhonov inverse. While the optimal Tikhonov parameter is already essentially known, we provide a new sleeker derivation of this result. We use random matrix theory to provide an explicit formula for the SINR as the number of users increases, which we believe is a new result. Lastly, forK = 4 and N = 5, we simulate our proposed hybrid schemes and compute the capacity of each experimentally