An Enhanced Interference Alignment Sum Rate Maximization Beamformer Design for the <i>M × N</i> MIMO X Channel

This letter proposes a new IA-compliant beamformer design for the multiple-input multiple-output (MIMO) X channel comprising M transmitters and N receivers. We first formulate the relaxed non-IA constrained sum-rate maximization beamformer design problem into a sequence of tractable subproblems, and then present an iterative Sum Rate Maximization (SRM) algorithm to obtain a stationary solution. A novel IGM (Inequality Gap Minimization) algorithm is later proposed to search for an IA-compliant beamformer near the SRM solution using the Majorization-Minimization (MM) method. Simulation results showed that the proposed IA-compliant beamformer can be used to enhance the sum rate of a number of existing designs under various MIMO X channel configurations.