Efficient Sum-Rate Maximization for Large-Scale MIMO AF-Relay Networks

We consider the problem of sum-rate maximization in multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks with multi-operator. The aim is to design the MIMO relay amplification matrix (i.e., the relay beamformer) to maximize the achievable communication sum-rate through the relay. The design problem for the case of single-antenna users can be cast as a non-convex optimization problem, which in general, belongs to a class of NP-hard problems. We devise a method based on the minorization-maximization technique to obtain quality solutions to the problem. Each iteration of the proposed method consists of solving a strictly convex unconstrained quadratic program; this task can be done quite efficiently such that the suggested algorithm can handle the beamformer design for relays with up to ∼ 70 antennas within a few minutes on an ordinary personal computer (PC). Such a performance lays the ground for the proposed method to be employed in large-scale MIMO scenarios.