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Low-complexity cooperative relay beamforming for multi-cluster relay interference networks

We consider a multi-cluster relay interference network and design relay beam matrix for each cluster to maximize the minimum signal-to-interference-and-noise ratio (SINR) at destinations subject to the relay power budget within each cluster. We propose a structured relay beam matrix as a weighted sum of two types of beam matrices: zero forcing (ZF) beam matrix for inter-cluster interference suppression and maximum ratio combing (MRC) beam matrix for maximizing beamforming gain within a cluster. The optimal beam matrix for each type is obtained with a closed-form solution. We then obtain the optimal weights to each type of beam matrix by transforming the max-min SINR problem and solving it via the SDR approach. Comparing with applying the direct SDR approach to the original problem, our solution offers similar performance with significantly lower computational complexity. In addition, our proposed structured beam matrix clearly revealed the power shift between interference suppression among clusters and beamforming gain maximization within the cluster as the distance among clusters changes.