Power-efficient distributed beamforming for multiple full-duplex MIMO relays

Full-duplex multiple-input-multiple-output (MIMO) relaying is capable of providing coverage for remote users with low power consumption, by exploiting the spatial dimensions of MIMO to suppress different types of interference, including self interference (SI) and multi-user interference (MUI). In a general network with multiple full-duplex MIMO relays, inter-relay interference (IRI) emerges and degrades system performance by consuming excessive transmit power. In this paper, distributed beamforming is investigated for interference suppression in multiple full-duplex MIMO relay network. Based on successive convex approximation and proximal point method, a distributed beamforming algorithm is proposed to suppress the three types of interference jointly, with the target of minimizing total transmit power under individual user rate constraints. The proposed iterative algorithm requires only local information exchange at the relays, which reduces the signaling overhead in largescale networks. An upper bound of the stepsizes that guarantee convergence is also given. Simulation results are presented to validate effectiveness of our proposal.