Sum Secrecy Rate Maximization for Full-Duplex Two-Way Relay Networks Using Alamouti-Based Rank-Two Beamforming

Abstract

Consider a two-way communication scenario where two single-antenna nodes,\noperating under full-duplex mode, exchange information to one another through\nthe aid of a (full-duplex) multi-antenna relay, and there is another\nsingle-antenna node who intends to eavesdrop. The relay employs artificial\nnoise (AN) to interfere the eavesdropper's channel, and amplify-forward (AF)\nAlamouti-based rank-two beamforming to establish the two-way communication\nlinks of the legitimate nodes. Our problem is to optimize the rank-two\nbeamformer and AN covariance for sum secrecy rate maximization (SSRM). This\nSSRM problem is nonconvex, and we develop an efficient solution approach using\nsemidefinite relaxation (SDR) and minorization-maximization (MM). We prove that\nSDR is tight for the SSRM problem and thus introduces no loss. Also, we\nconsider an inexact MM method where an approximately but computationally cheap\nMM solution update is used in place of the exact update in conventional MM. We\nshow that this inexact MM method guarantees convergence to a stationary\nsolution to the SSRM problem. The effectiveness of our proposed approach is\nfurther demonstrated by an energy-harvesting scenario extension, and by\nextensive simulation results.\n