Secrecy rate optimization for dual-functional radar-communication system with energy receiver

This article studies the secrecy rate optimization in the downlink transmission of a dual-functional radar-communication system, under the simultaneous wireless information and power transfer (SWIPT) setting. Specifically, the base station (BS) simultaneously transmits information and energy signals while detecting the target, where the energy receiver (ER) also behaves as a potential eavesdropper. In order to ensure secure information transmission, we design the beamformer to avoid information leakage by maximizing the secrecy rate under the total transmit power budget, the received signal-to-noise ratio (SNR) target at the BS, and the received energy requirement of the ER. To deal with the non-convexity of the cost function and constraints in the original problem, we first transform the problem into an equivalent semidefinite relaxation (SDR) version by linearizing the cost function with the introduced auxiliary variables. Thus, the off-the-shelf semidefinite programming (SDP) solver can be leveraged to obtain desired beamforming matrices, which is guaranteed to be rank-1. To alleviate the computational costs of SDP, we further propose a sub-optimal solution via the block coordinate descent method and the Taylor series expansion. Numerical results validate the effectiveness and superiority of the proposed algorithms.