Achievable ergodic secrecy rate for MIMO SWIPT wiretap channels

In this paper, we study the multiple-input multiple-output (MIMO) wiretap channel performing simultaneous wireless information and power transfer (SWIPT), where there are a multiple-antenna base station (BS), a multiple-antenna information decoding (ID) user, and a multiple-antenna energy harvesting (EH) user. The messages intended to the ID user need to be kept confidential to the EH user. The channels between BS and users are modeled as fading channels with different spatial correlations and line-of-sight (LoS) components. We assume that only statistical channel state information (CSI) is available at the BS. Our objective is to design the optimal transmit covariance matrix at the BS for maximizing the ergodic secrecy rate subject to the BS power constraint and the harvested energy requirement for the EH user. To this end, we present an approximation for the ergodic secrecy rate by using large dimensional random matrix theory and the method of Taylor series expansion. Based on this, an iterative algorithm is proposed to find the transmit covariance matrix. Simulation results are provided to verify the accuracy of the approximation and the performance of the design.