Secure precoding design for high-mobility systems with OTFS modulation

Abstract

This paper investigates a downlink high-mobility secure communication system with orthogonal time–frequency space (OTFS) modulation. In order to achieve secure transmission, a secure precoding scheme based on a privacy-preserving method is proposed, in which a projection matrix with artificial noise (AN) is introduced to disturb eavesdropper. Specifically, the normalized projection matrix of AN, the normalized precoding matrix of desired signals, and the power allocation coefficients are alternatively optimized. The projection matrix and precoding matrix are first derived in closed-form with the normalization constraints and fixed power allocation. Then, the power allocation coefficients are obtained by solving a secure rate maximization problem. Simulation results show that the proposed privacy-preserving projection matrix can effectively interfere with eavesdropping from the illegitimate user, and the proposed secure precoding scheme has significant performance gains over the existing schemes.