Relaxation-phase-based Robust Directional Modulation with Angle Estimation Error

Abstract

Stability and security are critical to modern wireless communication systems, which have attracted more and more attention in recent years. In this paper, physical layer security (PLS) between the transmitter and the legitimate user (LU) is greatly enhanced by inventing a robust directional modulation (RDM) scheme based on a relaxation phase constraint. Unlike the conventional perfect channel state information (CSI) assumption, the estimation error of LUs' azimuths is assumed, which corresponds to a more practical scenario. Moreover, the influence of the imperfect CSI on the design of artificial noise (AN) vector is investigated. Accordingly, a specific strategy to introduce AN at the transmitter is proposed with imperfect CSI. Numerical simulations suggested that the RDM scheme based on the relaxation phase constraint possesses great potential for the enhancement of security of wireless communications.