Secure Symbol-Level Precoding Design for QAM Signals in MU-MISO Wiretap Systems

Abstract

Recently emerged symbol-level precoding techniques can exploit multi-user interference (MUI) by transforming it into constructive signals at receivers and thus contribute to symbol detection. This paper adopts this concept and aims to investigate the exploitation of MUI to enhance both physical layer security against eavesdropping and the quality of legitimate transmissions. Particularly, we consider the problem of secure symbol-level precoding in multi-user multi-input single-output (MU-MISO) wiretap systems for M-ary quadrature amplitude modulation (M-QAM) signals. Our goal is to design the symbol-level precoder to minimize the average transmit power while guaranteeing the quality of service (QoS) of all legitimate transmissions as well as ensuring security against eavesdropping. In order to tackle this unaffordable large scale problem, we propose to decompose it into several sub-problems. Then, an efficient modified Hooke-Jeeves pattern search algorithm is further utilized to solve the Lagrangian dual functions of these sub-problems. Simulation results validate the exploitation of MUI for security and illustrate the effectiveness of our proposed secure symbol-level precoding algorithm.