Physical layer security is a way to realize the secure transmission of information by employing the characteristics of wireless channels. Thanks to its spatial and temporal focusing property, the time-reversal (TR) transmission can achieve effective secure communications even when the transmitter is only equipped with one antenna. This paper studies the design and optimization of the security scheme based on artificial noise (AN) with or without the eavesdropper's channel state information (ECSI) in a TR multi-user downlink multiple access system. The null-space AN is adopted when ECSI is unavailable, and the corresponding optimization problem is to minimize the signal power under each user's signal-to-interference-plus-noise ratio (SINR) target constraint, so that the power used to send AN is maximized and the interception rate of the eavesdropper is minimized. The problem is solved by transforming it into a semidefinite program (SDP) with semidefinite relaxation (SDR). The pre-processing filter and AN are jointly optimized to maximize the sum secrecy rate when ECSI is available. The problem is solved by transforming it into a convex program by using SDR and the first-order Taylor approximation. Simulation results show that the sum secrecy rate of the proposed scheme is significantly higher than that of the conventional TR transmission system with or without AN.

物理层安全性是通过利用无线信道的特性来实现信息的安全传输的一种方式。由于其时空聚焦特性，即使发射机仅配备一根天线，时间反转（TR）传输也可以实现有效的安全通信。本文研究了TR多用户下行链路多址系统中基于人工噪声（AN）和不存在窃听者的信道状态信息（ECSI）的安全方案的设计和优化。当ECSI不可用时，采用零空间AN，相应的优化问题是在每个用户的信号干扰加噪声比（SINR）目标约束下使信号功率最小，这样，发送AN的功率就可以最大化，窃听者的监听率也可以达到最小。通过将其转换为具有半确定松弛（SDR）的半确定程序（SDP）可以解决该问题。当ECSI可用时，对预处理滤波器和AN进行联合优化，以最大程度提高总保密率。通过使用SDR和一阶泰勒近似将其转换为凸程序，可以解决该问题。仿真结果表明，该方案的总保密率明显高于有或没有AN的传统TR传输系统。当ECSI可用时，对预处理滤波器和AN进行联合优化，以最大程度提高总保密率。通过使用SDR和一阶泰勒近似将其转换为凸程序，可以解决该问题。仿真结果表明，该方案的总保密率明显高于有或没有AN的传统TR传输系统。当ECSI可用时，对预处理滤波器和AN进行联合优化，以最大程度提高总保密率。通过使用SDR和一阶泰勒近似将其转换为凸程序，可以解决该问题。仿真结果表明，该方案的总保密率明显高于有或没有AN的传统TR传输系统。