This paper focuses on secure backscatter transmission in the presence of a passive multi-antenna eavesdropper through a symbiotic radio (SR) network. Specifically, a single-antenna backscatter device (BD) aims to transmit confidential information to a primary receiver (PR) by using a multi-antenna primary transmitter's (PT) signal, where the received symbols are jointly decoded at the PR. Our objective is to achieve confidential communications for BD while ensuring that the primary system's quality of service (QoS) requirements are met. We propose an alternating optimisation algorithm that maximises the achievable secrecy rate of BD by jointly optimising primary transmit beamforming and power sharing between information and artificial noise (AN) signals. Numerical results verify our analytical claims on the optimality of the proposed solution and the proposed methodology's underlying low complexity. Additionally, our simulations provide nontrivial design insights into the critical system parameters and quantify the achievable gains over the relevant benchmark schemes.

翻译：本文研究在共生无线电网络中，存在被动多天线窃听者时的安全反向散射传输问题。具体而言，单天线反向散射设备利用多天线主发射机的信号向主接收机传输机密信息，主接收机对接收符号进行联合解码。我们的目标是在确保主系统服务质量要求得到满足的同时，实现反向散射设备的保密通信。我们提出一种交替优化算法，通过联合优化主发射波束赋形、信息信号与人工噪声信号之间的功率分配，最大化反向散射设备可实现保密速率。数值结果验证了所提方案的最优性分析结论以及该方法的低复杂度特性。此外，仿真实验为关键系统参数提供了重要的设计启示，并量化了相对于相关基准方案的性能增益。