In this paper, we propose a robust secure transmission scheme for an active reconfigurable intelligent surface (RIS) enabled symbiotic radio (SR) system in the presence of multiple eavesdroppers (Eves). In the considered system, the active RIS is adopted to enable the secure transmission of primary signals from the primary transmitter to multiple primary users in a multicasting manner, and simultaneously achieve its own information delivery to the secondary user by riding over the primary signals. Taking into account the imperfect channel state information (CSI) related with Eves, we formulate the system power consumption minimization problem by optimizing the transmit beamforming and reflection beamforming for the bounded and statistical CSI error models, taking the worst-case SNR constraints and the SNR outage probability constraints at the Eves into considerations, respectively. Specifically, the S-Procedure and the Bernstein-Type Inequality are implemented to approximately transform the worst-case SNR and the SNR outage probability constraints into tractable forms, respectively. After that, the formulated problems can be solved by the proposed alternating optimization (AO) algorithm with the semi-definite relaxation and sequential rank-one constraint relaxation techniques. Numerical results show that the proposed active RIS scheme can reduce up to 27.0% system power consumption compared to the passive RIS.
翻译:本文提出了一种智能可重构表面(RIS)辅助下的共生式无线(SR)系统的鲁棒安全传输方案,可在多个窃听者(Eve)存在的情况下进行。在考虑到与Eve相关的不完美信道状态信息(CSI)的情况下,我们通过优化发射波束和反射波束,针对有界和统计CSI误差模型,以最小化系统能耗为目标,同时考虑到最坏情况下的信噪比(SNR)约束和Eve的SNR中断概率约束。具体地,采用S-Procedure和Bernstein-Type不等式将最坏情况下的SNR和SNR中断概率约束近似转化为可处理的形式。在此基础上,本文采用半定松弛和序列秩一约束松弛技术,通过建议的交替优化(AO)算法求解了这些问题。数值结果表明,相较于被动RIS,所提出的主动RIS方案可以将系统能耗降低高达27.0%。