Secure Energy Efficiency Maximization for Multi-Device Symbiotic Radio Communication System

Symbiotic radio (SR) communication is emerging as a promising solution for enabling low-power and large-scale Internet of Things (IoT) applications. However, it faces significant challenges in ensuring secure transmission due to its low-power feature. In this letter, we propose a secure transmission strategy for the multi-device SR system. Then, a secure energy efficiency maximization problem is formulated by jointly optimizing transceiver beamforming and backscattering, subject to the IoT transmission sum rate constraint. To solve the formulated non-convex and highly coupling problem, we first apply Jensen’s inequality to approximate ergodic achievable rates in the objective function, and then a semi-definite relaxation-based iteration algorithm is designed to obtain a high-quality suboptimal solution. Simulation results verify the effectiveness of the proposed joint beamformer and backscattering coefficient design approach in the considered system.