Abstract
This letter investigates and analyzes covert communications to safeguard backscatter systems, i.e., how to hide backscattering transmission for privacy and security, which is rarely a concern yet. Specifically, we consider a backscatter communication system in the presence of an eavesdropper (Eve), in which a passive tag supported by the power source (Alice) attempts to communicate reliably while simultaneously guaranteeing covertness to Eve. Furthermore, artificial noise (AN) is also injected from Alice to mislead Eve for security purposely. Our objective is to maximize the transmission rate via joint power control, AN injection, and reflection coefficient (RC) adjustment while satisfying the physical constraints on the total power budget, the circuit energy consumption, the minimum transmission rate, and the covertness requirement. To deal with this intractable non-convex problem, we reformulate the problem by utilizing the Kullback-Leibler divergence (KLD) and Lambert W function. Subsequently, an alternative iterative algorithm is designed to solve it. Besides, we derive the closed forms for RC and transmit power for more insight. Simulation results show that the proposed algorithm outperforms the benchmark algorithms in terms of both security and effectiveness.
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