RIS-Segmented Symbiotic Covert Cooperative Backscatter Communication Systems

In this work, we delve into the covertness performance of the reconfigurable intelligent surface (RIS) symbiotic ambient backscatter communication (AmBC) systems. The RIS is partitioned into backscatter device (BD) zone and enhance transmission (ET) zone to serve two distinct users. Through dynamically adjusting the number of ET zone elements, we aim to impede the detection of backscattered communication signals by the monitor. Considering the existence of imperfect successive interference cancellation (ipSIC) at receivers and mutual interference (MI) between zones, the closed-form expressions for the detection error probability and outage probabilities over the Nakagami-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> channels are derived. To maximize the effective covert throughput, we employ a block coordinated descent (BCD) method to optimize the power allocation factor and the number of zone reflective elements. Simulation results validate the accuracy of our analysis, underscoring that the RIS-segmented symbiotic AmBC systems can achieve better covertness and reliability by enhancing the interference cancellation capability and dividing the optimal RIS zones.