STAR-RIS Aided Secure Wireless Powered Communication with Indoor and Outdoor Users

This paper studies simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided secure wireless powered communication. Specifically, we propose an energy splitting protocol based STAR-RIS transmission scheme, combined with an uplink non-orthogonal multiple access (NOMA), to enhance both energy transfer and information transmission for indoor and outdoor users against eavesdropping attacks. The accurate and asymptotic connection outage probabil-ities, secrecy outage probability, and effective secrecy throughput are analyzed to evaluate the proposed scheme's performance and the impact of key parameters. Simulation results indicate that the proposed scheme significantly outperforms the dual transmit/reflect-only RIS scheme. Although slightly less effective than traditional direct transmission scheme at the low transmit power region, the proposed scheme's efficacy rapidly surpasses that of direct transmission as the transmit power increases.