Performance Analysis of STAR-RIS Assisted Secure Cognitive NOMA-HARQ Networks

In this letter, we carry out the performance analysis of the simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in the hybrid automatic repeat request (HARQ) assisted cognitive non-orthogonal multiple access (NOMA) networks, where a security-required user (SRU) with secure transmission requirements is paired with a quality of service (QoS)-sensitive user (QSU) with low delay requirements to perform NOMA. To characterize the performance of secure transmission, we derive the analytical expressions for connection outage probability (COP), average number of transmission (ANT) and secrecy outage probability (SOP) for the SRU in randomized retransmission NOMA (RR-NOMA) scheme, while a cognitive power allocation scheme is developed to meet QSU's QoS requirement. To obtain deeper insights, the asymptotic expressions of COP and SOP are also derived. Furthermore, some significant results are drawn from simulations: 1) There exist a balance between COP and ANT, COP and SOP, which are denoted by the security-reliability balance (SRB) and reliability-delay balance (RDB), respectively. 2) HARQ is benefit to improve the RDB and SRB performance of SRU. 3) The increase in the number of STAR-RIS elements ${K}$ improves the system reliability performance, while the secrecy performance deteriorates.