Physical Layer Security in HARQ-Assisted Non-Orthogonal Multiple Access Networks

This paper investigates physical layer security (PLS) in hybrid automatic repeat request (HARQ)-assisted non-orthogonal multiple access (NOMA) networks, where a security-required user is paired with a quality of service (QoS)-required user to perform NOMA in presence of an eavesdropper (Eve). We derive the closed-form expressions for connection outage probability (COP) of security-required and QoS-required users. In addition, the closed-form expressions for secrecy outage probability (SOP) secrecy transmission probability (RSP), and effective secrecy throughput (EST) of security-required user are also derived. Although the expression of SOP demonstrates that HARQ increases the risk of leaking confidential message to eavesdropper (Eve), however, from the perspective of Eve and security-required user, secrecy performance improves significantly, in terms of EST and RSP, when applying HARQ.