SecHARQ: A Secure Scheme for HARQ-Assisted NR V2X Communications

Hybrid Automatic Repeat reQuest (HARQ) feedback and retransmission, as one of the crucial technologies for reliability enhancement, may cause a security-reliability tradeoff in New Radio (NR) Vehicle-to-Everything (V2X) communications. Specifically, for NR V2X messages, the HARQ feedback and retransmission improve its success delivery probability but endanger its confidentiality. This paper proposes a secure scheme, namely SecHARQ, to maximize the security performance of HARQ-assisted NR V2X while satisfying the reliability requirement. To describe the performance of SecHARQ accurately, a stochastic geometric based theoretical framework is developed with the consideration of three specified factors, namely transmission rounds, resource allocation, and feedback option selection. With the help of this framework, we can formulate the SecHARQ scheme as a tractable optimization problem. Extensive numerical results show that the proposed scheme is beneficial for secure communication in HARQ-assisted NR V2X by carefully tuning the optimal parameters of SecHARQ.