Jamming-Aware Power Allocation and Secrecy Performance Analysis for Vehicular ISAC Systems

The future of integrated sensing and communication (ISAC) depends on secure information exchange between nodes. Communication and sensing functions must coexist under strict power constraints. This paper explores the physical layer security (PLS) of a vehicular ISAC system. We investigate the secrecy performance of a single-antenna ISAC roadside unit (RSU) that allocates its power budget among communication, sensing, and anti-eavesdropping jamming. Assuming independent Nakagami-m fading channels, we derive closed-form expressions for key secrecy metrics, including secrecy outage probability (SOP), average secrecy outage rate (ASOR), and average secrecy outage duration (ASOD). For sensing performance, the probability of detection (PoD) and probability of false alarm (PoFA) are evaluated under a Gamma-based approximation for the two-way sensing channel. We formulate an optimisation problem to minimise the SOP by determining the optimal jamming power fraction, subject to a fixed sensing power budget. The numerical results show that controlled jamming can significantly reduce SOP and that vehicular mobility strongly affects the temporal dynamics of secrecy outages. The results also demonstrate how channel asymmetry, vehicle speed, and receiver impairments influence the achievable secrecy performance.