Physical Layer Authentication in Radar-Communication Coexistence Systems

This paper addresses the security issues in Radar-Communication Coexistence (RCC) systems, focusing on verifying the origin of the received signal through a tag-based Physical Layer Authentication (PLA) scheme. Traditional PLA schemes face challenges in RCC systems due to radar interference, which affects robustness against impersonation attacks, security against eavesdropping, and compatibility with source message reception. To address these challenges, it is necessary to redesign the optimal constellation of the source message and the tag for an RCC system utilizing a tag-based PLA scheme. We propose three tag-based PLA schemes for RCC systems: the Unified-Phase Tag (UPT) scheme, where all constellation points of a transmitted message share the same initial phase from a tag constellation set; the Individual-Phase Tag (IPT) scheme, where each constellation point of a transmitted message has different initial phases from tag constellation sets; and the Joint-Optimization Tag (JOT) scheme, where the phase of a tag for each constellation point of a transmitted message is jointly optimized with the signal and tag constellation sets. Our theoretical analysis of the proposed schemes covers compatibility, security, and robustness, with closed-form or upper-bound expressions for the symbol error rate derived. Extensive performance comparisons through simulations demonstrate that the theoretical results closely align with the simulation outcomes. For an RCC system with eighth order modulation and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SNR</i> = 16 dB under low radar interference to noise ratio scenario, the UPT, IPT, and JOT schemes show compatibility improvements of 18%, 19%, and 58%, respectively, compared to prior schemes.