Adversarial Analysis of Antenna Subset Modulation for Physical Layer Security in mmWave Systems

Abstract

Millimeter-Wave Communications (mmWave) enable highly directional signal transmissions, but remain inherently vulnerable to passive interception due to the broadcast nature of wireless propagation. This motivates the need for physical-layer security which is not addressed by conventional encryption operating at higher layers of the communication stack. Antenna Subset Modulation has been proposed as a transmission obfuscation technique that generates randomness in sidelobe emissions while preserving coherent modulation toward an intended receiver. This work evaluates ASM under both single and coordinated passive adversarial models, with a focus on realistic deployment conditions. In particular, we investigate the impact of multipath propagation on both system performance and adversarial decoding capability. We show that previously proposed coordinated attacks relying on idealized channel assumptions degrade significantly in the presence of multipath, showing ASM's security dependence on complete channel knowledge. However, when the attack is extended to a complete sensing matrix capturing both line-of-sight and multipath components of the environment, and Moore-Penrose pseudoinverse reconstruction is applied, coordinated adversaries can recover transmitted signals. These results demonstrate that ASM does not provide unconditional security, but offers strong practical resilience in realistic environments where precise channel knowledge is difficult to obtain.