Physical Layer Defense against Eavesdropping Attacks on Low-Resolution Phased Arrays

Eavesdropping attacks are a severe threat to millimeter-wave (mmWave) networks that use low-resolution phased arrays. Although directional beamforming in mmWave phased arrays provides natural defense against eavesdropping, the use of low-resolution phase shifters induces energy leakage into unintended directions. This energy leakage can be exploited by the adversaries. In this paper, we propose a directional modulation (DM)-based defense against eavesdropping attacks on low-resolution phased arrays. Our defense technique applies random circulant shifts to the beamformer for every symbol transmission. By appropriately adjusting the phase of the transmitted symbol, the transmitter (TX) can maintain a high-quality link with the receiver while corrupting the symbols transmitted along unintended directions. We theoretically analyze the secrecy mutual information (SMI) achieved by the proposed defense mechanism and show that our defense induces artificial phase noise (APN) along unintended directions, which increases the SMI of the system. Finally, we numerically show the superiority of the proposed defense technique over the state-of-the-art defense techniques.