Physical Layer Security for Near-Field Communications via Directional Modulation

Recently, near-field communications (NFCs) have drawn great attention for the near-field region expansion in the context of extremely large-scale (XL) antenna arrays, tremendously high frequencies, and new types of antennas trends. Considering the distinctive spherical wave propagation model in NFC, multiple-input multiple-output (MIMO) techniques, such as channel modelling and estimation as well as hybrid beamforming technologies, have recently undergone reevaluation and redesign. Concurrently, as the NFC range continues to broaden, ensuring physical layer security (PLS) has emerged as an equally urgent concern, necessitating immediate attention and resolution. Therefore, in this contribution, we propose a single-user (SU) multiple-input single-output (MISO) near-field directional modulation (NFDM) system toward secure transmissions at both angular and distance scales. Furthermore, considering the hardware cost associated with XL arrays, a fully analog secure precoding algorithm integrated beamforming with artificial noise (AN) as well as power allocation is devised under the modulus-1 constraint of the phase shifters. Finally, simulation results indicate that the proposed NFDM scheme is capable of guaranteeing security at both angular and distance scales compared with its conventional far-field counterpart.