Imperfect Resolution of Near-Field Beamfocusing for NOMA-Aided Physical-Layer Security

Abstract

Since adopting the spherical wave model in near-field, the imperfect resolution of beamfocusing has significantly enabled nonorthogonal multiple access (NOMA) technique to enhance spectrum efficiency, where one user’s beam can be served for additional users. However, as additional users sharing the same radio resources to enhance network density, physical-layer security (PLS) becomes increasingly critical, especially in scenarios that eavesdroppers could potentially intercept communications intended for legitimate users. To address such issue, a comprehensive investigation of the resolution is proposed to distinguish NOMA users and eavesdroppers within a near-field communication (NFC) framework, considering both angular and distance domains. Furthermore, by leveraging the resolution capabilities, we individually consider the positions of NOMA users and eavesdroppers, which significantly impacts the power allocations, decoding orders and security performances. Moreover, our simulation results verify the analytical results and demonstrate the improvement of the average secrecy rate as well as secrecy outage probability (SOP), offering a novel perspective to enhance future NFC systems.