Optimized Beamforming Design for PLS in Near-Field Uplink Communications

Extremely large antenna arrays (ELAAs) are being envisioned for sixth-generation (6G) to increase spatial selectivity and achieve higher capacities. The use of larger arrays combined with higher carrier frequencies increases the near-field region, where the channel model must account for the curvature of the electromagnetic waves, and the plane wave regime is inaccurate. When conventional matched-filtering (MF) beamforming is de-signed for near-field, a beam-focusing effect is observed around the focal point. This can be used to mitigate the impact of a malicious user and increase the physical layer security (PLS). In this paper, we propose an optimized beamforming design for uplink near-field communications that accounts not only for the positioning of the legitimate user but also for the position of the jammer. It is shown that the jamming rejection capabilities of the proposed beamforming are superior to that of conventional MF.