Physical Layer Security With Near-Field Beamforming

Abstract

Extremely large antenna arrays (ELAAs) are being proposed for sixth-generation (6G) systems as an evolution of massive multiple-input, multiple-output (mMIMO). Besides having a large number of antennas, ELAAs can be physically large, which makes communication in the radiative near-field very likely. This means the plane wave approximation does not hold and channel models that accurately capture the propagation effects in the near-field are required. Recent works have highlighted the beamfocusing effect available in the near-field region, where antenna arrays can generate beams not only limited in width but also limited in depth. This work leverages a precise channel model for ELAAs with the aim of exploring the inherent physical layer security (PLS) features in the radiative near-field. For that purpose, it is presented a study on the power ratio between a legitimate and a malicious user, considering the effects of the field region, relative distance, and beamforming direction. By taking advantage of that analysis, it is shown that both the jamming rejection and the secrecy rate can be substantially improved when communicating in the near field, demonstrating that beam-focusing constitutes an interesting PLS technique for upcoming 6G communications.INDEX TERMS massive MIMO, extremely large antenna arrays, near-field, physical layer security, secrecy rate.

On the Use of Near-Field Constellation Focusing for Physical Layer Security with Extremely Large Antenna Arrays

“…Their study emphasized the impact of near-field beamforming on PLS, particularly in conjunction with the spherical-wavefront model. In [11,12], the authors considered the PLS features in radiative near-field communication for ELAAs, demonstrating that beamfocusing with Matched Filtering (MF) beamforming substantially improves jamming rejection and secrecy rates. In [16], the focus lies on achieving PLS through constellation shaping.…”

“…This necessity arises from the substantial increase in the far-field distance, implying a heightened likelihood that the communication occurs in the near field. Despite the propagation distance potentially exceeding the Fraunhofer distance of each antenna element, it is important to note that the distance might remain considerably lower than the Fraunhofer array distance, which is defined as D FA = 2D 2 sub λ , where D sub is the maximum distance between antennas of a given sub-array [11].…”

“…Therefore, an ELAA can potentially concentrate its large gain in a specific zone, which gives rise to a beamfocusing effect [9,10]. This effect can be used to increase PLS features [11][12][13].…”