NF-SecRIS: RIS-Assisted Near-Field Physical Layer Security via Secure Location Modulation

TL;DR

NF-SecRIS addresses the lack of range-secure physical layer techniques by delivering 2D near-field PLS via an ultra-large RIS. It introduces Secure Location Modulation (SLM), decoupling spatial-phase synthesis from temporal sequences across three modules: beam focusing with a constant phase, beam nulling with a perturbed phase, and time-domain phase interleaving, enabling real-time randomization without transmitter/receiver synchronization. A low-complexity squeeze-nulling model reduces the near-field optimization from $O(10^{3})$ to $8$ dimensions, and a closed-form criterion plus a pre-stored perturbation-sequence library support real-time deployment; closed-form bounds govern the interleaving time-slot ratios. A 14×56 RIS prototype at 5.8 GHz demonstrates 2D PLS across ASK, FSK, PSK, and QAM, with Bob BER below $10^{-4}$ and Eve BER exceeding $40\%$ in the secure region, validating practical near-field 2D security for future 6G deployments.

Abstract

The 6G wireless networks impose extremely high requirements on physical layer secure communication. However, the existing solutions usually can only achieve one-dimensional physical layer security (PLS) in the angle dimension, and cannot achieve PLS in the range dimension. In this paper, we propose the NF-SecRIS system, the first range-angle-dependent (2D) PLS near-field communication system based on ultra-large-scale reconfigurable intelligent surface (RIS). We propose the secure location modulation scheme to synthesize the near-field spatial-temporal coding pattern of RIS with extremely low complexity. It ensures that only legitimate user can receive the raw constellations, while potential eavesdroppers at other ranges or angles can only receive the obfuscated constellations. NF-SecRIS operates without requiring synchronization with either transmitter or receiver. We implement a prototype of NF-SecRIS and conduct comprehensive experiments with multiple modulation schemes. The results show that the bit error rate (BER) of legitimate user is below 10^{-4}, while eavesdroppers at other ranges or angles suffer from BER exceeding 40%. It validates the implementation of 2D PLS in near-field communications.

Figures (16)

• Figure 1: The scenario of NF-SecRIS. The blue dashed line denotes the boundary of the secure communication region of Bob, within which reliable communication is maintained.
• Figure 2: System architecture of NF-SecRIS: Secure Location Modulation. The SLM scheme comprises three modules: (i) beam focusing with constant phase sequence (blue dashed box); (ii) beam nulling with perturbed phase sequence (red dashed box); (iii) time-domain phase interleaving (black dashed box).
• Figure 3: Near-field phase compensation principle for beam focusing. (a) General spherical wave model. (b) Beam focusing model of RIS.
• Figure 4: Near-field beam focusing. (a) Power distribution in $xoz$ plane. (b) Power distribution versus distance $r$.
• Figure 5: The influence of constant phase sequence on constellations. (a) Constant phase sequence in time domain. (b) Ideal constellation at Alice. (c) Constellation at Bob. (d) Constellation at Eve.