Time-Modulated 1-Bit Metasurface-Based Secure Directional Transmission

Physical-layer security techniques can be added on top of the cryptography-based security framework, mainly relying on the multi-antenna-based beamforming and artificial noise, where yet the high-cost multiple radio frequency (RF) chains are typically required. In this letter, we exploit the emerging technique of 1-bit low-cost time-modulated metasurface alternatively, for discriminating the eavesdropper and the legitimate user. Specifically, time modulation sequences on the phase shift of each element in the metasurface enables to generate the fundamental and harmonic components with different radiation patterns. As a benefit, this controllable directional signal aliasing can be used for inducing distortion in the direction of the eavesdropper, while maintaining the signal integrity for the legitimate. A particle swarm optimization (PSO)-based optimization algorithm is proposed to optimize both the fundamental and the harmonic radiation patterns, for discriminating the signal-to-interference-plus-noise ratio (SINR) between the legitimate user and the eavesdropper. Simulation results demonstrate that the scheme proposed is capable of ensuring the reliable reception of information at the legitimate user, while restricting the bit error rate (BER) of the eavesdropper to 0.5.