Physically Secure Sub-THz Wireless Links

Abstract

Ensuring security is emerging as one of the grand challenges towards realization of a large-scale and high-speed wireless network fabric for 5G and beyond. In particular, enabling security at the network layer and application layers becomes computationally very challenging in multi-Gbps sub-THz and THz wireless links operating under strict energy constraints and latency requirements. To address this, there has been renewed interest in physical layer security techniques that attempt to exploit the physics of propagation in the channel to incorporate security features. Phased arrays, that are expected to be the foundational building blocks behind such sub-THz links, attempt to address such physical layer security by creating directive links and minimizing leakage power to undesired directions. However, the spectrum and constellation transmitted by such arrays at these off-axis angles are fully preserved allowing eavesdroppers with sensitive enough receivers to compromise the communication channel. In this paper, we demonstrate incorporation of physical layer security in sub-THz wireless links through spatio-temporal array architectures. Unlike phased arrays, these architectures enforce spectral aliasing, loss of information and constellation scrambling at undesired directions to mitigate eavesdropper attacks. We present the fundamental operation principle of such architectures and discuss various modulation techniques and their intended security features. We also demonstrate them experimentally with fully integrated sub-THz arrays in custom designed silicon ICs and packaged antennas operating at 76 GHz. The presented architectures can enable future large-scale deployment of multi-Gbps wireless networks with physically secure links operating at sub-THz frequencies for future 5G and beyond.