Secure space–time-modulated millimetre-wave wireless links that are resilient to distributed eavesdropper attacks

As wireless networks move to millimetre-wave (mm-wave) and terahertz (THz) frequencies for 5G communications and beyond, ensuring security and resilience to eavesdropper attacks has become increasingly important. Traditional encryption methods are challenging to scale for high-bandwidth, ultralow-latency applications. An alternative approach is to use physical-layer techniques that rely on the physics of signal propagation to incorporate security features without the need for an explicit key exchange. Ensuring security through the use of directional, narrow-beam-like features of mm-wave/THz signals has proven to be vulnerable to passive eavesdroppers. Here we report a space-time modulation approach that ensures security by enforcing loss of information through selective spectral aliasing towards the direction of eavesdroppers, even though the channel can be physically static. This is achieved by using custom-designed spatio-temporal transmitter arrays realized in silicon chips with packaged antennas operating in the 71–76 GHz range. We also analytically and experimentally demonstrate the resilience of our links against distributed and synchronized eavesdropper attacks in the mm-wave band. Directional 5G communication channels can be made secure at the physical layer by using a time-modulation approach that enforces the fundamental loss of information through selective spectral aliasing towards the direction of unwanted listeners.