SPP: Achieving Low-Probability-of-Intercept Cellular and Wi-Fi Communications via MIMO-based Spatial Pilot Perturbation

Low Probability of Intercept (LPI) wireless communication is a critical aspect of modern wireless technology. Despite various techniques developed for LPI wireless communication, most of them require some form of pre-existing knowledge (e.g., encryption keys) or specific information (e.g., eavesdropper location and channel details). In this paper, we propose a novel physical-layer precoding technique called spatial pilot perturbation (SPP) to achieve efficient LPI wireless communications. Unlike existing methods, SPP operates without the need for pre-shared information between the two communication devices, nor any knowledge about potential eavesdroppers. It remains transparent to users and thus backward-compatible with off-the-shelf 5G/WiFi user devices. The core idea of SPP is to use different precoders for pilot and data symbols in a signal frame at the physical layer. Through a systematic precoder design, the pilot and data symbols will experience identical compound channels upon arrival at intended receivers, but experience different compound channels when intercepted by eavesdroppers. Consequently, the intended receivers can demodulate the signal frame, while eavesdroppers cannot. We have implemented SPP on 5G and WiFi testbeds and evaluated its performance through over-the-air experiments. Extensive experimental results show that SPP achieves an eavesdropping rate of ≤0.2% for 5G and ≤0.9% for WiFi, both at the cost of less than 18% throughput.