Spatially Selective Radar Backscatter Communication

Abstract

This paper presents Serena, the first spatially selective radar backscatter communication system that is capable of delivering messages to radars at specific locations. Serena offers a low-power solution for properly delivering location-specific messages (e.g., no-fly-zone alert, speed-reduction warning, turning notification) to radar-equipped vehicles (e.g., automobile, UAV, UGV). Rather than manipulating RF signals with power-intensive components, Serena leverages the limited modulation capability of multiple low-power backscatter tags to generate spatially selective radar signal feature, and further utilizes such signal feature to represent bits. Such design philosophy is primarily realized by our two core designs: (i) a multi-tag distributed and synchronous modulation technique that generates spatially selective radar signal feature (i.e., the combination of the frequencies of tag-generated harmonics in radar IF spectrum); (ii) an intermittent mutual synchronization protocol that achieves 10-μs level inter-tag synchronization under only 10μW-level power consumption. Our extensive experiments demonstrate that Serena achieves desirable spatial selectivity in diverse environments: it achieves less than 1% average BER at target locations, while keeping the average BER around 30% at non-target locations.