Towards Spatial Selection Transmission for Low-end IoT devices with SpotSound

This paper tries to answer a question: "Can we achieve spatial-selective transmission on IoT devices?" A positive answer would enable more secure data transmission among IoT devices. The challenge, however, is how to manipulate signal propagation without relying on beamforming antenna arrays which are usually unavailable on low-end IoT devices. We give an affirmative answer by introducing SpotSound, a novel acoustic communication system that exploits the diversity of multi-path indoors as a natural beamformer. By judiciously controlling the way how the information is embedded into the signal, SpotSound can make the signal decodable only when this signal propagates along a certain multipath channel. Since the multipath channel decorrelates rapidly over the distance between different receivers, SpotSound can ensure the signal is decodable only at the target position, achieving precise physical isolation. SpotSound is a purely software-based solution that can run on most IoT devices where speakers and microphones are widely used. We implement SpotSound on Raspberry Pi connected with COTS microphone and speaker. Experimental results show that SpotSound achieves a 0.25m(2) location isolation.