RSSISPY: Inspecting Concurrent Transmissions in the Wild.

This paper presents RSSISPY, a software module that enables continuous RSSI measurements with very high time resolution on standard low-power wireless network nodes. Specifically, RSSISPY can be used to perform continuous RSSI sampling in parallel to normal Bluetooth Low Energy (BLE) receive operation on Nordic nRF52840 devices with a sampling rate of 1 Msps, i.e., one sample per bit in BLE 1M mode. RSSISPY provides this functionality without additional hardware and can be straightforwardly integrated into existing protocols, so it allows to record RSSI traces "in the wild", i.e., in existing networks running the protocols of interest. We use RSSISPY to further investigate important physical layer effects on COTS hardware, including interference in general, capture effect, and so-called constructive interference. Our systematic experiments combined with rigorous analyses uncover results that have not been known so far and are of high interest for concurrent-transmissions-based protocols. Besides that, RSSISPY enables all kinds of RSSI-stream-based functionality on standard hardware, e.g., signal detection, parameter estimation (instantaneous SNR, transmitter constellation, etc.), and cross-technology communication.