Reliable WiFi Backscatter Communication in WiTAG

Abstract

WiFi backscatter systems offer the potential to provide low-powered WiFi-compatible communication. This technology is especially promising when coupled with low-power sensors to periodically communicate readings from IoT devices. WiTAG is an extremely attractive approach because it greatly reduces power consumption by avoiding the use of WiFi receivers or signal detectors while ensuring compatibility with existing WiFi infrastructure. WiTAG operates at the MAC layer by corrupting or not corrupting subframes (MPDUs) within a transmitted frame (A-MPDU). For example, corruption of an MPDU signals a 0 and non-corruption signals a 1. Because it eschews the use of receivers and signal detectors WiTAG is unable to sense when frames are being sent by nearby WiFi devices that it relies on for communication.

In this thesis, we describe the significant challenges that arise when formulating, transmitting, and reliably detecting and decoding messages transmitted from WiTAG. We design a message encoding framework to overcome these challenges. We show that although WiTAG relies on probabilities for overlapping a tag’s message with an A-MPDU it is possible to increase the odds of an overlap, thus increasing message rates. This permits the transmission of highly reliable messages in a relatively short period of time.