PassiveOFDM: Flexible OFDM Backscatter with Commercial Compatibility

Abstract

To enable commercial-compatible Wi-Fi backscatter transmission, recent works either adopt off-tag mechanisms based on standard OFDM Wi-Fi exciters, or generate OFDM Wi-Fi waveforms on-tag using single-tone exciter. However, they result in either very limited communication range or exorbitant power consumption. We present PassiveOFDM, the first μW-level commercial-compatible OFDM Wi-Fi backscatter system that works at tens of meters exciter-to-tag distance. It enables low-power on-tag OFDM signal forming, decoupling tag placement from the exciter's location. We design a spectrum-filling shaping scheme that retains the spectrum structure of the OFDM Wi-Fi without IFFT, and a DAC-free waveform embedding scheme with low-power RF switches. Our field tests confirm that PassiveOFDM achieves reliable backscatter transmission 65m from the exciter or 80m from the receiver. Its power consumption is 2855.1× smaller than the SOTA on-tag system RF-Transformer. Its exciter-to-tag distance and throughput are 54.2× and 29× higher than those of the SOTA off-tag system TiScatter, respectively.