A Fully-Reflective Wi-Fi-Compatible Backscatter Communication System With Retro-Reflective MIMO Gain for Improved Range

Abstract

This article presents an integrated circuit (IC) designed to enable low-power long-range backscatter commu- nication with commodity Wi-Fi transceivers. The proposed chip endeavors to improve the most critical and difficult specification in Wi-Fi backscatter systems: range. It does so through two pro- posed techniques: 1) a fully-reflective single-antenna backscatter solution, whereby the termination of a power combiner always has a reflection coefficient near 1 to ensure high reflected power while enabling single-sideband (SSB) quadrature phase shift key- ing (QPSK) modulation with frequency-translation to separate Wi-Fi channel and 2) a retro-reflective multiple-in–multiple-out (MIMO) approach that redirects incident Wi-Fi signals, after SSB QPSK modulation, back to a colocated access point (AP) with MIMO gain. The proposed chip also implemented a counter- based wake-up scheme within a synchronization receiver (RX) to achieve standards-compatible wake-up with high synchroniza- tion accuracy. Implemented in 65-nm CMOS, the wake-up RX consumes 4.5 µW and achieves a sensitivity of −43.5 dBm, while the synchronization RX consumes an average power of 4.8 µW and achieves a synchronization accuracy of at least 150 ns for input power of −35 dBm or better. During backscattering, the IC consumes 32 and 38 µW and attains an AP-to-tag range of 13 and 23 m for the fully-reflective and retro-reflective MIMO approaches, respectively.