MIXIQ: re-thinking ultra-low power receiver design for next-generation on-body applications

ABSTRACTA long-standing challenge in radios for wearables is to design ultra-low power, yet high performance receivers with good sensitivity and spectral efficiency while being compatible with WiFi. The vanilla envelope detector used in standard UHF RFID is the most popular receivers on backscatter tags since they are passive but suffer from poor sensitivity and cannot decode complex modulations, which makes them a poor choice for directly decoding data from WiFi packets. In this paper, we present the design of an easy-to-prototype ultra-low power WiFi receiver called MIXIQ that operates at μWs of power while providing improved sensitivity and decode-ability of complex high-rate signals. MIXIQ uses the signaling capabilities of the newest standard of WiFi, 802.11ax, to turn a standard WiFi packet into a helper + data signal. The same non-linear RF circuit used in a vanilla envelope detector, when driven by this twin signal, now behaves like a passive mixer i.e. it down-converts the RF carrier data to the sub-MHz range without adding any energy overhead. MIXIQ then uses an ultra low-power largely digital baseband pipeline to (i) significantly boost sensitivity using ultra low power components; (ii) enable the demodulation of complex signals for substantial boost in spectral efficiency. We show that MIXIQ improves upon the vanilla envelope detector by 25dB in sensitivity and 89× in bandwidth efficiency, while consuming 0.3mW for a PCB-based implementation and 40μW for CMOS simulation. We also demonstrate a Hearable system that leverages MIXIQ to improve VOIP reception range by 10× compared to a vanilla envelope detector.