Enhanced PWM Backscattering System for Battery-Free Wireless Sensors

Backscatter communication enables a passive long-range wireless link for low-power wireless sensors and Internet-of-things devices. In this paper, we propose encoding analog sensor data by PWM and a method to receive for wireless sensor readers to recover and decode the sensor data at lower power levels than conventional RFID readers, using commercial open-source software-defined radios. The high Rx sensitivity can be used to relax the minimum modulating voltage (and power) requirement from the sensor tag. Consequently, the wireless power sensitivity and the range of the sensor tag are extended. The proposed backscattering system is prototyped, and the proposed technique is verified to recover and decode PWM backscattered signals at low received RF power below −70dBm and with low modulation efficiency from a subthreshold backscatter modulator.