Ultra-low-power Bluetooth Low Energy (BLE) compatible backscatter communication and energy harvesting for battery-free wearable devices
MetadataShow full item record
This thesis explores new wireless power and backscatter communication architectures for ultra-low-power wireless sensors and other devices such as wearables. We first present measurement, analysis and harvesting approaches for extracting energy from 2.4 GHz wireless communication signals, including an approach for powering a relatively high power sensor in burst mode at an input power level of -15 dBm. We present the first backscatter-based data uplink approach that achieves compatibility between backscatter devices and billions of completely unmodified standard wireless devices using the Bluetooth Low Energy standard. We show that this data uplink approach can communicate with BLE receivers with a radio communication efficiency of 28.4 pJ/bit. This is over 100x lower energy per bit than conventional BLE transmitters. One microcontroller based implementation consumes over 6x less power than the best commercially-available Bluetooth transmitters, and can leverage both modulated and unmodulated carriers to provide the backscatter uplink. This al- lows us to transform one BLE signal as a carrier source for another BLE-Backscatter signal. We investigate the range of the BLE-Backscatter system in both bistatic and monostatic, full-duplex application scenarios. The range analysis considers the BLE receiver sensitivity and performance in the presence of self-jamming interference from the external carrier source in the bistatic case. We also present a carrier cancellation architecture that reduces self-jamming in the monostatic case. We characterize the packet error rate and received signal strength in both cabled and over-the-air scenarios. Finally we present an ultra-low power superheterodyne receiver architecture that leverages an external carrier as the local oscillator, removing the need for on board (or on chip) generation of the local oscillator signal. The receiver uses a two- port mixer for simultaneous mixing and power harvesting of the external carrier and desired BLE signal. This thesis shows a path toward the widespread adoption of backscatter communication in low-power wireless devices such as smart watches, fitness bands, biomedical sensors, etc. Other wireless devices, such as sensors for the Internet of Things (IoT) where power consumption is a crucial consideration could also benefit from the approaches presented.
- Electrical engineering