Ambient ZeroScatter: Ambient BPSK and QPSK Backscatter Communication using Existing Digital I/O Pins

Thesis (Master's)--University of Washington, 2019ZeroScatter is an ultra-low-cost, minimum-complexity approach that enables backscatter wireless data uplink from billions of existing, commodity microcontrollers (MCUs) and field-programmable gate arrays (FPGAs). Existing MCU and FPGA based backscatter wireless sensors rely on external components such as RF FETs, PIN diodes, or varactors to perform the backscatter modulation function. We demonstrate that completely unmodied digital I/O pins on MCUs and FPGAs can be re-purposed as binary phase-shift keying (BPSK) backscatter modulators in the UHF and microwave bands with zero added components, and that multiple digital I/O pins can be used in combination with series or shunt impedances to produce quadrature phase-shift keying (QPSK) backscatter modulation. We additionally demonstrate a complete ambient backscatter communication system, consisting of the BPSK ZeroScatter tag, dipole antennas, and a direct sampling digital receiver. With an input clock frequency of 2.9 Gsps, the resolution of the receiver's analog-to-digital converter (ADC) is 14 bits and the effective number of bits (ENOB) is 9 bits. By leveraging RF signals already present in the environment, ambient backscatter does not require a dedicated carrier source as in traditional backscatter communication. The ambient ZeroScatter system uses ambient digital television (DTV) signals as the carrier source, enabling the ZeroScatter tag to transmit sensor data via backscatter. The data is then received and processed by the digital receiver