Enabling software-defined PHY for backscatter networks

BSTRACTIn this paper, we for the first time show how to enable software-defined PHY (SD-PHY) to achieve agile reprogrammability in wireless backscatter networks. This can facilitate innovations in this field by relieving researchers from unnecessary engineering work. With SD-PHY, the tag's PHY-layer behavior can be neatly defined by configuring a set of parameters, which allows the common hardware to generate backscattered signals complying with various wireless protocols. The SD-PHY architecture is based on the key insight that the tag's PHY-layer behavior is essentially determined by reflection coefficient sequence. The SD-PHY is factually to instruct the hardware: How to generate various reflection coefficient sequences that meet different protocols' requirements at the right time; under what clock rate to feed the generated sequence into RF switches on the tag. We abstract such instructions into a set of parameters. To make different parameter values take effect in the runtime, innovative designs of the generic wake-up receiver, baseband modulator, and clock signal generator on the tag, which are responsible for executing those parameterized instructions. We design and implement a general hardware platform to support the SD-PHY software. Moreover, we demonstrate that under the unified SD-PHY framework how the same tag can generate different kinds of backscatter signals, which could obey standardized protocols such as Wi-Fi (11b/g), BLE, LoRa, and LTE, as well as highly customized protocols such as OFDMA backscatter and NetScatter. Experimental results show that the system presents similar performance no matter it is realized with universal SD-PHY or a dedicated design approach.