All-Digital CSS Ambient Backscatter with 17.6 µW Power Consumption and a MISO Receiver

A fully-digital Chirp Spread Spectrum (CSS) backscatter system is presented that consumes tens of microwatts and uses a Multiple-Input Single-Output (MISO) receiver. The system uses ambient FM signals as carriers to wirelessly transmit information. The receiver uses a portable, low-cost Software-Defined Radio (SDR) that captures 6 MHz of spectrum, enabling reception from multiple FM stations to protect against outages, noise, and interference. The novelty of the tag design is removing the Digital-to-Analog Converters (DACs) and Voltage-Controlled Oscillators (VCOs) needed in similar works. Instead, the tag uses the Microcontroller’s (MCU) Inter-IC Sound (I2S) peripheral to create digitally sampled CSS chirps that control the Radio-Frequency (RF) switch. A tag prototype was built and tested, showing successful packet decoding beyond 100 m at a bit rate of 273 bps while receiving backscattered signals from 3 FM stations. The design confirms the long-range and low-power capabilities (17.6 µW) of low-cost ambient backscatter approaches.