Leveraging a Digital Chirp Spread Spectrum Detector for LPWAN Wake-Up Receivers

Wireless sensor networks are emerging as serious candidates to detect critical events in ecosystems and remote areas. To maximize their coverage in those environments, mesh networks can be used. However, they require more complex medium access control, at the cost of higher power consumption for the sensor-node RF receiver. The alternative paradigm of wake-up receivers (WuRXs) offers a possible solution to this issue. The objective is to offer an ultra-low-power detection mode to wake up the main receiver, placed in deep sleep, only when an incoming RF signal is found. Previous WuRXs designed for short-range communications fail to reach the sensitivity level required for longer distances, partly due to their simple digital baseband (DBB) processor. In this work, we investigate the use of chirp spread spectrum (CSS), already well-known thanks to LoRa, as an efficient modulation scheme for long-range WuRXs, leveraging its high processing gain and acceptable complexity. To validate this approach, we propose a digital hardware implementation and provide synthesis results in 65-nm CMOS. Compared to state-of-the-art long-range WuRXs, the proposed DBB improves the sensitivity by 11.8 dB with a limited 23- % power consumption overhead.