A CPFSK Transceiver With Hybrid CSS–DSSS Spreading for LPWAN PHY Communication

Traditional low-power wide-area network (LPWAN) transceivers typically compromise data rates to achieve deep coverage. This article presents a novel transceiver that achieves high-receiver sensitivity and low-computational complexity. At the transmitter, we replace the conventional direct sequence spread spectrum (DSSS) preamble with a chirp spread spectrum (CSS) preamble, consisting of a pair of down-chirp and up-chirp signals that are conjugate to each other, simplifying packet synchronization. For enhanced coverage, the payload incorporates continuous phase frequency shift keying (CPFSK) to maintain a constant envelope and phase continuity, in conjunction with DSSS to achieve a high-spreading gain. At the receiver, we develop a double-peak detection method to improve synchronization and a noncoherent joint despreading and demodulation scheme that increases receiver sensitivity while maintaining simplicity in implementation. Furthermore, we optimize the preamble detection threshold and spreading sequences for maximum noncoherent receiver performance. The software-defined radio (SDR) prototype, developed using GNU Radio and universal software radio peripheral (USRP), along with operational snapshots, showcases its practical engineering applications. Extensive Monte Carlo simulations and field-test trials demonstrate that our transceiver outperforms traditional ones in terms of receiver sensitivity, while also being low in complexity and cost-effective for LPWAN requirements.