A CPFSK Transceiver with Hybrid CSS-DSSS Spreading for LPWAN PHY Communication

TL;DR

This paper introduces a novel LPWAN transceiver combining CSS and DSSS spreading techniques, achieving high sensitivity, low complexity, and practical implementation through SDR, with superior performance demonstrated via simulations and field tests.

Contribution

It proposes a hybrid CSS-DSSS spreading scheme with a double-peak detection method, enhancing receiver sensitivity and synchronization in LPWAN transceivers.

Findings

Outperforms traditional transceivers in receiver sensitivity

Demonstrates effective synchronization with CSS preamble

Achieves low complexity suitable for practical LPWAN deployment

Abstract

Traditional low-power wide-area network (LPWAN) transceivers typically compromise data rates to achieve deep coverage. This paper 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 non-coherent 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 non-coherent receiver performance. The software-defined radio (SDR) prototype, developed using GNU Radio and 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.