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

2025-07-30

AI Summary

In LPWANs, achieving both deep coverage and high data rates remains challenging, while receiver sensitivity and computational complexity are inherently trade-offs. Method: This paper proposes a novel physical-layer transceiver architecture integrating chirp spread spectrum (CSS) and direct-sequence spread spectrum (DSSS). It introduces conjugate paired up-chirp/down-chirp preambles for low-overhead synchronization and designs a dual-peak detection scheme with non-coherent joint despreading and demodulation, optimizing detection thresholds and spreading sequences. The system employs continuous-phase frequency-shift keying (CPFSK) combined with hybrid CSS-DSSS modulation and is prototyped using GNU Radio and USRP. Contribution/Results: Monte Carlo simulations and hardware measurements demonstrate a 3–5 dB improvement in receiver sensitivity over conventional LPWAN schemes, enhanced synchronization robustness, and maintained low hardware complexity and cost—confirming strong feasibility for practical deployment.

Technology Category

• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Machine Learning: Hardware-aware ML

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements
• Economics, Online Markets and Human Computation: Architectures and workflows that use LLMs for crowd work

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.

Problem

• Enhances LPWAN transceiver sensitivity and reduces complexity
• Combines CPFSK and DSSS for improved coverage and spreading gain
• Optimizes synchronization and demodulation for low-cost LPWAN solutions

Innovation

• CSS preamble replaces DSSS for simpler synchronization
• CPFSK with DSSS enhances coverage and spreading gain
• Non-coherent joint despreading boosts receiver sensitivity