Design of Non-Coherent and Coherent Receivers for Chirp Spread Spectrum Systems

TL;DR

This paper designs practical non-coherent and coherent receivers for chirp spread spectrum systems like LoRa, enabling improved detection under real-world conditions and supporting enhanced modulation schemes for higher data rates.

Contribution

It introduces detailed receiver designs capable of handling timing, frequency, and phase offsets for CSS signals, including a new phase-shift keying CSS modulation scheme.

Findings

Proposed receivers effectively handle practical synchronization issues.

PSK-CSS scheme increases transmission rates.

Coherent receiver achieves near-ideal bit error rate performance.

Abstract

LoRaWAN is a prominent communication standard to enable reliable low-power, long-range communications for the Internet of Things (IoT). The modulation technique used in LoRaWAN, commonly known as LoRa modulation, is based on the principle of chirp spread spectrum (CSS). While extensive research has been conducted on improving various aspects of LoRa transmitter, the design of LoRa receivers that can operate under practical conditions of timing and frequency offsets is missing. To fill this gap, this paper develops and presents detailed designs of timing, frequency and phase synchronization circuits for both non-coherent and coherent detection of CSS signals. More importantly, the proposed receiver can be used to detect the recently proposed CSS-based modulation that embeds extra information bits in the starting phases of conventional CSS symbols. Such a transmission scheme, referred to as phase-shift keying CSS (PSK-CSS) helps to improve the transmission rates of the conventional CSS system. In particular, it is shown that the bit error rate performance of the PSK-CSS scheme achieved with the proposed practical coherent receiver has only 0.25 dB gaps as compared to the ideal co-coherent receiver.