LoRa Fine Synchronization with Two-Pass Time and Frequency Offset Estimation

TL;DR

This paper presents a two-pass synchronization method for LoRa that estimates and compensates sampling frequency offset early, significantly improving long-range synchronization accuracy in LPWAN networks.

Contribution

It introduces an extended synchronization algorithm for LoRa that estimates and corrects sampling frequency offset during the preamble, enhancing overall synchronization performance.

Findings

Early SFO compensation improves synchronization accuracy.

The method effectively estimates multiple impairments in long-range LoRa signals.

Enhanced synchronization robustness in low SNR conditions.

Abstract

LoRa is currently one of the most widely used low-power wide-area network (LPWAN) technologies. The physical layer leverages a chirp spread spectrum modulation to achieve long-range communication with low power consumption. Synchronization at long distances is a challenging task as the spread signal can lie multiple orders of magnitude below the thermal noise floor. Multiple research works have proposed synchronization algorithms for LoRa under different hardware impairments. However, the impact of sampling frequency offset (SFO) has mostly either been ignored or tracked only during the data phase, but it often harms synchronization. In this work, we extend existing synchronization algorithms for LoRa to estimate and compensate SFO already in the preamble and show that this early compensation has a critical impact on the estimation of other impairments such as carrier frequency offset and sampling time offset. Therefore it is critical to recover long-range signals.