B2LoRa: Boosting LoRa Transmission for Satellite-IoT Systems with Blind Coherent Combining

TL;DR

This paper introduces B2LoRa, a novel blind coherent combining method that significantly improves LoRa transmission reliability in satellite-IoT systems by aligning repeated broadcasts despite low SNRs and Doppler effects.

Contribution

B2LoRa leverages the repeated broadcasting in satellite-IoT to enable coherent combining, addressing challenges of low SNR, timing, and frequency offsets in satellite communications.

Findings

Enhanced link reliability demonstrated in real-world deployments

Effective alignment of packets despite Doppler shifts and low SNRs

Significant performance boost over traditional LoRa in satellite environments

Abstract

With the rapid growth of Low Earth Orbit (LEO) satellite networks, satellite-IoT systems using the LoRa technique have been increasingly deployed to provide widespread Internet services to low-power and low-cost ground devices. However, the long transmission distance and adverse environments from IoT satellites to ground devices pose a huge challenge to link reliability, as evidenced by the measurement results based on our real-world setup. In this paper, we propose a blind coherent combining design named B2LoRa to boost LoRa transmission performance. The intuition behind B2LoRa is to leverage the repeated broadcasting mechanism inherent in satellite-IoT systems to achieve coherent combining under the low-power and low-cost constraints, where each re-transmission at different times is regarded as the same packet transmitted from different antenna elements within an antenna array. Then, the problem is translated into aligning these packets at a fine granularity despite the time, frequency, and phase offsets between packets in the case of frequent packet loss. To overcome this challenge, we present three designs - joint packet sniffing, frequency shift alignment, and phase drift mitigation to deal with ultra-low SNRs and Doppler shifts featured in satellite-IoT systems, respectively. Finally, experiment results based on our real-world deployments demonstrate the high efficiency of B2LoRa.