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

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 measurements from our real-world setup. In this paper, we propose a blind coherent combining design named B2LoRa to boost LoRa transmission performance. The intuition is to leverage the repeated broadcasting mechanism inherent in satellite-IoT systems to achieve coherent combining under low-power, low-cost constraints, treating each re-transmission as a packet from a different antenna element. We present three designs — joint packet sniffing, frequency shift alignment, and phase drift mitigation — to deal with the ultra-low SNRs and extreme Doppler shifts featured in satellite-IoT systems. Experiments based on our real-world deployments demonstrate the high efficiency of B2LoRa.