Don't Miss Weak Packets: Boosting LoRa Reception with Antenna Diversities

LoRa technology promises to connect billions of battery-powered devices over a long range for years. However, recent studies and industrial deployment find that LoRa suffers severe signal attenuation because of signal blockage in smart cities and long communication ranges in smart agriculture applications. As a result, weak LoRa packets cannot be correctly demodulated or even be detected in practice. To address this problem, this paper presents the design and implementation of MALoRa: a new LoRa reception scheme which aims to improve LoRa reception performance with antenna diversities. At a high level, MALoRa improves signal strength by reliably detecting and coherently combining weak signals received by multiple antennas of a gateway. MALoRa addresses a series of practical challenges, including reliable packet detection, symbol edge extraction, and phase-aligned constructive combining of weak signals. Experiment results show that MALoRa can effectively expand communication range, increase battery life of LoRa devices, and improve packet detection and demodulation performance especially in ultra-low SNR scenarios.