mLoRa: A Multi-Packet Reception Protocol in LoRa networks

Abstract

We present mLoRa in this paper, a novel protocol that can decode multiple collided packets simultaneously from different transmitters in LoRa networks. As a recently proposed wireless technology designed for low-power wide-area networks, LoRa has been proverbially employed in many fields, such as smart cities, intelligent agriculture, and environmental monitoring. In LoRa networks, a star-of-stars topology is conventionally implemented, in which thousands of nodes connect to a single gateway. Accordingly, the convergecast scenario becomes common. For example, in intelligent agriculture, multiple sensor nodes send information with respect to the soil temperature and humidity to a LoRa gateway. Regularly, simultaneous transmissions result in the severe collision problem. Meanwhile, the ALOHA protocol is widely applied in LoRa networks, which further aggravates the collision problem. To conquer this challenge, we propose a protocol named mLoRa for multi-packet reception in LoRa networks, leveraging unique features inherent in LoRa’s physical layer including chirp spread spectrum (CSS), M-FSK modulation, and demodulation. In addition, design enhancements are developed to mitigate the noise and frequency offset influence. We implement mLoRa on a six-node testbed with USRPs. Experiment results demonstrate that mLoRa enables up to three concurrent transmissions. Correspondingly, mLoRa based throughput is around 3 times more than the conventional LoRa.