Multi-hop LoRaWAN uplink extension: specification and prototype implementation

Abstract

The coverage of a LoRaWAN network in a city is greatly hampered by the harsh propagation environment. Sensors are sometimes placed under the ground or in places with strong electromagnetic attenuation. Also, for users who have a contract with a network operator, installing another gateway to improve coverage of blind spots is not an option. In other cases, there is no or very weak connectivity (e.g. basements). In the present work, we design and implement a multi-hop uplink solution compatible with the LoRaWAN specification, which can act as an extension to already deployed gateways. End nodes transmit data messages to intermediate nodes, which relay them to gateways by choosing routes based on a simplified version of destination-sequenced distance vector routing. The routing protocol was successfully implemented and was assessed using a linear and bottleneck topology, where the packet reception rate (PRR) and throughput were measured. A carrier activity detection mechanism is also proposed. This paper presents the protocol specification and detailed description of a prototype implementation, as well as experimental performance results. On the bottleneck topology, it was observed that the PRR of each node did not significantly vary. On the linear topology, we observed that the throughput and PRR did not decrease considerably with the increase of hops. A listen-before talk multiple access mechanism is also proposed, which significantly reduces the probability of collision.