Joint Spreading Factor and Coding Rate Assignment in LoRaWAN Networks

LoRaWAN is a fast developing Low Power Wide Area Network technology that is predicted to support a large segment of the billions of estimated Internet of Things devices. It promises ubiquitous connectivity keeping network structures and management simple. One open key challenge is how to effectively assign a spreading factor so as to support a large number of end devices by a single gateway within a LoRaWAN cell. This paper confirms that if more clever spreading factor allocation than the conventionally deployed Adaptive Data Rate is considered, network performance will improve significantly. The proposed heuristics are based on two key features; first the fact that each subset of end devices allocated a certain spreading factor represents a spreading factor tier, each signify a logical pure Aloha network with a different packet length. Second, the datum to control coding rate transmission parameter which in turns control coverage sensitivities and thus system load in each spreading factor tier. Two proposed algorithms, namely sensitivitySF and assignmentSF, attempt to maximize the throughput of each spreading factor tier and thus enhance overall network performance. Simulation results show that the proposed algorithms can considerably improve network performance when compared to the basic adaptive data rate strategy, and particularly the assignmentSF algorithm consistently guarantees a high success rate for any generated traffic load.