An evaluation of coverage models for LoRa

Abstract: LoRaWAN is a wireless network technology based on the LoRa modulation technology. When planning such a network, it is important to estimate the network’s coverage, which can be done by calculating path loss. To do this, one can utilize empirical models of radio wave propagation. Previous research has investigated the accuracy of such empirical models for LoRa inside cities. However, as the accuracy of these models is heavily dependent on the exact characteristics of the environment, it is of interest to validate these results. In addition, the effect of base station elevation on the models’ accuracy has yet to be researched. Following the problems stated above, the purpose of this study is to investigate the accuracy of empirical models of radio wave propagation for LoRa in an urban environment. More specifically, we investigate the accuracy of the models and the effect of base station elevation on the models’ accuracy. The latter is the main contribution of this study. To perform these investigations, a quantitative experiment was conducted in the city of Jönköping, Sweden. In the experiment a base station was positioned at elevations of 30, 23, and 15m. The path loss was measured from 20 locations around the base station for each level of elevation. The measured path loss was then compared to predictions from three popular empirical models: the Okumura-Hata model, the COST 231-Walfisch-Ikegami model, and the 3GPP UMa NLOS model. Our analysis showed a clear underestimation of the path loss for all models. We conclude that for an environment and setup similar to ours, models underestimate the path loss by approximately 20dB. They can be improved by adding a constant correction value, resulting in a mean absolute error of at least 3,7-5,6dB. We also conclude that the effect of base station elevation varies greatly between different models. The 3GPP model underestimated the path loss equally for all elevations and could therefore easily be improved by a constant correction value. This resulted in a mean absolute error of approximately 4dB for all elevations.