LoRa Technology Demystified: from Link Behavior to Cell-Level Performance

In this paper we study the capability of LoRa technology in rejecting different interfering LoRa signals and the impact on the cell capacity. First, we analyze experimentally the link-level performance of LoRa and show that collisions between packets modulated with the same Spreading Factor(SF) usually lead to channel captures, while different spreading factors can indeed cause packet loss if the interference power is strong enough. Second, we model the effect of such findings to quantify the achievable capacity in a typical LoRa cell: we show that high SFs, generally seen as more robust, can be severely affected by inter-SF interference and that different criteria for deciding SF allocations within the cell may lead to significantly different results. Moreover, the use of power control and packet fragmentation can be detrimental more than beneficial in many deployment scenarios. Finally, we discuss the capacity improvements that can be achieved by increasing the density of LoRa gateways. Our results have important implications for the design of LoRa networks: for example, allocating high SFs to faraway end devices might not improve the experienced performance in case of congested networks because of the increased transmission time and vulnerability period.