Low Power Wide Area (LPWA) networks are making spectacular progress fromdesign, standardisation, to commercialisation. At this time of fast-pacedadoption, it is of utmost importance to analyse how well these technologieswill scale as the number of devices connected to the Internet of Things (IoT)inevitably grows. In this letter, we provide a stochastic geometry frameworkfor modelling the performance of a single gateway LoRa network, a leading LPWAtechnology. Our analysis formulates unique peculiarities of LoRa, including itschirp spread-spectrum modulation technique, regulatory limitations on radioduty cycle, and use of ALOHA protocol on top, all of which are not as common intoday's commercial cellular networks. We show that the coverage probabilitydrops exponentially as the number of end-devices grows due to interferingsignals using the same spreading sequence. We conclude that this fundamentallimiting factor is perhaps more significant towards LoRa scalability than forinstance spectrum restrictions. Our derivations for co-spreading factorinterference found in LoRa networks enables rigorous scalability analysis ofsuch networks.
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