Interleaved Chirp Spreading LoRa as a Parallel Network to Enhance LoRa Capacity

Abstract

LoRa has become a key enabler for multiple low-power wide-area network (LP-WAN) technologies. LoRa technology is pillared on its patented chirp spread spectrum modulation. Cyclic shifts of the LoRa base chirp signal create the whole orthonormal space of multidimensional signaling. Interleaved Chirp Spreading LoRa (ICS-LoRa)-based modulation has been recently introduced as a new multidimensional space generated from the interleaved versions of the nominal LoRa chirp signals. Since LoRa networks adopt an ALOHA-based medium access scheme, they typically suffer from inevitable collisions which limit the achievable underlying network capacity. This article proposes enhancing the LoRA network capacity by deploying ICS-LoRa as a parallel logical network that co-exists with the nominal LoRa networks. The capacity gain is attributed to the good cross-correlation properties between the ICS-LoRa and the nominal LoRa chirp signals. In order to provide capacity evaluation, this article introduces an analytical model for the bit error rate (BER) of nominal LoRa modulation under ICS-LoRa co-existence as a parallel logical network. The simulation/analytical BER models are validated practically and the resultant practical curves are shown to be in close proximity to the simulation curves. The analytical model is then used to define signal to noise/interference ratio coverage regions within the scope of assessing the achievable aggregate capacities of the parallel LoRa/ICS network. Finally, the attained coverage regions have been deployed in a simulation model and the results for an example Internet of Things (IoT) application show that introducing the ICS-LoRa as a parallel network can provide a capacity gain at the scale of 42%.