Practical Performance Evaluation of Multi-User Interleaved Chirp Spreading LoRa Networks

Abstract

LoRa has recently established itself as one of the prominent low power wide area networks (LP-WAN) technologies. LoRa technology is pillared on its patented chirp spread spectrum modulation. Cyclic shifts of the LoRa base chirp signal generate the entire multi-dimensional orthonormal space for non-binary LoRa signaling. The capacity of LoRa networks is limited due to the adopted ALOHA medium access scheme. Interleaved Chirps Spreading LoRa (ICS-LoRa) based modulation has been introduced as a new multi-dimensional space generated from the interleaved versions of the nominal LoRa chirp signals to increase the data rate. This paper proposes ICS-LoRa as a network supporting multiple users in order to significantly enhance the bit error rate (BER) performance compared to the case of LoRa users with the original ICS-LoRa interference. This is attributed to the good cross-correlation properties between ICS-LoRa signals of different interleaving patterns. In this paper, we study the interference effect of ICS-LoRa signals of different interleaving patterns at different signal to interference ratio (SIR) and at different signal to noise ratio (SNR) scenarios. Simulation curves have been practically verified over software-defined radio (SDR) testbed, and the obtained practical curves are shown to be in close proximity to the simulation curves. Upon utilizing the ICS-LoRa as parallel networks to support two simultaneous users, a significant enhancement on the BER performance is obtained. For instance, the BER performance witnessed an enhancement of 3.75dB compared to the case of an original ICS-LoRa signal interfered by another original ICS-LoRa signal for spreading factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$sf=7$</tex> and SIR <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\gamma=4dB$</tex> .