Superimposed LoRa Modulation for IoT Networks

Abstract

The emergence of Internet-of-Things (IoT) has led to the development of new energy efficient and long-range wireless technologies, which are necessary for the successful realization of IoT applications. In order to cater for these demands, long range (LoRa) has emerged as one of the prominent low power wide area network (LPWAN) technologies to provide low complexity, energy efficient and long range communication. However, current LoRa frameworks suffer from limited network capacity and poor spectral efficiency, particularly in dense deployments. Consequently, power domain-superposition modulation (PD-SPM) is integrated with LoRa to alleviate the aforementioned problem by enabling multiple access using shared channel resources. In this thesis, we first investigate the implementation of a spectrally efficient LoRa-enabled PD-SPM system, allowing concurrent transmission of multiple users using shared channel resources.Furthermore, two collision resolution schemes are proposed to enable resolution and accurate detection of overlapped symbols. The collision resolution schemes are shown to each offer trade offs in complexity, scalability, energy efficiency, and spectrum utilization. The second part of the thesis presents a comprehensive analytical framework to investigate the performance of a LoRa-enabled PD-SPM system in AWGN, Rayleigh fading, and Nakagami-m fading conditions. We present novel exact expressions of the symbol error rate (SER) performance for an arbitrary number of paired users, in addition to closed form approximated expressions. The third part of the thesis presents numerical and simulated results to offer useful insights into the system performance. The accuracy of the derived SER expressions in various channel conditions are verified through Monte Carlo simulations. Furthermore, the diversity order of each user is shown to be directly proportional to the user's order. Additionally, it is shown that the considered system achieves an M-fold increase in throughput for M paired users, when compared to a conventional LoRa system. Moreover, the impact of inter-spreading factor interference is investigated, where it is observed that there exists a signal-to-interference ratio (SIR) threshold below which the signal reliability of the user of interest is degraded.

Date of Award	Jul 2022
Original language	American English