Design of A New Multiple-Chirp-Rate Index Modulation for LoRa Networks

TL;DR

This paper introduces a multiple chirp rate index modulation system for LoRa networks that improves spectral efficiency and supports large-scale access, using Zadoff-Chu sequences and a novel interference cancellation algorithm.

Contribution

It proposes a new MCR-IM system with Zadoff-Chu sequences, deriving BER expressions and introducing a PD-SIC algorithm to enhance user capacity and reduce error rates.

Findings

Achieves higher spectral efficiency than existing systems.

Lower BER levels compared to orthogonal scatter chirp spreading spectrum.

Enhances throughput by 16% to 21% with PD-SIC.

Abstract

We propose a multiple chirp rate index modulation (MCR-IM) system based on Zadoff-Chu (ZC) sequences that overcomes the problems of low transmission rate and large-scale access in classical LoRa networks. We demonstrate the extremely low cross-correlation of MCR-IM signals across different spread factors, showing that the proposed MCR-IM system also inherits the characteristics of ZC sequences modulation. Moreover, we derive an approximate closed-form expression for the bit-error rate (BER) of the proposed MCR-IM system over Nakagami-m fading channels. Simulation results confirm the accuracy of the derived closed-form expression and demonstrate that the MCR-IM system achieves higher levels of spectral efficiency (SE) compared to existing systems. In this context, assigning multiple chirp rates to each user results in a reduction in the number of parallel channels. To mitigate this issue, we propose a peak detection based successive interference cancellation (PD-SIC) algorithm to accommodate more users. Compared to orthogonal scatter chirp spreading spectrum system that names OrthoRa, the MCR-IM system with PD-SIC algorithm achieves lower BER levels. For a similar number of collision signals, the throughput of the MCR-IM system is enhanced by 16% to 21%. Owing to these advantages, the proposed MCR-IM is well suited for large-scale, high-rate LoRa network applications.