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

2025-07-16

AI Summary

To address the low spectral efficiency and limited massive access capability of conventional LoRa networks, this paper proposes a multi-chirp-rate indexing modulation (MCRM) system based on Zadoff–Chu (ZC) sequences. Leveraging the low cross-correlation property of ZC sequences, we design an orthogonal chirp-rate index mapping and integrate it with a peak-detection-assisted successive interference cancellation (PD-SIC) receiver. A closed-form bit error rate (BER) expression is derived under Nakagami-m fading channels. Simulation results validate the theoretical analysis: compared to OrthoRa, the proposed scheme achieves 16–21% higher throughput at the same collision probability, significantly lower BER, and concurrently improved spectral efficiency and multi-user access capacity. This work provides a novel, high-reliability, high-capacity physical-layer design for low-power wide-area networks (LPWANs).

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Machine Learning: Large Multimodal Models (LMMs)

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

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.

Problem

• Enhances LoRa network transmission rate and access scale
• Reduces bit-error rate in Nakagami-m fading channels
• Improves spectral efficiency with multiple chirp rates

Innovation

• Uses Zadoff-Chu sequences for MCR-IM system
• Implements PD-SIC algorithm for user accommodation
• Enhances spectral efficiency in LoRa networks