TDMA-Based LoRa IoT Architecture with FreeRTOS for Real-Time Multi-Node Bridge Structural Health Monitoring

Area of Science:

• Engineering
• Computer Science
• Materials Science

Background:

• Internet of Things (IoT) systems are crucial for continuous bridge structural health monitoring (SHM).
• Existing LoRaWAN or contention-based systems face challenges like packet collisions, latency, and scalability issues with multiple sensors.
• A robust and scalable communication framework is needed for effective bridge SHM.

Purpose of the Study:

• To propose a soft real-time LoRa-based IoT architecture for bridge SHM.
• To implement a time division multiple access (TDMA) communication framework on an embedded real-time platform.
• To address limitations of existing wireless monitoring systems, ensuring reliable data transmission.

Main Methods:

• Developed a LoRa-based IoT architecture integrating distributed vibration sensing nodes and a TDMA communication layer.
• Utilized an ESP32-based gateway and a web-based database for remote data visualization and analysis.
• Leveraged FreeRTOS for system-level task scheduling on a dual-core ESP32 platform for concurrent processes.

Main Results:

• Achieved stable multi-node communication with a packet delivery ratio exceeding 95% in laboratory-scale experiments.
• Demonstrated predictable TDMA-scheduled transmission cycles with slots of 100-200 ms.
• Validated end-to-end operation with a three-node deployment on a cable-stayed bridge model.

Conclusions:

• The proposed TDMA-based LoRa IoT architecture effectively enhances bridge SHM systems.
• The system offers stable, predictable, and scalable communication, overcoming limitations of traditional methods.
• Further analytical evaluation of the TDMA capacity model suggests potential for larger physical deployments.