A Low Overhead Positioning Framework for Satellite-Based IoT Devices

The Internet of Things (IoT) has expanded its reach through applications like environmental monitoring and smart agriculture. Its growth is often limited by the need for extensive IoT gateways and base stations. Satellite-based IoT, using low Earth orbit (LEO) satellites, offers a solution by enabling global sensing without terrestrial infrastructure. This technology allows IoT devices to transmit data to satellite gateways, which is crucial for dynamic environments like the ocean where nodes drift with currents. In such applications, position information is valuable for data analysis and tracing. Traditional GPS modules, while affordable and low-energy, can be inefficient due to the large payload space required for precise positioning data. The payload used to report the position might be as long as the sensed data itself. This paper proposes a novel approach to terrestrial IoT device positioning using LoRa or FSK modulation, where positioning is performed on the satellite, saving GPS bytes and reducing packet size. By utilizing Doppler effects and satellite motion, the method calculates device positions, forming a positioning equation set without interfering with communication tasks. Challenges in Doppler effect measurement and positioning are addressed with a fine-grained frequency shift measurement method using ZoomFFT and zero-padding FFT, and a non-linear equation set is solved to determine the positions of terrestrial nodes, with constraints added to ensure practical solutions. The framework is validated through simulations, demonstrating a significant reduction in payload length and positioning accuracy comparable to GPS. In ideal cases, the framework can locate nodes with errors less than 60 meters without any GPS information from data packets.