Researchers from the University of California, San Diego, led by Rohith Reddy Vennam, Maiyun Zhang, Raghav Subbaraman, Deepak Vashist, and Dinesh Bharadia, have developed a novel communication protocol designed to enhance the performance of non-terrestrial networks (NTN). Their work, titled “Free Signal Multiple Access (FSMA): Scalable and Reliable LoRa for Non-Terrestrial Networks with Mobile Gateways,” addresses critical challenges faced by Low Earth Orbit (LEO) satellites and drone-based networks, which are increasingly used in various sectors, including emergency services, agriculture, and military operations.
The proliferation of LEO satellites and drones has opened up new possibilities for universal IoT applications. However, these non-terrestrial networks encounter significant hurdles, primarily due to their large coverage footprints and the dynamic nature of their gateways. The extensive coverage areas often lead to frequent signal collisions, while the movement of gateways creates unpredictable links that demand synchronization-free, link-aware transmissions. Traditional random access schemes such as ALOHA, Carrier Sense Multiple Access (CSMA), and Backoff-based Slotted Multiple Access (BSMA) prove inadequate in these scenarios, suffering from high collision rates, hidden terminals, or excessive energy overhead for gateways.
To overcome these challenges, the researchers propose Free Signal Multiple Access (FSMA), a gateway-controlled protocol that introduces a lightweight free signal chirp (FreeChirp). FreeChirp ensures that nodes transmit only when the channel is idle and when the link quality is reliable. This approach significantly reduces collisions and enables link-aware access without the need for synchronization or complex scheduling. The protocol’s simplicity and efficiency make it particularly suitable for the dynamic and extensive coverage areas characteristic of non-terrestrial networks.
The effectiveness of FSMA was demonstrated through extensive evaluations using 25 commercial LoRa devices with a drone-mounted moving gateway. The results were impressive, showing up to 2x higher throughput, 2x to 5x better packet reception ratio, and 5x improved energy efficiency compared to baseline protocols. To further validate the scalability of FSMA, the researchers conducted large-scale simulations using a custom Satellite IoT Simulator. These simulations confirmed that FSMA can scale to support 5000+ devices per satellite pass, making it a highly scalable and energy-efficient solution for NTN IoT networks.
The practical applications of FSMA in the defence and security sector are manifold. For instance, in military operations, drones equipped with FSMA-enabled IoT devices can communicate more reliably and efficiently over vast and dynamic areas, enhancing situational awareness and coordination. Similarly, in emergency services, FSMA can facilitate better communication and data exchange between drones and ground stations, improving response times and operational effectiveness. The protocol’s ability to reduce collisions and improve energy efficiency also makes it ideal for long-term surveillance and monitoring missions, where reliable and sustained communication is crucial.
In conclusion, the development of FSMA represents a significant advancement in the field of non-terrestrial networks. By addressing the key challenges of large coverage footprints and dynamic gateways, FSMA offers a scalable, energy-efficient, and reliable solution for IoT applications in various sectors, including defence and security. The researchers’ innovative approach and impressive results highlight the transformative potential of FSMA, paving the way for more robust and efficient non-terrestrial communication networks.
This article is based on research available at arXiv.