Researchers at the Universitat Oberta de Catalunya (UOC) in Spain are studying a model to synchronise the needs of IoT devices with satellite access times for low Earth orbit (LEO) satellites such as Starlink.

The method being proposed for synchronising IoT devices and satellites results in greater energy efficiency for devices communicating via satellite.

One of the main barriers to IoT deployment involves connecting objects to the internet in places where there is no mobile network infrastructure. The answer seems to lie with LEO satellites, although this presents its own difficulties.

A study (ieeexplore.ieee.org/document/10190364) led by Guillem Boquet and Borja Martínez, two researchers from the UOC working in the Wireless Networks (Wine) group of the university’s Internet Interdisciplinary Institute (IN3), examined possible ways to improve the coordination between the billions of connected objects on the surface of the Earth and the satellites in its atmosphere.

LEO satellite constellations have emerged in recent years as capable of overcoming the limitations of terrestrial networks.

“LEO satellites are particularly relevant when it comes to the IoT because, being closer to the Earth, they need less transmit power to achieve reliable communication,” said Boquet. “This means devices can save energy, extending battery life and saving on maintenance costs. Among other advantages, deploying a low Earth orbit satellite is considerably cheaper, which means connectivity services can be provided at prices that are more reasonable for the IoT.”

Furthermore, LEO satellites – such as the SpaceX Starlink and Eutelsat OneWeb satellites and Amazon’s Kuiper project – have much lower latency than geostationary satellites, have many more satellites in operation and greater coverage, can be deployed much more quickly, and are suitable for use in communications in many sectors. However, using this option for the IoT brings its own problems.

Some relate to the development of the unlikeliness of being able to deploy mega satellite constellations to ensure uninterrupted coverage in the short term, and others relate to limitations linked to the way the technology itself has been designed, such as the increased likelihood of interference between communications, limitations regarding IoT devices’ use of power, and the difficulties involved in synchronising these devices’ duty cycles with satellite communication availability intervals.

“IoT devices tend to be battery-powered and have regular sleep and wake-up duty-cycling intervals to save energy,” said Boquet. “These regular duty cycles are commonly used in terrestrial communications, where they are even standardised. However, as LEO constellations don’t provide uninterrupted coverage, what you end up with is short, irregular communication windows. We therefore need to develop more advanced synchronisation strategies to ensure reliable communication and access to the connection opportunities provided by the satellite network.”

The power-saving modes in IoT devices, based on the energy conservation times during which they can extend their battery life by going into sleep mode, rely on regular periods. But this is not how satellite constellations work. To synchronise the needs of connected objects with LEO satellite access times means predicting where each satellite is going to be and when the communication window will open.

“Our proposal is to synchronise the IoT application’s transmission needs and the network’s communication needs on the one hand with the satellite’s availability times on the other,” said Boquet. “This synchronisation is based on the ability to predict these times by using a model of the satellite’s orbital path, starting from a known initial point. However, making predictions has a cost in terms of energy, as it requires regular calculation operations to be made and the predictive model to be updated when it deviates from the actual situation.”

The development by the researchers at the UOC was tested in a real communication situation with the Enxaneta nanosatellite, the first satellite deployed by the government of Catalonia under its NewSpace project. The results were promising: the satellite access ratio improved by up to 99%, ensuring long-term access to the network while reducing the device’s energy consumption.

“The next steps are to complete the cost-benefit analysis of implementation, taking into account various applications, service networks, types of satellite constellation, IoT devices and communication technologies, and then to propose and put in place energy-saving modes that automatically adapt to communication needs and the changing conditions of non-terrestrial networks,” said Boquet.