Scientists from VSL, TU Delft and VU Amsterdam developed a highly accurate alternative navigation system. This system has an accuracy of 10 centimetres. It offers a glimpse of the future. In it, telecommunication networks can provide connectivity as well as time- and location-dependent applications. And this with an accuracy much higher and faster than that of satellite navigation systems such as GPS.
The scientists implemented the system in a mobile network specially developed for this purpose. The results represent the first demonstration of a system that can provide both connectivity such as mobile and Wi-Fi networks, and accurate location and time information such as GPS. The researchers expect this technology to be of interest for various applications. These include automated driving vehicles, quantum communications, renewable energy generation and next-generation mobile networks.
SuperGPS project
The results flow from the SuperGPS project. This is a collaboration between VU Amsterdam, TU Delft and VSL - the National Metrological Institute of the Netherlands. "The aim of the project was to develop an alternative positioning system, based on the mobile network instead of satellites. The system is also more robust and accurate than GPS." So says Jeroen Koelemeij, assistant professor at VU University Amsterdam.
Growing need for alternative navigation system
Many vital infrastructures depend on satellite navigation systems such as the US GPS and the European Galileo. However, these systems have limitations and vulnerabilities. The radio signals received are weak. And positioning becomes inaccurate when radio signals are reflected or blocked by buildings. In addition, national authorities are growing concerned that more and more (illegal) jamming devices are interfering with radio waves.
"Quite a lot of vital infrastructure but also citizens and authorities, depend on GPS and similar satellite navigation systems. But there is no backup system." Speaking is Christian Tiberius of Delft University of Technology and coordinator of the project. "We realised that with a few clever innovations we could transform the telecommunications network into a very accurate alternative to GPS."
A hybrid fibre-wireless system
One of the innovations involves connecting a highly accurate atomic clock to the mobile network. This allows the system to send perfectly timed messages for positioning. This is done just as GPS does using atomic clocks in the satellites. This connection uses the existing fibre-optic network. "With this technique, we can turn the network into a nationwide distributed atomic clock, with numerous new applications such as accurate positioning. And with the hybrid fibre-wireless system we have now developed, basically anyone can access our atomic time. It provides an extremely accurate radio clock that is accurate to a billionth of a second," says Erik Dierikx, scientist at VSL.
Large bandwidth
In addition, the system uses radio signals with a much higher bandwidth than usual. This helps to recognise confusing reflections in the navigation equipment. As a result, positioning accuracy can be increased. "At the same time, bandwidth in the radio spectrum is scarce and therefore expensive. We get around that by using signals in a number of narrower bandwidths spread over a large 'virtual' bandwidth. So the signals actually use only a small part of the radio spectrum, and they are also more similar to what is currently used in mobile networks," said Gerard Janssen of TU Delft.
The results, published in *Nature*, were made possible in part by grants from the Netherlands Organisation for Scientific Research (NWO), Applied Technical Sciences domain.
Photo: TU Delft/Stephan Timmers
