Ultra-accurate navigation uses mobile towers instead of satellites

Created as the result of work researchers at Delft University of Technology, Vrije Universiteit Amsterdam and VSL, the working prototype achieved a location accuracy of 10 centimetres.

The new technology could be important for the implementation of a range of location-based applications, including automated vehicles, quantum communication and next-generation mobile communication systems.

A lot of vital infrastructure relies on global navigation satellite systems such as the US’s GPS and the EU’s Galileo. Reliance on satellites means both have their limitations and vulnerabilities. Their radio signals are weak when received on Earth, and accurate positioning is no longer possible if the radio signals are reflected or blocked by buildings.

“This can make GPS unreliable in urban settings, for instance” said project co-ordinator Christiaan Tiberius of Delft University of Technology, “which is a problem if we ever want to use automated vehicles.  Also, citizens and our authorities actually depend on GPS for many location-based applications and navigation devices. Furthermore, so far we had no back-up system.”

The aim of the new ‘SuperGPS’ project was to develop an alternative positioning system that makes use of the mobile telecommunication network instead of satellites and could be more robust and accurate than GPS.

“We realised that with a few cutting-edge innovations, the telecommunication network could be transformed into a very accurate alternative positioning system that is independent of GPS,” said Jeroen Koelemeij of Vrije Universiteit Amsterdam.

“We have succeeded and have successfully developed a system that can provide connectivity just like existing mobile and Wi-Fi networks do, as well as accurate positioning and time distribution like GPS.”

One of these innovations is to connect the mobile network to a very accurate atomic clock, so that it can broadcast perfectly timed messages for positioning, just like GPS satellites do with the help of the atomic clocks they carry on board.

These connections are made through the existing fibre-optic network. “We had already been investigating techniques to distribute the national time produced by our atomic clocks to users elsewhere through the telecommunication network,” said Erik Dierikx of VSL.

“With these techniques we can turn the network into a nationwide distributed atomic clock – with many new applications such as very accurate positioning through mobile networks. With the hybrid optical-wireless system that we have demonstrated now, in principle anyone can have wireless access to the national time produced at VSL. It basically forms an extremely accurate radio clock that is good to one-billionth of a second.”

The system employs radio signals with a bandwidth much larger than is commonly used.

“Buildings reflect radio signals, which can confuse navigation devices. The large bandwidth of our system helps sorting out these confusing signal reflections, and enables higher positioning accuracy,” said Gerard Janssen of Delft University of Technology.

“At the same time, bandwidth within the radio spectrum is scarce and therefore expensive. We circumvent this by using a number of related small bandwidth radio signals spread over a large virtual bandwidth. This has the advantage that only a small fraction of the virtual bandwidth is actually used and the signals can be very similar to those of mobile phones.”