Navigation is a breeze thanks to GPS. But in the city it sometimes works poorly because buildings interfere with the GPS signals. Dutch researchers have developed a new positioning system that solves this problem and is also much more accurate.
If you turn on your navigation system while driving out of a garage or your street, it usually takes a while for the route planner to work. The buildings in the area block and reflect the signals from GPS satellites, preventing them from reaching your navigation system properly. As a result, the device has no idea where it is for the first few seconds or even minutes.
A new positioning system, which could use the existing telecommunications network, is not affected by this. Researchers have demonstrated this on a 50-metre stretch of road, next to buildings, on the TU Delft grounds. There, a prototype of this new system outperformed GPS and also achieved an accuracy of ten centimetres. The technique was developed by researchers from Delft University of Technology, VU Amsterdam and the national metrology institute VSL.
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Buildings interfere with GPS
“GPS is a great system,” says satellite navigation researcher Christian Tiberius from Delft University of Technology. ‘But it is a military system that was mainly developed for positioning fighter jets in the air, aircraft carriers at sea and tanks driving around in a desert, for example. So it was never designed for navigation in cities.’
The GPS navigation system determines your location by receiving radio signals from at least four different GPS satellites. These signals arrive at your navigation system at different times, because the satellites are at different distances. By determining how long it takes for all signals to arrive, the navigation system can calculate its position relative to those satellites. From this the weather can deduce the position on earth.
In order to receive those GPS signals, the line between you and the satellite must be clear. If there is a tree or a building in between, there is less or no signal. That’s why GPS works less well in cities. There you also have the problem that the GPS signals reflect off buildings. As a result, your navigation system receives, in addition to the original signal, up to fifty reflected signals. ‘It becomes such a mess that he can no longer determine where he is,’ says Tiberius.
Pulses and atomic clock
The new system works in a similar way to GPS. But instead of satellites, it uses cell towers. The researchers have these cell towers transmit radio signals with much shorter pulses than the GPS signals. These signals have been chosen in such a way that they can be integrated into the 5G infrastructure.
‘Thanks to those short pulses, we are not bothered by reflections’, explains Gerald Jansen from Delft University of Technology. Due to the reflection, the longer GPS pulses can overlap, making it a mess. The shorter pulses overlap much less, so reflections are hardly a problem anymore.
Another reason for the accuracy of the new system is the atomic clock, which ensures that all transmission towers are based on exactly the same time. GPS satellites each have their own atomic clock on board. They are synchronized as accurately as possible, but because they are different clocks, they can still be out of sync by a few billionths of a second.
The new system uses a central atomic clock that is connected to all transmission towers via fiber optic cables. As a result, they are synchronized to a ten-billionth of a second. An additional advantage is that the current telecom masts already have a fiber optic connection, so you don’t have to install it specially.
The extreme time accuracy is necessary to determine the distance between the transmitter and the receiver very precisely. That is close. If the transmitters are out of sync for a billionth of a second, the accuracy drops to 30 centimetres. The researchers have now demonstrated with transmitters and a prototype that this system achieves an accuracy of 10 centimeters in built-up areas.
Self-driving cars and delivery drones
You don’t need that accuracy if you want to find a store or know which exit to take on the highway. The GPS accuracy of a few meters is sufficient for this. But that does not apply to new technology such as steering assistance and self-driving cars. ‘If cars and trucks have to keep driving side by side on the highway at 100 kilometers per hour, the accuracy of a few meters is not enough,’ says Tiberius. Such an inaccuracy could also lead to a future delivery drone delivering your pizza to the neighbor.
The fact that the researchers achieved an accuracy of one decimeter with existing equipment is impressive, write Hui Chen and Henk Wymeersch, of Chalmers University of Technology in Sweden. a comment that appeared with the publication about the system. ‘The researchers are bringing “smart cities” a step closer.’