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I/O Magazine > October 2020

Somewhere in the foreseeable future, self-driving cars will fill accuracy of one decimetre instead of metres. In contrast to
the streets. Unfortunately, in densely built-up areas with tall satellite navigation, they use transmitters the size of a Wi-Fi
buildings, tunnels or parking garages, the built-in GPS fails. modem that emit very short radio pulses on the ultra-wide-
Even when smart software determines the precise location of band. The signal receiver of could eventually be placed in a
a vehicle, it remains an educated guess. To allow self-driving small chip. Sending short pulses implicates that more band-
cars to drive around in urban areas without causing trouble, width of the radio spectrum is required. ‘But the great thing
a more accurate positioning system is needed. is that the bandwidth is not needed all the time, probably
just a millisecond every second.’ The receivers could be
combined with the 5G communication network because
FAILING GPS the range should be similar.

‘GPS was developed for military purposes in the 1960s’, says It already works in the lab, says Tiberius. ‘Now the biggest
Christian Tiberius, Associate Professor of Geoscience and challenge is to make it work in practice.’ This summer a trial
Remote Sensing at TU Delft. ‘It was used to determine the in The Green Village started, an experimental village on the
position of tanks, fighter planes and ships, but now it is also TU Delft campus where a real living environment is simu-
used in commercial ships and smartphones. It was never lated with streets, houses, traffic and, of course, residents.
intended for those applications.’ GPS satellites send a signal to The researchers will attach their transmitters to lampposts
a receiver on earth. The receiver determines its location based and build a receiver themselves. ‘For now, the receiver will be
on the time it takes for the signal to travel from the satellite to put in a large storage box from IKEA, but ideally it will fit in a
the receiver, multiplied by the speed of light. The location is navigation system or smartphone.’ For this test it is essential
then determined by measuring the distance between the satel- that the transmitters are all well synchronized. Therefore
lites and the receiver. The problem is that there is a lot of sig- a fibre optic connection will be established with VSL, the
nal reflection in built-up areas: the GPS signal bumps into all Netherlands Metrology Institute, which is also in Delft.
A laser pulse with the time indication is sent from the
kinds of objects such as buildings before it reaches the
receiver. Tiberius: ‘At the Weena in Rotterdam, near the sky institute with picosecond accuracy.
scraper of Nationale Nederlanden, I once did a position calcu-
lation with a simple receiver. It was hundreds of meters off.’ To accurately know the time, an important role is reserved
for the so-called time-frequency reference equipment, which
Tiberius and his colleagues are now working on a solution to has been developed by OPNT, a spin-off of VU Amsterdam.
this problem. They are developing a land-based GPS with an OPNT was also one of the initiators of the SuperGPS project.

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