Scientists from Norway have created ‘SmartNav’, a technological development that merges satellite science and Google’s city mapping to transform GPS into an ultra-precise system, functioning even in the toughest urban canyons found in the world’s most densely packed cities.
Standard GPS, as found on a car’s in-built computer or on a smartphone, struggles in “urban canyons.” This is where skyscrapers bounce satellite signals, confusing navigation systems. This is similar to being at the bottom of a deep gorge, where signals reach a device only after multiple reflections from the walls.
GPS – the Global Positioning System – comprises many small satellites orbiting the Earth. The satellites send out signals using radio waves, which are received by a GPS receiver. When the receiver receives these signals from at least four satellites, it is able to calculate its position. The signal consists of a message with a code indicating the satellite’s position and the exact time the signal was transmitted – like a text message from the satellite.
To combat this, Norwegian University of Science and Technology scientists have created SmartNav. The technology combines satellite corrections, wave analysis, and Google’s 3D building data for remarkable precision. This method achieved accuracy within 10 centimetres during testing. Such high accuracy will be important for the autonomous vehicles of the future.
Why the problem exists
According to lead researcher Ardeshir Mohamadi: “In cities, glass and concrete make satellite signals bounce back and forth. Tall buildings block the view, and what works perfectly on an open motorway is not so good when you enter a built-up area.”
When GPS signals reflect off buildings, they take longer to reach the receiver. This delay throws off the calculation of distance to the satellites, which makes the reported position inaccurate. Not only are the satellite signals disrupted down between the tall buildings, but the signals that are correct do not have sufficient precision.
The solution
In terms of the solution, the researchers combined several different technologies to correct the signal. The result is a computer program that can be integrated into the navigation system of autonomous vehicles. This is based on combining multiple technologies:
Radio waves
Instead of using the GPS code, researchers looked at the accompnying radio wave. Whether the wave travels upwards or downwards when it reaches the receiver is called the carrier phase of the wave. Using the carrier phase can provide very high accuracy, but it takes time, meaning by itself it is not a solution. Yet the radiowave can be combined with other technologies.
Real Time Kinetics
A service that can be used in combination corrects the signal using base stations called RTK (Real Time Kinetics). RTK works effectively provided the user is in the vicinity of one of these stations.
Precise Point Positioning – Real-Time Kinematic
The third approach is PPP-RTK (Precise Point Positioning – Real-Time Kinematic), which combines precise corrections with satellite signals. The European Galileo system now supports this by broadcasting such corrections.
Google 3D
Google has rolled out 3D models of buildings in almost 4000 cities around the world. The company is using these models to predict how satellite signals will be reflected between the buildings.
The combination breakthrough
By combining these four technologies, the researchers state they have developed a navigation sytem superior to conventional GPS.
It is hoped the new breakthrough will lead to reliable urban navigation in the form of platforms which are accessible and affordable worldwide.
The technology appears in the Journal of Spatial Science, with the research paper titled “Phase-Only positioning in urban environments: assessing its potential for mass-market GNSS receivers.”
A second paper will be issued within the next month: “FLP-Aided GNSS RTK Positioning: A Means of Supporting Smartphone High-Precision Positioning in Dynamic Urban Environments”, Journal of the Institute of Navigation
