25 February 2008

Global Positioning System technology (GPS) is a great invention, able to map your movements and save you from getting lost in strange city streets – until you go into a tunnel, between tall buildings or hit any other barrier that might block the satellite signal your device relies on.

To combat this shortfall, spatial information systems researchers have been working to combine satellite-reliant GPS with a non-satellite-based technology called Inertial Navigation System (INS) to provide a positioning system which will work accurately and seamlessly indoors and out.

So far effective GPS/INS systems have been built by major defence and technology companies but the enormous cost of these high-tech systems puts them well out of the reach of consumers.

Now the work of Dr Yong Li and colleagues in UNSW Engineering’s Satellite Navigation And Positioning Lab (SNAPLab) could be the breakthrough that makes seamless GPS/INS navigation available for everyday use.

“GPS alone is a radio frequency, satellite-based navigation system. The signal is broadcast from space some 20,000km up and when it reaches Earth it is very weak,” Dr Li says.

“As a result the signal can be blocked by buildings and trees and there are also errors in the signal which means GPS is not good in a lot of locations.”

“INS however is self-contained. It uses a computer and motion sensors to track and record movements, acceleration, direction and velocity without needing an external signal. All it needs is an initial reference point.

“However INS has its own problems in that there is a ‘drift’ in its accuracy over time – slight errors compound on top of each other. For high accuracy, an INS system can last in a self-contained way for about one hour before it drifts too far.”

“We want a cheap and faster solution to implement the integration of GPS and INS,” Dr Li says.

GPS/INS integration is most often implemented on a PC or application-specific integrated circuit (ASIC) platform. The SNAPLab researchers have successfully developed a far more flexible platform based on field programmable gate array (FPGA) technology. The biggest advantage of the FPGA-based system is that all the hardware and software components of the system are field re-programmable without any hardware changes.

This approach can shorten the research and development period and allows maximum flexibility, being able to integrate a wide range of GPS and INS sensor packages.

The SNAPLab research has led to the development of systems to synchronise the UTC-based timing of GPS with the internal timing of INS systems – with time synchronisation being an essential part of accurate navigation.

The UNSW technology can also perform positioning calculations in real time – a task other PC-based solutions cannot match.