Seamless navigation through GPS outages - A low-cost GPS/INS solution

GPS signal blockage can be experienced in many environments a vehicle mayencounter; a forested road, the urban jungle, a tunnel, road spaghetti you get thepicture. Inertial sensors complement GPS well, potentially bridging the gaps in GPScoverage and provide vehicle attitude information as a bonus. But there is a catch,the data streams from a GPS receiver and inertial sensors are independent andmust be fused together to generate a useful stream of navigation (position, velocity,and attitude) data. In this article the hardware and software algorithms that havebeen developed at the University of New South Wales to do this fusing operation arepresented along with an example of the capabilities of the system. The articleconcludes with a look at some applications presently being explored and ideas forfuture work.The complimentary nature of GPS and Inertial Navigation System (INS) is wellknown; GPS provides absolute XYZ coordinates at a low data rate, while INSessentially provides changes in XYZ (and attitude) at a high data rate. While GPScan suffer loss of satellite signals that can lead to no XYZ at all, INS just keeps ongoing but will drift as errors compound. So its a happy marriage; GPS can bound theINS errors and INS can fill the gaps between GPS fixes.Broadly speaking there are four parts to our GPS/INS system; the sensors, thesynchronization component, the integration / fusion component and data output. Thesystem can operate in real-time or post-processing mode, the data fusion algorithmsfor both modes are essentially the same. In the real-time mode the algorithms run onan embedded processor on the prototype hardware device. In the post-processmode, the algorithms run on a PC. The hardware and the system components will bedetailed shortly, but first lets see what the system is capable of