A MEMS accelerometer and a MEMS gyroscope are used to provide accurate measurement of angular and acceleration forces, and these are combined with GNSS data to provide an instantaneous location fix should the GNSS signal be interrupted or become unreliable. By storing the vehicle’s last known position when, for example, it is parked in a multi-story or underground car park, provides an almost instant ability to navigation once the vehicle is started up again. An example of the accuracy achieved by UDR within a build up city area surrounded by tall buildings can be seen in Figure 2.
The test results illustrated in Figure 2 show the comparative accuracy between GNSS and UDR using an antenna mounted on the test vehicle’s windscreen. In this test, the UDR positional accuracy is a factor of 3 times better than using GNSS alone. To further demonstrate UDR’s capabilities under poor signal conditions another test run was made, this time with the antenna placed in the vehicle’s foot, well underneath the dashboard. The results can be seen in Figure 3. UDR continued to maintain a factor of three better results in positional accuracy even though the relative position accuracy was not as good as having the antenna screen or dash mounted. Using GNSS alone navigation was clearly impossible.