Odometer-Aided Ultra-Tight GPS/MIMU Integration for Land Vehicle Navigation in Urban Canyons

The ultra-tightly coupled (UTC) integration of a Global Positioning System (GPS) receiver and a microelectromechanical inertial measurement unit (MIMU) uses inertial navigation solutions to control tracking loops of the GPS receiver. In an urban canyon environment, the signal blockage from buildings will reduce the number of visible satellites for the land vehicle navigation system. When the visible satellites are fewer than four, inertial navigation solutions derived from a low-cost MIMU gradually diverges, which in turn causes the receiver's tracking errors to increase, and even causes the tracking loops to lose lock. To address this issue, this paper implements an odometer-aided ultra-tight GPS/MIMU integration system. Odometer is a common velocity sensor that can be integrated with other navigation equipment to form an integrated navigation system. Also, odometer is a self-contained sensor and does not rely on external signals. The proposed UTC navigation system exploits odometer information to improve the tracking performance of the GPS receiver and the navigation accuracy in a low-visibility satellite environment. The proposed navigation system was evaluated using field test data. Test results show that the odometer-aided ultra-tightly coupled GPS/MIMU navigation system can significantly improve the navigation accuracy of the navigation system in low-visibility satellite environment. If the number of visible satellites is only one, odometer information can extend the virtual lock time of the interrupted signal.