GPS Based Map Matching in the Pseudorange Measurement Domain

Accurate vehicle location is important for various Intelligent Transportation System (ITS) applications such as route guidance and collaborative driving. The Global Positioning System (GPS) has become popular for locating vehicles for many ITS applications due to the 24hour, all weather and free-of-charge availability. Although GPS-based vehicle navigation systems are accurate in open sky conditions, it is challenging to navigate vehicles in dense urban canyon conditions where GPS is affected by many issues, with the primary being availability. The other effect which severely degrades the accuracy of GPS-derived navigation solutions in such environments is multipath. High Sensitivity GPS (HS GPS) receivers, can increase the availability, but are affected by multipath and cross correlation due to weak signal tracking. These factors may hamper the use of GPS for vehicle positioning in urban canyons. This paper describes a map matching algorithm to tackle the problems discussed above with the goal to successfully navigate a vehicle in an urban canyon, amidst low signal availability and multipath conditions. The algorithm is based on tight integration of the map information with the GPS measurements. The novelty of the approach is the use of map information to eliminate “erroneous” pseudorange measurements. An optimal map matched solution is then computed using the outlier-free measurements from GPS. The algorithm identifies the road link using a Fuzzy Inference System (FIS). The input to the system comes from a HS GPS receiver, a low cost gyro and a digital map. The algorithm was tested in an urban canyon under low signal availability conditions. The performance of the map matching algorithm was evaluated in terms of number of correct and false fix on the road map. It is found that the proposed algorithm gave 98% correct and no false fixes, showing the effectiveness of the algorithm in mitigating navigation errors and increase in the availability of reliable navigation solution.