Decimeter level vehicle navigation combining multi-GNSS with existing sensors in dense urban areas

The increasing demand for navigation and automation has led to the development of a number of accurate and precise navigation applications that make use of the Global Positioning System (GPS) and other sensors. However, GPS tends to suffer from multipath error, especially in urban environments. To overcome this problem, a method was developed for improving real-time kinematic GPS (RTK-GPS) using a low-cost inertial measurement unit (IMU) and conventional vehicle speed sensors. Additionally, RTK-GNSS was also evaluated to improve the RTK performance using GPS, Quasi-Zenith Satellite System (QZSS) and BeiDou. In the study, the quality of the complete observation data was assessed based on the carrier-to-noise ratio and satellite elevation angle, and the popular least-squares ambiguity decorrelation adjustment method and the ratio test were used to obtain the fix positions. We used speed information obtained from Doppler measurements as an alternative source of information, while information from the IMU and vehicle speed sensor (integrated with the RTK-GPS via a Kalman Filter) was used during the outage of visible satellites. We also used the IMU and vehicle speed sensors to detect the wrong fixes in the RTK-GPS. A Position and Orientation System for Land Vehicles (Applanix) was used to estimate the reference positions. During GPS outage, it is important to accurately determine the last heading of the car for precise navigation. In this study, it was found that a suitable measurement quality check is required to obtain better direction information. The results of the experiment demonstrate that, to some extent, our proposed method is beneficial as an alternative to the conventional RTK-GPS in an urban environment.