Integration of GNSS Precise Point Positioning and Inertial Technologies for Land Vehicle Navigation
The last decade has witnessed a growing demand for precise positioning in many applications such as autonomous car navigation and precision agriculture. Precise positioning can be obtained from the global navigation satellite systems (GNSS) through either differential techniques or precise point positioning (PPP). PPP is currently favored over differential GNSS because it provides a global solution without the need for local reference stations. Nevertheless, PPP must address the error sources that are canceled in differential GNSS, and hence, it requires a longer time to converge. Therefore, employing PPP for land vehicles would be challenging due to frequent signal degradation and blockage. Integrating PPP with an inertial navigation system (INS) can solve the solution continuity issue; however, the INS solution drifts over time which can result in losing the desired accuracy. The implementation of a reliable PPP/INS system that can preserve the required accuracy is not a trivial task, especially with financial and computational cost constraints. In this work, two PPP/INS systems were developed. The first system integrates the single-frequency (SF) PPP measurements from a low-cost GNSS receiver with low-cost micro-electro-mechanical systems (MEMS) inertial sensors. The purpose of this system is to provide a reliable, low-cost navigation solution for land vehicles with sub-meter level accuracy. The system was evaluated through two road tests where it could maintain sub-meter position accuracy with short GNSS outages and reliable performance with long-term outages. The second system integrates the dual- frequency (DF) PPP with the Reduced Inertial Sensor System (RISS) for car lane-level navigation. The high-precision needed in lane-level positioning can be achieved by integrating DF-PPP with high-end INS. Since high-end INS are expensive, this work proposed the use of RISS instead of the traditional INS. RISS uses only one gyroscope and two accelerometers which can contribute to saving more than half the cost of a high-end INS. The proposed DF-PPP/RISS system was tested through three road tests that included highway driving under several overpasses, and the system was able to maintain horizontal position errors less than 50 cm. The developed PPP/INS systems are expected to play an essential role in the different applications of land vehicle navigation.