This paper aims to develop a more precise vehicular positioning system during GPS outages by integrating GPS, a tactical grade HG1700 IMU, as well as Wheel Speed Sensor and a Yaw Rate Sensor. Using a tight coupling strategy, three types of sensor integration schemes are proposed, namely GPS/INS/Wheel Speed Sensor, GPS/INS/Yaw Rate Sensor and GPS/INS/Yaw Rate Sensor/Wheel Speed Sensor. The models for each of the schemes are discussed in detail including the sensor error models. The benefits after integrating the Wheel Speed Sensor and the Yaw Rate Sensor are investigated in terms of positioning accuracy during GPS data outages. Furthermore, the reduction in the time to fix the carrier phase ambiguities after various GPS outage durations is analyzed. INTRODUCTION To meet the requirements for vehicle safety and stability control such as forward-collision avoidance, significant attention has been paid to new sensor systems in recent years. Among them are anti-lock brake systems (ABS), traction control (TC), and vehicle stability control systems (VSC) which have already found their way into production passenger vehicles (Tseng et al., 1999). In most autonomous vehicle control and vehicle stability control systems, GPS and other dead-reckoning sensors are being employed to provide navigation and positioning information (Bevly, 1999). With respect to GPS, centimeter-level accuracies can be achieved by using carrier phase measurements in a double difference approach whereby the integer ambiguities are resolved correctly. However, difficulties arise during significant shading from obstacles such as buildings, overpasses and trees. This has led to the development of integrated systems whereby GPS is complemented by an inertial navigation system (INS). In such a system, GPS provides long-term, accurate and absolute positioning information which is subject to the blockage of line-ofsight signals as well as signal interference or jamming. Additionally, its measurement update rate is relatively low (typically less than 20 Hz). By contrast, an INS is autonomous and non-jammable, and most IMU data rates exceed 50 Hz with some reaching into several hundreds of Hertz. However, the weak points of INS are that its
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