Design and performance of a robust GPS/INS attitude system for automobile applications

The increasing demand for navigation aids and sophisticated control systems in modern cars has led to a growing number of GPS applications in the automobile industry. In addition to position and velocity, precise attitude measurements are needed for many emerging control applications in cars, such as lane-keeping and collision avoidance systems. GPS can also be used to measure the attitude of a vehicle, and this approach offers a significant advantage over other methods in the tradeoff of accuracy vs. cost. However, few commercial GPS products exist with the capability of measuring attitude, and those that are available perform poorly in most urban environments and are prohibitively expensive for use in consumer vehicles.; This thesis presents the system design and performance analysis of an inexpensive and robust attitude system based on GPS and inertial sensors, suitable for use in automobiles. This system utilizes a variety of techniques and unique algorithms to improve GPS attitude robustness and availability under the high phase-noise and limited visibility conditions encountered during normal urban driving. Such methods include tight coupling with the inertial subsystem, and the ability to measure attitude with as few as one satellite. A prototype of the system was realized with inexpensive GPS and automotive grade inertial components, and demonstrated comparable accuracy and superior robustness to commercial systems that depend on multiple-satellite attitude solutions in urban driving environments.; A section of this thesis is also dedicated to GPS carrier-tracking loop design with Doppler aiding, in which the phase-lock loops for each channel are aided with information from an inertial navigation system. The resulting system benefits from higher bandwidth dynamic tracking of GPS signals, improved resistance to phase-noise, and enhanced robustness against cycle slips. These features vastly improve the quality and reliability of GPS carrier-phase measurements for attitude determination and other applications. Detailed analysis and simulation results are presented to illustrate the benefits of Doppler aiding at the signal tracking level and in the higher-level application of attitude determination. An experiment was also performed to collect real inertial navigation data from a moving car, and synchronized GPS signal samples from a commercial software receiver. Doppler aiding was implemented with this data, and the results from this experiment validate those from simulation. This experiment also demonstrated the viability of implementing Doppler aiding with automotive-grade inertial components.