| Traditionally, navigation systems have been very large, expensive and used only in aviation or military applications. However, recent advances in satellite-based positioning and the proliferation of small, low-cost motion sensors have made possible navigation systems that are small and inexpensive enough to be used in consumer products. Commercial consumer-grade navigation systems are, in fact, readily found today in Japan, Europe, and the United States, with one of the largest potential markets being in automobile navigation. Although the concept of in-vehicle navigation systems is not new, implementations of such systems are relatively recent. The research in this thesis advances the understanding of these systems through a quantitative examination of the impact that various navigation sensors have on the performance of a land-vehicle navigation system. A range of navigation sensor performance levels and their influence on vehicle positioning accuracy are examined. In addition, the impact of incorporating information from a digital map database in the navigation solution is also examined. The information produced by this research can help today's navigation system designers understand cost/performance tradeoffs in various candidate system designs. In addition, it can also help navigation system designers in the future, as the quality of navigation sensors improves through technological advancements. The work in this thesis can also be used to guide sensor designers--to reveal to them those sensor error parameters which contribute most to positioning error and to guide them into a design with appropriate performance tradeoffs. Results show that, for a typical navigation system, positioning error is dominated by the accuracy of the position fixes provided by the Global Positioning System (GPS) receiver when GPS position fixes are available and by the rate gyro's bias drift when GPS position fixes are not available. Furthermore, results show that the accuracy of the GPS position fixes that are used has a significant impact on the relative contributions that various navigation sensor errors make. The implications of these results for navigation system design and sensor design are discussed. Finally, results show that using input from a digital map database to aid in navigation can degrade heading sensor calibration. |
