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The Use of GPS and INS for Centimeter Positioning Accuracy During Long GPS Outages | 269.51 KB |
The problem with IMUs is that the error from the sensors results in a drift of the position solution over time. To overcome this, other sensors (such as odometer, speedometer, compass or GPS) can be integrated with the INS to provide additional position information. For instance, GPS can be used for real-time calibration of the INS using global latitude and longitudinal coordinates. In addition, GPS and INS are ideal for integration, as their error dynamics are totally different and uncorrelated (Kaplan E. and Hegarty C., 2006). This integration between GPS and INS significantly improves the overall accuracy and reliability compared with the stand alone units (Cramer 1997).
Research into GPS and INS integration is well established. There are two primary integration schemes performed through the process of Kalman filtering: loosely and tightly coupled. In the loosely coupled mode, the GPS receiver and the INS are treated as separate navigation systems. The GPS provides with a position, velocity, and time solution. The INS implements its navigation/attitude algorithms to give a position, velocity, and attitude. An integrated Kalman filter is then applied to combine the GPS and INS solutions. However, in the tightly coupled mode, only a single Kalman filter is applied to process both sets of GPS observables (code and/or phase) and INS measurements (Hide 2003).