Application of DGPS/INS to automobile navigation with latency compensation

Differential Global Positioning System (DGPS) techniques are frequently used to correct for ranging errors common to two receivers, one of which is at a known position. One such source of error is selective availability (SA). A time delay (latency) is inherent between the generation of pseudo-range corrections and their application by the user, and can result in large residual errors. The data latency of the DGPS correction is a fundamental limitation on DGPS performance accuracies. These corrections can be predicted for relatively short periods of time. In this paper, an innovative methodology is developed which predicts the corrections and compensates the GPS data in real time. It also takes care of any transients in the DGPS data and/or GPS data in real time. This methodology has been applied to automobile navigation and tested in a DGPS/INS system. For these experiments, we used a 12-channel Ashtech XII GPS receiver. The INS system included a 3-axis Hitachi HGA-D fiber-optic gyro, a 3-axis 177 2g accelerometer by NeuwGhent Technology, Inc., and a Vector 2x electronic compass by Precision Navigation.