An Attitude Navigation System Based on the GPS


In this paper, the use of multi-GPS receiver to estimate the parameters ofattitude (orientation) of a platform is developed. The GPS receiver has twomeasurements; pseudorange and carrier phase. The latter is highly accurate (subcentimeter-level).Therefore, it is used to give precise attitude parameters. But thecarrier phase has one problem; an initial integer ambiguity must be resolved first.Without resolution of this integer, the carrier phase is meaningless. Therefore, theattitude determination technique based on the carrier phase observable of the GPSinvolves two steps; integer ambiguity resolution and attitude estimation. Here, twomethods are used for attitude estimation; first, Single-point method that is based onthe least square approach is developed using the quaternion representation. Second,Eigenproblem algorithm that is used to minimize a quartic quaternion-based costfunction. In order to resolve the integer ambiguity, an attitude-independentalgorithm is developed. This algorithm first incorporates an instantaneous integersearch to significantly reduce the search space using a geometric inequality. Then,a batch-type loss function is used to check the remaining integers in order todetermine the optimal integer. The results show that the Single-point method ismore accurate (with RMS 0.137, 0.079 and 0.197 degree in yaw, pitch and rollrespectively), and it convergences exponentially to the correct solution. TheEigenproblem may diverge when the initial quaternion is far.