Engineering and Technology Journal

Abstract

In this paper, the use of multi-GPS receiver to estimate the parameters of
attitude (orientation) of a platform is developed. The GPS receiver has two
measurements; pseudorange and carrier phase. The latter is highly accurate (sub
centimeter-level).Therefore, it is used to give precise attitude parameters. But the
carrier phase has one problem; an initial integer ambiguity must be resolved first.
Without resolution of this integer, the carrier phase is meaningless. Therefore, the
attitude determination technique based on the carrier phase observable of the GPS
involves two steps; integer ambiguity resolution and attitude estimation. Here, two
methods are used for attitude estimation; first, Single-point method that is based on
the least square approach is developed using the quaternion representation. Second,
Eigenproblem algorithm that is used to minimize a quartic quaternion-based cost
function. In order to resolve the integer ambiguity, an attitude-independent
algorithm is developed. This algorithm first incorporates an instantaneous integer
search 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 to
determine the optimal integer. The results show that the Single-point method is
more accurate (with RMS 0.137, 0.079 and 0.197 degree in yaw, pitch and roll
respectively), and it convergences exponentially to the correct solution. The
Eigenproblem may diverge when the initial quaternion is far.