Performance Evaluation of the Ambiguity Filter as an Alternative of Using Dual-Frequency Measurements for GPS Heading and Pitch Estimation

The Global Positioning System can be used to determine the attitude of a vehicle by using multiple receivers in fixed positions. The carrier phase measurements, which have millimetric precision, can be used for this purpose. However, these measurements have an unknown number of integer cycles named phase ambiguities, which have to be determined. Of all the methods known, LAMBDA is currently acknowledged as the most efficient method for determining these phase ambiguities. This method has been successfully applied mainly by using dual-frequency measurements (in L1 and L2). Alternatively, the L1 and L2 frequency measurements can be combined to create a new set of observables (wide-lane) with which the LAMBDA can also be applied. Using only the L1 frequency, LAMBDA is not enough to solve the ambiguities. In this situation, the method known as the Ambiguity Filter can be used, in conjunction with LAMBDA, to stabilize the solution obtained. Having the ambiguities solved, it is possible to determine the relative position between the GPS antennas and, thus, determine the attitude of a vehicle. The main motivation for using only L1 measurements is related with the fact that dual-frequency receivers are much more expensive than L1 only receivers. In this paper, the heading and pitch are estimated by using measurements in both L1 and L2, wide-lane and only in L1, in order to compare these three options and verify that the results obtained with L1 frequency, using the Ambiguity Filter, can achieve the same precision as the other two options.