ICNPAA 2010: Mathematical Problems in
Engineering, Aerospace and Sciences

If three or more GPS antennas are mounted properly on a platform and difference of GPS signals measurements are collected simultaneously, the baselines vectors between antennas can be determined and the platform orientation defined by these vectors can be calculated. Thus, the prerequisite for attitude determination technique based on GPS is to calculate baselines between antennas. For accurate attitude solutions can be obtained, carrier phase double differences are used as main type of measurements, including all independent combinations of antenna positions. Baselines between antennas must be determined in millimeter level of accuracy. The use of carrier phase measurements leads to the problem to determine precisely the ambiguous integer number of cycles in the initial carrier phase (integer ambiguity). To increase confidence and accelerate the process by limiting the search space, three types of restrictions can be established from the knowledge of antenna system fixed geometry. In this work was implemented and tested algorithms for ambiguity resolution allowing accurate real-time attitude determination using measurements given by GPS receivers in the uncoupled form, which is, estimating baselines independently from each other, and in coupled form, which the platform orientation (Euler angles) is obtained through processing all baselines. The results showed that LSAST method performance is similar to LAMBDA as the number of epochs which are necessary to resolve ambiguities, but with processing time significantly higher. The final result accuracy was similar for both methods, better than 0.1° to 0.2°, when considered baselines decoupled form.