I.A. Tsikin - Dr. Sc. (Eng.), Professor, St. Petersburg State Polytechnical University. E-mail: tsikin@mail.spbstu.ru
E.A. Shcherbinina - Assistant, St. Petersburg State Polytechnical University. E-mail: lizspbstyle@gmail.com

Interferometric attitude systems are very precise. Triple antenna configuration to obtain aircraft attitude by processing the signals of global navigation satellite systems is used. Two baselines composed of three antennas completely define the Euler angles associated with aircraft attitude and used to compute pitch, roll and yaw angles. The maximum likelihood estimate of angles has been investigated by many researchers. However, direct obtaining these estimates is connected with implementation difficulties on the programmable hardware components: DSP and FPGA. Maximum likelihood attitude estimation by using reference phase differences, which calculated the time before or in a real time for all possible relative spatial positions between satellite and aircraft, is suggested. Special features of reference phase differences, calculated for one and more satellites, are shown in the research. The degree in which angles accuracy depends on phase measurements variance for a various number of satellites in view is analyzed. It has been demonstrated that obtained for pitch, roll and yaw accuracies are not less than accuracies guaranteed by direct maximization of likelihood function joined with some difficulties based on solving equations set. Increase angles accuracy is not significant by processing the signals of more than nine satellites. Factor involved in using carrier phase measurements to determine attitude is the resolution of the integer ambiguity inherent in the carrier phase measurements. In any configuration where antenna separation exceeds , there are potentially multiple solutions for the attitude problem, and therefore abnormal errors can take place. Relationship between abnormal error probability and number of satellites is made and recommendation for number of using satellites, given in terms of accuracy angles, is saved for abnormal errors.