A New Instantaneous Method for Attitude Determination Using GPS Phase Measurement

This article proposes a new algorithm for attitude determinations using GPS phase signals. The proposed method is an instantaneous method along with the small-angle assumption. Different from the existing methods, this method uses a newly defined performance index 'BDOP' to determine search sequences for different satellite signals, phase measurement noise, and baseline geometry to define the search space and ambiguity candidates' properties determined in previous search steps to reduce the search space for the subsequent searches. Consequently, the proposed method reduces the computation time and improves the attitude determination accuracy. The proposed method is verified both by numerical simulations and experiments. Simulation results indicate that the computation time of the proposed method is 0.01 s, the success rate 85%, and the angle estimation accuracy less than 1° when three antennas are installed 1 m apart, receiving GPS signals from five satellites, and the standard deviation of the phase measurement noise of 0.5 cm. In experiments, we verify the algorithms using a homemade three-antenna GPSR and a three-axis gimbal platform. The three antennas are installed 0.5 m apart and receive GPS signals from six satellites. The angle estimation error is less than 2° when the platform rotates in three axes simultaneously. In that experimental setup, the angle estimation degenerates at the large platform angles due to the signal interference from the ground effect and gimbal platform geometry.