Performance Enhancement of Attitude Determination System by Combining Single and Multiple Antennas

J. Jang, S. Lee and C. Kee

Abstract:	As a cheap and precise attitude sensor we can use multiple GPS antennas on a flight vehicle, which start to be widely used for various applications like space or air vehicles. And ambiguity resolution of attitude is relatively easy compared with precise positioning because it has two advantages of a very short base line and a known base length. If there are three or four GPS antennas, it is possible to determine attitude immediately. Steep turn of flight vehicle may cause instance signal blockages and it will force receiver to determine new cycle ambiguity. Though recent researches show cycle ambiguities estimated by multiple antennas are almost true, we can say that it is still not free from correctness of stochastic verification result. Integration with other sensor is good way to increase the performance, but it will increase overall costs and complexity of system. So it is needed to use additional information from GPS itself. In this paper we developed new algorithm to improve performance of conventional attitude determination system based on multiple antennas, which uses combination between multiple GPS antenna and single GPS antenna. For a vehicle on the flying, ambiguity resolution using multiple antennas are not the only way to estimate attitude. It is possible to estimate attitude using just single GPS antenna also. Accuracy of the system is over some degrees and strongly depends on dynamic of vehicles. But recent researches show it is possible to use the single antenna attitude for non-precise control of UAV (Unmanned Aerial Vehicle). We used pseudo attitude estimated by single GPS antenna to know whether multiple antenna attitude or cycle ambiguity estimated is reasonable. It will increase the success rate and efficiency effectively. The single GPS antenna attitude could be derived from velocity and acceleration based on GPS PVT (Position, Velocity and Time) output, which has a slowly varying bias from multiple antennas attitude. We have composed Kalman filter to update pseudo-attitude of single antenna using angular rate estimate by multiple antennas. And we have estimated the bias (Angle of attack and sideslip angle) to give the controller them. We will show flight simulation results using UAV (Unmanned Aerial Vehicle) model to verify our algorithm. The results include how efficiently it can resolve correct cycle ambiguities after instance signal blockages and whether attitude boundary estimated works well to verify multiple GPS antenna attitude.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2066 - 2073
Cite this article:	Jang, J., Lee, S., Kee, C., "Performance Enhancement of Attitude Determination System by Combining Single and Multiple Antennas," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2066-2073.
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