Modified Algorithm for Eliminating User Position Biases Caused by Satellite Constellation Changes

H-W. Chen, H.S. Wang, Y.T. Chiang, F.R. Chang, C.H. Li

Abstract:	When the user-satellite constellation is changed (gaining and/or losing satellites), it may result in the user position biases. The biases are undesirable in some applications. In [1], an algorithm called Position Bias Filter (PBF) was designed to solve the problem. The concept of the filter is to calculate the difference before and after the satellite constellation changed which can be used for correcting the position vector. However, their method is not very efficient for they need to re-calculate the position fix before and after the constellation change. From the algebraic operations' point of view, the difference can be derived by a recursive way. Therefore, in this paper, we proposed a modified algorithm named modified position bias filter (MPBF) to enhance the efficiency and performance of the previous one. In the proposed algorithm, we derive a recursive update process so that the time consumption can be greatly reduced. On the other hand, we notice that there may be another bias introduced by the usual PBF algorithm for the method just keeps subtracting a constant positioning bias. In our experiment, the result shows that the positioning bias (caused by satellite constellation change) tends to decrease with time. Therefore, in this paper a forgetting factor (means that the influence of the positioning bias is forgot as time goes by) is also introduced for reducing the biases and the result of the experiment shows that the performance of PBF may be significantly improved.
Published in:	Proceedings of the 2011 International Technical Meeting of The Institute of Navigation January 24 - 26, 2011 Catamaran Resort Hotel San Diego, CA
Pages:	577 - 582
Cite this article:	Chen, H-W., Wang, H.S., Chiang, Y.T., Chang, F.R., Li, C.H., "Modified Algorithm for Eliminating User Position Biases Caused by Satellite Constellation Changes," Proceedings of the 2011 International Technical Meeting of The Institute of Navigation, San Diego, CA, January 2011, pp. 577-582.
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