Use of Residual DOP and Genetic Algorithm in Weighted-Least-Square GPS Positioning

C-C. Lin, L-S. Wang, F-R. Chang, and C-C. Chen

Abstract:	The accuracy of GPS positioning basically depends on two major factors. The first one comes from the sensing errors due to satellite clock bias, ionospheric and tropospheric delays, ephemeris error and multipath effect, etc. for a particular satellite. While these errors may be compensated by using suitable models, the un-modeled errors may still exist which depends on the elevation angle and signal-to-noise (S/N) ratio, among others. On the other hand, the second factor is from the geometry of the satellite configuration, which magnifies the positioning errors through the geometric dilution of precision (GDOP) parameter. The elevation angle and the S/N ratio have been used before to determine the weightings with respect to the pseudoranges in the Weighted-Least-Square (WLS) GPS positioning algorithm. However, it is not clear how to assess the influence of a particular satellite on the dilution of precision, which may be essential in giving the weightings. To appropriately accommodate the aforementioned effect, the concept of residual DOP (RDOP) is introduced in the paper. A fuzzy controller is then used to determine the weighting for the signal from each satellite based on three factors: the elevation angle, the S/N ratio, and the corresponding RDOP. Moreover, instead of by trials and errors, Genetic Algorithms (GAs) are applied to train the fuzzy controller to have suitable number and appropriate shapes of membership functions, and proper rule-based inference engine. Applications of the trained fuzzy controller to either simulated environments or experimental data show that the designed WLS GPS positioning scheme can effectively enhance the accuracy of the positioning results.
Published in:	Proceedings of the 2006 National Technical Meeting of The Institute of Navigation January 18 - 20, 2006 Hyatt Regency Hotel Monterey, CA
Pages:	508 - 514
Cite this article:	Lin, C-C., Wang, L-S., Chang, F-R., Chen, C-C., "Use of Residual DOP and Genetic Algorithm in Weighted-Least-Square GPS Positioning," Proceedings of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, January 2006, pp. 508-514.
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