Analysis of a Three-Frequency GPS/WAAS Receiver to Land an Airplane

Shau-Shiun Jan

Abstract:	This paper investigates the vertical guidance performance of a multiple frequency Global Positioning System (GPS) (L1, L2, and L5)/Wide Area Augmentation System (WAAS) receiver in the presence of inclement weather and radio frequency interference (RFI). There are several ways to take advantage of the multiple frequencies. For example, one can calculate ionosphere delay in the airplane. This would be used in place of the grid of ionosphere delay corrections broadcast by WAAS. This direct use of multiple frequencies would be more accurate and offer higher availability. Another way to take advantage of the multiple frequencies is to use the additional GPS frequencies as a backup navigation method when RFI is present. This would require the user to continue using the grid. This paper presents the results of a trade-off study evaluating the performance of various architectures for a multiple-frequency GPS landing system. The architectures evaluated depend on the number of available GPS frequencies and include the following: • Case 1: All three GPS frequencies are available, • Case 2: Two of three GPS Frequencies are available, • Case 3: One of three GPS frequencies is available. The design evaluation criterion compares the coverage of availabilities versus the vertical alert limit (VAL) under these three cases. This paper also investigates the effects on the WAAS master station (WMS) using coded L1 and coded L5 signals instead of using coded L1 and codeless L2 signals. This paper discusses the parameter changes in the protection level calculation of the WAAS MOPS (RTCA DO-229C) for the above three cases. These changes affect the fast and long term correction degradation confidence ( flt ó ), user ionosphere range error confidence ( ó , i UIRE ), airborne receiver confidence ( ó , i air ), and troposphere delay confidence ( ó , i tropo ). The MATLAB Algorithm Availability Simulation Tool (MAAST) [5] was used to simulate these parameter changes in the WAAS confidence estimation algorithm and evaluate the effect of service availability with these parameter changes.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2576 - 2586
Cite this article:	Jan, Shau-Shiun, "Analysis of a Three-Frequency GPS/WAAS Receiver to Land an Airplane," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2576-2586.
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