Worst-Case Analysis of a 3-Frequency Receiver to Land a General Aviation Airplane

Shau-Shiun Jan, Demoz Gebre-Egziabher, Todd Walter and Per Enge

Abstract:	This paper investigates the vertical guidance performance of a multiple frequency WAAS receiver (L1, L2, and L5) 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 replace the grid of ionosphere delay corrections used currently by the Wide Area Augmentation System (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 by using 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 multiplefrequency GPS landing system. The architectures evaluated depend on the number of the 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. Our criterion is to compare the coverage of availabilities versus the vertical alert limit (VAL) under these three cases. In addition to the three system architectures, this paper also investigates the effect of using a barometric altimeter. We treat a barometric altimeter as a virtual satellite with a known clock directly above the user’s position. Historical meteorological observation data is used to develop a barometric altimeter simulator in MATLAB“. We then compared the estimated altitude with the true altitude to generate altitude error data. We analyze the altitude error data, and calculate the 68% (1s) and worst-case error bounds in the probability density function (PDF) of the altitude error. We apply a linear least-square estimation technique to the resulting error bounds in different regions, and we build up an altitude error model, which shows that the altitude error is function of the distance between a user and reference location. We evaluated a worst-case model of barometric altimeter based on the historical meteorological observation data.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	235 - 245
Cite this article:	Jan, Shau-Shiun, Gebre-Egziabher, Demoz, Walter, Todd, Enge, Per, "Worst-Case Analysis of a 3-Frequency Receiver to Land a General Aviation Airplane," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 235-245.
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