Matt Harris, Paul Schlais, Tim Murphy, Boeing Commercial Airplanes; Angelo Joseph, Jeremy Kazmierczak, Collins Aerospace

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This paper presents GPS and Galileo airframe multipath statistics derived from more than 50 flight hours on an experimental Boeing 777 airplane using prototype Collins Aerospace Dual-Frequency, Multi-Constellation (DFMC) receivers. These results are an important step toward validation of the integrity and accuracy algorithms that will be used in the first aviation industry standards for use of combined GPS and Galileo for safety of life services such as navigation, landing, and surveillance for aircraft separation. This paper presents the experimental flight test program and equipment setup. Prior work to derive airframe multipath is referenced, then the algorithms and methods used to estimate multipath on GPS L1 and L5, Galileo E1 and E5a, and the ionosphere free combinations of those signals are described in detail. Multiple potential techniques for estimating airframe multipath and deriving integrity bounds appropriate for precision approach and landing are described. Handling of antenna group delay variation with angle of arrival, ionosphere delay, and receiver noise are discussed, and multiple ways to visualize the results are presented to address various trades for consideration in standards bodies. Multipath error statistics are shown to be minimally dependent on the signal direction of arrival for this particular test setup. By aggregating data from all satellite elevation angles, enough samples were available to evaluate the impact of carrier smoothing time with statistical significance. The effect of carrier smoothing on multipath error bounds is explored using 100, 300, and 600 seconds smoothing time constants, showing larger smoothing times as a viable means to reduce multipath errors and increase availability of DFMC position accuracy and integrity bounds.