Analysis of Positioning Performance of Time-Differenced Carrier Phase RAIM for UAM

Hojoon Jeong, Changdon Kee, and Junsesol Song

Abstract:	Urban areas are challenging environment for satellite navigation due to various factors, such as frequent signal blockage and reflection caused by tall buildings. This makes it impossible for users to achieve stable position through performing satellite navigation in conventional standalone method. Recently, various technologies have been developed to create a novel transportation system called Urban Air Mobility (UAM), which operates aircraft in urban environments. Navigation is crucial for UAM as it directly relates to safety. It requires navigation system to ensure both accuracy and integrity. Traditional pseudorange measurements are vulnerable to multipath errors in urban environments. While carrier phase measurements in GNSS are robust against multipath, they require integer ambiguity resolution. However, the use of using carrier phase time-differencing can eliminate the need for ambiguity resolution. In the past, we proposed a receiver autonomous integrity monitoring (RAIM) technique based on time-differenced carrier phase (TDCP) called TDCP-RAIM. Depending on the method of differencing the carrier phase measurements, it can be divided into conventional Relative RAIM (RRAIM) and TDCP-RAIM. TDCP-RAIM and RRAIM differ in their positioning methods, with TDCP-RAIM’s approach being advantageous in urban environments where visible satellite conditions change rapidly. In this study, we analyzed the performance of position determination when conducting integrity monitoring based on TDCP in situations where the number of visible satellites decreases significantly in urban areas. Through simulations, we confirmed that TDCP-RAIM’s time-differencing method provides continuous positioning results and tight protection levels compared to conventional RRAIM in scenarios with reduced visible satellites.
Published in:	Proceedings of the ION 2024 Pacific PNT Meeting April 15 - 18, 2024 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	491 - 501
Cite this article:	Jeong, Hojoon, Kee, Changdon, Song, Junsesol, "Analysis of Positioning Performance of Time-Differenced Carrier Phase RAIM for UAM," Proceedings of the ION 2024 Pacific PNT Meeting, Honolulu, Hawaii, April 2024, pp. 491-501. https://doi.org/10.33012/2024.19600
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