Time differenced carrier phase RAIM for urban air mobility

Urban areas are challenging environments for satellite navigation because of large multipath errors and frequent satellite signal loss. Urban air mobility (UAM) has a concept for operating aircraft in urban environments, where it is important to have accurate and integrity-assured positions. In response, this paper proposes a receiver autonomous integrity monitoring (RAIM) method using the time-differenced carrier phase (TDCP). TDCP measurements are robust to multipath and do not require the resolution of integer ambiguity because time differences eliminate any integer ambiguity. TDCP RAIM differentiates measurements at fixed time intervals and accumulates the estimated displacement vector. In this study, a general formulation for positioning and protection level of TDCP RAIM is introduced. The performance of TDCP RAIM was evaluated through simulation and validated using real urban measurement data, and was compared with that of Relative RAIM. The results indicate that TDCP RAIM is robust to changes in visible satellites and provides continuous positioning and protection level.