The Proposed State Vector Representation of Broadcast Navigation Message for User Equipment Implementation of GPS Satellite Ephemeris Propagation

Raymond DiEsposti, James DiLellio, Clifford Kelley, Arthur Dorsey, Henry Fliegel, John Berg, Clyde Edgar, Thomas McKendree, and Pradipta Shome

Abstract:	A new navigation message type is outlined for use with the Global Positioning System (GPS) modernized signals -- an alternative representation of the Space Vehicle (SV) ephemeris and accuracy information, which could be implemented within the new L2C, L5, M-code and/or any future NAV signal flexible message structure. It consists of the precise state vector of satellite position and velocity in Earth-Centered-Inertial (ECI) coordinates, at an epoch time and a covariance matrix representation of the SV state vector and clock uncertainties. Additional broadcast parameters are the solar pressure, yaw bias and earth orientation parameters for the complete description of a detailed perturbation model, enabling propagation with minimal error. User equipment (UE) would read the broadcast information and numerically integrate the SV dynamical equations of motion to determine the position and velocity at required future time. Doing so avoids the curve fit error completely and enables other benefits, such as fast Timeto- Subsequent-Fix (TTSF), enhanced anti jam (AJ), and improved performance in low Signal-to-Noise Ratio (SNR) environments. The covariance matrix can be propagated forward in time through the state transition matrix obtained by successive integrations and projected onto the Line-of-Sight (LOS) to determine Signal-in- Space (SIS) measurement error uncertainties associated with range and range rate measurements. The incorporation of the covariance of state vector and clock uncertainties allows for improved estimation of LOS measurement uncertainty, and thereby yielding improved position, velocity, and time (PVT) solution and tighter error bounds. It also enables weighted measurement processing in UE to improve PVT estimation error performance and Receiver Autonomous Integrity Monitoring (RAIM) performance. This paper describes the proposed SIS interface, proposes an integration algorithm, along with a high fidelity special perturbation model, for use in the UE. A discussion of UE impacts, and an illustration of how this implementation can improve user performance relative to the current ephemeris representation, is provided.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	294 - 312
Cite this article:	DiEsposti, Raymond, DiLellio, James, Kelley, Clifford, Dorsey, Arthur, Fliegel, Henry, Berg, John, Edgar, Clyde, McKendree, Thomas, Shome, Pradipta, "The Proposed State Vector Representation of Broadcast Navigation Message for User Equipment Implementation of GPS Satellite Ephemeris Propagation," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 294-312.
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