SET estimation algorithm for precise navigation and surveying applications

Abstract

Global Positioning System (GPS) positional accuracy depends on time measurements. This calls for extremely precise satellite clock synchronization as the GPS Radio Frequency (RF) signal travels at speed of light. Time parameter determines the pseudorange between known position (satellites orbiting in the space) and unknown position (receiver located on or above the earth). Positional accuracy also depends on the propagation path delays, pseudorange correction, instrument bias errors and integer ambiguity resolution, and sufficient research and analysis is done with respect to these error sources. But enough analysis and impact of clock error or impairment in time measurement was given. In this paper a novel algorithm is presented to estimate the time instant at which the signal emitted from the satellite antenna phase center considering onboard clock correction and the impact of relativistic error (due to eccentricity). This precise estimation of Signal Emission Time (SET) will improve the accuracy of the satellite position, which minimise the error in pseudorange and inturn receiver position accuracy is enhanced. In this paper the Signal Emission Time (SET) from satellite antenna phase center is modelled by considering the clock correction parameters, signal reception time at the receiver and eccentric correction. The impact of SET error on orbital and navigation solution are estimated and analysed. In critical navigation applications like CAT I/II aircrafts landing and missile navigation the proposed SET algorithm can be implemented to achieve the higher accuracy.