2005, “Comparative Analysis of GPS Clock Performance Using Both Code-Phase and Carrier-Derived Pseudorange Observations

The Naval Research Laboratory (NRL) has, for many years, determined the GPS space ve-hicle clock offsets by differencing the pseudorange observations and the post-fit orbit provided by the National Geospatial-Intelligence Agency (NGA). On 14 March 2004, NGA put into pro-duction a new class of pseudorange observations called carrier-derived pseudorange observa-tions (CDP). Because the measurement noise of the new CDP observations is much lower than that of the code-phase pseudorange observations, NRL has begun to use the newer CDP obser-vations in its analysis of GPS clock performance. A number of differences between the two types of data are pointed out, and a comparative analysis of clock performance with respect to frequency stability is reviewed. This work was performed under the sponsorship of the GP