Frequency transfer using GPS: a comparative study of code and carrier phase analysis results

摘要

This paper investigates the use of GPS codes and carrier phases for frequency transfer applications. Three types of baselines have been studied. First, the noise of the code and phase methods has been evaluated using a zero-baseline with two geodetic GPS receivers driven by the same H-Maser clock, or by a cesium and an H-Maser clock respectively. From the common frequency reference we were able to derive a frequency stability of 6.10~(-16) for averaging times of one day. The different response of the hardware of the two receivers to small identical temperature variations is emplasized; the differential effect is about 30 ps/deg C. The difference between the L1 and L2 carrier phase delays is shown too. Secondly, on-site tests over a 95-m baseline allowed checking the influence of combining two antennae/receivers in different environments. In this case, the effect of the varying temperature on the hardware delays of the receivers and cables is shown; this effect limits the frequency stability to 6.10~(-15) for an averaging time of one day. The possibility to obtain frequency stabilities of a few parts in 10~(16) is shown; this can be reached if all the instruments are located in temperature-stabilized rooms. Finally, the frequency stability obtained with different code methods is compared on a longer baseline (640 km) between Brussels and Wettzell. In particular, the influence of using IGS satellite ephemerides instead of broadcast ephemerides is shown to be very small. The "all-in-view" methods based on the code, as well as on the carrier phases, are compared to the classic frequency transfer by common view. Preliminary results, using carrier phases, lead to a frequency stability of a few parts in 10~(15) for averaging times of one day. Again, the main limitations are the hardware delay variations due to the changes in ambient conditions.