Frequency syntonization using GPS carrier phase measurements

A new methodology of frequency syntonization using a global positioning system (GPS) carrier phase double differences is presented. The proposed scheme can achieve the traceability of frequency dissemination and obtain the very high frequency stability in the short term, as well as in the long term. The GPS receivers used in our system were elaborately modified in order to estimate the frequency offset of the remote low-cost oven-controlled crystal oscillator (OCXO) clock with respect to the primary cesium atomic clock in real time by performing the double differences on the GPS carrier phase observables. The fuzzy controller and the proportional-derivative (PD) controller were employed to implement the controllers of our system, respectively. Through the D/A converter, the remote clock was then steered to synchronize with the primary clock. For averaging times of one day under the configuration of about a 30-m baseline, our experimental results show that the accuracy of the remote clock can be improved from about 3 X 10(-9) to about 3 x 10(-14), and the stability of the remote clock can be improved from about 3 x 10(-10) to about 2 x 10(-14). Moreover, the 30-m baseline tests with the common high-performance cesium clock revealed that our system has a frequency stability of about 2 X 10(-16) for averaging times of one day.