Frequency syntonization using GPS carrier phase measurements

A new methodology of frequency syntonization using a global positioning sys tem (GPS) carrier phase double differences is presented. The proposed schem e can achieve the traceability of frequency dissemination and obtain the ve ry 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 cryst al 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) cont roller were employed to implement the controllers of our system, respective ly. Through the D/A converter, the remote clock was then steered to synchro nize with the primary clock. For averaging times of one day under the confi guration of about a 30-m baseline, our experimental results show that the a ccuracy 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 abo ut 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 fr equency stability of about 2 X 10(-16) for averaging times of one day.