Development of Carrier-Phase-Based Two-Way Satellite Time and Frequency Transfer (TWSTFT)

Abstract : For the dissemination of precise time and frequency, the use of the Two-Way Satellite Time and Frequency Transfer (TWSTFT) method has, in recent years, become increasingly valuable. By the application of spread-spectrum technology, a client station, located anywhere within a common satellite s footprint, can link to a reference station and compare or synchronize its clock to the reference clock within nanoseconds or better with high levels of confidence. But as the frequency stabilities of today's sophisticated atomic-level clocks improve, so must the stability of a Two-Way system s method of time and frequency transfer. Carrier-phase information holds the promise of improving the stabilities of TWSTFT measurements, because of the great precision at which frequency transfers can be achieved. The technique requires that each site observe both its own satellite-translated signal and that of the cooperating site. As was reported in earlier papers, the translation frequency of the satellite itself is an additional unknown factor in the measurement, and it must be taken into consideration. However, it can be shown that simple estimates of the satellite s local oscillator (LO) frequency will suffice. Recent work has been conducted with implementation of the signal carrier-phase in operational TWSTFT links. The purpose of this paper is to discuss this recent work, with emphasis on the system's development.