Real-time formation of a time scale using GPS carrier-phase time transfer network

This paper presents a prototype real-time clock ensemble system that utilizes a Kalman filter-based ensemble algorithm to combine remote clocks linked via a real-time GPS carrier-phase time transfer network. The calculated ensemble clock is realized by the use of an optimal control technique, where emphasis is placed on seeking a balance between the short-term stability of a hydrogen maser clock and the long-term stability of the ensemble clock. The performance of the system is investigated by conducting a five-month long ensemble experiment based on local realizations of UTC from four timing laboratories, and the frequency stability of the real-time ensemble time scale as well as its realizations are assessed with reference to UTC.