A Kalman filter clock algorithm for use in the presence of flicker frequency modulation noise

Abstract

The National Physical Laboratory (NPL) has developed a Kalman filter based algorithm for combining measurements from its three active hydrogen masers. The algorithm is designed to produce a near optimal composite clock when the dominant noise process of at least one of the masers is flicker frequency modulation (FFM), and significant linear frequency drift is exhibited. The FFM is modelled approximately by a linear combination of Markov noise processes. Each Markov process is included in the Kalman filter and contributes an additional component to the state vector. Both the validity of the model and the effectiveness of adding these additional components are examined. The performance of the new algorithm is investigated when applied to simulated measurements and also to measurements obtained from NPL's hydrogen masers.