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Operational Use of the Hadamard Variance in GPS
NAVAL OBSERVATORY ALTERNATE MASTER CLOCK SCHRIEVER AFB CO
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With upcoming GPS Block IIR hunches scheduled, rubidium clock estimation will require more attention than ever before during the next decade of GPS operations GPS Master Control Station MCS estimation architecture relies on a three-state polynomial clock model, which does not include a time-variant decay parameter for frequency drift. Since current GPS rubidium frequency standard exhibit signifiant time-dependent frequency drift changes, the MCS is compelled to make precise utilization of the random run process noise parameter, known as q sub 3. The work of various scientists over the past three decades has shown the Hadamard variance to converge for random run FM. At PTTI 95, the 2d Space Operations Squadron 2 SOPS introduced an algorithm that presented a simple, convergent polynomial relationship between the Hadamard variance and the MCSs Kalman filter process noise parameters. Until recently, however, neither the Hadamard variance nor the Hadamard-Q equation had actually been put to use in GPS. The Naval Research Laboratory NRL has now created analysis software designed to employ the Hadamard variance in their GPS clock analyses, to supplement their already existing software, which makes use of the Allan variance. This paper presents results of the NRL analysis using both the Allan and Hadamard variances for several operational GPS rubidium frequency standard, as well as results from the recent operational use of the Hadamard-Q equation, by 2 SOPS personnel, based on the NRL analysis data.
APPROVED FOR PUBLIC RELEASE