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Synchronization of time scales of ground-based measuring complex of radio navigation systems and time scales of remote standards via fiber-optic communication line

DOI 10.18127/j20700784-201812-26

Keywords:

O.V. Kolmogorov – Ph.D. (Eng.), Head of Laboratory, FSUE «VNIIFTRI»
E-mail: kolmogorov@vniiftri.ru
S.S. Donchenko – Ph.D. (Eng.), Research Scientist, FSUE «VNIIFTRI»
D.V. Prokhorov – Leading Engineer, FSUE «VNIIFTRI»


Ground-based measuring complex of global navigation satellite systems (GNSS) require reference frequency and time signals [1,2]. Such signals can be transmitted from remote standards or produced by generators of ground measuring complexes, which are synchronized to standard via special comparison channel.
Modern requirements to the accuracy of the time scales synchronization are less than 100…200 ps. The distances between the mea-suring complexes and the standards can range from tens of meters to tens of kilometers. Time scales comparison with such accuracy can be realized using fiber-optic communication lines (FOCL) [3,4]. Advantages of FOCL are low signal attenuation and high noise immunity.
The operation principle of the reference signals transmission system via fiber optical link from time and frequency standard (TFS) placed on object 1 to GNSS measurement complex (object 2) is described below. The system consists of reference frequency signal transmitting system (RFTS), time scales comparison system (TSCS) and a generator of reference frequency and time scale signals (GRFTS). TFS forms the time scale TS1 in the form of pulses – 1 PPS (pulse per second) and a reference frequency signal. The reference frequency signal from the TFS is transmitted by the RFTS from object 1 to object 2 to the input of the generator GRFTS that produces the reference frequency signals (5, 10 or 100 MHz) and the 1 PPS of the TS2, necessary for the operation of the GNSS measurement complex. The TSCS determines the difference between time scales 1 and 2. The correction signal, based on measured time difference between TS1 and TS2 is applied to generator GRFTS to keep time scales synchronized.
Different schemes for TSCS systems are proposed in the articles [6–8], the choice of which depends on the fiber optic link length and the required synchronization accuracy of the time scales. The operation principle of the TSCS is based on the transmission of optical pulses via FOCL, registering of their reception moments at objects 1 and 2, the processing of data and the computer calculation of the time scales difference. The calculated result also takes in consideration the hardware signal delays and chromatic dispersion of the optical fiber.
Based on the results of experimental studies, the possibility of the time scales synchronization of remote objects with an error of less than ±100 ps is confirmed. The ways decreasing the time scale synchronization error to values not more than ±(30 ... 50) ps are proposed.
The results of the research are proposed to be used in the development of time scales synchronization systems, communication systems, and in metrological research.

References:
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  6. Pat. 2547662 RF. MPK G04C 10/02. Sposob slicheniya shkal vremeni i ustrojstvo dlya ego osuschestvleniya. Kolmogorov O.V., Prohorov D.V. Zayavl. 30.12.2013; opubl. 10.04.2015. Byul. № 10.
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