Inside GNSS Media & Research

JUL-AUG 2019

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22 Inside GNSS J U L Y / A U G U S T 2 0 1 9 www.insidegnss.com A n increasing number of applica- tions require accurate, reliable, and traceable signals for time and synchronization. Key fields of appli- cation include banking and finance, telecom networks and electricity grids. GMV's WANTime is a new time service for the city of Madrid, Spain, distributed using the White-Rabbit network proto- col over optical fiber. A pilot customer of the service is currently the Madrid Stock Exchange (Bolsa de Madrid), connected to GMV's datacenter by a network link of around 50 kilometers. For redundancy, the service is based on two parallel and independent time generation chains (A and B), each of them driven by a highly stable atomic clock, namely a Passive Hydrogen Maser (PHM). e clocks can be synchronized to UTC by means of GNSS time-trans- fer to any national timing laboratory. This well-known technique is known Today, more and more integral fields of application including banking and finance, telecom networks and electricity grids, rely heavily on accurate, reliable, and traceable signals for time and synchronization. Here, the authors address a new time service for the city of Madrid, Spain, distributed using the White-Rabbit network protocol over optical fiber, with the Madrid Stock Exchange serving as a pilot customer of the service. as Common-View (CV) and is based on differencing pseudoranges from the same GNSS satellites recorded at the two sites (GMV and the UTC lab). Dual- frequency (DF) pseudorange combina- tions are normally used in CV to remove ionospheric errors, but single-frequency (SF) CV is also possible. Clock Synchronization CV provides the difference between the loca l clock and the remote UTC time sc a le. Cu r rent ly t he aut hors of t h is article are collaborating with PTB, the Physikalisch-Technische Bundesanstalt i n Brau nschweig, Germa ny, to a l ig n their clocks to PTB's realization of UTC, called UTC(PTB). By calculating clock differences over several days it is pos- sible to model and predict the behavior of the clock, and thus to adjust the clock frequency periodically to minimize its dev iat ion f rom U TC. In our case we adjust our PHMs to UTC using a qua- dratic model that accounts for the clock phase of fset (A0 term, ns), t he mea n clock frequency offset (A1 term, ns/day), and the frequency drif t (A2 term, ns/ day 2 ). Every day, we fit the PHM model to the CV results from the 15 previous days, we extrapolate the model to the current day at noon, and we calculate a corresponding frequency correction, that is applied to the PHM by means of a frequency stepper connected at its out- put. Each PHM is steered independently of the other one. Rooftop GNSS antennas used to help deliver robust timing for the financial sector. RICARDO PÍRIZ PEDRO ROLDÁN ESTEBAN GARBIN GMV GPS Combined With Galileo to Provide Robust Timing for the Financial Sector

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