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8/6/2019 Implementazione di una Virtual Time Scale in LabVIEW realizzando un clock di riferimento atomico locale UTC(k)
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All rights reserved 2011, Telespazio
Implementing a Virtual Time scalewith LabVIEW, realization of local
UTC(k) reference clock
Presented by:
Stefano Lagrasta
Cromazio Valerio Innocenzi
Marco Cicchinelli
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*** Why ?
Some introductive information
to understand the reason for work done
Implementing a Virtual Time scalewith LabVIEW, realization of local
UTC(k) reference clock
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Keeping International Time Reference Scales
The Bureau International des Poids et Mesures (BIPM) in France is in
charge to provide standard time scales to be adopted by the entire
World
International reference time scales TAI and UTC have been maintained
and disseminated by the BIPM via monthly Circular T. 56 time
laboratories are contributing their clock and time transfer data to the
BIPM. Participating clocks are about 300
Once a month, these data are used to produce the standard
international references for frequency and time:
International Atomic Time ( TAI ) Universal Coordinated Time ( UTC )
Real time realizations of UTC are produced at most of the BIPM
contributing laboratories and denoted as UTC( k )
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Navigation systems like GPS an Galileo useCDMA for one-way ranging
Satellite Navigation systems implement one-way ranging technology toallow user receiver position computation
User equipment determines first the time shift PRN between received signal
CDMA profile and a self-generated replica of it:
relative time shift, PRN
Receiverown replica
of CDMA
CDMA asreceived from
satellite
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One-way ranging strongly depends on timekeeping (1)
Let t be a reference (absolute) scale, measuring elapsing time at Earthsurface
Let T be the time scale implemented by user receiver clock; T exhibits a
time error dT with respect to the time scale t :
Let TSV be the time scale implemented by on-board Navigation satellite
payload clock; TSV exhibits a time error dTSV and a relativistic offset tREL
with respect to the time scale t :
T = t + dT
TSV = t + dTSV tREL
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One-way ranging strongly depends on timekeeping (2)
One-way ranging distance, which is the primary measurement needed byreceiver for calculating its own coordinates, is proportional to the RF signal
propagation time,
One has:
In order to obtain the desired interval from correlation measurement PRN ,
the receiver needs to implement precise estimates for the time offsets dT,
tREL and dTSV
Now, dT will be determined as unknown of positioning equations, along with
{ x, y, z } coordinates
= PRN dT + ( dTSV tREL )
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One-way ranging strongly depends on timekeeping (3)
No problem with
tREL , that comes from reconstruction of satellite orbitprofile and Einsteins Relativity modelling equations
But estimating and predicting the evolution of dTSV depends on:
good quality of the on-board clock. Must be regular and with predictable
(future) time error: atomic is a good choice;
the existence of a real, ground (atomic) reference, able to implement the
best possible realization of the absolute time scale t
t
In other words: the Ground Mission
Control segment needs to implement a
physical time scale, best model for t :
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*** What ?
And now,
lets go right to the point .!
Implementing a Virtual Time scalewith LabVIEW, realization of local
UTC(k) reference clock
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Definition of the activity
The objective of the activity is the design, development andimplementation of a timing laboratory capable to generate and
maintain a local atomic time scale UTC(K) continuous, stable,
accurate and recognized by the international scientific community
This work arises from the collaboration between National
Instruments and Telespazio S.p.A., under the plan of industrial
training for students participating the Master in Space and
Communication Systems
ESA (European Space Agency) also took part in this initiative, by
making available its timing laboratory infrastructure located at
ESTEC(NoordWijk, NL).
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ESTEC UTC Lab Overview (1)
The objectives that the time laboratory pursues are: ensure the quality of generated time, through certification by the
International Community of Time
ensure continuity and reliability of service, through guaranteed
performances of stability and accuracy, by removing possible
interruptions due to maintenance operations
develop and enhance the expertise acquired in the realization of
a time scale
support test activities of space missions (especially those
concerned with satellite radio-assisted Navigation) exploit research, in order to guarantee a continuous optimization
of timing generation and monitoring algorithms
define new applications
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ESTEC UTC Lab Overview (2)
The ESTEC UTC Laboratory includes the following equipment,relevant for this project:
an Active Hydrogen Maser (AHM) atomic clock;
four (4) Cesium clocks;
a Multi-Channel Phase Comparator (MCPC);
a FemtoStepper;
a GNSS (Global Navigation Satellite System) Common View
receiver.
In addition, it is worth to mention the object of work done:
a set of algorithms for the realization and monitoring of the UTC(k)
time
the MCPC driver;
the FemtoStepper driver
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Processing chain & data flow
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Processing chain & data flow
It has to acquire mutual clock offset measurementsfrom the Multi-Channel Phase Comparator,
via a UDP(User Datagram protocol) interface,
with a data rate of 1Hz.
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Processing chain & data flow
It is able to eliminate the impact of the MCPC outputsignal anomalies (e.g. phase spikes) on the EnsembleAlgorithm
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Processing chain & data flow
It provides the offset between the AHM clock and theEnsemble Clock, i.e.: self-generated virtual time scale
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Processing chain & data flow
It computes the frequency corrections to steer theAHMclock towards the Ensemble Time, by means ofthe FemtoSteppercomponent
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Processing chain & data flow
It instructs the FemtoStepper through a serial port,sending it command strings and acquiring theconfirmation for the execution of commands
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Monitoring Algorithm (1)
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Monitoring Algorithm (2)
This algorithm aims to facilitate a supervisor to better manage the clock
system, ensuring continuity of operations and limiting the expected
degradation of performance due to contingencies and anomalies
The algorithm processes the clock output phase/frequency measurements,
being targeted to detect the Feared Events such as phase jumps, frequency
jumps and frequency instabilities, which commonly affect atomic clocks
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ESTEC UTC Lab Front Panel (1)
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ESTEC UTC Lab Front Panel (2)
Real Dataset provided byPhysikalisch-TechnischeBundesanstalt Time
Laboratory - UTC(PTB).
Data Rate = 1 h;
Period:
from 07/Mar/2007 to 10/Aug/2007
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ESTEC UTC Lab Front Panel (3)
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ESTEC UTC Lab Front Panel (4)
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Conclusions and Future Developments (1)
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Conclusions and Future Developments (2)
In its final configuration, the Time Laboratory will be able to: generate a stable and continuous time reference, in an
autonomous operational mode
offer the operation of clocks within a controlled environment
perform a continuous performance monitoring of implemented
time scale
determine the offset between the official (BIPM) UTC and own
UTC(k), steering its time scale to the world UTC reference
disseminate its own UTC(k) time reference to users
exchange data with the operating/institutional time servers, suchas those ones of the Bureau International des Poids et Mesures
(BIPM) and of the various UTC(k) laboratories, spread around
the world.
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Special Thanks
We thank, for their drive and their willingness, bodies andpeople without whom this work would never have been done:
Ing. Marco Lisi (ESA)
Ing. Pierluigi De Simone (ESA)
Dr. Alexander Mudrak (ESA)
Ing. Raffaele Fiengo (National Instruments)
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Telespazio HeadquartersVia Tiburtina 96500156 [email protected]+39 06 4079 1
www.telespazio.com
Thank You for Your Attention
Authors:
Stefano [email protected]
Cromazio Valerio [email protected]
Marco [email protected]