implementazione di una virtual time scale in labview realizzando un clock di riferimento atomico...

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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All rights reserved 2011, Telespazio

*** Why ?

Some introductive information

to understand the reason for work done




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All rights reserved 2011, Telespazio 3

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 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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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 :


8/27All rights reserved 2011, Telespazio

*** What ?

And now,

lets go right to the point .!





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).



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



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



Processing chain & data flow


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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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It is able to eliminate the impact of the MCPC outputsignal anomalies (e.g. phase spikes) on the EnsembleAlgorithm


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It provides the offset between the AHM clock and theEnsemble Clock, i.e.: self-generated virtual time scale


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It computes the frequency corrections to steer theAHMclock towards the Ensemble Time, by means ofthe FemtoSteppercomponent


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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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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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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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All rights reserved 2011 Telespazio 27

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]

implementazione di una virtual time scale in labview realizzando un clock di riferimento atomico...

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