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UTC Time Service and T&F Applications Using Galileo

Andreas Bauch

Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

Workshop on Time and Frequency Serviceswith Galileo

Herrsching, December 2005

PTB Braunschweig

Outline

Metrological Time Keeping in Galileo – why?

The Galileo Timing System (as viewed froma European metrology institute)

Time Transfer for GNSS Operations

Brainstorming:Applications and how to make them real

Metrological Time Keeping

• enables dissemination of accurate time to users• enhances competitiveness of Galileo with GPS• allows operation of secondary frequency standards disciplined

by Galileo SIS reception traceable to national standards• ………• makes the expertise of the European time and frequency

community accessible for Galileo• stimulates more intense collaboration of European timing

institutes

Metrological Timekeeping

Galileo System Time vs TAI

predicted offset shall be in this region, 2σ

0 ns

-50 ns

50 ns

any yearly interval

95% of time GST shall be in this region

+28 ns

-28 ns

time

offs

et (G

ST-T

AI)

5 days

data available a posteriori

+28 ns

-28 ns

Metrological Time-keeping: The GST requirements cannot be guaranteed without thesupport of PTF operations by European timing institutes.

The Galileo Timing System:viewed from a European Metrology institute

The Galileo Timing System

PTF GGCUTClabs

BIPM

IERS

GTSPTiming community

Time transferdata to UTC(k)

Satellite time transfer links

UTC-UTC(k)

UTC-TAIGGC data: GST-UTC(k)

Time transfer datato GST, other data

GST-TAI offsetand correction,UTC-TAI

Galileo promotion

The Making of GST

PTF

UTC(2) UTC(3)UTC(1) UTC(4)

Individual clocksand local measurements

Time Transfer

GMS

GTSP

The Making of GST

Step 1: Physical realization of GST(MC) in PTF (following talk)

Step 2: Comparison of GST(MC) with UTC(k)

Step 3: Comparison of UTC(k) / GST(MC) with clocks Ci(k)

Step 4: Calculation of a composite time scale C(GTSP)based on all clocks Ci(k)

Step 5: Prediction of C(GTSP) - UTC

Step 6: Combine Step 5 and Step 2 to determine steering ofGST(MC) to UTC

Step 7: Forward steering parameters to PTF for use in Step 1

Time and Frequency Transfer for GNSS Operations

Two-Way Satellite Time and Frequency Transfer (TWSTFT)

GNSS Common ViewTime and Frequency Transfer ( GNSS CV)

TWSTFT

Comparison of the timereadings of the clocks atstations A and B

Quasi-simultaneousexchange of pseudo-randomphase-modulated signalsmodulated on carriers inthe standard communcationbands (Ku- or X-band)

Measurement quantities:Time differences ΔT(A) and ΔT(B), representing the time of arrivalof the signals from B in A (from A in B)

T(A)-T(B) = {ΔT(A) - ΔT(B)} / 2 + corrections

TWSTFT

Advantages:The time transfer results are practically independent of

•Satellite position and satellite movement•Ionospheric and tropospheric signal delays• Time Comparison Uncertainty < 1 ns • Frequency Transfer Capability 10-15 at tau = 1 day

Disadvantages:expensive hardware at both stations• license for transmission by national regulatory body• transponder lease from satellite operating agency

GNSS Common View

Reception of the GNSSsignal in space at stations1 and 2

Simultaneous comparisonof the time readings of theclocks at stations 1 and 2with the clock in the SV

Correction for thebroadcast time differenceSV_clock – System Time,and signal delays in theionosphere and troposphere

Ground clock difference accessible after exchange of data between stations

GNSS Common View

Advantages of GNSS CV:

•Receive-only technique•Easy to install and to operate•Requires exchange of rather small amount of data

Disadvantages:•One-way signal transmission: propagation delays must bemodelled, models sometimes not sufficiently accurate

•Post-processing required for high accuracy, which leadsto delay in availability

Frequency Transfer CapabilityTime and Frequency Comparisons between four

European Timing Institutes and NIST Using Multiple Techniques:

Comparison of three techniques for the link OP-NPL

Source:

EFTF 2005andMetrologianext issue

Brainstorming:Applications and how to make them real

Definition of classes of timing services:

•Services for Galileo

•Services distributing correct time

•Services distributing precise time

•The Time Service Provider as developed today is a prototype installation for support of the Galileo GMS during IOV.

•The Concessionaire will stimulate itsconversion to a continuous service, based on service level agreements with UTC(k) laboratories and a TSP legal entity.

•PTB is ready to provide continuous services as this fits to its general mission.

Services for Galileo

•The Galileo Time Service Provider can serve as institution which collects and re-distributes time information within Europe also for other applications.

•It may offer calibration and verification services to third parties.

Services not only for Galileo

•Based on the Galileo Signal-in-Space correct time can be generated and distributed

•Application in time stamping authorities, ntp stratum-1 servers

•More ideas expected tomorrow

What time is it?

•Scientific Applications of standardfrequency signals with uncertainty < 10-14

and instability of < 10-15 over 10 daysin institutes in academia (talk tomorrow)in VLBI / radio astronomy / astronomy /

geophysics

• Could be supported by a Service Provider, which supervises receiversand local frequency sources remotely.

Precise T+F applications

What time is it?

Thank you for

listening

andreas.bauch@ptb.de