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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
