Accuracy of Broadcast GLONASS Time and UTC(SU) A. S. Bandura, P. P. Bogdanov, A. E. Tiuliakov, A. Y. Feoktistov Russian Institute of Radionavigation and Time 120, letter EC, Obukhovskoy Oborony prospect, Saint-Petersburg, Russia Phone (812) 665 -5880, Fax (812) 665 -5888, e-mail: office@rirt. ru
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time broadcast to Users 2
Accuracy of Broadcast GLONASS Time and UTC(SU) broadcast by GLONASS 3
Accuracy of Broadcast GLONASS Time and UTC(SU) 2 1 -1 -2 CS Relative Frequency Error 4
Accuracy of Broadcast GLONASS Time and UTC(SU) – CS Time offset 5
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time Tay. C GLONASS Time, Tay. C and UTC(SU) broadcast to Users 6
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring At the same time, there has been a paradox situation: - according to the data provided by Russian monitoring services UTC(SU)GLONASS Time offset is within specified above values and the error of UTC(SU) broadcast by GLONASS does not contain a systematic component; - according to BIPM Timing Department UTC(SU)-GLONASS Time offset is about 200 ns and the error of UTC(SU) broadcast by GLONASS contains a systematic component of about 200 ns. 7
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring In Russia GLONASS Time and UTC(SU) broadcast by GLONASS are monitored by Main Metrological Center (MMC) of Russian Time and EOP Service with using approved TTS-3, TTS-4 time receivers developed by Pik Time System, Poland as well as by two receivers in test mode: GTR-51 developed by Dicom, Czech Republic and Time Transfer Unit TTU-1 developed by «RIRT» JSC. The results provided by the receivers at MMC are identical and it can be concluded that they are correct. Till recently the data provided by BIPM have been obtained on the bases of TTS-3 measurements by Astro-Geodynamic Observatory (AOS) of the Space Research Centre, Polish Academy of Science, located in Borowiec, Poland. 8
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring The analysis shows that in spite of the fact that TTS-3 receivers located in MMC and AOS are similar they use different values of GLONASS signal delays «INT DLY» calculated on the results of receiver calibration. These signal delays for TTS-3 receivers at MMC and AOS differ by exactly the same 200 ns. Since the results provided by different receivers at MMC are identical, as it was mentioned above, it means that the calibration of TTS-3 receiver at MMC is correct and the calibration of TTS-3 receiver at AOC is doubtful. At the same time, the values of GPS signal delays «INT DLY» for TTS-3, TTS-4 receivers used at European laboratories and MMC are identical. So, they provide very similar monitoring results for GPS Time and UTC(USNO). 9
Accuracy of Broadcast GLONASS Time and UTC(SU) Thank you for your attention! 10
Accuracy of Broadcast GLONASS Time and UTC(SU) Introduction Global Navigation Satellite Systems GLONASS is purposed for high-accuracy determination of position, motion velocity and time by land, marine, air and other kinds of users. To achieve this purpose the time scales of all space vehicles are synchronized relative to GLONASS Time and GLONASS Time is synchronized relative to Reference Time. Universal Time of Russia UTC(SU) generated by State Time/Frequency Reference (STFR) is used as GLONASS Reference Time. Now the accuracy of transmitted GLONASS Time and UTC(SU) meet specified requirements. However, the results of monitoring for broadcast GLONASS Time and UTC(SU) provided by Russian and international services are substantially different. 11
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time Generation GLONASS Time is generated as a continuous “paper” time scale on the basis of the Main and/or Reserved Central Synchronizers (CS) using the following equation: where - GLONASS Time offset relative to Reference Time; - Main/Reserved CS time offset relative to Reference Time; - corrections for Main/Reserved CS phase steering; - corrections for Main/Reserved CS frequency steering; - correction for controlling GLONASS Time-Reference Time offset; - offset between Main and Reserved CS Time. CS time scale is corrected simultaneously with one-second adjustment applied to UTC and, as a result, there is no whole second offset between GLONASS Time and UTC(SU). However, there is a three-hour constant offset due to GLONASS operational principles. 12
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time Generation Till August 2014 the offset of GLONASS Time relative to UTC(SU) was about 400 ns. It met specified requirements but was not satisfactory for time users. Therefore, to increase the accuracy of GLONASS Time synchronization to UTC(SU) on 18 th August, 2014 the procedure for GLONASS Time correction by changing the value of controlling correction was started. To keep the specified accuracy of space vehicles (SV) time scales synchronization to GLONASS Time the value of daily correction change was 3 ns. The results of monitoring proved the efficiency of the correction procedure: GLONASS Time offset relative to UTC(SU) changed from -392. 6 ns 19. 08. 2014 to 29. 4 ns 31. 12. 2014. In 2015 GLONASS Time – UTC(SU) offset was maintained within ± 35 ns, and in the first half of 2016 within ± 25 ns. 13
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time Broadcast to Users calculate GLONASS Time in accordance with the following formula: where t – onboard satellite time; , – frequency/time corrections (FTC) for SV–GLONASS Time offset broadcast in the navigation message. Thus, the error of time determined by the user in GLONASS Time caused by the errors of frequency/time data depends directly on the accuracy of broadcast FTC. In case all GLONASS facilities are in Full Operational Capability mode the error of FTC and, as a result, the error of time determined by the user in GLONASS Time caused by the errors of frequency/time data is about (3. 0 – 6. 0) ns (rms). 14
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time broadcast to Users 15
Accuracy of Broadcast GLONASS Time and UTC(SU) Broadcast to Users UTC(SU) is determined by users in accordance with the following formula: = 03 hrs 00 min + where - correction to GLONASS Time relative to UTC(SU) broadcast in the navigation message. Till 18 th August, 2014 the error of broadcast corrections for GLONASS Time – UTC(SU) offset contained a systematic component of approximately 200 ns. Therefore, on 18 th August 2014 the generated corrections to GLONASS Time were also changed. Now the error of broadcast corrections to GLONASS Time relative to UTC(SU) is below 10 ns (rms). 16
Accuracy of Broadcast GLONASS Time and UTC(SU) broadcast by GLONASS 17
Accuracy of Broadcast GLONASS Time and UTC(SU) 2 1 -1 -2 CS Relative Frequency Error 18
Accuracy of Broadcast GLONASS Time and UTC(SU) – CS Time offset 19
Accuracy of Broadcast GLONASS Time and UTC(SU) GLONASS Time Tay. C GLONASS Time, Tay. C and UTC(SU) broadcast to Users 20
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring At the same time, there has been a paradox situation: - according to the data provided by Russian monitoring services UTC(SU)GLONASS Time offset is within specified above values and the error of UTC(SU) broadcast by GLONASS does not contain a systematic component; - according to BIPM Timing Department UTC(SU)-GLONASS Time offset is about 200 ns and the error of UTC(SU) broadcast by GLONASS contains a systematic component of about 200 ns. 21
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring In Russia GLONASS Time and UTC(SU) broadcast by GLONASS are monitored by Main Metrological Center (MMC) of Russian Time and EOP Service with using approved TTS-3, TTS-4 time receivers developed by Pik Time System, Poland as well as by two receivers in test mode: GTR-51 developed by Dicom, Czech Republic and Time Transfer Unit TTU-1 developed by «RIRT» JSC. The results provided by the receivers at MMC are identical and it can be concluded that they are correct. Till recently the data provided by BIPM have been obtained on the bases of TTS-3 measurements by Astro-Geodynamic Observatory (AOS) of the Space Research Centre, Polish Academy of Science, located in Borowiec, Poland. 22
Accuracy of Broadcast GLONASS Time and UTC(SU) Results of GLONASS Time and UTC(SU) Monitoring The analysis shows that in spite of the fact that TTS-3 receivers located in MMC and AOS are similar they use different values of GLONASS signal delays «INT DLY» calculated on the results of receiver calibration. These signal delays for TTS-3 receivers at MMC and AOS differ by exactly the same 200 ns. Since the results provided by different receivers at MMC are identical, as it was mentioned above, it means that the calibration of TTS-3 receiver at MMC is correct and the calibration of TTS-3 receiver at AOC is doubtful. At the same time, the values of GPS signal delays «INT DLY» for TTS-3, TTS-4 receivers used at European laboratories and MMC are identical. So, they provide very similar monitoring results for GPS Time and UTC(USNO). 23
Accuracy of Broadcast GLONASS Time and UTC(SU) Increasing the Accuracy of Broadcast GLONASS Time and UTC(SU) Further accuracy improvement of broadcast GLONASS Time and UTC(SU) can be achieved on the basis of increased accuracy of GLONASS Time and its referencing to UTC(SU). So, the following work is planned: – increasing CS accuracy parameters; – increasing the accuracy of referencing GLONASS Time to UTC(SU); – decreasing the error of broadcast corrections to GLONASS Time relative to UTC(SU). 24
Accuracy of Broadcast GLONASS Time and UTC(SU) Conclusion At present the accuracy of broadcast to users GLONASS Time and UTC(SU) meets specified requirements. By 2020, as a result of further GLONASS development, the following accuracy parameters are planned to be achieved: – GLONASS Time - UTC(SU) offset below 4 ns; – the error of broadcast corrections to GLONASS Time below 2 ns. 25
Accuracy of Broadcast GLONASS Time and UTC(SU) Thank you for your attention! 26
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