GPS World

Tag: Coordinated Universal Time

  • GPS Directorate to test legacy receivers in February

    GPS Directorate to test legacy receivers in February

    U.S. Coast Guard issues testing notice on GPS Week Number Rollover.

    The GPS Directorate has released a Federal Register Notice announcing plans to execute a test in February to investigate legacy receiver week roll-over behavior and analyze any off-nominal behavior exhibited, according to a U.S. Coast Guard notice.

    Photo: andrey_l/Shutterstock.com
    Photo: andrey_l/Shutterstock.com

    The GPS week number rollover occurs in the GPS legacy navigation (LNAV) message every 1024 weeks due to the GPS week number being represented by only 10 bits within the LNAV message.

    The next GPS week number roll over will occur 18 seconds prior to the 0000Z boundary (Coordinated Universal Time) between April 6/7 2019.

    In most cases, any negative response from a GPS receiver caused by a problem accounting for the 10-bit week number roll over would likely affect the calendar conversion from GPS time to UTC date/time and could result in the GPS receiver thinking it had jumped backward in time by 1024 weeks to 21/22 August 1999.

    To participate in the test, submit the answers to the nine questions in the Federal Register Notice to the SMC/GPE mailbox by Feb. 4. After the submission of the questionnaire, the team will schedule individual meetings with interested civil vendors to further discuss their participation in the test in more detail.

  • UTC to retain leap second at least until 2023

    The ITU World Radiocommunication Conference (WRC-15), in session in Geneva Nov. 2-27, has decided that further studies are required on the impact and application of a future reference time-scale, including the modification of Coordinated Universal Time (UTC) and suppressing the so-called “leap second.”

    Leap seconds are added periodically to adjust to irregularities in the earth’s rotation in relation to UTC, the current reference for measuring time, in order to remain close to mean solar time (UT1). A leap second was added most recently on June 30 at 23:59:60 UTC. The proposal to suppress the leap second would have made continuous reference time-scale available for all modern electronic navigation and computerized systems to operate while eliminating the need for specialized ad hoc time systems.

    The decision by WRC-15 calls for further studies regarding current and potential future reference time-scales, including their impact and applications. A report will be considered by the World Radiocommunication Conference in 2023. Until then, UTC shall continue to be applied as described in Recommendation ITU‑R TF.460‑6 and as maintained by the International Bureau of Weights and Measures (BIPM).

    WRC-15 also calls for reinforcing the links between ITU and the International Bureau of Weights and Measures (BIPM). ITU would continue to be responsible for the dissemination of time signals via radiocommunication and BIPM for establishing and maintaining the second of the International System of Units (SI) and its dissemination through the reference time scale.

    Studies will be coordinated by ITU along with international organizations such as the International Maritime Organization (IMO), the International Civil Aviation Organization (ICAO), the General Conference on Weights and Measures (CGPM), the International Committee for Weights and Measures (CIPM), the International Bureau of Weights and Measures (BIPM), the International Earth Rotation and Reference Systems Service (IERS), the International Union of Geodesy and Geophysics (IUGG), the International Union of Radio Science (URSI), the International Organization for Standardization (ISO), the World Meteorological Organization (WMO), and the International Astronomical Union (IAU).

    “Modern society is increasingly dependent on accurate timekeeping,” said ITU Secretary-General Houlin Zhao. “ITU is responsible for disseminating time signals by both wired communications and by different radiocommunication services, both space and terrestrial, which are critical for all areas of human activity.”

    “The worldwide coordination of time signals is critical for the functioning and reliability of systems that depend on time,” said François Rancy, Director of the ITU Radiocommunication Bureau. “ITU will continue to work with international organizations, industry and user groups towards providing coherent advice on current and potential future reference time-scales.”