Detection of leap second correction between GPS time and UTC time

5 thoughts on “Detection of leap second correction between GPS time and UTC time

  1. Hi,

    We could detect that the UTC time from NMEA message RMC is wrong after a cold start. There are 16 leap seconds between GPS time and UTC time. After 15 minutes the time we receive by NMEA message RMC is adjusted to UTC time. Is it possible to detect by NMEA message when the correction (GPS time + leap seconds = UTC time) is done. Or is there an AT command to detect it?

    For further information what I mean about GPS time https://en.wikipedia.org/wiki/Global_Positioning_System#Timekeeping

    Best regards

    Chris

    1. After 15 minutes the time we receive by NMEA message RMC is adjusted to UTC time. Is it possible to detect by NMEA message when the correction (GPS time + leap seconds = UTC time) is done. Or is there an AT command to detect it?

      Hi Chris,

      Sadly, there is not a NMEA sentence or unsolicited message that notifies the reception of the leap second information from the GPS system. You can detect the reception of the timing correction by monitoring the NMEA sentences:

      1. When the GPS system is applying the leap second correction, the GPS receiver will show a timestamp 23:59:59 followed by a 23:59:60 timestamp.
      2. When the GPS receiver is applying a leap second correction already applied by the GPS system, the receiver will show two equal timestamps.

      What GPS receiver are you using in your application?

      Best regards,

      Simone Andrea Muscas
      Technical Support – EMEA Application Engineering

      Telit Communications S.p.A.

      1. Hi

        Thank you for your quick answer.

        1. When the GPS system is applying the leap second correction, the GPS receiver will show a timestamp 23:59:59 followed by a 23:59:60 timestamp.

        The first one I do not unterstand what you exactly mean by that. Is the time information date 1.1.1970 and time 23:59:59 and next is 2.1.1970 00:00:00 (60 seconds is not possible it should be 00)

        2. When the GPS receiver is applying a leap second correction already applied by the GPS system, the receiver will show two equal timestamps.

        The second issue I could see in the NMEA messages.

        Best regards

        Chris

        1. Hi Chris,

          The leap second propagations in the GPS system are scheduled by the GPS control segment (the next one is scheduled for June 30th), the standard followed by the manufacturers is to skip or add seconds in the sentences based on the type of correction.

          The first behavior reflects a scenario in which the receiver is acquiring the GPS signal in a temporal window in which the leap second propagation has been scheduled. If a leap second is deleted, then the 59th second of the last minute before UTC midnight is just skipped, and an inserted leap second is simply counted as second 60 before midnight.

          The second behavior (that your module is experiencing) reflects a scenario in which the GPS receiver is storing a wrong leap second count in his firmware and is gathering the correct leap second count from the GPS signal. The GPS signal has a very small bitrate so you can wait up to 12 minutes before receiving that information from the GPS system.

          Best Regards,

          Simone Andrea Muscas
          Technical Support – EMEA Application Engineering

          Telit Communications S.p.A.