Test process guide and overview
– Leap Seconds

Which LabSat should I use?

We recommend using LabSat 3 & SatGen software when testing GPS Leap Seconds.

Although all LabSat models can perform this testing if required – our recommendation of LabSat 3 is based on the sole requirement to GPS leap Second testing.

Overview

The global time standard used is called Coordinated Universal Time (UTC), all national time standards around the world are based on this UTC time with the appropriate offset for their time zone. To keep UTC time synchronised to the Earth’s rotation, additional seconds can be added or removed to compensate for slight variations in the rotation rate of the Earth and other factors. When required, leap seconds are applied either on December 31st or June 30th.

The GPS system uses GPS time, which does not include these leap seconds. In order to allow accurate UTC time to be determined from GPS the GPS system transmits the number of leap seconds difference between the two times.

On December 31st 2016, the offset was increased to 18 seconds:

Before the 2016 leap second: GPS-UTC was 17 (GPS  ahead of UTC by 17 seconds)
After the 2016 leap second: GPS-UTC became 18 (GPS ahead of UTC by 18 seconds)

The sequence of dates of the UTC second markers are:

2016 December 31,        23h 59m 59s
2016 December 31,        23h 59m 60s
2017 January 1,            00h 00m 00s

Each version of SatGen Software includes a list of all past leap seconds and any future leap seconds that had been announced at the time of release, these will automatically be taken into account for any scenarios which span a leap second event.

GPS Leap Second Date Table

GPS Leap Second Dates

Leap Seconds

01/01/1980 - 01/07/1981

0

01/07/1981 - 01/07/1982

1

01/07/1982 - 01/07/1983

2

01/07/1983 - 01/07/1985

3

01/07/1985 - 01/01/1988

4

01/01/1988 - 01/01/1990

5

01/01/1990 - 01/01/1991

6

01/01/1991 - 01/07/1992

7

01/07/1992 - 01/07/1993

8

01/07/1993 - 01/07/1994

9

01/07/1994 - 01/01/1996

10

01/01/1996 - 01/07/1997

11

01/07/1997 - 01/01/1999

12

01/01/1999 - 01/01/2006

13

01/01/2006 - 01/01/2009

14

01/01/2009 - 01/07/2012

15

01/07/2012 - 01/07/2015

16

01/07/2015 - 31/12/2016

17

31/12/2016 - xx/xx/xxxx

18

Test Process

This process example is using the LabSat inbuilt GNSS receiver as the DUT.

  1. Connect the LabSat to a PC with the USB A to USB B cable.
  2. Start the LabSat leap second scenario. (In this example the scenario used has a start time and date of 30/06/2015 at 23:45 with a 20 minute duration).
  3. Launch ublox u-center software, available from here.
    • Connect to the relevant USB port on the PC at 115200 baud.
    • Open the messages window F9.
    • Select UBX from the Messages NMEA window.
    • Select the NAV (Navigation) drop down. Right click and select Enable child messages.
    • Select TIMEUTC (UTC Time), note the Time display – leap second alert message. – View screenshot.
    • Select TIMEGPS (GPS Time), note the Leap Seconds display (Leap Seconds display will change from invalid to 16 seconds by 23:49 minutes) – View screenshot.
    • Wait till 23:59 to observe the display change from 16 seconds to 17 seconds. – View screenshot.