Leap Second May Affect Some Units
Joint Program Office is seeking to alert the GPS
community that a leap second insertion into Coordinated Universal Time on 27 November 2003 might cause a brief anomaly in some receivers.
Exactly 256 weeks will have passed since the last leap second insertion into UTC (on 31 December 1998). Because the counter in the GPS signal’s subframe data message is 8 bits and only goes to the value 256, the “leap second event” will happen after the counter resets. This might cause some receivers to lose track for about 1 second before recovering, which might create a brief problem for receivers with critical timing applications.
According to GPS World’s Innovation column editor Richard Langley of the University of New Brunswick, the GPS week number corresponding to the date of the last leap second insertion on 31 December 1998 (990 in the previous week cycle) is also represented by only an 8-bit truncated version (222).
Receivers must account for the truncated nature of these parameters as well as the end-of-week rollover when determining UTC from GPS Time, Langley says.