Re: [LEAPSECS] RAS hits the news

From: Tom Van Baak <tvb_at_LEAPSECOND.COM>
Date: Mon, 26 Sep 2005 07:52:10 -0700

> In addition, since GPS time is TAI - 19s, the GPS-UTC difference will
> eventually overflow any fixed-sized transmission packet (if transmitted
> as a delta or as a table, it makes no difference in the end).

True, but the GPS signal format has a number of
fixed length fields and they do not cause a roadblock
for receiver firmware engineers. There are fixed-sized
256 and 1024 week number fields that "overflow",
for example, and all modern GPS receivers get them
right. It is trivial for a receiver to handle the equivalent
256 leap second rollover should one occur in the next
hundred years.

On the question of UTC updates; it's true that a cold
GPS receiver has to wait up to 12 minutes for the
correct GPS/TAI/UTC delta. I am wondering, though,
if anyone knows of an example of a GPS receiver
that caches the delta value from the last power-up?
It seems to me this would take care of the delay in
all but the most extreme cases.

Come to think of it my Garmin comes up with the
correct UTC time within seconds of power-up so it
must be doing something right.

/tvb
Received on Mon Sep 26 2005 - 07:58:40 PDT