[7069] in cryptography@c2.net mail archive
Re: GPS integrity
daemon@ATHENA.MIT.EDU (Phil Karn)
Thu May 11 16:57:14 2000
Date: Thu, 11 May 2000 10:25:41 -0700
Message-Id: <200005111725.KAA14072@homer.ka9q.ampr.org>
From: Phil Karn <karn@ka9q.ampr.org>
To: gdt@fnord.ir.bbn.com
Cc: cryptography@c2.net
In-reply-to: <rmihfc7y4pn.fsf@fnord.ir.bbn.com> (message from Greg Troxel on
09 May 2000 14:10:44 -0400)
Reply-To: karn@ka9q.ampr.org
>If I were worried about integrity of timing signals, I'd use a
>GPS-disciplined rubidium oscillator. I think most of the available
>devices like this are not quite as concerned with integrity as phase
>noise reduction in the normal case, so some tweaking of the
These are actually quite common in stationary timing applications. In
the early days of CDMA digital cellular development, we used GPS
receivers with rubidium oscillators in each cell site because the GPS
constellation was too incomplete to guarantee continuous coverage. I
think the commercial base stations still have rubidium oscillators
along with a spec to stay within 1 microsecond (the tolerance required
to permit soft handoff) for at least 24 hrs without seeing a GPS
satellite. This is to cover local blockages and interference as well
as any outage of the GPS constellation.
Phil
