[ntp:questions] Start of new GPS 1024 week epoch

Magnus Danielson magnus at rubidium.dyndns.org
Fri Aug 16 17:39:28 UTC 2013


On 08/16/2013 03:34 PM, David Taylor wrote:
> On 16/08/2013 13:02, John Hasler wrote:
>> David Taylor writes:
>>> A pity that they haven't been able to find two or three spare bits to
>>> reduce the 1024 week ambiguity to nearer a half-century or even 100
>>> years.
>>
>>  From the Wikipedia article:
>>
>> To determine the current Gregorian date, a GPS receiver must be
>>    provided with the approximate date (to within 3,584 days) to
>> correctly
>>    translate the GPS date signal. To address this concern the modernized
>>    GPS navigation message uses a 13-bit field that only repeats every
>>    8,192 weeks (157 years), thus lasting until the year 2137 (157 years
>>    after GPS week zero).
>
> Oh, that /is/ good news, John!  Many thanks.  I couldn't see that from
> a quick scan of the referenced documents, so that's most helpful to know.
>
> I wonder whether there is any way to determine which satellites are
> sending this modernised message, perhaps they all do, or whether a
> particular receiver is using the full 13-bit field?  It's something
> I've not seen listed in various specifications I've read, but perhaps
> it's taken for granted after a certain date?
None will do that on the L1 C/A signal. It occurs on the new signals
such as L2C and L1C which is code-wise separate from the L1 C/A signal.
None of the traditional receivers will benefit from this shift.

So far I have only seen advanced receivers to receive those signals.
Hopefully things will change.

As I said, even if you add the bits in the signal, just because they are
there, if you haven't upgrade FW which includes it's interpretation, the
GPS receiver will not be able to use it and the problem remains.

Cheers,
Magnus


More information about the questions mailing list