[time-nuts] Trimble Resolution SMT - good/bad/indifferent?

[bg at lysator.liu.se]

> On 5/11/12 2:38 AM, Hal Murray wrote:
>>
>>> Why in the hell would anybody build a 50 channel receiver?  At most you
>>> MIGHT see 12 usable GPS sats...  I don't think that I've seen over 10.
>>> WAAS
>>> should be fairly useless for a timing receiver.
>>
>> I can think of a couple of reasons.  I'm sure there are more.
>>
>> One would be marketing type bragging rights.  I can scan more channels
>> than
>> you.
>>
>> Another area would be cold-start time.  If you have to search N slots,
>> more
>> searchers runing in parallel is likely to speed things up.
>>
>>
> Searchers and trackers are often different logic, these days..
>
> Searching is very efficiently done with a FFT correlator, because you
> can search all lags simultaneously with NlogN effort as opposed to
> O(N/2) effort with a sequential search.  Same for Doppler.
>
> But once you've acquired, you track with a conventional
> Early/Prompt/Late scheme.
>
> When you get into full-up implementations, where there is coupling
> between the tracking loops (think of a 2 frequency receiver.. L1 and L5
> will have related doppler), there are other "economies of scale" possible.

Here is an example of tracking loops coupled even more.

    http://www.javad.com/downloads/jns/papers/coop_tracking.pdf

--

    Björn