[OpenSource_GPS] a question about pull_in function in the open code

[Clifford Kelley]

Tongtong,

In this part of the code we are trying to create a "pseudo" prompt correlator by coherently
integrating the dither and prompt correlators which are actually being used as "early" and "late"
correlators with 1/2 chip spacing.  This creates a higher signal to noise than a non-coherent integration.

I hope this answers your question.

Best regards,

Cliff

-----Original Message-----
>From: tongtong wang <tongtongwang at gmail.com>
>Sent: May 21, 2007 10:53 AM
>To: opensource_gps at lists.psas.pdx.edu
>Subject: [OpenSource_GPS] a question about pull_in function in the open code
>
>hi, there
>
>Many thanks for your sharing the GPS code.
>
>I got a question about the tracking lock loop function in the
>CH_PULL_IN procedure.
>
>"  q_sum = c->accum.q_dith + c->accum.q_prompt;
>  i_sum = c->accum.i_dith + c->accum.i_prompt;
>  if (i_sum != 0 || q_sum != 0)
>    theta = fix_atan2 (q_sum, -i_sum); "
>
>Is fix_atan2 (q_sum, -i_sum) the phase detecter?
>Why you use Q=q_sum & I=-i_sum instead of rss(c->accum.q_dith ,
>c->accum.q_prompt) & rss(c->accum.i_dith ,  c->accum.i_prompt) in the
>atan2 part?
>
>Hope I can get answer here.
>Thanks again.
>
>//tongtong
>
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