Re: code tracking (Re: a question about pream function)

Tak,

That is correct.  It provides some advantages for
both code and carrier tracking.

Cliff
----- Original Message ----- 
From: "tebinuma" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Thursday, May 20, 2004 3:26 AM
Subject: code tracking (Re: [OpenSource_GPS] a question about pream
function)


> Hello Zhu,
>
> Not quite sure, but I guess it uses a narrow
> correlator technique, in which the dither arm
> is set 1/2 chip early (or late) of the prompt.
> The prompt arm looks like a late arm thus the
> loop will lock 1/4 chip early of the prompt.
> As a result, dfreq acts like a early-minus-late
> discriminator with a narrower chip spacing.
>
> Cliff, am I right?
>
> Tak
>
> --- [email protected] wrote:
> >   Thank you Tak!
> >      I have another question:
> >
> >    The open source gps code use the fowllowing
> > algorith to do code phase tracking :
> >   Track Code loop code
> >   prompt_mag  = RSS(prompt_I, prompt_Q)
> >   dith_mag       = RSS(dither_I, dither_Q)
> >   dfreq             =
> > trk_code_k*(prompt_mag-dith_mag)
> >   ddf                = (dfreq - dfreq1)*trk_code_d
> >   code_freq     = (dfreq + ddf)/trk_div+code_freq
> >   dfreq1           = dfreq
> >
> > ?  My question is why dfreq=
> > trk_code_k*(prompt_mag-dith_mag)?
> >    I think prompt_mag is always great than dith_mag!
> > It seems it was unreasonable.
> >    could you give me an explanation?
> >
> > ?? Regards,
> >
> > ?? Zhu Di
> >
>
>
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