code tracking (Re: 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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