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During Cross-correlation process:

xcorr=ifft(fft(a)fft(b)∗)

we have frequency offset and code phase offset.

enter image description here

How is it used later in the process of finding a user location?

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  • $\begingroup$ Hi Eugene! This question is a little broad – the answer would be explaining GPS receivers, and that is covered in very many places, and the fact that you've made this plot indicates you've read something like that already. So, could you, based on the literature you've read, explain what exactly your remaining question is? $\endgroup$ – Marcus Müller Mar 13 at 17:12
  • $\begingroup$ I wonder how this code phase is used later in pseudo range estimation? We get this code phase during acquisition step but what we do with this number in tracking step? $\endgroup$ – Eugene Mar 14 at 8:55
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To make it simple, finding user location is done by using four pseudo-range measurements (approximative distance from user/receiver to satellite) to resolve a four unknown equation. As information, these unknown are receiver's (X,Y,Z) coordinates and it's clock offset.

These pseudo-range measurements are done by tracking stage of the receiver. Acquisition results (code phase and Doppler shift) are used to initialize delay and phase tracking loops. I let you the following simple explanation of the receiver behaviour : https://gssc.esa.int/navipedia/index.php/Generic_Receiver_Description

Please let me know if my explanation are not sufficient,

Math

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