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Now I am trying to design FIR based adaptive filter for rejection of Jamming in GPS device. (just self-learning purpose, Jamming is simple tone)

I've designed NOT-BAD performance adaptive filter for low sampling frequency. (~44100 Hz)

But when I use this adaptive filter for high sampling frequency (16 MHz), transient width of filter is greatly increased. (I think it is sure because transient width is proportional to 1/degree)

Since it is self learning purpose, I just want to know how big sampling frequency of normal GPS signal for digital filtering is.

If it is not so high as above, I'll quit this design and concentrate on other issues(quantization error etc).

If sampling frequency of normal GPS signal is high as above, I'll study more about that issue.

So, my question is :

How high sampling frequency of normal GPS is ?

Thank you.

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  • $\begingroup$ Why adaptive filter? Just use a band pass around the center frequency of the GPS signal before getting the phase difference. The sampling frequency in your case, since you assume a jamming tone, need to be twice the jamming tone frequency (assuming it could be higher that the GPS frequency). This will allow you to nicely filter the jamming out. Your filter is designed based on how close you anticipate the jamming frequency to the GPS one. $\endgroup$
    – Moti
    Commented Aug 8, 2015 at 3:03
  • $\begingroup$ @Moti Thank you for your comment. I've already use BPF for getting signal with center freq = 4MHz, band width = 2MHz. Since Jamming frequency can be in this band [3MHz, 5MHz], I used adaptive filter. (Jamming frequency is totally unknown). $\endgroup$ Commented Aug 8, 2015 at 3:11
  • $\begingroup$ Do you know the specific carrier you look for? As far as I understand a GPS signal is very narrow frequency. You want to filter out the jamming with a simple filter around the specific GPS carrier. $\endgroup$
    – Moti
    Commented Aug 8, 2015 at 7:10

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C/A code (the main civilian channel as of now) has a main lobe of around 2MHz and depending on how much processing you want to do, it is normally sampled in the low MHz range, which you are in. (you could pull it off with 2-5MHz).

Do know that the signal must be mixed down to a lower frequency before you sample it. The original signal is at 1.57GHz.

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