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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 Aug 8 '15 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). $\endgroup$ – Won Seok Lee Aug 8 '15 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 Aug 8 '15 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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The minimum practical sampling rate for the L1 C/A signal that I've seen is 1.023MHz complex sampling (or 2.046MHz real) at baseband. That's the width of the first lobe in the frequency domain, the bandwidth of the actual signal is much wider than that so you do lose some energy due to anti-alias filtering. See also here.

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    $\begingroup$ This actually isn't true. That's the minimum sample rate to intake the DSSS signal's main lobe without any aliasing, but I've seen (successful) GPS receiver designs that first lowpass filter the signal to a somewhat smaller bandwidth (e.g. 1.6 MHz) to reduce the required computational load (with the loss of a bit of performance). $\endgroup$ – Jason R Sep 27 '17 at 11:44
  • $\begingroup$ Thank you for the downvote. I've personally acquired satellites at 1.024MHz complex sampling rate in an actual commercial product. $\endgroup$ – ZiglioUK Sep 27 '17 at 14:59
  • $\begingroup$ I didn't downvote your answer, but the fact is that it isn't accurate for the reason I cited above. To be completely pedantic, there is no "bare minimum" sample rate at all, given good enough SNR and a sophisticated enough receiver. $\endgroup$ – Jason R Sep 27 '17 at 15:00
  • $\begingroup$ Sorry for assuming that then :-) $\endgroup$ – ZiglioUK Sep 27 '17 at 15:01
  • $\begingroup$ Anyway, to the downvoters, feel free to edit the answer if you think it's worth correcting. My point of view is practical, while theoretically there is no "bare minimum", I haven't come across anybody sampling the GPS signal at a rate<1.024MHz. $\endgroup$ – ZiglioUK Sep 28 '17 at 8:37

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