Matlab matched filtering help

Question

vsee 2011-9-28

0
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此问题的直接链接

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Hello

Here is a code that I wrote to analyze the prp(pulse repetition pattern) of a signal I am getting from an oscilloscope.

      [signal_1,path_1] = uigetfile('*.csv','Select the .csv file to analyze');
  if isequal(signal_1,0)
     disp('User selected Cancel');
  end
  sig = csvread(fullfile(path_1, signal_1),0,3);
amp_1 = sig(1:2000000,2);
ts_1 = sig(2,1) - sig(1,1);
time_1 = ([0:2000000 - 1]*ts_1)';
ax1 = plot(time_1,amp_1);grid;
axis([0 max(time_1) -0.1 1.8]);
ax_handle = gca;
ii = 1;
fig_handle = gcf;
xlimit_orig = get(ax_handle, 'Xlim');
  win_xlimit = [0 0.001];
  offset = 0.001;
 starter = uicontrol('parent',fig_handle,'Style','ToggleButton','String','start pan','Value',0,'Position',[150, 5, 60, 20]);
 handle = uicontrol('parent',fig_handle,'Style','ToggleButton','String','pause/run','Value',1,'Position',[100, 5, 60, 20]);
 getvalue = uicontrol('parent',fig_handle,'Style','ToggleButton','String','get value','Value',1,'Position',[20, 5, 60, 20]);
 %Iterativley change the xlimit for the axes to pan across the figure
       while win_xlimit(1) <= xlimit_orig(2) && ii <= 9
           pause(5);
           if get(starter,'Value') == 1
           if get(handle,'Value') == 1
               set(ax_handle, 'Xlim', win_xlimit);
               win_xlimit = win_xlimit + offset;
           end   
           end
           if get(getvalue,'Value') == 0
                   [x(ii),y(ii)] = ginput(1);
                   ii = ii + 1;
                   set(getvalue,'Value',1);
           end
       end
   prp = (x(2:ii-1)-x(1:ii-2))*1e+06;
   disp('approximate prp is');
   disp(prp);

The signal is huge (as you see I am reading in 2 million samples of my raw data). I am panning the signal in x-axis to find the pulses of interest and then conditionally use the ginput command to get values when needed. The problem is that ginput requires manual interference. I am trying to see if I can avoid this by implementing a matched filter that will retain the pulses and remove the noise. Can anybody please help on how to start designing a matched filter for a signal like this?

Thanks

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Answer 1

Daniel Shub 2011-9-28

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Depending on how noisy your data is you might just be able to use a simple threshold ...

time_1(amp_1 > threshold)

where you set an appropriate threshold.

If your data is noisy, then you probably want to do a crosscorrelation:

[y, lags] = xcorr(amp_1, template);
lags(y > threshold)

where you pick the appropriate threshold and template.

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Answer 2

Honglei Chen 2011-9-28

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Hi vsee

Here is an earlier post regarding matched filter

http://www.mathworks.com/matlabcentral/answers/4502-matched-filter

Since you have a huge data set, it may be better for you to process them in a streaming way. If you have Phased Array System Toolbox, you can take a look at

>> doc phased.MatchedFilter

HTH

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vsee 2011-9-29

True, the signal is distinguishable from the noise. However, I am only plotting 10000 points of the full signal. The full signal has multiple pulses staggered all over. What I am trying to achieve is an algorithm that can retain the pulses and get rid of the noise completely so I can calculate the prp.

Thanks again

Honglei Chen 2011-9-29

In this particular case, because you are reverting signal, it is an FIR filter so a is always 1.

I don't think there is an algorithm exist to retain the signal while completely get rid of the noise. There will always be some tradeoff between losing some signal vs. removing noise. If your goal is to make the pulse look clean, what you can do is to pass the pulse through a lowpass filter to get rid of some noise. However, your pulses then will not look like perfect rectangles.

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