how to design a moving window and apply DWT on each sample?

hi, i have 4 different DC signals and i have to apply a moving window with a width of 1024 sample data and then apply DWT on each sample to calculate details and approximation coefficients. please help.

Answer 1

[Adam Danz]

Here's a template using a vector of fake data. Within the loop the window starts at the beginning of the vector and moves down one index value every iteration. The outputs are stored in a matrix where each row is the result of one window and each column is a different window. You could put all 4 DC signals within the loop and store their outputs in separate variables.

% fake data
vec = rand(1,2000); 

% window size
windSz = 1024; 

% Number of iterations given window size
nWindows = length(vec) - windSz + 1;

% Allocate loop variables
cA = zeros(nWindows, 515);  % don't hard code this - I did it for simplicity
cD = cA; 

% Loop through each window
for i = 1:nWindows
    tempIdx = i:i+windSz-1; 
    [cA(i,:),cD(i,:)] = dwt(vec(tempIdx),'sym4'); 
end

[heba mahmoud]

thank you Adam Danz, i appreciate your help. i used your code in the algorithm i work on but i still have some problems. the algorithm is work as follow, apply a moving window with 1024 samples data on 4 different signal each signal is an array with 67501x1 dimension and then apply multi-level DWT on each sample and if the first level detail coefficient exceed a specific threshold it begin to calculate fifth level approximation coefficient at this sample and for 1000 sample after that sample and if not it continue calculating detail coefficient until moving window ends and move to the other moving window. i hope you help me in my code below:

sig = [Ip12,Ip21, In12,In21];

WindSz =1024;
nWindows = length(Ip12) - WindSz + 1;
cd1 = zeros (nWindows,515);
cd2 =  cd1
for j = 1:4
for i = 1 :nWindows
    k = i:i+WindSz-1;
    s(k) =  sig(k,j)
    Lev = 5;
    [C(k),L] = wavedec(s(k),5,'db4');
    [cd1(i,:),cd2(i,:),cd3(i,:),cd4(i,:),cd5(i,:)] =  detcoef(C(k),L,[1,2,3,4,5])  
    if cd1(k) >= 0.1           % is cd1 of each signal exceed threeshold??
        for x = k:k+1000
          [C(x),L] = wavedec(s(x),5,'db4');  
          a5(x) = appcoef(C(x),L,'db4',Lev)
        end
    else
        return
    end
end
end

[Adam Danz]

You mentioned you have problems and you explained how the algorithm should work but you never explained what the problem is or what's not working. If the problem has to do with the moving window I can help. If the problem has to do with details of the DWT analysis I may or may not be able to help since I'm largely unfamiliar with that.

[heba mahmoud]

 tempIdx = i:i+windSz-1; 
    [cA(i,:),cD(i,:)] = dwt(vec(tempIdx),'sym4');

I apply this step on my code but with different symbols and the following massage always shown after running the algorithm.

 In an assignment  A(I) = B, the number of elements in B and I must be the same.
Error in flowchart1 (line 12)
    [C(k),L] = wavedec(s(k),5,'db4')

so i think the problem is how to make moving window work on multi-level DWT if you agree with me.

[Adam Danz]

You'll have to share all of the relevant code for me to identify the source of error.

From the error message I understand that the size of

dwt(vec(tempIdx),'sym4')

doesn't fit in the size of

   [cA(i,:),cD(i,:)]

[heba mahmoud]

In the attached file i wrote your code and beside it my code and the relevant code of yours. hope you fix the problem.

[Adam Danz]

Question 1) What are the values of

Ip12,Ip21,In12,In21

Could you attach them in a mat file?

Question 2) Is your moving window moving across the vector sig or are trying to perform the moving window analysis only on each of the 4 variables listed above in isolation? This is critical for me to understand before I can suggest changes.

[heba mahmoud]

The attached files are the values of Ip12,Ip21,In12,In21. Actually I need to perform the moving window analysis on each of the 4 variables in isolation.