how can i write a program that transmits a signal through a AWGN channel .. showing the effect of the noise?? how can i compute bit error rate and signal to noise ration and then plot them togother using matlab

l=10^4; // total number of transmitted bits (no. of si)

errorcounter=0;

snr=[1:15]; // range of signal to noise ratio

nni=randn(l); // the noise before multiplying it by std (standard deviation)

si=[+1 +1 -1 -1 -1 +1 -1 +1]; // my signal (is there a way to create such array without writting the whole elements like i did?)

for i=1:15

    stdn=sqrt(10^(-snr/10))
    ni=nni*stdn; // this is the noise that will affect the signal si 
    ri=ni+si; // my output
    if ri>0
        sdi=1; //my new array element the final result
    elseif ri<=0
            sdi=-1;
    elseif sdi ~= si then errorcounter=errorcounter+1 // error occured 
    end
end
ber=errorcounter/l;
end
plot(snr,ber)

i tried to run this prog on matlab and there were lots of errors .. is there an alternate prog .. thanx alot

[Rick Rosson]

Please format your code. Please add comments to the code so we can understand it. Please ask a specific question.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Walter Roberson]

What is the reason you think the program is not working properly?

[mary]

thanx for the comments i rewrote my question and tried to be clear and more specific hope it is better now .. and the reason why i think it is not working is that i tried to make it work on matlab and i could not i found errors that i couldn't solve.. can you help me plz?

[Walter Roberson]

What errors do you see? Or do you mean that the errorcounter goes much higher than you expect?

Please do not use // comments on MATLAB code: it prevents people from copying and pasting your code to test it themselves.

[mary]

l=10^4;

errorcounter=0;

snr=[1:15];

nni=randn(l);

si=[+1 +1 -1 -1 -1 +1 -1 +1];

for i=1:15

    stdn=sqrt(10^(-snr/10))
    ni=nni*stdn; 
    ri=ni+si;
    if ri>0
        sdi=1;
    elseif ri<=0
            sdi=-1;
    elseif sdi ~= si then errorcounter=errorcounter+1 
    end
end
ber=errorcounter/l;
end
plot(snr,ber)

[mary]

could you copy this plz? the issue is that the prog is not even running it is not working .. it is not about the error counter

[mary]

it says that the inner dimentions matrix must agree!!

Answer 1

[Walter Roberson]

Your nii is randn(l) and l is 10^4. According to the randn documentation,

r = randn(n) returns an n-by-n matrix containing pseudorandom values drawn from the standard normal distribution.

so nii will be a 10^4 by 10^4 matrix.

You calculate,

stdn=sqrt(10^(-snr/10))

and your snr is [1:15] which is a 1 x 15 matrix, so your stdn will be a 1 x 15 matrix.

Then you have

ni=nni*stdn;

so you are asking to multiply a 10^4 x 10^4 matrix, by a 1 x 15 matrix. What output were you hoping for from the multiplication?

If you had created nii = rand(10^4,1) then you would be multiplying a 10^4 x 1 matrix by a 1 x 15 matrix. The "*" operator is matrix multiplication, which is defined when the two inner dimensions (the second dimension of the first matrix, the first dimension of the second matrix) are the same size. In that case the output would be a 10^4 x 15 matrix. Is that what you were hoping for, to multiply each different random value by each different snr value ?

[mary]

okey you helped me with this it worked properly.. thanx alot

Answer 2

[Rick Rosson]

MATLAB Interactive Tutorial