add white gaussian noise to signal

the original siganl is right above iamge and left above image is my output, that's not my problem but the paper says "The Gauss white noise is added to the signal when signal to noise ratio is 5dB".

I try to build b prime image in the right bottom corner but my output is b image. I use " awgn(x,SNR) " with SNR=5, but output image is not like b prime image.

I know my output image shouldn't be exactly like b prime image because of randomness property of noise, but my b image is not like b prime image in terms of magnitude and appearence and ..., does anyone know why?

N=512;  n=1:1:N;
y=4*cos(8.*pi*n./N)+(N/5);
x=cos(2*pi.*y.*(n/N));
subplot(2,1,1)
plot(n, x); axis([0 512 -1.5 1.5]); title('x')
xn= awgn(x,5);
subplot(2,1,2)
plot(n, xn); axis([0 512 -1.5 1.5]); title('x+white guass noise')

[Mathieu NOE]

hello

I believe the b prime signal is not only a prime + noise but there is a gain factor between the two

are you sure that b prime = a prime x gain + noise with gain = 1 ?

[rohollah hosseyni]

I don't think so

paper just say , a gussian white noise is added to original siganl with snr=5dB