Noise Generated using awgn and randn do not match!!!

Question

chess 2017-7-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/348335-noise-generated-using-awgn-and-randn-do-not-match

回答： Darel 2021-8-4

I am generating noise in two different cases with the same SNR once using awgn command which is a built in command and second time using randn function with the correct scaling however I am getting different noise power in each case.

Following is the script to generate noise using different techniques. Can anyone help me why I am not getting the correct result?

Method 1

     A=[1-1i 1+5i 5-4i 3+2i  6-1i  1-3i 2 1+1i -1-0.5i];
      Esym=sum(abs(A).^2)/length(A);
      SNR=0;
      snr=10^((SNR)/10);
  Noise=sqrt(Esym/(2*snr))*(randn(1,length(A))+1i*randn(1,length(A))); 
  A_noisy=A+Noise;

sum(abs(C).^2)/length(C) sum(abs(Noise).^2)/length(Noise) Method 2

   B=awgn(A,SNR,'measured');
  C=B-A;
The result is as follow:
sum(abs(C).^2)/length(C)
sum(abs(Noise).^2)/length(Noise)
>> noise_testing
ans =
     19.4895
ans =
      7.9002

As you can see the result is so much different. Can anyone help me to figure out the problem.

Thanks

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Darel 2021-8-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/348335-noise-generated-using-awgn-and-randn-do-not-match#answer_761057

You were on the right track. The issue is just that your noise sequence is so short that the noise power for your samples may be substantially different from the overall average power. If you just make the signal and noise sequences longer (maybe something like a thousand points instead of just nine), the results should be much closer whether you use randn() or awgn().