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26th March 2010, 19:05 #1
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AWGN Channel
Hello,
In AWGN channel, how is white noise generated using MATLAB? I mean, I have a code at hand, but I did not understand it. For example, it says somewhere in the code:
y = s + 10^(Eb_N0_dB(ii)/20)*n;
where s is the transmitted sequence, Eb_N0_dB is the SNR, and n is the additive white noise. Can anyone explain to me the noise term, please? Why do we use the expression 10^(Eb_N0_dB(ii)/20)*n?
Regards

26th March 2010, 19:05

27th March 2010, 10:41 #2
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Re: AWGN Channel
Originally Posted by mathuranathan
Actually, I still do not get why we use the expression 10^(Eb_N0_dB(ii)/20)*n for the noise. Anyway, from the link you gave me, I found a builtin function in MATLAB which is AWGN() function that adds noise depending on the SNR. I tried it as in the following code:
Code:function BER clear; N=10^6; SNRdB=[3:10]; SNR=10.^(SNRdB/10); b=rand(1,N)>0.5; s=2*b1; for ii=1:length(SNRdB) y=awgn(s,SNRdB(ii),'measured'); bHat=real(y)>0; Diff=xor(bHat,b); nErr(ii)=length(find(Diff)); end simBER=nErr/N; theoryBER=0.5*erfc(sqrt(SNR)); semilogy(SNRdB,simBER,'k*',SNRdB,theoryBER,'bx'); legend('Simualtion','Theory');
Thanks in advance

8th April 2010, 09:41 #3
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Re: AWGN Channel
Originally Posted by mathuranathan
Regards

8th April 2010, 10:25 #4
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Re: AWGN Channel
Originally Posted by mathuranathan
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9th April 2010, 13:56 #5
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Re: AWGN Channel
Originally Posted by mathuranathan
Thanks in advance

10th April 2010, 15:08 #6
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Re: AWGN Channel
I have noticed that, when I set the range of errors from 10^7 up to 0.5, the simulation curve stopped on 10^6. Why is that?

12th April 2010, 15:54 #7
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Re: AWGN Channel  generating noise for required SNR
I think it is clear now the concept of adding AWGN to the transmitted signal over AWGN channel. Let me summarize:
For a specific SNR we need to add a noise term to the transmitted symbol such that the SNR is as specified, i.e.: if the SNR(dB)=15, we need to add a noise term such that the SNR(dB)=15 dB. To do this, we assume that the signal energy is unity (Why?), and then:
Code:y=s+10.^(15/20)*n
. But, is the assumption that the energy of the signal = 1 is valid?
Now, let us turn to the multipath fading channles. In this case the receiced signal will be:
Code:y=h*s+10.^(15/20)*n
Shall we assume that the numerator is unity? I.e.: h^2*Es =1? Why?
Thanks in advanceLast edited by BlackMamba; 27th August 2010 at 13:19.

20th April 2010, 15:00 #8
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Re: AWGN Channel
Originally Posted by mathuranathan
Thanks in advance

20th April 2010, 15:00

23rd April 2010, 16:07 #9
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Re: AWGN Channel  generating noise for required SNR
Originally Posted by mathuranathan
Regards

10th December 2011, 05:28 #10
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Re: AWGN Channel  generating noise for required SNR
Is y=s(20 log(SNR)*n) the same with y = s + 10^(Eb_N0_dB(ii)/20)*n?
please reply me as soon as possible.
 Post added at 05:28  Previous post was at 05:21 
Is y=s(20 log(SNR)*n) the same with y = s + 10^(Eb_N0_dB(ii)/20)*n?
please reply me as soon as possible. And then, i would like to know the value of n?

10th December 2011, 18:54 #11
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Re: AWGN Channel  generating noise for required SNR
Is SNR here in dB or linear?

10th December 2011, 19:19 #12
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10th December 2011, 22:41 #13
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Re: AWGN Channel  generating noise for required SNR
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24th December 2011, 20:35 #14
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Re: AWGN Channel  generating noise for required SNR
Thank u for ur reply!! but i need to change a little bit. how can i change the equation, y = s + 10^(Eb_N0_dB(ii)/20)*n to another way? Please tell me! i am not so clear ! Thank u! Is this equation y=s+(1/sqrt(SNR))*n right and same with y = s + 10^(Eb_N0_dB(ii)/20)*n?

26th December 2011, 02:10 #15
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1st May 2013, 11:43 #16
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Re: AWGN Channel  generating noise for required SNR
How to include the path loss exponent and the distance between the source & destination in the channel H???

1st May 2013, 11:43

11th May 2013, 23:48 #17
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Re: AWGN Channel  generating noise for required SNR
i thinck it will be y=s+(1/sqrt(2*SNR))*n not ........ y=s+(1/sqrt(SNR))*n
because σ = √(N0/2)
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