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5th March 2011, 20:08 #1
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Noise Variance N0 of AWGN
Hi,
I am trying to calculate the SNR from the source to the destination of a Rayleigh flatfading channel with AWGN using the following formula:
SNR = (P*(h_sd^2))/N0;
where P=transmit power
h_sd=channel gain
N0=noise variance
I know the transmit power is going to be a constant so I considered it to be 27dB.
I have modeled the channel gain as
h_sd=abs((sqrt(0.5))*(randn(1)+j*randn(1)));
Am I on the right track? and I have no idea how to get N0

5th March 2011, 20:08

6th March 2011, 05:25 #2
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Re: Noise Variance N0 of AWGN
Actually sir, the formula of the received SNR over flatfading channel is . Now for problem, you can define using MATLAB syntax the SNR, as:
Code:SNRdB=0:2:20 % in dB scale SNR=10.^(SNRdB./10)% in linear scale
Please refer to the following link BER for BPSK in Rayleigh channel which includes the MATLAB how to simulate the BER of a coherent BPSK signaling over flat Rayleigh fading channel. If you have more questions, do not hesitate to ask.
Regards

6th March 2011, 08:07 #3
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Re: Noise Variance N0 of AWGN
thank you for the reply. however i am working on relay selection based on hybrid forwarding schemes such as AF and DF.
The calculation I mentioned earlier is only a part of the over all code.
This is the formula that I wish to simulate:
SNR_af = ((P1*h_sd^2)/N0) + (P1*P2*h_sr^2*h_rd^2)/((P1*h_sr^2 + P2*h_rd^2 + N0)*N0)
where P1=transmit power at the source
P2=transmit power at the relay
So is N0 just another constant (noise power) like the transmit power? Do I have to relate it to the BER?

6th March 2011, 08:07

6th March 2011, 19:13 #4
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Re: Noise Variance N0 of AWGN
You just include the noise in the SNR term, and yes it is constant, this is the characteristic of white noise, that it has a flat power spectral density.
Regarding the AF relaying, the endtoend SNR is:
Actually, I am looking for this simulation, too. So, if you come up with some thing new, please post it here.
Note: Why you continue to use instead of ? In bandlimited channel of bandwidth , the SNR is given in one of two equivalent forms: or , where , which means that , where .
Thanks

6th March 2011, 19:13

6th March 2011, 20:43 #5
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Re: Noise Variance N0 of AWGN
I do not understand with Noise Variance NO of AWGN who can explain to me.
help me. thanks.

6th March 2011, 23:39 #6
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7th March 2011, 08:41 #7
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Re: Noise Variance N0 of AWGN
no i understand it, its jus that in the matlab program would i consider it fixed or varying randomly

7th March 2011, 19:00 #8
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Re: Noise Variance N0 of AWGN
As I said, is in the SNRdB variable. I will give you a simple example for coherent BPSK signaling over AWGN channel:
Code:SNRdB=0:2:30; SNR=10.^(SNRdB./10); Pe=0.5.*erfc(sqrt(SNR)); semilogy(SNRdB,Pe); axis([0 30 10^6 1]);
I hope it is more clear now.

13th March 2011, 09:37 #9
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Re: Noise Variance N0 of AWGN
GREAT the expressing power of david is excellent hatsoff

13th March 2011, 19:23 #10
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Re: Noise Variance N0 of AWGN
i agree thanks

13th March 2011, 19:23

17th February 2013, 10:12 #11
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