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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 flat-fading 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

    •   Alt5th March 2011, 20:08

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    Re: Noise Variance N0 of AWGN

    Actually sir, the formula of the received SNR over flat-fading 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
    and continue using the linear scale in your calculation. You have to compute the BER over a range of SNRs, so or equivalently is not constant. I mean, if is constant you will get a point, not a curve of BER. Later on, you can fix after you see the performance of the system versus SNR, and which SNR satisfies the target BER.

    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



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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?



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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 end-to-end 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



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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.




    •   Alt6th March 2011, 20:43

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    Re: Noise Variance N0 of AWGN

    Quote Originally Posted by angel18 View Post
    I do not understand with Noise Variance NO of AWGN who can explain to me.
    help me. thanks.

    What do not you understand about noise variance?



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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



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    Re: Noise Variance N0 of AWGN

    Quote Originally Posted by mish111990 View Post
    no i understand it, its jus that in the matlab program would i consider it fixed or varying randomly
    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]);
    So, again, you don't have to define explicitly. However, it is constant. For example, when you say that the SNR=1, it means that the signal power equals the noise power in effective bandwidth. If SNR<1, then the signal power is less than the noise power, and likewise if SNR>1, then the signal power is greater than the noise power.

    I hope it is more clear now.



    •   Alt7th March 2011, 19:00

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    Re: Noise Variance N0 of AWGN

    GREAT the expressing power of david is excellent hatsoff



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    Re: Noise Variance N0 of AWGN

    i agree thanks



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    Re: Noise Variance N0 of AWGN

    hello guys,

    i am trying to code the below SINR equation

    any clue how to calculate the path gain and if i should keep everything in dB or not

    Click image for larger version. 

Name:	SINR.png 
Views:	9 
Size:	32.4 KB 
ID:	87062



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