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# matlab awgn psd generation

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##### Newbie level 6
i wanted to add awgn of -140db to the ,psd of other signals in matlab .How to generate or add awgn of -140 db to that psd.I don't have any snr value to use awgn(x,snr )function.plz suggest me

1. convert -140dB into linear scale. Say it is NoiPow

2. let Sig is a vector containing your other signals

3. In Matlab type

Noise = [randn(1,length(Sig))+j*randn(1,length(Sig))]/sqrt(2);
NoisySignal = Sig + Noise*sqrt(NoiPow)

I hope I have not made a mistake here.

by the way, a noise of -140dB is too small. I wonder how much power your signal has. If it is large -140dB should not cause you any trouble.

what is "j" (red colour)in the given noise expression?

Noise = [randn(1,length(Sig))+j*randn(1,length(Sig))]/sqrt(2);

sqrt(-1), to generate complex white noise

can u tell me whats the significance of the 'complex' noise?

if your transmission is complex i.e. real and quadrature, the complex white noise is used to add noise to both the component parts

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