matlab awgn psd generation

[mohammadriyaz.g]

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

 

[Communications_Engineer]

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.

 

[mohammadriyaz.g]

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

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

 

[Communications_Engineer]

sqrt(-1), to generate complex white noise

 

[commworld]

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

 

[Communications_Engineer]

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