Effect of noise on Power Spectral Density

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ipmax

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Hi all,

How does noise affect the PSD of a received signal.
y = x + n
PSD = PSD(x) + PSD
So, the PSD of received signal is higher in all frequencies as compared to the transmitted signal.
So, if my understanding is correct, if at a particular frequency PSD(x) = -10 dB and white noise PSD = -25dB, the received signal will have PSD of -35 dB at that frequency. Is this understanding correct?

Thanks,
Max
 

The signal represention

y=x+n

refers to linear quantities (e.g.: Watt). Then if you have the PSD in dBm you have to conver it first to linear.
in your example:

PSD(x) = -10 dBm/Hz --> 10exp(-4) W/Hz
PSD = -25 dBm/Hz --> 3.2exp(-6) W/Hz

PSD = 10*Log[10exp(-4)+3.2exp(-6)]+30 = -9.86 dBm/Hz
 

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