Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

One sided noise spectral density VS double sided noise spectral density

  1. Apr 5, 2011 #1
    No is the one sided noise spectral density in communication systems. N is the double sided noise spectral density.

    The relationship between them is given by 2N = No but I don't understand why it is like that. Why isn't it N = 2No instead?!
     
  2. jcsd
  3. May 6, 2011 #2

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    A complex signal like [tex]\exp{i\omega_0 t}[/tex] has a one-sided spectrum, in this case [tex]\delta(\omega-\omega_0)[/tex]. Its real counterpart [tex]\cos{\omega_0 t}[/tex] has the two-sided spectrum

    [tex]\frac{1}{2}[\delta(\omega-\omega_0)+\delta(\omega+\omega_0)][/tex]

    The same power is spread in the real-signal case over positive and negative frequencies, each of which is half as large as the complex spectrum.

    When you talk of the power spectral density (PSD) of thermal noise, it again matters whether you are using a real or a complex representation. Audio engineers often use the former, for instance, communications engineers generally the latter. For white noise where the PSD is a constant, and using your notation where N is two-sided and N0 is one-sided, they are related by N0 = 2N.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: One sided noise spectral density VS double sided noise spectral density
  1. Noise Problems (Replies: 4)

  2. Side thrust (Replies: 2)

Loading...