Flat fading:

• Channel response in flat fading impaired signal has flat gain/linear phase over bandwidth (BW) which is greater than signal BW.
• In the flat fading all the components of the frequency of the signal will have the same magnitude of fading with respect to each other.
• Flat fading, is that type of fading in which all frequency components of the received signal fluctuate in the same proportions simultaneously.

• Signal undergoes flat fading if following conditions are met:

  Bs << Bc

  Ts >>στ

Selective Fading:

• In selective fading, channel response of signal has constant gain/linear phase over bandwidth (BW) which is less than that of signal BW.

• Here different components of the frequency signal will not experience the same fading.

• Selective fading affects unequally the different spectral components of a radio signal.

• Signal undergoes selective fading if following conditions are met:

  Bs >Bc

  Ts <στ