Relationship between 'Channel Decimation Ratio' and fading waveform?

Did you mean Discrimination ratio? Like in signal to noise ratio? If so, are you asking what happens when your waveform fades or gets weaker and your received signal to noise ratio gets worse (ie 3dB vs 12 dB)?

Hi - it sounds as though you have a flat fading channel model where a new set of channel gain and phase shift characteristics are calculated only occasionally (i.e. the fade charactristics change only slowly compared with the signal that you want to receive so the description of the fading only needs to change every few tens/hundreds of signal samples.