The document discusses key parameters for characterizing multipath channels: 1) Coherence bandwidth is the range of frequencies over which the channel can be considered flat and two frequency components will be correlated. It is inversely proportional to the root mean square (RMS) delay spread. 2) Doppler spread is the range of frequencies over which the received Doppler spectrum is non-zero. It characterizes the time-varying nature of the channel. 3) Coherence time is the duration over which the amplitude of two received signals will be correlated. It is inversely proportional to the maximum Doppler shift and characterizes the time-varying nature of the channel.