# Frequency selective fading Frequency response of the channel is not flat. Thus different frequency components have different attenuations (fading) when [BW](Bandwidth.md) of the [Tx](Transmitter.md) signal is > [coherence bandwidth](Coherence%20bandwidth.md). i.e. $y(t) = \alpha_1x(t-t_1)+\alpha_2x(t-t_2)+\alpha_3x(t-t_3)+...+n(t)$ ## How many paths? There are approximately $B/B_C$ possible paths (since you chop the [BW](Bandwidth.md) into slots of [coherence bandwidth](Coherence%20bandwidth.md)) ## Assumptions 1. Paths are assumed to be independent ## How to fix? - A [channel equaliser](channel%20equaliser.md) is needed. - [OFDM](Orthogonal%20frequency%20division%20multiplexing.md) # References 1. # Footnotes