Editing Fading (section)

==Mitigation==

Fading can cause poor performance in a communication system because it can result in a loss of signal power without reducing the power of the noise. This signal loss can be over some or all of the signal bandwidth. Fading can also be a problem as it changes over time: communication systems are often designed to adapt to such impairments, but the fading can change faster than the adaptations can be made. In such cases, the probability of experiencing a fade (and associated bit errors as the [[signal-to-noise ratio]] drops) on the channel becomes the limiting factor in the link's performance.

The effects of fading can be combated by using [[Diversity scheme|diversity]] to transmit the signal over multiple channels that experience independent fading and coherently combining them at the receiver.  The probability of experiencing a fade in this composite channel is then proportional to the probability that all the component channels simultaneously experience a fade, a much more unlikely event.

Diversity can be achieved in time, frequency, or space.  Common techniques used to overcome signal fading include:

* [[Diversity reception|Diversity reception and transmission]]
* [[Multiple-input multiple-output communications|MIMO]]
* [[OFDM]]
* [[Rake receiver]]s
* [[Space–time code]]s
* [[Forward error correction]]
* [[forward error correction#Interleaving|Interleaving]]

Besides diversity, techniques such as application of [[cyclic prefix]] (e.g. in [[OFDM]]) and [[channel estimation]] and [[Equalization (communications)|equalization]] can also be used to tackle fading.