Coherence time (communications systems)
In communications systems, a communication channel may change with time. Coherence time is the time duration over which the channel impulse response is considered to be not varying. Such channel variation is much more significant in wireless communications systems, due to Doppler effects.
Simple model
In a simple model, a signal transmitted at time will be received as
where is the channel impulse response (CIR) at time . A signal transmitted at time will be received as
Now, if is relatively small, the channel may be considered constant within the interval to .
Coherence time () will therefore be given by
Relation with Doppler frequency
Using Clarke's model, from the maximum Doppler frequency we can obtain 50% coherence time [1][2]
Usually, we use the following relation[2]
References
This article is issued from Wikipedia - version of the Saturday, April 16, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.