How are the Intersymbol Interference and Symbol Time (duration) related to each other

basicModulationmultiplexerwireless

In a lecture slide I noticed that OFDM(Orthogonal frequency-division multiplexing) mitigates the problem of Intersymbol Intereference over wireless systems because the symbol time is increased, in the case when we multiplex a channel into two subchannels, each with bandwidth half of the bandwidth of the original channel.

However, I can not grasp how the length of the Symbol time is related to Intersymbol Interference?

Best Answer

Intersymbol interference is a property of the communications channel; it causes information to be spread out in the time domain.

To reduce ISI, you can either decrease the time spread in the channel or increase the symbol time of the encoding method — either way, the smearing expressed as a fraction of the total symbol time is reduced.