Page "Intersymbol interference" Paragraph 1

One of the causes of intersymbol interference is what is known as multipath propagation in which a wireless signal from a transmitter reaches the receiver via many different paths.

The causes of this include reflection ( for instance, the signal may bounce off buildings ), refraction ( such as through the foliage of a tree ) and atmospheric effects such as atmospheric ducting and ionospheric reflection.

Since all of these paths are of different lengths-plus some of these effects will also slow the signal down-this results in the different versions of the signal arriving at the receiver at different times.

These delays mean that part or all of a given symbol will be spread into the subsequent symbols, thereby interfering with the correct detection of those symbols.

Additionally, the various paths often distort the amplitude and / or phase of the signal thereby causing further interference with the received signal.