ABSTRACT
Adaptive channel equalization is required for channels whose characteristics change with time. Many communication channels, including telephone channels and some radio channels, may be generally characterized as band-limited linear filters. The extent of the intersymbol interference on a telephone channel can be appreciated by observing a frequency response characteristic of the channel. Besides telephone channels, there are other physical channels that exhibit some form of time dispersion and, thus, introduce intersymbol interference. Radio channels, such as short-wave ionospheric propagation, tropospheric scatter, and mobile cellular radio are three examples of time-dispersive wireless channels. The total time duration of the channel response is approximately 0.7 µs on the average, and the spread between half-power points in Doppler frequency is a little less than 1 Hz on the strongest path and somewhat larger on the other paths. In practice, the intersymbol interference caused by channel distortion is usually limited to a finite number of symbols on either side of the desired symbol.
