Advances in Equalization for Intersymbol Interference

Publisher Summary This chapter discusses the advances in equalization for intersymbol interference. In data transmission, the time dispersion imparted on the transmitted signal results in an overlap in time between successive symbols that is called intersymbol interference. All physical channels exhibit some form of time dispersion and, thus, introduce intersymbol interference. The signal processing technique that is employed to cope with time-variant intersymbol interference conditions must include some means of measuring and tracking the channel response. Such operations are most conveniently performed at the receiving terminal of the communication system. All signals and filter response functions are written for convenience in complex-valued low pass equivalent form although in the physical system, they are real-valued band pass signals and filters. The channel through which the signal is transmitted is characterized in general by a time-variant impulse response. It is necessary that a time-variant channel have time variations that are much slower than the duration of the signaling interval. Fixed equalizers are designed to compensate the response characteristics of a typical or average telephone channel. As a probe signal for the channel, a series of nonoverlapping pulses were transmitted that were then compared with the desired—undistorted—pulses at the receiving terminal. The error signal generated at the receiver by comparing the distorted received pulses with the undistorted replicas was used to adjust the parameters of the transversal equalizer.