INTERSYMBOL INTERFERENCE IN BINARY COMMUNICATION SYSTEMS.

When a binary communication system transmits symbols through a bandlimited channel, the received symbols will generally overlap in time, giving rise to intersymbol interference. In the presence of noise, intersymbol interference produces a significant increase in the system probability of error. The problem of intersymbol interference and noise is considered here for known, linear, time invariant channels and with added white Gaussian noise. Although a particular underwater acoustic channel is used as a source of motivation, the results presented are equally applicable to other communication channels. Traditional approaches to the intersymbol interference problem--spectrum and transversal time equalization are examined. A basis for the comparison of intersymbol interference problems using the concept of phase equalization, is given. A major assumption which limits the interference to that caused by adjacent symbols is made. This assumption is shown to be equivalent to restricting the transmitter to reasonable signalling rates relative to the bandwidth of the channel power spectrum. All subsequent analysis and evaluation are done under this assumption. Several linear filter receivers prevalent in the literature are reviewed and evaluated. Two easily implemented nonlinear receivers are considered as alternatives to the more complex optimized linear filter receivers. The iterated switched-mode receiver is shown to perform better than any optimized linear receiver when intersymbol interference is moderate. Author