Eliminating intersymbol interference -- A state-space approach

The problem of eliminating intersymbol interference is studied from the viewpoint of channel-state estimation. The channel state vector, at the beginning of the present message baud, contains the information required to eliminate the effects of past channel inputs. A receiver is proposed that makes a maximum-likelihood estimate of the channel state vector conditioned upon all previous digits having been received correctly. The channel-state estimate is used to control the motion of a variable decision threshold. Correct adjustment of the threshold removes the effects of past symbols on the present decision. The receiver performance is studied via certain approximation techniques used in the study of threshold learning systems. In particular, the performance of one- and two-pole channels is evaluated. In these cases, the receiver is shown to effectively eliminate intersymbol interference and perform as well as a matched-filter receiver that uses only the signal energy received during one message interval.