An apparatus and method for implementing an equalizer which combines the
benefits of a decision feedback equalizer (DFE) with a
maximum-a-posterori (MAP) equalizer (or a maximum likelihood sequence
estimator, MLSE) to provide an equalization device with significantly
lower complexity than a full-state MAP device, but which still provides
improved performance over a conventional DFE. The equalizer architecture
includes two DFE-like structures, followed by a MAP equalizer. The first
DFE forms tentative symbol decisions. The second DFE is used thereafter
to truncate the channel response to a desired memory of L.sub.1 symbols,
which is less than the total delay spread of L symbols of the channel.
The MAP equalizer operates over a channel with memory of L.sub.1 symbols
(where L.sub.1<=L), and therefore the overall complexity of the
equalizer is significantly reduced.