HIGH PERFORMANCE EQUALIZER WITH ENHANCED DFE HAVING REDUCED COMPLEXITY
An apparatus and method for implementing an equalizer which (1) combines the benefits of a decision feedback equalizer (DFE) with a maximum-a-posterori (MAP) equalizer (or a maximum likelihood sequence estimator, MLSE) (2) performs equalization in a time-forward or time-reversed manner based on the channel being minimum-phase or maximum-phase 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 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 1 symbols (where L 1 <=L), and therefore the overall complexity of the equalizer is significantly reduced.
1 . An equalizer apparatus for equalizing a data signal received from a channel, the apparatus:
a channel estimator for providing an estimated channel response of the channel; and
a decision feedback equalizer operable to perform equalization of the signal in one of a time-forward manner and a time-reversed manner based on the estimated channel response.
2 . The equalizer apparatus of claim 1 , wherein the decision on whether to perform equalization of the signal in a time-forward manner or in a time-reversed manner is based on the estimated channel response.
3 . The equalizer apparatus of claim 1 , wherein the channel estimator is operable to determine the relative energies of a leading part and a trailing part of a channel profile.
4 . The equalizer apparatus of claim 3 , wherein the decision feedback equalizer is operable to perform equalization of the signal in a time-forward manner if the energy of the leading part of the channel profile is greater than the energy of the trailing part and in a time-reversed manner if the energy of the leading part of the channel profile is less than the energy of the trailing part.
5 . The equalizer apparatus of claim 1 , wherein the apparatus is used in a Global System for Mobile Communication (GSM) system.
6 . The equalizer apparatus of claim 1 , wherein the apparatus is used in an Enhanced Data for Global Evolution (EDGE) system.
7 . The equalizer apparatus of claim 1 , wherein the channel response is classified on a burst/time slot basis.
8 . A method for equalizing data signals received from a channel, the method comprising:
estimating a channel response of the channel; and
performing decision feedback equalization of the signal in one of a time-forward manner and a time-reversed manner based on the estimated channel response.
9 . The equalizer apparatus of claim 8 , wherein the decision on whether to perform decision feedback equalization of the signal in a time-forward manner or in a time-reversed manner is based on the estimated channel response.
10 . The method of claim 8 wherein estimating the channel response comprises determining the relative energies of a leading part and a trailing part of a channel profile.
11 . The method of claim 10 wherein performing decision feedback equalization comprises performing equalization of the signal in a time-forward manner if the energy of the leading part of the channel profile is greater than the energy of the trailing part and performing decision feedback equalization in a time-reversed manner if the energy of the leading part of the channel profile is less than the energy of the trailing part.
12 . The method of claim 8 , wherein estimating the channel response includes utilizing a sequence of training symbols in the received signal to facilitate estimation of the channel response.
13 . The method of claim 8 , wherein the method is applied to a receiver in a GSM system.
14 . The method of claim 8 , wherein the method is applied to a receiver in an EDGE system.
15 . The method of claim 8 , wherein the estimated channel response is classified on a burst/time slot basis.