Combined feedforward filter for a decision feedback equalizer
View Patent ↗A method and apparatus for mitigating for inter-symbol interference in a communication system using a multi-rate adaptive decision feedback equalizer (DFE) with a feedforward filter which is a combination of a first feedforward filter (FF 1 ) that performs match filtering and a second feedforward filter (FF 2 ) which runs at a lower sampling rate than first feedforward filter (FF 1 ), thereby, reducing the total the number of computation done at the receiver, and removes ISI and white noise. The present invention also employs a method and apparatus where the initial training is done separately for the first feedforward filter (FF 1 ) and the second feedforward filter (FF 2 ). An approximate solution of the optimal receiver has the first feedforward filter (FF 1 ) maximize the output signal to noise ratio (SNR) which is used to train first feedforward filter (FF 1 ).
1. A method for adaptively mitigating inter-symbol interference, the method comprising:
receiving an impaired signal that comprises a successive number of symbols transmitted at a predetermined transmit symbol time;
filtering the successive number of symbols with a first feedforward filter to maximize a signal to noise ratio and produce a filtered output;
filtering the filtered output with a second T-spaced feedforward filter; and
training the first feedforward filter and the second T-spaced feedforward filter separately, wherein a helper filter is used to train first feedforward filter wherein the helper filter that is used to train the first feedforward filter receives ideal reference samples as an input.
2. The method of claim 1 , wherein first feedforward filter uses a criterion of maximizing the signal to noise ratio to train first feedforward filter.
3. An apparatus for adaptively mitigating for inter-symbol interference, comprising:
a receiver for receiving an impaired signal that comprises a successive number of symbols transmitted at a predetermined transmit symbol time;
a first feedforward filter for filtering the successive number of symbols to maximize a signal to noise ratio and produce a filtered output;
a second T-spaced feedforward filter for filtering the filtered output; and
a training device for training the first feedforward filter and the second T-spaced feedforward filter separately, wherein a helper filter is used to train the first feedforward filter wherein the helper filter that is used to train the first feedforward filter receives ideal reference samples as an input.
4. The apparatus of claim 3 , wherein the first feedforward filter uses a criterion of maximizing a signal to noise ratio to train first feedforward filter.