Decision feedback equalizers with constrained feedback taps for reduced error propagation

Error propagation is a serious concern when a decision feedback equalizer (DFE) is used in a communication system. This paper describes a method of mitigating the effects of error propagation by constraining the feedback tap coefficients. It is shown that the most natural method of constraining the feedback taps is to constrain the 1-norm of the tap vector. The paper also considers a constraint on the 2-norm of the feedback tap vector. The proposed method is demonstrated using the trellis coded 8-VSB system used by the ATSC terrestrial broadcast standard for digital television. Results show that the constraints do reduce error propagation in the DFE, but the performance is considerably better when a zero delay trellis decoder is used to determine the decisions in the feedback filter.