Error propagation in decision feedback equalization for a terrestrial digital television receiver

In the U.S. terrestrial digital television receiver, when the channel presents additive white Gaussian noise and multipath, particularly strong multipath, error propagation in the feedback filter of a decision feedback equalizer severely affects the performance at the output of the trellis decoder. In these cases, the output of the trellis decoder may present a worse performance when the equalizer is in automatic switching mode rather than in blind mode, even though the opposite is true at the output of the equalizer. In the automatic switching the mode, the equalizer is in blind mode before convergence is detected and switches to decision directed mode after convergence. This work studies the use of a soft automatic switching mode, that is, the equalizer is in blind mode before convergence is detected and switches to a soft decision directed mode after convergence. In the soft decision directed mode, the input to the equalizer feedback filter is the equalizer output, instead of the slicer output, yielding a linear equalizer implementation. By utilizing the soft automatic switching mode in such channel conditions, the performance at the output of the trellis decoder is improved not only with respect to automatic switching mode, but also with respect to blind mode.