A concatenated equalizer/trellis decoder architecture for a terrestrial digital television receiver

Abstract

In the U.S. terrestrial digital television receiver, when the terrestrial channel presents multipath and additive white Gaussian noise, particularly strong multipath, error propagation in the feedback filter of a decision feedback equalizer (DFE) severely affects the performance at the output of the trellis decoder. The performance degradation occurs when incorrectly detected symbols are fed through the feedback filter. Then, instead of mitigating intersymbol interference (ISI) from the cursor symbol, the DFE enhances ISI. Error propagation causes bursts of decision errors and a corresponding increase in the average probability of bit or symbol error. This work evaluates the performance improvement achieved by a concatenated equalizer/trellis decoder architecture for the receiver whereby the re-encoded trellis decoder outputs are used as the input to the DFE feedback filter. In addition, the soft output Viterbi algorithm (SOVA) is proposed for trellis decoding in order to achieve additional gains.