Robust decision-feedback equalization with a noncausal filter for ATSC DTV receivers

A robust decision-feedback equalization method for ATSC DTV receivers is presented. Under severe channels, such as 0-dB ghost or a distributed transmission environment, decision-feedback equalizers (DFEs), which have been commonly used in ATSC DTV receivers, suffer from error propagation. To improve the robustness to the error propagation, we incorporate a channel-matched filter (CMF) and an intelligent sheer (IS). The use of the CMF prior to the DFE makes severe channels manageable in the DFE, The IS, a trellis decoder with a trace-back depth of 1, enhances a correct-decision probability in the DFE, especially under low SNR conditions. Adoption of the CMF and the IS clearly enhances the robustness of the DFE but may degrade the output SNR due to unwanted pre-ghosts caused by channel-matched filtering. We employ a noncausal all-pass filter operating in reversed time to preserve the robustness acquired by the CMF and the IS without the degradation of the output SNR. The noncausal filter changes an input channel with pre-ghosts into an approximately minimum-phase channel without pre-ghosts. Simulation results show that the proposed equalization scheme achieves the more stable convergence and the higher SNRs than the existing DFEs.