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Hierarchical modulation can be effectively used to enhance terrestrial digital multimedia broadcasting (T-DMB) or digital audio broadcasting (DAB) systems in response to both the demand for higher data-rate and the need to be backward compatible with legacy receivers. QAM-type modulations are well-liked for hierarchical transmission but require coherent detection based on pilot symbol aided channel estimation. In the T-DMB or the DAB system using DQPSK modulation, however, any available pilot symbols except for the phase reference symbol do not exist. Differential amplitude phase shift keying (DAPSK) modulation is easily applied to the T-DMB system for a hierarchical modulation but may be susceptible to fast fading. As a good candidate for a hierarchical modulation of T-DMB to solve the above problems, we propose an amplitude differential phase shift keying (A-DPSK) modulation which is robust to fast fading by estimating only amplitude coefficients of the channel transfer function with the use of amplitude pilots. To raise the accuracy of channel estimation, we arrange the amplitude pilots in a come-type and introduce a noise-reduction scheme of averaging estimated channel coefficients. Simulation results show that the proposed A-DPSK provides a good choice for achieving a higher data-rate over other possible modulation schemes for advanced T-DMB or DAB systems. Index Terms--A-DPSK, DAB, DAPSK, DMB, hierarchical modulation.

This paper proposes an iterative extrapolation method to improve the channel-equalization performance for DVB-T receivers. The coefficients of a one-tap equalizer are conventionally obtained by taking the reciprocals of the estimated channel coefficients. Inversion of the channel coefficients, however, may cause noise enhancement at those frequencies corresponding to spectral nulls. To reduce such undesirable noise amplification, iterative extrapolation based on the time-domain truncation is performed, resulting in smooth nulls. Simulation results show that the proposed method improves the channel-equalization performance compared to the conventional zero-forcing equalization method in terms of bit error rates in DVB-T receivers at all SNRs. Index Terms--DVB-T, equalization, extrapolation, noise enhancement, OFDM.

A novel pre-equalization method for terrestrial DTV transmitters is presented. A pre-equalizer is used in transmitters to correct group delay and amplitude distortions caused by a channel filter. In the proposed pre-equalizer, an equation-error adaptive IIR filtering scheme is adopted unlike the conventional pre-equalization using FIR filtering. The pole-zero modeling property of IIR filters improves the signal-to-noise ratio by compensating for various linear distortions existing in DTV transmitters as well as the channel filter distortion. Simulation results show that the proposed IIR pre-equalizer performs better than the FIR pre-equalizer in terms of the residual mean-square error. Index Terms--Channel filter, DTV, IIR, pre-equalizer, transmitter.

This paper analyzes the error propagation phenomenon in the decision feedback equalizer (DFE) for the receivers of Advanced Television Systems Committee (ATSC) digital television (DTV) and presents the performance upper-limits of the DFE by comparing various error propagation cases and the no-error propagation case. As one approach to the performance limit, we consider a blind DFE, adopting a trellis decoder with a trace-back depth of 1 as a decision device. Through simulation, we show how much the DFE performance in ATSC DTV receivers is affected by error propagation. We found that while blind equalization is preferable to decision-directed (DD) equalization at signal-to-noise ratio (SNR) values less than 18 dB, DD equalization is superior to blind equalization at SNR values greater than 18 dB. In addition, symbol error rate curves quantitatively show that the performance difference in the DFE caused by error propagation becomes clearer at the trellis decoder following the DFE. The analysis results presented in this paper will be very informative for developing equalization algorithms for ATSC DTV receivers. Index Terms--ATSC, blind equalization, DFE, DTV, error propagation.