Coherent Detection for T-DMB Receivers in Hierarchical Modulation Mode

Hierarchical modulation has been considered for achieving higher data rates in Terrestrial-DMB (T-DMB) systems, which yields man-made noise caused by the shortened symbol distance. Such noise may produce a serious problem on a fast-fading channel for the proper operation of conventional T-DMB receivers using noncoherent differential detection because it can increase the required SNR larger than the securable SNR of the receivers. To overcome the weakness of being susceptible to fast fading of the noncoherent detection, we propose a novel decision-directed channel estimation method for the coherent detection of phase correction. In the proposed method, least-squares channel estimation is carried out with hard-decision symbols due to the absence of known pilots and then the estimated coefficients are exponentially averaged using a forgetting factor to compensate for the probable inaccuracy of the instantaneous estimation. Simulation results show that the proposed method secures higher data-rate transmission of advanced T-DMB systems by reducing the degradation caused by hierarchical modulation and fast fading.