Jong Soo Lim

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.

Coded Decision-Directed Channel Estimation for Coherent Detection in Terrestrial DMB Receivers

This paper proposes a coded decision-directed (DD) channel-estimation method with two-dimensional averaging for T-DMB receivers. Since the noncoherent differential demodulation of existing T-DMB receivers can not track channel variation, it may not work well in fast-fading channels. To overcome this problem, coherent detection based on channel estimation is introduced. The proposed method re- modulates the output of the soft-decision Viterbi decoder for coded DD channel estimation to obtain more accurate decision symbols than hard-decision symbols. To both mitigate the effects of noise and smooth incorrectly-estimated coefficients, the estimated channel coefficients are two- dimensionally averaged. The enhanced accuracy leads to the high-performance DQPSK demodulation robust to Doppler spread and noise. The proposed method may also contribute to the launch of the future T-DMB service of providing a higher data rate. Simulation results show that the proposed scheme performs much better than the conventional method, especially at high speed-moving receivers.

A Robust Symbol Synchronization Method for Terrestrial-DMB Receivers in the Hierarchical Modulation Mode

Recently, hierarchical modulation has been considered as a way to increase the payload data in terrestrial digital multimedia broadcasting (T-DMB) transmission systems. This paper proposes a robust symbol synchronization method for T- DMB receivers working in the hierarchical modulation mode. The proposed method employs a timing error detector (TED) which produces a timing phase error at OFDM symbol rate instead of the frame rate. This method thus results in the robust synchronization of symbol timing in the presence of a sampling frequency offset (SFO). Simulation results show that the proposed method outperforms the conventional one especially at a large SFO .

Directional diversity reception for ATSC 8VSB

We propose a reception improvement method for ATSC (Advanced Television Systems Committee) 8 VSB in severe multipath channel using directional diversity. The VSB system has only about 0.3% of known training signal for the receiver in a data field and the reception performance of VSB receiver is degraded significantly when there are near-0 dB ghosts in received signal. To overcome this problem, the directional diversity is suggested. By applying directional diversity, we can eliminate undesired multipaths, so improve 8 VSB reception performance. We demonstrate the performance of proposed method under severe multipath channel and show it can improve the reception of 8 VSB system.

Implementation of Transmitter Identification Signal Analyzer in Single Frequency Network

This paper presents the transmitter identification (TxID) signal analyzer for the ATSC terrestrial digital TV system in single frequency networks (SFNs). The structure of the TxID signal analyzer and its practical use in SFN environment are presented with a theoretical approach of the performance measurement The proposed TxID signal analyzer shows robustness at low carrier to noise ratio (CNR), and improvement of analyzing performance using ensemble averaging scheme. The laboratory test results are provided to evaluate the performance of TxID signal analyzer.

Data Broadcasting Server and Receiver for Middleware based Data Services in Terrestrial DMB

In this paper we present a data broadcasting server and receiver that can be used for middleware based data services in T-DMB. The middleware for interactive data service in T-DMB is known as T-DMB MATE (mobile application terminal environment), defining a context for running the applications and APIs. The presented data server and T-DMB MATE receiver are effectively designed to supply applications through several way including broadcasting network and to execute on the various type of receiver, so that the high-level functionalities can be provided to users in the interactive data service. Finally, the performance of the implement system is confirmed through the T-DMB experimental data broadcasting.

A Novel On-Channel Repeater for Terrestrial-Digital Multimedia Broadcasting System of Korea

This paper presents an equalization on-channel repeater (OCR) for terrestrial-digital multimedia broadcasting (T-DMB) system of Korea. The proposed OCR uses a time-domain equalizer based on adaptive complex FIR filtering to remove a feedback signal due to incomplete antenna isolation and multipath signal existing between a main transmitter and the OCR. This makes it possible to emit a high-power error- corrected signal from the OCR.

New Bit Mapping for Hierarchically Modulated DAB and Terrestrial DMB

Hierarchical modulation is considered for increased data rate in the next-generation DAB (digital audio broadcasting) or T-DMB (Terrestrial digital multimedia broadcasting) system, which supports backward compatibility to the conventional DAB or T-DMB. Since dedicated pilot signal is not available due to the constraint of backward compatibility, decision-directed channel estimation schemes should be employed at the receiver. In this paper, we propose a new bit mapping scheme for hierarchical modulation which guarantees robust channel estimation against decision errors.

Pre-equalization Method to Minimize Time Delay of Equalization Digital On-Channel Repeater in ATSC System

This paper presents a novel pre-equalization method to minimize the signal processing time delay of the equalization digital on-channel repeater (EDOCR) for the ATSC terrestrial digital TV system. The proposed pre-equalization method is to calculate pre-equalizer filter coefficients by using a baseband signal as a reference signal and a demodulated repeater output signal, then to create new VSB pulse shaping filter coefficients by the convolution of the equi-ripple (ER) filter and the pre-equalizer filter coefficients. The new VSB pulse shaping filter minimizes the time delay of the EDOCR by adjusting the number of its pre-taps and also compensates the linear distortions due to the use of the ER filter and mask filter.

Coded Decision Directed Channel Estimation for Terrestrial DMB Receivers

This paper presents a coded decision-directed channel estimation method with two-dimensional averaging for T-DMB receivers. The proposed channel estimator produces channel coefficients robust to Doppler spread and noise, making it possible for high-performance coherent DQPSK demodulation. Simulation results show that the proposed method has better performance than the conventional method, especially at high speed-moving receivers.