Wan-Jin Kim

A Higher Data-Rate T-DMB System Based on a Hierarchical A-DPSK Modulation

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.

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.

Detection of Hierarchically-Modulated Data for Advanced T-DMB Receivers

This paper proposes an efficient detection method of hierarchically-modulated data for an advanced terrestrial digital multimedia broadcasting (AT-DMB) receiver. Hierarchical modulation, where low-priority (LP) symbols are hierarchically added to the existing high-priority (HP) symbols, has been considered to be useful for increasing the data rate in AT-DMB systems. The distance between two neighboring LP symbols is limited by the noise margin of HP symbols and thus should be shortened to minimize the effect on the detection of HP symbols. To cope with the poor condition of LP symbols, we introduce a coherent detection method based on coded decision-directed (CDD) channel estimation (CE). CDD-CE may provide an accurate estimation result even under the infrequent pilot arrangement of the T-DMB system. Additionally, we propose a moving average (MA) method in frequency direction to reduce noise existing in the estimated channel coefficients. Simulation results show that the proposed method can be a good solution to successfully detect LP data.

Denoising method for weak-power radar signals using the modified sinc wavelet

Electronic warfare (EW) is commonly divided into three subfields: electronic warfare support (ES), electronic attack (EA), and electronic protection (EP). Among them, ES systems take charge of collecting and analyzing the received signal from enemys emitters and then provide the processed information to friendly EA and EP systems. The information is of critical importance because it is the first prerequisite for the proper discharge of duties of EA and EP systems and is directly linked to the issue of a battle. However, ES systems have difficulty in carrying out their jobs because there are some cases of having no information about enemys operating frequency and the received signal power is sometimes seriously weak. In this paper, we propose a novel method to solve these problems at once based on the modified wavelet transform by using the unique scaling property of continuous time wavelet transform and the frequency shifting property. Computer simulation results show that the proposed method can be useful and practical to cope with low SNR environment.

Performance analysis on demodulation of the base layer in the AT-DMB system

In the advanced T-DMB (AT-DMB) system, the performance of the base layer is affected by both modulation noise and a demodulation method. The amount of modulation noise is determined by the hierarchy parameter of the transmitter, and thus it is not controllable at the receiver. On the other hand, a demodulation method for the base layer can be freely selected by the designer and it dominates the performance of the base layer. This paper focuses on the performance analysis of the base layer in the AT-DMB system according to the choice of a demodulation method and provides useful information for designing receivers for the AT-DMB system.

An Adaptive IIR Pre-Equalizer for Terrestrial DTV Transmitters

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

Range Estimation Method in a Short-Range FMCW Sonar

We propose a range estimation method for a short-range frequency-modulated continuous wave (FMCW) sonar. Due to the slower sound wave and the greater Doppler effect of the FMCW sonar, the beat frequency of the FMCW sonar cannot keep the constant duration unlike the beat frequency of the FMCW radar. To cope with the drawback of the FMCW sonar, in the proposed method the rising edge and the falling edge of the beat frequency are utilized. This leads us to normally estimate the range of a high-speed underwater vehicle in short-range situation. Simulation results show that the proposed method can estimate the range from the measurements where the Doppler effect is exactly reflected according to the maneuver scenario of high-speed underwater vehicles.

Analysis of performance penalties in hierarchical DQPSK modulation systems

In hierarchical modulation (HM) based on DQPSK modulation, the performance of the receiver is influenced by the modulation noise and the demodulation method for base layer. To design an HM system, these performance penalty factors should be analyzed. This paper presents useful information for designing HM systems by doing mathematical and numerical analysis on their performance penalties.

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.