• Journal of the Korea Society of Computer and Information
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• v.9 no.2
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• pp.97-104
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• 2004

As a channel of a DS-CDMA system is shared among several users, the receivers face the problem of MAI. Also the bandlimited channel leads to ISI. Both components are undesired, but unlike the additive noise process, which is usually completely unpredictable, their space-time structure helps to estimate and remove them. This paper investigates a DS-CDMA system with a fading multipath channel. The investigations have been separated into a channel estimation part and a reception part. In the estimation part of seperated two parts, the multipath parameters such as DOA and TOA are evaluated in this paper. In the part of receiver. we used these parameters and tested the performance of this receiver about space-time beamformers. To assess many different estimation techniques and beamformers, the simulation compared with theoretical values is performed.

• 전자공학회논문지 IE
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• v.49 no.2
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• pp.46-51
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• 2012

Transmit signal of Enhancement Layer in AT-DMB system is received by Coherent Detection, but in Base Layer of AT-DMB, a differential modulation and demodulation is adopted, same as the T-DMB. Especially for the coherent dectection of enhancement layer in AT-DMB system, a channel estimation must be employed. In this paper, I will show that the BER performance of Base-Layer in AT-DMB system will be improved by using the channel estimation information. The suggested method is focusing the constallations after Equalizaing to the nearlest ${\pi}$/4-shift DQPSK constallation points. Simulation results show that for the non-coding environment, the BER performance of AWGN channel, about 2-dB gain can be achieved at $10^{-4}BER$.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.1-7
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• 2004

The effect of the sub-optimal beam-forming and the fading channel correlation on the closed loop transmit antenna diversity(CTD) system is investigated in frequency flat Rayleigh fading channels. The fast channel fading prevents the perfect channel estimation at a mobile station, hence the imperfect weight is applied to the antenna branch of transmitter. The weight causes sub-optimalbeam-forming and aggravates the performance of CTD system. The fading correlation or a wireless channel also is one of the factors decreasing the diversity gain. A bit error rate expression for the CTD system is analytically derived as a function of the channel estimation error, the channel correlation coefficient the feedback delay, and fading index. It is shown that the channel estimation error gives more severe effect to the system performance than the channel correlation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7C
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• pp.481-487
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• 2011

Cyclic delay diversity (CDD) is a simple transmit diversity technique for an OFDM system using multiple transmit antennas. However, the performance of post-FFT estimation, i.e., integer frequency offset (lFO) is deteriorated by high frequency selectivity introduced by CDD. In this paper, the IFO estimation scheme is proposed for OFDM-based DRM+ system with CDD. Based on the pilot subset partitioning, the proposed IFO estimation scheme reduces the effect of performance degradation caused by frequency selectivity in OFDM systems with CDD . The simulation results show that the performance of the proposed IFO estimator is significantly improved when compared to that of the conventional IFO estimator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4C
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• pp.207-216
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• 2011

Motion compensated extrapolation (MCE) techniques show inferior performance compared to motion compensated interpolation techniques, since only past frames are used in MCE. MCE techniques are used for the reconstruction of corrupted frames, the up-conversion of frame rates and the generation of side information in the distributed video coding system. In this paper, the performance of various MCE techniques are evaluated and an efficient MCE technique using the forward and backward motion estimation is proposed. In the proposed technique, the present frame is extrapolated by averaging two frames which are generated by forward and backward motion estimation respectively. It is shown that the proposed method produces better PSNR results and less blocking phenomena than conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.2
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• pp.191-200
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• 2013

In this paper, we propose a new estimation method of time offset, frequency offset, and signal to interference plus noise ratio (SINR) using the synchronization channel preamble to provide IEEE 802.16.1a based talk-around direct communications (TDC). The proposed scheme estimates the time offset and frequency offset both in the time domain and in the frequency domain considering the preamble structure. In addition, it improves the estimation accuracy by combining the estimated values in two domains taking into account TDC synchronization scenarios. Through numerical simulations in the TDC channel environments, the performance of the proposed algorithm is compared with those of existing techniques such as the time domain estimation and the frequency domain estimation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9A
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• pp.882-890
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• 2008

To overcome the limit of the time-domain based channel estimation caused by the ADC speed, this paper present a new BPM-UWB receiver where the channel estimations and the compensations are digitally performed in the frequency domain. We theoretically show that the channel estimation can be accomplished by exploiting the periodicity of a training sequence consisting of finite number of pulses. We also present the digital receiver structure to implement the proposed system and derive its BER performances. Through computer simulations, we show the proposed receiver can dramatically improve the BER performances due to the incorporation of the estimated channel frequency response.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.175-183
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• 2021

This paper studies measurement of sonic boom created by supersonic flight and its arrival angle estimation techniques. Since sonic boom propagates as an impulsive noise and includes infrasound frequency, we propose measurement instrumentation acquiring sonic boom signature without distortion. And we suggest the methodology for an arrival angle estimation with its performance analysis in accordance with sensor array configurations. The performance of our estimator is verified by comparing theoretical performance bound with statistics of its Monte-Carlo simulation results. Furthermore, we presents the analysis of the sonic boom measurement from real flight tests. This work provides an intuitive concept for sensor array configurations and measurement instrumentation.

• Journal of Broadcast Engineering
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• v.27 no.6
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• pp.944-947
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• 2022

Due to the coronavirus pandemic, the wearing of a mask has been increasing worldwide; thus, the importance of image analysis on masked face images has become essential. Although head pose estimation can be applied to various face-related applications including driver attention, face frontalization, and gaze detection, few studies have been conducted to address the performance degradation caused by masked faces. This study proposes a new data augmentation that synthesizes the masked face, depending on the face image size and poses, which shows robust performance on BIWI benchmark dataset regardless of mask-wearing. Since the proposed scheme is not limited to the specific model, it can be utilized in various head pose estimation models.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10A
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• pp.992-1003
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• 2007

In this paper, a channel estimation technique based on pilot tones, which does not degrade channel estimation performance even with the existence of symbol timing offset (STO) in OFDM systems, is proposed. The proposed technique performs channel estimation by interpolating channels with respect to amplitude and phase with a minimum computational complexity, differently from the conventional interpolation techniques. The proposed technique requires neither the estimation of fine STO in advance nor trigonometric operation for phase interpolation, signifying a significant reduction in computational complexity. Since the performance of the proposed technique does not depend on the STO present in OFDM systems. It can be directly applied to the following areas in OFDM-based communication system: elimination of fine STO estimation step in the synchronization procedure, elimination of STO estimation step in multiuser uplink, and channel estimation in multi-hop relay system. It is verified by computer simulation that the proposed technique can improve the performance of channel estimation significantly in the presence of STOs, compared with previous channel estimation techniques based on pilot tones.