• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.709-712
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• 2001

본 논문은 광대역 무선통신 채널환경에서 3GPP 표준안에 기반한 비동기식 IMT-2000 시스템의 송수신기를 구성하여 수신단의 기지국 수신성능을 분석한다. 다중 경로 페이딩 모델로는 ITU-R M.1225에서 제시된 모델을 적용하였으며, 이동국과 기지국의 Uplink 채널환경을 고려하였다. 성능개선 기법으로 어레이 안테나를 채용하였고, 동일채널 간섭제거기와 레이크 수신기를 혼합하여 기존의 레이크 수신기에서 제거할 수 없었던 자기 간섭(Auto Interference)을 제거하는 새로운 레이크 수신기를 제안하였다. 성능 분석 결과, 제안된 레이크 수신기는 자기 간섭 제거로 인한 성능개선 효과를 얻을 수 있었으며 또한, 어레이 안테나를 채용하여 다중접속간섭으로 인한 성능열화를 보상할 수 있었다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.319-322
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• 2001

본 논문에서는 단거리 M/W 전송장비에서 사용 가능한 10Mbps 급 OFDM/QPSK 시스템을 제안하였다. OFDM 변조 신호는 two-ray 다중경로 페이딩의 영향을 받는다. 채널 모델은 Rummler가 제안한 마이크로파 대역의 two-ray 채널 모델을 사용하였다. 수신단에서는 다중 경로 채널에 따른 성능 왜곽을 보상하기 위해 여분의 Training Sequence 또는 Pilot 심볼 없이 등화를 행할 수 있는 Blind 적응 등화기를 채택하였다. OFDM 시스템에 따른 두 가지의 등화기, Pre-FFT 적응 등화기와 주파수 적응 등화기 및 두 개의 등화기를 결합한 병행 적응 등화기를 각각 시스템에 도입하여 성좌도와 SER 성능 곡선을 통해 성능 개선 정도를 분석하였다. 분서결과로부터 주파수 적응 등화기와 Pre-FFT 적응 등화기의 각각의 특성을 확인할 수 있었으며, 또한 병행 적응 등화기의 도입에 따른 시스템 개선 정도를 확인할 수 있었다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2004.11a
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• pp.193-196
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• 2004

본 논문에서는 열악한 주파수 선택적 페이딩이나 고속 페이딩 채널 환경에서 ATSC(Advanced Television System Committee) DTV 수신기의 등화 성능 향상을 위해 필터 탭을 선택적으로 사용하는 스파스 적응 등화기 구조를 제안한다. 제안된 등화기는 채널 추정을 수행한 후 등화기 초기화를 위한 탭 계수를 찾는다. 구해진 등화기 탭의 초기화 계수에 대해 특정 임계값을 적용하여 유효한 탭을 선택하여 활성화시킨다. 그리고 활성화 된 탭만을 이용하여 채널 등화를 수행한다. 결과적으로 기존 등화기와 동일한 탭 길이를 가지 고 있지만, 실제 사용하는 탭 수가 작아지므로 등화기의 단계상수를 크게 만들어 고속 페이딩 채널의 변화를 빠르게 추적할 수 있게 된다. 제안된 등화기 알고리듬의 성능 개선을 확인하기 위한 실험으로 ATSC DTV 성능분석 시 일반적으로 사용되는 브라질 채널 및 ATSC등화 성능 요구 조건에 대해 기존의 등화기와 비교 분석하였다. 그 결과 기존의 등화기와 같은 안정성을 가지면서 빠른 수렴 속도를 가지고 고속 페이딩 채널 보상 능력의 큰 향상을 보였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.4
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• pp.884-892
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• 1996

An adaptive blind equalizer is used to combat the distortions caused by a nonideal channel without resorting to a training sequence, given the received signal and statistical information of the transmitted signal. Incidentally, a multipath channel may result in a fade which produces intersymbol interference in the received signal. Therefore, a new type of algorithm which can compenste the effects of this fade is required in the multipath channel environment. In this paper, a modified form of adaptive blind equalization algorithm using stop-and-go algorithm for multichannel system is proposed. It is demonstrated via computer simulations that the performance of the proposed multichannel stop-and-go algorithm is much better than that of the conventional multichannel algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3A
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• pp.168-177
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• 2005

In this paper, we numerically investigated the optimum pump light power resulting best compensation of pulse distortion due to both chromatic dispersion and self phase modulation (SPM) in long-haul 3×40 Gbps wavelength division multiplexing (WDM) systems. We used mid-span spectral inversion (MSSI) method with path-averaged intensity approximation (PAIA) as compensation approach, which have highly nonlinear dispersion shifted fiber (HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that HNL-DSF is an useful nonlinear medium in OPC for wideband WDM transmission, and in order to achieve the excellent compensation the pump light power is selected to equal the conjugated light power into the latter half fiber section with the input light power of WDM channel depending on total transmission length. Also we confirmed that compensation degree of WDM channel with small conversion efficiency is improved by using pump light power increasing power conversion ratio upper than 1.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.128-134
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• 2003

In this paper, we investigated the degree of compensation for WDM channel signal distortion due to chromatic dispersion, self phase modulation (SPM) and cross phase modulation (XPM) as a function of transmission length using mid-span spectral inversion (MSSI) compensation method. The considered system is $3{\times}40$ Gbps intensity modulation direct detection (IM/DD) WDM transmission system. This system has highly nonlinear dispersion shifted fiber (HNL-DSF) as a nonlinear medium in optical phase conjugator (OPC). We confirmed that the transmission length is more increased by applying MSSI to distorted signal due to chromatic dispersion, SPM and XPM as dispersion coefficient of fiber becomes higher. And the compensation degree of distorted WDM channels due to chromatic dispersion, SPM and XPM becomes better stable as dispersion coefficient of fiber becomes higher.

• Journal of Advanced Navigation Technology
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• v.26 no.1
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• pp.22-28
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• 2022

In order to install ultra wide band and ultra long-haul transmission link based on standard single mode fiber, optical signal distortion due to chromatic dispersion and nonlinear Kerr effect must to be compensated. In this paper, optical link consisted of dispersion management and optical phase conjugation is proposed for compensation of the distorted wavelength division multiplexed (WDM) channels. Dispersion map profile in the proposed dispersion-managed link is configured by periodic repetitive shape, and optical phase conjugator is placed at various position including the midway of total transmission length. It is confirmed from simulation results that when the residual dispersion per span (RDPS) selected in the proposed dispersion-managed link to be large, the compensation of distorted WDM channels in the non-midway OPC system is more improved than the conventional dispersion-managed link.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.166-173
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• 2022

In this paper, the performance of joint equalizer and phase-locked loop in underwater communications is analyzed. In the channel where the Doppler frequency exists, it is difficult to recover the transmitted data only by the equalizer. To compensate for the Doppler frequency, the phase-locked loop is used. For removing the time-varying multipath and the Doppler frequency simultaneously, the equalizer and the phase-locked loop operate jointly. Also, if the initial Doppler frequency error obtained by Fast Fourier Transform (FFT) is compensated, the convergence speed of the joint equalizer and phase-locked loop can be improved. To verify the performance, lake and sea experiments were conducted. As a result, it was showed that the joint equalizer and phase-locked loop converges sufficiently in the preamble (known data) period regardless of whether the Doppler frequency is compensated or not. And, the bit error in random data period is not occurred. However, we can increase the convergence speed of the equalizer more than twice through the compensation of Doppler frequency.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.1-7
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• 2020

In recent years, as LED display systems are actively spread, study on effective control methods for an LED driver for driving the systems has been in progress. The most representative among them is the uniform brightness control method for the LED driver channel. In this paper, we propose an LED driver IC for BLU with current compensation and system protection functions to minimize channel luminance deviation. It is designed for current accuracy within ±3% between channels and a channel current of 150 mA. In order to satisfy the design specifications, the channel amplifier offset was canceled out by a chopping operation using a channel-driving PWM signal. Also, a pre-charge function was implemented to minimize the fast operation speed and luminance deviation between channels. LED error (open, short), switch TR short detection, and operating temperature protection circuits were designed to protect the IC and BLU systems. The proposed IC was fabricated using a Magnachip 0.35-um CMOS process and verified using Cadence and Synopsys' Design Tool. The fabricated LED driver IC has current accuracy within ±1.5% between channels and 150-mA channel output characteristics. The error detection circuits were verified by a test board.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.3
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• pp.678-684
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• 2013

This paper describes a low-power baseband circuit for SAW-less LTE-Advanced transmitters. The proposed transmitter baseband circuit consists of a 2nd-order Tow-Thomas type active RC-LPF and a 1st-order passive RC LPF. It can provide a 7 multi-channel cut-off frequencies and wide gain control range of -41 dB ~ 0 dB with a 1-dB step. The proposed 2nd-order active RC-LPF adopts an op-amp in which three other sub-op amps are in parallel connected to reduce DC current for different cutoff frequency. In addition, each sub-op amp adopts both Miller and feed-forward phase compensation method to achieve an UGBW of more than 1-GHz with a small DC power consumption. The proposed baseband circuit is implemented in 65-nm CMOS technology, consuming DC power from 6.3 mW to 24.1 mW from a 1.2V supply voltage for each different cut-off frequency.