• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.872-875
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• 2016

본 연구에서는 무구속적으로 사용자의 활동상태를 모니터링하고 이를 기반으로 산만도를 추정하기 위한 연구를 수행하였다. 사용자의 활동상태 모니터링을 위해서는 키넥트 센서를 활용하여 머리에서의 관절정보와 어깨관절정보를 검출하고, 각 검출지점의 시간당 좌표변화를 인덱스화하여 움직임 변화정도를 측정하였다. 이러한 움직임정보로부터 산만도의 추정을 위하여 움직임의 빈도와 움직임의 강도를 분석하고 이로부터 산만도를 추정하기위한 인덱스를 개발하였다. 실제 사용자의 활동상태로부터 추출된 움직임정보 및 산만도 추정인덱스의 모니터링을 위하여 PC기반의 모니터링 및 스마트폰기반의 어플리케이션을 구현하였다. 구현된 시스템의 성능평가를 위하여 키넥트를 이용한 산만도 추정 어플리케이션과 동시에 비디오 계측을 통해 움직임의 정도에 따른 산만도 추정식의 결과를 비교분석한 결과 개발된 산만도 추정시스템과 비디오분석결과의 상관관계가 높음을 실험으로 확인하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2523-2529
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• 2014

Location estimation service can be provided outdoors using various location estimation system based on GPS. However, location estimation system is based on existing indoor resources as GPS cannot be used because of insufficient visible satellites and weak signals. The fingerprinting technique that uses WLAN signal, in particular, is good to use indoors because it uses RSSI provided by AP to estimate location. However, its accuracy may vary depending on how accurate data the offline stage used where the fingerprinting map is built. The study sampled various data at the stage that builds the fingerprinting map and suggested a location estimation system that enhances its precision by saving the data of high frequency among them to improve this problem. The suggested location estimation system based on majority sampling data estimates location by filtering RSSI data of the highest frequency at the client and server to be saved at a map, building the map and measuring a similar distance. As a result of the test, the location estimation precision stood at minimum 87.5 % and maximum 90.4% with the margin of error at minimum 0.25 to 2.72m.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.461-469
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• 2008

This paper proposes a hybrid symbol offset estimation algorithm for MIMO(Multiple Input Multiple Output) OFDM system. As MIMO OFDM systems are multiple transmitter and receiver antenna systems, apart from SISO(Single Input Single Output) system, it is possible to use several combining techniques which are used in multiple receive antenna system. In this paper, we propose hybrid symbol offset estimation algorithms using combining techniques in multiple receive antenna systems, simulate and show the performances in MIMO system environments. The proposed equal gain combining correlation algorithm has better performance 1.8 times in searching the ideal symbol offset rather than the conventional early symbol offset algorithm in severe ISI channel.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.46-52
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• 2009

In this paper, the timing estimator based on the principle of the best linear unbiased estimator (BLUE) is proposed in OFDMA uplink systems. The proposed timing estimator exploits the phase information of the differential correlation between adjacent subcarriers. The differential correlation can extract the information about timing offset and mitigate the distortion of the signal caused by the frequency selectivity of channel. Compared with conventional methods, the proposed estimator shows more accurate capability in estimation. In addition, the estimator is hardly affected by the distortion caused by the frequency selectivity of channel. Simulation results confirm that the proposed estimator shows a small error mean and a relatively small error variance. In addition, the performance of the estimator is evaluated by means of SNR loss. It is shown by simulations that the SNR loss of the proposed estimator by estimation errors is less than 0.4 dB for the SNR values between 0 and 20 dB. This might indicate that the proposed estimator is suitable for the timing synchronization of multiple users in OFDMA uplink systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.215-222
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• 2008

This paper introduces an experimental verification of a tension estimation method based on system identification approach for a double hanger system on a suspension bridge. A laboratory model of such double hanger system has been made for this study. Total nine cases of the vibration tests have been conducted with respect to three levels of applied tension and three cases of the location of clamp. For a set of the collected acceleration response data, modal analysis has been followed in order to extract the natural frequencies and mode shapes of the selected cable systems. For the extracted modal parameters, the existing tension estimation methods based on the string theory and axially loaded beam theory have been firstly applied to estimate the tensile force on the double hanger cable system. Next, the tensile force on cables has been estimated by the system identification approach. It is seen that the errors in the tension estimation using the frequency-based system identification technique are about 3% for all cases while the estimation error using the existing method is up to 53.1%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6A
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• pp.660-666
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• 2004

Transmitted data may be compensated by using estimated channel values that are obtained with pilot symbols in OFDM-CDMA systems. Generally, a USE (Minimum Mean-Squared Error) estimator using correlations between pilot symbols gives good results, but its structure is so complicated. Starting with a modification of PA (Pilot-Aided) algorithm using pilot symbols and PADD (Pilot-Aided Decision-Directed) algorithm using both pilot and data symbols, a new channel estimation algorithm with more simpler structure is proposed. The performance of this algorithm is evaluated with varying mobile speed in a Ralyleigh multipath fading environment through computer simulations. The simulation results show that the proposed channel estimation algorithm outperforms a conventional PA algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9C
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• pp.661-668
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• 2008

In this paper, a channel estimation technique based on pilot tones is proposed for cooperative SFBC-OFDM systems with a STO(Symbol Timing Offset). In a cooperative SFBC-OFDM system, the STO between RS(Relay Station) and MS(Mobile Station) varies depending on the location of MS. Since the STO causes distortion in the form of phase rotation, a channel estimation technique based on linear interpolation with respect to phase and amplitude is proposed for the case of orthogonal pilot allocation. Also, a channel estimation technique is proposed by solving nonlinear equation for the case of pilot structure with orthogonal code. It is shown by computer simulation that the performance of channel estimation can be significantly improved when the proposed techniques are applied to cooperative SFBC-OFDM systems with STO.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.6A
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• pp.480-487
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• 2012

In multicarrier code-division multiple access (MC-CDMA) systems, conventional blind channel estimation schemes require the inverse matrix calculation or eigenvalue decomposition of the received signal covariance matrix. Therefore, computational complexity of the conventional schemes is too high and they cannot be employed in downlink systems. In this paper, we propose a simple blind channel estimation scheme with very low computational complexity. Simulation results show that the proposed scheme has better channel estimation and bit error rate (BER) performance than the conventional schemes.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.06a
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• pp.28-30
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• 2018

본 논문에서는 전이중 통신 방식을 사용하는 DOCSIS 3.1 시스템의 자기간섭 제거를 위한 자기간섭신호의 채널 및 비선형 왜곡 요소를 추정하는 기술을 제안한다. DOCSIS 3.1 시스템의 전이중 통신 방식은 일반적으로 가입자 단말인 CM (Cable Modem) 과 케이블방송신호 송신 시스템인 CMTS (Cable Modem Termination System) 사이의 상하향 통신을 시간/주파수의 분할 없이 동시에 수행하는 통신 방식이다. CMTS 에서 CM 의 신호를 수신함과 동시에 CMTS 신호를 송신하는 경우 고출력의 CMTS 송출신호가 CMTS 의 수신기로 인가되는 자기간섭 현상이 발생하게 된다. 이렇게 인가되는 자기간섭신호는 고출력 증폭기 (HPA: High - Power Amplifier) 및 Feedback 채널의 영향으로 크게 왜곡되어 수신된다. 따라서 자기간섭신호를 제거하고 CM 의 신호를 원활하게 복조하기 위해서는 자기간섭신호의 왜곡 요소룰 추정 및 보상하는 절차가 반드시 필요하다. 본 논문에서는 자기간섭신호의 HPA 에서 발생하는 비선형 왜곡 요소 및 Feedback 채널의 영향으로 발생하는 채널 요소를 추정하는 기술을 제안하고 성능을 분석한다. 제안된 기술은 간단한 연산기반으로 왜곡요소의 추정이 가능하며 반복추정을 통해 성능을 효과적으로 향상시키는 것이 가능하다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.63-66
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• 2010

본 논문은 차세데 3D-TV 방송을 위해 수정된 ATSC (Modified Advanced Television Systems Committee) 시스템 [1]에서 파일럿 (Pilot)을 이용한 채널 추정 대신, PN 시퀀스 (Pseudo-Noise Sequence)를 이용한 채널 추정 방식의 문제점에 대하여 2가지 방법으로 연구하였다. PN 시퀀스를 이용하여 채널을 추정하는 TDS-OFDM (Time Domain Synchronous - Orthogonal Frequency Division Multiplexing)시스템은 QAM (Quadrature Amplitude Modulation) 변조 방식을 사용하기 때문에 수신측 PN 시퀀스의 위상 변화가 일어나지 않는다. 하지만 수정된 ATSC 시스템에서 사용하는 VSB (Vestigial Side Band)변조 방식에서 직교위상 (Quadrature) 채널을 통해 전송되는 값은 동위상 (In-Phase) 채널을 통해 전송되는 값의 단순한 힐버트 변환 (Hilbert Transform)에 의해 생성되어 불규칙한 위상 변화가 발생한다. 따라서 수정된 ATSC 시스템에서 채널 추정을 위해 PN 시퀀스를 사용하게 된다면 상관 (Correlation) 특성을 잃어버릴 것이며 올바른 채널 임펄스 응답 (Channel Impulse Response)을 얻을 수 없다.