• Journal of electromagnetic engineering and science
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• 제4권2호
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• pp.63-67
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• 2004

DAM(Delay-And-Multiplier) intercept receiver usually detects the symbol rate of the transmitted DS spread spectrum signal for the feature extraction. It is important for secure communication to reduce the normalized output signal-to-noise ratio that is generated at the DAM intercept receiver as a measure of detectability. In this paper, several kinds of chip waveforms are novelly analyzed for LPI(Low-Probability of Intercept) communication against DAM intercept receiver. Consequently, it is shown that the rectangular chip waveform shows the best LPI performance in the bandwidth of 2/$T_c$TEX>, 4/$T_c$TEX>, and 6/$T_c$TEX>/. Except the rectangular waveform, kaiser chip waveform show better LPI performance than the other waveforms in the bandwidth of 4/$T_c$TEX> and 6/$T_c$TEX>.

• Journal of Information Processing Systems
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• 제13권1호
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• pp.141-151
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• 2017

Effective identification of wireless channel in different scenarios or regions can solve the problems of multipath interference in process of wireless communication. In this paper, different characteristics of wireless channel are extracted based on the arrival time and received signal strength, such as the number of multipath, time delay and delay spread, to establish the feature vector set of wireless channel which is used to train backpropagation (BP) neural network to identify different wireless channels. Experimental results show that the proposed algorithm can accurately identify different wireless channels, and the accuracy can reach 97.59%.

• Journal of Information Processing Systems
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• 제15권5호
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• pp.1029-1035
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• 2019

In recent years, artificial intelligence (AI) services have become one of the most essential parts to extend human capabilities in various fields such as face recognition for security, weather prediction, and so on. Various learning algorithms for existing AI services are utilized, such as classification, regression, and deep learning, to increase accuracy and efficiency for humans. Nonetheless, these services face many challenges such as fake news spread on social media, stock selection, and volatility delay in stock prediction systems and inaccurate movie-based recommendation systems. In this paper, various algorithms are presented to mitigate these issues in different systems and services. Convolutional neural network algorithms are used for detecting fake news in Korean language with a Word-Embedded model. It is based on k-clique and data mining and increased accuracy in personalized recommendation-based services stock selection and volatility delay in stock prediction. Other algorithms like multi-level fusion processing address problems of lack of real-time database.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2000년도 하계종합학술대회논문집
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• pp.69-72
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• 2000

Multilevel modulation schemes are known to be highly bandwidth efficient. By varying modulation level adaptively according to channel conditions (i.e. adaptive QAM schemes or AQAM), high bandwidth efficiency can be achieved. This paper considers the effect of time delay on the adaptive QAM schemes in dispersive fading channels. In order to undertake investigations effectively, a simulator has been developed. The simulation results show that the BER performance obtained for the wideband channel with a delay spread of 0.75 $\mu$sec is better than 10$^{-4}$ with a SNR value of 40 ㏈ and ABPS is found to be approximately 5.5.

• 한국정보통신학회논문지
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• 제4권2호
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• pp.417-426
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• 2000

본 논문에서는 송신기의 전력효율을 고려하여 C급 전력증폭기를 사용함에 있어서 기존의 대역제한된 BPSK 변조의 경우 증폭기의 비선형성으로 인해 출력 스펙트럼의 측대파가 증폭기를 통과하기 전보다 증가되는 현상이 발생하는데 이를 줄여주기 위해 일정 진폭특성을 갖는 CE-CPSK변조 직접대역확산 송수신기를 제안하였다. 직접대역확산 수신기의 동기 추적루프의 성능을 분석하기 위해 두경로 레일리 페이딩 채널로 모델링하였다. 동기추적 장치는 아날로그 지연동기루프의 단점인 조, 만 간의 이득 불균형을 개선한 디지털 지연동기루프로 구현하였다. 동기 추적 과정인 디지털 지연동기 루프의 성능은 칩당 샘플링의 수가 증가할수록 신호 대잡음비가 증가할수록 전압 제어 발진기의 최대주파수 편차가 작을수록 좋아짐을 볼 수 있다.

• Journal of Mechanical Science and Technology
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• 제15권1호
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• pp.1-9
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• 2001

The recent spread of scaled telemanipulation into microsurgery and the nano-world increasingly requires the identification of the possible operation region as a main system specification. A teleoperation system is a complex cascaded system since the human operator, master, slave, and communication are involved bilaterally. Hence, a small time delay inside a master and slave system can be critical to the overall system stability even without communication time delay. In this paper we derive an upper bound of the scaling product of position and force by using Llewellyns unconditional stability. This bound can be used for checking the validity of the designed bilateral controller. Time delay from the sample and hold of computer control and its effects on stability of scaled teleoperation are modeled and simulated based on the transfer function of the teleoperation system. The feasible operation region in terms of position and force scaling decreases sharply as the sampling rate decreases and time delays inside the master and slave increase.

• Journal of Preventive Medicine and Public Health
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• 제53권3호
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• pp.164-167
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• 2020

Objectives: As of March 3, 2020, the Shincheonji religious group accounted for the majority of Korean cases of coronavirus disease 2019 (COVID-19). Nonetheless, the most likely cause of the broad spread of COVID-19 among members of the Shincheonji religious group remains largely unknown. Methods: We obtained data of laboratory-confirmed cases related to the Shincheonji religious group from press releases by Korean public health authorities and news reports. We measured the period from the date of illness onset to the date of COVID-19 confirmation. Results: We analysed data from 59 cases (median age, 30 years). The estimated median period between the date of symptom onset and the date of COVID-19 confirmation was 4 days (95% confidence interval, 1-12). Conclusions: There was a delay in COVID-19 confirmation from the date of illness onset among the cases linked to the Shincheonji religious group. This delay likely contributed to the occurrence of many cases of COVID-19 in the group.

• 대한전자공학회논문지
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• 제25권8호
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• pp.867-873
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• 1988

The degradation due to channel distortion in a quadrature modulation system from the ideal constant values over the bandwidth of a direct sequence spread spectrum signal are considered. Through using series expansion for the channel gain and phase response, the degradation in the correlator output at the receiver is found as a function of the parameters involved , including phase error, delay error, linear gin variation, quadratic gain variation, and quadratic phase variation.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2001년도 종합학술발표회 논문집 Vol.11 No.1
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• pp.34-38
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• 2001

This paper proposes a CP-OFDM(Orthogonal Frequency Division Multiplexing using Circular Polarization) system for improving the system performance. The circular polarization has a characteristic that it cannot receive the reflected waves which are reflected by odd times. By reducing the influences of the reflected waves, the circular polarization can reduce the time delay spread and the inter-channel interference. The guard interval needed for the OFDM frame can be minimized and the orthogonality between subchannels can be improved by using circular polarization. Therefore the proposed CP-OFDM system can improve the system performance as well as the spectrum efficiency. Both theoretical analysis and system simulation results are described.

• 한국통신학회논문지
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• 제25권11A호
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• pp.1613-1619
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• 2000

이 논문에서는 전파재널 측정 시스템을 이용하여 건물내 무선 채널의 전파특성인 실효 시간지연 확산과 경로손실을 측정하고 분석한 결과를 제시한다. 구성된 측정 시스템은 미끄럼 상관기를 이용한 대역확산 채널 측정 시스템에서 2 GHz에서 동작하며 3 m 의 분해능을 갖는다. 건물내 무선 채널 특성의 측정환경은 송신 안테나와 수신 안테나가 같은 층에 있을때, 서로 다른 층에 있을때, 그리고 사무실 안에 같이 위치할 때의환경으로구분하여 실험한다.