• 한국전자파학회논문지
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• 제21권9호
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• pp.965-970
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• 2010

NC-OFDM(Non-Contiguous Orthogonal Frequency Division Multiplexing) 기반의 무선 통신 시스템은 많은 부반송파의 수로 인해 높은 PAPR(Peak-to-Average Power Ratio)을 갖는다. Comb type pilot은 시변 채널 추정에 있어서 block type pilot보다 낮은 계산 복잡도를 가지며 더 효율적이다. 그러나 CAZAC(Constant Amplitude Zero Auto-Correlation) 행렬 변환이 뛰어난 PAPR 저감 효과를 보임에도 불구하고, comb type pilot이 데이터 심볼에 삽입되게 되면 PAPR이 다시 증가하는 문제가 있다. 따라서, 본 논문에서는 이러한 comb type pilot 배치로 인해 증가된 PAPR을 개선하기 위해 추가적으로 새로운 방식의 SLM(Selective Mapping)을 적용하였다. 또한, 본 논문에서 사용된 새로운 방식의 SLM 기법은 일반적인 SLM 기법과 달리, SLM의 선택 정보를 전송하기 위한 추가적인 대역폭을 사용하지 않음으로써 대역 효율을 높인다. 따라서, 본 논문에서 제안된 시스템은 제한된 주파수 대역을 이용하여 고효율의 데이터 전송을 얻을 수 있다.

• 한국항공운항학회지
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• 제23권4호
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• pp.57-65
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• 2015

In this study, MBTI(Myers-Briggs Type Indicator) test was carried out targeting flight instructors and student pilots in charge of introductory flight training course. The results was analyzed in accordance with the personality type, the preferred indicator, and the combination of preferred indicators in order to see how these characteristics affect the flight training results. Most of personality types of the instructor, regardless of the attitude category such as E or I, were -STJ(70.6%), however the student pilot showed a variety of personality types, rather than professors. Sensing-type(S) students showed higher academic achievement scores than Intuition-type(N), and Judging-type(J) students showed higher academic achievement scores and pilot qualification scores than Perceiving-type(P). The success rate of Extraversion-type(E) student pilots was higher than that of Introversion-type(I) student pilots. As the personality combinations of instructor and student pilot, the academic achievement scores of Judging-Judging(J-J) type were higher than those of Perceiving-Perceiving(P-P) type. The combination of Extraversion-Extraversion(E-E) type showed higher success rate than Extraversion-Introversion(E-I). This result suggests that if both instructor and student pilot have same attitude of Extroversion(E), good training results can be expected.

• 한국연소학회:학술대회논문집
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• 대한연소학회 2003년도 제27회 KOSCO SYMPOSIUM 논문집
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• pp.251-256
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• 2003

The capability of pilot injection with small fuel quantity at all engine operating conditions is one of the main feature of the common rail system. The purpose of the pilot injection is to lower the engine noise and to reduce the NOx emissions. This study describes the pilot spray structure characteristics of the common-rail diesel injectors, solenoid-driven and piezo-driven type, with different electric driving characteristics So, three common-rail injectors with different electric current wave were used in this study. The pilot spray characteristics such as spray speed, spray tip penetration, and spray angle were obtained by spray images, which is measured by the back diffusion light illumination method with optical system for high-speed temporal photography. Also the CFD analysis was carried out for fuel behavior under high pressure in between needle and nozzle of solenoid-driven injector to know the condition of initial injection at experiment test. It was found that pilot injection of common-rail system was effected by rate of injection and temperature of injected fuel and electrical characteristic of the driven injector.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.1063-1068
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• 2005

• 한국전자파학회논문지
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• 제21권4호
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• pp.399-407
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• 2010

SC-FDMA(Single Carrier-Frequency Division Multiple Access)는 DFT(Discrete Fourier Transform)-spreading 방식을 사용하여 OFDM(Orthogonal Frequency Division Multiplexing) 신호의 PAPR(Peak to Average Power Ratio) 저감하여 전력효율을 향상시키는 방식이다. 그러나, PAPR을 저감하기 위하여 블록 type 파일럿을 사용하기 때문에 이동 환경에 따른 도플러 주파수와 송수신기 사이의 주파수 불일치로 인한 주파수 옵셋과 시간 도메인에서의 위상 잡음으로 주파수 도메인에서 ICI(Inter Channel Interference)가 발생하여 SC-FDMA 시스템의 성능은 저감된다. 그러므로 이동 환경 및 위상 잡음을 제거하기 위하여 comb type 파일럿을 고려하고, 이에 대한 PAPR을 감소시키기 위하여 SLM(Selective Mapping) 기법을 사용하며, 효과적인 채널 추정 및 ICI 제거를 위한 기법을 제안한다. 그러므로 기존 블록 type에 비해 comb type을 사용함으로써 이동 수신 성능이 향상될 수 있으며 효과적으로 주파수 옵셋 및 위상 잡음을 효과적으로 제거 가능함을 보인다.

• 한국전자파학회논문지
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• 제21권1호
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• pp.1-7
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• 2010

SC-FDMA(Single Carrier-Frequency Division Multiple Access) 통신 시스템에서 채널 추정을 위한 파일럿은 CAZAC 시퀀스를 이용하여 OFDM(Orthogonal Frequency Division Multiplexing) 신호의 높은 PAPR(Peak-to-Average Power Ratio)을 낮추는 방식을 사용한다. 그런데, 채널 추정을 위한 파일럿이 블록 타입으로 전송되므로, 수신단에서 파일럿 블록 사이의 여러 OFDM 심볼들은 시간 영역에서의 보간법을 시용하여 채널 추정하여야 하므로 매우 복잡하고 처리 시간이 길어질 수 있다. 또한 심한 fast fading 채널에서는 이러한 문제점이 더욱 커진다. 한편, 효과적인 고속 채널 추정을 위하여 OFDM 심벌 단위로, 주파수 영역에서 보간법을 수행하는 comb 타입의 파일럿을 사용하게 되면 OFDM 신호의 PAPR이 다시 높아지는 문제가 발생한다. 본 논문에서는 PAPR 감소와 효과적 채널 추정이 가능한 comb 타입의 파일럿을 배치 방법을 연구하였다. 이를 위하여 CAZAC 행렬 변환된 OFDM 신호에 comb 타입의 파일럿을 배치하고, 추가로 SLM 기법을 사용하였다. 그러나 기본적인 SLM(Selected Mapping) 기법은 위상 회전에 관한 부가 정보 전송이 필요하기 때문에 대역폭의 손실을 가져온다는 단점이 있다. 따라서, 본 연구에서는 파일럿은 SLM 위상 시퀀스와 곱해지지 않으며, SLM 위상 회전 시퀀스에 따라 서로 다른 파일럿을 신호에 삽입하여, 부가 정보를 사용하지 않고 대역폭의 손실이 없는 개선형 SLM 기법을 연구하였다. 시뮬레이션 결과, 4개의 위상 회전 시퀀스를 갖는 SLM을 사용하였을 때, 파일럿 삽입으로 인해 높아진 신호의 PAPR을 원래 수준과 비슷한 성능으로 감소되는 것을 알 수 있다.

• 한국자동차공학회논문집
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• 제2권3호
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• pp.75-84
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• 1994

In general direct-operated pressure reducing valves have been gardly applied to a dynamic control system such as active suspension control because of their poor control stability. But they are more robust than pilot-operated type and do not need pilot control flow. In this paper development of a new direct-operated proportional pressure reducing valve for low-band type active suspension control is reported. By means of a special damper directly linked to the valve spool, the control stability could be effectively improved without drawback in response time. The linearity error was less than $\pm$3.5%. Applied to an experimental active suspension system the new valve showed the $-90^{\circ}$ phase delay at 4Hz with 20% sinusoidal signal input and could control the suspension system with almost same performance as that with a pilot-operated type valve.

• 한국항공운항학회지
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• 제28권2호
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• pp.1-11
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• 2020

This study was carried out to verify how much instructor's communication skill affects the student pilot's study motivation and satisfaction. The instructor's communication styles are classified into 3 groups by pre-analysis. Three types are cooperative type, control type and professional type. Intellectual cause, performance proficiency cause, social cause and stimulation avoidance cause are extracted and analyzed for the cause of study motivation. Cooperative and control type affected all of 4 factors of student's study motivation by influence analysis. Intellectual cause affected control and cooperative type positively, especially more to cooperative type. Performance proficiency cause also had positive influence to control and cooperative type. Stimulation avoidance cause didn't appear to affect all sub-classified 4 factors of instructor's communication type. Influence analysis of student's study satisfaction from instructor's communication style showed that independent variable affected all sub factors positively. Degree of positive influence affected the control type the most, cooperative type was the 2nd, and professional type was the 3rd.

• Journal of Electrical Engineering and Technology
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• 제4권4호
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• pp.429-437
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• 2009

This paper proposes a hybrid voltage controller based on a hierarchical control structure for implementation in the Jeju power system. The hybrid voltage controller utilizes the coordination of various reactive power devices such as generators, switched shunt devices and LTC to regulate the pilot voltage of an area or zone. The reactive power source can be classified into two groups based on action characteristics, namely continuous and discrete. The controller, which regulates the pilot bus voltage, reflects these characteristics in the coordination of the two types of reactive power source. However, the continuous type source like generators is a more important source than the discrete type for an emergency state such as a voltage collapse, thereby requiring a more reactive power reserve of the continuous type to be utilized in the coordination in order to regulate the pilot bus voltage. Results show that the hybrid controller, when compared to conventional methods, has a considerable improvement in performance when adopted to control the pilot bus voltage of the Jeju island system.

• 전기학회논문지
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• 제59권11호
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• pp.2108-2113
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• 2010

The Long Term Evolution (LTE) system is based on the Orthogonal Frequency Division Multiplexing (OFDM) and relies its channel estimation on the lattice-type pilot samples in the multipath fading channel environment. The estimation of the channel frequency response (CFR) makes use of the least squares estimate (LSE) for each pilot samples, followed by an interpolation both in time- and in frequency-domain to fill up the channel estimates for subcarriers corresponding to data samples. Any interpolation scheme could be adopted for this purpose. Depending on the requirements of the target system, we may choose a simple linear interpolation or a sophisticated one. For any choice of an interpolation scheme, these is a trade-off between estimation accuracy and numerical cost. For those wireless communication systems based on the OFDM and the preamble-type pilot structure, the DFT-based channel estimation and its variants have been successfully. Yet, it may not be suitable for the lattice-type pilot structure, since the pilot samples are not sufficient to provide an accurate estimate and it is known to be sensitive to the location as well as the length of the time-domain window. In this paper, we propose a simple interpolated based on the upsampling mechanism in the multirate signal processing. The proposed method provides an excellent alternative to the DFT-based methods in terms of numerical cost and accuracy. The performance of the proposed technique is verified on a multipath environment suggested on a 3GPP LTE specification.