• Survey Research
• /
• v.3 no.2
• /
• pp.91-122
• /
• 2002

The use of internet is expanding globally in a rapid way. The situation is similar in Korea. The growth of internet affects the various aspects of a social system. Such an impact is not an exception in the field of survey data-collection. The internet survey method has gained a recognition as an important survey approach in the U.S and Europe. A number of Korean research organizations have already started implementing the new survey method, too. The time is quite ripe for the internet survey in Korea. However, it is hard to find ever a good literature review on the subject. This study intends to review the results of the past studies about the question of what factors influence the response rate, speed, and quality. The influencing factors incorporated in this review include six elements: personalization, the survey sponsorship, incentives, the questionaire format, prenotification, and follow-ups. Regarding there sis factors, the results of the past studies relating to the internet survey response are reviewed in a systematic way.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.4 no.4
• /
• pp.318-324
• /
• 1999

In this paper. a control method based on finite element analysis is presented to improve the control characteristics of t the permanent magnet linear synchronous motor (PMLSM). In the control method. additional compensation current is a added to the conventional control current according to the position of mover. The characteristics of thrust ripple a according to the position of mover and the current are analyzed by using finite element method (FEM). And. the value of current to compensate the thrust ripple due to the cog밍ng force is calculated from the analysis results. The c characteristics according to control method are compared in case of speed control. and to conform the validity of the p presented method, a test set is built and experiments are performed.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.4 no.4
• /
• pp.368-376
• /
• 1999

This paper studies the operational characteristics of thyristor controlled shunt compensator in a simple power t transmission system. With Fourier series representation of the thyristor switching action and the system parameters, t the thyristor current equations are derived, which transmit the required real power of the simple power transmission s system. Bisection algorithm is used to solve the thyristor current equations, which informs the thyristor firing an밍e, t the thyristor conduction an밍e, the power flows and the harmonic characteristics. The stability analysis is performed w with the theory of Poincare mapping for the nonlinear discrete periodic dynamic system. EMTP simulations at the v various operating points show the transient characteristics of the thyristor controlled shunt compensator and C correspond to the results calculated with Fourier series representation and the stability analysis.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2010.11a
• /
• pp.257-259
• /
• 2010

본 논문에서는 지상파 3D HDTV 방송 서비스를 제공하기 위해 수정된 ATSC (Advanced Television Systems Committee) 전송 시스템 [2]을 위한 시변다중경로채널에 강인한 프레임 구조를 제안하고 성능을 측정하였다. 수정된 ATSC 전송 시스템 [2]은 기존 ATSC 전송 시스템[1]의 채널 부호화부를 수정하고, 변조 성상도를 증가 시키면서 적정한 수준의 TOV (Threshold of Visibility)에서의 전송 용량 증대 가능성을 확인하였다. 이를 토대로, 증가된 전송 데이터 전송률에 대한 순수 데이터 전송률을 최대한 보장하면서 시변다중경로채널에서 효율적으로 채널을 추정하고 복구하기 위해, ISI (Inter Symbol Interference)를 방지하기 위한 프레임 헤더의 보호구간에 알려진 PN (Pseudorandom Noise) 심벌을 삽입하였다. PN 심벌을 보호 구간에 이용할 경우 시간 영역에서 채널 임펄스 응답 (CIR: Channel Impulse Response)을 추정하여, 주파수 영역에서의 채널 보상을 가능케 하여 정확한 채널 추정 및 보상을 수행할 수 있다. 또한 수신기의 속도에 따른 다양한 최대 도플러 주파수가 존재하는 채널에 강인한 프레임 구조들을 제안하였다. 컴퓨터 시뮬레이션을 통해 수정된 ATSC 전송 시스템에 제안된 프레임 구조를 적용하여 TU (Typical Urban)-6 채널에서의 SER (Symbol Error Rate) 성능을 측정하였다.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.189-192
• /
• 1999

수중소음체의 음원 특징을 해석하기 위해서는 배경잡음과 해면$\cdot$해저반사파의 영향이 적은 심해에서 측정하여 분석하여야 한다. 그러나 측정의 어려움으로 인공 수조에서 측정하여 수면과 수조벽에 의해 발생되는 반사파들을 제거하여 신호 고유의 특징을 해석한다 이러한 반사파들의 부가효과를 보상하여 수중소음체의 신호특징을 해석하기 위하여 정합필터배열처리(Matched Filter Array Process : MFAP)기법을 적용하고자 할 때 각 센서에 적용되는 정합필터는 처리시간의 문제로 인해 필터길이를 제한하여 구성되게 된다 정합필터는 수조의 임펄스응답함수의 시역전함수로 정의되는데 필터길이에 따라 수신신호 특징 개선 정도가 좌우된다 본 연구에서는 인공수조에서 부가되는 반사파들의 효과를 보상하여 수신신호 특징 개선을 위해 정합필터배열처리기법을 적용할 때 각 센서의 정합필터의 시간길이가 특징 개선에 미치는 영향을 신호대잡음비(SNR)로 정의하여 분석하였고 수조의 특성에 따른 최적의 정합필터 시간길이를 제안하고자 한다.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.9 no.3
• /
• pp.253-259
• /
• 2004

This paper presents a speed controller method based on the disturbance torque observer for high-performance speed control of the brushless DC (RLDC) motor. In case of the speed control of robot arms and tracking applications with lower stiffness, we cannot design the speed controller gain to be very large from the viewpoint of the system stability Thus, the feedforward compensation method using disturbance torque observer was proposed. This method can improve the speed characteristic without increasing the speed controller gain. The speed characteristic against disturbance torque can be improved when the bandwidth of the speed controller cannot be made large enough. Consequently, the speed control of the BLDC motor for the high-performance application become achieved.

• Journal of Advanced Navigation Technology
• /
• v.13 no.5
• /
• pp.756-762
• /
• 2009

As nonlinear friction, stick-slip friction in hydraulic actuators are a problem for accuracy and repeatability. Therefore friction compensation has been approached through various control algorithms. A Adaptive discrete time sliding mode tracking controller has been applied in order to compensate the nonlinear friction characteristics in a hydraulic Actuator. Based on the diophantine equation, a new discrete time sliding function is defined and utilized for the control law which includes a friction and modeling error. Robustness is increased by using both a projection algorithm and a sliding function-based nonlinear feedforward. From the results of simulation and experiment good tracking performance is achieved.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.4
• /
• pp.335-341
• /
• 2010

To improve the performance of inner loop based on PD controller for a unmanned helicopter, neural networks are applied. The performance of PD controller designed on the response characteristics of error dynamics decreases because of uncertain nonlinearities of the system. The nonlinearities are decoupled to modified dynamic inversion model(MDIM) and are compensated by the neural networks. For the training of the neural networks, online weight adaptation laws which are derived from Lyapunov's direct method are used to guarantee the stability of the controller. The results of the improved performance of PD controller by neural networks are illustrated in the simulation of unmanned helicopter with nonlinearities,

• Journal of the Institute of Convergence Signal Processing
• /
• v.13 no.4
• /
• pp.233-237
• /
• 2012

In this paper, We propose a control system which compensate a output of a main Neual Network using a RTDNN(Recurrent Time Delayed Neural Network) with a FLC(Fuzzy Logic Controller)After a learn of main neural network, it can occur a Over shoot or Under shoot from a disturbance or a load variations. In order to adjust above case, we used the fuzzy compensator to get an expected results. And the weight of main neural network can be changed with the result of learning a inverse model neural network of plant, so a expected dynamic characteristics of plant can be got. We can confirm good response characteristics of proposed neural network controller by the results of simulation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.8A
• /
• pp.1265-1272
• /
• 2000

A data warehouse is able to accommodate efficient data mining query processing and subsequent response by providing information needed for decision making. In such an environment, the data warehouse stores materialized view derived from various sources to enhance query processing. The compensating algorithm to maintain materialized view is well known for a single source site environment. In the compensating algorithm, several problems arise to get results in view maintenance. The problems are due to the overhead in query management within the data warehouse, increased complexity to manage queries in the warehouse as updates occur and increased volume of message traffic between the data source and the warehouse. In this paper, we propose a new algorithm that reduces the overhead in managing queries for new maintenance and that enhances the correctness. We also measured the performance of the new algorithm by evaluating the performance of the existing recomputing view and compensating algorithm and comparing the results with the proposed algorithm.