• International Journal of Control, Automation, and Systems
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• 제1권4호
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• pp.412-430
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• 2003

In many practical problems in signal processing and control, the signal values are often restricted to belong to a finite number of levels. These questions are generally referred to as "finite alphabet" problems. There are many applications of this class of problems including: on-off control, optimal audio quantization, design of finite impulse response filters having quantized coefficients, equalization of digital communication channels subject to intersymbol interference, and control over networked communication channels. This paper will explain how this diverse class of problems can be formulated as optimization problems having finite alphabet constraints. Methods for solving these problems will be described and it will be shown that a semi-closed form solution exists. Special cases of the result include well known practical algorithms such as optimal noise shaping quantizers in audio signal processing and decision feedback equalizers in digital communication. Associated stability questions will also be addressed and several real world applications will be presented.

• 한국항행학회논문지
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• 제13권5호
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• pp.736-741
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• 2009

본 논문은 분할된 선형배열안테나를 사용하는 다중 사용자 MIMO 기술에서 코드북(codebook)을 운용 환경에 따라 최적화 하는 기술을 제안한다. 제안하는 기술은 공간상관도가 없는 MIMO 채널을 가정하여 디자인된 코드북을 각 순방향 링크의 송신 공간상관행렬을 이용하여 컬러링(coloring)하는 기술이며, 이를 위해 필요한 각 링크의 송신 상관행렬을 제한된 양의 long-term 피드백을 통해 피드백하는 기술을 제안한다. Zero-forcing maximum eigenmode transmission 기술을 사용하는 다중 사용자 MIMO 시스템에서, 제안하는 코드북 최적화 기술의 성능을 분석하였으며, 제안하는 기술이 적은양의 추가 피드백 정보량으로 다양한 운용 환경에 적응적으로 코드북을 최적화함을 보인다.

• Journal of Communications and Networks
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• 제18권1호
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• pp.95-104
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• 2016

Massive multiple-input multiple-output (MIMO) is a promising approach for cellular communication due to its energy efficiency and high achievable data rate. These advantages, however, can be realized only when channel state information (CSI) is available at the transmitter. Since there are many antennas, CSI is too large to feed back without compression. To compress CSI, prior work has applied compressive sensing (CS) techniques and the fact that CSI can be sparsified. The adopted sparsifying bases fail, however, to reflect the spatial correlation and channel conditions or to be feasible in practice. In this paper, we propose a new sparsifying basis that reflects the long-term characteristics of the channel, and needs no change as long as the spatial correlation model does not change. We propose a new reconstruction algorithm for CS, and also suggest dimensionality reduction as a compression method. To feed back compressed CSI in practice, we propose a new codebook for the compressed channel quantization assuming no other-cell interference. Numerical results confirm that the proposed channel feedback mechanisms show better performance in point-to-point (single-user) and point-to-multi-point (multi-user) scenarios.

• 한국통신학회:학술대회논문집
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• 한국통신학회 1987년도 춘계학술발표회 논문집
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• pp.27-30
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• 1987

Some modification of laplacian pyramidal coding have been done and tested for a test image, From our studies, its apperar that 3-D redictor which exploits inter and intra plane redundancy simultaneously somewhat imporves the image quality, We also have tried to reduce the bit rate by only sending zeroth plane image values that correstpond to estimated dege points which can be obtained from the first plane For both cases the feedback of quantization errof in the previous plane has been in the reconstruction of each plane. Subjective and SNR tests show the better performance of the studied methods oner the conventional one.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1012-1017
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• 2003

The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications with various external loads is described in this paper. A novel modified pulso width modulation (MPWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. A comparison between the system response of standard PWM technique and that of the novel modified PWM technique shows that the control performance is significantly increased. A state feedback controller with position, velocity and acceleration feedback is successfully implemented as the continuous controller. Switching algorithm of control parameter using learning vector quantization neural network (LVQNN) is newly proposed. which estimates the external loads of the pneumatic actuator. The effectiveness of the proposed control algorithms are demonstrated through experiments with various loads.

• 한국정밀공학회지
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• 제20권8호
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• pp.86-93
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• 2003

The development of a fast, accurate, and inexpensive position-controlled pneumatic actuator that may be applied to a variety of practical positioning applications with various external loads is described in this paper. A novel modified pulse width modulation (MPWM) valve pulsing algorithm allows on/off solenoid valves to be used in place of costly servo valves. A comparison between the system response of standard PWM technique and that of the novel modified PWM technique shows that the control performance is significantly increased. A state feedback controller with position, velocity and acceleration feedback is successfully implemented as the continuous controller. Switching algorithm of control parameter using learning vector quantization neural network (LVQNN) is newly proposed, which estimates the external loads of the pneumatic actuator. The effectiveness of the proposed control algorithms are demonstrated through experiments with various loads.

• 제어로봇시스템학회논문지
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• 제11권2호
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• pp.103-108
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• 2005

Loading/Unloading task in the real industry is performed by crane, but most of the loading/unloading task with the weight of 5kg∼30kg is done by human workers and this kind of work causes industrial disaster of workers. Therefore it is necessary to develop low cost loading/unloading manipulator system to prevent this kind of industrial accidents. This paper is concerned with the design and fabrication of 2 axis pneumatic manipulators using on/off solenoid valves and accurate position control without respect to the external load and low damping in the pneumatic rotary actuator. To overcome the change of external load, switching of control parameter using LVQNN (Learning Vector Quantization Neural Network) is newly applied, which estimates the external loads in the pneumatic cylinder. As an underlying controller, a state feedback controller using position, velocity and acceleration is applied to the switching control system. The effectiveness of the proposed control algorithms are demonstrated through experiments of pneumatic cylinder with various loads.

• 방송공학회논문지
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• 제28권1호
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• pp.141-144
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• 2023

최근에 심층신경망(DNN)을 활용하여 채널 추정, 채널 양자화, 피드백, 프리코딩 과정을 통합하여 모델링하는 연구가 진행되었다. 해당연구는 기존에 이론적으로 어렵던 통합 최적화를 deep learning (DL)을 기반으로 수행하여 기존의 실제 codebook을 활용하는 프리코딩기법에 비해 높은 잠재력이 있음을 보였다. 하지만 기존의 기법은 랜덤하게 정해진 소수의 사용자만을 대상으로하며, 기존의 기법과 다르게 스케줄링이 포함된 환경에는 적응이 어렵다. 따라서 본 연구에서는 심층신경망기반의 프리코딩기법이 활용가능한 스케줄링 방식을 연구하여 기존의 결과와 비교한다.

• 한국정보통신학회논문지
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• 제21권7호
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• pp.1299-1305
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• 2017

본 논문에서는 다중 안테나를 사용하는 두 개의 송신단이 각각 하나의 안테나를 가지고 있는 수신단을 서비스 할때 구성되는 두 유저 간섭 채널에서 불완전한 채널 정보를 사용하는 송신단들의 빔포밍 게임을 고려한다. 빔포밍 게임에서는 송신단(i.e., 플레이어)이 자신들의 전송률(i.e., 보상)을 높이기 위해서 경쟁을 하고, 빔포밍 기법을 위해서는 완전한 채널 상황에서 최적이라고 알려진 maximum ratio transmission (MRT) 기법과 zero forcing (ZF) 빔포밍 기법을 선형으로 결합하는 기법(i.e., 전략)을 사용한다. 우리가 제안하는 게임에서는 송신단이 불완전한 채널 정보를 사용하므로, 최적의 전략을 찾더라도 그 전략이 유효하지 않을 수 있다. 본 논문에서는 불완전한 채널 정보로부터 양자화 오차의 영향을 고려한 송신단의 효율적인 빔포밍 전략을 제안한다.

• 한국인터넷방송통신학회논문지
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• 제19권1호
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• pp.225-229
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• 2019

자기베어링은 기계적인 마찰이 없고 안정적인 동역학 특성을 갖기 때문에 진공 및 청정 환경이나 고정도가 요구되는 분야에서 많이 활용되고 있다. 그러나 자기베어링은 다양한 장점에도 불구하고 일반적으로 제어기가 복잡해서 적용 범위의 확산이 제한적이다. 본 논문에서는 복잡도가 낮은 디지털 방식의 자기베어링 제어기를 제안하였다. 또한 디지털 제어기 성능열화의 주된 원인인 아날로그 신호를 디지털 신호로 변환하는 과정에서 발생하는 오류와 제어 알고리즘 구현상의 문제점들을 분석하고 해결하였다. 제안한 제어기를 실제 자기베어링에 적용한 실험을 통해 제어기가 자기부상 목표 정밀도를 갖는 것을 확인하였다.