• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1828-1847
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• 2014

Coordinated multi-point (CoMP) transmission has been regarded as a potential technology for LTE-Advanced. In frequency division duplexing systems, channel quantization is applied for reporting channel state information (CSI). Considering the dynamic number of cooperation base stations (BSs), asymmetry feature of CoMP channels and high searching complexity, simply increasing the size of the codebook used in traditional multiple antenna systems to quantize the global CSI of CoMP systems directly is infeasible. Per-cell codebook based channel quantization to quantize local CSI for each BS separately is an effective method. In this paper, the theoretical upper bounds of system throughput are derived for two codeword selection schemes, independent codeword selection (ICS) and joint codeword selection (JCS), respectively. The feedback overhead and selection complexity of these two schemes are analyzed. In the simulation, the system throughput of ICS and JCS is compared. Both analysis and simulation results show that JCS has a better tradeoff between system throughput and feedback overhead. The ICS has obvious advantage in complexity, but it needs additional phase information (PI) feedback for obtaining the approximate system throughput with JCS. Under the same number of feedback bits constraint, allocating the number of bits for channel direction information (CDI) and PI quantization can increase the system throughput, but ICS is still inferior to JCS. Based on theoretical analysis and simulation results, some recommendations are given with regard to the application of each scheme respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권4호
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• pp.703-719
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• 2011

In multi-user wireless communication systems, adaptive modulation and scheduling are promising techniques for increasing the system throughput. However, a mass of wireless recourse will be occupied and spectrum efficiency will be decreased to feedback channel quality indication (CQI) of all users in every subcarrier or chunk for adaptive orthogonal frequency division multiplexing (OFDM) systems. Thus numerous limited feedback schemes are proposed to reduce the system overhead. The recently proposed compressive sensing (CS) theory provides a new framework to jointly measure and compress signals that allows less sampling and storage resources than traditional approaches based on Nyquist sampling. In this paper, we proposed two novel CQI feedback schemes based on general CS and subspace CS, respectively, both of which could be used in a wireless OFDM system. The feedback rate with subspace CS is greatly decreased by exploiting the subspace information of the underlying signal. Simulation results show the effectiveness of the proposed methods, with the same feedback rate, the throughputs with subspace CS outperform the discrete cosine transform (DCT) based method which is usually employed, and the throughputs with general CS outperform DCT when the feedback rate is larger than 0.13 bits/subcarrier.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권4호
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• pp.692-710
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• 2013

Conventional interference alignment (IA) for a MIMO interference channel (IFC) requires global and perfect channel state information at transmitter (CSIT) to achieve the optimal degrees of freedom (DoF), which prohibits practical implementation. In order to alleviate the global CSIT requirement caused by the coupled relation among all of IA equations, we propose an IA scheme with a single feedback link of each receiver in a limited feedback environment for a three-user MIMO IFC. The main feature of the proposed scheme is that one of users takes out a fraction of its maximum number of data streams to decouple IA equations for three-user MIMO IFC, which results in a single link feedback structure at each receiver. While for the conventional IA each receiver has to feed back to all transmitters for transmitting the maximum number of data streams. With the assumption of a random codebook, we analyze the upper bound of the average throughput loss caused by quantized channel knowledge as a function of feedback bits. Analytic results show that the proposed scheme outperforms the conventional IA scheme in term of the feedback overhead and the sum rate as well.

• 전자공학회논문지
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• 제51권6호
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• pp.26-33
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• 2014

LTE-A (Long Term Evolution-Advanced) 이후 무선 통신 시스템에서는, 시스템 전송률의 향상을 위해 증가한 개수의 입출력 안테나를 사용하는 MIMO (multiple-input multiple-output) 시스템이 활용될 것이다. 이러한 증가한 개수의 안테나 어레이를 사용하는 경우, 채널 정보의 궤환에 있어서 과도한 오버헤드가 문제가 될 수 있다. 본 논문에서는 이러한 상황에서 채널 정보의 궤환 오버헤드를 줄이기 위한 방안과, 특히 수신단에서 두 개 혹은 그 이상의 수신 안테나를 사용하는 다중 랭크 전송시의 적용 방안을 제안한다. 수신단에서 송신단으로 일시에 궤환되는 정보의 양을 줄이기 위해 안테나 어레이를 분할하여 추정하는 채널을 기반으로 특이값 분해 (SVD, Singular Value Decomposition)를 활용하는 빔포밍 방안을 제시한다. SVD의 연산과정의 특성 상, 분할된 행렬에 대한 SVD 연산은 원 행렬의 특성을 상실시킬 수 있으므로 이에 대한 대응 방안에 대해서도 설명한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.81-84
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• 2005

In this paper, we investigate the method for reducing the amount of feedback in multi-user downlink orthogonal frequency division multiple access (OFDMA) systems. The objective is to maximize the total throughput of the system under the constraints of transmit power. In previous methods, each user in a cell transmits channel quality information (CQI) of its all sub-bands to the base station, which requires extremely high feedback overhead. Thus, we propose an efficient sub-band allocation algorithm in which each user transmits partial CQI and one additional information to reduce the amount of feedback. Simulation results show that we can greatly reduce the amount of feedback than full feedback system.

• 한국통신학회논문지
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• 제33권6A호
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• pp.643-651
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• 2008

본 논문에서는 다중 사용자 다중 안테나직교 주파수 분할 다중 접속 방식 (MIMO-OFDMA) 시스템에서 부분 궤환 정보를 이용한 정규화된 신호 대 잡음비 기반 비례적 공정 스케줄링 (normalized SNR based proportional fair scheduling, NSNR-PFS)을 수행할 경우의 시스템 성능에 대하여 분석하였다. 선택적 부분 채널 품질 정보 궤환 기법 (selective partial channel quality information feedback scheme, SPCQI)이 사용되었을 경우의 하향 링크 채널 용량의 정확한 식을 유도하고, 그것의 점근적 특성을 분석하였다. 이론적 성능 분석과 모의 실험을 통하여 사용자의 수와 상관없이 한정된 평균 궤환량만을 이용하여 최적의 하향 링크 채널 용량 증가율을 얻을 수 있음을 보였다.

• 제어로봇시스템학회논문지
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• 제13권5호
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• pp.452-461
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• 2007

Adaptive anti-sway and trajectory tracking control of overhead crane is presented, which utilizes Fuzzy Uncertainty Observer(FUO) and Fuzzy based Variable Structure Control(FVSC). We consider an overhead crane system which can be decoupled into the actuated and unactuated subsystems with its own lumped uncertainty such as parameter uncertainties and external disturbance. First, a new method for anti-sway control using FVSC is proposed to improve the conventional method based on Lyapunov direct method, while a conventional trajectory tracking control law using feedback linearization is directly adopted. Second, FUO is designed to estimate one of the two lumped uncertainties which can compensate both of them, based on the fact that two lumped uncertainties are coupled with each other. Then, an adaptive anti-sway control is proposed by incorporating the proposed FVSC and FUO. Under the condition that the observation error is Uniformly Ultimately Bounded(UUB) within an arbitrarily shrinkable region, the overall closed-loop system is shown to be Globally Uniformly Ultimately Bounded(GUUB). In addition, the Global Asymptotic Stability(GAS) of it is shown under the vanishing disturbance assumption. Finally, the effectiveness of the proposed scheme has been confirmed by numerical simulations.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1683-1693
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• 1997

In this paper, a new nonlinear dynamic model is derived for a 2-dimensional overhead crane based on a new definition of 2-degree-of-freedom swing angle, and a new anti-swing control law is proposed for the crane. The dynamic model and control law take simultaneous travel and traverse motions of the crane into consideration. The model is first linearized for small motions of the crane load about the vertical stable equilibrium. Then the model becomes decoupled and symmetric with respect to the travel and traverse axes of the crane. From this result, a decoupled anti-swing control law is proposed based on the linearized model via the loop shaping and root locus methods. This decoupled method guarantees not only fast damping of load-swing but also zero steady state position error with optimal transient response for the 2-dimensional motion of the crane. Finally, the proposed control method is evaluated by controlling the simultaneous travel and traverse motions of a 2-dimensional prototype overhead crane. The effectiveness of the proposed control method is then proven by the experimental results.

• 조명전기설비학회논문지
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• 제17권2호
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• pp.49-57
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• 2003

천정크레인 설비의 자동화에 사용될 수 있는 반진동 제어알고리즘을 제안하였다. 제안하는 제어알고리즘은 1) 복잡한 비선형계통 제어에 유용한 것으로 알려진 보상 FLC를 갖는 FCL, 2) 화물의 진동을 적게 하도록 가속도, 속도, 위치 기준 궤적을 발생하는 기준패턴발생기, 3) 속도, 위치 오차를 궤환하는 가속도 궤환제어기로 구성된다. 특히, 제안한 알고리즘은 화물의 진동각 정보를 제어에 활용하지 않으므로 고가의 진동각 센서가 필요 없다는 특징을 갖는다. 시뮬레이션에 의한 연구와 모형 크레인에 대한 실험 연구에 의해 제안하는 알고리즘의 유용성을 보인다.

• 한국통신학회논문지
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• 제39A권7호
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• pp.431-436
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• 2014

본 논문에서는 높은 공간 상관도(spatial correlation)를 가지는 massive MIMO(multiple-input multiple-output) 시스템에서 Compressive Sensing 기반의 제한적 피드백 알고리즘을 제안한다. 현실적으로 많은 안테나를 설치하기 위해 기지국에서는 조밀한 uniform square array를 가정하였다. 또한 다중 사용자를 지원하기 위해 기지국에서는 영점강제(zero-forcing) 프리코더를 사용하였다. 시뮬레이션 결과, 제안한 피드백 알고리즘이 기존의 random vector quantization 코드북 보다 더 좋은 성능을 보이고 피드백 오버헤드와 코드북 인덱스를 찾는 계산량이 감소함을 보였다.