• 한국통신학회논문지
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• 제37권4A호
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• pp.250-259
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• 2012

본 논문에서는 반복계산에 따라 비선형 최소점을 탐색하는 최적화 알고리즘의 선택이 선형배열음원의 지향성합성에 미치는 영향을 목적지향성의 설계사양에 대한 만족도, 수렴성, 그리고 적응성의 면에서 비교 검토하였다. 지향성합성은 최적화 알고리즘인 DFP(Davidon-Fletcher-Powell)법과 BFGS (Broyden-Fletcher-Goldfarb-Shanno)법을 이용하였으며, 준이상 빔과 회전 빔, 그리고 멀티 빔을 목적지향성으로 설정하였다. 수치계산 결과, 지향성합성에 대한 준뉴톤법의 유효성 확인과 함께 수치계산 과정에서 발생된 문제점에 대한 해결 방법도 제시하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.2237-2242
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• 2005

The original RRT is iteratively expanded by applying control inputs that drive the system slightly toward randomly-selected states, as opposed to requiring point-to-point convergence, as in the probabilistic roadmap approach. It is generally known that the performance of RRTs can be improved depending on the selection of the metrics in choosing the nearest vertex and bias techniques in choosing random states. We designed a path planning algorithm based on the RRT method for a remote-controlled mobile robot. First, we considered a bias technique that is goal-biased Gaussian random distribution along the command directions. Secondly, we selected the metric based on a weighted Euclidean distance of random states and a weighted distance from the goal region. It can save the effort to explore the unnecessary regions and help the mobile robot to find a feasible trajectory as fast as possible. Finally, the constraints of the actuator should be considered to apply the algorithm to physical mobile robots, so we select control inputs distributed with commanded inputs and constrained by the maximum rate of input change instead of random inputs. Simulation results demonstrate that the proposed algorithm is significantly more efficient for planning than a basic RRT planner. It reduces the computational time needed to find a feasible trajectory and can be practically implemented in a remote-controlled mobile robot.

• 한국주거학회논문집
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• 제24권6호
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• pp.111-121
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• 2013

Recently housing demands are going to be diversified, and many suggestions are driven for the housing consumer's right of choice and expectation for welfare services. These require the policy change from the clear division between houses and facilities toward more market-oriented concept capable of mixed-use development of houses with facilities. The research explores the possibilities to provide various types of mixed-use developments of houses and facilities in the level of architectural design and political implication. Major case studies focus on the elderly welfare housing with serviced residence with the comparison of similar cases in Japan. The policy implications are, first, expanding the production of elderly housing with more elderly care services, second, challenging time-sharing residence composed of serviced residence and small dwelling units, third, activating the production of small scale housing development with small public facilities. The simulation shows the merits and demerits of this concepts and the efficacy of the policy implications.

• 한국통신학회논문지
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• 제34권12B호
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• pp.1506-1513
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• 2009

본 논문은 ISO 18000-3 mode 3 PJM 모드에서 프리엠블을 이용해서 데이터 복조 시작점을 추출하는 동기화기법 및 이를 구현하는 하드웨어 구조를 제시한다. 제안된 시스템은 초기시간 선택부 및 코릴레이터로 초기 피크를 검출 후 이어지는 두 개의 코릴레이터를 이용해서 검출된 피크의 위치를 확인하여 동기를 맞춘다. 각각의 코릴레이터 템플릿 및 피크검출 알고리즘을 제시하며 제안된 시스템이 잡음 환경에서도 성공적으로 동작함을 시뮬레이션을 통해 보인다.

• 전기전자학회논문지
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• 제22권2호
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• pp.384-392
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• 2018

다중출력 LDO 레귤레이터는 다양한 공급 전압이 필요한 임베디드 시스템에서 변환 효율을 개선할 수 있는 방안이 된다. 다중 출력을 위한 시분할 구조에서 LDO의 피드백 인자가 작아지면 정착시간이 길어져서 리플 전압이 커진다. 제안하는 토폴로지에서는 기준 전압을 가변하여 일정한 피드백 인자를 구현함으로써 정착시간과 리플 특성을 개선한다. $0.35{\mu}m$ 표준 CMOS 공정으로 설계한 4 채널 프로토타입의 시뮬레이션 결과 제안하는 구조는 피드백 인자가 0.4 이하인 기존 회로보다 정착시간과 리플 특성이 2배 이상 개선되는 것을 입증하였다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제2권1호
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• pp.43-48
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• 2002

This paper discusses the application of fuzzy-ARTMAP neural network to compensate the nonlinearity of satellite communication channel. The fuzzy-ARTMAP is the class of ART(adaptive resonance theory) architectures designed fur supervised loaming. It has capabilities not fecund in other neural network approaches, that includes a small number of parameters, no requirements fur the choice of initial weights, automatic increase of hidden units, and capability of adding new data without retraining previously trained data. By a match tracking process with vigilance parameter, fuzzy-ARTMAP neural network achieves a minimax teaming rule that minimizes predictive error and maximizes generalization. Thus, the system automatically leans a minimal number of recognition categories, or hidden units, to meet accuracy criteria. As a input-converting process for implementing fuzzy-ARTMAP equalizer, the sigmoid function is chosen to convert actual channel output to the proper input values of fuzzy-ARTMAP. Simulation studies are performed over satellite nonlinear channels. QPSK signals with Gaussian noise are generated at random from Volterra model. The performance of proposed fuzzy-ARTMAP equalizer is compared with MLP equalizer.

• 한국인터넷방송통신학회논문지
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• 제17권1호
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• pp.107-113
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• 2017

이 논문은 벡터 양자기가 포함된 부대역 코덱의 분석과 설계에서 벡터 양자기를 모델링하는 새로운 방법을 제시해준다. 우리는 각 코드북의 시작점들의 수(N), 각 코드워드의 길이(k), 필터 대역 계수들에 의존하는 부대역 코덱 시스템의 입력과 출력의 평균자승 회복 오차(MSE)를 계산한다. 본 논문은 확률밀도함수로 최적화된 벡터양자기가 존재하는 최적의 M밴드 필터 뱅크 구조는 등가의 스칼라 양자기의 변수들의 적절한 선택으로 구현될 수 있음을 보였다. 특정한 구현 예를 두 개의 다른 필터뱅크 구조인 Paraunitary 필터 뱅크와 Biorthogonal 필터 뱅크를 2채널 경우에 개발하였다. 이 이론적인 결과들은 확장의 Monte Carlo 시뮬레이션으로 확인되었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권12호
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• pp.5150-5169
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• 2015

Mobile Ad hoc NETworks (MANETs) are the best choice when mobility, scalability, and decentralized network infrastructure are needed. Because of critical mission applications of MANETs, network security is the vital requirement. Most routing protocols in MANETs assume that every node in the network is trustworthy. However, due to the open medium, the wide distribution, and the lack of nodes' physical protection, attackers can easily compromise MANETs by inserting misbehaving nodes into the network that make blackhole attacks. Previous research to detect the misbehaving nodes in MANETs used the overhearing methods, or additional ACKnowledgement (ACK) packets to confirm the reception of data packets. In this paper a special lightweight acknowledgement-based method is developed that, contrary to existing methods, it uses ACK packets of MAC layer instead of adding new ACK packets to the network layer for confirmations. In fact, this novel method, named PIGACK, uses ACK packets of MAC 802.11 to piggyback confirmations from a receiver to a sender in the same transmission duration that the sender sends a data packet to the receiver. Analytical and simulation results show that the proposed method considerably decreases the network overhead and increases the packet delivery ratio compared to the well-known method (2ACK).

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.507-515
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• 2013

This paper proposes a compensation method for the $2^{nd}$-order harmonic of single-phase grid-connected wind power generation systems. Theoretically, a single-phase grid-connected inverter system has no choice but to cause the $2^{nd}$-order harmonic to DC-link voltage. The reference active current is affected by the DC-link voltage. The output current from the reference active current is distorted by the $1^{st}$ and $3^{rd}$-order harmonic. The proposed method can compensate, conveniently, the reference active current with the $2^{nd}$-order harmonic. To reduce the $2^{nd}$-order ripple in the reference active current, proposed method takes a PR controller as a feed-forward compensator. PR controllers can implement selective harmonic compensation without excessive computational requirements; the use of these controllers simplifies the method. Both the simulation and experimental results agree well with the theoretical analysis.

• Journal of Advanced Marine Engineering and Technology
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• 제39권10호
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• pp.1023-1030
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• 2015

The purpose of this paper is to present the basic mathematical modeling of a hexacopter, which could be used to develop proper methods for stabilization and trajectory control. A hexacopter consists of six rotors with three pairs of counter-rotating fixed-pitch blades. This mechanism is an under-actuated, dynamically unstable, six-degrees-of-freedom system. The whole motion of this object consists of translational and rotational motion in three dimensions, where the translational motion is created by changing the direction and magnitude of the upward propeller thrust. The hexacopter is controlled by adjusting the angular velocities of the rotors, which are spun by electric motors. It is assumed to be a rigid body; thus, the differential equation of the hexacopter dynamics can be derived from the Newton-Euler equation. The Euler-angle parametrization of the three-dimensional rotations contains singular points in the coordinate space that can cause failure of both the dynamical model and control. In order to avoid singularities, the rotations of the hexacopter are parametrized in terms of quaternions. This choice has been made considering the linearity of the quaternion formulation and their stability and efficiency. Further, control simulation of a hexacopter applying cascaded-PID control is also presented in this paper.