• 제어로봇시스템학회논문지
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• 제16권3호
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• pp.249-255
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• 2010

The paper proposes a new type of robust speed control strategy for permanent magnet synchronous motor by using PD-sliding mode hybrid control. The PD control has a good performance in the transient region while the sliding mode controller provides the robustness against system uncertainties. Taking advantages of the two control strategies, the proposed control method utilizes the PD control in the approaching region to the sliding surface and the sliding mode control near at the sliding surfaces. The chattering problem of the sliding mode controller is eliminated by applying the saturation function for the switching function of the sliding mode control. The stability of the sliding mode control is verified by using Lyapunov function with the proper selection of variable gains. It is shown that with this simple switching algorithm, stability of the overall hybrid control system is ensured. Through the simulations, the PD-sliding mode algorithm is shown to have a good performance in the transient response as well as being robust against disturbances. The robustness of the PD-sliding mode algorithm is further demonstrated against various external disturbances in the real experiments of SPMSM motor control.

• 한국산업정보학회논문지
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• 제22권1호
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• pp.1-9
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• 2017

무선 네트워크 기술과 무선 전송 기술의 발전으로 인해 무선 전달망(Wireless Transit Network) 구성 기술로서 무선 메시 네트워크(WMN)가 관심을 받고 있다. 오랜 기간 다양한 영역에서 WMN에 대한 연구가 진행되었지만 아직 해결되지 않은 문제들이 많이 남아있다. 그 중 하나가 무선 링크로 구성된 다중 홉 네트워크에서 최적 경로를 찾는 라우팅 문제이다. WMN의 3가지 구성유형 중 하나인 하이브리드 WMN에서 최적 경로 선택을 위해서는 우수한 성능의 메트릭 연구와 함께 효과적으로 인프라스트럭처 메시를 전달망으로 사용하기 위한 경로 검색 프로토콜 연구가 필요하다. 따라서 본 논문에서는 하이브리드 WMN을 위한 듀얼모드-AODV(Ad hoc On-demand Distance Vector)를 제안한다. 본 논문에서 제안된 듀얼모드-AODV를 하이브리드 WMN에 적용하는 경우 AODV에 비하여 경로 검색 지연시간이 52% 감소하는 것을 시뮬레이션을 통해 확인하였다.

• 한국통신학회논문지
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• 제34권2A호
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• pp.147-154
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• 2009

안테나 그룹화(antenna grouping)는 빔 형성(beamforming)파 공간 다중화 기법(spatial multiplexing)의 결합이라 할 수 있다. 안테나 그룹화는 $N_t$개의 송신 안테나를 $N_r$개의 그룹으로 나누고, 한 그룹 내에서는 빔 형성으로 하나의 데이터 정보를, 각 그룹 사이에서는 공간 다중화 기법으로, 전체 $N_r$개의 데이터 정보를 전송하는 시스템을 가정한다. 안테나 그룹화를 통하면 빔 형성을 통하여 다이버시티 이득을 얻을 수 있는 동시에 공간 다중화 기법에 따른 다중화 이득을 통하여 주파수 효율을 높일 수 있다. 하지만 통신 채널이 조건 나쁜(ill-conditioned) 행렬로 모델링 되거나, 안테나 사이에 상관관계가 있는 경우에는 안테나 그룹화의 BER 성능이 열화될 수 있으므로, 이 경우에는 전체 시스템에서 하나의 데이터 정보만 전송하는 빔 형성의 성능이 가장 좋다. 이 논문에서는 채널이 안테나 그룹화에 적합하면 안테나 그룹화 모드를 선택하여 전송하고, 빔 형성에 적합하면 빔 형성 모드를 선택하여 전송하는 시스템을 가정하였다. 그리고 간단한 모드 선택 기법을 제안한다. 이 모드 선택 기법을 사용하면 매 시간동안 일정한 데이터를 전송할 때, 채널 상태에 따른 BER 성능의 열화를 막고, 최적의 BER 성능을 얻을 수 있다.

• Journal of Power Electronics
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• 제15권5호
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• pp.1178-1189
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• 2015

A non-isolated Multiple Input Converter (MIC) with an input port, two storage ports and a load port is proposed. The synthesis of the proposed four port converter with its switch realization is presented. A steady state analysis of each operating mode with a small-signal model is derived, and a stability analysis is done. A mode selection controller is proposed to automatically choose a specific operating mode based on the voltage levels of the different source and storage units. In addition, a voltage control loop is used to regulate the output voltage. A 200W prototype is built with a TMS320F28027 DSP controller to test the feasibility of the operating modes. Simulation and experimental results show the ability of the proposed converter to handle multiple inputs either individually or simultaneously.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권3호
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• pp.950-975
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• 2016

Device-to-Device (D2D) communication underlaying cellular networks is a promising add-on component for future radio communication systems. It provides more access opportunities for local device pairs and enhances system throughput (ST), especially when mobile relays (MR) are further enabled to facilitate D2D links when the channel condition of their desired links is unfavorable. However, mutual interference is inevitable due to spectral reuse, and moreover, selecting a suitable transmission mode to benefit the correlated resource allocation (RA) is another difficult problem. We aim to optimize ST of the hybrid system via joint consideration of mode selection (MS) and RA, which includes admission control (AC), power control (PC), channel assignment (CA) and relay selection (RS). However, the original problem is generally NP-hard; therefore, we decompose it into two parts where a hierarchical structure exists: (i) PC is mode-dependent, but its optimality can be perfectly addressed for any given mode with additional AC design to achieve individual quality-of-service requirements. (ii) Based on that optimality, the joint design of MS, CA and RS can be viewed from the graph perspective and transferred into the maximum weighted independent set problem, which is then approximated by our greedy algorithm in polynomial-time. Thanks to the numerical results, we elucidate the efficacy of our mechanism and observe a resulting gain in MR-aided D2D communication.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권5호
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• pp.1303-1315
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• 2012

In the draft of the IEEE 802.11s standard, a tree topology is established by the proactive tree-building mode of the Hybrid Wireless Mesh Protocol (HWMP). It is used for cases in which the root station (e.g., gateway) is an end point of the majority of the data connections. In the tree topology, the root or central stations (e.g., parent stations) are connected to the other stations (e.g., leaves) that are one level lower than the central station. Such mesh stations are likely to suffer heavily from contention in bottleneck links when the network has a high traffic load. Moreover, the dependence of the network on such stations is a point of vulnerability. A failure of the central station (e.g., a crash or simply going into sleep mode to save energy) can cripple the whole network in the tree topology. This causes performance degradation for end-to-end transmissions. In a connected mesh topology where the stations having two or more radio links between them are connected in such a way that if a failure subsists in any of the links, the other link could provide the redundancy to the network. We propose a scheme to utilize this characteristic by organizing the network into concentric tiers around the root mesh station. The tier structure facilitates path recovery and congestion control. The resulting mode is referred to as Tier-based Proactive Path Selection Mode (TPPSM). The performance of TPPSM is compared with the proactive tree mode of HWMP. Simulation results show that TPPSM has better performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.711-732
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• 2019

Many unmanned aerial vehicle (UAV) applications have been employed for performing data collection in facilitating tasks such as surveillance and monitoring objectives in remote and dangerous environments. In light of the fact that most of the existing UAV relaying applications operate in conventional half-duplex (HD) mode, a full-duplex (FD) based UAV relay aided wireless network is investigated, in which the UAV relay helps forwarding information from the source (S) node to the destination (D). Since the activated UAV relays are always floating and flying in the air, its channel state information (CSI) as well as channel capacity is a time-variant parameter. Considering decode-and-forward (DF) relaying protocol in UAV relays, the cooperative relaying channel capacity is constrained by the relatively weaker one (i.e. in terms of signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR)) between S-to-relay and relay-to-D links. The channel capacity can be optimized by adaptively optimizing the transmit power of S and/or UAV relay. Furthermore, a hybrid HD/FD mode is enabled in the proposed UAV relays for adaptively optimizing the channel utilization subject to the instantaneous CSI and/or remaining self-interference (SI) levels. Numerical results show that the channel capacity of the proposed UAV relay aided wireless networks can be maximized by adaptively responding to the influence of various real-time factors.

• Journal of Power Electronics
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• 제19권1호
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• pp.220-233
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• 2019

This work aims to study and analyze the various operating modes of universal power converter which is powered by solar and thermoelectric generators. The proposed converter is operated in a DC-DC (buck or boost mode) and DC-AC (single phase) inverter with high efficiency. DC power sources, such as solar photovoltaic (SPV) panels, thermoelectric generators (TEGs), and Li-ion battery, are selected as input to the proposed converter according to the nominal output voltage available/generated by these sources. The mode of selection and output power regulation are achieved via control of the metal-oxide semiconductor field-effect transistor (MOSFET) switches in the converter through the modified stepped perturb and observe (MSPO) algorithm. The MSPO duty cycle control algorithm effectively converts the unregulated DC power from the SPV/TEG into regulated DC for storing energy in a Li-ion battery or directly driving a DC load. In this work, the proposed power sources and converter are mathematically modelled using the Scilab-Xcos Simulink tool. The hardware prototype is designed for 200 W rating with a dsPIC30F4011 digital controller. The various output parameters, such as voltage ripple, current ripple, switching losses, and converter efficiency, are analyzed, and the proposed converter with a control circuit operates the converter closely at 97% efficiency.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송∙미디어공학회 2016년도 하계학술대회
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• pp.50-53
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• 2016

조건부 대체 알고리즘 (CRA: Conditional Replenishment Algorithm)은 융합형 3DTV 서비스에서 부가정보를 전송함으로써 수신기에서의 화질을 개선하는 방법이다. 이 알고리즘은 비용함수를 도입함으로써 가변크기의 처리단위 (PU: Processing Unit) 마다 최적의 모드를 결정하는데, 이 과정에서 시공간적 인접 PU 사이에 모드의 불연속이 발생하는 경우에 블록화 또는 플리커링 현상 등 주관적 화질을 저하시키는 문제가 생길 수 있다. 본 논문에서는 모드를 결정하는 과정에서 시간적으로 연속적인 PU 사이의 상관성을 고려함으로써 플리커링 현상을 방지하는 기법을 제안하고 모의실험을 통해 주관적 화질이 향상됨을 보였다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2002년도 정기총회 및 학술대회
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• pp.105-109
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• 2002

The main ideas of hybrid video coding methods are to reduce the spatial and temporal redundancy for efficient data compression. If compressed video stream is transmitted through the error-prone channel, bitstream can be critically damaged and the spatio-temporal error propagates through successive frames at the decoder because of drift noise in the references between encoder and decoder. In this paper, I propose the lagrangian multiplier selection method in the error-prone environment. Finally, it is shown that the performance comparisons of the R-D optimized mode decision are made against the conventional method and simulation results are given in the following.