• Journal of Power Electronics
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• 제18권1호
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• pp.251-265
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• 2018

To enable a master-slave control independent microgrid system (MSCIMGS) to supply electricity continuously, the microgrid inverter should perform mode transfer between grid-connected and islanding operations. Transient oscillations should be reduced during transfer to effectively conduct a seamless mode transfer. This study uses a typical MSCIMGS as an example and improves the mode transfer strategy in three aspects: (1) adopts a status-tracking algorithm to improve the switching strategy of the outer loop, (2) uses the voltage magnitude and phase pre-synchronization algorithm to reduce transient shock at the time of grid connection, and (3) applies the hybrid-sensitivity $H_{\infty}$ robust controller instead of the current inner loop to improve the robustness of the controller. Simulations and experiments show that the proposed strategy is more practical than the traditional proportional-derivative control mode transfer and effective in reducing voltage and current oscillations during the transfer period.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권10호
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• pp.4015-4033
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• 2015

The future mobile networks consist of hyper-dense heterogeneous and small cell networks of same or different radio access technologies (RAT). Integrating mobile networks of different RATs to provide seamless and smooth mobility service will be the target of future mobile converged network. Generally, handover from high-speed networks to low-speed networks faces many challenges from application perspective, such as abrupt bandwidth variation, packet loss, round trip time variation, connection disruption, and transmission blackout. Existing inter-RAT handover solutions cannot solve all the problems at the same time. Based on the high-layer convergence sublayer design, a new receiver-aided soft inter-RAT handover is proposed. This soft handover scheme takes advantage of multihoming ability of multi-mode mobile station (MS) to smooth handover procedure. In addition, handover procedure is seamless and applicable to frequent handover scenarios. The simulation results conducted in UMTS-WiMAX converged network scenario show that: in case of TCP traffics for handover from WiMAX to UMTS, not only handover latency and packet loss are eliminated completely, but also abrupt bandwidth/wireless RTT variation is smoothed. These delightful features make this soft handover scheme be a reasonable candidate of mobility management for future mobile converged networks.

• 한국인터넷방송통신학회논문지
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• 제13권6호
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• pp.29-35
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• 2013

우리나라 재난관리 기관에서는 재난발생시 대응활동을 위해 이종의 재난통신 무전기를 사용하고 있다. 이러한 무전기들은 통신 방식에 따라 각기 다른 통신접속지연을 보이므로 이들 간에 원활한 음성통신을 위해서는 시간차에 따른 보정기술이 필요하다. 이에 본 논문에서는 아날로그와 디지털 그리고 직접 통신과 기지국 통신에 따른 각각의 통신지연에 따른 무전기간 음성 전송권 획득 및 음성데이터의 손실 문제를 해결하기 위한 방안을 제시하였다.

• IEIE Transactions on Smart Processing and Computing
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• 제3권5호
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• pp.325-330
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• 2014

The era of convergence is being applied to all areas of Information and Communication Technology (ICT). The convergence of broadcasting service and communication service almost occurs on smart devices including smartphone. The smart hybrid Digital Multimedia Broadcasting (DMB) is a typical example of the convergence of broadcasting and wireless communication service. The hybrid mobile broadcasting service can support seamless video, 3D, high quality, and additional data services based on network connection between the broadcasting and wireless network. The gateway and terminal (including apps on the smartphone) take the role of the main components on the hybrid service. This paper presents the service concept, main components structure, the implementation of gateway and terminals, and field test to the urban areas for the mobile hybrid system.

• 한국디지털정책학회:학술대회논문집
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• 한국디지털정책학회 2005년도 추계학술대회
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• pp.299-311
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• 2005

This article introduces developing trends of an "Ubiquitous Interface" as an access method for use of various network resources, such as public wireless networks and un-licensed wireless networks in ubiquitous sensor network environments, without troublesome settings or operations by users. "Ubiquitous Interface" is include a relatively wide sense meaning not only physical interface of specified device or between processors, but anything method for access USN. These "Ubiquitous Interface" able to provide seamless services that adapt autonomously to the user's movements and changes in the state of wireless resources. Recently, strongly recommended candidates are RFID, NFC, Multi-mode mobile terminal, Wearable computer and OSGi for integrated digital home networking system as a future ubiquitous interface. These candidates are have to have flexibility and multiple physical communication channel for seamless service hand over and serve easy connection at huge USN to user. And, must have flexible software structure and multi-functional middleware. Consequently, for more enhance performance of an ubiquitous interface and developing, need more structured and integrated future plan.

• Journal of Communications and Networks
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• 제15권2호
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• pp.207-216
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• 2013

Vehicular ad-hoc networks (VANETs) are self-organizing, self-healing networks which provide wireless communication among vehicular and roadside devices. Applications in such networks can take advantage of the use of simultaneous connections, thereby maximizing the throughput and lowering latency. In order to take advantage of all radio interfaces of the vehicle and to provide good quality of service for vehicular applications, we developed a seamless flow mobility management architecture based on vehicular network application classes with network-based mobility management. Our goal is to minimize the time of flow connection exchange in order to comply with the minimum requirements of vehicular application classes, as well as to maximize their throughput. Network simulator (NS-3) simulations were performed to analyse the behaviour of our architecture by comparing it with other three scenarios. As a result of this work, we observed that the proposed architecture presented a low handover time, with lower packet loss and lower delay.

• Journal of Information Processing Systems
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• 제11권4호
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• pp.616-629
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• 2015

A mobile terminal will expect a number of handoffs within its call duration. In the event of a mobile call, when a mobile node moves from one cell to another, it should connect to another access point within its range. In case there is a lack of support of its own network, it must changeover to another base station. In the event of moving on to another network, quality of service parameters need to be considered. In our study we have used the Markov decision process approach for a seamless handoff as it gives the optimum results for selecting a network when compared to other multiple attribute decision making processes. We have used the network cost function for selecting the network for handoff and the connection reward function, which is based on the values of the quality of service parameters. We have also examined the constant bit rate and transmission control protocol packet delivery ratio. We used the policy iteration algorithm for determining the optimal policy. Our enhanced handoff algorithm outperforms other previous multiple attribute decision making methods.

• 한국전산구조공학회논문집
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• 제36권1호
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• pp.27-38
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• 2023

본 논문에서는 최근 4차 산업혁명을 통해 최신 ICT 기술을 접목하여 대한민국의 항만, 해운, 조선 및 기자재 산업이 물샐틈없는 완벽 공조를 통한 가치 사슬, Seamless Value Chain이 Smart Seamless Value Chain 성공적인 구축을 위한 산업 간의 협력관계를 정의하고, 이들 산업의 지속 가능한 발전을 위한 핵심 요소가 무엇인지를 고찰해 보았다. 이를 통해 오늘날 디지털화를 통한 탈탄소화를 실현하여 ESG 경영 달성을 위한 방향도 제시하였다. 그리고 특히 중소기업의 관점에서 미래시장을 대응하기 위한 방안으로서의 디지털화의 중요성과, 특히 중소 기자재 업체가 실현하는 디지털 화가 산업계 전반에서 어떤 역할을 하는지 중점적으로 고찰하였다. 이를 통해 산업 간의 연계 상태와 가치 사슬이 원활한 관계를 반드시 유지해야할 필요 사유를 동시에 보여준다. 그리고 대한민국의 산업에서 얻은 실패 사례를 통한 교훈으로 발판 삼아 향후 지능형 연결의 전략적 통로를 만드는 초석을 구축하는 방향성도 제시하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.209-211
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• 2004

We can categorize mobility two main fields in IP environment. If Mobile IP manages macro mobility, Cellular IP deal with micro mobility. For seamless connection, it is major problem to reduce packet loss in the network layer during handoff. This paper will introduce a scheme which reduces packet loss during micro mobility which use indirect handoff mechanism in Cellular IP, and will verify the efficiency of that scheme by computer simulation.

• 산업기술연구
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• 제28권B호
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• pp.245-250
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• 2008

Recently, mobile devices have supported wireless LAN as well as bluetooth, where the services such as heterogeneous network access and seamless mobility connection are important. Even though the mobility and physical network might be varied, an efficient communication mechanism for the network access and a robust mobility management of mobile devices are needed. In this paper, we design and implement a Bluetooth system with mobile LAN access capability. The proposed system has the following features; 1) IP connection is enabled by BENP in the link layer, 2) The networks devices of heterogeneous mobile devices are integrated into a single virtual network interface, 3) IP mobility between the bluetooth and wireless LAN is supported by mobile IP. The experimented results show that the packet loss and delay time during the handover duration is reduced by predicting the handover among different networks followed by the setup of any required parameters in advance.