• ETRI Journal
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• 제35권6호
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• pp.1144-1147
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• 2013

Dual-mode terminals (DMTs) equipped with cellular and WLAN interfaces have become popular in recent years. Users of DMTs can enjoy high-speed WLAN Internet access and wide area Internet access to cellular networks. However, a DMT may consume power inefficiently when discovering a WLAN with inherently limited service coverage. In this letter, we propose to use smart WLAN discovery (SWD) to minimize the power consumption required for WLAN discovery. To minimize the power consumption of a DMT, an SWD DMT activates its WLAN interface only when the DMT transfers data within the WLAN coverage area. The simulation results of SWD show an improved power-saving performance compared to previous WLAN discovery schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권1호
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• pp.123-140
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• 2011

In this paper, we propose an Energy Efficient Media Access Control (EE-MAC) protocol for wireless sensor networks. The proposed scheme is designed to save power consumption and guarantee quality-of-service for real-time traffic. EE-MAC uses the superframe structure which is bounded by the transmission of a beacon frame and can have an active and an inactive portion. The active period is divided into the contention free period (CFP) for real-time traffic transmission and the contention access period (CAP) for non-real-time traffic transmission. We propose the exclusively allocated backoff scheme which assigns a unique backoff time value to each real-time node based on bandwidth allocation and admission control. This scheme can avoid collision between real-time nodes by controlling distributed fashion and take effect a statistical time division multiple access. We also propose the algorithm to change the duty cycle adaptively according to channel utilization of media depending on network traffic load. This algorithm can prolong network lifetime by reducing the amount of energy wasted on idle listening.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 추계종합학술대회
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• pp.464-467
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• 2001

통신기술의 발전에 따라 통신서비스 제공을 위한 네트웍이 다양화되고 있는 반면, 점점 더 광대역화되고 있다는 데에는 논란의 여지가 거의 없다. 우리나라는 최근 ADSL 등 초고속인터넷접속서비스의 보급율이 세계에서 가장 높은 국가로서 주목을 받고 있으며, 정책적으로는 새로운 규제를 도입하고 있다. 이에 과연 우리나라의 초고속인터넷접속서비스 시장에 언번들링과 같은 규제가 필요한 것인지를 주요 국가의 사례를 중심으로 검토하고자 한다. 본 연구결과 우리나라의 초고속인터넷접속서비스 시장은 다른 국가의 초고속인터넷접속서비스 시장과는 다른 특성을 가지고 있기 때문에 규제도입 여부를 다시 한번 검토해야 하며, 규제를 도입한다 하더라도 규제의 관점을 소비자 지향적인 관점으로 전환하여 체계를 정립할 필요가 있다고 판단된다.

• 한국인터넷방송통신학회논문지
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• 제13권5호
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• pp.249-258
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• 2013

다중-홉 애드 혹 네트워크(multi-hop ad hoc networks)에서 실효 대역폭과 단-대-단 처리량을 높이기 위한 방법으로 다중-인터페이스 다중-채널 구조가 주목을 받고 있다. 그러나 단일 인터페이스 기반 네트워크를 위해서 설계된 기존의 라우팅 메트릭들은 다중-인터페이스 다중-채널 기반 네트워크의 특성을 정확히 반영할 수 없으므로, 처리량 개선의 효과를 기대할 수 없다. 따라서 채널 다양성, 인터페이스 전환 비용과 같은 메트릭들을 사용하여 높은 처리량을 갖는 경로를 발견하는 MCR이 제안되었다. 하지만 MCR은 트래픽 부하의 영향을 반영하지 않기 때문에 혼잡한 네트워크에서 성능이 저하되는 문제점이 있다. 본 논문에서는 MCR에 채널 접근 시간 메트릭을 결합하여 혼잡한 조건에서도 높은 처리량을 갖는 경로를 선택하는 MAMCR 메트릭을 제안하고, ns-2 시뮬레이션을 통해 성능 개선 효과를 확인한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권4호
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• pp.1076-1089
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• 2012

Home automation networks are good environments for merging sensor networks and consumer electronics technologies. It is very important to reduce the energy consumption of each sensor node because sensor nodes operate with limited power based on a battery that cannot be easily replaced. One of the primary mechanisms for achieving low energy operation in energy-constrained wireless sensor networks is the duty-cycle operation, but this operation has several problems. For example, unnecessary energy consumption occurs during synchronization between transmission schedules and sleep schedules. In addition, a low duty-cycle usually causes more performance degradation, if the network becomes congested. Therefore, an appropriate control scheme is required to solve these problems. In this paper, we propose UDC (Unsynchronized Duty-cycle Control), which prevents energy waste caused by unnecessary preamble transmission and avoids congestion using duty-cycle adjustment. In addition, the scheme adjusts the starting point of the duty-cycle in order to reduce sleep delay. Our simulation results show that UDC improves the reliability and energy efficiency while reducing the end-to-end delay of the unsynchronized duty-cycled MAC (Media Access Control) protocol in sensor-based home automation networks.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2000년도 추계종합학술대회
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• pp.216-219
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• 2000

최근 들어 위성 통신 기술의 발전으로 위성을 이용한 네트워크 액세스가 기존 액세스망의 또 다른 보완 수단으로 유력해지고 있다. 위성을 이용하여 멀티미디어 서비스를 가입자에게 제공할 수 있는 액세스망에서 인터넷 접속은 빼놓을 수 없는 중요한 서비스가 될 것이다. 특히, 실시간 트래픽이 급증하고 있는 인터넷 접속 서비스에서 이를 지원할 수 있는 실시간 전달 프로토콜의 연구는 긴요하다. 본 연구에서는 그동안 IETF에서 표준 프로토콜로 개발되어 온 실시간 전달 프로토콜 (RTP: Real Time Protocol)의 위성 멀티미디어 액세스망 적용을 위해 동 프로토콜을 구현하였다. RTP는 현 인터넷을 통해 오디오/ 비디오를 전달할 때 실시간 트래픽의 엄격한 시간 제약성을 만족시키기 위해 개발된 프로토콜로서, 위성 액세스망과 같은 고유한 링크 특성을 갖는 환경에서 적용성을 확인할 필요가 있다. 본 논문에서는 RTP 프로토콜의 개요를 살펴보고, 프로토콜 설계 구조와 주요 구성 요소 및 그 구현 내용을 기술한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4367-4386
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• 2015

The concept of Internet of Things (IoT) has shed new light on WSN technologies. MAC protocol issues improving the network performance are important in WSNs because of the increase in demand for various applications to secure spectrum resources. Cognitive radio (CR) technology is regarded as a solution to the problems in this future wireless network. In recent years, energy efficiency has become an issue in CR networks. However, few relevant studies have been conducted. In this paper, an energy-efficient non-overlapping channel MAC (ENC-MAC) for CR-enabled sensor networks (CRSNs) is proposed. Applying the dedicated control channel approach, ENC-MAC allows the SUs to utilize channels in a non-overlapping manner, and thus spectrum efficiency is improved. Moreover, the cooperative spectrum sensing that allows an SU to use only two minislots in the sensing phase is addressed to en-hance energy efficiency. In addition, an analytical model for evaluating the performance, such as saturation throughput, average packet delay, and network lifetime, is developed. It is shown in our results that ENC-MAC remarkably outperforms existing MAC protocols.

• ETRI Journal
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• 제36권1호
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• pp.1-11
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• 2014

In this paper, we propose a distributed synchronization algorithm for wireless mesh networks based on orthogonal frequency division multiple access. For time and frequency synchronization, a node requests its neighbor nodes for a change of fast Fourier transform starting points, transmission times, and carrier frequencies needed for synchronization. The node also updates its own time and frequency elements through simple formulas based on request messages received from neighbor nodes using a guard interval and a cyclic prefix. This process with the cooperation of neighbor nodes leads to a gradual synchronization of all nodes in the network. Through a performance comparison with a conventional scheme, we obtain simulation results indicating that the proposed scheme outperforms the conventional scheme in random topologies and a grid topology.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권7호
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• pp.2454-2467
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• 2015

Increasing traffic and bandwidth requirements bring challenges to the next generation wireless networks (5G). As one of the main technology in 5G networks, Ultra-Dense Network (UDN) can be used to improve network coverage. In this paper, a radio over fiber based model is proposed to solve the load balancing problem in ultra-dense network. Stochastic differential game is introduced for the load balancing algorithm, and optimal load allocated to each access point (RAP) are formulated as Nash Equilibrium. It is proved that the optimal load can be achieved and the stochastic differential game based scheme is applicable and acceptable. Numerical results are given to prove the effectiveness of the optimal algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권11호
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• pp.2980-2991
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• 2012

Since wireless sensor networks are broadly used in various areas, there have been a number of protocols developed to satisfy specific constraints of each application. The most important and common requirements regardless of application types are to provide a long network lifetime and small end-to-end delay. In this paper, we propose Early Preamble MAC (EP-MAC) with improved energy conservation and low latency. It is based on CMAC but adopts a new preamble type called 'early preamble'. In EP-MAC, a transmitting node can find quickly when a next receiving node wakes up, so EP-MAC enables direct data forwarding in the next phase. From numerical analysis, we show that EP-MAC improves energy consumption and latency greatly compared to CMAC. We also implemented EP-MAC with NS-2, and through extensive simulation, we confirmed that EP-MAC outperforms CMAC.