• Journal of Information Processing Systems
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• 제6권4호
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• pp.501-510
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• 2010

Wireless sensor networks consist of sensor nodes which are expected to be battery-powered and are hard to replace or recharge. Thus, reducing the energy consumption of sensor nodes is an important design consideration in wireless sensor networks. For the implementation of an energy-efficient MAC protocol, a Sensor-MAC based on the IEEE 802.11 protocol, which has energy efficient scheduling, has been proposed. In this paper, we propose a Dynamic S-MAC that adapts dynamically to the network-traffic state. The dynamic S-MAC protocol improves the energy consumption of the S-MAC by changing the frame length according to the network-traffic state. Using an NS-2 Simulator, we compare the performance of the Dynamic S-MAC with that of the S-MAC protocol.

• 전자공학회논문지
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• 제53권2호
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• pp.3-9
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• 2016

본 논문에서는 무선 및 이동통신을 위한 클라우드 무선 가입자 네트워크를 지원하는 프론트홀에서 무선 라디오파의 광섬유 전송망의 기술을 제안하고 구현한다. 하향 링크는 OFMD (orthogonal frequency division multiplexing) (O기법을 사용하였고 상향방향의 전송은 SC-FDMA (single carrier-frequency multiple access) 방식으로 구현하였다. 64, QAM, 16QAM, QPSK 등 다양한 변조 방식에 대해 시스템 파라메터를 도출하고 측정치를 기반으로 성능을 분석하였다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2012년도 한국컴퓨터종합학술대회논문집 Vol.39 No.1(D)
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• pp.262-264
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• 2012

Dynamic spectrum access and cognitive radio is a viable solution to solve congestion in ISM band. The dynamic environment of multi-channel wireless LAN is modeled by using continuous time Markov process. Bayes theorem is applied to infer channel access decisions dynamically to ensure current data transmission is switched to only likely candidate channels.

• 한국정보기술학회 영문논문지
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• 제8권2호
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• pp.1-11
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• 2018

Multimedia contents have been increasingly available over the Internet as wireless networks systems are continuously growing popular. Unlimited access from various users has led to unauthorized access of third parties or adversaries. This paper deals with the implementation of elliptic curve cryptography (ECC) based user authentication for securing multimedia contents over the Internet. The ECC technique has been incorporated with the advanced encryption standard (AES) algorithm to ensure the complexity of the proposed authentication scheme and to guarantee authenticity of multimedia services.

• 한국인터넷방송통신학회논문지
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• 제10권3호
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• pp.111-119
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• 2010

오늘날 무선 기술의 급속한 발전으로 인해 복수개의 액세스 인터페이스를 갖는 이동단말들이 나타나고 있다. 최근 WLAN이 근거리 통신을 위해 많은 가정과 기업에서 사용되고 있으며, WiMAX 또한 장거리 데이터 전달을 위한 무선 표준으로 부각되고 있다. 따라서 이기종 무선망간에 멀티미디어 데이터를 전달하기 위한 효율적인 접속 방안 연구가 필요하다. 본 논문에서는 WiMAX와 WLAN 인터페이스를 갖고 모바일 IP를 이용해 두 망사이를 이동할 수 있는 멀티홈드 노드의 시뮬레이션 모델과 환경을 개발하였다. 개발된 모델을 검증하기 위해 단방향/양방향 UDP 패킷, FTP 트래픽, SIP 프로토콜을 이용한 음성 전송 등과 같은 다양한 트래픽 환경하에서 여러가지 시뮬레이션 시나리오 즉, WiMAX와 WLAN 망간 이동, 그룹 이동성, MANET, 중첩 모바일 IP 등을 설계하고 구성하였으며, 시뮬레이션 결과를 분석함으로써 개발된 모델이 다양한 무선망 접속 시나리오에서의 이동성 연구에 효율적임을 보였다.

• ETRI Journal
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• 제30권1호
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• pp.13-20
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• 2008

We evaluate the sink capacity of wireless code division multiple access (CDMA) sensor networks with layered architecture. We introduce a model of interference at a sink considering two kinds of interference: multiple access interference (MAI) and node interference (NI). We also investigate the activity of sensor nodes around the sink in relation to gathering data under a layered architecture. Based on the interference model and the activity of sensor nodes around the sink, we derive the failure probability of the transmission from a source node located one hop away from the sink using Gaussian approximation. Under the requirement of 1% failure probability of transmission, we determine the sink capacity, which is defined as the maximum number of concurrent sensor nodes located one hop away from the sink. We demonstrate that as the node activity of the MAI decreases, the variation of the sink capacity due to the node activity of the NI becomes more significant. The analysis results are verified through computer simulations.

• 한국항행학회논문지
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• 제10권1호
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• pp.34-40
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• 2006

유무선 혼합 네트워크에서 다수의 무선 단말기들은 한 접속점 (Access Point, AP)에 접속을 하여 통신을 한다. 이때 AP는 네트워크에서의 병목점이 되어 버퍼오버플로우가 자주 발생하며, TCP 성능 저하의 주된 원인이 된다. 본 논문에서는 유무선 혼합 네트워크에서 AP의 버퍼 오버플로우를 방지하고, TCP fairness를 향상시키기 위한 새로운 알고리즘을 제안한다. 새 알고리즘은 AP의 버퍼 사용량에 따라 각 송신측의 전송률을 적응적으로 제어하여 버퍼 오버플로우를 방지하고, 향상된 TCP fairness를 보장한다. 시뮬레이션을 통해 제안한 알고리즘을 사용했을 때, 버퍼 오버플로우 방지를 통해 처리율 및 TCP fairness가 향상됨을 검증하였다.

• Journal of Communications and Networks
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• 제17권4호
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• pp.419-427
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• 2015

There have been increases in the elderly population worldwide, and this has been accompanied by rapid growth in the health-care market, as there is an ongoing need to monitor the health of individuals. Wireless body area networks (WBANs) consist of wireless sensors attached on or inside the human body to monitor vital health-related problems, e.g., electrocardiograms (ECGs), electroencephalograms (EEGs), and electronystagmograms (ENGs). With WBANs, patients' vital signs are recorded by each sensor and sent to a coordinator. However, because of obstructions by the human body, sensors cannot always send the data to the coordinator, requiring them to transmit at higher power. Therefore, we need to consider the lifetime of the sensors given their required transmit power. In the IEEE 802.15.6 standard, the transmission topology functions as a one-hop star plus one topology. In order to obtain a high throughput, we reduce the transmit power of the sensors and maintain equity for all sensors. We propose the multiple-hop transmission for WBANs based on the IEEE 802.15.6 carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. We calculate the throughput and variance of the transmit power by performing simulations, and we discuss the results obtained using the proposed theorems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.1805-1824
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• 2013

Recently, the use of wireless body area networks (WBAN) has been increasing rapidly in medical healthcare applications. WBANs consist of smart nodes that can be used to sense and transmit vital data such as heart rate, temperature and ECG from a human body to a medical centre. WBANs depend on limited resources such as energy and bandwidth. In order to utilise these resources efficiently, a very well organized medium access control (MAC) protocol must be considered. In this paper, a new, adaptive and energy-efficient MAC protocol, entitled isMAC, is proposed for WBANs. The proposed MAC is based on multi-channel communication and aims to prolong the network lifetime by effectively employing (i) a collision prevention mechanism, (ii) a coordinator node (WCN) selection algorithm and (iii) a transmission power adjustment approach. The isMAC protocol has been developed and modelled, by using OPNET Modeler simulation software. It is based on a networking scenario that requires especially high data rates such as ECG, for performance evaluation purposes. Packet delay, network throughput and energy consumption have been chosen as performance metrics. The comparison between the simulation results of isMAC and classical IEEE 802.15.4 (ZigBee) protocol shows that isMAC significantly outperforms IEEE 802.15.4 in terms of packet delay, throughput and energy consumption.

• 한국정보컨버전스학회:학술대회논문집
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• 한국정보컨버전스학회 2008년도 International conference on information convergence
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• pp.199-204
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• 2008

Sensor nodes have various energy and computational constraints because of their inexpensive nature and ad-hoc method of deployment. Considerable research has been focused at overcoming these deficiencies through faster media accessing, more energy efficient routing, localization algorithms and system design. Our research attempts to provide a method of improvement MAC performance in these issues. We show that traditional carrier-sense multiple access(CSMA) protocols like IEEE 802.11 do not handle the first constraint adequately, and do not take advantage of the second property, leading to degraded latency and throughput as the network scales in size, We present more efficient method of a medium access for real-time wireless sensor networks. Proposed MAC protocol is a randomized CSMA protocol, but unlike previous legacy protocols, does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports, it carefully decides a fixed-size contention window, non-uniform probability distribution of transmitting in each slot within the window. We show that it can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using widely used simulator ns-2. We, finally show that proposed MAC scheme comes close to meeting bounds on the best latency achievable by a decentralized CSMA-based MAC protocol for real-time wireless sensor networks which is sensitive to latency.