• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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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.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.5
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• pp.107-116
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• 2011

In this paper, a traffic adaptive sleep based medium access control (TAS-MAC) protocol for wireless sensor networks (WSNs) is proposed. The protocol aims for WSNs which consist of clustered sensor nodes and is based on TDMA-like schema. It is a typical schedule based mechanism which is adopted in previous protocols such as LEACH and Bit-Map Assisted MAC. The proposed MAC, however, considers unexpected long silent period in which sensor nodes have no data input and events do not happen in monitoring environment. With the simple traffic measurement, the TAS-MAC eliminates scheduling phases consuming energy in previous centralized approaches. A frame structure of the protocol includes three periods, investigation (I), transmission (T), and sleep-period (S). Through the I-period, TAS-MAC aggregates current traffic information from each end node and dynamically decide the length of sleep period to avoid energy waste in long silent period. In spite of the energy efficiency of this approach, the delay of data might increase. Thus, we propose an advanced version of TAS-MAC as well, each node in cluster sends one or more data packets to cluster head during the T-period of a frame. Through simulation, the performance in terms of energy consumption and transmission delay is evaluated. By comparing to BMA-MAC, the results indicate the proposed protocol is more energy efficient with tolerable expense in latency, especially in variable traffic situation.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.274-276
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• 2003

센서 기술과 통신 기술의 발달로 센서 네트워크에 대한 연구가 활발히 진행되고 있다. 센서 노드는 주변환경을 관찰하고 그 결과를 센서 노드로 이루어진 네트워크를 통하여 사용자에게 전달한다. 센서 네트워크는 특정 기반 구조 없이 수행되어야 하기 때문에 데이터의 전달이 애드혹 네트워크에서의 라우팅 기법과 비슷하다. 하지만 센서 노드는 배터리 전력량에 의하여 수명이 결정되기 때문에 전력 소비를 줄이는 것이 매우 중요한 문제이다. 본 논문에서는 센서 노드의 위치에 따라 통신 상태를 유휴(idle) 상태에서 정지(sleep)상태로 변경하는 방법으로 전력 소비를 줄이는 MAC 프로토콜을 제안한다.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06d
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• pp.267-268
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• 2011

Recent research activities in cooperative communication focus on achieving energy efficiency and reliability. Relay selection strategy for cooperative communication improves the performance significantly. However, due to imbalance consumption of power, network might die earlier and more than 90% energy remains unused. In this paper, we provide a framework of an energy-efficient medium access control protocol that minimizes these problems and improves energy efficiency.

• Journal of information and communication convergence engineering
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• v.11 no.1
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• pp.7-11
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• 2013

Wearable computer systems use the wireless universal serial bus (WUSB), which refers to USB technology that is merged with WiMedia physical layer and medium access control layer (PHY/MAC) technical specifications. WUSB can be applied to wireless personal area network (WPAN) applications as well as wired USB applications such as PAN. WUSB specifications have defined high-speed connections between a WUSB host and WUSB devices for compatibility with USB 2.0 specifications. In this paper, we focus on an integrated system with a WUSB over an IEEE 802.15.6 wireless body area network (WBAN) for wireless wearable computer systems. Due to the portable and wearable nature of wearable computer systems, the WUSB over IEEE 802.15.6 hierarchical medium access control (MAC) protocol has to support power saving operations and integrate WUSB transactions with WBAN traffic efficiently. In this paper, we propose a low-power hibernation technique (LHT) for WUSB over IEEE 802.15.6 hierarchical MAC to improve its energy efficiency. Simulation results show that the LHT also integrates WUSB transactions and WBAN traffic efficiently while it achieves high energy efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.943-961
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• 2020

With the advent of IoT technology and Big Data computing, the importance of WSNs (Wireless Sensor Networks) has been on the rise. For energy-efficient and collection-efficient delivery of any sensed data, lots of novel wireless medium access control (MAC) protocols have been proposed and these MAC schemes are the basis of many IoT systems that leads the upcoming fourth industrial revolution. WSNs play a very important role in collecting Big Data from various IoT sensors. Also, due to the limited amount of battery driving the sensors, energy-saving MAC technologies have been recently studied. In addition, as new IoT technologies for Big Data computing emerge to meet different needs, both sensors and sinks need to be mobile. To guarantee stability of WSNs with dynamic topologies as well as frequent physical changes, the existing MAC schemes must be tuned for better adapting to the new WSN environment which includes energy-efficiency and collection-efficiency of sensors, coverage of WSNs and data collecting methods of sinks. To address these issues, in this paper, a self-organization scheme for mobile sensor networks with mobile multiple sinks has been proposed and verified to adapt both mobile sensors and multiple sinks to 3-dimensional group management MAC protocol. Performance evaluations show that the proposed scheme outperforms the previous schemes in terms of the various usage cases. Therefore, the proposed self-organization scheme might be adaptable for various computing and networking environments with big data.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.131-140
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• 2009

A key challenge for Wireless Body Area Network (WBAN) is to maximize the network lifetime with power-efficient and flexible duty cycling techniques on energy-constraint sensor nodes. In this paper, we propose a novel power-efficient MAC protocol for WBAN that accommodates normal, emergency, and on-demand traffic in a reliable manner. This protocol supports two wakeup mechanisms, a traffic-based wakeup mechanism, which accommodates normal traffic by exploiting the node's traffic patterns, and a wakeup radio mechanism, which accommodates emergency and on-demand traffic by using a wakeup radio. It can be seen that the proposed protocol not only improves the lifetime of WBAN but also provides a reliable method to handle sporadic events. Simulation results show that the proposed protocol outperforms WiseMAC in terms of low-power consumption and delay.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.10a
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• pp.429-431
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• 2013

In this paper, we propose a low-power hibernation technique (LHT) for WUSB over IEEE 802.15.6 hierarchical MAC to improve its energy efficiency. Simulation results show that the LHT also integrate WUSB transactions and WBAN traffic efficiently while it achieves high energy efficiency.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.361-364
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• 2014

무선 센서 네트워크를 구성하는 각 센서 노드들은 한정된 전력의 배터리로 동작하므로, 센서 네트워크에서의 에너지 효율성은 중요한 이슈이다. 따라서, 센서 노드의 에너지 소모를 줄여서 전체 네트워크 수명을 최대화하기 위해 MAC 계층에서의 다양한 프로토콜이 제안되었다. 본 논문에서는 센서 네트워크의 에너지 효율성을 향상시키기 위한 에너지 효율적인 CA-MAC(Context Adaptive MAC) 프로토콜을 제안한다. 제안된 CA-MAC 프로토콜은 데이터의 전송 여부를 결정하는 각 버퍼 임계값을 싱크와 노드의 거리에 따라 차등적으로 설정함으로써 노드의 에너지 소비를 감소시켜 전체 네트워크의 에너지 효율성을 크게 향상 시킨다. 또한, 전송 지연 시간을 감소시키기 위하여 센싱된 데이터의 긴급 여부에 따른 전송을 수행한다. 본 논문의 성능 평가는 OMNeT++을 이용한 모의실험을 통해 진행하였으며, 그 결과 기존에 제안되었던 S-MAC 및 T-MAC 프로토콜과 비교하여 제안된 기법이 데이터 전송 시간과 에너지 효율성을 향상시키고 네트워크 수명을 연장하였음을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3152-3165
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• 2012

Wireless sensor networks (WSN) often employ asynchronous MAC scheduling, which allows each sensor node to wake up independently without synchronizing with its neighbor nodes. However, this asynchronous scheduling may not deal with collisions due to hidden terminals effectively. Although most of the existing asynchronous protocols exploit a random back-off technique to resolve collisions, the random back-off cannot secure a receiver from potentially repetitive collisions and may lead to a substantial increase in the packet latency. In this paper, we propose a new collision resolution algorithm called Transient Coordinator (TC) for asynchronous WSN MAC protocols. TC resolves a collision on demand by ordering senders' transmissions when a receiver detects a collision. To coordinate the transmission sequence both the receiver and the collided senders perform handshaking to collect the information and to derive a collision-free transmission sequence, which enables each sender to exclusively access the channel. According to the simulation results, our scheme can improve the average per-node throughput by up to 19.4% while it also reduces unnecessary energy consumption due to repetitive collisions by as much as 91.1% compared to the conventional asynchronous MAC protocols. This demonstrates that TC is more efficient in terms of performance, resource utilization, and energy compared to the random back-off scheme in dealing with collisions for asynchronous WSN MAC scheduling.