• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2006년도 춘계학술발표대회
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• pp.1287-1290
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• 2006

무선 네트워크의 전송 방식은 유선 네트워크와 다르며, 따라서 유선 네트워크를 기반으로 설계된 인터넷 프로토콜(TCP/IP)은 무선네트워크 환경에서 불안정 하게 작동한다. 본 논문에서는 기존의 유선 인터넷에 맞춰진 전송 프로토콜인 UDP와 TCP를 802.15.4 MAC기반의 ZigBee Protocol 환경에서 사용되는 특성과 AODV 및 확장 프로토콜인 AOMDV를 통해 인터넷에 결합된 네트워크 인터페이스를 가진 노드들의 특성과 관리의 중요함을 확인한다

• Journal of Information Technology Applications and Management
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• 제12권4호
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• pp.13-24
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• 2005

The sensor network is a key component of the ubiquitous computing system which is expected to be widely utilized in logistics control, environment/disaster control, medical/health-care services, digital home and other applications. Nodes in the sensor network are small-sized and exposed to adverse environments. They are demanded to perform their missions with very limited power supply only. Also the sensor network is composed of much more nodes than the wireless ad hoc networks are. In case that some nodes consume up their power capacity, the network topology should change, and rerouting/retransmission is necessitated. Communication protocols studied for conventional wireless networks or ad hoc networks are not suited for the sensor network resultantly. Schemes should be devised to control the efficient usage of node power in the sensor network. This paper proposes a medium access protocol to enhance the efficiency of energy consumption in the sensor network node. Its performance is analyzed by simulation.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2003년도 봄 학술발표논문집 Vol.30 No.1 (C)
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• pp.331-333
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• 2003

본 논문에서는 802.11을 기반으로 한 무선 링크에서 인터넷 상의 대표적인 전송계층 프로토콜인 TCP(Transmission Control Protocol)와 HDP(User Datagram Protocol)의 성능을 비교한다. 또한 이들 프로토콜이 무선 환경에서 보이는 문제점을 지적하고 원인을 분석한다. 무선 네트워크의 용량은 유선 네트워크와 다르며, 따라서 유선 네트워크 용량을 기반으로 설계된 TCP는 불안정하게 작동한다. 본 논문에서는 주목할만한 전송 프로토콜의 병목현상을 나타내는 원인으로 MAC(Medium Access Control)에 의해 채널을 잡기 위한 경쟁이 심각함과 전송 계층 프로토콜의 네트워크 용량 예측이 올바르지 않음을 지적하고, TCP와 HDP를 비교하여 무선 망에서도 네트워크 상황에 적응하는 기법이 중요함을 확인한다.

• 한국통신학회논문지
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• 제31권9A호
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• pp.856-867
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• 2006

This paper proposes a new algorithm for opportunistic scheduling that take advantage of both multiuser diversity and power control. Motivated by the multicast RTS and priority-based CTS mechanism of OSMA protocol, we propose an opportunistic packet scheduling with power control scheme based on IEEE 802.11 MAC protocol. The scheduling scheme chooses the best candidate receiver for transmission by considering the SINR at the nodes. This mechanism ensures that the transmission would be successful. The power control algorithm on the other hand, helps reduce interference between links and could maximize spatial reuse of the bandwidth. We then formulate a convex optimization problem for minimizing power consumption and maximizing net utility of the system. We showed that if a transmission power vector satisfying the maximum transmission power and SINR constraints of all nodes exist, then there exists an optimal solution that minimizes overall transmission power and maximizes utility of the system.

• Journal of information and communication convergence engineering
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• 제12권4호
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• pp.199-207
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• 2014

A new cooperative MAC protocol called the busy tone cooperative medium access control (BT-COMAC) protocol is proposed to overcome the drawbacks and maximize the advantages of existing schemes. This scheme uses a new metric called decibel power to decide an appropriate helper node. Using received power strength is more efficient in selecting an appropriate helper node, especially in a densely populated network, than the effective transmission rates used in conventional schemes. All communication nodes in a communication service area are assumed to move independently. Two performance metrics are used: System throughput and channel access delay. A performance evaluation of the BT-COMAC protocol is conducted using a computer simulation over a slow fading wireless channel, and its performance results are compared with those of four existing schemes. The numerical results show that the BT-COMAC protocol improves the system throughput by approximately 15% as compared to the best existing scheme.

• 융합신호처리학회논문지
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• 제10권3호
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• pp.181-185
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• 2009

Recently, much attention to a self-organizing mobile ad-hoc network is escalating along with progressive deployment of wireless networks in our everyday life. Being readily deployable, the MANET (mobile ad hoc network) can find its applications to emergency medical service, customized calling service, group-based communications, and military purposes. In this paper we investigate a time slot exchange problem found in the time slot based MAC, that is designed for IEEE 802.11b interfaces composing a MANET. The paper provides a method to maintain the quality of voice call by providing a new time slot when the channel assigned for that time slot gets noisy with interferences induced from other nodes, which belong to the same and/or other subgroups. In order to assess the performance of the proposed algorithm, a set of simulations using the OPNET modeler has been performed assuming that the IEEE 802.11b interfaces are operating under a modified MAC, which is a time slot based reservation MAC implemented in the PCF part of the superframe. In a real-time voice call service over a MANET of a size 500 ${\times}$ 500 meter squares with the number of nodes up to 100, the simulation results are collected and analyzed with respect to the packet loss rate and packet delay. The results show us that the proposed time slot exchange protocol improves the quality of voice call over that of plain DCF.

• Journal of information and communication convergence engineering
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• 제5권2호
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• pp.104-108
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• 2007

Ad hoc networks are a type of mobile network that function without any fixed infrastructure. One of the weaknesses of ad hoc network is that a route used between a source and a destination is to break during communication. To solve this problem, one approach consists of selecting routes whose nodes have the most stable link cost. This paper proposes a method for improving the low power distributed MAC. This method is based on the context awareness of the each nodes energy in clustering. We propose to select a new scheme to optimize energy conserving between the clustering nodes in MANET. And this architecture scheme would use context-aware considering the energy related information such as energy, RF strength, relative distances between each node in mobile ad hoc networks. The proposed networks scheme could get better improve the awareness for data to achieve and performance on their clustering establishment and messages transmission. Also, by using the context aware computing, according to the condition and the rules defined, the sensor nodes could adjust their behaviors correspondingly to improve the network routing.

• 한국항행학회논문지
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• 제12권6호
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• pp.627-633
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• 2008

MANET(mobile adhoc networks)기반 통신 프로토콜은 고속으로 이동하는 VANET(vehicular adhoc networks)환경에서 차량 상호간의 메시지 전송과 긴급메시지 전송이 불가능 할 수 있다. 메시지 전송의 신뢰성을 보장하기 위해 본 논문에서는 특정 구간에서 교통사고 및 구간정체로 인한 통신의 포화상태 발생과 긴급통신 중 히든노드 개입으로 인한 데이터 충돌과 전송지연을 해결하기 위해 방향성 안테나 기반 은닉노드 방지 기법을 제안한다. 제안하는 프로토콜은 메시지의 신뢰성 있는 전송을 위해 양방향성 안테나를 이용하여 노드 간 간섭과 제어 메시지 전송 지연을 최소화 한다. 시뮬레이션을 통해 메시지의 신뢰성 있는 전달 및 메시지 간 충돌을 줄일 수 있음을 보이고, 결론에서는 연구 내용 및 우수성을 나타내었다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2007년도 가을 학술발표논문집 Vol.34 No.2 (D)
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• pp.520-524
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• 2007

제한된 전지를 사용하는 노드들로 이루어진 이동 애드혹 네트워크 환경에서 멀티 홉 간의 에너지 효율적인 경로 설정은 매우 중요한 이슈이다. 이러한 문제를 해결하기 위해서 본 논문에서는 이동 애드혹 네트워크 환경에서 자주 사용되는 라우팅 프로토콜 중 하나인 AODV(Ad-hoc On-demand Distance Vector) 라우팅 프로토콜을 기반으로, 네트워크 계층과 MAC계층의 자원을 크로스 레이어 기법을 활용하여 에너지 효율적인 크로스 레이어 라우팅 프로토콜을 제안한다. 네트워크 계층에서의 이웃노드에 관한 상태 정보를 크로스 레이어 기법을 활용하여 MAC 계층의 back-off time을 적절히 조절함으로써 프레임의 충돌을 줄이고, 패킷의 경로를 설정하는데 있어서 신뢰성과 효율성을 부여하기 위한 방법으로 MAC계층의 자원을 활용하여 얻은 Collision-Level을 사용한다. 또한 Collision Level은 패킷 경로 선택에 사용되는 지연시간을 적응성 있게 줄이는 자원으로 사용된다.

• International Journal of Contents
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• 제10권2호
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• pp.9-17
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• 2014

Since vehicles' trajectories are so complex and dense traffic changes in nature frequently, the VANET (Vehicles Ad-hoc Network), using Omni-directional Antenna, has many channel collisions (or overlapping) on Data Link phrases (MAC layers). It is not easy to keep a good seamless communication status for VANET because of its unpredictable network environment. Among VANET research, Directional Antenna have been proposed as one of the most common systematical solutions to reduce (or to mitigate) this miss-communication problems by narrowing communicational ranges and making use of its customized error-detection process. However, even though Directional Antennas help VANET keep good seamless communication, many VANET researchers have reported that Directional VANET still has miss-communicational problems - this has lead to problems like 'Directional Hidden Terminal Problem', 'Deafness', 'Un-accuracy Lobe Scopes' and 'High Deployment Cost' being reported in various papers. To establish well-organized design assessments for a good Directional VANET MAC protocol to overcome these problems, we rearranged and grouped current Directional VANET' qualitative criteria from several current survey papers using these categories- 'Directional Discovery', 'Directional Forwarding' and 'Directional Handover'. In addition, based on the results of the following analysis, we show the essential design concerns that need to be looked at in order to develop a well-designed Directional-VANET MAC protocol.