• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.2
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• pp.70-80
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• 2008

CSMA(Carrier Sense Multiple Access) is a media access control protocol when nodes use a shared channel. To reduce the probability of collision and increase the performance, the station lust checks the state of the channel. In this paper, we study the performance improvement method based on p-persistent strategy. The p-persistent method reduces the chance of collision and improves the efficiency. However, a probability p and the number of station affect the performance. This paper proposes a dynamic CSMA multiple access based on the network status. If the possibility of collision is low, the station increases the probability p to improve the performance. In the opposite case, the station decreases the probability p. Our simulation results show that the proposed scheme outperforms any methods of CSMA multiple access according to the current persistent strategy.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6B
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• pp.527-533
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• 2006

In this paper, we analyze the performance of MAC (Media Access Control) layer in DSRC (Dedicated Short Range Communication). It will be widely applied for ITS (Intelligent Transportation System) services; for example ETC (Electric Toll Control), BIS (Bus Information System) etc., needed to small packet size. But If ITS service is evolving to advance ITS, ADIS (Advanced Driver Information Systems) and AVHS (Advanced Vehicle Highway System) etc, be needed larger packet size. In the future, it may offer more various services such as traffic information, collection, and multimedia information. There are two kind of physical media, IR(Infrared) and RF(Radio frequency). And each system has their own protocol that is adaptive in special characteristics of physical medium for using efficiently limited radio resources. In this paper, we analyze the special characteristics of each system. And we study practical use of some related services expected to be used in the near future, by analyzing the transmission efficiency in each DSRC system.

• Journal of Digital Contents Society
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• v.15 no.3
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• pp.319-326
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• 2014

IEEE 802.11 WLAN uses CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance) method in MAC(Media Access Control) protocol, and through the carrier sense checks whether other users use the channel during the data transmission to avoid the data collision. Currently, IEEE 802.11 standard recommends the use of a fixed threshold which gives an impact on carrier sensing range. However, the existing scheme using the fixed threshold causes the operation of network to be inefficiency owing to the mobility in MANET(Mobile Ad hoc NETwork). In this paper, we found the better network throughput to be obtained by applying the proposed scheme, which chooses properly the carrier sensing threshold and transmission rate considering SINR(Signal to Interference-plus-Noise Ratio), to the MANET.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.83-87
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• 2009

The MAC protocol of HiperLAN/2 is based on TDMA/TDD. Mobile terminal acquires a data transmission opportunity as successfulness in channel competition through RCH (Random CHannel) phase. Therefore, AP (Access Point) be able to dynamically assign optimum RCH at next frame according to the number of success and collision. In this paper, we suggest scheme that fluctuate RCH (Random CHannel) number as fixed value considering success and collision for improvement of performance in HiperLAN/2. To prove efficiency of proposed scheme, a lots of simulations are conducted and analyzed in view of throughput and access delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1640-1650
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• 2010

To prepare for the network centric warfare, Korea Joint Tactical Data Link System(KJTDLS) has been developed by the South Korean military recently and its development is divided into two phases: basic and complete ones. Due to the limited bandwidth and low transmission efficiency of the developing KJTDLS (basic), lots of problems could be occurred when the TDMA protocol in Link-16 is applied. In this paper, a new dynamic TDMA frame structure for KJTDLS(basic) is proposed and the performance of the proposed is evaluated through the implementation of simulation.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10e
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• pp.637-639
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• 2002

현재 인터넷은 저렴한 사용료와 정보에 대한 욕구를 충족시키는 방대한 공개 자료를 바탕으로 그 규모를 더욱 확대하여 가고 있으며, 이러한 인터넷 사용자의 확대는 새로운 서비스에 대한 요구를 창출하게 되었다. 이러한 저렴하고 규모가 큰 인터넷을 이용하여 기존의 통신망을 대체하는 연구가 활발히 이루어지고 있으며, VoIP(Voice over Internet Protocol)가 인터넷의 대표적인 서비스로 등장하고 있다. VoIP 서비스에 대한 연구는 IETF와 ITU가 중심이 되어 이루어지고 있으며 IETF에서 제안한 MGCP, SIP 와 ITU에서 제안한 H.323 과 같은 프로토콜을 기반으로 VoIP 서비스를 위한 다각적인 접근과 연구가 진행중이다. 본 연구는 VoIP 서비스를 위한 여러 프로토콜 중 IETF가 주관하고 있는 MGCP(Media Gateway Control Protocol ) 스팩에 따라 MGCP를 이용한 ADSL-VoIP Gateway를 개발하여 보다 효율적인 망 자원 활용을 가능하게 하며, 향후 제공될 다양한 음성／동영상 서비스에 대한 기반을 마련하고자 한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.1
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• pp.42-48
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• 2006

This paper proposes the new efficient system design strategies for the acoustic-based underwater multiple modem and media access control protocol. The system aims to establish the acoustic-based communication network of an underwater vehicles for deep sea mining, which ensures a certain level of maximum throughput regardless of the propagation delay of acoustic and allows fast data transmission through the acoustic-based multiple channel.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2004.11a
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• pp.291-294
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• 2004

Wireless sensor network을 위 한 MAC(Medium Access Control) layer를 low-rate WPAN을 목적으로 한 IEEE 802.15.4 사양에 따라 구현하고 검증하였다. 센서 네트워크의 노드는 배터리로 동작하므로 에너지 소모가 가장 큰 걸림돌이 된다. power saving을 위한 몇 가지 방법을 포함한 IEEE 802.15.4 MAC protocol을 구현함으로써 wireless sensor network에 적용 가능함을 보였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.235-242
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• 2006

This paper proposes the new efficient system design strategies for the acoustic-based underwater communication system and it's media access protocol, which make it possible to control the multiple vehicles for underwater duty working by the surface plant. For an approach to implementation of the system, it is inevitable to establish acoustic-based underwater digital communication network to exchange the information between a surface plant and multiple vehicles in underwater.

• Journal of Broadcast Engineering
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• v.10 no.2
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• pp.182-189
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• 2005

In this paper, an asymmetric WDM-EPON transmission scheme is proposed to be used in a high speed access network system, which is required to implement the convergence of broadcast and communication. WDM is used for downstream transmission from OLT to access nodes, satisfying wide bandwidth requirement for broadcasting and various multimedia services. And an EPON scheme, which is cheaper than WDM, is applied to upstream transmission where less bandwidth is required. A transmission test in physical layer was performed successfully and the results are provided. If ONUs are to be used in a home gateway, its protocol should be appropriate to its traffic pattern. Voice is sensitive to a time delay while data is not. A new dynamic bandwidth assignment protocol for PON system, which can cope with various types of data in access network is proposed and its performance is analysed. A maximum cycle time is specified to achieve the QoS of signals sensitive to time delay. And a minimum window is specified to prevent the downstream control signals from uprising. It is shown by simulation that the proposed EPON protocol can provide a better performance than previous ones.