• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.126-130
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• 1999

In packet CDMA networks, it is important to design a MAC protocol that meets the QoS requirements , of the different traffic types and allocates the radio channels efficiently. In this paper, a RRS$^2$-CDMA MAC protocol is proposed for integrating voice and data services in the microcellular packet CDMA networks. In PRS$^2$-CDMA, a voice terminal can resolve a spreading code to transmit voice packets during a talkspurt while a data terminal has to contend for a code for each packet transmission. The numerical results show that the proposed protocol can improve the system capacity, while guaranteeing the QoS of voice and data services.

• Journal of Korea Multimedia Society
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• v.19 no.3
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• pp.567-572
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• 2016

N-screen is an emerging technology to support multimedia multicasting, content sharing and content mobility. N-screen service providers should obtain the technology that provides the highest quality content seamlessly. Distributed nature of WiMedia distributed-MAC protocol can provide full mobility support, and achieves seamless medium access method in contrast to IEEE 802.15.3. So, in this paper, WiMedia distributed-MAC protocol is adopted and an asynchronous multicast transmission (AMT) technology is proposed to enhance performance of seamless N-screen wireless service based on distributed-MAC. The ACK frame transmissions are not required for multicast transmissions. By using this property in AMT, if a device is a multicast receiver, its reserved time slots can be reserved by the other devices with 1-hop distance. Furthermore, each N-screen device broadcasts and shares the information including an order in asynchronous traffic reservations to reduce conflicts in determining the transmission order of asynchronous N-screen packets. Therefore, AMT scheme expands the number of time slots available and throughputs for multicast and asynchronous traffic reservations when comparing with the distributed-MAC standard system. N-screen communications based on distributed-MAC with the proposed AMT shows a new framework for realizing N-screen wireless service with the full content mobility.

• The KIPS Transactions:PartC
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• v.9C no.4
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• pp.523-530
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• 2002

Earlier efforts on optical access concentrated on the design of PONs for the collection and distribution portion of the access network. PON architecture is very simple but it requires MAC protocol for control of upstream traffic. This paper proposes a MAC protocol for a broadband access network using an ATM Passive Optical Network supporting CBR/rtYBR, nrtYBR, UBR and ABR traffic. For the proposed MAC scheme, we present grant field format, minislot format, and bandwidth allocation algorithm. From the simulation result, we have confirmed that our proposed scheme can reduce the average cell delay in comparison to that of conventional MAC schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1435-1440
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• 2014

Nodes in WSNs must operate under limited energy resource. Controlling access to the channel in WSNs plays a key role in determining channel utilization and energy consumption. This paper introduces a priority-based time slot allocation protocol for hybrid TDMA/CSMA MAC in WSNs. This protocol combines both TDMA and CSMA techniques while introducing prioritization by (m,k)-firm constraint. The performance of this protocol is obtained through simulations for various number of nodes and show significant improvements in delay and packet delivery ratio compared to S-MAC.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3046-3060
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• 2012

Low power listening (LPL) MAC protocols based on duty-cycling mechanism have been studied extensively to achieve ultra low energy consumption in wireless sensor networks (WSNs). Especially, recent ACK-based LPL schemes such as X-MAC employ strobe preambles and an early ACK, and show fair performances in communications and energy efficiencies. However, the state-of-the-art ACK-based LPL scheme still suffers from collision problems due to the protocol incompleteness. These collision effects are not trivial and make WSNs unstable, aggravate energy consumptions. In this paper, we propose two novel schemes; (i) ${\tau}$-duration CCA to mitigate the collision problem in ACK-based LPL MAC protocols. (ii) Short Preamble Counter (SPC) to conserve more energy by reducing unnecessary overhearing. We demonstrate the performance improvement of our scheme via a mathematical analysis and real-time experiments. Both analysis and experimental results confirm that our proposed scheme saves energy by up to 36% compared to the naive ACK-based LPL MAC protocol thanks to ${\tau}$-duration CCA and SPC.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.54-57
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• 2010

Vehicular Ad-hoc Network the core technology of ITS supports safety service or information service to driver and passenger on the roads utilizing V2V and V2I communication. WAVE, the standard of the vehicular ad hoc networks, adopts IEEE 802.11p as MAC protocol and includes the channel coordination algorithm to utilize multiple channels. However, this standard shows the problem related with QoS guarantee of urgent data for driver's safety and the limitation of the performance improvement. In this paper, we introduce WAVE-based Multi-channel MAC protocols that have proposed to resolve above problems and describe their features.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5425-5448
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• 2018

Wireless sensor network has been widely used in Internet of Things (IoT) applications to support large and dense networks. As sensor nodes are usually tiny and provided with limited hardware resources, the existing multiple access methods, which involve high computational complexity to preserve the protocol performance, is not available under such a scenario. In this paper, we propose an intelligent Medium Access Control (MAC) protocol selection scheme based on machine learning in wireless sensor networks. We jointly consider the impact of inherent behavior and external environments to deal with the application limitation problem of the single type MAC protocol. This scheme can benefit from the combination of the competitive protocols and non-competitive protocols, and help the network nodes to select the MAC protocol that best suits the current network condition. Extensive simulation results validate our work, and it also proven that the accuracy of the proposed MAC protocol selection strategy is higher than the existing work.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.566-570
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• 2005

A digital controller for nonlinear time-delay system is proposed in this paper. A nonlinear time-delay system is discretized by using Taylor's discretization method. And the discretized system can be converted to a general nonlinear system. For this reason, general nonlinear controller synthesis can be applied to the discretized time-delay system. We adopted MAC controller synthesis for this study. Computer simulations are conducted to verify the performance of the proposed method. The results of simulation show good performance of the proposed controller synthesis and the proposed method is useful to control nonlinear time-delay system easily.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.59-60
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• 2006

TCP applied to the wireless-wired integrated network is the one that was applied to the existing wired network. In the wireless-wired integrated network, both wireless and congestion loss can occur. When wireless packet losses occur, the congestion control of TCP causes performance degradation by reducing its transmission rate. In this paper, we propose the algorithm to distinguish the wireless packet loss from congestion packet loss using MIB of the 802.11 MAC which has been generally used recently in wireless links.