• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.11B
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• pp.985-998
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• 2003

본 논문에서는 IEEE 802.11 규격을 기반으로 다중 홉 Ad Hoc 모드에서 비 실시간 및 실시간 트래픽에 대한 통합 서비스를 지원하는 Wireless LAN을 구성할 때, 분산 방식으로 실시간 서비스의 우선권을 고려한 채널 액세스의 차별화를 제공할 수 있는 매체접근제어(Medium Access Control: MAC) 프로토콜의 구현 방안을 제안한다. 이를 위해 실시간과 비 실시간 트래픽의 Contention Window (CW)를 서로 분리하며, 실시간 서비스의 지연 바운드에 따라 정해진 잔여 수명(residual time)을 우선권 설정에 반영함으로써 실시간 트래픽의 지연 요구 사항을 보장할 수 있도록 한다. 또한 실시간 트래픽의 부하에 따라서 적응적으로 offset 값을 조정함으로써 offset에 의해 발생될 수 있는 수율의 저하를 최소화한다. 제안된 방식은 기존 IEEE 802.11 MAC 규격의DCF (Distributed Coordination function) 방식을 그대로 사용하면서 CSMA/CA 기반의 경쟁 방식을 통해서도 비 실시간 트래픽과의 차별화가 가능하고, 또한 잔여 수명 시간을 고려한 동적인 우선권 할당이 가능하도록 하였다. 시뮬레이션에 의한 분석 결과에 따르면 기존 DCF와 비교할 때 실시간 단말의 용량을 2배까지 향상시킬 수 있으며, 트래픽 부하에 따라 적응적 제어를 통해 추가적인 성능 개선 효과를 확인하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.3C
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• pp.224-232
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• 2012

Priority MAC is an important issue in every communication system when we consider differentiated service applications. In this paper, we propose a mechanism to support priority MAC based on multi-parameters for IEEE 802.15.7 visible light communication (VLC). By using three parameters such as number of backoff times (NB), backoff exponent (BE) and contention window (CW), we provide priority for multi-level differentiated service applications. We consider beacon-enabled VLC personal area network (VPAN) mode with slotted version for random access algorithm in this paper. Based on a discrete-time Markov chain, we analyze the performance of proposed mechanism under non-saturation environments. By building a Markov chain model for multi-parameters, this paper presents the throughput and transmission delay time for VLC system. Numerical results show that we can apply three parameters to control the priority for VLC MAC protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10B
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• pp.862-875
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• 2003

본 논문에서는 IEEE 802.11 규격을 기반으로 다중 홉 Ad Hoc 모드에서 비실시간 및 실시간 트래픽에 대한 통합 서비스를 지원하는 Wireless LAN을 구성할 때, 분산 방식으로 실시간 서비스의 우선권을 고려한 채널 액세스의 차별화를 제공할 수 있는 매체접근제어(Medium Access Control: MAC) 프로토콜의 구현 방안을 제안한다. 이를 위해 실시간과 비실시간 트래픽의 Contention Window (CW)를 서로 분리하며, 실시간 서비스의 지연 바운드에 따라 정해진 잔여 수명(residual time)을 우선권 설정에 반영함으로써 실시간 트래픽의 지연 요구 사항을 보장할 수 있도록 한다. 또한 실시간 트래픽의 부하에 따라서 적응적으로 offset 값을 조정함으로써 offset에 의해 발생될 수 있는 수율의 저하를 최소화한다. 제안된 방식은 기존 IEEE 802.11 MAC 규격의DCF (Distributed Coordination Function) 방식을 그대로 사용하면서 CSMA/CA 기반의 경쟁 방식을 통해서도 비실시간 트래픽과의 차별화가 가능하고, 또한 잔여 수명 시간을 고려한 동적인 우선권 할당이 가능하도록 하였다. 시뮬레이션에 의한 분석 결과에 따르면 기존 DCF와 비교할 때 실시간 단말의 용량을 2배까지 향상시킬 수 있으며, 트래픽 부하에 따라 적응적 제어를 통해 추가적인 성능 개선 효과를 확인하였다.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.6
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• pp.676-688
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• 2014

The IEEE 802.11e EDCA (Enhanced Distributed Channel Access) mechanism has been proposed to improve the QoS (Quality of Service) of various services in WLANs (Wireless Local Area Networks). By differentiating the channel access delay depending on ACs (Access Categories), this mechanism can provide the relative service differentiation among ACs. In this paper, we consider that WLAN is deployed in medical environments to transfer medical traffic and we reveal that the quality of the medical traffic (in particular, ECG signals) is significantly deteriorated even with the service differentiation by IEEE 802.11e EDCA. Also, we analyze the reason for performance degradation and show that IEEE 802.11e EDCA has difficulty in protecting the transmission opportunity of high-priority traffic against low-priority traffic. In order to assure medical-grade QoS, we firstly define the service priority of medical traffic based on their characteristics and requirements, and then we propose the enhanced channel access scheme, referred to as DIFF-CW. The proposed scheme differentiates CW (Contention Window) depending on the service priority and modifies the channel access procedure for low-priority traffic. The simulation results confirm that the DIFF-CW scheme not only assures the QoS of medical traffic but also improves the overall channel utilization.

• The KIPS Transactions:PartC
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• v.17C no.1
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• pp.1-14
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• 2010

IEEE 802.15.4[1] has been standardized for the physical layer and MAC layer of LR-PANs(Low Rate-Wireless Personal Area Networks) as a technology for operations with low power on sensor networks. The standardization is applied to the variety of applications in the shortrange wireless communication with limited output and performance, for example wireless sensor or virtual wire, but it includes vulnerabilities for various attacks because of the lack of security researches. In this paper, we analyze the vulnerabilities against the denial of sleep attacks on the MAC layer of IEEE 802.15.4, and propose a detection mechanism against it. In results, we analyzed the possibilities of denial of sleep attacks by the modification of superframe, the modification of CW(Contention Window), the process of channel scan or PAN association, and so on. Moreover, we comprehended that some of these attacks can mount even though the standardized security services such as encryption or authentication are performed. In addition to, we model for denial of sleep attacks by Beacon/Association Request messages, and propose a detection mechanism against them. This detection mechanism utilizes the management table consisting of the interval and node ID of request messages, and signal strength. In simulation results, we can show the effect of attacks, the detection possibility and performance superiorities of proposed mechanism.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.7
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• pp.783-788
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• 2016

An LTE enhancement for licensed-assisted access (LAA) to unlicensed spectrum has been studied recently and the first version of its design has been released in early 2016. As both 2.4 and 5GHz ISM bands have multiple channels and Wi-Fi devices already support multi-channel operation, LTE LAA has also been designed such that an eNB can access multiple channels at the same time. In this paper, we review several design variants of listen before talk (LBT) procedure for multi-channel transmission in downlink and perform simulation to investigate coexistence of Wi-Fi and LAA as well as the performance of both.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1551-1557
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• 2006

Since subscribers, who pay the same communication fees, have a strong desire to take similar services with the other users, it is an important issue to provide fairness among those subscribers wherever they are located. Therefore, in this paper we propose a QoS packet scheduler that can provide fairness among wireless LAN terminals and evaluate its performance using computer simulation. The key idea of this scheduler is to reduce the CW value of the wireless LAN terminal that has failed in sending its packets due to channel transmission error in order to offer the wireless MM terminal a higher transmission priority which is the idea of service compensation. We evaluate its performance using NS-2 network simulator, compare its numerical results to those of IEEE 802.11e without this scheme, and conclude that this scheme can reduce throughput difference between similar wireless LAN terminals.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.132-138
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• 2012

VANET(Vehicular Ad-hoc Network), standardization of IEEE 802.11p specification is in process. 802.11 MAC protocol grants all nodes equal opportunity to acquire channel without regard to their bit-rates, making it possible for lower bit-rate nodes to occupy communication channel for a fair amount of time thus keeping the higher bit-rate nodes from acquiring connection channel which downward-equalize the overall network performance. Also with the 802.11p MAC protocol, the probability of collision occurring increases as the number of nodes grow. The proposed algorithm is a new MAC protocol that guarantees nodes with acquired channel a firm priority over other nodes for a fixed amount of time with TXOP concept added to 'packet burst' according to the current transmitting speed. This newly designed algorithm allows the construction of wireless network with enhanced network throughput, decreased probability of collisions as well as providing the means to grant each node a fair chance of acquiring connection according to their channel conditions. The algorithm sets the CW's (Contention Window) width wider than the standard's and modulates the continuous transmitting threshold value depending on channel acquired time, thus improving the overall performance of the network.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1386-1390
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• 2011

The IEEE 802.11 MAC uses DCF for media access among the participating network nodes. But DCF alone is neither capable nor suitable for fulfilling the QoS requirements of realtime applications. There are many ways in which QoS is provided by modifying DCF based MAC. This paper proposes (m,k)-collision scheme which is based on IEEE 802.11 and (m,k)-firm scheme tries to improve DCF functionality. The proposed scheme uses different Contention Window according to the number of collision in the node. The simulation result shows that the proposed scheme helps improve the throughput of the DCF.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.05a
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• pp.796-798
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• 2011

The IEEE 802.11 MAC uses DCF for media access among the participating network nodes. But DCF alone is neither capable nor suitable for fulfilling the QoS requirements of realtime applications. There are many ways in which QoS is provided by modifying DCF based MAC. This paper proposes (m,k)-collision scheme which is based on IEEE 802.11 and (m,k)-firm scheme tries to improve DCF functionality. The proposed scheme uses different Contention Window according to the number of collision in the node. The simulation result shows that the proposed scheme helps improve the throughput of the DCF.