• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.111-118
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• 2008

In this paper a novel medium access control mechanism is investigated as a means to support real-time services. The primary goal is to provide constant-bit-rate voice call services to pairs of autonomous mobile nodes operating in ad hoc networks. Here, a time-slot reservation based MAC is considered to provide real-time voice calls and a new MAC called the time-slot reservation coordination function(TRCF) is presented. In addition to this isochronous type MAC protocol development, the proposed protocol is modeled using a Markov chain in order to predict its behavior. The performance of TRCF is analytically derived and the performance measures such as average wait time taken for a call connection and throughput are obtained.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1492-1512
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• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.1-9
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• 2002

본 논문은 현재 무선 LAN 환경에서 적용되고 있는 매체접근제어 프로토콜인 IEEE 802.11 CSMA/CA를 이용함으로써, 음성 위주의 항공이동통신에서 음성과 데이터 채널을 통합하여 사용하도록 하고 있다. 또한, 표준으로 제정되어 있는 기존의 CSMA/CA 매체접근제어 프로토콜에 대한 이해를 바탕으로 성능 개선 방안을 제안하였으며, 이를 바탕으로 채널 효율을 향상시켰다. IEEE 802.11 매체접근제어(MAC, Medium Access Control) 프로토콜은 데이터 유형에 따라 채널을 두 개의 구간(PCF와 DCF 구간)으로 나누어 전송하도록 하고 있다. 본 논문에서는, 데이터 유형별로 적용되는 구간 중, DCF 구간에서의 패킷간의 충돌 가능성을 줄임으로써 데이터 전송 효율을 높이는데 주안점을 두고 있다. 제안 방안으로는 경쟁 구간에서의 전송에서 충돌에 따른 손실을 보완할 수 있도록 Wireless Window Protocol(이하, WWP)을 적용한 후 전송 과정을 제어하였다. Hidden 터미널의 영향이 적으므로 가시권내 통신에 적합한 기존의 2-Way CSMA/CA 프로토콜을 항공통신에 적용하여 상태 천이 과정을 5개에서 6개로 세분화하였고, 주어진 확률에 의하여 나누어진 두 개의 그룹별로 상태 천이 과정을 다르게 적용하였다. 따라서, 채널이 한 항공기에 의해 점유되는 PCF를 제외한, DCF 구간에서의 데이터 전송 효율을 높일 수 있었다. 시뮬레이션은 채널 대역폭과 패킷 크기 등을 파라미터 값으로 하여 수행하였으며, 시뮬레이션 결과 CSMA/CA에 비해 새로 제안한 알고리즘이 데이터 전송 과정에서 발생하는 충돌 가능성을 감소시킴으로써 성능이 향상됨을 알 수 있었다.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.10a
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• pp.90-93
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• 2016

본 논문에서는 Sub-GHz band module을 Drone에 탑재하여 Drone과 전원공유로 Node(Drone)간 Low power and Long range Ad-hoc communication을 할 수 있는 방법을 제안하고자 한다. 또한 이동성이 있는 Node(Drone)의 Low power and Long range communication을 위해서 Drone에 적합한 Asynchronous MAC (medium access control) protocol을 비교분석하여 적용하였다. 본 고에서는 무선 센서 네트워크의 응용 범위가 확대되면서 고정된 인프라 없이 Drone간에 실시간 정보를 통신 할 수 있게 하고 사람의 이동이 어렵고 위험한 재난지역, 방사선노출지역 또는 우천시 유인기와 사람의 접근이 불가능한 지역을 Drone이 대신 이동하여 인명피해를 줄이고 안전하게 필요한 데이터를 수집하여 상황관제실로 전송하는 서비스를 제공하고자 한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.8
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• pp.1404-1422
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• 2011

In this paper, a new clear channel assessment (CCA) method: cascaded-CCA, is proposed. The primary motivation for the proposed approach is to integrate the respective advantages of two standard CCA mechanisms, energy detect and preamble detect, to arrive at a new dual threshold CCA family that can provide greater flexibility towards tuning MAC performance. Cascaded-CCA integrates energy efficiency of the energy detector (ED) and the reliability of the preamble detector (PD). The probability of detection/false alarm and power consumption of cascaded-CCA in the CCA modules of IEEE 802.11b are analyzed and compared with ED and PD as an example. The performance of cascaded-CCA is explored via MATLAB simulations that implement the CCA modules and medium access control (MAC) protocol for IEEE 802.11 and IEEE 802.15.4. Simulation results showed that cascaded-CCA improves the energy efficiency significantly compared to ED-only or PD-only CCA. In addition, ED, PD, and cascaded CCA are applied to a cognitive network scenario to validate the effectiveness of the proposed cascaded-CCA.

• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.87-91
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• 2010

The IEEE 802.15.4 and IEEE 802.15.7 standard are the typical of low rate wireless and Visible Light Wireless personal area networks. Its Medium Access Control protocol can support the QoS traffic flows for real-time application through guaranteed time slots (GTS) in beacon mode. However, how to achieve a best allocation scheme is not solved clearly. The current analytical models of IEEE 802.15.4 MAC reported in the literature have been mainly developed under the assumption of saturated traffic or non-bursty unsaturated traffic conditions. These assumptions don't capture the characteristics of bursty multimedia traffic. In this paper, we propose a new analytical model for GTS allocation with burst Markov modulated ON-OFF arrival traffic.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1410-1418
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• 2007

This paper analyzes the throughput of DCF protocol at the MAC layer in the 802.11a wireless LAN. The throughput of DCF protocol is related on probability of backoff, depends on retransmission of each terminal. This paper applied to nonmarcov discrete model for each terminal BER in the base station versus the packet throughput is progressing with the data rate of 6,12,24,54 Mbps, We find the fact that the less the data rate be the higher the throughput. We also find from the throughput calculation by means of traffic intensity in OFDM wireless LAN.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.387-394
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• 2005

Every MAC (Medium Access Control) sub-layers of IEEE 802.11x, including IEEE 802.11e, defines Connection-based and CF (Contention Free)-based service functions in common. In this paper, a New-CF method is proposed. In the proposed method, conventional Round Robin method, which is used as a polling method by IEEE 802.11x PCF (Point Coordination Function) or IEE 802.11e HCCA, is modified to give weights to channels with heavier traffic load and to provide those weighted channels with more services. Based on NS-2 simulations, it is verified the proposed method shows better throughput in general, particularly under unbalanced traffic load conditions.

• Electronics and Telecommunications Trends
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• v.29 no.4
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• pp.110-122
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• 2014

무선환경은 가짜 클론 디바이스가 진짜인 것처럼 위장한 해킹공격에 매우 취약한 것으로 잘 알려져 있다. 그것은 단말기와 기지국(AP: Access Point)이 위변조가 쉬운 디바이스 식별자(예로 MAC(Medium Access Control) 주소, SSID, BSSID(Basic Service Set Identification) 등)를 이용하여 상호 인증하기 때문이다. 무선핑거프린팅(Wireless Fingerprinting)은 통신과정에서 발생되는 무선신호 특성으로부터 디바이스를 고유하게 식별하는 핑거프린트를 추출하여 송신 디바이스가 가짜 클론 디바이스인지 아닌지 여부를 식별하는 기술이다. 본 기술은 무선물리계층 보안을 위한 인증 및 키 생성, 무선 침입탐지, 공격자의 위치/방향/거리 추적, 무선 포랜식 및 보안관제의 성능을 결정하는 핵심기술로 활용되고 있다. 향후 등장이 예상되는 M2M 무선랜, 무선인지네트워크, 무선센서, 무선차량통신, IoT 무선통신환경에서도 본 기술의 중요성은 더욱 증가하리라 본다. 본고에서는 무선 디바이스의 핑거프린팅 개념을 이해하고, 기술 분류에 따른 세부기법 연구 및 보안응용 동향을 분석함으로써 본 기술의 발전방향을 조망해보고자 한다.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.1045-1046
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• 2006

The IEEE 802.11e medium access control (MAC) is an emerging standard to support Quality of Service (QoS). A HCCA (HCF controlled channel access) scheduler of the standard IEEE 802.11e is only efficient for flows with strict constant bit rate (CBR) characteristics. In this paper, we propose a new HCCA scheduling scheme that aims to be efficient for both CBR and VBR flows. The proposed scheme uses fuzzy queue length predictions to tune its time allocation to stations. We present a set of simulations and provide performance comparisons with the reference HCCA scheduler.