• Proceedings of the Korea Society for Simulation Conference
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• 2002.05a
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• pp.249-252
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• 2002

IEEE 802.11의 매체 접근 제어 MAC 프로토콜은 두가지 운영 방법을 제공한다. 하나는 실시간 응용 서비스가 아닌 데이터를 지원하기 위한 임의 접근 (random access)모드이고 다른 하나는 실시간 응용 서비스를 지원하기 위한 폴링 (polling) 모드이다. 폴링 모드는 PCF (Point Coordination Function) 라 불리우는 비경쟁 (non contention) 방식의 MAC 프로토콜이다. PCF 는 노드의 지연 (delay)의 증가와 처리율(throughput) 의 감소가 가장 큰 문제가 된다. 처리율 향상을 위해 ERR (Embedded Round Robin) 방식이 제안되었다. 그러나 ERR은 노드의 지연이 여전히 문제로 남아있다. 본 논문에서는 노드의 지연과 처리율을 동시에 향상시킬 수 있는 QRR (Request Round Robin)을 제안한다. 시뮬레이션에 의하여 제안한 QRR 이 ERR보다 성능향상이 됨을 보인다.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.2
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• pp.237-245
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• 2007

In this paper, a modified PCF (Point Coordination Function) MAC (Medium Access Control) Protocol is proposed to support the multiple direct link communication between STAs (STAtions) in infrastructure mode IEEE 802.11 wireless LANs. By the proposed MAC protocol, the direct link communication between STAs, which are located within the communication range of each other, is allowed without the use of AP (Access Point) as a relay. Moreover, when multiple direct data communication between STAs can be simultaneously performed with a sufficiently small interference, multiple simultaneous direct link communication is allowed for the efficient use of radio bandwidth. AP polls STAs to grant the transmission opportunities using the direct link communication by transmitting the polling frames to STAs. An efficient polling method for granting the transmission opportunities to STAs is proposed to reduce the number of the polling frame transmissions and enhance the PCF MAC performance.

• 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 the Korea Institute of Military Science and Technology
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• v.15 no.1
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• pp.16-27
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• 2012

In multi-interface multi-channel(MIMC) based tactical ad hoc networks, QoS support for required operational capacity is one of the main challenging issues for multi-hop transmissions. To support QoS in such a harsh environment, we propose a novel MAC scheme to minimize multi-hop as well as per-hop delay. The current IEEE 802.11 MAC protocols should contend to reserve the channel resource at every hop by each sender. The every-hop channel contention results in a degradation of end-to-end delay for multi-hop transmissions. The basic idea of our scheme is to make a "multi-hop reservation" at the MAC layer by using the modified RTS frame. It contains additional information such as destination information, packet priority, and hop count, etc. In addition, we differentiate the contention window area according to the packet priority and the number of hops to deliver packets in the predefined allowed latency. Our scheme can minimize the multi-hop delay and support the QoS of the critical data in real time(i.e., VoIP, sensing video data, Video conference between commanders). Our simulation study and numerical analysis show that the proposed scheme outperforms the IEEE 802.11 MAC.

• Proceedings of the Korean Information Science Society Conference
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• 2010.06a
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• pp.179-180
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• 2010

• Journal of KIISE:Information Networking
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• v.37 no.5
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• pp.386-395
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• 2010

Widespread deployment of infrastructure WLANs has made Wi-Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end-to-end performance, past research has focused on MAC protocol enhancement, analysis, and simulation-based performance evaluation without sufficiently considering a misbehavior stemming from capture effect. It is well known that the capture effect occurs frequently in wireless environment and incurs throughput unfairness between nodes. In this paper, we propose a novel Fair MAC algorithm which achieves fairness even under physically unfair environment. While satisfying the fairness, the proposed algorithm maximizes the system throughput. Extensive simulation results show that the proposed Fair MAC algorithm substantially improves fairness without throughput reduction.

• IE interfaces
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• v.16 no.2
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• pp.195-200
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• 2003

In this paper, the selective use of RTS and CTS frames is considered to analyze the capacity of IEEE 802.11 WLAN (Wireless Local Area Network). The RTS and CTS frames are used to transmit the data frames longer than dot11RTSThreshold according to IEEE 802.11 specification. The analysis of the optimal RTS-CTS threshold is derived to maximize the capacity of IEEE 802.11 WLAN. And, numerical examples are also presented for IEEE 802.11 a and b WLANs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11B
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• pp.1685-1695
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• 2010

In this paper, we propose a new reliable multicast MAC protocol over the IEEE 802.11-based tactical ad hoc networks. The major contribution compared to the previous reliable multicast schemes using consecutive CTSs/ACKs is that the proposed scheme can send multiple CTS/ACK messages concurrently assisted by MC-DS/CDMA mechanisms. When multiple receivers receive the RTS/DATA message from a sender, they respond with the CTS/ACK message spread with pre-assigned code in the same time interval. The proposed scheme can reduce the overhead of multiple CTSs/ACKs. It is also possible to alleviate the received signal strength at the enemy detector and thus it improves low probability of detection performance. Through simulations and analysis, the proposed scheme outperforms that of the multiple CTSs/ACks in terms of the throughput, transmission delay and low probability of detection.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.53-54
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• 2006

In this paper, we analytically evaluate packet delay and energy consumption of S-MAC protocol with a modified Markov chain model. Although some models, based on IEEE 802.11 MAC protocol, to analyze the S-MAC protocol in wireless sensor network (WSN) have been proposed, they fail to consider the differences in architecture between the S-MAC and the 802.11 MAC. Therefore, by reflecting the significant features in the S-MAC function, we model the operation of S-MAC protocol, and derive its packet delay and energy consumption in single-hop WSN. Numerical results show the delay and the dissipated energy at various duty cycle values according to offered load, where a practical mote is used.

• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.564-568
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• 2008

In this paper, MAC(Medium Access Control) algorithm for the IEEE 802.11 DCF(Distributed Coordination Function) improving the performance is proposed and analyzed mathematically. The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF(Point Coordination Function). The DCF controls the transmission based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance). The DCF shows excellent performance relatively in situation that competition station is less but has a problem that performance is fallen from throughput and delay viewpoint in situation that competition station is increased. This paper proposes an enhanced DCF algorithm that increases the CW to maximal CW after collision and decreases the CW smoothly after successful transmission in order to reduce the collision probability by utilizing the current status information of WLAN. To prove efficiency of proposed algorithm, a lots of simulations are conducted and analyzed.