• Journal of Digital Contents Society
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• v.12 no.3
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• pp.299-307
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• 2011

The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF. The DCF controls the transmission based on CSMA/CA The BEB backoff algorithm of DCF shows relatively excellent performance in situation that the number of competing station is less, but has a problem that performance of throughput and delay is degraded in situation that the number of competing station is increased. This paper mathematically analyzes an MIMD backoff algorithm considering retry limit that increases the CW to doubled after collision and decreases smoothly the CW to halves after successful transmission in order to reduce the collision probability. To prove efficiency of the MIMD backoff algorithm, lots of simulations are conducted and analyzed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.3
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• pp.556-562
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• 2007

In this paper we propose a new method which adjusts the collision resolution depending on busy status of the channel to improve performance of IEEE 802.11 DCF. This scheme reduces the number of collisions in wireless channel by decreasing the amount of movements of each station's backoff stage based on busy event count and the one stage backoff model. Through simulation, we compared the performance of our scheme with that of DCF, ADCF and SD.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1229-1237
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• 2006

IEEE 802.11 has employed distributed coordination function (DCF) adopting carrier sense multiple access with collision avoidance (CSMA/CA). To effectively resolve collisions, DCF uses binary exponential backoff (BEB) algorithm with three parameters, i.e., backoff stage, backoff counter and contention window. If a collision occurs, stations involving in the collision increase their backoff stages by one and double their contention window sizes. However, DCF with BEB wastes wireless resource when there are many contending stations. Therefore, in this paper, to enhance the performance of wireless LAN, we propose binary negative-exponential backoff (BNEB) algorithm which maintains a maximum contention window size during collisions and reduces a contention window size to half after successful transmission of a frame without retransmissions. For IEEE 802.11, 802.11a and 802.11b standards, we also compare the performance of DCF with BEB to that with BNEB.

• The Journal of the Korea Contents Association
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• v.11 no.11
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• pp.34-41
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• 2011

The MAC of IEEE 802.11 WLAN to control data transmission uses two control methods called DCF and PCF. The DCF uses BEB backoff algorithm based on CSMA/CA. The BEB backoff algorithm shows excellent performance relatively in situation that competition between stations is less, but its performance is decreases as the competition increases. This paper proposes and analyses mathematically an enhanced backoff algorithm. To reduce the collision probability, the proposed algorithm increases the contention window to maximum after collision and decreases the contention window smoothly after successful transmission. To prove efficiency of proposed algorithm, simulations are conducted and analyzed.

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.467-470
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• 2010

본 논문에서는 IEEE 802.11 WLAN의 MAC인 DCF의 성능을 개선하는 알고리즘을 제안하고 이를 해석적으로 분석한다. IEEE 802.11 WLAN의 MAC에서는 데이터 전송을 제어하기 위한 방법으로 DCF와 PCF를 사용하며, DCF의 경우 CSMA/CA를 기반으로 한다. DCF는 경쟁 스테이션이 적은 상황에서는 비교적 우수한 성능을 보이나 경쟁 스테이션의 수가 많은 경우 처리율, 지연 관점에서 성능이 저하되는 문제점이 있다. 본 논문에서는 패킷 전송 후 충돌이 발생하면 윈도우 값을 최대 CW로 증가시키고 연속적으로 c번 패킷전송에 성공하면 CW를 감소함으로써 패킷 충돌 확률을 낮추는 알고리즘을 제안하고 이를 수학적으로 분석한다. 제안하는 알고리즘의 효율성을 입증하기 위해 시뮬레이션을 수행하여 그 타당성을 제시하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.39-50
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• 2005

In this paper, we propose a performance improving MAC algerian for the IEEE 802.11 DCF. WLAN based IEEE 802.11 uses two control methods called 'Distributed Coordination Function(UF)' and 'Point Coordination Function(PCF)'. The nF controls the Urnsmission based on carrier sense multiple access with collision detection(CSMA/CA), that decides a random backoff time with the range of contention window for each terminal. Normally, each terminal the CW double after collision, and reduces the CW to the minimum after successful transmission. This paper proposes an enhanced DCF algorithm that decreases the CW smoothly after successful transmission in order to reduce the collision Probability by utilizing the current status information of WLAN. We also analyze the throughput and delay performance for the unsaturated case mathematically. Simulation results show that our algorithm enhances the saturation throughput of WLAN. They also coincide well with the analytical results.

• Proceedings of the Korea Contents Association Conference
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• 2007.11a
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• pp.130-134
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• 2007

DCF(Distributed Coordination Function) of IEEE 802.11 WLAN(Wireless Local Area Network) MAC Layer apply to CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) for solution of collision when the station try to access at the same time. But DCF happens falling performance as increasing a number of stations. In this paper, we suggest algorithm that improved performance in congestion. And we compare DCF, DCF+ and proposed algorithm respect to saturation throughput, delay, collision rate and drop rate using NS2(Network Simulator 2) simulation tool.

• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.388-394
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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 by simulation. 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1075-1082
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• 2004

Wireless LAN is a rather mature communication technology connecting mobile terminals. IEEE 802.11 is a representative protocol among Wireless LAN technologies. The basic medium access control (MAC) mechanism of IEEE 802.11 is called distnbuted coordination function (DCF). DCF shows poor throughput and high drop rate as the number of stations and offered traffic load increase. In this paper we propose an effective mechanism using dynamic mimmum contention window(CWmin) in wireless LAN~ and show that performance improves via simulations. Proposed dynamic CWmin scheme exhibits superior performance as the number of stations and offered load grow. As, our proposed scheme is expected to be more effective in highly densed wireless LAN environment.