• 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 Korea Society of Industrial Information Systems
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• v.11 no.3
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• pp.1-9
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• 2006

The handoff in IEEE 802.11 WLAN is a hard handoff. In hard handoff, a station has to stop the communication. As a result, the station is likely to miss some packets that arrival during the handoff process. To recover these lost packets, buffer-and-forward scheme is used. But, buffer-and-forward scheme is not efficient for real time service. In this paper, we propose new handoff scheme for real time service in home network based WLAN. The scheme uses priority queue which is recommended in IEEE 802.lie, and priority of priority queue is given to real time handoff calls. The simulation results show that the proposed scheme reduces traffic loss and transmission sequence error.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.8 no.1
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• pp.18-23
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• 2009

The conventional channel selection method for a ZigBee communication network basically detects the energy values in all channels. In the ISM band, no license is required to use channels in this band, so there may exist various interference factors in this band. It is well known that WLAN is the major interference factor degrading the performance of ZigBee in the ISM band. In this paper, we propose an efficient channel selection algorithm which uses the pattern of two types of WLAN channel uses as the a priori information of IEEE 802.11 band IEEE 802.11g. By using the proposed algorithm, we may save the time required to select channels for the ZigBee communications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6B
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• pp.338-348
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• 2005

Currently, IEEE 802.11 Wireless LAN (WLAN) is rising as the most popular means for the broadband wireless access network. In this thesis, we propose a QoS(Quality of Service)-Oriented mechanism using handshaking method of scanning phase in IEEE 802.11 handoff. In conventional process for handoff, the major criterion to select the best AP(Access Point) among candidates is normally based on the RSS(Received Signal Strength), which does not always make the selected network guarantee the maximum achievable performance. Even though the link quality with a neighboring AP is excellent, the AP may not be a good candidate to handoff to simply because MAC(Medium Access Control) protocol of IEEE 802.11 standard is contention-based such as CSMA/CA. Therefore, if we apply network level information to AP selection criteria, we can achieve better handoff efficiency rather than before. The analysis and simulation results applied to our new mechanism show clearly better performance than AP selection based on traditional handoff method.

• 한국ITS학회:학술대회논문집
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• 2008.11a
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• pp.376-379
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• 2008

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.2
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• pp.437-444
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• 2014

The unmanned ship control system controls the unmanned ship at a distance in ocean. Expecially, in order to control the unmanned ship, it needs the wireless communication networks and we use the IEEE 802.11 based WLAN. The IEEE 802.11 based WLAN technology for supporting a wide bandwidth is suitable for unmanned ship control system which has to transmit the multimedia data. First, we design the system structure for controlling the unmanned ship. Then, in order to overcome the limited communication area, we design the network structure for the unmanned ship communication network which can use a various communication network. we implemented and evaluated the unmanned ship system based on WLAN. We controlled the unmanned ship by use the WLAN and confirmed the signal feature of WLAN in the ocean.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.1003-1013
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• 2006

There is a serious problem in an 802.11g VoWLAN (Voice over Wireless LAN) terminal that talk time is less than 30% compared with an 802.11b terminal. It is almost impossible to achieve talk time level of the 802.11b MAC transmission method because IEEE 802.11g uses OFDM modulation, which is a kind of multi-carrier method and OFDM transmission speed is 54 Mbps faster than normal modulation. In this paper, a new concept of a Holdover time as a power saving method during a call with 802.11g terminal is suggested for the first time. Increase in the number of engaged terminals as a result of holdover time causes to QoS problem because of the increase in the number of back-off and then contention window. In this paper, to solve the QoS problem, a new approach is suggested such that when in down lint the sequence number of 802.11 G.711 is analyzed in the MAC of the terminal and then the Hold over time depending on loss rate is changed. Also, consumption of an electric current of 802.11b/g and MAC parameter's performance due to busy traffic caused by increase in the number of terminal are analyzed and then real data using VQT and Airopeek are analyzed.

• Journal of Internet of Things and Convergence
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• v.6 no.4
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• pp.15-19
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• 2020

In this paper, we propose a optimal CW(Conention Window) synchronization scheme in IEEE 802.11 WLANs. IEEE 802.11 WLANs support DCF(Distributed Coordination Function) mode for the MAC(Medium Access Control) operation. In DCF, the CW increases exponentially according to the collisions and becomes minimum CW according to the success of data transmissions. However, since the base minimum CW value is hardware or standard specific, the number of active stations and network status are not considered to determine the CW value. Even though the researches on optimal CW have beend conducted, they do not consider the optimal CW synchronization among mobile stations which occur network performance degradation. Therefore, this paper calculates the optimal CW value and shares it with mobile stations in the network.

• 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.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.4
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• pp.29-38
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• 2005

Because IEEE 802.11 has several security vulnerabilities, IEEE 802.11i was proposed and accepted. But IEEE 802.11i has much overhead for most of users for the web surfing. Besides not only node the authentication but also the packet authentication is needed to communicate. Although IEEE 802.11i uses TKIP(Temporal Key integrity Protocol) and CCMP(CTR with CBC-MAC Protocol), they have a lot of overheads. In this paper, Lightweight Packet Authentication(LIPA) is proposed. LIPA has less overhead and short delay so that it can be affordable for simple web-surfing which does not need stronger security. After comparing performances of LIPA with those of TKIP and CCMP, LIPA is more efficient than other schemes for transmitting packets.