• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8A
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• pp.820-827
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• 2010

In these days, video applications for special purposes such as video conference systems among multiple users and video surveillance systems require multiple video connections and QoS guarantee. The video systems employ IEEE 802.11 Wireless LAN devices to support broadband wireless interfaces and easy internet accesses for cheaper prices. However, according to the current IEEE 802.11e HCCA standard, if more than three video sessions are established in WSTA services, some of them must share the TXOP because the available number of TSIDs for video transmission is two. In order to resolve the problem, we devised a method which can establish up to 15 video sessions by slightly modifying the frame structure while maintaining the compatibility with current standard. Our method is implemented on the NCTUns 4.0 network simulator, and evaluated not only numerically in terms of throughput, delay, and PSNR, but also experimentally in the sense of real video clips that are used as input to our simulation. The results showed that our method sufficiently guarantees the transmission bandwidth requested by each video session.

• Journal of the Korea Society of Computer and Information
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• v.10 no.4 s.36
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• pp.249-257
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• 2005

A Markov model for the IEEE 802.11 standard which is the most widely deployed wireless LAN protocol, is designed and the channel throughput is evaluated. The DCF of 802.11, which is based on CSMA/CA protocol, coordinates transmissions onto the shared communication channel. In this paper, under a finite load traffic condition and the assumption of packet loss after the final backoff stage. We present an algorithm to find the transmission probability and derive the formula for the channel throughput. The proposed model is validated through simulation and is compared with the case without packet losses.

• The KIPS Transactions:PartC
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• v.11C no.2
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• pp.219-228
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• 2004

Wireless LAN(wireless Local Area Network) is constructed network environment by radio in indoors or outdoors environment and that to use electric wave or light instead of wire to client such as PC(Personal Computer), notebook, PDA in hub(Hub) in technological side. Now, among IEEE 802.11 WG(Working Group), there is TGf(Task Group F) that develop standard protocol between AP's(Access Point). In this group, proposed IAPP(Inter Access Point Protocol) to secure interoperability between AP producing in different manufacturer, this offers seamless connectivity between STA by sharing Security Context information or Layer 2 forwarding information between AP without passing through re-authentication process when STAs(Station) move by protocol to secure mobility between AP that differ in equal serve network. In this paper, I wish to suggest method that change avenue of communication of message to block information leakage that can occur at security message or WEP Key transmission between above AP, and uses public key to offer wireless area security little more.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.5
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• pp.980-987
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• 2009

A timing synchronization method is presented for IEEE 802.11a wireless OFDM system. First the signal detection is achieved by measuring the moving energy of the received OFDM signal in two consecutive windows. By measuring the correlation between the short training signal and received envelope signal, fine OFDM symbol synchronization can be acquired. The variance and average value of the correlation value is acquired. And the theoretical values are compared with computer simulation results.

• Journal of IKEEE
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• v.2 no.1 s.2
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• pp.76-84
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• 1998

In this paper, CSMA/CA with bridging is analyzed which is an added function of relaying directly between access points when wireless terminals can not communicate each other, and is also compared to the CSMA/CA without bridging which is IEEE 802.11 MAC standard. Through simulations, it is shown that the two methods have the similar performance in terms of the throughput but the bridging CSMA/CA improves the delay compared to the non-bridging CSMA/CA.

• Journal of Korea Society of Industrial Information Systems
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• v.16 no.2
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• pp.1-11
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• 2011

A lot of works on the throughput analysis of the IEEE 802.11 DCF have been studied since last few years. However, we should predict the throughput of the IEEE 802.11g that we mostly use today because the existing numerical results do not consider exactly the IEEE 802.11g with the physical layer ERP-OFDM parameters. In particular, we might have different results in the working WLAN s compared with the simple predictions of the throughput using the previous results. In this paper, we directly monitor the ERP-OFDM physical layer parameters on the operating WLANs, and then analyze the saturated DCF throughput with the well-known analytic model. Moreover, we measure the bandwidth utilization on the real WLANs working with FTP services, and then compare them with the analytic results. According to the experiment results, we confirm the usefulness of the analytic models which assume the saturated traffic sources.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11b
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• pp.1023-1026
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• 2002

The demand for Wireless LAN (WLAN) access to use their network and the Internet is surged dramatically over the past year. Since WLAN provides users' access from anywhere in the workplace without having to plug in, it therefore leads the WLAN market to grow steadily. Unfortunately, the first WLAN implementation designed primarily for home networking did little to address these security issues. Moreover, although the 802.11b standard published by IEEE in 1999 improved WLAN connections LAN-equivalent speed and security from the 802.11 standard. However, there still are several flaws such as the weaknesses in the Authentication and WEP encryption schemes in the IEEE 802.11 WLAN standard. In this paper, we propose WLAN architecture for providing the strong centralized authentication, encryption, and dynamic key distribution on a WLAN. Additionally, this proposed architecture is able to support roaming users and is flexible and extensible to future developments in the network security.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.4
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• pp.753-757
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• 2005

Wireless LAN was developed by alternative of LAN and because establishment was easy, have used into special field and special expenditure. Recently, Standard and a technology developed by leaps and bounds. Present is used into purpose of the Building to Building or wide connection etc. and relay of the high speed Internet and usage of picture communication that require multimedia band width. Specially, campus wireless LAM is thought that must secure radius $100\;\~\;200\;m$ dimension at the minimum 10Mbps speed as Internet transit trunk. But, there is difference as degressive here. In this paper, wireless LAN measured for effectiveness proof as Internet transit trunk in actuality utilization environment. Proved that should compose IEEE802.11b as AP more than minimum 3 when compose network to base as measuring result. Hereafter, there is the purpose that achieve performance evaluation of wireless UM in marine environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.581-593
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• 2004

The interest in wireless LAN security is on the increase owing to a role of high-speed wireless Internet infrastructure of wireless LAN. Wi-Fi has released WPA standard in order to overcome drawbacks of WEP algorithm that is security element of current IEEE 802.11-based wireless LAN system. Pairwise key management and group key management in a mixed-mode which supports both terminals running WPA and terminals running original WEP security are very complicate. In this paper, we analyze flaws in WPA authenticator key management state machine for key distribution and propose the countermeasures to overcome the analyzed problems. Additionally, WPA authenticator key management state machine to which the solutions are applied is described. The reconstructed WPA authenticator key management state machine helps the AP perform efficiently group key exchange and group key update in the mixed-mode.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.200-203
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• 2003

By minimizing the burst error of data and correcting the error, we can define the convolution coding and interleaving in IEEE 802.11a wireless tan system. Two step block interleaver was decided by coded bits per OFDM symbol and due to this it comes to the delay time in IEEE 802.11a. This is the point of the question which we must consider. We try to decrease the delay time by all 48-clock from interleavings, and we have proposed a way carried out the interleaving outputs per symbol. So in comparison with the existing interleaver, we can decrease the delay time in reading and writing data, as well as reduce the delay time of bit re-ordering per symbol. Also this scheme is apply in all x-QAM cases.