• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.2A
• /
• pp.168-175
• /
• 2006

To cope with channel variation, wireless networks such as IEEE 802.11 WLAN provide multiple transmission rates by employing different channel modulation and coding schemes. However, the coexistence of different transmission rates degrades the total system performance of the network. In order to eliminate this performance abnormality and improve protocol capacity, we propose a new Packet transmission algorithm, the RAT(Rate-Adapted Transmission) scheme. The RAT scheme distributes the wireless channel fairly based on the channel occupancy time. Moreover, it efficiently transmits packets even in a single station using rate-based queue management. Therefore, the RAT scheme obtains not only the inter-rate contention gain among stations but also the intra-rate contention gain among connections in a single station.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.9
• /
• pp.1983-1989
• /
• 2012

The IEEE 802.1x standard provides an architectural framework which can be used various authentication methods. But, IEEE 802.1x also has vulnerabilities about the DoS(Denial of Service), the session hijacking and the MiM(Man in the Middle) attack due to caused by structural of authentication protocol. In this paper, we propose a WLAN system which can offer safety communication by complement of IEEE 802.1x vulnerabilities. The WLAN system accomplishes mutual authentications between authentication servers, clients and the AP using PKI and prevents an illegal user from intervening in communication to disguise oneself as a client, the AP or authentication servers. Also, we guarantee the safety of the communication by the Dynamic WEP key distribution between clients and the AP.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.2
• /
• pp.232-238
• /
• 2004

In this paper, radio propagation in a subway tunnel is investigated using fan beam antennas, circular polarization antennas and directional antennas at 2.4㎓ and 5.8㎓ band, respectively. The results of narrowband channel measurements show that received power level for NLOS(Non-Line-Of-Sight) path is decreased drastically as compared with LOS(Line-Of-Sight) path. Wideband channel measurements are obtained using a PN sliding correlation method. The parameters of the channel such as mean access delay and RMS delay spread are compared as to different types of directional beam at IEEE 802.11 WLAN(Wireless Local Area Network) band including 2.4㎓ and 5.8㎓ bands, respectively.

• Journal of Digital Contents Society
• /
• v.14 no.1
• /
• pp.25-33
• /
• 2013

P2P(Peer-to-Peer) architecture can reduce the network bandwidth and resource on the server since peers exchange data chunks with each other, while server-client architecture causes a lot of traffic on the server. Peers receive a data more reliably when the number of participating peer increases. Currently, P2P traffic has accounted for about 65% of the world's Internet traffic and diverse P2P streaming services have launched combining to video streaming technology. However, the requirements and data chunk delivery algorithms for mobile P2P streaming service should be investigated, since the existing P2P technologies have been developed and designed for the wired network. In particular, the bandwidth fluctuation caused by user mobility, wireless packet collisions, and packet losses brings about different problems on the mobile P2P streaming service compared to existing P2P streaming service. In this paper, we analyzed the problem of mobile P2P streaming services in the 802.11n wireless LAN environment through experiments.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.13 no.6
• /
• pp.107-112
• /
• 2003

Handover in IEEE 802.11 requires repeated authentication and key exchange procedures, which are an obstacle to seamless services of wireless LAM. We propose a fast authentication and key exchange mechanism using IEEE 802.11f. Especially, by proposing a modified version of the 4-way handshake of IEEE 802.11i, we solve the perfect forward secrecy problem that arises when the pre-authentication is adopted. The scheme can be implemented only using the Context Block of IEEE 802.11f and the 4-way handshake of IEEE 802.11i without involving authentications server's interaction or non-standard behavior between access points. Our scheme is applicable to devices not supporting the us-authentication of IEEE 802.11i and also, it can substitute the pre-authentication when the pre-authentication is failed.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2014.11a
• /
• pp.203-206
• /
• 2014

무선 LAN(Wireless Local Area Networks 의 DCF(Distributed Coordination Function) 방식은 랜덤 백 오프 방식으로 매체에 접근하기 때문에 지연이 발생하여 정해진 시간 내에 전송을 보장할 수 없다는 단점이 있다. [1] 이는 곧 실시간 멀티미디어 트래픽(비디오, 음성 등)의 QoS(Quality Of Service)를 보장할 수 없다는 것을 뜻한다. 또한 IEEF 802.11e 표준 [2]에서 제공하는 QoS 를 위한 EDCA(Enhanced Distributed Channel Access)라는 프로토콜은 제시되어있으나 실제로 구현되어있는 디바이스의 부재로 QoS 를 지원하기가 어렵다. 따라서 무선 랜에서 IEEE 802.11e 를 지원하지 않는 망내 디바이스, 즉 큐가 1 개인 STA, 즉 기본적인 802.11 표준 기술인 DCF 를 사용하는 STA 을 위해서 멀티미디어 트래픽의 실시간 전송을 보장하기 위한 기법을 제시한다.

• Proceedings of the IEEK Conference
• /
• 2003.07a
• /
• pp.517-520
• /
• 2003

Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology for high speed multimedia communication in a frequency selective multipath channel. In this paper, Software IPs for the synchronizer of IEEE 802.11a Wireless LAN system are designed and optimized for TI's TMS320C6201 fixed point DSP. As a result of the execution cycles of the target DSP for each functions of the system, an efficient HW/SW partitioning method can be considered.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.43 no.11 s.353
• /
• pp.77-82
• /
• 2006

Analog channel selection filter is described which is designed for a direct-conversion receiver of a IEEE 802.11a wireless LAN. The channel selection filter is an active-RC fifth-order Chebyshev filter with 10MHz cut-off frequency. Two-stage operational amplifier of the filter employs a current re-using feedforward frequency compensation scheme to minimize the power consumption. The filter has been implemented in a 0.18mm CMOS technology and the experimental results show 20mW power consumption with 1.8V supply voltage and 19dB out-of-band iIP3.

• Journal of the Korea Society of Computer and Information
• /
• v.13 no.6
• /
• pp.225-232
• /
• 2008

When a single source of multimedia contents is distributed to multiple reproduction devices, the audio and video contents require synchronous play for multi-channel stereo sound and lip-synchronization. The multimedia system in vehicle, especially, has researched to move to wireless environments from legacy wired environments. This paper proposes the advanced algorithm for providing synchronized services of real-time multimedia traffic in IEEE 802.11 WLANs [1]. For these, we implement the advanced IEEE 1588 Precision Time Protocol [2] and the environments for simulation. Also, we estimate and analysis performance of the algorithm, then we experiment and analysis after the porting of algorithm in wireless LAN devices (Linksys wrt-350n AP network device) to characterize timing synchronization accuracy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.22 no.8
• /
• pp.797-804
• /
• 2011

Network coding has recently emerged as an effective solution for multicast and broadcast communications in wireless ad hoc networks. In this paper, we propose a throughput performance model for IEEE 802.11 wireless networks with network coding. Specifically, we consider IEEE 802.11 DCF protocol and linear topology in which traffic sources are located at both ends and intermediate nodes act as relays performing network coding. The proposed analytic model has the form of nonlinear equations in terms of throughput of each node. The solution of the nonliear equations thus correspond to the end-to-end throughput. Extensive simulation experiments have been performed to validate accuracy of the proposed model. Numerical results show that the results of the proposed analytic model agree fairly well with the corresponding simulation results.