• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.3B
• /
• pp.174-180
• /
• 2012

As the number of a smart phone user over the world surprisingly grows and a wireless Internet market expands, service requirement of a mobile terminal is increasing. However, because there is no consideration of mobility in the early standard step, it is difficult to expect to improve the service performance in handover procedure. This paper proposes a PFMIPv6 handover scheme by using probe request message and authentication message and by using buffering scheme in IEEE 802.11. In addition, we simulated this proposal scheme and verified that the proposed handover scheme is improved in terms of handover delay, and average FTP throughput during the handover period.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.8
• /
• pp.1768-1773
• /
• 2005

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, the session hijacking and the Man in the Middle attack due to the absence of AP authentication. In this paper, we propose a WLAN secure system which can offer a robust secure communication and a user authentications with the IEEE 802.1x framework. The user authentication on the WLAN secure system accomplishes mutual authentications between authentication severs, 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 doing secure communication between clients and the AP by the Dynamic WEP key distribution.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.6
• /
• pp.1275-1279
• /
• 2012

In this paper, we design of dual-band microstrip antenna for wireless communication. We used IEEE 802.11a and Hyper LAN (5.725~5.825 GHz). The proposed antenna substrate is FR-4, size is $22mm{\times}23mm$, thickness is 1.6mm and used to CST Microwave Studio 2010 program. As a result the simulation has good result and good return loss below -10 dB at 5 GHz and 5.8 bandwidth.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2002.05a
• /
• pp.643-646
• /
• 2002

In this paper, we analyse the performance of the system connected with several networks, that is, the system has one bulk input and several server by using queueing model - G $I^{⒳}$/M/c/N. in this paper we investigate some parameters from steady state probability and examine the average waiting time and blocking probability from those parameters.s.

• Journal of the Korea Society of Computer and Information
• /
• v.19 no.1
• /
• pp.31-41
• /
• 2014

This paper proposes a virtual mobile ad-hoc network (VMANET) model that automatically divides heterogeneous mobile devices of a MANET into a number of network groups depending on the communication capacity(data rate) of different network operational models such as IEEE 802.11g, IEEE 802.11b, and Frequency Hopping. In addition, it supports a distinct routing protocol for each network group of VMANETs, resulting in running multiple routing protocols concurrently on different groups of VMANETs. To reduce the network congestion and improve the network load balance, a default MANET gateway is configured in each VMANET and these gateways are responsible for integrating the MANET and IP networks. Experiment results show that the proposed model outperforms the conventional IMANET by significantly increasing throughput and reducing network congestion and network delay.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.9
• /
• pp.1015-1022
• /
• 2007

In this paper, we proposed a wideband design of planar inverted-F antenna(PIFA) using two-layer, patches and modified ground structure. The antenna consists of two layer patches with common feed and modified ground plane to control resonance frequency and antenna input impedance. The measured bandwidth is 1,492 MHz(BW: 67.7 %, 1,457${\sim}2,949$ MHz) for VSWR<2, and 1,170 MHz(BW: 21 %, 4,970${\sim}$6,140 MHz) for VSWR<2.5. It covers service bands of DCS1800, DCS1900, UMTS(WCDMA), WiBro, WLAN(IEEE 802.11b), satellite DMB. WLAN(IEEE 802.11a) in Korea and radiation patterns shows constant figure with frequency change.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.9
• /
• pp.47-54
• /
• 2004

The previous works for WLAN system based on OFDM is mainly individual study for independent frequency offset or symbol synchronization. In this paper, the performance of IEEE 802.11a WLAN(Wireless Local Area Network) system in the realistic indoor multipath channel models is analyzed with frequency offset compensation and channel estimation methods. For the performance analysis of the WLAN system indoor Rayleigh multipath channels are adopted, and the BER(Bit Error Rate) of WLAN system is calculated with y2 code-rate 16-QAM based on standard specification. From the simulation results, the difference of required Eb/No for BER of 10-3 is 1-2dB between the channel estimation and frequency offset compensation, and perfect channel estimation and no frequency offset.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.11B
• /
• pp.965-971
• /
• 2003

This paper suggests a low-complexity frame timing synchronization system for IEEE802.11a wireless LAN systems. The proposed timing synchronization scheme has been implemented by correlating the received OFDM preamble with quantized coefficients composed of ｛0, ${\pm}$2$^{0}$ , ${\pm}$2$^1$‥‥‥ ${\pm}$2$^{i}$ ), where i is an integer number. The 2$^{i}$ -valued coefficients enable the multipliers in the correlation system to be simplified to i-bit shifters. So we can design the correlation system using shifters instead of multipliers. We estimate the performance of the proposed scheme in comparison with conventional systems under the AWGN and Rayleigh fading channels. In this paper we show that the complexity can be reduced by 90% while still maintaining a performance comparable to that of the conventional system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.11B
• /
• pp.974-979
• /
• 2004

In the IEEE 802.1 Ib, DCF provides contention based services and PCF provides contention free services for QoS suppof. DCF uses CSMA/CA (Carrier Sense Multiple Access/collision Avoidance) as an access protocol. In this paper, an enhanced PCF, which gives weights to channels with heavy traffic load, was proposed. The weight is depending on the partial queue length information from STAs. NS-2 simulation results show that the proposed scheme is an promising approach for enhancing the PCF.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2007.05a
• /
• pp.1498-1501
• /
• 2007

디지털 홈 네트워크가 활성화되면서 IEEE 802.11 기술 덕분에 가정은 물론 사무실과 학교, 병원, 역 등지에서도 무선 LAN을 이용한 인터넷 사용이 가능하다. 현재 가장 많이 사용되는 2.4GHz 대역의 802.11b, 802.11g 프로토콜에 대하여 RSSI를 판독할 수 있는 모듈을 C# 언어에서 구현한 사례와 이 모듈의 이용에 대하여 소개한다.