• 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.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.154-160
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• 2005

Microwave Otters are essential device in modem wireless systems. A compact dimension BPF(Band-pass Filter) for IEEE 802.11a WLAN service is realized using LTCC multi-layer process. To extrude 2-stage band-pass equivalent circuit, band-pass and J-inverter transform applied to Chebyshev low-pass prototype filter. Because parallel L-C resonator is complicate and hard to control the inductor characteristics in high frequency, the shorted $\lambda/4$ stripline is selected for the resonator structure. The passive element is located in the different layers connected by conventional via structure and isolated by inner GND. The dimension of fabricated stacked band-pass filter which is composed of six layers, is $2.51\times2.27\times1.02\;mm^3$. The measured filter characteristics show the insertion loss of -2.25 dB, half-power bandwidth of 220 MHz, attenuation at 5.7 GHz of -32.25 dB and group delay of 0.9 ns at 5.25 GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8A
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• pp.640-647
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• 2009

IEEE 802.11i is an amendment to the original IEEE 802.11/b,a,g standard specifying security mechanism by stipulating RSNA for tighter security. The RSNA uses TKIP(Temporal Key Integrity Protocol) and CCMP(Counter with CBC-MAC Protocol) instead of old-fashioned WEP(Wired Equivalent Privacy) for data encryption. This paper describes a design of a communication security engine for IEEE 802.11i MAC layer. The design includes WEP and TKIP modules based on the RC4 encryption algorithm, and CCMP module based on the AES encryption algorism. The WEP module suffices for compatibility with the IEEE 802.11 b,a,g MAC layer. The CCMP module has about 816.7Mbps throughput at 134MHz, hence it satisfies maximum 600Mbps data rate described in the IEEE 802.11n specifications. We propose a pipelined AES-CCMP cipher core architecture, which has lower hardware cost than existing AES cores, because CBC mode and CTR mode operate at the same time.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.52-57
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• 2006

In this paper, the triple-band planar monopole antennas are designed for cellular communication, WiBro and WLAN(IEEE802.11b/g) communication and WLAN(IEEE802.11a) communication of 5GHz band to using filled mobile convergence subscriber unit. Various types of antennas are designed and examined experimentally as bended in the low and middle band radiation elements to decrease antennas size and increased the width of radiation elements to improve bandwidth The proposed antennas are reduced by 11% in antenna size with bended low-band radiation elements down and are extended by $30%{\sim}40%$ in bandwidth by increasing the width of the radiation element at 800MHz band.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.1
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• pp.103-107
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• 2009

In this paper, we designed and implemented a dual band chip antenna for WLAN, which contains within the small LAN card contrary to the enternal AP(Access Point) antenna. Limiting about the antenna size, we used dielectrics of high permittivity. Totally considering problems of demand-supply, price and characteristics, we used that relative dielectrics of ceramic is 9.8 and the thickness is 3.5mm and 5mm. Ceramic antenna can be used not only triple mode of IEEE 802.11.a,g and b but also broadband. The frequency bands have wideband characteristics of 2.4~2.5GHz and 4.9~5.85GHz and relatively constant performance.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.285-288
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• 2003

Code Select CDMA(CS/CDMA)(1)는 입력 데이터 열에 의하여 여러 채널의 직교코드를 선택하여 전송하는 기술로, 멀티코드 CDMA 의 구조를 가지면서도 전송신호의 크기가 일정하여 저가의 비선형 증폭기를 사용하여 구현 할 수 있다. 특히 입력 비트열을 부호화하여 직교코드들의 합을 일정하게 만드는 constant amplitude coded (CA-) CS/CDMA (2) 전송 기술은 2.4GHz ISM 대역의 WPAN을 위한 전송방식의 하나로 고려되고 있다. 이주파수 대역은 WLAN, 블루투스 등을 비롯한 여러 시스템이 존재하는 대역이므로 다른 종류의 시스템과의 상호 간섭의 문제를 분석할 필요가 있다. 본 논문에서는 2.4GHz ISM 대역을 같이 사용하게 될 IEEE 802.11b WLAN 과 CA-CS/CDMA 기반의 WPAN 상호 영향을 물리계층 측면에서 분석한다. IEEE 802.11b 모델로 11MHz 대역폭을 갖는 CCK (Complementary Code Keying) 변조방식을 대상으로 하며, CA-CS/CDMA 와의 중심주파수 차이에 따른 비트오율 성능을 신호대 간섭전력의 비를 변화시켜가면서 컴퓨터 모의실험을 통하여 분석하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.9
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• pp.47-54
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• 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 the Institute of Internet, Broadcasting and Communication
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• v.8 no.3
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• pp.81-86
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• 2008

The paradigm of information & communication is rapidly changed into ubiquitous environment based electromagnetic wave, and antenna technology in the wireless ubiquitous communication is remarkably developed. Mini chip antenna has its within small card compared to the external AP antenna. Designed and Fabricated WLAN antenna has a broadband characteristics of 2.4~2.5GHz and 4.9~5.85GHz, and can be used triple mode of IEEE 802.11.a,g.b, and it has comparatively a constant performance in the dual frequency band.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.243-244
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• 2008

센서 네트워크는 그 특성 상 에너지 제약이 심하며, 최근에는 움직이는 대상에 deploy이 되어 mobile 환경에서의 연구가 활발히 진행되고 있다. Mobile 센서 네트워크의 자원 최적 할당을 위해 논문에서는 WPAN과 같은 채널 대역을 쓰는 IEEE 802.11과 공존 문제에 대해서 다루고 이런 상황에서 간섭을 회피하고 QoS를 높이기 위한 채널 선택 방법에 대해 연구하였다. 본 방식의 channel allocation 알고리즘을 사용하면 효과적으로 WPAN에서 WLAN의 interference를 피할수 있게 된다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.95-103
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• 2009

An efficient symbol time synchronization scheme for IEEE 802.11n MIMO-OFDM based WLAN systems using cyclic shift diversity (CSD) preamble is proposed. CSD is used to prevent unintentional beamforming when the same preamble signal is transmitted through transmit antennas. However, it is difficult to find a proper starting-point of the OFDM symbol with the conventional algorithms because of time offset by multi-peaks which are result from cross-correlation of received CSD preamble with a known short training symbol. In addition, the performance of symbol time sync. is affected by AGC and packet detection position. In this paper, an optimal symbol time synch. algorithm which is composed of the boundary detection scheme between LTS and OFDM symbols, the verification scheme for enhancement of boundary detection accuracy, and the SNR-varying threshold estimation scheme is proposed. Simulation result show that the proposed algorithm has performance gains of 4.3dB in SNR compared to the conventional algorithms at the rate of 1% sync. failure probability for $2{\times}2$ MIMO-OFDM system and 18dB at 0.1% when maximum frequency offset exists. It also can be applied to $4{\times}4$ MIMO-OFDM system without any modification. Hence, it is very suitable for MIMO-OFDM WLAN systems using CSD preamble.