• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.3
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• pp.51-57
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• 2010

A dual-mode direct conversion receiver is developed in $0.13\;{\mu}m$ RF CMOS process for IEEE 802.11n based wireless LAN and IEEE 802.16e based mobile WiMAX application. The RF receiver covers the frequency band between 2.3 and 2.7 GHz. Three-step gain control is realized in LNA by using current steering technique. Current bleeding technique is applied to the down-conversion mixer in order to lower the flicker noise. A frequency divide-by-2 circuit is included in the receiver for LO I/Q differential signal generation. The receiver consumes 56 mA at 1.4 V supply voltage including all LO buffers. Measured results show a power gain of 32 dB, a noise figure of 4.8 dB, a output $P_{1dB}$ of +6 dBm over the entire band.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.518-528
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• 2009

IEEE 802.11 wireless local area network (WLAN) has become the prevailing solution for wireless Internet access while transport control protocol (TCP) is the dominant transport-layer protocol in the Internet. It is known that, in an infrastructure-based WLAN with multiple stations carrying long-lived TCP flows, the number of TCP stations that are actively contending to access the wireless channel remains very small. Hence, the aggregate TCP throughput is basically independent of the total number of TCP stations. This phenomenon is due to the closed-loop nature of TCP flow control and the bottleneck downlink (i.e., access point-to-station) transmissions in infrastructure-based WLANs. In this paper, we develop a comprehensive analytical model to study TCP dynamics in infrastructure-based 802.11 WLANs. We calculate the average number of active TCP stations and the aggregate TCP throughput using our model for given total number of TCP stations and the maximum TCP receive window size. We find out that the default minimum contention window sizes specified in the standards (i.e., 31 and 15 for 802.11b and 802.11a, respectively) are not optimal in terms of TCP throughput maximization. Via ns-2 simulation, we verify the correctness of our analytical model and study the effects of some of the simplifying assumptions employed in the model. Simulation results show that our model is reasonably accurate, particularly when the wireline delay is small and/or the packet loss rate is low.

• Journal of Practical Engineering Education
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• v.13 no.2
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• pp.321-326
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• 2021

Wireless communication is a core technology constituting the Internet of Things (IoT), but there is no suitable educational equipment to learn various wireless communication technologies used in the Internet of Things through practice. This paper deals with the development of advanced education and training equipment that can perform various IoT wireless communication practices. It uses an Arduino mega board as a device to control various sensors. As wireless network technologies to send and receive the sensing date wirelessly, it makes use of RFID/NFC and Bluetooth among WPAN technologies, WiFi among WLAN technologies and LoRa and 2.4GHz wireless transceiver among WWAN technologies. In addition, GPS, infrared communication, I2C communication, and SPI communication are organized so that various IoT wireless communication technologies can be learned through practice. In addition, since the educational equipment developed in this paper is equipped with two devices, it is designed to perform transmission and reception experiments for wireless network technology within the equipment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.1
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• pp.88-91
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• 2016

In this paper, we have proposed the frequency interference analysis system using both LabVIEW and Universal Software Radio Peripheral(USRP) for performance degradation analysis of Multi Input Multi Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM) Wireless Local Area Network(WLAN) due to Wireless Local Area Network(WPAN) interferer. The proposed system consists of three part, i.e., victim, channel, and interferer. Both victim and interferer are implemented by LaBVIEW and a USRP board. Then interfering signal and additive white Gaussian noise are combined with the wanted signals of a victim. Measured Bit Error Rate(BER) at the victim receiver is compared with theoretical BER according to various signal to interference plus noise power ratio (SINR) values. Measured and theoretical BER curves show good agreement.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.311-314
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• 2002

본 논문에서는 저가의 FR4 칩의 전면과 후면을 이용하여 ISM대역을 만족하는 이중대역 특성의 평면 역F 칩 안테나(PIFcA)를 설계ㆍ분석하였다. 제안된 PIFcA의 크기는 21$\times$5$\times$1mm이고, 10㏈ 반사손실을 기준으로 하여 2.45㎓에 9.54%(2390~2630MHz), 5.775㎓에서 13.89%(5670~6520MHz)의 이중대역 특성을 갖는다. 안테나는 2.45㎓에서 2.2㏈i, 5.77㎓에서 5.2㏈i의 이득특성을 나타내며, 방사패턴은 일반적인 PIFA 방사패턴과 유사하다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.100-103
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• 2002

본 논문에서는 무선 인터넷 사업 및 초고속 정보통신 인프라 구축과 관련하여 WRC-2003에서 새롭게 분배하기로 결정된 5GHz대역(5.135~5.35GHz, 5.47~5.725GHz)과 기존의 ISM 대역(5.75~5.85GHz)에 동시에 사용할 수 있는 스트립 라인 급전을 이용한 슬롯 안테나를 설계하였다. 무선통신 시스템의 박형화를 위하여 평면 내장형으로 설계하였으며 안테나의 크기는 5.04$\times$12.55$\times$2.0[mm]이며 FR-4($\varepsilon$$_{r}$=4.6)를 substrate로 사용하였다. 중심주파수 5.749GHz를 중심으로 10㏈ 기준대역폭 28.54%(4.929~6.561GHz)fmf 갖는다. 안테나의 이들은 약 4.2㏈i이다.

• 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.

• The KIPS Transactions:PartC
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• v.16C no.3
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• pp.317-324
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• 2009

In this paper, a 4-way Handshake protocol in the IEEE 802.11i is analyzed in terms of both security and reliability. It is shown that the 4-way Handshake protocol breaks down under some conditions due to a MIC (message integrity code) failure, and a solution to fix it is proposed. It is also proposed that a new 2-way Handshake protocol which is more secure and efficient than the 4-way Handshake protocol.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.6
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• pp.105-112
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• 2010

Recently, wireless communication systems have been developed and the circuits which operate with the broad-band for multiband uses were introduced. However, broad-band circuits have problems that inevitably increase the size. Dual-band circuit operates only two frequency, therefore, it will be able to miniaturize through unnecessary decreased elements. The Wilkinson power divider is the one of the most commonly used components in wireless communication system for power division. Nowaday, the Wilkinson power divider is also demanded dual-band. In this paper, I propose miniaturized dual-band Wilkinson power divider operating at 2.45 GHz and 5.2 GHz for IEEE 802.11n standard. Proposed dual-band Wilkinson power divider is used in parallel stub line. The design is accomplished by transforming the electrical length and impedance of the quarter wave sections of the conventional Wilkinson power divider into dual band ${\pi}$-shaped sections.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.12
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• pp.1655-1660
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• 2014

In this paper, we propose a design of a triple-band microstrip circular patch antenna. The proposed antenna generates the triple frequency resonance at 1.85GHz(LTE), 2.45GHz(ISM) and 5.5GHz(WLAN). Firstly, we design the dual-band antenna. The dual-band antenna consist of the circular patch, slits, and the slot. The circular patch and slot are designed for dual frequency of 2.45GHz and 5.5GHz, respectively. And then the dual-band antenna is combined with additional arm-shaped structure for the triple-band characteristic. The arm-shaped structure is operated as the dipole. It is designed for lowest frequency of 1.85GHz. Each part of the antenna unites to a new structure. In order to design the proposed antenna automatically and optimally, APSO algorithm is adopted. During APSO, the mismatch of the proposed antenna is resolved. The optimal designed antenna has an acceptable return loss(-10dB) at each bands(i.e, 1.85GHz, 2.45GHz and 5.5GHz).