• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.5
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• pp.568-575
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• 2011

In this paper, we propose a small broadband antenna for mobile device. The proposed antenna consists of a printed rectangular monopole antenna and a parastic element connected to ground using narrow meander line and it is designed on a FR-4 substrate that has a thickness of 0.8 mm and a dielectric constant of 4.4. The FR-4 substrate's size is 50 mm${\times}$90 mm comparable to the real mobile device. The fabricated antenna's size is 12.5 mm${\times}$10.5 mm${\times}$0.8 mm and the measurement shows -10 dB return loss bandwidth of 2,200~6,000 MHz and gains of 2.86~4.01 dBi. Accordingly, the proposed antenna can support mobile device for WiBro(2,300~2,380 MHz), WLAN(IEEE 802.11b/g/n: 2,400~2,480 MHz, IEEE 802.11a: 5,150~5,825 MHz), and mobile WiMAX(IEEE 802.16e : 2,500~2,690 MHz, 3,400~3,600 MHz) service bands.

• 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.

• Journal of the Korea Society of Computer and Information
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• v.28 no.8
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• pp.103-109
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• 2023

In this paper, we propose a smart wall switch based on IEEE 802.11b/g/n standard 2.4GHz band communication. As the 4th industrial era evolves, smart home solution development is actively underway, and application cases for smart wall switches are increasing. Most of the Chinese products that preoccupy the market through price competitiveness use Bluetooth and Zigbee communication switches. However, while ZigBee communication is low power, communication speed is slower than Bluetooth and network configuration through a separate hub is additionally required. The Bluetooth method has problems in that the communication range and speed are lower than Wi-Fi communication, the communication standby time is relatively long, and security is weak. In this study, an IEEE 802.11b/g/n smart wall switch applied with Wi-Fi communication technology was developed. In addition, through the two-wire structure, it is designed so that no additional cost is incurred through the construction of a separate neutral line in the building. The result of the study is more than 30% cheaper than the existing wall switch, so it is judged that it will be able to preoccupy the market not only in terms of technological competitiveness but also price competitiveness.

• Electronics and Telecommunications Trends
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• v.19 no.3 s.87
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• pp.84-95
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• 2004

홈 네트워크, 기업의 무선 네트워크 그리고 핫스폿 등과 같은 다양한 환경이 가능하면서 무선 LAN 기술 및 무선 LAN 제품에 대한 요구는 더욱더 증가하고 있으며, 기존 제품과의 호환성을 바탕으로 고속으로 무선 데이터 서비스를 지원할 수 있는 차세대 무선 LAN 기술에 대한 관심이 집중되고 있다. 본 논문에서는 현재 표준화가 진행중인 IEEE 802.11n의 차세대 무선 LAN 기술에 있어 주요하게 언급되고 있는 MAC 프로토콜 및 전송방식들에 대하여 소개한다. IEEE 802.11n은 IEEE 802.11e에서 논의중인 EDCA 및 HCCA를 기반으로 QoS를 보장하고 고속의 무선 LAN 서비스를 지원하기 위해 보다 개선된 MAC 프로토콜의 요구사항을 정의하여 물리계층의 관점에서 MIMO, spatial division multiplexing, space-time block coding 등과 같은 다중 안테나 방안을 고려하고 있다. 또한 주파수의 효율을 증가시키는 방식, 대역폭을 증가하는 방식 그리고 적응 변조를 적용하는 방식 등을 차세대 무선 LAN 전송 방식으로 논의하고 있다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1013-1017
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• 2005

This paper proposes an effective algorithm, P-DCF(Polling DCF) to satisfy real-time requirements in the industrial environments, based on 802.11 DCF protocols. Theoretical analysis and actual experiments are carried out, which shows that the proposed P-DCF brings several benefits: 1) it reduces the time delay for frame transmission 2)it guarantees bounded upper limit of maximum transmission delay 3) it maintains fairness

• Journal of Satellite, Information and Communications
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• v.11 no.1
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• pp.6-11
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• 2016

In this paper, we have analyzed the effects of co-channel, adjacent-channel, and the human shield(Body Blockage) for wideband WLAN based on the IEEE802.11n 40MHz channel bandwidth required for high speed digital signage service. Simulation results show that wideband WLAN can be operated with 78 interferers over 63m distance in co- channel, 80 interferer over 61m distance in adjacent channel. By applying the mitigation method for reducing the interference, we have confirmed that protection distance is improved to 51m using beamforming, and 40m using cognitive radio in co-channel interference. Also body blockage interference is reduced using adaptive channel bandwidth, C/I ratio, beamforming, power control mitigation methodology.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.11
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• pp.2437-2445
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• 2012

This paper presents the efficient measurement method of radio resource by analyzing various medium occupied elements. The medium occupied time consists of 802.11 frames, wireless interference, and protocol waiting time from a wireless node on a current channel. And it is used to performance metric. Existing research is only measured partial occupied elements, and is lack of validation of measurement unit and scalability on various IEEE 802.11 radio. This paper presents the measurement method of classified occupied elements. To achieve this, we modified 802.11n based OpenHAL device driver to collect the register information of wireless chipset, and to analyze receiving frames in an virtual monitor mode. We conclude accurate medium occupied time measurement system from various validation methods.

• Information and Communications Magazine
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• v.23 no.6
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• pp.63-72
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• 2006

CDMA 기술을 기반으로 하는 이동통신시스템의 발전과 DSL 기반의 유선통신시스템의 발전은 우리나라를 세계적인 정보통신 강국으로 성장시키고 있다. 세계적으로 높은 수준의 개인용 컴퓨터와 이동통신단말기 보유율을 바탕으로 폭발적인 인터넷서비스 사용량의 증가뿐만 아니라 무선인터넷 서비스에 대한 요구사항도 증가하고 있다. 이에 맞춰 무선LAN은 고속의 가입자 전송속도를 지원하기 위해 발전하고 있다. 이미 high throughput을 목표로 하는 국제 표준화가 진행되어 마무리 단계에 있고, 이에 세계적인 칩셋 업체들이 앞다투어 IEEE 802.11n draft 이전의 EWC버전을 이용한 칩셋을 발표하고 있다. 현재 ETRI에서는 802.11n draft 표준안을 기반으로 하는 칩셋 개발이 완성 단계에 이르렀으며, 이미 그 기능 및 성능에 대해 FPGA를 이용한 시스템구축으로 확인하였다. 앞으로 네트워크, 오피스 네트워크 및 휴대폰 탑재 칩 등에 대한 대규모 시장 형성이 예상되고 있어 경제적 기대효과를 기대할 수 있다.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.53-56
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• 2015

In this paper, we want provide improved services with faster transmission, IEEE 802.11n was standardized. A-MPDU (Aggregation MAC Protocol Data UNIT) is a vital function of the IEEE 802.11n standard, which was proposed to improve transmission rate by reducing frame transmission overhead. In this paper, we show the problems of TCP retransmission with A-MPDU and propose a solution utilizing the property of TCP cumulative ACK. If the transmission of an MPDU subframe fails, A-MPDU mechanism allows selective re-transmission of failed MPDU subframe in the MAC layer. In TCP traffic transmission, however, a failed MPDU transmission causes TCP Duplicate ACK, which causes unnecessary TCP re-transmission. Furthermore, congestion control of TCP causes reduction in throughput. By supressing unnecessary duplicate ACKs the proposed mechanism reduces the overhead in transmitting redundant TCP ACKs, and transmitting only a HS-ACK with the highest sequence number. By using the RACK mechanism, through the simulation results, it was conrmed that the RACK mechanism increases up to 20% compared the conventional A-MPDU, at the same time, it tightly assures the fairness among TCP flows.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.7
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• pp.653-660
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• 2013

This paper deals with the problem of unfairness among uplink TCP (Transmission Control Protocol) flows associated with frame aggregation employed in IEEE 802.11n WLANs (Wireless Local Area Networks). When multiple stations have uplink TCP flows and transmit TCP data packets to an AP (Access Point), the AP has to compete for channel access with stations for the transmission of TCP ACK (acknowledgement) packets to the stations. Due to this contention-based channel access, TCP ACKs tend to be accumulated in the AP's downlink buffer. We show that the frame aggregation in the MAC (Medium Access Control) layer increases TCP ACK losses in the AP and leads to the serious unfair operation of TCP congestion control. To resolve this problem, we propose the TAC (TCP ACK Compression) mechanism operating at the top of the AP's interface queue. By exploiting the properties of cumulative TCP ACK and frame aggregation, TAC serves only the representative TCP ACK without serving redundant TCP ACKs. Therefore, TAC reduces queue occupancy and prevents ACK losses due to buffer overflow, which significantly contributes to fairness among uplink TCP flows. Also, TAC enhances the channel efficiency by not transmitting unnecessary TCP ACKs. The simulation results show that TAC tightly assures fairness under various network conditions while increasing the aggregate throughput, compared to the existing schemes.