• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.9 s.351
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• pp.17-22
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• 2006

CMOS LC VCO with fast response adaptive frequency calibration (AFC) technique for IEEE 802.11a/b/g WLANs is designed in 1.8V $0.18{\mu}m$ CMOS process. The possible operation is verified for 5.8GHz band, 5.2GHz band, and 2.4GHz band using the switchable L-C resonators. To linearize its frequency-voltage gain (Kvco), optimized multiple MOS varactor biasing tecknique is used. In order to operate in each band frequency range with reduced VCO gain, 4-bit digitally controlled switched- capacitor bank is used and a wide-range digital logic quadricorrelator (WDLQ) is implemented for fast frequency detector.

• Journal of Digital Contents Society
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• v.10 no.2
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• pp.357-365
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• 2009

To effectively exploit the underlying network bandwidth while maximizing user perceivable QoS, mandatory to make proper estimation on packet loss and queuing delay of the underling network. This issue is further emphasized in wireless network environment where network bandwidth is scarce resource. In this work, we focus our effort on developing performance model for wireless network. We collect packet trace from actually wireless network environment. We find that packet count process and bandwidth process in wireless environment exhibits long range property. We extract key performance parameters of the underlying network traffic. We develop an analytical model for buffer overflow probability and waiting time. We obtain the tail probability of the queueing system using Fractional Brown Motion (FBM). We represent average queuing delay from queue length model. Through our study based upon empirical data, it is found that our performance model well represent the physical characteristics of the IEEE 802.11b network traffic.

• The KIPS Transactions:PartC
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• v.12C no.3 s.99
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• pp.395-400
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• 2005

The IEEE 802.11b WLAN supports multiple transmission rates and the rate is chosen in an adaptive manner by an auto rate control algorithm. This auto rate control algorithm deeply affects the total system performance of the IEEE 802.11b WLAN. In this paper, we examine the WLAN performance with regard to the auto rate control algorithm especially the ARF scheme. The experimental results indicate that the ARF scheme works well in the face of signal noise due to node location. However, the ARF scheme severely degrades system performance when multiple nodes contend to obtain the wireless channel and the packet is lost due to signal collision. In addition, TCP prevent the performance degradation due to ARF scheme by retaining number of active nodes. However, some applications, such as transporting multimedia data, adopt the UDP. Therefore, the TCP cannot be an optimal solution for all WLAN applications.

• 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.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.301-303
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• 2002

요즘 사무 빌딩이나 공항에서의 ISM(Industrial Scientific and Medical) 밴드 사용이 증가함에 따라 동일 주파수 대역을 사용하는 BT(Bluetooth)와 무선 랜은 상호 충돌 발생이 일어난다. 이러만 문제점이 최근 연구과 제로 등장하고 있다. 본 논문은 채널 간섭의 모델에 의거하는 UL(unlicensed) ISM 주파수 대역에서 BT와 802.11에 있어서 충돌 평가 모델에 의한 간섭을 분석 한다. 전파 평가 모델 방법론에 의한 AP와 STA간의 범위에 따른 BT 간섭 의 수와 허용할 수 있는 최대 BT 신호를 알아본다. 그리고, BT를 바탕으로 한 액세스 네트워의 실행에서 802.l1b 시스템에 관한 BT의 기본 간섭 메커리즘 및 간섭이 어느 정도 미치는지에 관한 예비 결과를 나타낸다.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.73-76
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• 2007

국내의 홈네트워크 서비스는 홈오토메이션 제공 중심에서 엔터테인먼트 요소가 강화된 멀티미디어 기반의 네트워크 서비스로 변모하고 있다. 홈네트워크를 구성하는 요소 중 PC와 TV는 댁내에 멀티미디어 기반의 네트워크 서비스를 구축하는데 있어 가장 중요한 역할을 수행할 것으로 예상된다. 그에 따라 PC와 TV 간 네트워크를 구축하는 것이 중요한 이슈로 떠오르고 있다. 그러나 PC와 TV 간 네트워크 구축을 위해서는 댁내 노출 배선 등의 문제로 인하여 무선 기술을 사용하는 것이 유용하지만, 현재 기존 무선 전송 기술(IEEE 802.11 a/b/g, Bluetooth 등)들은 HD 등의 대용량 컨텐츠 전송 및 QoS 를 제공하기가 어렵다. 따라서 본 논문에서는 PC와 TV 간 무선으로 네트워크 구축시 고려사항 및 무선전송기술개발 요소를 살펴본다. 특히 무선전송기술로는 고속 데이터 전송이 가능한 UWB(Ultra Widebnad)와 IEEE 802.11n 기술을 중심으로 고려한다. 또한 UWB와 IEEE 802.11n을 이용하여 네트워크가 구축되었을 때 제공 가능한 서비스 시나리오에 대해서도 소개한다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.6 s.312
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• pp.61-67
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• 2006

In this paper it was introduced that embedded RFID Reader /Writer system including PXA255 ARM chip which enables the Tag signal to be used by data and video processing via IEEE 802.11 communication protocol. Embedded RFID R/W middle ware was developed which transmit the searched result in the data base using the received Tag signal via IEEE 802.11 communication protocol. Developed embedded RFID R/W system was composed of three parts - PXA255 ARM chid (Core Part) 13.56 MHz RFID Reader /Writer, wireless LAN for data communication with server and TFT-LCD terminal. Once this system receives the Tag signal through the serial port, it transmits the data through the wireless LAN to the server and it displays the received image data which was processed by the server onto the TFT-LCD screen. Embedded RFID R/W Middle ware transmits the received Tag signal from RFID R/W to the embedded system, which activates the socket program to connect to the window server via IEEE 802.11 communication protocol and transmits the Tag signal. Window server program searches the Database using this Tag information and displays the result on to the TFT-LCD window in the embedded system via IEEE 802.11 protocol.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.3 s.333
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• pp.39-44
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• 2005

The OFDM modulation and transmission block have been modeled in order to analyse the relationship between the 2.4GHz power amplifier distortion and output ACPR for the IEEE 802.11g wireless LAN. The nonlinear characteristic of the power amplifier has been modeled as AM-to-AM and AM-to-PM using the behavioral model, and the output spectrum is analysed with the phase distortion variation. Also, amplifier back-off value from P1dB to satisfy the required IEEE 802.11g standard spectrum mask s been simulated with modeled phase distortion, and the simulation data have been compared to the measured result by using the pre-distortion technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4B
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• pp.192-198
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• 2008

In this paper, we propose a scheme that improves the transmission performance of realtime multimedia data in wireless Local Area Network (LAN) environment, through the dynamical control of Transmission Opportunity (TXOP) period of the IEEE 802.11e HCCA Medium Access Control (MAC). The existing schedulers which determine the frame transmission time and its duration could not appropriately cope with the change of physical transmission rate, since the TXOP period has remained unchanged with the change of transmission rate of the wireless station. Our scheme is devised to keep the transmission performance of real-time multimedia data effectively unchanged by making TXOP period be extended when the transmission rate gets reduced. The proposed scheme is experimented along with IEEE 802.11e reference model using NCTUns simulator, which shows that the multimedia data is effectively delivered with the change of transmission rate as the distance between the wireless station and its access point increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2B
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• pp.107-118
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• 2009

In this paper, we present design and implementation for identification and location tracking techniques for vehicle information terminals in high-speed mobile environment using IEEE 802.11 wireless LAN technology. RSU be installed at a specific point. RSU recognizes it and then aware identification and location tracking for target vehicle when target vehicle that is equipped with information terminals pass near point. Issue of quick recognition using IEEE 802.11 access management frame, issue of weak wireless LAN security and tracking a range of restrictions be raised and we present solutions. Vehicle information terminal, RSU and a server-side GUI-based management program be implemented based on proposed solution. Implementation system be performed experiment at actual road environment and effectiveness be verified.