• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10B
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• pp.862-875
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• 2003

본 논문에서는 IEEE 802.11 규격을 기반으로 다중 홉 Ad Hoc 모드에서 비실시간 및 실시간 트래픽에 대한 통합 서비스를 지원하는 Wireless LAN을 구성할 때, 분산 방식으로 실시간 서비스의 우선권을 고려한 채널 액세스의 차별화를 제공할 수 있는 매체접근제어(Medium Access Control: MAC) 프로토콜의 구현 방안을 제안한다. 이를 위해 실시간과 비실시간 트래픽의 Contention Window (CW)를 서로 분리하며, 실시간 서비스의 지연 바운드에 따라 정해진 잔여 수명(residual time)을 우선권 설정에 반영함으로써 실시간 트래픽의 지연 요구 사항을 보장할 수 있도록 한다. 또한 실시간 트래픽의 부하에 따라서 적응적으로 offset 값을 조정함으로써 offset에 의해 발생될 수 있는 수율의 저하를 최소화한다. 제안된 방식은 기존 IEEE 802.11 MAC 규격의DCF (Distributed Coordination Function) 방식을 그대로 사용하면서 CSMA/CA 기반의 경쟁 방식을 통해서도 비실시간 트래픽과의 차별화가 가능하고, 또한 잔여 수명 시간을 고려한 동적인 우선권 할당이 가능하도록 하였다. 시뮬레이션에 의한 분석 결과에 따르면 기존 DCF와 비교할 때 실시간 단말의 용량을 2배까지 향상시킬 수 있으며, 트래픽 부하에 따라 적응적 제어를 통해 추가적인 성능 개선 효과를 확인하였다.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.3B
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• pp.174-180
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• 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 Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.75-80
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• 2006

This paper has proposed a novel dual band transmitter module which can be operating either as an amplifier or as a frequency multiplier according to the input frequency. A conventional dual band transmitter consists of separate amplifiers operating at each frequency band, but the proposed dual band module operates as an amplifier for the IEEE 802.11b/g signal, and as a frequency doubler for the IEEE 802.11a signal according to input frequency and bias voltage. In this paper, we have obtained sharp stop band characteristics by using microstrip DGS(Defected Ground Structure) to suppress the fundamental frequency of the frequency doubler as well as the second harmonic of the amplifier. From measurement result, second harmonic suppression is below -59dBc in the amplifier mode, and fundamental suppression is below -35dBc in the frequency doubler mode. And the designed module has 17.8dBm output P1dB at 2.4GHz and 10.1dBm power for 5.8GHz output, and the output power in the two modes are 0.8dB and 2.8dB larger than the module with ${\lambda}g/4$ reflector, respectively.

• Journal of Korea Society of Digital Industry and Information Management
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• v.10 no.4
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• pp.109-116
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• 2014

In recent, ISM (Industrial Scientific Medical) band that is 2.4GHz band authorized free of charge is being widely used for smart phone, notebook computer, printer and portable multimedia devices. Accordingly, studies have been continuously conducted on the possibility of coexistence among nodes using ISM band. In particular, the interference of IEEE 802.11b based Wi-Fi device using overlapping channel during communication among IEEE 802.15.4 based wireless sensor nodes suitable for low-power, low-speed communication using ISM band causes serious network performance deterioration of wireless sensor networks. This paper examined a method of identifying channel status to avoid interference among wireless communication devices using IEEE 802.11b (Wi-Fi) and other ISM bands during communication among IEEE 802.15.4 based wireless sensor network nodes in ISM band. To identify channels occupied by Wi-Fi traffic, various studies are being conducted that use the RSSI (Received Signal Strength Indicator) value of interference signal obtained through ED (Energy Detection) feature that is one of IEEE 802.15.4 transmitter characteristics. This paper examines an algorithm that identifies the possibility of using more accurate channel by mixing utilization of interference signal and RSSI mean value of interference signal by wireless sensor network nodes. In addition, it verifies such algorithm by using OPNET Network verification simulator.

• 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 Korea Institute of Information and Communication Engineering
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• v.17 no.2
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• pp.363-371
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• 2013

This paper describes a multi-standard LDPC decoder which supports 19 block lengths(576~2304) and 6 code rates(1/2, 2/3A, 2/3B, 3/4A, 3/4B, 5/6) of IEEE 802.16e mobile WiMAX standard and 3 block lengths(648, 1296, 1944) and 4 code rates(1/2, 2/3, 3/4, 5/6) of IEEE 802.11n WLAN standard. To minimize hardware complexity, it adopts a block-serial (partially parallel) architecture based on the layered decoding scheme. A DFU(decoding function unit) based on sign-magnitude arithmetic is used for hardware reduction. The designed LDPC decoder is verified by FPGA implementation, and synthesized with a 0.13-${\mu}m$ CMOS cell library. It has 312,000 gates and 70,000 bits RAM. The estimated throughput is about 79~210 Mbps at 100 MHz@1.8v.

• ETRI Journal
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• v.40 no.5
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• pp.561-569
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• 2018

Modern communication systems employ wideband antennas with circular polarization (CP) radiation. In this work, asymmetric modified bow-tie (ABT) and symmetric modified bow-tie (SBT) slotted circularly polarized single-point probe-fed circular patch antennas with dimensions of $40mm{\times}40mm$ for wideband applications are proposed. A 10 dB RL bandwidth of 350 MHz with CP, 3 dB axial ratio (AR) bandwidth of 100 MHz, peak gain of 4.9 dBic, and 10 dB RL bandwidth of 530 MHz with CP, 3 dB AR bandwidth of 140 MHz, peak gain of 5 dBic are obtained for ABT and SBT slotted circular patch antennas, respectively. The proposed SBT slotted patch is scaled up and down to $50mm{\times}50mm$ and $30mm{\times}30mm$, respectively. The proposed scaled-up version offers 10 dB RL and 3 dB AR bandwidths of 340 MHz and 80 MHz, with a peak gain of 5 dBic. The scaled-down version offers 10 dB RL and 3 dB AR bandwidths of 710 MHz and 180 MHz, with a peak gain of 5.25 dBic. These prototypes are suitable to work in IEEE 802.11a WLAN, ISM, and IEEE 802.11ac applications. The measured and simulated results are then discussed and compared.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.3 s.357
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• pp.78-84
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• 2007

A multistandard direct-conversion mixer for WCDMA, Wibro, and 802.11a/b/g is designed in 0.18 um CMOS technology To support multistandard and to reduce the chip area the switched inductor is used as the matching method. This switched inductor matching network selects the mixer's operation frequency band by turning on or off the switch transistor. Since the performances of mixer and operation frequency can be affected by the parasitic of switch transistor the mixer should be designed with the optimized size of switch to minimize parasitic effects. Proposed mixer is able to achieve return loss less than -13 dB in $2.1\sim2.5GHz$ and $5.1\sim5.9GHz$ bands with the suitable performance to meet requirements of WCDMA, WiBro, and 802.11a/b/g.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.865-868
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• 2007

Recently, wireless LANs are often applied in home or office because of its various of convenience. Frequency range of wireless LANs specified by IEEE 802.11b is at 2.4 GHz. The bluetooth, the microwave oven, and the PDA(Personal Digital Assistants) uses, however, the same frequency band. So problems will be produced in these environments, such as multi-pass interference and system-to-system interference. These problems can be eliminated by using EM wave absorber. In this paper, we designed and fabricated EM wave absorber using MnZn-Ferrite, Sendust, and CPE( Chlorinated Polyethylene). The EM wave absorber with the ratio of material (MnZn-Ferrite : Sendust : CPE = 64 : 16 : 20 wt.%) has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz.