• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.426-435
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• 2013

In this paper, we propose the MIMO circular polarization feed network to enhance the communication performances from the previous $2{\times}2$ MIMO channel to $4{\times}4$ channel for Land Mobile Satellite communication system. The only possibility to extend the communication channel is to use the additional satellite because of the limitation of satellite spaces to install additional antennas. For overcoming this problems, we propose the MIMO circular polarization feed network to secure the isolation characteristics without the distant antenna space. The port isolation characteristics and each port impedance matching conditions are numerically verified and we suggest the $4{\times}4$ MIMO channel model of the proposed system and the performances are verified. The fabricated circular polarization patch antennas with the proposed feed network are measured in the reverberation chamber and 7~10 dB of diversity gain and 80 % increasement of channel capacity are obtained.

• Electrical & Electronic Materials
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• v.5 no.3
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• pp.320-327
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• 1992

Twin-tub CMOS 공정에 의해 제작된 서브마이크로미터 채널길이를 갖는 n채널 및 p채널 MOSFET의 특성을 고찰하였다. n채널 및 p채널 영역에서의 불순물 프로파일과 채널 이온주입 조건에 따른 문턱전압의 의존성 및 퍼텐셜 분포를 SUPREM-II와 MINIMOS 4.0을 사용하여 시뮬레이션하였다. 문턱전압 조정을 위한 counter-doped 보론 이온주입에 의해 p채널 MOSFET는 표면에서 대략 0.15.mu.m의 깊이에서 매몰채널이 형성되었다. 각 소자의 측정 결과, 3.3[V] 구동을 위한 충분한 여유를 갖는 양호한 드레인 포화 특성과 0.2[V]이하의 문턱전압 shift를 갖는 최소화된 짧은 채널 효과, 10[V]이상의 높은 펀치쓰루 전압과 브레이크다운 전압, 낮은 subthreshold 값을 얻었다.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.1-5
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• 2006

초소형 저전력 기기간의 무선 통신을 위한 표준인 IEEE 802.15.4는 하나의 PAN 내부에서의 데이터 교환을 위한 메커니즘만을 제공한다. 따라서 다수의 PAN이 인접해 있을 경우 비콘 프레임 및 데이터 프레임의 충돌이 발생할 수 있으며 이러한 문제는 PAN의 이동성이 증가됨에 따라 더욱 심각해진다. 또한 ISM 주파수 대역을 사용하는 다른 무선 통신 장치들과의 충돌이 발생할 수 있다. 그러나 현재 IEEE 802.15.4 에서는 이러한 혼잡한 채널을 회피할 수 있는 메커니즘이 없다. 본 논문에서는 이러한 문제점을 해소하기 위하여 PAN을 구성하는 코디네이터와 종단장치들의 채널 변경을 통한 신뢰성 있는 혼잡 채널 회피 기능을 제공하는 채널 스위칭 프로토콜(Channel Switching Protocol, CSP)을 제안하며, 제안한 프로토콜 모듈을 상용 임베디드 장치인 옥타컴의 Nano-24에 구현하여 동작을 검증 하였다.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.12
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• pp.40-48
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• 2013

This paper presents multi-channel transimpedance amplifier(TIA) arrays in short-range LADAR systems for unmanned vehicles, by using a 0.18um CMOS technology. Two $4{\times}4$ channel TIA arrays including a voltage-mode INV-TIA and a current-mode CG-TIA are introduced. First, the INV-TIA consists of a inverter stage with a feedback resistor and a CML output buffer with virtual ground so as to achieve low noise, low power, easy current control for gain and impedance. Second, the CG-TIA utilizes a bias from on-chip bandgap reference and exploits a source-follower for high-frequency peaking, yielding 1.26 times smaller chip area per channel than INV-TIA. Post-layout simulations demonstrate that the INV-TIA achieves 57.5-dB${\Omega}$ transimpedance gain, 340-MHz bandwidth, 3.7-pA/sqrt(Hz) average noise current spectral density, and 2.84mW power dissipation, whereas the CG-TIA obtains 54.5-dB${\Omega}$ transimpedance gain, 360-MHz bandwidth, 9.17-pA/sqrt(Hz) average noise current spectral density, and 4.24mW power dissipation. Yet, the pulse simulations reveal that the CG-TIA array shows better output pulses in the range of 200-500-Mb/s operations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.220-223
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• 2006

In this paper, we studied about the level controller of optical signal with 40 channels by 4 VOA(Variable Optical Attenuator) with 12 channels. Total 8 microprocessors control 40 chamois for control of optical signal level so that a microprocessor controls 5 channels each. Moreover a microprocessor was added to communicate with outside and transfer instruction to each microprocessor. The output optical signal is measured and VOA is controlled as a result of it. The VOA outputs is inputted into PD(Photo Detector) at once. We could control multi-channel optical signals simply like this.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.4
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• pp.1005-1014
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• 2010

When reader collect tags, we found that they tend to get together to specific interface in Multi-Interface Multi-Channel 2.4GHz Active RFID system. To solve this problem, we designed the LP-Combind and AP-Balanced protocol for load distribution between interfaces, then verified its superiority of the performance through the simulation. There are three problems to implement designed protocols in hardware of firmware-level. first, tag selects randomly the channel of reader and reader need the method which can change the channel of tags. second, reader has the synchronization problem between reader and tag. third, reader has problem that MCU of reader have to operate simultaneously dual interface. To slove this problems, we designed the message and implemented method for tag channel change and the protocol in order to adjust synchronization between reader and tag, Therefore, we compared and analyzed the performance of protocols by experiment. If LP windows size is same, the performance of LP-Combined protocol and AP-Balanced protocol which lower collision probability by its load distribution is more outstanding than single interface protocol performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.138-144
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• 2009

This paper proposes an efficient scheme to estimate the channel parameters such as channel gain and delay for the IEEE802.15.4a LR-UWB systems. Sliding window (SW) method is generally used for the channel estimation of LR-UWB systems, which extracts the channel parameters by performing the cross-correlation with the repeatedly transmitted signal. However, the SW method experiences the severe performance degradation because the cross-correlation is performed just once for the received signal. In this paper, we propose a novel channel estimation scheme, which can achieve a great performance gain by performing the cross-correlation repeatedly with the repeated receive signal. In order to verify the performance gain of the proposed scheme, we performed the intensive simulation with the Saleh-Valenzuela channel model. Simulation results show that the proposed scheme has a performance improvement of 4dB compared to the conventional SW channel estimation scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.139-142
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• 2009

RFID(Radio Frequency IDentification) technology is an automatic identification method using radio frequencies between RFID reader which collects the information and tag which transmits the information. RFID technology develops passive RFID which transmit the only ID to active RFID which transmit the additional information such as sensing information. However, ISO/IEC 18000-7 as active RFID standard has a problem which cannot use multiple channel. To solve this problem, we use the 2.4GHz bandwidth technology and we propose the dynamic channel allocation method which can efficiently allot a channel. we show the operation of the dynamic channel allocation method through design and implement with CC2500DK of Taxas Instrument.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.5 no.2 s.10
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• pp.19-28
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• 2006

In the IEEE 802.15.4a system, they require simple, economical and low power consumption transmitter and receiver to transmit low rate data and to identify distance and location. To meet these requirements, LR-WPAN system use transmitter and receiver with simple modulation and demodulation scheme. In this paper, use PPM+BPSK modulation and windowing scheme to overcome multipath fading effect. Then we apply this channel estimation scheme to LR-WPAN system and compare performance depends on transmitter scheme. Proposed method using preamble to find channel characteristic out and we compensate distorted data with that information. Therefore we can detect signal easily at the demodulation part. Simulation result shows that performance evaluation is greater at the NLOS channel than LOS channel no matter what the receiver scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12C
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• pp.1006-1013
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• 2008

CZZ (Concatenated Zigzag) Code is a class of fast encodable LDPC codes. In the case that LDPC codes including CZZ codes have short length, short cycles seriously affect the code performance. In this paper, we construct CZZ codes using various degree-2 polynomial interleavers which eliminate cycles of length 4 and through simulation, compare the performance of these CZZ codes and turbo codes in many different fading channels. Especially, quasi-static fading channel, block fading channel, uncorrelated fading channel, and correlated fading channel are considered. Since CZZ codes show similar performance as turbo codes, they can be used in the next generation wireless communication systems.