• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.217-220
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• 2005

무선 다중경로 채널에서 데이터를 고속으로 전송할 경우, 신호는 페이딩, ISI(inter-symbol interfrence) 등의 영향으로 높은 에러율을 가지게 된다. 현재의 DSRC 시스템은 1Mbps 이상의 데이터 서비스가 어려울 것으로 예상되므로 개선된 변복조방식이 요구된다. OFDM(orthogonal frequency division multiplexing) 방식은 보호기간의 삽입을 통하여 ISI를 방지할 수 있으므로 고속 데이터 전송에 적합하다. 따라서 본 논문에서는 다중경로 페이딩 환경에서 시뮬레이션을 통하여 12 Mbps 전송 속도를 갖는 OFDM/QPSK 통신 시스템의 BER 성능을 비교${\cdot}$분석하고 다중경로 페이딩 환경에서 채널 상태를 추정 보상하기 위하여 판정 궤환경 등화기(Decision Feedback Equalizer)를 적용하여 시스템 성능을 개선하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.223-226
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• 2005

본 논문에서는 지능형 교통망 시스템 서비스에 사용하는 5.8GHz 대역에서 OFDM을 이용한 단거리 전용 통신 시스템의 성능을 분석하였다. 현재의 DSRC 시스템은 1Mbps 이상의 데이터 서비스가 어려울 것으로 예상되므로 개선도니 변복조방식이 요구된다. OFDM(orthogonal frequency division multiplexing) 방식은 보호구간의 삽입을 통하여 ISI를 방지할 수 있으므로 고속 데이터 전송에 적합하다. 따라서, 본 논문에서는 데이터 변조 방식으로는 IEEE 802.11a에 근거한 부 반송파의 수가 64개인 QPSK변조 방식을 사용하는 OFDM 시스템을 모델링 하고, 도플러 천이 효과를 고려한 Clark & Gans 페이딩 환경에서 성능을 분석하였다. 또한 페이딩 환경에서는 성능의 열화 정도가 크기 때문에 이를 극복하기 위해 채널 예측기를 사용하여 채널 응답을 근사적으로 예측${\cdot}$보상하였다.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.109-110
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• 2008

본 논문은 MIMO(Multiple Input Multiple Output)- OFDM(Orthogonal Frequency Division Multiplexing) 시스템에서 V-BLAST (Vertical-Ball Laboratories Layered Space Time) 수신기에 대하여 성능을 비교하고 평가한다. 신호는 각각 송신 안테나에서 독립적으로 전송되며 QPSK(Quadrature Phase Shift Keying) 방식을 이용하여 변조 되고, 송 수신단에 각각 2개의 안테나와 각각 4개의 안테나를 사용한다. V-BLAST 수신기로 ZF(zero-Forcing), MMSE(Minimum Mean Squared Error), ZF-OSIC(Zero Forcing - Ordered Successive Interference Cancellation), MMSE-OSIC(Minimum Mean Squared Error - Ordered Successive Interference Cancellation)를 사용한다. 모의실험 결과에서 MMSE 방식이 ZF 방식 보다 좋은 BER(Bit Error Rate)을 보이고, ZF-OSIC 방식은 ZF 방식과 MMSE 방식 보다 더 좋은 BER을 가지는 것을 확인 할 수 있으며, MMSE-OSIC 방식은 사용된 방식 중 가장 좋은 성능을 보인다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.153-156
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• 2006

본 논문에서는 무선공중망을 이용하여 재택 혹은 원거리에서도 환자의 상태를 확인하고 감시함으로써 의료서비스의 이동성을 제공하기 위한 의료정보 무선전송 시스템을 제안하고, 시뮬레이션 하였다. 제안한 방법은 응급상황 발생 시 의료정보를 디지털 데이터로 변환하여 PDA와 같은 이동형 단말에 전송함으로써 신속한 응급처치 등이 가능토록 한다. 시뮬레이션은 이동 무선채널환경에서 신뢰성 있는 의료정보의 전송을 위하여 IEEE 802.11a에 근거한 OFDM/QPSK 전송방식을 사용하였고, AWGN과 3-ray 이동 다중경로 페이딩 환경에서 신뢰성 있는 정보전송을 위하여 콘볼루션 코딩을 적용하여 시스템 성능을 분석하였다.

• Journal of Advanced Navigation Technology
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• v.10 no.4
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• pp.364-370
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• 2006

In this paper, the decision method of optimal sub-band which is supposed to embedded watermark incorporating fuzzy inference into transform-based watermarking is proposed. After performing the DCT, maximum variation of human visual properties, such as text degree, contrast sensitivity function is calculated, and by using these, membership function is generated. After embedding the watermark to the selected bands obtained from fuzzy inference, performance of imperceptibility and robustness are evaluated. In order to testify the proposed scheme, such attacks as JPEG, filtering, cropping are utilized. and in addition, by using an AWGN channel of OFDM/QPSK system, PSNR as well as correlation are calculated, and finally evaluated the performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.2
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• pp.3-9
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• 2016

In this paper, we propose a Radio over Fiber system for small cell applications and for mobile fronthaul networks supporting cloud-radio access networks(RAN). We built a system with a downlink employing orthogonal frequency division multiplexing (OFDM) techniques and an uplink using single carrier-frequency multiple access(SC-FDMA). System parameters are evaluated for various subcarrier modulations and the results of link performance measurements are analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9A
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• pp.835-843
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• 2010

Energy spreading transform (EST) based equalization is a very effective technique to remove inter symbol interference (ISI) in frequency selective channel. EST based system uses cyclic prefix (CP) similar to orthogonal frequency division multiplexing (OFDM) system. Since CP is a redundancy, it degrades the data transmission rate. RISIC is an algorithm that removes an inter block interference (IBI) caused by insufficient CP length and reconstructs CP. In this paper, we propose a system that combines the existing EST system with quadrature phase shift keying (QPSK) modulation and RISIC algorithm to enhance the efficiency of the transmission. Also we extend the proposed system to 16 quadrature amplitude modulation (QAM) modulation. The proposed system is shown to performance close to matched filter bound (MFB) even with insufficient CP.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1780-1786
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• 2008

The performance of underwater wireless communication system is influenced on channel characteristic. Especially, a delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we study the application of high speed data transmission in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the reverberation and multi-path. we confirm the performance of communication in underwater to use the model for actually underwater channel simulation model. As a result, we acquired the BER of modulation techniques. The BER of single carrier is $2{\times}10^{-1}$ and BER of multi currier is $8{\times}10^{-2}$ in 1000m. Transmission of single carrier is 5 kbps.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.4
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• pp.381-388
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• 2015

In this paper, a wireless video streaming system is designed and implemented for TV white space applications. It consists of a RF transceiver module, a digital modem, a camera, and a LCD screen. A VGA resolution video is captured by a camera, modulated by modem, and transmitted by RF transceiver module, and finally displayed at a destination 2.6-inch LCD screen. The RF transceiver is based on direct-conversion architecture. Image leakage is improved by low pass filtering LO, which successfully covers the TVWS. Also, DC offset problem is solved by current steering techniques which control common mode level at DAC output node. The output power of the transmitter and the minimum sensitivity of the receiver is +10 dBm and -82 dBm, respectively. The channel bandwidth is tunable among 6, 7 and 8 MHz according to regulations and standards. Digital modem is realized in Kintex-7 FPGA. Data rate is 9 Mbps based on QPSK and 512ch OFDM. A VGA video is successfully streamed through the air by using the developed TV white-space RF communication module.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.156-161
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• 2007

In a TDD system, the length of slots can be unequal, and the number of downlink (DL) and uplink (UL) slots per frame can be different as well. The advantage of using TDD is the capability to accommodate asymmetric high-bit-rate services for the DL and It, which will be one of the prominent features in 4G systems. This paper analyzes the performance of TDD system on mobile channel environments like indoor pedestrian and vehicular channel, and proposes optimum modulation/demodulation method in TDD system. A rectangular QAM (RQAM) used in various communication systems has good BER performance but the much more signal amplitudes also have become one of the barriers to implement receiver. While PSK receiver is implemented easily because it has a constant amplitude, but it's BER performance is worse than RQAM. APSK proposed in this paper integrates merits of RQAM and PSK, and minimizes demerits of then And a simple method is also proposed to demodulate the soft symbol. The results indicate that the proposed APSK has a little worse performance than RQAM but the dynamic range of APSK is about 4 dB, 8 dB better than RQAM at 16-ary, 64-ary modulation/demodulation respectively.