• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.169-175
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• 2004

We analyzed about digital watermarking embedded transmission of still image in wireless multimedia communication environment. Also, we proposed improved watermark techniques. It effects that get in original image than method to use conventional image is less and shows robust watermark restoration ability from outside attack. Performance analysis achieved about still image and restoration of watermark information using OFDM/QPSK still image transmission system in wireless channel environment. Analysis result, VI watermark performance that influence in original image is very small. And it could know that show high restoration performance. Also, It showed superior copyright information extraction performance than image watermark in wireless channel environment of same transmission error condition.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.2
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• pp.9-17
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• 2010

Recently, there has been much interest in orthogonal frequency division multiplexing (OFDM) for next generation wireless wideband communication systems. OFDM is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarriers. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. However, in the radio systems it is also important to distortion introduced by high power amplifiers (HPA's) such as solid state power amplifier (SSPA) considered in this paper. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. In this paper, we propose a canonical piecewise-linear (PWL) model based digital predistorter to prevent signal distortion and spectral re-growth due to the high peak-to-average power ratio (PAPR) of OFDM signal and the nonlinearity of HPA's. Computer simulation on an OFDM system under additive white Gaussian noise (AWGN) channels with QPSK, 16-QAM and 64-QAM modulation schemes and modulator/demodulator implemented with 1024-point FFT/IFFT, demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinearity introduced by the SSPA.

• The Journal of the Korea Contents Association
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• v.9 no.5
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• pp.84-90
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• 2009

In this paper, the new channel estimation was proposed that have the low complexity and high performance using Fuzzy inference method uses recently from various field for estimation about uncertainty in channel estimation of OFDM. Proposed method is channel estimation performance improve, calculation and interpolation for statistics character of channel using the pilot before LS channel estimation by Fuzzy inference method. Simulation result in QPSK proposed channel estimation method shows the enhancement of 5.5dB compared to the LS channel estimation and the deterioration of 1.3dB compared to the MMSE channel estimation in mean square error point $10^{-3}$. symbol error rate shows similarity performance the MMSE $10^{-1.96}$, proposed channel estimation $10^{-1.93}$ and enhancement of $10^{-0.35}$ compared to the LS channel estimation in signal to noise ratio point 20dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.715-725
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• 2010

Orthgonal Frequency Division Multiplexing(OFDM) system is effective for the high data rate transmission in the frequency selective fading channel. In this paper we propose PAPR(Peak to Average Power Ratio) reduction method of problem in OFDM system used Fuzzy theory that often control machine. This thesis proposes PAPR reducing method of OFDM system using Fuzzy theory. The advantages for using Fuzzy theory to reduce PAPR are that it is easy to manage the data and embody the hardware, and required smaller amount of operation. Firstly, we proposed simple algorithm that is reconstructed at receiver with transmitted overall PAPR which is reduced PAPR of sub-block using Fuzzy. Although there are some drawbacks that the operation of the system is increased comparing conventional OFDM system and it is needed to send the information about Fuzzy indivisually, it is assured that the performance of the system is enhanced for PAPR reducing. To evaluate the perfomance, the proposed search algorithm is compared with the proposed algorithm in terms of the complementary cumulative distribution function(CCDF) of the PAPR and the computational complexity. As a result of using the QPSK and 16QAM modulation, Fuzzy theory method is more an effective method of reducing 2.3 dB and 3.1 dB PAPR than exiting OFDM system when FFT size(N)=512, and oversampling=4 in the base PR of $10^{-5}$.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2000.11b
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• pp.3-8
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• 2000

본 논문에서는 고품질의 DTV, HDTV와 인터넷 등의 고속 광대역 멀티미디어 서비스를 위한 HFC(Hybrid Fiber Coaxial)-CATV망의 상향채널을 SPW(Signal Processing Worksystem)를 사용하여 모델링하고, HFC-CATV망 상향채널의 문제점인 유입잡음의 영향을 전산모의 실험을 통해 분석하였다. 그리고 상향채널의 열악성을 극복할 수 있는 방법으로 트렐리스 부호화 변조(Trellis-Coded Modulation)와 OFDM(Orthogonal Frequency Division Multiplexing)을 결합한 OFDM-TC8PSK 시스템을 제안하고 그 성능을 CATV 상향채널 환경에서 전산모의 실험하고 기존의 QPSK 시스템의 성능과 비교 분석하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.908-915
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• 2001

In this paper, it is analyzed theoretically that the performance degradation, caused by carrier frequency offset, in an OFDM/M-ary PSK system. Then, when Turbo coding is adopted to an OFDM/M-ary PSK system, the degree of performance enhancement is evaluated. Finally, the maximum frequency offset is calculated to satisfy the BER performance required in a Turbo coded OFDM/M-ary PSK system. As results of analysis, it is shown that the more the number of M-ary is, the worse the BER performance is. Moreover, 7dB, 9dB, and 17dB of $E_b/N_o$ are required in QPSK, 8PSK and 16PSK systems, respectively in order to satisfy the error performance, $BER=10^{-3}$ for voice communication. If $E_b/N_o$ are 10㏈ and 15㏈, the frequency offset should be below 0.05 and 0.075, respectively, for voice communication. When Turbo coding is adopted to an OFDM/M-ary PSK system, the less the number of M-ary is, the greater the performance enhancement of Turbo coding is. If the number of a M-ary system of the system is below 16, it is found that required $E_b/N_o$ is about 8dB to satisfy $BER=10^{-5}$ Moreover, in the system the Turbo coding scheme, voice communication is available with greatly low$E_b/N_o$, and 8dB of $E_b/N_o$ is enough for data communication regardless of the permission range of frequency offset.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.237-240
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• 2000

In this paper, we design the system that support data rate of 6Mbps(BPSK), 12Mbps(QPSK), 24Mbps(16-QAM) with OFDM, and the performance of this system analyze in the indoor channel when BER is 10$\^$-3/. In this simulation, first, we analyze performance of the system with and without channel coding. As the result, the coding gain of each system is 2㏈, 1.6㏈, 2㏈ when BER is 10$\^$-3/ Second, In the case of 16-QAM/OFDM, The effect of soft decision channel decoding method improve 2㏈ than hard decision when BER is 10$\^$-3/.

• Proceedings of the KIEE Conference
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• 2005.07d
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• pp.2989-2991
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• 2005

전력선 통신(Power Lire Communication)은 홈오토메이션, 원격 검침(AMR) 분야에서 많이 사용되어진다. 전력선 통신은 많은 유용성에도 불구하고 전력선 채널에 대한 정확한 채널 모델링과 전력선 모뎀에 관해서는 많은 문제점을 나타내고 있다. 본 논문에서는 고속 전력선 통신을 위한 전송선로의 주파수에 대한 잡음과 임피던스 특성 및 전력선 채널에 OFDM 신호를 QPSK 변조기법으로 전송하였을 때의 시뮬레이션 결과와 설계된 FPGA 보드를 비교 분석 하였다. 채널 모델은 잡음과 감쇠 특성만을 고려하여 모델링 하였으며, 전력선 채널 상에서의 OFDM 기법을 적용한 모뎀의 성능을 분석하였다.

• Proceedings of the KIEE Conference
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• 2005.07d
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• pp.3001-3003
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• 2005

이 논문에서는 OFDM(orthogonal frequency division multiplexing) 통신 시스템에서 고려해야할 중요한 문제 중의 하나인 PAPR(peak to average power ratio) 문제를 다루었다. SLM(selected mapping) OFDM 시스템을 기반으로 구현하였고, PAPR을 줄이기 위한 방법으로 새로운 위상 가중치를 곱하는 방법을 제안하였다. 여기서는 여러 가지 방법들(PSK, QPSK, 랜덤)로 위상 가중치를 발생시켰고, 발생된 위상 가중치를 병렬 조합으로 적용하여, 최저의 PAPR을 가져오는 값을 선택했다. 실험결과에서, 단일의 위상 가중치만을 곱하여 사용할 때 보다 위상 가중치를 복합적으로 사용했을 때 큰 PAPR 감소를 보임으로서, 제안된 방법의 우수성을 보였다. 그러나 아직 해결해야할 것들 중에서, 여러가지 위상 가중치를 사용함에 따른 시스템 복잡도가 증가하는 문제점이 존재한다. 본 연구에서 제안하는 방법은 비록 복잡도의 증가라는 단점을 가지고 있지만, 성능면에서의 향상은 커다란 장점이다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.133-136
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• 2005

전력선 통신(Power Line Communication)은 홈오토메이션, 원격 검침(AMR) 분야에서 많이 사용되어진다. 전력선(Power line) 통신의 사용은 많은 유용성이 있음에도 불구하고 전력선 채널에 대한 정확한 채널 모델링과 전력선 통신용 모뎀에 관해서는 많은 문제성을 나타내고 있다. 본 논문에서는 고속 전력선 통신을 위한 전송선로의 주파수에 대한 잡음과 임피던스 특성 및 전력선 채널에 OFDM 신호를 QPSK 변조기법으로 전송하였을 때의 시뮬레이션 결과와 설계된 FPGA 보드를 비교분석 하였다. 채널 모델은 잡음과 감쇠 특성만을 고려하여 모델링 하였으며, 전력선 채널 상에서의 OFDM기법을 적용한 모뎀의 성능을 분석하였다.