• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1408-1418
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• 2007

In this paper, we analyze the performance of pilot symbol assisted channel estimation and equalization schemes for OFDM systems over frequency-selective time-varying channels and propose methods to improve the system performance. In the least square(LS) and linear minimum mean square error(MMSE) channel estimation, time domain windowing is introduced for banding the frequency domain channel matrix. The linear MMSE and decision feedback equalization schemes are employed with the pilot symbols for channel estimation taken into account in the equalization process. To reduce computational complexity, the band LU matrix factorization algorithm is introduced in solving the linear systems involved in the equalization, and the performances are compared with the known previous results by computer simulations. When time domain windowing is employed in the decision feedback equalization, the matrix related with the decision feedback process is shown to be unhanded and the resultant performance degradation is analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.7
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• pp.1283-1288
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• 2007

An equalization technique for OFDM systems in tine variant fading environment is described. Time variant channels lead to interchannel interference which increases the bit mr rate. A frequency domain equalizer using pilot symbols is proposed. The equalizer decreases the interchannel interference affecting the error performance. The effectiveness of the proposed technique is analyzed via computer simulation.

• Journal of Broadcast Engineering
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• v.16 no.6
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• pp.986-995
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• 2011

In this paper, we propose a noise whitening decision feedback equalizer for single carrier frequency division multiple access (SC-FDMA) receivers. SC-FDMA has the same advantage as that of orthogonal frequency division multiple access (OFDMA) in which the multipath effect can be removed easily, and also solves the problem of high peak to average power ratio (PAPR) which is the main drawback of OFDMA. Although SC-FDMA is a single carrier transmission scheme, a simple frequency domain linear equalizer (FD-LE) can be implemented as in OFDMA, which can dramatically reduce the equalizer complexity. Moreover, some residual intersymbol interference in the output of the FD-LE can be further removed by an additional nonlinear decision feedback equalizer (DFE) in time domain, because the time domain signal is a digitally modulated symbol. In the conventional DFE, however, the noise is not white at the input of the decision device and correspondingly the decision is not optimum. In this paper, we propose an improved DFE scheme for SC-FDMA systems where a linear noise whitening filter is inserted before the decision device of the conventional DFE scheme. Through computer simulations, we compare the bit error rate performance of the proposed DFE scheme with the conventional equalizers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.11
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• pp.1034-1042
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• 2004

In this paper, as one of countermeasure techniques for a frequency selective fading, an adaptive analog slope equalizer(ASE) applicable to 64-QAM digital radio relay system is presented in terms of principle, implementation, and its performance. Also interference of cross-talk between I- and Q-channel caused by a fiequency selective lading has been analyzed by doing channel model in the baseband, which make it possible to derive the solution for implementing ASE in If-band. The effects of signal for the faded channel are investigated in the time and the frequency domains, respectively, with/without ASE. As system performance, it is shown that the signature is improved up to 6.2 dB at the edge of signal bandwidth for a given BER 10$\^$-3/.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.9-18
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• 1998

In this paper, an equalization technique for OFDM(orthogonal frequency division multiplexing) in a time-variant multipath fading environment is described. A loss of subchannel orthogonality due to time-varying multipath fading channels leads to interchannel interference (ICI) which increases the error floor in proportion to Doppler frequency. A simple frequency-domain equalizer which can compensate the effect of ICI caused by time variation of multipath fading channel is proposed by modifying the previous frequency-domain equalization technique with taking into account only the ICI terms significantly affecting the error performance. The effectiveness of the proposed approach is demonstrated via computer simulation by applying it to OFDM systems when the multipath fading channel is slowly time variant.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.587-596
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• 2005

In this paper, we propose an OFDMA/CDM-based cellular system, which accommodates multiple users in frequency-domain and multiplexes user data with frequency-domain spreading. The proposed system utilizes random codes to discriminate cells and adopts the pre-equalization to enhance the performance. For cellular applications, a number of pre-equalization techniques are compared and an efficient power allocation scheme is suggested with a transmit power constraint. Especially, the validity of OFDMA/CDM based cellular system is investigated, by comparing the performance for varying the number of multiplexed data symbols at different locations. Finally the pre/post-equalization is proposed to reduce the performance degradation caused by time delay.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.219-222
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• 2010

OFDM시스템의 대안으로, SC-FDE시스템은 주파수 선택적 페이딩 환경에서 구현상의 복잡도가 크지 않으면서 낮은 PAPR로 다중 경로 지연에 의한 영향을 완화시키기 위한 기술로 연구되어 왔다. SC-FDE시스템에서 보호 구간으로 PN신호를 훈련 심볼(Training Sequence)로 둠으로써 CP에 비해 빠른 동기화와 채널 추정에 사용될 수 있는 장점이 있으며, 채널 추정을 위해 Correlation과 LMS기법을 동시에 적용함으로써 에러가 최소가 되기까지 수렴 시간을 줄일 수 있다. 본 논문에서는 PN시퀀스를 기반으로 추정한 채널 값으로, ISI를 효과적으로 제거할 수 있는 MMSE-FDE 등화 기법을 제안한다. SFN 채널 환경과 같이 스펙트럼 널이 강한 다중 경로 페이딩환경에서 ISI를 선 제거 하는 ISI cancellation 기법을 통해 정확한 SNR추정을 할 수 있고, 이를 통해 MMSE-FDE 등화 성능을 향상 시킬 수 있다.

• Journal of Broadcast Engineering
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• v.21 no.3
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• pp.391-403
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• 2016

FBMC/OQAM(Filterbank multicarrier on offset-Quadrature Amplitude Modulation) system is a multicarrier modulation which is not need to use cyclic prefix(CP). The CP of OFDM/QAM (orthogonal frequency division multiplexing on Quadrature Amplitude Modulation) system decreases data transmission rate. However, SER(symbol error rate) performance of FBMC/OQAM system is worse than OFDM/QAM system with frequency 1-tap equalization scheme in the frequency selective channel. In this paper, an iterative channel estimation and equalization scheme is performed in a frequency oversampling domain about each sub-channel of FBMC/OQAM system and SER performance using computer simulation is shown. Using the proposed scheme, the SER performance approaches to that of OFDM/QAM system in a frequency selective channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.755-761
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• 2007

In this paper the uplink single carrier scheme is proposed for wireless Internet application and its performance is evaluated in terms of PAPR (peak to average power ratio) and ABR (achievable bit rate) compared with the uplink OFDM scheme. There exist constraints regarding the signal amplification because the non-linear amplifier should be exploited instead of the linear amplifier due to its high cost of linear amplifier and power inefficiency at the WiBro terminal. Therefore characteristics in the uplink scheme design are discussed in order to maximize ABR and relieve the requirements for the amplifier specifications.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.8
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• pp.981-987
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• 2019

In this paper, we propose a new SC-FDE (single carrier frequency domain equalization) structure to cope with narrow band interference signals or jammers and reduce pilot overhead. The conventional SC-FDE structure has a problem that the receiver performance degrades severely due to difficulty in time-domain channel estimation when narrow band jammers exist. In addition, the spectral efficiency is lowered by transmitting pilot at every SC-FDE block to estimate channel response. In order to overcome those problems, the proposed structure is devised to estimate frequency domain channel directly without time domain channel estimation. To reduce the pilot overhead, several data blocks are transmitted between two pilots. The channel estimate of each data block is found through linear interpolation of two channel estimates at two pilots. By performing frequency domain channel equalization using this channel estimate, the distortion by the channel is well compensated when narrow band jammers exist. The performance of the proposed structure is confirmed by computer simulation.