• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1031-1037
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• 2011

Pilot symbol assisted modulation (PSAM) can be used for the channel estimation in orthogonal frequency division multiplexing (OFDM) transmission systems. However, imperfect channel estimates in PSAM systems degrade the bit error rate (BER) performance. I derive the BER of PSAM OFDM systems over time dispersive fading channels. The BER performance of OFDM systems with SFBC antenna diversity are analyzed, where data is transmitted over time and frequency selective Rayleigh fading channel. The performance of this PSAM SFBC OFDM systems, gauged by the average bit error rate, is analyzed considering the channel estimation error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.1-7
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• 2010

PAPR of the pilot symbols can be reduced down by the CAZAC sequence in the SC-FDMA communication system. However, it is very complicated and takes quite a long time to compute the interpolation between the OFDM information symbols for the channel estimation because the pilot data are trasmitted in the block type. Furthermore, situation will be much more serious in the severe fading channel. Actually the pilot insertion of the comb type is much efficient and convenient for the channel estimation since the calculation of the interpolation can be made in the frequency domain symbol by symbol. But, the PAPR will be regrown when the pilot data are inserted with the information data in the comb type. So, in this paper, we like to study the PAPR reduction and comb type pilot assignment for the efficient channel estimation. Unlike the conventional SLM(selected mapping) method requiring the side information, our improved SLM method is to use the phase rotation sequence into information data without rotating phase of pilot. We use different pilot data according to the different phase rotation sequence. From the simulation result, it can be confirmed that when SLM method of 4 phase rotation sequence is used, PAPR is almost same to the block type method without pilot.

• Journal of IKEEE
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• v.16 no.3
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• pp.258-264
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• 2012

Although linear channel estimation for the frequency selective fading channel has been widely deployed, its accuracy depends on the number of pilots to probe the channel. Thus, it is unavoidable to employ large number of pilots to enhance the channel estimation performance, which essentially leads to the degradation of the transmission efficiency. It even does not utilize the sparseness of the multipath channel. In this paper a sparse channel estimation scheme based on the matching pursuit algorithm and a pilot assignment method, which minimizes the coherence, are proposed. The simulation results reveal that the proposed algorithm shows superior channel estimation performance with fewer pilots to the LS based ones.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.223-224
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• 2013

본 논문은 차등 위상 편이 변조(DPSK) 시스템에서 파일럿 없이 주파수 추정하는 기법을 제안한다. 제안하는 주파수 동기오차 추정 방식은 파일럿을 사용하지 않고 DPSK 변조 방식에서 연속되는 신호의 차등 위상신호를 전송하는 특성을 사용하는 블라인드 기법이다. DPSK 신호의 위상 차분은 주파수 오차 추정을 실행 할 때 페이즈를 증가시켜 왜곡으로 작용하게 되는데, 본 논문에서는 간단한 상관기와 제곱기로 이러한 특성을 제거하여 주파수 추정 성능을 증가 시킨다. 알고리즘의 검증은 수식과 컴퓨터 시뮬레이션으로 수행한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.6
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• pp.111-117
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• 2009

In the wideband code division access (WCDMA) systems, a pilot channel is used to determine WCDMA network coverage, cell identification, synchronization, timing acquisition and tracking, user-set handoff, channel estimation, and so on. A wireless repeater, which is deployed in the urban area for the WCDMA system to meet the growing demand on wireless communication services, has the possibility to receive several pilot signals from a large number of base stations, however, cannot distinguish its service base station's signal among them. This pilot interference results in frequent handoffs in the user equipment, which degrades the radio reception, transmission efficiency, quality of service, and channel capacity and increases the unwanted power consumption. In this paper, thus, we propose a pilot pollution interference cancellation scheme using one of the adaptive estimation algorithms, normalized least mean square (NLMS), which is applicable to a wireless repeater. We carried out link-level and network-level computer simulations to evaluate the performance of the proposed scheme in a wireless repeater. The simulation results verify the bit error rate (BER) improvement in the link level and the call drop probability improvement in the network level.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.4
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• pp.1-9
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• 2003

Many CDMA systems provide pilot channels in order to help channel estimation process. Especially in wideband CDMA systems, the number of receive diversity paths can be large due to small chip duration and high multi-path resolution capability. Hence, the received signal power of each path is small for a given total SNR (signal-to-noise ratio) and the pilot power of each path may not be sufficiently large for accurate channel estimation. When the pilot power is small, one can use decision-directed channel estimation to utilize more energy of the received data. However, the decision errors can deteriorate the quality of decision-directed channel estimation. This paper proposes a novel channel estimation method that optimally utilizes receiver decisions as well as pilot symbols with the help of estimated SER (symbol error rate) and SNR. The proposed method computes two channel estimates using the pilot and the data channel filters and optimally combines them. The simulation results show that the proposed method is robust and outperforms the conventional pilot-symbol-aided channel estimation method.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.11a
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• pp.47-50
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• 2009

CMMB(China Multimedia Mobile Broadcasting) 방식은 중국의 휴대이동방송 표준으로서 프레임에 하나의 ID 신호와 두개의 동기 신호 40개의 OFDM(Orthogonal Frequency Division Multiplexing) 데이터 심볼을 포함하고 있다. 다른 OFDM 시스템의 모바일 방송과는 달리 CMMB는 별도의 동기 심볼을 두고 있다. 또한 BPSK 성상으로 전송되는 OFDM 심볼내의 연속 파일럿은 CMMB의 시스템 정보를 전송하고 있어 이미 수신기에서 송신 연속 파일럿을 알고있는 유럽의 DVB-H나 일본의 원세그와는 다르다. 그러므로 CMMB의 프레임 구조에 특화를 시킨 동기 알고리듬이 필요하다. 본 논문은 CMMB 동기신호를 이용한 정수배 주파수 동기, OFDM 심볼을 이용한 소수배 동기 알고리듬을 제안한다. 제안된 알고리듬은 각각 컴퓨터 시뮬레이션으로 검증하였다.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.37.1-37.1
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• 2010

이 연구는 국제항법서비스(IGS)에서 진행 중인 실시간 IGS 산출물 서비스 구축을 위한 실시간 파일럿 프로젝트(Real-Time Pilot Project; RTPP)의 진행 현황의 파악을 위한 것이다. 본 동향조사에서는 RTPP의 구성요소 별 진행현황과 현재 기술 수준 및 해결해야 할 이슈 등에 대해 분석하였다. 조사결과 현재 4개의 분석센터의 실시간 산출물이 예비 서비스를 하고 있으며, 이를 활용한 연구도 활발히 진행되고 있는 현황이다. 하지만, 실시간 자료 전송을 위한 자료형식과 전송방식의 표준이 정해지지 않았고, 이온층과 대류층 정보의 경우도 아직 논의가 진행 중이다. IGS가 목표로 하는 실시간 서비스는 고정밀 위치결정, 우주환경, 자연재해 감시, 기상 및 기후 연구 등의 분야에 매우 활용도가 높은 서비스로 본 동향 조사를 통해 이를 활용하기 위한 관련 연구와 기술 개발에 있어 참고자료가 될 것으로 기대된다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5C
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• pp.351-360
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• 2008

In cellular mobile radio systems with frequency reuse, the interference signals degrade the channel estimation and signal detection performance due to the low signal-to-interference ratio near coverage boundaries. When the preamble pilot sequences from different cells are orthogonal or located in disjointed positions, they can be used for multi-cell channel estimation and interference cancellation. In time-varying channels caused by Doppler spread, data pilot symbols are needed for channel estimations. However, data pilot symbols are usually located in identical positions for the overhead reduction, which degrades the channel estimation performance. In this paper, we demonstrate a significant amount of performance improvement is achieved by multiplying different pseudonoise(PN) sequences to the data pilot symbols from adjacent interference cells. In particular, for detection scheme using maximal ratio combining(MRC) and inter-cell spatial demultiplexing(ISD), quantitative performance gain of spectral efficiency for different values of Doppler frequency and interference power is presented.

• Journal of IKEEE
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• v.15 no.3
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• pp.235-240
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• 2011

The scattered pilots employed in DVB-T take advantage of the merits of both the block type and comb type pilot arrangement to increase the transmission efficiency. To estimate the channel transfer functions for data subcarriers, it is required to conduct time-frequency domain 2D estimation using the pilots. Though 2D Wiener estimator is optimal in sense of MSE (mean square error), it is too complex to implement in hardware. In this paper a new channel estimation method for the scattered pilot based OFDM system by measuring the power of AWGN and removing the noise in the LS (least square) estimate of the channel is proposed. And the simulation results reveal the proposed method outperforms the 2D linear interpolation in the fading channel.