• Journal of Communications and Networks
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• 제14권3호
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• pp.237-242
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• 2012

One of the major problems for accurate channel estimation in power line communication systems is impulsive noise. Traditional channel estimation algorithms are based on the assumption of Gaussian noise, or the need to locate the positions of impulsive noise. The algorithms may lose optimality when impulsive noise exists in the channel, or if the location estimation of impulsive noise is inaccurate. In the present paper, an effective channel estimation algorithm based on a robust cost function is proposed to mitigate impulsive noise. The proposed method can provide a closed-form solution, and the application of robust estimation theory enables the proposed method to be free from localization of impulsive noise and thus can guarantee that the proposed method has better performance. Simulations verified the proposed algorithm.

• 디지털산업정보학회논문지
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• 제7권3호
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• pp.107-113
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• 2011

An OFDMA(Orthogonal Frequency Division Multiple Access) includes a MIMO(Multi-Input Multi-Output) scheme for improving spectral efficiency and data throughput. Recognizing that the performance of MIMO system is heavily dependent upon the accuracy of channel estimation, we propose a novel channel estimation for the MIMO scheme based on OFDMA. Conventional interpolation-based channel estimation suffers from poor estimation error at specific subcarriers. Proposed scheme makes use of a planar interpolation instead of linear interpolation for those subcarriers of bad accuracy. Simulation results show that the proposed scheme improves the performance of MIMO system by improving the accuracy in channel estimation especially for the adverse subcarrier positions. It is observed that the proposed scheme outperforms the conventional method by about 2dB in terms of both mean squared error and overall bit error rate with a reasonable computational complexity.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -2
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• pp.982-985
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• 2000

This paper presents channel estimation of an asynchronous W-CDMA reverse link using the interpolation and moving average algorithm in frequency-selective Rayleigh fading channel. The proposed algorithm is an interpolated decision-directed (IDD) block-wise moving average (BWMA) algorithm. The IDD-BWMA algorithm performs two- stage processes. The first stage performs data decision to make a virtual pilot channel by using linear interpolation channel estimation scheme. Then, the second stage performs the channel estimation of the “block-wise moving average” type by using a virtual pilot channel obtained in the first stage. By using Monte-Carlo computer simulations, we show that the proposed channel estimator is superior to other estimation schemes such as the WMSA(K=1) and DD-RAKE at higher Doppler frequencies, especially.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권12호
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• pp.4967-4986
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• 2015

Multi-hop relaying communications have great potentials in improving transmission performance by deploying relay nodes. The benefit is critically dependent on the accuracy of the channel state information (CSI) of all the transmitting links. However, the CSI has to be estimated. In this paper, we investigate the channel estimation problem in one-way multi-hop MIMO amplify-and-forward (AF) relay system, where both the two-hop and three-hop communication link exist. Traditional point-to-point MIMO channel estimation methods will result in error propagation in estimating relay links, and separately tackling the channel estimation issue of each link will lose the gain as part of channel matrices involved in multiple communication links. In order to exploit all the available gains, we develop a novel channel estimation model by structuring different communication links using the PARAFAC and PARATUCK2 tensor analysis. Furthermore, a two-stage fitting algorithm is derived to estimate all the channel matrices involved in the communication process. In particular, essential uniqueness is further discussed. Simulation results demonstrate the advantage and effectiveness of the proposed channel estimator.

• 한국군사과학기술학회지
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• 제24권6호
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• pp.655-663
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• 2021

In this paper, DFT-Based channel estimation with channel response mirroring is proposed and analyzed. In General, pilot symbols for channel estimation in MIMO(Multi-Input Multi-Output) OFDM(Orthogonal Frequency-Division Multiplexing) Systems have a diamond shape in the time-frequency plane. An interpolation technique to estimate the channel response of sub-carriers between reference symbols is needed. Various interpolation techniques such as linear interpolation, low-pass filtering interpolation, cubic interpolation and DFT interpolation are employed to estimate the non-pilot sub-carriers. In this paper, we investigate the conventional DFT-based channel estimation for noise reduction and channel response interpolation. The conventional method has performance degradation by distortion called "edge effect" or "border effect". In order to mitigate the distortion, we propose an improved DFT-based channel estimation with channel response mirroring. This technique can efficiently mitigate the distortion caused by the DFT of channel response discontinuity. Simulation results show that the proposed method has better performance than the conventional DFT-based channel estimation in terms of MSE.

• Journal of Communications and Networks
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• 제16권4호
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• pp.447-457
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• 2014

In this paper, we investigate the frequency domain channel estimation for multiple-input multiple-output (MIMO) single-carrier frequency-division multiple-access (SC-FDMA) systems. In MIMO SC-FDMA, code-division multiplexed (CDM) pilots such as cyclic-shifted Zadoff-Chu sequences have been adopted for channel estimation. However, most frequency domain channel estimation schemes were developed based on frequency-division multiplexing of pilots. We first develop a channel estimation error model by using CDM pilots, and then analyze the mean-square error (MSE) of various minimum MSE (MMSE) frequency domain channel estimation techniques. We show that the cascaded one-dimensional robust MMSE (C1D-RMMSE) technique is complexity-efficient, but it suffers from performance degradation due to the channel correlation mismatch when compared to the two-dimensional MMSE (2D-MMSE) technique. To improve the performance of C1D-RMMSE, we design a robust iterative channel estimation (RITCE) with a frequency replacement (FR) algorithm. After deriving the MSE of iterative channel estimation, we optimize the FR algorithm in terms of the MSE. Then, a low-complexity adaptation method is proposed for practical MIMO SC-FDMA systems, wherein FR is performed according to the reliability of the data estimates. Simulation results show that the proposed RITCE technique effectively improves the performance of C1D-RMMSE, thus providing a better performance-complexity tradeoff than 2D-MMSE.

• Journal of Communications and Networks
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• 제5권2호
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• pp.167-173
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• 2003

We treat the problem of channel estimation and interference cancellation in multiuser ultra-wide-band (UWB) communication systems over multipath fading channels. The UWB system under consideration employs a random time-hopping impulse radio format. We develop a channel estimation method based on linear weighted algorithm. An iterative channel estimation and interference cancellation scheme is proposed to successively improve the receiver performance. We also consider systems employing multiple transmit and/or receive antennas. For systems with multiple receive antennas, we develop a diversity receiver for the wellseparated antennas. For systems with multiple transmit antennas, we propose to make use of Alamouti’s space-time transmission scheme, and develop the corresponding channel estimation and interference cancellation receiver techniques. Simulation results are provided to demonstrate the performance of various UWB receiver techniques developed in this paper.

• 대한전자공학회논문지TC
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• 제37권9호
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• pp.1-10
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• 2000

본 논문에서는 페이딩 채널환경에서 COFDM 시스템에 대한 채널 추정과 결합된 심볼 검출 방법에 대해 제안하였다. 제안된 방법은 1) 심볼의 길이에 채널 부호화기의 코드워드 길이를 배합하는 기법과, 2) 세가지 채널 추정 기법과의 조합으로 나타내었다. 첫째 방법은 훈련 신호를 이용한 채널추정 기법과 제안한 심볼 검출 기법을 결합시킨 것이며, 둘째 방법은 첫째 방법에 결정지향 채널추정(Decision-Directed Channel Estimation) 기법을 결합시킨 방법이다. 마지막으로, 근접 부채널간의 AWGN(Additive White Gaussian Noise)의 영향을 줄이기 위해 디인터리브된 평균 채널추정(Averaged Channel Estimation) 기법을 둘째 방법에 결합시켰다. 제안한 3가지 방법들은 영 강압 등화(Zero Forcing Equalizing)방법과 비교하여 커다란 성능 개선 효과가 있음을 컴퓨터 시뮬레이션을 통하여 검증하였다.

• 전기전자학회논문지
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• 제16권3호
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• pp.258-264
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• 2012

주파수 선택적 페이딩 채널을 위한 선형 채널 추정 방식의 성능은 파일럿의 개수에 비례하므로 채널 추정의 정확도를 높이기 위해서 많은 파일럿을 쓰지 않을 수 없으며 필연적으로 전송 효율성이 낮아지는 단점이 있다. 또한 다중경로 채널의 희소(sparse)한 특성을 활용하지 않고 있다. 본 논문에서는 압축센싱 기법을 이용하여 아주 적은 수의 파일럿으로 희소한 채널을 추정하는 정합추구 기반 알고리듬과 간섭도(coherence)를 최소화하기 위한 파일럿 배치 방법을 제안한다. 또한 모의 실험을 통해 LS (least square) 채널 추정 방식보다 적은 수의 파일럿으로 우수한 채널 추정 성능을 보임을 확인한다.

• 대한전자공학회논문지TC
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• 제49권8호
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• pp.25-32
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• 2012

본 논문에서는 고속 시변 채널 OFDM을 위한 저복잡도 LS(Least Squares) 채널 예측의 성능 개선 방안을 제안한다. 저복잡도 LS 채널 예측을 위해 사용하는 CE-BEM(Complex Exponential-Basis Expansion Model) 채널 모델의 경우 채널 모델 자체의 문제점으로 인하여 채널 예측 성능 저하가 발생한다. 본 논문에서는 우선 시간 영역 윈도우를 이용하여 데이터 심볼에 의한 ICI(Interchannel Interference)의 영향을 제거한다. LS 채널 예측 결과에서 샘플을 취하여 윈도우의 영향을 제거한 후 특성이 채널 변화의 표현에 적합한 DPSS(Discrete Prolate Spheroidal Sequences)를 기저함수(basis function)로 하는 보간 (interpolation) 방식으로 채널 응답을 복원하여 CE-BEM의 문제점을 해결한다. 컴퓨터 모의실험을 통한 성능 확인 결과 제안된 채널 예측 방식은 기존의 방식과 비교하여 특히 고속 시변 채널에서 우수한 성능 개선 효과를 보여주며, 선택된 기저함수의 형태뿐만 아니라 기저함수의 개수의 설정이 성능을 크게 좌우하는 또 다른 요소임을 확인하였다.