• Title/Summary/Keyword: decision-directed error

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Symbol Decoding Schemes Combined with Channel Estimations for Coded OFDM Systems in Fading Channels. (페이딩 채널환경에서 CDFDM 시스템에 대한 채널 추정과 결합된 심볼검출 방법)

  • Cho, Jin-Woong;Kang, Cheol-Ho
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.37 no.9
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    • pp.1-10
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    • 2000
  • This paper proposes symbol decoding schemes combined with channel estimation techniques for coded orthogonal frequency division multiplexing (COFDM) systems in fading channels. sThe proposed symbol decoding schemes are consisted of a symbol decoding technique and channel estimation techniques. The symbol decoding based on Viterbi algorithm is achieved by matching the length of branch word from encoder trellis to the codeword length of symbol candidate on decoder trellis. Three combination schemes are described and their error performances are compared. The first scheme is to combine a symbol decoding technique with a training channel estimation technique. The second scheme joins a decision directed channel estimation technique to the first scheme. The time varying channel transfer functions are tracked by the decision directed channel estimation technique and the channel transfer functions used in the symbol decoder are updated every COFDM symbol. Finally, In order to reduce the effect of additive white Gaussian noise (AWGN) between adjacent subchannels, deinterleaved average channel estimation technique is combined. The error performances of the three schemes are significantly improved being compared with that of zero forcing equalizing schemes.

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Trellis Defection of Tamed FM with the DLMS and Convergence

  • Kang, Min-Goo;Lee, Yang-Won;Cho, Hyung-Rae;Kang, Sung-Chul
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.1 no.2
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    • pp.199-207
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    • 1997
  • The Maximum Likelihood Sequence Estimation scheme is modified to improve the error performance of the correlative coding in the Tamed FM. To remove intersymbol interference, the Decision Feedback Equalization scheme with the delayed LMS algorithm and the Viterbi algorithm(10-symbol delay) in the delayed adaptive equalization are proposed for the performance of decision-directed adaptive equalization under the High Frequency channels, and the condition of convergence is analyzed.

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Soft Decision Approaches for Blind Decision Feedback Equalizer Adaptation (소프트 판정을 이용한 자력복구 적응 판정궤환 채널등화 기법)

  • Chung Won-Zoo
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.43 no.8 s.350
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    • pp.69-76
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    • 2006
  • In this paper, we propose blind adaptation strategies for decision feedback equalizer (DFE) optimizing the operation mode between acquisitionand tracking modes based on adjustable soft decision devices. The proposed schemes select an optimal soft decision device to generate feedback samples for the DFE at a given noise to signal ratio, and apply corresponding adaptation rules which combine a blind infinite impulse response (IIR) filtering adaptation and the decision-directed least mean squared (DD-LMS) DFE adaptation. These adaptation approaches attempt to achieve not only smooth transition between acquisition and tracking of DFE but also mitigation of error propagation.

A New Implementation of the LMS Algorithm as a Decision-directed Adaptive Equalizer with Decoding Delay

  • Ahn, Sang-Sik
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.1E
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    • pp.89-94
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    • 1996
  • This paper deals with the application of the LMS algorithm as a decision-directed adaptive equalizer in a communication receiver which also employs a sophisticated decoding scheme such as the Viterbi algorithm, in which the desired signal, hence the error, is not available until several symbol intervals later because of decoding delay. In such applications the implemented weight updating algorithm becomes DLMS and major penalty is reduced convergence speed. Therefore, every effort should by made to keep the delay as small as possible if it is not avoidable. In this paper we present a modified implementation in which the effects of the decoding delay can be avioded and perform some computer simulations to check the validity and the performance of the new implementation.

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Two-step a priori SNR Estimation in the Log-mel Domain Considering Phase Information (위상 정보를 고려한 로그멜 영역에서의 2단계 선험 SNR 추정)

  • Lee, Yun-Kyung;Kwon, Oh-Wook
    • Phonetics and Speech Sciences
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    • v.3 no.1
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    • pp.87-94
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    • 2011
  • The decision directed (DD) approach is widely used to determine a priori SNR from noisy speech signals. In conventional speech enhancement systems with a DD approach, a priori SNR is estimated by using only the magnitude components and consequently follows a posteriori SNR with one frame delay. We propose a phase-dependent two-step a priori SNR estimator based on the minimum mean square error (MMSE) in the log-mel spectral domain so that we can consider both magnitude and phase information, and it can overcome the performance degradation caused by one frame delay. From the experimental results, the proposed estimator is shown to improve the output SNR of enhanced speech signals by 2.3 dB compared to the conventional DD approach-based system.

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Speech Enhancement Using Phase-Dependent A Priori SNR Estimator in Log-Mel Spectral Domain

  • Lee, Yun-Kyung;Park, Jeon Gue;Lee, Yun Keun;Kwon, Oh-Wook
    • ETRI Journal
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    • v.36 no.5
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    • pp.721-729
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    • 2014
  • We propose a novel phase-based method for single-channel speech enhancement to extract and enhance the desired signals in noisy environments by utilizing the phase information. In the method, a phase-dependent a priori signal-to-noise ratio (SNR) is estimated in the log-mel spectral domain to utilize both the magnitude and phase information of input speech signals. The phase-dependent estimator is incorporated into the conventional magnitude-based decision-directed approach that recursively computes the a priori SNR from noisy speech. Additionally, we reduce the performance degradation owing to the one-frame delay of the estimated phase-dependent a priori SNR by using a minimum mean square error (MMSE)-based and maximum a posteriori (MAP)-based estimator. In our speech enhancement experiments, the proposed phase-dependent a priori SNR estimator is shown to improve the output SNR by 2.6 dB for both the MMSE-based and MAP-based estimator cases as compared to a conventional magnitude-based estimator.

A Novel Enhanced Decision-Directed Channel Estimation Scheme in High-Speed Mobile Environments (고속 이동 전파환경에서 결정지향 채널 추정 기법의 개선)

  • Ren, Yongzhe;Park, Dong Chan;Kim, Suk Chan
    • Journal of Satellite, Information and Communications
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    • v.10 no.1
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    • pp.29-32
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    • 2015
  • It has been a big trend of the convergence technologies about communication systems and vehicular industry to improve safety and convenience. To achieve a number of infotainment vehicular applications, vehicles should transmit information with high reliability. A robust and accurate channel estimation scheme is of great importance to achieve the goal. In this paper, we present a novel enhanced decision-directed channel estimation scheme called FADP (Frequency Averaging Data Pilot) for dynamic time-varying vehicular channels in IEEE 802.11p. We use linear averaging filtering in frequency domain, and utilize the correlation characteristic of the channels between the adjacent two data symbols, update the CR in time domain to get more accuracy. Finally, analysis and simulation results reveal that compared with exist schemes, the proposed scheme has a good performance in mean square error (MSE) and bit error rate (BER).

A Channel Estimation Technique for OFDM-CDMA Systems (OFDM-CDMA 시스템을 위한 채널 추정 기법)

  • 송동욱;박중후
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.6A
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    • pp.660-666
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    • 2004
  • Transmitted data may be compensated by using estimated channel values that are obtained with pilot symbols in OFDM-CDMA systems. Generally, a USE (Minimum Mean-Squared Error) estimator using correlations between pilot symbols gives good results, but its structure is so complicated. Starting with a modification of PA (Pilot-Aided) algorithm using pilot symbols and PADD (Pilot-Aided Decision-Directed) algorithm using both pilot and data symbols, a new channel estimation algorithm with more simpler structure is proposed. The performance of this algorithm is evaluated with varying mobile speed in a Ralyleigh multipath fading environment through computer simulations. The simulation results show that the proposed channel estimation algorithm outperforms a conventional PA algorithm.

Performance Experimentation and an Optimal Iterative Coding Algorithm for Underwater Acoustic Communication (수중음향통신에서 최적의 반복부호 알고리즘 및 성능 실험)

  • Park, Gun-Yeol;Lim, Byeong-Su;Jung, Ji-Won
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.16 no.11
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    • pp.2397-2404
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    • 2012
  • Underwater acoustic communication has multipath error because of reflection by sea-level and sea-bottom. The multipath of underwater channel causes signal distortion and error floor. In order to improve the performance, it is necessary to employ an iterative coding scheme. Among the iterative coding scheme, turbo codes and LDPC codes are dominant channel coding schemes in recent. This paper concluded that turbo coding scheme is optimal for underwater communications system in aspect to performance, coded word length, and equalizer combining. Also, decision directed phase recovery was used for correcting phase offset induced by multipath. Based on these algorithms, we confirmed the performance in the environment of oceanic experimentation.

A Novel Channel Estimation Method for Downlink Wideband CDMA Mobile Communication Systems (하향링크 광대역 CDMA 이동통신 시스템을 위한 새로운 채널추정 방법)

  • 임민중
    • 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.