• Title, Summary, Keyword: MMSE

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A Low-Complexity 2-D MMSE Channel Estimation for OFDM Systems (OFDM 시스템을 위한 낮은 복잡도를 갖는 2-D MMSE 채널 추정 기법)

  • Kim, Jung-In;Jang, Jun-Hee;Choi, Hyung-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.5C
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    • pp.317-325
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    • 2011
  • For OFDM (Orthogonal Frequency Division Multiplexing) systems, 2-D MMSE (2-Dimensional Minimum Mean Square Error) channel estimation provides optimal performance in frequency/time selective fading channel environment. However, the 2-D MMSE channel estimation has high computational complexity due to the large matrix size, because the 2-D MMSE channel estimation considers time as well as frequency axis for channel estimation. To reduce the computational complexity, we propose a modified 2-D MMSE channel estimator which is based on 1-D MMSE channel estimation with weighted sum. Furthermore, we consider RMS delay spread and Doppler frequency estimation for 2-D MMSE channel estimation. We show that the proposed method can significantly reduce computational complexity as well as that it can perform close to 2-D MMSE channel estimation.

Modified MMSE Estimator based on Non-Linearly Spaced Pilots for OFDM Systems

  • Khan, Latif Ullah
    • IEIE Transactions on Smart Processing and Computing
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    • v.3 no.1
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    • pp.35-39
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    • 2014
  • This paper proposes a Modified Minimum Mean Square Error (M-MMSE) estimator for an Orthogonal Frequency Division Multiplexing (OFDM) System over fast fading Rayleigh channel. The proposed M-MMSE estimator considered the effects of the efficient placement of pilots based on the channel energy distribution. The pilot symbols were placed in a non-linear manner according to the density of the channel energy. Comparative analysis of the MMSE estimator for a comb-type pilot arrangement and M-MMSE estimator for the proposed pilot insertion scheme revealed significant performance improvement of the M-MMSE estimator over the MMSE estimator.

MRC MMSE Equalization for SC-FDE in Amplify-and-Forward Relaying Networks (AF 방식 중계기 네트워크에서의 SC-FDE를 위한 MRC MMSE 등화 기법)

  • Won, Hui-Chul
    • Journal of the Korea Industrial Information Systems Research
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    • v.16 no.4
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    • pp.19-26
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    • 2011
  • Relay-assisted multiple input multiple output (MIMO) technique has become a promising candidate for next generation broadband wireless communications. In this paper, we propose maximum ratio combining (MRC) minimum mean-square-error (MMSE) equalization for single carrier-frequency domain equalizer (SC-FDE) in amplify-and-forward (AF) relaying networks. The performance of SC-FDE system can be improved considerably by achieving both the diversity gain and the MMSE equalization gain when the signals from source-destination (S->D) and source-relay-destination (S->R->D) are combined and equalized by means of the MMSE criteria. We find the weighting coefficients of MRC combining and the tap coefficients of MMSE equalizer for SC-FDE in AF relaying networks. Simulation results show that the proposed relay-based system considerably outperforms the conventional SC-FDE system.

A new structure and algorithm for adaptive MMSE receivers in fading environments (페이딩 환경에서의 적응형 MMSE 수신기를 위한 새로운 구조 및 알고리듬)

  • 김성락;정영균;이정구;최인경
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.23 no.7
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    • pp.1667-1676
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    • 1998
  • It is known that adaptive minimum mean square error (MMSE) receivers exhibit better performance than coventional single-user code division multiple access (CDMA) receivers in fixed (or static) channels and have the simple structure compared to other multi-user CDMA receivers. In practice, the radio channels are fading channels where the amplitude and phase of the received signal are time-varying and the sufficient signal-to-noise ratio is not always guaranteed. Thus, the performance of adaptive MMSE receivers is severely degraded in fading environments. We propose a new structure and adaptation algorithm for an adaptive MMSE receivers. Based on computer simulation results, it is observed that the proposed receiver demonstrates substantial performance improvement over currently available adaptive MMSE receivers in fading environments.

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Reduction of Speckle Noise in Images Using Homomorphic Wavelet-Based MMSE Filter with Edge Detection (에지 영역을 고려한 호모모르픽 웨이브렛 기반 MMSE 필터를 이용한 영상 신호의 스펙클 잡음 제거)

  • 박원용;장익훈;김남철
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.28 no.11C
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    • pp.1098-1110
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    • 2003
  • In this paper, we propose a homomorphic wavelet-based MMSE filter with edge detection to restore images degraded by speckle noise. In the proposed method, a noisy image is first transformed into logarithmic domain. Each pixel in the transformed image is then classified into flat and edge regions by applying DIP operator to the image restored by homomorphic directional MMSE filter. Each pixel in flat region is restored by homomorphic wavelet-based MMSE filter. Each pixel in edge region is restored by the weighted sum of the output of homomorphic wavelet-based MMSE filtering and that of homomorphic directional MMSE filtering. The restored image in spatial domain is finally obtained by applying the exponential function to the restored image in logarithmic domain. Experimental results show that the restored images by the proposed method have ISNR improvement of 3.3-4.0 ㏈ and ${\beta}$, a measurement parameter on edge preservation, improvement of 0.0103-0.0126 and superior subjective image quality over those by conventional methods.

Performance Analysis of Block Linear MMSE Equalization for OFDM Systems in Doubly Selective Channels (이중 선택적 채널 OFDM 시스템을 위한 블록 선형 MMSE 등화 방식의 성능 분석)

  • Lim, Dong-Min
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.21 no.1
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    • pp.76-82
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    • 2010
  • In this paper, we analyze the performance of the block linear MMSE equalization for OFDM systems in doubly selective channels by computer simulations. The block linear MMSE equalization shows somewhat unusual BER characteristics in that the BER curve drops at first as SNR increases but then rises up as SNR increases further beyond some point. In this paper, we investigate the BER characteristics of the block linear MMSE equalization by analyzing the condition number of the coefficient matrix in the linear system involved in the equalization process, and propose a new method to avoid the BER performance degradation at high SNR.

Performance Analysis of Linearly Constrained, Modified MMSE Detection for DS-CDMA Systems in Fading Channels (페이딩 채널에서 DS-CDMA 시스템을 위한 선형제약 변형 MMSE 검출의 성능 해석)

  • Lee Seo young;Kim Seong Rag;Lim Jong Seul;Ann Seong Joon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.10A
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    • pp.1159-1166
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    • 2004
  • This paper follows up the previous work on the linearly constrained, modified minimum mean-squared error(MMSE) detection for direct-sequence code-division multiple-access DS-CDMA) systems in fading channels. We find a condition to avoid the breakdown of joint modified MMSE detection and pilot symbol-aided channel estimation (PSACE). The linearly constrained, modified MMSE solution is theoretically shown to be robust against time variations in Rayleigh fading channels. This fact is consistent with the simulation results. We also show that under some conditions the linearly constrained, modified MMSE detection maximizes the output signal-to-interference-plus-noise ratio.(SINR)

Correlations between Cognitive Function and Functional Ability in Strokes using MMSE and FIM

  • Kim, Eun-Joo
    • International Journal of Contents
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    • v.5 no.3
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    • pp.86-90
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    • 2009
  • The Purpose of this study was to investigate correlations between the Mini-Mental State Examination (MMSE) and the Functional Independence Measure (FIM) in strokes. The data collected retrospectively from fifty-five stroke rehabilitation patients. The MMSE and FIM at the time of admission and discharge were obtained from patients' medical records. Firstly, Pearson correlation coefficients of the MMSE score at the time of admission revealed $0.286{\sim}0.747$ with FIM at the time of discharge (p<0.05). Also, the change of MMSE score significantly correlated with the change of total FIM scores in strokes (r=0.409, p<0.05). Because the MMSE scores at the time of admission and FIM at the time of discharge are correlated, the MMSE scores can be used to predict the FIM at the time of discharge and establish a rehabilitation program.

A Joint ML and ZF/MMSE Detection Algorithm in Uplink for BS Cooperative System (셀간 협력 통신을 위한 상향링크 환경에서의 ML 및 ZF/MMSE를 결합한 검출 기술)

  • Kim, Jurm-Su;Kim, Jeong-Gon;Kim, Seok-Woo
    • The Journal of Advanced Navigation Technology
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    • v.15 no.3
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    • pp.392-404
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    • 2011
  • In this paper, we address the issue of joint detection schemes for uplink cellular system when base station cooperation is possible for multi-user detection in multi-cell scenario. The ZF, ML, MMSE and SIC detection are analyzed and evaluated as a conventional scheme. ML attains the optimal performance but the complexity increases exponentially, ZF/MMSE have simple structure but have poor detection performance and SIC has better performance but it has large complexity and potential of the error propagation. However, they need the increased decoder complexity as the number of iteration is increased. We propose a new joint ML and ZF/MMSE detection scheme, which combines the partial ML decoding and ZF/MMSE detection, in order to decrease the decoder complexity. Simulation results show that the proposed scheme attains same or a little bit better BER performance and expect reduced decoder complexity, specially in the case of large number of Base Station are cooperated each other.

A Study on Adaptive MMSE RAKE Detector for Forward-link CDMA Communication Systems (순방향 링크의 CDMA통신 시스템에 적용 가능한 적응 MMSE 레이크 수신기)

  • 안태기;이병섭
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.9A
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    • pp.1265-1275
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    • 1999
  • An adaptive MMSE detector can be used to cancel the MAI in CDMA system. But standard adaptive MMSE detector cannot be used in real mobile environment due to fast fading channel. Furthermore multipath reception make it more difficult to converge to optimum weight values. In this paper we discuss and model the multipath fading environment in Forward-link Synchronous CDMA channels and propose adaptive MMSE RAKE detector structure which can be applied in the mobile station. A proposed adaptive MMSE detector requires estimation of received signal delay and complex channel coefficients such as amplitude and phase variation. These burden can be solved by utilizing the common pilot channel. The pilot channel may have higher power than the traffic channel, which give more exact channel estimation. Moreover RAKE structure gives more accurate and stable result which can be used as reliable reference signal in multipath fading channel environment. With this structure, conventional adaptive algorithm such as LMS or NLMS can be applied in adaptive MMSE detector.

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