• Title/Summary/Keyword: Channel-estimation

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Performance of Closed-loop Transmit Antenna Diversity System with Sub-optimal Beam-forming and Fading Corrrelation (준 최적 빔 형성과 페이딩 상관을 갖는 송신 안테나 다이버시티 시스템의 성능)

  • Kim, Nam-Soo
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.8
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    • pp.1-7
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    • 2004
  • The effect of the sub-optimal beam-forming and the fading channel correlation on the closed loop transmit antenna diversity(CTD) system is investigated in frequency flat Rayleigh fading channels. The fast channel fading prevents the perfect channel estimation at a mobile station, hence the imperfect weight is applied to the antenna branch of transmitter. The weight causes sub-optimalbeam-forming and aggravates the performance of CTD system. The fading correlation or a wireless channel also is one of the factors decreasing the diversity gain. A bit error rate expression for the CTD system is analytically derived as a function of the channel estimation error, the channel correlation coefficient the feedback delay, and fading index. It is shown that the channel estimation error gives more severe effect to the system performance than the channel correlation.

Performance Evaluation of Pilotless Channel Estimation with Limited Number of Data Symbols in Frequency Selective Channel

  • Wang, Hanho
    • International Journal of Contents
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    • v.14 no.2
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    • pp.1-6
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    • 2018
  • In a wireless mobile communication system, a pilot signal has been considered to be a necessary signal for estimating a changing channel between a base station and a terminal. All mobile communication systems developed so far have a specification for transmitting pilot signals. However, although the pilot signal transmission is easy to estimate the channel,(Ed: unclear wording: it is easy to use the pilot signal transmission to estimate the channel?) it should be minimized because it uses radio resources for data transmission. In this paper, we propose a pilotless channel estimation scheme (PCE) by introducing the clustering method of unsupervised learning used in our deep learning into channel estimation.(Ed: highlight- unclear) The PCE estimates the channel using only the data symbols without using the pilot signal at all. Also, to apply PCE to a real system, we evaluated the performance of PCE based on the resource block (RB), which is a resource allocation unit used in LTE. According to the results of this study, the PCE always provides a better mean square error (MSE) performance than the least square estimator using pilots, although it does not use the pilot signal at all. The MSE performance of the PCE is affected by the number of data symbols used and the frequency selectivity of the channel. In this paper, we provide simulation results considering various effects(Ed: unclear, clarify).

Joint Symbol Detection and Channel Estimation Methods for an OFDM System in Fading Channels (페이딩 채널환경에서 OFDM 시스템에 대한 심볼 검출 및 채널 추정 기법)

  • Cho, Jin-Woong;Kang, Cheol-Ho
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.38 no.3
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    • pp.9-18
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    • 2001
  • In this paper, we present the joint symbol detection and channel estimation for an orthogonal frequency division multiplexing (OFDM) system in fading channels. The proposed methods are based on decision-directed channel estimation (DDCE) method and their symbol detection is achieved by using Viterbi algorithm. This Viterbi decision-directed channel estimation (VDDCE) method tracks time-varying channels and detects a maximum likelihood symbol sequence. Recursive Viterbi decision-directed channel estimation (RVDDCE) method based on VDDCE method is proposed to shorten the detecting depth. In this method, channel estimate and Viterbi processing are recursively performed every interval of training symbol. Also, average chann'el estimation (ACE) technique to reduce the effect of additive white Gaussian noise (AWGN) is applied VDDCE method and RVDDCE method. These proposed methods arc demonstrated by computer simulation.

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A Measurement Study of Midamble based Cannel Estimation in IEEE 802.11p WAVE System (IEEE 802.11p WAVE 시스템에서 미드엠블을 이용한 채널추정 기법의 측정)

  • Cho, Woong
    • The Journal of the Korea institute of electronic communication sciences
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    • v.8 no.5
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    • pp.733-738
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    • 2013
  • Orthogonal Frequency Division Multiplexing (OFDM) based IEEE 802.11 a/g systems which are widely used in wireless LAN carry out channel estimation in one time per packet since the systems use only preamble. Whereas, midamble based channel estimation supports continuous channel estimation by tracking the channel state information periodically. Using IEEE 802.11p Wireless Access in Vehicular Environments (WAVE) system, we analyze the performance of the proposed system via practical measurements. Based on these results, practical issues on midamble based channel estimation are investigated.

BLUE-Based Channel Estimation Technique for Amplify and Forward Wireless Relay Networks

  • PremKumar, M.;SenthilKumaran, V.N.;Thiruvengadam, S.J.
    • ETRI Journal
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    • v.34 no.4
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    • pp.511-517
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    • 2012
  • The best linear unbiased estimator (BLUE) is most suitable for practical application and can be determined with knowledge of only the first and second moments of the probability density function. Although the BLUE is an existing algorithm, it is still largely unexplored and has not yet been applied to channel estimation in amplify and forward (AF)-based wireless relay networks (WRNs). In this paper, a BLUE-based algorithm is proposed to estimate the overall channel impulse response between the source and destination of AF strategy-based WRNs. Theoretical mean square error (MSE) performance for the BLUE is derived to show the accuracy of the proposed channel estimation algorithm. In addition, the Cram$\acute{e}$r-Rao lower bound (CRLB) is derived to validate the MSE performance. The proposed BLUE channel estimation algorithm approaches the CRLB as the length of the training sequence and number of relays increases. Further, the BLUE performs better than the linear minimum MSE estimator due to the minimum variance characteristic exhibited by the BLUE, which happens to be a function of signal-to-noise ratio.

A Novel Expectation-Maximization based Channel Estimation for OFDM Systems (Expectation-Maximization 기반의 새로운 OFDM 채널 추정 방식)

  • Kim, Nam-Kyeom;Sohn, In-Soo;Shin, Jae-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.4C
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    • pp.397-402
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    • 2009
  • Accurate estimation of time-selective fading channel is a difficult problem in OFDM(Orthogonal Frequency Division Multiplexing) system. There are many channel estimation algorithms that are very weak in noisy channel. For solving this problem, we use EM (Expectation-Maximization) algorithm for iterative optimization of the data. We propose an EM-LPC algorithm to estimate the time-selective fading. The proposed algorithm improves of the BER performance compared to EM based channel estimation algorithm and reduces the iteration number of the EM loop. We simulated the uncoded system. If coded system use the EM-LPC algorithm, the performance are enhanced because of the coding gain. The EM-LPC algorithm is able to apply to another communication system, not only OFDM systems. The image processing of the medical instruments that the demand of accurate estimation can also use the proposed algorithm.

A Modified Pilot Symbol based Channel Estimation Technique Using Cross-Correlation for OFDM Systems (OFDM 시스템에서 상호상관을 이용한 파일럿 심볼 기반 채널 추정 성능 향상 기법)

  • Wee, Jung-Wook;Cho, Yong-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.7C
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    • pp.467-474
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    • 2011
  • The performance of pilot-symbol-assisted channel estimation widely used for OFDM systems is degraded due to the small number of pilot symbols used for higher transmission efficiency. In this paper, we propose a pilot symbol based channel estimation using cross-correlation to improve the estimation performance of the OFDM system with small number of pilot symbols. The proposed technique detects a data symbol using the channel estimated by the pilot symbol and estimates the channel using the estimated data symbol and the pilot symbol. It is shown by computer simulations that the proposed technique outperforms the conventional pilot symbol assisted estimation technique.

Evolutionary Algorithm-based Space Diversity for Imperfect Channel Estimation

  • Ghadiri, Zienab Pouladmast;El-Saleh, Ayman A.;Vetharatnam, Gobi
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.8 no.5
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    • pp.1588-1603
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    • 2014
  • In space diversity combining, conventional methods such as maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SC) are commonly used to improve the output signal-to-noise ratio (SNR) provided that the channel is perfectly estimated at the receiver. However, in practice, channel estimation is often imperfect and this indeed deteriorates the system performance. In this paper, diversity combining techniques based on two evolutionary algorithms, namely genetic algorithm (GA) and particle swarm optimization (PSO) are proposed and compared. Numerical results indicate that the proposed methods outperform the conventional MRC, EGC and SC methods when the channel estimation is imperfect while it shows similar performance as that of MRC when the channel is perfectly estimated.

Pilot Symbol Assisted Low Complexity LS Channel Estimation for OFDM in Fast Time Varying Channels (고속 시변 채널 OFDM을 위한 파일럿 심볼을 이용한 저복잡도 LS 채널 예측)

  • Lim, Dong-Min
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.48 no.11
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    • pp.17-21
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    • 2011
  • In this paper, we propose a pilot symbol assisted low complexity LS channel estimation method for OFDM in fast time varying channels. The proposed method shows low complexity characteristics in terms of memory space and processing time compared with conventional BEM channel model LS estimation methods.

Decision-directed channel estimation in TETRA system (TETRA 시스템에서 Decision-directed 기법을 이용한 채널 추정 기법)

  • Hwang, Won-Sik;Lee, Yong-Hwan
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.2C
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    • pp.234-241
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    • 2009
  • TETRA Enhanced Data Service (TEDS), which is an upgrade version of narrow-band ETSI TETRA Release 1 system, can support high speed packet data services in frequency selected fading channel. The performance of M-QAM transceivers employed in the TEDS is significantly affected by the accuracy of channel estimation. In this paper, we consider the design of a decision-directed channel estimation scheme robust to fast fading by estimating the channel by means of a per-survivor processing (PSP) method. The performance of the proposed channel estimation scheme is verified by computer simulation.