• Title/Summary/Keyword: Iteration scheme

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Low Computational Complexity LDPC Decoding Algorithms for DVB-S2 Systems (DVB-S2 시스템을 위한 저복잡도 LDPC 복호 알고리즘)

  • Jung Ji-Won
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.16 no.10 s.101
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    • pp.965-972
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    • 2005
  • In this paper, we first review LDPC codes in general and a belief propagation algorithm that works in logarithm domain. LDPC codes, which is chosen for second generation digital video broadcasting standard, are required a large number of computation due to large size of coded block and iteration. Therefore, we presented two kinds of low computational algorithm for LDPC codes. First, sequential decoding with partial group is proposed. It has same H/W complexity, and fewer number of iteration's are required at same performance in comparison with conventional decoder algerian. Secondly, early detection method for reducing the computational complexity is proposed. Using a confidence criterion, some bit nodes and check node edges are detected early on during decoding. Through the simulation, we knew that the iteration number are reduced by half using subset algorithm and computational complexity of early detected method is about $50\%$ offs in case of check node update, $99\%$ offs in case of check node update compared to conventional scheme.

Self-consistent Solution Method of Multi-Subband BTE in Quantum Well Device Modeling (양자 우물 소자 모델링에 있어서 다중 에너지 부준위 Boltzmann 방정식의 Self-consistent한 해법의 개발)

  • Lee, Eun-Ju
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.39 no.2
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    • pp.27-38
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    • 2002
  • A new self-consistent mathematical model for semiconductor quantum well device was developed. The model was based on the direct solution of the Boltzmann transport equation, coupled to the Schrodinger and Poisson equations. The solution yielded the distribution function for a two-dimensional electron gas(2DEG) in quantum well devices. To solve the Boltzmann equation, it was transformed into a tractable form using a Legendre polynomial expansion. The Legendre expansion facilitated analytical evaluation of the collision integral, and allowed for a reduction of the dimensionality of the problem. The transformed Boltzmann equation was then discretized and solved using sparce matrix algebra. The overall system was solved by iteration between Poisson, Schrodinger and Boltzmann equations until convergence was attained.

Stall Prediction of Wing Using the Nonplanar Lifting Surface Theory and an Iterative Decambering Approach (비평면 양력면 이론과 반복적 캠버변형 기법을 이용한 날개의 실속 특성 예측)

  • 조정현;조진수;조연우
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.10
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    • pp.1-6
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    • 2006
  • This paper predicts the stall characteristics of three-dimensional wings. An iterative decambering approach is introduced into the nonplanar lifting surface method to take into consideration the stall characteristics of wings. An iterative decambering approach uses known airfoil lift curve and moment curve to predict the stall characteristics of wings. The multi-dimensional Newton iteration is used to take into consideration the coupling between the different sections of wings. Present results are compared with experiments and other numerical results. Computed results are in good agreement with other data. This scheme can be used for any wing with the twist or control surface and for wing-wing configurations such as wing-tail configuration or canard-wing configuration.

A Fast Scheme for Inverting Single-Hole Electromagnetic Data

  • Kim Hee Joon;Lee Jung-Mo;Lee Ki Ha
    • Proceedings of the KSEEG Conference
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    • 2002.04a
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    • pp.167-169
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    • 2002
  • The extended Born, or localized nonlinear approximation of integral equation (IE) solution has been applied to inverting single-hole electromagnetic (EM) data using a cylindrically symmetric model. The extended Born approximation is less accurate than a full solution but much superior to the simple Born approximation. When applied to the cylindrically symmetric model with a vertical magnetic dipole source, however, the accuracy of the extended Born approximation is greatly improved because the electric field is scalar and continuous everywhere. One of the most important steps in the inversion is the selection of a proper regularization parameter for stability. Occam's inversion (Constable et al., 1987) is an excellent method for obtaining a stable inverse solution. It is extremely slow when combined with a differential equation method because many forward simulations are needed but suitable for the extended Born solution because the Green's functions, the most time consuming part in IE methods, are repeatedly re-usable throughout the inversion. In addition, the If formulation also readily contains a sensitivity matrix, which can be revised at each iteration at little expense. The inversion algorithm developed in this study is quite stable and fast even if the optimum regularization parameter Is sought at each iteration step. Tn this paper we show inversion results using synthetic data obtained from a finite-element method and field data as well.

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Boundary-adaptive Despeckling : Simulation Study

  • Lee, Sang-Hoon
    • Korean Journal of Remote Sensing
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    • v.25 no.3
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    • pp.295-309
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    • 2009
  • In this study, an iterative maximum a posteriori (MAP) approach using a Bayesian model of Markovrandom field (MRF) was proposed for despeckling images that contains speckle. Image process is assumed to combine the random fields associated with the observed intensity process and the image texture process respectively. The objective measure for determining the optimal restoration of this "double compound stochastic" image process is based on Bayes' theorem, and the MAP estimation employs the Point-Jacobian iteration to obtain the optimal solution. In the proposed algorithm, MRF is used to quantify the spatial interaction probabilistically, that is, to provide a type of prior information on the image texture and the neighbor window of any size is defined for contextual information on a local region. However, the window of a certain size would result in using wrong information for the estimation from adjacent regions with different characteristics at the pixels close to or on boundary. To overcome this problem, the new method is designed to use less information from more distant neighbors as the pixel is closer to boundary. It can reduce the possibility to involve the pixel values of adjacent region with different characteristics. The proximity to boundary is estimated using a non-uniformity measurement based on standard deviation of local region. The new scheme has been extensively evaluated using simulation data, and the experimental results show a considerable improvement in despeckling the images that contain speckle.

Design and Architecture of Low-Latency High-Speed Turbo Decoders

  • Jung, Ji-Won;Lee, In-Ki;Choi, Duk-Gun;Jeong, Jin-Hee;Kim, Ki-Man;Choi, Eun-A;Oh, Deock-Gil
    • ETRI Journal
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    • v.27 no.5
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    • pp.525-532
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    • 2005
  • In this paper, we propose and present implementation results of a high-speed turbo decoding algorithm. The latency caused by (de)interleaving and iterative decoding in a conventional maximum a posteriori turbo decoder can be dramatically reduced with the proposed design. The source of the latency reduction is from the combination of the radix-4, center to top, parallel decoding, and early-stop algorithms. This reduced latency enables the use of the turbo decoder as a forward error correction scheme in real-time wireless communication services. The proposed scheme results in a slight degradation in bit error rate performance for large block sizes because the effective interleaver size in a radix-4 implementation is reduced to half, relative to the conventional method. To prove the latency reduction, we implemented the proposed scheme on a field-programmable gate array and compared its decoding speed with that of a conventional decoder. The results show an improvement of at least five fold for a single iteration of turbo decoding.

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Analysis of Frictional Contact Problems of Nonlinearly Deformable Bodies by Using Contact Error Vector (접촉 오차 벡터를 이용한 비선형 변형체의 마찰접촉 해석)

  • Lee, Kisu;Kim, Bang-Won
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.13 no.3
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    • pp.305-319
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    • 2000
  • Numerical solution lot frictional contact problems of nonlinearly deformable bodies having large deformation is presented. The contact conditions on the possible contact points are expressed by using the contact error vector, and the iterative scheme is used to reduce the contact error vector monotonically toward zero. At each iteration the solution consists of two steps : The first step is to revise the contact force by using the contact error vector given by the previous geometry, and the second step is to compute the displacement and the contact error vector by solving the equilibrium equation with the contact force given at the first step. Convergence of the iterative scheme to the correct solution is analyzed, and the numerical simulations we performed with a rigid-plastic membrane and a nonlinear elastic beam.

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Transceiver Design Using Local Channel State Information at Relays for A Multi-Relay Multi-User MIMO Network

  • Cho, Young-Min;Yang, Janghoon;Kim, Dong Ku
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.7 no.11
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    • pp.2616-2635
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    • 2013
  • In this paper, we propose an iterative transceiver design in a multi-relay multi-user multiple-input multiple-output (MIMO) system. The design criterion is to minimize sum mean squared error (SMSE) under relay sum power constraint (RSPC) where only local channel state information (CSI)s are available at relays. Local CSI at a relay is defined as the CSI of the channel between BS and the relay in the $1^{st}$ hop link, and the CSI of the channel between the relay and all users in the $2^{nd}$ hop link. Exploiting BS transmitter structure which is concatenated with block diagonalization (BD) precoder, each relay's precoder can be determined using local CSI at the relay. The proposed scheme is based on sequential iteration of two stages; stage 1 determines BS transmitter and relay precoders jointly with SMSE duality, and stage 2 determines user receivers. We verify that the proposed scheme outperforms simple amplify-and-forward (SAF), minimum mean squared error (MMSE) relay, and an existing good scheme of [13] in terms of both SMSE and sum-rate performances.

Unsteady cascade flow calculations of using dual time stepping and the k-$\omega$ turbulence model (이중시간전진법과 k-$\omega$ 난류모델을 이용한 익렬 내부 비정상 유동해석)

  • Choe, Chang-Ho;Yu, Jeong-Yeol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.12
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    • pp.1624-1634
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    • 1997
  • A numerical study on two-dimensional unsteady transonic cascade flow has been performed by adopting dual time stepping and the k-.omega. turbulence model. An explicit 4 stage Runge-Kutta scheme for the compressible Navier-Stokes equations and an implicit Gauss-Seidel iteration scheme for the k-.omega. turbulence model are proposed for fictitious time stepping. This mixed time stepping scheme ensures the stability of numerical computation and exhibits a good convergence property with less computation time. Typical steady-state convergence accelerating schemes such as local time stepping, residual smoothing and multigrid combined with dual time stepping shows good convergence properties. Numerical results are presented for unsteady laminar flow past a cylinder and turbulent shock buffeting problem for bicircular arc cascade flow is discussed.

A 18-Mbp/s, 8-State, High-Speed Turbo Decoder

  • Jung Ji-Won;Kim Min-Hyuk;Jeong Jin-Hee
    • Journal of electromagnetic engineering and science
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    • v.6 no.3
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    • pp.147-154
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    • 2006
  • In this paper, we propose and present implementation results of a high-speed turbo decoding algorithm. The latency caused by (de) interleaving and iterative decoding in a conventional maximum a posteriori(MAP) turbo decoder can be dramatically reduced with the proposed design. The source of the latency reduction is come from the combination of the radix-4, dual-path processing, parallel decoding, and rearly-stop algorithms. This reduced latency enables the use of the turbo decoder as a forward error correction scheme in real-time wireless communication services. The proposed scheme results in a slight degradation in bit-error rate(BER) performance for large block sizes because the effective interleaver size in a radix-4 implementation is reduced to half, relative to the conventional method. Fixed on the parameters of N=212, iteration=3, 8-states, 3 iterations, and QPSK modulation scheme, we designed the adaptive high-speed turbo decoder using the Xilinx chip (VIRTEX2P (XC2VP30-5FG676)) with the speed of 17.78 Mb/s. From the results, we confirmed that the decoding speed of the proposed decoder is faster than conventional algorithms by 8 times.