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Frequency-Limited H_∞ Model Reduction for Positive Systems

IEEE TRANSACTIONS ON AUTOMATIC CONTROL 2015年第4期60卷 1093-1098页

作者： Li, Xianwei Yu, Changbin Gao, Huijun Harbin Inst Technol Res Inst Intelligent Control & Syst Harbin 150080 Heilongjiang Pr Peoples R China Hangzhou Dianzi Univ Hangzhou 310018 Zhejiang Peoples R China Australian Natl Univ Canberra ACT 2601 Australia NICTA Ltd Canberra ACT 2601 Australia King Abdulaziz Univ Jeddah 22254 Saudi Arabia

In this paper, the problem of frequency-limited H-infinity model reduction for positive linear time-invariant systems is investigated. Specifically, our goal is to find a stable positive reduced-order model for a given positive system such that the H-infinity norm of the error system is bounded over a frequency interval of interest. A new condition in terms of matrix inequality is developed for characterizing the frequency-limited H-infinity performance. Then an equivalent parametrization of a positive reduced-order model is derived, based on which, an iterative algorithm is constructed for optimizing the reduced-order model. The algorithm utilizes coarse reduced-order models resulting from (generalized) balanced truncation as the initial value. Both continuous- and discrete-time systems are considered in the same framework. Numerical examples clearly show the effectiveness and advantages of the proposed model reduction method.

关键词： Frequency-limited H-infinity performance iterative algorithm model reduction positive systems

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Ranking online quality and reputation via the user activity

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PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS 2015年 436卷 629-636页

作者： Liu, Xiao-Lu Guo, Qiang Hou, Lei Cheng, Can Liu, Jian-Guo Univ Shanghai Sci & Technol Res Ctr Complex Syst Sci Shanghai 200093 Peoples R China

How to design an accurate algorithm for ranking the object quality and user reputation is of importance for online rating systems. In this paper we present an improved iterative algorithm for online ranking object quality and user reputation in terms of the user degree (IRUA), where the user's reputation is measured by his/her rating vector, the corresponding objects' quality vector and the user degree. The experimental results for the empirical networks show that the AUC values of the IRUA algorithm can reach 0.9065 and 0.8705 in Movielens and Netflix data sets, respectively, which is better than the results generated by the traditional iterative ranking methods. Meanwhile, the results for the synthetic networks indicate that user degree should be considered in real rating systems due to users' rating behaviors. Moreover, we find that enhancing or reducing the influences of the large-degree users could produce more accurate reputation ranking lists. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Online rating system User reputation Object quality iterative algorithm

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Pricing and resource allocation for multimedia social network in cloud environments

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KNOWLEDGE-BASED SYSTEMS 2015年第Nov.期88卷 1-11页

作者： Nan, Guofang Zang, Chao Dou, Runliang Li, Minqiang Tianjin Univ Coll Management & Econ Tianjin 300072 Peoples R China

Distributed resource allocation is critical for efficient sharing multimedia contents in cloud-based wireless multimedia social network environments. In this paper, a cloud-based multimedia service system architecture is proposed to overcome the limited bandwidth allocation problem in the context of social network, in which bandwidth limited mobile users are allowed to directly acquire live multimedia streaming from the desktop users rather than the cloud based on their social relationships. We also present a theoretical framework for bandwidth allocation from desktop users to mobile users by a dynamic resource pricing process in the proposed bandwidth management system, where price-sensitive users and QoS-sensitive users are considered, and all users target at maximizing their total utilities. Finally, an iterative allocation algorithm is designed to simulate the bandwidth allocation process with respect to shared bandwidth and price. Simulation results verify the effectiveness of our proposed pricing model and allocation algorithm in terms of convergence and efficiency. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Resource allocation Resource pricing Multimedia social network iterative algorithm Cloud computing

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Fixed point iteration in identifying bilinear models

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SYSTEMS & CONTROL LETTERS 2015年 83卷 28-37页

作者： Li, Guoqi Wen, Changyun Zhang, Aiming Tsinghua Univ Ctr Brain Inspired Comp Res Dept Precis Instrumentat Beijing 100084 Peoples R China Nanyang Technol Univ Sch Elect & Elect Engn Singapore 639798 Singapore Xi An Jiao Tong Univ Sch Elect & Informat Xian 710049 Peoples R China

Inspired by fixed point theory, an iterative algorithm is proposed to identify bilinear models recursively in this paper. It is shown that the resulting iteration is a contraction mapping on a metric space when the number of input-output data points approaches infinity. This ensures the existence and uniqueness of a fixed point of the iterated function sequence and therefore the convergence of the iteration. As an application, one class of block-oriented systems represented by a cascade of a dynamic linear (L), a static nonlinear (N) and a dynamic linear (L) subsystems is illustrated. This gives a solution to the long-standing convergence problem of iteratively identifying LNL (Winer-Hammerstein) models. In addition, we extend the static nonlinear function (N) to a nonparametric model represented by using kernel machine. (C) 2015 Elsevier B.V. All rights reserved.

关键词： Bilinear models Wiener-Hammerstein models LNL systems Fixed point iterative algorithm Contraction mapping Kernel machine Nonlinear systems identification

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Blind deconvolution of dynamic-scene image sequences

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OPTIK 2015年第21期126卷 3072-3078页

作者： Ma Long Zhang Rongzhi Du Xinpeng Lu Fangyun State Key Lab Astronaut Dynam Xian 710043 Shaanxi Peoples R China Xian Satellite Control Ctr Xian 710043 Shaanxi Peoples R China Natl Univ Def Technol Changsha 410073 Hunan Peoples R China

This work devotes to the image sequences deconvolution problem that restores each clear image from a sequence of blurred and noisy measurements with little blur prior. In this paper, a simple but effective sequences blind deconvolution (SBD) method is developed in a Bayesian framework. The method alternately estimates each image and blur, only using the measurement of current frame and the estimations of the former frame, thus it is very memory-saving. Compared with the relative OBD method and the famous RLBD method, it achieves superior performance in almost all case studies. Experiments performed on both synthetic and actual astronomical images, without and with noise, show that the proposed method yields good results on all test data. (C) 2015 Elsevier GmbH. All rights reserved.

关键词： Image restoration Blind deconvolution Bayesian reference iterative algorithm

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Trust Region Methods for the Estimation of a Complex Exponential Decay Model in MRI With a Single-Shot or Multi-Shot Trajectory

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IEEE TRANSACTIONS ON IMAGE PROCESSING 2015年第11期24卷 3694-3706页

作者： Hu, Chenxi Reeves, Stanley J. Auburn Univ Dept Elect & Comp Engn Alabama AL 36830 USA

Joint estimation of spin density R-2* decay and OFF-resonance frequency maps is very useful in many magnetic resonance imaging applications. The standard multi-echo approach can achieve high accuracy but requires a long acquisition time for sampling multiple k-space frames. There are many approaches to accelerate the acquisition. Among them, single-shot or multi-shot trajectory-based sampling has recently drawn attention due to its fast data acquisition. However, this sampling strategy destroys the Fourier relationship between k-space and images, leading to a great challenge for the reconstruction. In this paper, we present two trust region methods based on two different linearization strategies for the nonlinear signal model. A trust region is defined as a local area in the variable space where a local linear approximation is trustable. In each iteration, the method minimizes a local approximation within a trust region so that the step size can be kept in a suitable scale. A continuation scheme is applied to reduce the regularization gradually over the parameter maps and facilitates convergence from poor initializations. The two trust region methods are compared with the two other previously proposed methods-the nonlinear conjugate gradients and the gradual refinement algorithm. Experiments based on various synthetic data and real phantom data show that the two trust region methods have a clear advantage in both speed and stability.

关键词： R-2* estimation field map estimation trust region method iterative algorithm

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Relative Computer Vision-Based Navigation for Small Inspection Spacecraft

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2015年第5期38卷 969-977页

作者： Tweddle, Brent E. Saenz-Otero, Alvar MIT Aeronaut & Astronaut Cambridge MA 02141 USA

A study was conducted to implement and experimentally evaluate relative computer vision-based navigation for small inspection spacecraft. A minimum of four coplanar or six non-coplanar points were required to find a solution to the exterior orientation problem without ambiguity. An iterative method was used to solve the exterior orientation problem, which was proposed and shown to be monotonically globally convergent. Photogrammetry was also used to determine a nonlinear least-squares estimate of the relative pose between two spacecraft.

关键词： Spacecrafts Vision Based Navigation Image Segmentation Satellites Connected Component Labeling iterative algorithm Power System Extended Kalman Filter Quaternions NASA Goddard Space Flight Center

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Finite algorithms for solving the coupled Sylvester-conjugate matrix equations over reflexive and Hermitian reflexive matrices

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INTERNATIONAL JOURNAL OF SYSTEMS SCIENCE 2015年第3期46卷 488-502页

作者： Hajarian, Masoud Shahid Beheshti Univ Dept Math Fac Math Sci Tehran Iran

It is known that solving coupled matrix equations with complex matrices can be very difficult and it is sufficiently complicated. In this work, we propose two iterative algorithms based on the Conjugate Gradient method (CG) for finding the reflexive and Hermitian reflexive solutions of the coupled Sylvester-conjugate matrix equations [GRAPHICS] (including Sylvester and Lyapunov matrix equations as special cases). The iterative algorithms can automatically judge the solvability of the matrix equations over the reflexive and Hermitian reflexive matrices, respectively. When the matrix equations are consistent over reflexive and Hermitian reflexive matrices, for any initial reflexive and Hermitian reflexive matrices, the iterative algorithms can obtain reflexive and Hermitian reflexive solutions within a finite number of iterations in the absence of roundoff errors, respectively. Finally, two numerical examples are presented to illustrate the proposed algorithms.

关键词： coupled Sylvester-conjugate matrix equations Hermitian reflexive matrix reflexive matrix iterative algorithm

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Generic iterative Downlink Interference Alignment

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IEICE TRANSACTIONS ON COMMUNICATIONS 2015年第5期E98B卷 834-841页

作者： Shin, Won-Yong Yoon, Jangho Dankook Univ Dept Comp Sci & Engn Yongin 448701 South Korea Korea Adv Inst Sci & Technol Dept Elect Engn Taejon 305701 South Korea

In this paper, we introduce a promising iterative interference alignment (IA) strategy for multiple-input multiple-output (MIMO) multi-cell downlink networks, which utilizes the channel reciprocity between uplink/downlink channels. We intelligently combine iterative beamforming and downlink IA issues to design an iterative multiuser MIMO IA algorithm. The proposed scheme uses two cascaded beamforming matrices to construct a precoder at each base station (BS), which not only efficiently reduce the effect of inter-cell interference from other-cell BSs, referred to as leakage of interference, but also perfectly eliminate intra-cell interference among spatial streams in the same cell. The transmit and receive beamforming matrices are iteratively updated until convergence. Numerical results indicate that our IA scheme exhibits higher sum-rates than those of the conventional iterative IA schemes. Note that our iterative IA scheme operates with local channel state information, no time/frequency expansion, and even relatively a small number of mobile stations (MSs), unlike opportunistic IA which requires a great number of MSs.

关键词： beamforming interference alignment (IA) iterative algorithm leakage of interference multi-cell downlink network

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Using Bent Ellipsoids to Represent Large Position Covariance in Orbit Propagation

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2015年第9期38卷 1775-1784页

作者： Coppola, Vincent T. Tanygin, Sergei Analyt Graph Inc 220 Valley Creek Blvd Exton PA 19341 USA

When the uncertainty of an orbit state estimate is large, the choice of coordinates is important in properly characterizing the probability distribution. Coordinates that naturally incorporate orbital motion in their definition, like the equinoctial elements, are better able to model the statistics of large deviations from the mean estimate. The shortcoming with equinoctial elements is their difficulty in characterizing position uncertainty apart from velocity uncertainty, making them inconvenient for visualizing position uncertainty. On the other hand, Hill's curvilinear coordinates (denoted herein as downrange coordinates) depend only on position and are defined relative to the Keplerian ellipse defined by the mean estimate. In these coordinates, an equal probability density surface for position uncertainty is shaped like an ellipsoid bent along the curved path of the ellipse. These coordinates are suitable for displaying large position covariance. Explicit equations are developed for the downrange coordinates, their derivatives, and the matrix of partials used for covariance transformations. The amount of the expected bending is assessed as the covariance size increases.

关键词： Probability Density Functions Curvilinear Coordinates Unscented Kalman Filter Eccentric Anomaly Computing Earth Graphics Processing Unit iterative algorithm Lagrange Multipliers Nonlinear Systems

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