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26 February 2010, Volume 21 Issue 1
Approach to blind estimation of the PN sequence in DS-SS signals with residual carrier
Tianqi Zhang, Shaosheng Dai, Guoning Ma, Wei Zhang, and Pu Miao
2010, 21(1):  1-8.  doi:10.3969/j.issn.1004-4132.2010.01.001
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This paper presents an approach of singular value decomposition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise (PN) sequence estimation in low signal to noise ratios (SNR) direct sequence spread spectrum (DS-SS) signals with residual carrier. This approach needs some given parameters, such as the period and code rate of PN sequence. The received signal is firstly sampled and divided into non-overlapping signal vectors according to a temporal window, whose duration is two periods of PN sequence. An autocorrelation matrix is then computed and accumulated by those signal vectors one by one. The PN sequence with residual carrier can be estimated by the principal eigenvector of the autocorrelation matrix. Further more, a digital phase lock loop is used to process the estimated PN sequence, it estimates and tracks the residual carrier and removes
the residual carrier in the end. Theory analysis and computer simulation results show that this approach can effectively realize the PN sequence blind estimation from the input DS-SS signals with residual carrier in lower SNR.

High-resolution algorithm based on temporal-spatial extrapolation
Xueya Yang, Baixiao Chen, and Feilin Qi
2010, 21(1):  9-15.  doi:10.3969/j.issn.1004-4132.2010.01.002
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To enhance the resolution of parameter estimation with limited samples received by a short passive array, an iterative nonparametric algorithm for estimating the frequencies and direction-of-arrivals (DOAs) of signals is proposed. The cost function is constructed using l2-norm Gaussian entropy combined with an additional constraint, l2-norm constraint or linear constraint. By minimizing the cost functions in the temporal and the spatial
dimensions using corresponding iteration algorithms respectively, the sparse discrete Fourier transforms (DFTs) of temporal and spatial samples are obtained to represent the extrapolated sequences with much larger sizes than the original samples. Then frequency and angle estimates are obtained by performing the traditional simple
methods on the extrapolated sequences. It is shown that the proposed algorithm offers increased resolution and significantly reduced sidelobes compared with the periodogram and beamforming based methods. And it achieves high precision compared with the high-resolution method with lower computational burden. Some numerical simulations and real data processing results are presented to verify the effectiveness of the method.

Design of an anti-jamming GPS receiver based on orthogonal projection method
Youguo Hou, Wei Guo, and Xiaozhang Jin
2010, 21(1):  16-19.  doi:10.3969/j.issn.1004-4132.2010.01.003
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Code delay and Doppler shifted frequency could not be captured by using the conventional GPS receiver in strong interference environments because the received GPS signals which traveled a long distance are very weak. An anti-jamming GPS receiver is proposed. The interferences in the received signals are cancelled by using subspace projecting technique, and the resulting interference-free signals are processed by a weight vector which
maximizes the signal-to-noise ratio. Simulation is conducted, and the results show that the method is valid.

Design and realization of synchronization circuit for GPS software receiver based on FPGA
Xiaolei Yu, Yongrong Sun, Jianye Liu, and Jianfeng Miao
2010, 21(1):  20-26.  doi:10.3969/j.issn.1004-4132.2010.01.004
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With research on the carrier phase synchronization and symbol synchronization algorithm of demodulation module, a synchronization circuit system is designed for GPS software receiver based on field programmable gate array (FPGA), and a series of experiment is done on the hardware platform. The result shows the all-digital synchronization and demodulation of GPS intermediate frequency (IF) signal can be realized and applied in
embedded real-time GPS software receiver system. It is verified that the decision-directed joint tracking algorithm of carrier phase and symbol timing for received signals from GPS is reasonable. In addition, the loop works steadily and can be used for receiving GPS signals using synchronous demodulation. The synchronization
circuit for GPS software receiver designed based on FPGA has the features of low cost, miniaturization, low power and realtime. Surely, it will become one of the development directions for GPS and even GNSS embedded real-time software receiver.

Method for determining number of coherent signals in the presence of colored noise
Jiaqi Zhen, Xicai Si, and Lutao Liu
2010, 21(1):  27-30.  doi:10.3969/j.issn.1004-4132.2010.01.005
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The approach of estimating the number of signals based on information theoretic criteria has good performance
in the assumption of white noise, but it always leads to false estimation of the coherent sources in colored noise. An approach combining the combined information theoretic criteria and eigenvalue correction, is presented to determine number of signals. The method uses maximum likelihood (ML) and information theoretic criteria to estimate coherent signals alternately, then eliminate the inequality of the eigenvalues caused by colored noise by correcting the noise eigenvalues. The computer simulation results prove the effective performance of the method.

Fast segmentation approach for SAR image based on simple Markov random field
Xiaogang Lei, Ying Li, Na Zhao, and Yanning Zhang
2010, 21(1):  31-36.  doi:10.3969/j.issn.1004-4132.2010.01.006
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Traditional image segmentation methods based on MRF converge slowly and require pre-defined weight. These disadvantages are addressed, and a fast segmentation approach based on simple Markov random field (MRF) for SAR image is proposed. The approach is firstly used to perform coarse segmentation in blocks. Then the image is modeled with simple MRF and adaptive variable weighting forms are applied in homogeneous and heterogeneous regions. As a result, the convergent speed is accelerated while the segmentation results in homogeneous regions and boarders are improved. Simulations with synthetic and real SAR images demonstrate the effectiveness of the proposed approach.

Fast and accurate analysis of electromagnetic scattering from targets situated in dielectric half space
Yongpin Chen, Zaiping Nie, and Jun Hu
2010, 21(1):  37-40.  doi:10.3969/j.issn.1004-4132.2010.01.007
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Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green’s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green’s function can be divided into two parts: primary term and reflected term.
In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table
is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.

Rotational parameters estimation of maneuvering target in ISAR imaging
Wenchen Li, Jin Liu, Xuesong Wang, Shunping Xiao, and Guoyu Wang
2010, 21(1):  41-46.  doi:10.3969/j.issn.1004-4132.2010.01.008
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The rotational parameters estimation of maneuvering target is the key of cross-range scaling of ISAR (inverse synthetic aperture radar), which can be used in the target feature extraction. The cross-range signal model of rotating target with fixed acceleration is presented and the weighted linear least squares estimation of rotational parameters with fixed velocity or acceleration is proposed via the relationship of cross-range FM (frequency modulation) parameter, scatterers coordinates and rotational parameters. The FM parameter is calculated via RWT (Radon-Wigner transform). The ISAR imaging and cross-range scaling based on scaled RWT imaging method are implemented after obtaining rotational parameters. The rotational parameters estimation and cross-range scaling are validated by the ISAR processing of experimental radar data, and the method presents good application foreground to the ISAR imaging and scaling of maneuvering target.

Fuzzy Nash equilibrium of fuzzy n-person non-cooperative game
Xiaohui Yu and Qiang Zhang
2010, 21(1):  47-56.  doi:10.3969/j.issn.1004-4132.2010.01.009
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The fuzzy non-cooperative game with fuzzy payoff function is studied. Based on fuzzy set theory with game theory, the fuzzy Nash equilibrium of fuzzy non-cooperative games is proposed. Most of researchers rank fuzzy number by its center of gravity or by the real number with its maximal membership. By reducing fuzzy number into a real number, we lose much fuzzy information that should be kept during the operations between fuzzy numbers. The fuzzy quantities or alternatives are ordered directly by Yuan’s binary fuzzy ordering relation. In doing so, the existence of fuzzy Nash equilibrium for fuzzy non-cooperative games is shown based on the utility function and the crisp Nash theorem. Finally, an illustrative example in traffic flow patterns of equilibrium is given in order to show the detailed calculation process of fuzzy Nash equilibrium.

Condition-based maintenance policy for gamma deteriorating systems
Lin Tan, Zhijun Cheng, Bo Guo, and Shiyu Gong
2010, 21(1):  57-61.  doi:10.3969/j.issn.1004-4132.2010.01.010
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A condition-based maintenance model for gamma deteriorating system under continuous inspection is studied. This methodology uses a gamma distribution to model the material degradation, and the impact of imperfect maintenance actions on the system reliability is investigated. The state of a degrading system immediately after the imperfect maintenance action is assumed as a random variable and the maintenance time follows a geometric process. Furthermore, the explicit expressions for the long-run average cost and availability per unit time of the system are evaluated, an optimal policy (ξ∗) could be determined numerically or analytically according to the optimization model. At last, a numerical example for a degrading system modeled by a gamma process is presented to demonstrate the use of this policy in practical applications.

Rough law energy and measurement of ¯F-decomposition rough law
Shunliang Huang, Huafeng Yang, and Kaiquan Shi
2010, 21(1):  62-66.  doi:10.3969/j.issn.1004-4132.2010.01.011
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By employing function one-direction S-rough sets and rough law generation method based on function S-rough sets, ¯ f-decomposition law and ¯ F-decomposition rough law are proposed, and the measurement of rough law variation in the process of rough law ¯ F-decomposition is researched. The concepts of law energy and attribute ¯ f-interference degree are presented, which make the variation of rough law become measurable. ¯ f-decomposition law energy characteristic theorem, ¯ fdecomposition law energy inequality theorem, ¯ F-decomposition rough law energy characteristic theorem, and ¯ f-decomposition law energy mean value theorem are presented.

Hybrid ant colony optimization for the resource-constrained project scheduling problem
Linyi Deng, Yan Lin, and Ming Chen
2010, 21(1):  67-71.  doi:10.3969/j.issn.1004-4132.2010.01.012
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To solve the resource-constrained project scheduling problem (RCPSP), a hybrid ant colony optimization (HACO) approach is presented. To improve the quality of the schedules, the HACO is incorporated with an extended double justification in which the activity splitting is applied to predict whether the schedule could be improved. The HACO is tested on the set of large benchmark problems from the project scheduling problem library (PSPLIB). The computational result shows that the proposed algorithm can improve the quality of the schedules efficiently.

Kernel matrix learning with a general regularized risk functional criterion
Chengqun Wang, Jiming Chen, Chonghai Hu, and Youxian Sun
2010, 21(1):  72-80.  doi:10.3969/j.issn.1004-4132.2010.01.013
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Kernel-based methods work by embedding the data into a feature space and then searching linear hypothesis among the embedding data points. The performance is mostly affected by which kernel is used. A promising way is to learn the kernel from the data automatically. A general regularized risk functional (RRF) criterion for kernel matrix learning is proposed. Compared with the RRF criterion, general RRF criterion takes into account the geometric distributions of the embedding data points. It is proven that the distance between different geometric distributions can be estimated by their centroid distance in the reproducing kernel Hilbert space. Using this criterion for kernel matrix learning leads to a convex quadratically constrained quadratic programming (QCQP) problem. For several commonly used loss functions, their mathematical formulations are given. Experiment results on a collection of benchmark data sets demonstrate the effectiveness of the proposed method.

Output-feedback adaptive stochastic nonlinear stabilization using neural networks
Weisheng Chen
2010, 21(1):  81-87.  doi:10.3969/j.issn.1004-4132.2010.01.014
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For the first time, an adaptive backstepping neural network control approach is extended to a class of stochastic nonlinear output-feedback systems. Different from the existing results, the nonlinear terms are assumed to be completely unknown and only a neural network is employed to compensate for all unknown nonlinear functions so that the controller design is more simplified. Based on stochastic LaSalle theorem, the resulted closed-loop system is proved to be globally asymptotically stable in probability. The simulation results further verify the effectiveness of the control scheme.

Second-order consensus in networks of dynamic agents with communication time-delays
Bo Yang, Huajing Fang, and Hua Wang
2010, 21(1):  88-94.  doi:10.3969/j.issn.1004-4132.2010.01.015
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This paper proposes second-order consensus protocols with time-delays and gives the measure of the robustness of the protocols to the time-delay existing in the network of agents with second-order dynamics. By employing a frequency domain method, it is proven that the information states and their time derivatives of all the agents in the network achieve consensus asymptotically, respectively, for appropriate communication timedelay
if the topology of weighted network is connected. Particularly, a tight upper bound on the communication time-delay that can be tolerated in the dynamic network is found. The consensus protocols are distributed in the sense that each agent only needs information from its neighboring agents, which reduces the complexity of connections between neighboring agents significantly. Numerical simulation results are provided to demonstrate the effectiveness and the sharpness of the theoretical results for second-order consensus in networks in the presence of communication time-delays.

Research on robust mean square stability of networked control systems with packet dropout
Dexiao Xie, Xiaodong Han, He Huang, and Zhiquan Wang
2010, 21(1):  95-101.  doi:10.3969/j.issn.1004-4132.2010.01.016
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This paper is concerned with the robust stabilization problem of networked control systems with stochastic packet
dropouts and uncertain parameters. Considering the stochastic packet dropout occuring in two channels between the sensor and the controller, and between the controller and the actuator, networked control systems are modeled as the Markovian jump linear system with four operation modes. Based on this model, the necessary and sufficient conditions for the mean square stability of the deterministic networked control systems and uncertain networked
control systems are given by using the theory of the Markovian jump linear system, and corresponding controller design procedures are proposed via the cone complementarity linearization method. Finally, the numerical example and simulations are given to illustrate the effectiveness of the proposed results.

SINS/CNS/GPS integrated navigation algorithm based on UKF
Haidong Hu and Xianlin Huang
2010, 21(1):  102-109.  doi:10.3969/j.issn.1004-4132.2010.01.017
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A new nonlinear algorithm is proposed for strapdown inertial navigation system (SINS)/celestial navigation system
(CNS)/global positioning system (GPS) integrated navigation systems. The algorithm employs a nonlinear system error model which can be modified by unscented Kalman filter (UKF) to give predictions of local filters. And these predictions can be fused by the federated Kalman filter. In the system error model, the rotation vector is introduced to denote vehicle’s attitude and has less variables than the quaternion. Also, the UKF method is simplified to estimate the system error model, which can both lead to less calculation and reduce algorithm implement time. In the information fusion section, a modified federated Kalman filter is proposed to solve the singular covariance problem. Specifically, the new algorithm is applied to maneuvering vehicles, and simulation results show that this algorithm is more accurate than the linear integrated navigation algorithm.

Robust reliable guaranteed cost control for uncertain singular systems with time-delay
Qixun Lan, Yuxiao Liu, Huawei Niu, and Jiarong Liang
2010, 21(1):  110-117.  doi:10.3969/j.issn.1004-4132.2010.01.018
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The robust reliable guaranteed cost control for uncertain singular delay systems with actuator failures and a given quadratic cost function is studied. The system under consideration involves constant time-delay and norm-bounded parameter uncertainties. The purpose is to design state feedback controllers which can tolerate actuator failure, such that the closed-loop system is stable, and the specified cost function has an upper bound for all admissible uncertainties. The sufficient conditions for the solvability of this problem are obtained by a linear matrix inequality (LMI) method. Furthermore, a numerical example is given to demonstrate the applicability of the proposed approach.

Person-independent expression recognition based on person-similarity weighted expression feature
Huachun Tan, Yujin Zhang, Hao Chen, Yanan Zhao, and Wuhong Wang
2010, 21(1):  118-126.  doi:10.3969/j.issn.1004-4132.2010.01.019
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A new method to extract person-independent expression feature based on higher-order singular value decomposition (HOSVD) is proposed for facial expression recognition. Based on the assumption that similar persons have similar facial expression appearance and shape, the person-similarity weighted expression feature is proposed to estimate the expression feature of test persons. As a result, the estimated expression feature can reduce the influence of individuals caused by insufficient training data, and hence become less person-dependent. The proposed method is tested on Cohn-Kanade facial expression database and Japanese female facial expression (JAFFE) database. Person-independent experimental results show the superiority of the proposed method over the existing methods.

Image retrieval based on color features integrated with anisotropic directionality
Jing Bai, Xiaohua Wang, and Licheng Jiao
2010, 21(1):  127-133.  doi:10.3969/j.issn.1004-4132.2010.01.020
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A novel image retrieval approach based on color features and anisotropic directional information is proposed for content based image retrieval systems (CBIR). The color feature is described by the color histogram (CH), which is translation and rotation invariant. However, the CH does not contain spatial information which is very important for the image retrieval. To overcome this shortcoming, the subband energy of the lifting directionlet transform (L-DT) is proposed to describe the directional information, in which L-DT is characterized by multi-direction and anisotropic basis functions compared with the wavelet transform. A global similarity measure is designed to implement the fusion of both color feature and anisotropic directionality for the retrieval process. The retrieval experiments using a set of COREL images demonstrate that the higher query precision and better visual effect can be achieved.

Ruling out small stopping sets and small girth in Tanner graph of QC-LDPC code
Lingjun Kong and Yang Xiao
2010, 21(1):  134-137.  doi:10.3969/j.issn.1004-4132.2010.01.021
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The existing constructions of quasi-cyclic low-density parity-check (QC-LDPC) codes do not consider the problems of small stopping sets and small girth together in the Tanner graph, while their existences will lead to the bit error rate (BER) performance of QC-LDPC codes being much poorer than that of randomly constructed LDPC codes even decoding failure. To solve the problem, some theorems of the specific chosen parity-check matrix of QC-LDPC codes without small stopping sets and small girth are proposed. A novel construction for QC-LDPC codes with long block lengths is presented by multiplying mmin or the multiple of mmin, which is the minimum order of the identity matrix for the chosen parity-check matrix. The simulation results show that the specific chosen parity-check matrix of QC-LDPC codes can effectively avoid specified stopping sets and small girth and exhibit excellent BER performance than random LDPC codes with the same longer codes length.

Hooke and Jeeves algorithm for linear support vector machine
Yeqing Liu, Sanyang Liu, and Mingtao Gu
2010, 21(1):  138-141.  doi:10.3969/j.issn.1004-4132.2010.01.022
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Coordinate descent method is a unconstrained optimization technique. When it is applied to support vector machine (SVM), at each step the method updates one component of w by solving a one-variable sub-problem while fixing other components. All components of w update after one iteration. Then go to next iteration. Though the method converges and converges fast in the beginning, it converges slow for final convergence. To improve the
speed of final convergence of coordinate descent method, Hooke and Jeeves algorithm which adds pattern search after every iteration in coordinate descent method was applied to SVM and a global Newton algorithm was used to solve one-variable sub-problems. We proved the convergence of the algorithm. Experimental results show Hooke and Jeeves’ method does accelerate convergence specially for final convergence and achieves higher testing accuracy more quickly in classification.

Modelling method with missing values based on clustering and support vector regression
Ling Wang?, Dongmei Fu, Qing Li, and Zhichun Mu
2010, 21(1):  142-147.  doi:10.3969/j.issn.1004-4132.2010.01.023
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Most real application processes belong to a complex nonlinear system with incomplete information. It is difficult to
estimate a model by assuming that the data set is governed by a global model. Moreover, in real processes, the available data set is usually obtained with missing values. To overcome the shortcomings of global modeling and missing data values, a new modeling method is proposed. Firstly, an incomplete data set with missing values is partitioned into several clusters by a K-means with soft constraints (KSC) algorithm, which incorporates soft constraints to enable clustering with missing values. Then a local model based on each group is developed by using SVR algorithm, which adopts a missing value insensitive (MVI) kernel to investigate the missing value estimation problem. For each local model, its valid area is gotten as well. Simulation results prove the effectiveness of the current local model and the estimation algorithm.

Bayesian sequential state estimation for MIMO-OFDM systems
Maoge Xu and Yaoliang Song
2010, 21(1):  148-153.  doi:10.3969/j.issn.1004-4132.2010.01.024
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For the estimation of MIMO frequency selective channel, to mitigate the curse of dimensionality, a novel particle filtering scheme combined with time delay domain processing is proposed. In order to extract the time delay domain channel impulse response from the observed signal, the least-squares (LS) and minimum mean squared error (MMSE) criteria are discussed and the comparable performance of LS with MMSE for samplespaced channel is revealed. Incorporated the dynamical channel model, gradient particle filtering is further introduced to improve the estimation performance. The robustness of the channel estimator for underestimated Doppler frequency and the effectiveness of the new estimation scheme are illustrated through simulation at last.

Confidentiality-aware message scheduling for security-critical wireless networks
Wei Jiang, Guangze Xiong, Xuyang Ding, Zhengwei Chang, and Nan Sang
2010, 21(1):  154-160.  doi:10.3969/j.issn.1004-4132.2010.01.025
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Without considering security, existing message scheduling mechanisms may expose critical messages to malicious threats like confidentiality attacks. Incorporating confidentiality improvement into message scheduling, this paper investigates the problem of scheduling aperiodc messages with time-critical and security-critical requirements. A risk-based security profit model is built to quantify the security quality of messages; and a dynamic programming based approximation algorithm is proposed to schedule aperiodic messages with guaranteed security performance. Experimental results illustrate the efficiency and effectiveness of the proposed algorithm.

Malicious code passive propagation model and vaccine distribution model of P2P networks
Xiaolong Xu, Ruchuan Wang, and Fu Xiao
2010, 21(1):  161-167.  doi:10.3969/j.issn.1004-4132.2010.01.026
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To fight against malicious codes of P2P networks, it is necessary to study the malicious code propagation model of P2P networks in depth. The epidemic of malicious code threatening P2P systems can be divided into the active and passive propagation models and a new passive propagation model of malicious code is proposed, which differentiates peers into 4 kinds of state and fits better for actual P2P networks. From the propagation model of malicious code, it is easy to find that quickly making peers get their patched and upgraded anti-virus system is the key way of immunization and damage control. To distribute patches and immune modules efficiently, a new exponential tree plus (ET+) and vaccine distribution algorithm based on ET+ are also proposed. The performance analysis and test results show that the vaccine distribution algorithm based on ET+ is robust, efficient and much more suitable for P2P networks.

Quorum systems for intrusion-tolerance based on trusted timely computing base
Hua Zhou, Xiangru Meng, Li Zhang, and Xiangdong Qiao
2010, 21(1):  168-174.  doi:10.3969/j.issn.1004-4132.2010.01.027
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Quorum systems have been used to solve the problem of data consistency in distributed fault-tolerance systems. But when intrusions occur, traditional quorum systems have some disadvantages. For example, synchronous quorum systems are subject to DOS attacks, while asynchronous quorum systems need a larger system size (at least 3f+1 for generic data, and f fewer for self-verifying data). In order to solve the problems above, an intrusion-tolerance quorum system (ITQS) of hybrid time model based on trust timely computing base is presented (TTCB). The TTCB is a trust secure real-time component inside the server with a well defined interface and separated from the operation system. It is in the synchronous communication environment while the application layer in the server deals with read-write requests and executes update-copy protocols asynchronously. The architectural hybridization of synchrony and asynchrony can achieve the data consistency and availability correctly. We also build two kinds of
ITQSes based on TTCB, i.e., the symmetrical and the asymmetrical TTCB quorum systems. In the performance evaluations, we show that TTCB quorum systems are of smaller size, lower load and higher availability.