Software rejuvenation is a recently proposed practive fault-tolerance approach to counteract software-aging phenomenon. Compared with clusters of a flat architecture, all the nodes share the same functions. The applic...Software rejuvenation is a recently proposed practive fault-tolerance approach to counteract software-aging phenomenon. Compared with clusters of a flat architecture, all the nodes share the same functions. The application of software rejuvenation on dispatcher-based web server farms is discussed, which employ rejuvenation both on the dispatcher and the worker pool. Stochastic reward net (SRN)models for time-based and prediction-based rejuvenation policies are constructed respectively and solved by stochastic Petri net package (SPNP). Numerical results show that appropriate rejuvenation strategies on the dispatcher and the worker pool could significantly reduce the expected downtime cost of the whole web server farm.展开更多
In order to establish the sufficient and necessary condition that arbitrarily reliable systems can not be constructed with function elements under interference sources, it is very important to expand set of interferen...In order to establish the sufficient and necessary condition that arbitrarily reliable systems can not be constructed with function elements under interference sources, it is very important to expand set of interference sources with the above property. In this paper, the models of two types of interference sources are raised respectively: interference source possessing real input vectors and constant reliable interference source. We study the reliability of the systems effected by the interference sources, and the lower bound of the reliability is presented. The results show that it is impossible that arbitrarily reliable systems can not be constructed with the elements effected by above interference sources.展开更多
To enhance the robustness of video transmission over noisy channels, this paper presents a multiple description video coding algorithm based on chessboard-interpolation. In the algorithm, the input image is decomposed...To enhance the robustness of video transmission over noisy channels, this paper presents a multiple description video coding algorithm based on chessboard-interpolation. In the algorithm, the input image is decomposed according to the chessboard pattern, and then interpolated to produce two approximate images with the same resolution. Consequently, the state-of-the-art DCT+MC (Discrete Cosine Transform + Motion Compensation) video codec is independently applied to the two approximate images to generate two descriptions of the original image. In this framework, a fairely good reconstructed image quality is obtained when two descriptions are received simultaneously, while an acceptable reconstructed image quality could be yielded if only one description is available. Moreover, the mismatch between the encoder and the decoder could be effectively controlled through partial coding of the difference signal between two descriptions. In bidirectional video communications, a drift control scheme is further proposed, in which the error drift could be eliminated after the encoder imitating the error concealment actions of the decoder. Since the inherent correlation among adjacent blocks of DCT+MC video coding is efficiently exploited, this algorithm has a better redundancy-rate-distortion (RRD) performance than other multiple description algorithms. Simulation results show that the proposed algorithm is fairly robust while preserves a high compression rate. A more constant reconstructed image quality is achieved over extremely noisy channels, compared with traditional single description coding. In addition, it is observed that the mismatch and the error drift are effectively controlled.展开更多
With independence assumption, this paper proposes and proves the superior step-size theorem on least mean square (LMS) algorithm, from the view of minimizing mean squared error (MSE). Following the theorem we construc...With independence assumption, this paper proposes and proves the superior step-size theorem on least mean square (LMS) algorithm, from the view of minimizing mean squared error (MSE). Following the theorem we construct a parallel variable step-size LMS filters algorithm. The theoretical model of the proposed algorithm is analyzed in detail. Simulations show the proposed theoretical model is quite close to the optimal variable step-size LMS (OVS-LMS) model. The experimental learning curves of the proposed algorithm also show the fastest convergence and fine tracking performance. The proposed algorithm is therefore a good realization of the OVS-LMS model.展开更多
文摘Software rejuvenation is a recently proposed practive fault-tolerance approach to counteract software-aging phenomenon. Compared with clusters of a flat architecture, all the nodes share the same functions. The application of software rejuvenation on dispatcher-based web server farms is discussed, which employ rejuvenation both on the dispatcher and the worker pool. Stochastic reward net (SRN)models for time-based and prediction-based rejuvenation policies are constructed respectively and solved by stochastic Petri net package (SPNP). Numerical results show that appropriate rejuvenation strategies on the dispatcher and the worker pool could significantly reduce the expected downtime cost of the whole web server farm.
基金Tsinghua University Research Foundation(JC2000025)
文摘In order to establish the sufficient and necessary condition that arbitrarily reliable systems can not be constructed with function elements under interference sources, it is very important to expand set of interference sources with the above property. In this paper, the models of two types of interference sources are raised respectively: interference source possessing real input vectors and constant reliable interference source. We study the reliability of the systems effected by the interference sources, and the lower bound of the reliability is presented. The results show that it is impossible that arbitrarily reliable systems can not be constructed with the elements effected by above interference sources.
文摘To enhance the robustness of video transmission over noisy channels, this paper presents a multiple description video coding algorithm based on chessboard-interpolation. In the algorithm, the input image is decomposed according to the chessboard pattern, and then interpolated to produce two approximate images with the same resolution. Consequently, the state-of-the-art DCT+MC (Discrete Cosine Transform + Motion Compensation) video codec is independently applied to the two approximate images to generate two descriptions of the original image. In this framework, a fairely good reconstructed image quality is obtained when two descriptions are received simultaneously, while an acceptable reconstructed image quality could be yielded if only one description is available. Moreover, the mismatch between the encoder and the decoder could be effectively controlled through partial coding of the difference signal between two descriptions. In bidirectional video communications, a drift control scheme is further proposed, in which the error drift could be eliminated after the encoder imitating the error concealment actions of the decoder. Since the inherent correlation among adjacent blocks of DCT+MC video coding is efficiently exploited, this algorithm has a better redundancy-rate-distortion (RRD) performance than other multiple description algorithms. Simulation results show that the proposed algorithm is fairly robust while preserves a high compression rate. A more constant reconstructed image quality is achieved over extremely noisy channels, compared with traditional single description coding. In addition, it is observed that the mismatch and the error drift are effectively controlled.
文摘With independence assumption, this paper proposes and proves the superior step-size theorem on least mean square (LMS) algorithm, from the view of minimizing mean squared error (MSE). Following the theorem we construct a parallel variable step-size LMS filters algorithm. The theoretical model of the proposed algorithm is analyzed in detail. Simulations show the proposed theoretical model is quite close to the optimal variable step-size LMS (OVS-LMS) model. The experimental learning curves of the proposed algorithm also show the fastest convergence and fine tracking performance. The proposed algorithm is therefore a good realization of the OVS-LMS model.
