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991.
Due to the increasing deployment of conversational real-time applications like VoIP and videoconferencing, the Internet is
today facing new challenges. Low end-to-end delay is a vital QoS requirement for these applications, and the best effort Internet
architecture does not support this natively. The delay and packet loss statistics are directly coupled to the aggregated traffic
characteristics when link utilization is close to saturation. In order to investigate the behavior and quality of such applications
under heavy network load, it is therefore necessary to create genuine traffic patterns. Trace files of real compressed video and audio are text files containing the number of bytes per video and audio frame. These can serve
as material to construct mathematical traffic models. They can also serve as traffic generators in network simulators since
they determine the packet sizes and their time schedule. However, to inspect perceived quality, the compressed binary content
is needed to ensure decoding of received media. The EvalVid streaming video tool-set enables this using a sophisticated reassembly
engine. Nevertheless, there has been a lack of research solutions for rate adaptive media content. The Internet community fears a congestion collapse if the usage of non-adaptive media content continues to
grow. This paper presents a solution named Evalvid-RA for the simulation of true rate adaptive video. The solution generates
real rate adaptive MPEG-4 streaming traffic, using the quantizer scale for adjusting the sending rate. A feedback based VBR
rate controller is used at simulation time, supporting TFRC and a proprietary congestion control system named P-AQM. Example
ns-2 simulations of TFRC and P-AQM demonstrate Evalvid-RA’s capabilities in performing close-to-true rate adaptive codec operation
with low complexity to enable the simulation of large networks with many adaptive media sources on a single computer. 相似文献
992.
It has been a common consensus that general techniques for stabilization of nonlinear systems are available only for some
special classes of nonlinear systems. Control design for nonlinear systems with uncertain components is usually carried out
on a per system basis, especially when physical control constraints, and certain control performance measures such as optimum
time control are imposed. Elegant adaptive control techniques are difficult to apply to this type of problems. A new neural
network based control design is proposed and presented in this paper to deal with a special class of uncertain nonlinear systems
with multiple inputs. The desired system dynamics are analyzed and utilized in the process of the proposed intelligent control
design. The theoretical results are provided to justify the design procedures. The simulation study is conducted on a second-order
bilinear system with two inputs and uncertainties on its parameters. The simulation results indicate that the proposed design
approach is effective. 相似文献
993.
The behaviour of chromatographic simulated moving bed processes is described by the movement of concentration profiles through a circle of separation columns. A closed-loop control manipulates the profiles in order to meet demands concerning specified product purity and disturbance attenuation. If steep wave fronts of the concentration profiles occur, the controlled variables undergo fast changes in case of a transient of the process. In this case, a reconstruction of the wave fronts is necessary for a successful control.A simple and effective decentralised controller structure is proposed based on cascaded discrete-time PI controllers. On-line product purity measurements and the reconstructed wave fronts are used for control purposes. Two kinds of process models are used: a rigorous model for dynamic simulations, and strongly simplified plant models for the design of the wave front reconstruction and the controller. The latter models are identified based on experimental step tests with the reference plant and numerical simulations. The performance of the control system is evaluated by numerical simulations. 相似文献
994.
The impact of steady-state multiplicities on the control of a simulated industrial scale methyl acetate reactive distillation (RD) column is studied. At a fixed reflux rate, output multiplicity, with multiple output values for the same reboiler duty, causes the column to drift to an undesirable steady-state under open loop operation. The same is avoided for a fixed reflux ratio policy. Input multiplicity, where multiple input values give the same output, leads to “wrong” control action under feedback control severely compromising control system robustness. A new metric, rangeability, is defined to quantify the severity of input multiplicity in a steady-state input–output (IO) relation. Rangeability is used in conjunction with conventional sensitivity analysis for the design of robust control structures for the RD column. Results for the two synthesized control structures show that controlling the most sensitive reactive tray temperature results in poor robustness due to low rangeability causing “wrong” control action for large disturbances. Controlling a reactive tray temperature with acceptable sensitivity but larger rangeability gives better robustness. It is also shown that controlling the difference in the temperature of two suitably chosen reactive trays further improves robustness of both the structures as input multiplicity is avoided. The article brings out the importance of IO relations for control system design and understanding the complex dynamic behavior of RD systems. 相似文献
995.
Multivariate statistical process control based on multiway locality preserving projections 总被引:1,自引:0,他引:1
An approach for multivariate statistical process control based on multiway locality preserving projections (LPP) is presented. The recently developed LPP is a linear dimensionality reduction technique for preserving the neighborhood structure of the data set. It is characterized by capturing the intrinsic structure of the observed data and finding more meaningful low-dimensional information hidden in the high-dimensional observations compared with PCA. In this study, LPP is used to extract the intrinsic geometrical structure of the process data. Hotelling’s T2 (D) and the squared prediction error (SPE or Q) statistic charts for on-line monitoring are then presented, and the contribution plots of these two statistical indices are used for fault diagnosis. Moreover, a moving window technique is used for the implementation of on-line monitoring. Case study was carried out with the data of industrial penicillin fed-batch cultivations. As a comparison, the results obtained with the MPCA are also presented. It is concluded that the Multiway LPP (MLPP) outperforms the conventional MPCA. Finally, the robustness of the MLPP monitoring is analyzed by adding noises to the original data. 相似文献
996.
997.
A steady-state interval operability methodology is introduced here for multivariable non-square systems with fewer inputs than output variables to be used in the design of model-based constrained controllers (MPC, DMC). For such systems, set-point control is not possible for all the outputs and interval control is needed. The proposed iterative approach enables the selection of the needed interval constraints systematically, so that the tightest possible control is achieved without rendering the control problem infeasible. The application of this methodology to high-dimensional industrial problems characterizing processes of Air Products and Chemicals and DuPont shows that very significant reduction of the constrained region can be achieved from the steady-state point of view. Ratios of the initial to the calculated volume of the constrained regions examined range between 104 and 108. 相似文献
998.
This paper describes a new method for increasing the computational efficiency of nonlinear robust model-based predictive control. It is based on the application of neuro-fuzzy networks and improves the computation efficiency by arranging the online optimisation to be done offline. The offline optimisation is realized by offline training a neuro-fuzzy network, consisting of zero-order T–S fuzzy rules, which is designed to approximate the input–output relationship of a robust model-based predictive controller. The design and the training of the neuro-fuzzy network are described, and the corresponding control algorithm is developed. Experiment results performed on the temperature control loop of an experimental air-handling unit (AHU) demonstrate the effectiveness of this approach. 相似文献
999.
We present a stabilizing scheduled output feedback Model Predictive Control (MPC) algorithm for constrained nonlinear systems with large operating regions. We design a set of local output feedback predictive controllers with their estimated regions of stability covering the desired operating region, and implement them as a single scheduled output feedback MPC which on-line switches between the set of local controllers and achieves nonlinear transitions with guaranteed stability. This algorithm provides a general framework for scheduled output feedback MPC design. 相似文献
1000.
Statistical process control (SPC) is a conventional means of monitoring software processes and detecting related problems,
where the causes of detected problems can be identified using causal analysis. Determining the actual causes of reported problems
requires significant effort due to the large number of possible causes. This study presents an approach to detect problems
and identify the causes of problems using multivariate SPC. This proposed method can be applied to monitor multiple measures
of software process simultaneously. The measures which are detected as the major impacts to the out-of-control signals can
be used to identify the causes where the partial least squares (PLS) and statistical hypothesis testing are utilized to validate
the identified causes of problems in this study. The main advantage of the proposed approach is that the correlated indices
can be monitored simultaneously to facilitate the causal analysis of a software process.
Ching-Pao Chang is a PhD candidate in Computer Science & Information Engineering at the National Cheng-Kung University, Taiwan. He received his MA from the University of Southern California in 1998 in Computer Science. His current work deals with the software process improvement and defect prevention using machine learning techniques. Chih-Ping Chu is Professor of Software Engineering in Department of Computer Science & Information Engineering at the National Cheng-Kung University (NCKU) in Taiwan. He received his MA in Computer Science from the University of California, Riverside in 1987, and his Doctorate in Computer Science from Louisiana State University in 1991. He is especially interested in parallel computing and software engineering. 相似文献
Chih-Ping ChuEmail: |
Ching-Pao Chang is a PhD candidate in Computer Science & Information Engineering at the National Cheng-Kung University, Taiwan. He received his MA from the University of Southern California in 1998 in Computer Science. His current work deals with the software process improvement and defect prevention using machine learning techniques. Chih-Ping Chu is Professor of Software Engineering in Department of Computer Science & Information Engineering at the National Cheng-Kung University (NCKU) in Taiwan. He received his MA in Computer Science from the University of California, Riverside in 1987, and his Doctorate in Computer Science from Louisiana State University in 1991. He is especially interested in parallel computing and software engineering. 相似文献