Incremental demand rerouting: optimization models and algorithms

This investigation addresses an important and difficult combinatorial optimization problem in the design and management of telecommunication systems known as the path assignment problem. The path assignment problem is specified by a set of demands on a network with given link capacities. Each demand must be assigned to exactly one routing path in such a way that the total amount of traffic routed over any link does not exceed that link’s capacity. Given a network and a path assignment, the problem of interest is to maximize the available bandwidth (throughput) for a new demand. Network managers are concerned with the quality of service provided by their networks, and so they are reluctant to make major changes to an operating network that may inadvertently result in service disruptions for numerous clients simultaneously. Therefore, the objective of this investigation is to develop and test optimization models and algorithms that produce a series of throughput-improving modifications to the original path assignment. This allows network managers to implement the improved routing in stages with minimal changes to the overall routing plan between any two consecutive stages. Although the procedure may only reroute a few demands at each stage, the routing after the last stage should be as close as possible to an optimal routing. That is, it must maximize the throughput for the new demand. We present integer programming models and associated solution algorithms to maximize the throughput with a sequence of incremental path modifications. The algorithms were implemented with the AMPL modeling language and the CPLEX ILP solver, and tested on a family of five different data sets based on a European network widely studied in the literature. Empirical results show that the incremental approach finds near-optimal results within reasonable limits on CPU time.     

Robust control of the DC–DC boost converter based on the uncertainty and disturbance estimator

In this paper, a robust non-linear controller based on the uncertainty and disturbance estimator (UDE) scheme is successfully developed and implemented for the output voltage regulation of the DC–DC boost converter. System uncertainties, external disturbances and unknown non-linear dynamics are lumped as a signal that is accurately estimated using a low-pass filter and their effects are cancelled by the controller. This methodology forms the basis of the UDE-based controller. A simple procedure is also developed that systematically determines the parameters of the controller to meet certain specifications. Using simulation, the effectiveness of the proposed controller is compared against the sliding-mode control (SMC). Experimental tests also show that the proposed controller is robust to system uncertainties, large input and load perturbations.     

Robust Stochastic Stabilization and H �� Control for?Neutral Stochastic Systems with Distributed Delays

This paper considers the problem of robust stabilization and H _∞ control for a class of uncertain neutral stochastic systems, in which delay is distributed and the parametric uncertainties are norm-bounded. By designing a state feedback controller, we obtain a delay-dependent criterion such that the resulting closed-loop system is robustly stochastically asymptotically stable in the mean square and the effect of the disturbance input on the controlled output is less than a prescribed level for all admissible parameter uncertainties. New sufficient conditions are presented based on the linear matrix inequality approach. Finally, numerical examples are used to illustrate the effectiveness and feasibility of the approaches proposed in this paper.     

Robust H �� Filtering for Uncertain Nonlinear Stochastic Systems with Mode-dependent Time-delays and Markovian Jump Parameters

This paper investigates the problem of robust H _∞ filtering for a class of uncertain nonlinear stochastic time-delay systems with Markovian jump parameters. The system under consideration contains parameter uncertainties, It?-type stochastic disturbances, unknown nonlinearities as well as time-varying delays, which vary in a range and dependent on the mode of the operation. We aim to design a full-order Markovian jump filter such that, for all admissible uncertainties, the filtering error system is robustly asymptotically stable in the mean square, and a prescribed H _∞ disturbance attenuation level is guaranteed. By using the Lyapunov stability theory and It? differential rule, some sufficient conditions in terms of linear matrix inequality (LMI) are proposed to guarantee the existence of the desired H _∞ filter. Then, the explicit expressions of the desired filter parameters are given. Illustrative examples are provided to demonstrate the effectiveness and applicability of the proposed method.     

Parameter estimation and optimization techniques for discrete-time semi-Markov models of H.264/AVC video traffic

We investigate a variety of known and new approaches for the estimation of the parameters of discrete-time semi-Markovian traffic models. We focus on modeling video traffic, since the accurate representation of its long-term autocorrelation is a challenge to the parameter estimation methods. The modeling techniques are applied to sample H.264/AVC-encoded video traces. We study their ability to reflect the autocorrelation and variability of the original traffic and also the delay probabilities of a resulting SMP/GI/1 queueing system. The delay probabilities are determined both by simulation and verified analysis of the queue.     

Comparing the degradation effect of a ‘two-cell’ Supercapacitor-module with and without voltage equalization circuit(s) under experimental self-discharge and load cycling tests

The problem of over-voltage is common in SC modules under cycling conditions. To prevent this, the voltage equalization circuit is usually used as a tool to balance SC cells in a module to increase the life expectancy of the system. There is lack of detailed experimental analysis on its performance on degradation proximity testing. This paper therefore focuses on demonstrating the importance of voltage equalization circuits specifically on their performance in degradation proximity between two-cell modules experimentally. Three types of common active balancing equalization circuits were first tested and the best performing circuit was used to compare with a commercial Maxwell voltage equalization circuit under self-discharge and load cycling tests after 1115 h of continuous cycles under high temperature. The periodic capacitance (C) and ESR parameters calculated from charge-discharge characterization test results over 1115 h shows that the active balancing circuit produced a more even/balance parameter regression between each two-cells in a module over time.