Robust performance of the multiloop perturbation compensator

A novel perturbation attenuation method is proposed for robust performance of mechanical systems. First, we give a unified view on a class of existing perturbation observers and define the residual perturbation. In terms of the view and the definition, a new perturbation compensator with multiloop structure is developed. It effectively compensates the perturbation (i.e., model uncertainty and external disturbance) to the plant in a hierarchical and recursive fashion. In the multiloop perturbation compensator (MPEC) proposed, as the number of loops increases, the external disturbance condition for system stability is greatly relaxed and the perturbation attenuation performance is gradually enhanced but the robust stability margin on the modeling error becomes more strict. A recursive algorithm for general n-loop case of the MPEC is derived. By combining the developed robust perturbation compensator with a nominal feedback controller, a robust motion controller is synthesized. Experimental results for XY positioner and 2-DOF robot arms demonstrate the excellent robust tracking performance in spite of arbitrary large perturbation inputs     

Multi-Channel Assignment Schemes and Handoff Study in CDMA Cellular Systems

The CDMA system promisingly provides more capacity than AMPS. However, providing multi-channels for a CDMA system is requisite for satisfying the demand of capacity. In this paper, three schemes of multi-channel assignment are proposed. Based on computer simulation, performance measures, e.g. blocking probabilities, the overall capacity, the capacity of each channel, and the number of re-accesses, are obtained. Since the same frequency channel may be assigned to two adjacent cells, the effect of soft handoff is also considered. Numerical results demonstrate that scheme 3 (i.e., the random re-selection scheme) performs the best of the proposed three schemes because it provides the highest system capacity while keeping the cost of accessing channels (i.e., in terms of number of channel accesses) to a minimum.     

A management architecture for client‐defined cloud storage services

Cloud service providers offer virtual resources to users, who then pay for as much as they use. High‐speed networks help to overcome the limitation of geographical distances between clients and cloud servers, which encourage users to adopt cloud storage services for data backup and sharing. However, users use only a few cloud storage services because of the complexity of managing multiple accounts and distributing data to store. In this paper, we propose the client‐defined management architecture (CLIMA) that redefines a storage service by coordinating multiple cloud storage services from clients. We address practical issues of coordinating multiple cloud service providers using a client‐based approach. We implement a prototype as a realization of CLIMA, which achieves both reliability and privacy protection using erasure code and higher performance by optimally scheduling data transmission. We use our prototype to evaluate the benefits of CLIMA on commercial cloud storage service providers. Finally, CLIMA empowers clients to increase the manageability and flexibility of cloud storage services. Copyright © 2015 John Wiley & Sons, Ltd.     

Real‐Time License Plate Detection in High‐Resolution Videos Using Fastest Available Cascade Classifier and Core Patterns

We present a novel method for real‐time automatic license plate detection in high‐resolution videos. Although there have been extensive studies of license plate detection since the 1970s, the suggested approaches resulting from such studies have difficulties in processing high‐resolution imagery in real‐time. Herein, we propose a novel cascade structure, the fastest classifier available, by rejecting false positives most efficiently. Furthermore, we train the classifier using the core patterns of various types of license plates, improving both the computation load and the accuracy of license plate detection. To show its superiority, our approach is compared with other state‐of‐the‐art approaches. In addition, we collected 20,000 images including license plates from real traffic scenes for comprehensive experiments. The results show that our proposed approach significantly reduces the computational load in comparison to the other state‐of‐the‐art approaches, with comparable performance accuracy.     

A partial variational analysis of planar dielectric antennas

The reflection and radiation characteristics of a planar dielectric antenna with arbitrary geometrical configuration are analyzed numerically. A variational equation is first established based on the partial variational principle (PVP), and then solved by the finite element method coupled with the frontal solution technique. The radiation and boundary conditions are incorporated by combining the modal expansion method and the Green's function approach for exterior field representation. The reflection coefficients, the radiation patterns, and the directive and power gains of several antennas with linearized structures are studied and compared     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>     

Proton-exchanged LiNbO/sub 3/ optical waveguides using stearic acid

Proton-exchanged optical waveguides have been fabricated in z-cut LiNbO/sub 3/ using a new proton source: stearic acid. These waveguides were characterized optically and were found to exhibit a step index profile with Delta n=0.118 measured at 0.633 mu m. The propagation losses were typically around 1.5 dB/cm, and the diffusion constant and the activation energy for the proton-exchange process were measured to be 5*10/sup 6/ mu m/sup 2//h and 69 kJ/mol, respectively.<>     

Explicit finite difference vectorial beam propagation method

A vectorial beam propagation method (VBPM) is formulated and implemented using the explicit finite difference (EFD) scheme. The accuracy of semivectorial EFD-BPM, where the polarisation coupling is ignored but polarisation dependence is included, is found to be as good as that of full-vectorial EFD-BPM.<>     

Intermodulation distortion in a multiple-quantum-well semiconductor optical amplifier

The measurement of intermodulation distortion (IMD) induced by carrier-density modulation in a multiple-quantum-well (MQW) semiconductor amplifier is reported. The results show that MQW amplifiers have 15 dB less IMD than conventional buried-heterostructure semiconductor amplifiers. The IMD is dependent on the output power of the amplifiers, which confirms that the carrier-density modulation is the dominant nonlinear mechanism in MQW amplifiers. In addition, the results show that, unlike conventional buried-heterostructure amplifiers, MQW amplifiers have at least two time constants (200-250 ps and <10 ps) for the gain recovery process.<>