On the Robustness of Scheduling Against Channel Variations

In this paper, we study the robustness of scheduling against channel variations. Specifically, we consider a class of generalized proportional fairness (PF) schedulers that achieve optimal throughput-fairness trade-off and study their robustness in terms of maintaining a certain fairness criterion when the channel statistics change from the additive white Gaussian noise (AWGN) to Rayleigh fading for all users. We conclude that the scheduler is robust only when it is configured to achieve the proportional fairness. For the other scheduler configurations, which are not robust, we show how fairness deviates from the ideal one when the channel statistics change and show how scheduler parameters need to be adjusted to restore the desired fairness. We also show simulation results.     

Wavelength and repetition rate tunable optical pulse source using a chirped fiber Bragg grating and a nonlinear optical loop mirror

We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range.     

Structural Fault Based Specification Reduction for Testing Analog Circuits

Specification reduction can reduce test time, consequently, test cost. In this paper, a methodology to reduce specifications during specification testing for analog circuit is proposed and demonstrated. It starts with first deriving relationships between specifications and parameter variations of the circuit-under-test (CUT) and then reduces specifications by considering bounds of parameter variations. A statistical approach by taking into account of circuit fabrication process fluctuation is also employed and the result shows that the specification reduction depends on the testing confidence. A continuous-time state-variable benchmark filter circuit is applied with this methodology to demonstrate the effectiveness of the approach.     

New collector undercut technique using a SiN sidewall for low basecontact resistance in InP/InGaAs SHBTs

A new collector undercut process using SiN protection sidewall has been developed for high speed InP/InGaAs single heterojunction bipolar transistors (HBTs). The HBTs fabricated using the technique have a larger base contact area, resulting in a smaller DC current gain and smaller base contact resistance than HBTs fabricated using a conventional undercut process while maintaining low C_bc. Due to the reduced base contact resistance, the maximum oscillation frequency (f_max) has been enhanced from 162 GHz to 208 GHz. This result clearly shows the effectiveness of this technique for high-speed HBT process, especially for the HBTs with a thick collector layer, and narrow base metal width     

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