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Dynamic Performance of a Wind Generation System with Thyristor Controlled Capacitor Compensation
Get PDFA dynamic model of a variable speed cage machine wind generation unit, including wind profile, wind turbine, induction generator, local load and transmission line connecting the grid is developed. The steady state as well as the dynamic performance of the wind energy system is explored. The performance of the system under wind gust conditions has been studied and the amount of transient injection to the grid investigated. A stabilizing control scheme which minimizes the transient injection through a thyristor controlled variable capacitance at the generator terminal is explored. PI controller with optimized gain settings is included in the control loop. The ‘optimal’ parameters of the PI controller are obtained through a pole-placement technique. The PI controlled variable capacitance strategy has demonstrated very good damping profile for the wind turbine-generator power system
Dynamic Performance of a Wind Generation System with Thyristor Controlled Capacitor Compensation
Get PDFA dynamic model of a variable speed cage machine wind generation unit, including wind profile, wind turbine, induction generator, local load and transmission line connecting the grid is developed. The steady state as well as the dynamic performance of the wind energy system is explored. The performance of the system under wind gust conditions has been studied and the amount of transient injection to the grid investigated. A stabilizing control scheme which minimizes the transient injection through a thyristor controlled variable capacitance at the generator terminal is explored. PI controller with optimized gain settings is included in the control loop. The ‘optimal’ parameters of the PI controller are obtained through a pole-placement technique. The PI controlled variable capacitance strategy has demonstrated very good damping profile for the wind turbine-generator power system
Performance Analysis and Comparison of Interrupt-Handling Schemes in Gigabit Networks
Get PDFInterrupt processing can be a major bottleneck in the end-to-end performance of Gigabit networks. The performance of Gigabit network end hosts or servers can be severely degraded due to interrupt overhead caused by heavy incoming traffic. In particular, excessive latency and significant degradation in system throughput can be encountered. Also, user applications may livelock as the CPU power gets mostly consumed by interrupt handling and protocol processing. A number of interrupt handling schemes has been proposed and employed to mitigate the interrupt overhead and improve OS performance. Among the most popular interrupt handling schemes are normal interruption, polling, interrupt coalescing, and disabling and enabling of interrupts. In previous work, we presented a preliminary analytical study and models of normal interruption and interrupt coalescing. In this article, we extend our analysis and modeling to include polling and the scheme of interrupt disabling and enabling. For polling, we study both pure (or FreeBSD-style) polling and Linux NAPI polling. The performances for all these schemes are compared using both mathematical analysis and discrete-event simulation. The performance is studied in terms of three key performance indictors: throughput, system latency, and the residual CPU bandwidth available for user applications. As opposed to our previous work, we consider not only Poisson traffic, but also bursty traffic with empirical packet size distribution. Our analysis and simulation work gives insight into predicting the system performance and behavior when employing a certain interrupt handling scheme. It is concluded that no single interrupt handling scheme outperforms all other schemes under all traffic conditions. Based on obtained results, we propose and discuss a novel hybrid scheme of interrupt disabling-enabling and pure polling in order to attain peak performance under low and heavy traffic loads
A Chip-Level BSOR-based linear GSIC multiuser Detector for Long-Code CDMA Systems
Get PDFIn this work, we introduce a chip-level linear group-wise successive interference cancellation (GSIC) multi-user structure that is asymptotically equivalent to block successive over-relaxation (BSOR) iteration, which is known to outperform the conventional block Gauss-Seidel iteration by an order of magnitude in terms of convergence speed. The main advantage of the proposed scheme is that it uses directly the spreading codes instead of the cross-correlation matrix and thus doesn’t require the calculation of the cross-correlation matrix (requires 2NK2 floating point operations (flops), where N is the processing gain and K is the number of users) which reduces significantly the overall computational complexity. Thus it is suitable for long-code CDMA systems such as IS-95 and UMTS where the cross-correlation matrix is changing every symbol. We study the convergence behavior of the proposed scheme using two approaches and prove that it converges to the decorrelator detector if the over-relaxation factor is in the interval ]0, 2[. Simulation results are in excellent agreement with theory
"Multiuser Diversity with Quantized Feedback"
Get PDFIn this paper, we propose an optimal discrete rate switch-based multiuser diversity system (DSMUDiv) that reduces the feedback load while preserving the essential of the scheme’s performance in some cases. We examine the DSMUDiv scheme using two scheduling criteria depending on the distribution of the mobile users in the cell: (i) absolute signal-to-noise ratio (SNR)-based scheduling in the case of independent and identical distributed (i.i.d.) users, and (ii) normalized SNR-based scheduling in the case of non-i.i.d. users. The paper includes the derivation of closed-form expressions of the feedback load in the case of absolute and normalized SNR-based scheduling and the spectral efficiency in the case of absolute SNR-based scheduling. Computer simulation is used to evaluate the spectral efficiency in the case of normalized SNR-based scheduling. Under slow Rayleigh fading assumption, we compare our scheme with the optimal (full feedback load) selective diversity scheme
On Optimal Firewall Rule Ordering
Get PDFIn today's online connected world, almost all corporate networks use some form of perimeter firewalls to manage Internet connections and enforce a security policy at the corporate gateway. Although it can considerably enhance network security and protect business-critical information, a firewall with thousands of rules can become a bottleneck for network performance. The primary goal of this paper is to present a new rule order optimizer based on simulated annealing to find optimal configurations that minimize the average number of rule comparisons while preserving precedence relationships among disjoint rules. The proposed approach is evaluated and its effectiveness is compared with another approximate solution under several firewall configurations and policy profiles
A Reconfigurable Broadcast Scan Compression Scheme Using Relaxation Based Test Vector Decomposition
Get PDFIn this paper, we propose an effective reconfigurable broadcast scan compression scheme that employs partitioning and relaxation-based test vector decomposition. Given a constraint on the number of tester channels, the technique classifies the test set into acceptable and bottleneck vectors. Bottleneck vectors are then decomposed into a set of vectors that meet the given constraint. The acceptable and decomposed test vectors are partitioned into the smallest number of partitions while satisfying the tester channels constraint to reduce the decompressor area. Thus, the technique by construction satisfies a given tester channels constraint at the expense of increased test vector count and number of partitions, offering a tradeoff between test compression, test application time and test decompression circuitry area. Experimental results demonstrate that the proposed technique achieves better compression ratio in comparison to other test compression techniques
Theoretical Analysis of Magnetically switchable shorted patch antenna
Get PDFSwitchable magnetic media and shorting posts are popular in controlling the radiation characteristics and the size of microstrip antennas or array. In this paper, a ferrite based shorted patch antenna is designed to demonstrate magnetically switchable frequency response. Simulated resonance and radiation responses of the probe feed antenna revealed improved impedance bandwidth, antenna size reduction, tunable and non-tunable switched resonance and low biasing requirement for switching the antenna
“Three Dimensional Full-Vectorial Analysis of Strong Optical Waveguide Discontinuities Using Padé Approximants”
No full textA full-vectorial 3-D numerical method applicable to high-index contrast optical waveguide discontinuities is presented. Rigorous treatment of the longitudinal boundary condition is incorporated in the formulation. The square root of the characteristic matrix is approximated using Padé approximants which results in an efficient implementation. The biconjugate gradient stabilized method is utilized to iteratively calculate the reflected and transmitted fields. A preconditioner is proposed which results in reduced number of iterations. The proposed method is applied to various optical waveguide facets exhibiting strong transverse and longitudinal refractive index discontinuities. In all cases, the modal reflectivities of the fundamental TE-Like and TM-Like modes are calculated for both the full-vectorial and the semivectorial formulations. Significant difference in the calculated modal reflectivity is seen between the full and semi-vectorial models. The error in the power balance remains low in the full-vectorial case irrespective of the waveguide dimensions. However, in the semi-vectorial case, the error in the power balance is found to increase when the waveguide width is reduced
An Approximate Analysis of Buffered S-ALOHA in Fading Channels Using Tagged User Analysis
No full textTagged user analysis (TUA) is a generic approximate method of analyzing random access protocols for finite-user finite-buffer systems. This technique decouples the channel contention behavior from the user queuing behavior and allows the use of classical queuing theory results to be directly applicable to the analysis of finite-user finite-buffer random access methods. In this paper, we extend TUA to analyze finite buffer S-ALOHA operating over flat fading radio channels and derive expressions for system performance indices like throughput, average packet delay, blocking probability and queue length. It is shown that for a moderate number of active users, the simulation and analytical results fit closely