سال:1384 | دوره: | شماره: |تعداد مقالات:11

ATM as a high-speed cell switching technology can support multiple classes of traffic with different quality of service (QoS) requirements and diverse traffic characteristics. A main QoS requirement is the cell loss ratio (CLR). We need an expression for the CLR calculation in ATM networks where the statistical multiplexing is an important factor. The existing analytical methods for the CLR estimation are mostly based on fluid-flow and stationary approximation models. In this paper, we first evaluate these methods against the results obtained through simulation. The simulation is done at the cell level that provides very accurate results with buffer size as a variant. It is shown that the CLR estimation based on existing analytical models are widely overestimated. We have, then, proposed two new approaches that yield significant improvement in the accuracy of the CLR approximation. First, we have found global correction coefficients to compensate for the error of the current analytical methods. Second, we have proposed a new upper bound based on exact modeling of system behavior in the finite buffer case. This is a novel approach that combines fluid-flow and stationary approximation models and outperforms all the previous ones. The accuracy of the proposed model is verified by simulation.

In this paper we have presented a robust watermarking procedure for digital audio. The procedure embeds a watermark imperceptibly in the time domain exploiting the temporal and simultaneous masking properties of the human auditory system (HAS). The spectral characterization of the audio is done using the short time Fourier transform (STFT), which provides a better description of non-stationary signals when compared to using the discrete Fourier transform. The watermark is a perceptually shaped pseudorandom sequence, which is used to modify the audio samples. The original audio is not required during the extraction of the watermark, except when the audio signal is subjected to cropping attack. The watermarking procedure exhibits resilience towards several audio distortions occurring from MPEG 1 Layer 3 coding, colored noise, cropping, temporal resampling and jittering.

In this paper an optimized E-shaped patch antenna is presented, the bandwidth of the E-shaped microstrip antenna is optimized using the genetic algorithm (GA) based on fuzzy decision-making. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters such as recombination to produce the next generation. Fuzzy inference system is used for the control of the parameters of the genetic algorithm. Simulation results show the high ability of genetic optimization based on fuzzy system for about 33% BW. Dimensions of the slots have been optimized with the novel design approach presented herein. A prototype element is also constructed in order to validate the approach. The measured results on fabricated antenna structure are in reasonable agreement with theoretical calculations and simulation predictions.

A new type of interconnect structures called S-L-S (Signal-Load-Signal) interconnects is proposed. In these interconnect structures an extra loaded line is inserted between two signal traces. The performance of these interconnects is studied and compared for some values of the load of the loaded lines in order to get efficient and wideband interconnects.

This paper concentrates on the error rate analysis of wireless communication systems with diversity combining to derive exact closed-form expressions for QAM and PSK signals in order to provide system designers a precise and more convenient evaluation. Maximal ratio combining (MRC) with L independent and identical (i.i.d) diversity reception paths over slowly Nakagami-m fading channel is considered. The novel results obtained in this paper, via moment generation function (MGF) approach overcome the limitations of earlier works both in terms of generality and ease of simulation as they are presented in integral-free forms. At the end, several numerical results are included.

High performance induction motor (IM) drive system fed from space vector pulse width modulated (SVPWM) inverter and based on optimal preview control theory is realized. The synthesized control algorithm achieves motor speed control, constant flux control and field orientation control via an optimized control input command contains the synchronous angular speed and the two synchronously rotating components of the stator voltage vector. The novel error system used in building the optimal preview controller can cure the adverse phenomena caused by parameter uncertainty and unmodeled dynamics. With few feature values of the desired and disturbance signals the transient performance can be improved. A laboratory prototype was built and the overall control system is implemented using low cost multifunction data acquisition card (DAC). Where, the SVPWM switching patterns representing the control input command is realized by generating successive sector dependent digital words on DAC digital lines. Accordingly, the storage memory is minimized and the sawtooth carrier generator is eliminated. Extensive experimental results have been carried out to show the effectiveness and applicability of the proposed control system.

A simple method for estimating rotor resistance in an indirect vector-controlled induction motor drive is proposed in this paper. The proposed rotor resistance estimator which uses fuzzy logic principle is based on the improvement of control performance when mismatch between estimated rotor resistance and actual one occurs. Analysis, design, and digital simulations are carried out to demonstrate the effectiveness of the proposed estimator. Moreover, simplicity and direct approach for estimating the rotor resistance are other significant features for the described method.

The paper analyses current unbalance caused by loads connected either to line or phase voltages. Follow-up voltage unbalance is calculated for receiving end of HV line. Different definitions of balanced system of phasors are discussed and illustrated by examples. Current unbalance factors for all possible load connections are described and analysed in detail and the ranges of their possible values are determined. Also formulae for these factors are shown for two single-phase loads.

Ever since inception, the electric power and communication systems are exposed to dangerous overvoltage surges starting from lightning to service frequency temporary overvoltage waves with disastrous consequences. The operation of electronic devices in this environment had led to a situation wherein they are severely affected. All sorts of electronic equipment are at risk: these calls for an effective protection against transient overvoltages. It includes adequate equipment protection, inherent capability of the equipment to withstand overvolage surges, good installation and a sound earthing arrangement. This paper describes an incident involving the exposure of wireless equipment and the operating personnel to frequent lightning activities in a hilly place and the need of a good installation practice, better earthing and adequate protection against direct lightning strokes.

An Intelligent Particle Swarm classifier (IPSclassifier) is proposed in this paper. This classifier is described for finding the decision hyperplanes to classify patterns of different classes in the feature space using particle swarm optimization (PSO) algorithm. An intelligent fuzzy controller is designed to improve the performance and efficiency of proposed swarm intelligence based classifier by adapting three important parameters of PSO (i.e., swarm size, neighborhood size, and constriction coefficient). Three pattern recognition problems with different feature vector dimensions were used to demonstrate the effectiveness of the proposed classifier. They are the Iris data classification, the Wine data classification, and radar targets classification from backscattered signals. The experimental results show that the performance of the IPS-classifier is comparable to or better than the k-nearest neighbor (k-NN) and multi-layer perceptron (MLP) classifiers, which are two conventional classifiers.

In this paper, the step track subsystem, suitable for geosynchronous orbit (GEO) satellites, is simulated. By using Standard MATLAB® Package and its features such as Simulink toolbox, Data Acquisition toolbox, Real Time Workshop (RTW) and Real Time Windows Target (RTWT), it is possible to completely simulate a control system. Also, by using these properties it is possible to construct a practical real-time system, change its parameters and view their effects on the system during operation.