IRANIAN JOURNAL OF ELECTRICAL AND COMPUTER ENGINEERING (IJECE)
Year:2003 | Volume:2 | Issue:2|Papers Count:10

Discrete multitone (DMT) is a line code which has been adopted as a standard for the asymmetric digital subscriber line (ADSL) systems by the American National Standards Institute (ANSI). The DMT uses the IFFT and FFT for modulation and demodulation, respectively. The large size of the IFFT/FFT results in a heavy computational load on the programmable DSP processors. It also proves that a costefficient hardware implementation of radix-2 IFFT/FFT butterfly structure is not feasible, since it requires a large number of multipliers and adders. For cost-efficient hardware implementation, we have proposed two schemes to develop the IFFT/FFT architecture based on the time-recursive approach. In fact, these methods require approximately a maximum of only 12.5% of the multipliers and 15.6% of the adders when compared to the conventional butterfly type of implementation.

Non-linear image processing operators give excellent results in a number of image processing tasks such as restoration and object recognition. However they are frequently excluded from use in solutions because the system designer does not wish to introduce additional hardware or algorithms and because their design can appear to be ad hoc. In practice the median filter is often used though it is rarely optimal. This paper explains how various non-linear image processing operators may be implemented on a basic linear image processing system using only convolution and thresholding operations. The paper is aimed at image processing system developers wishing to include some non-linear processing operators without introducing additional system capabilities such as extra hardware components or software toolboxes. It may also be of benefit to the interested reader wishing to learn more about non-linear operators and alternative methods of design and implementation. The non-linear tools include various components of mathematical morphology, median and weighted median operators and various order statistic filters. As well as describing novel algorithms for implementation within a linear system the paper also explains how the optimum filter parameters may be estimated for a given image processing task. This novel approach is based on the weight monotonic property and is a direct rather than iterated method.

The main objective of this paper is to develop component model architecture to construct a distributed environment through which the contingency selection for voltage security analysis, line overloads and the reactive power limit violations of multiple power systems can be monitored and controlled. A component, which is based on single-server serving multiple clients, has been proposed. It enables all neighboring power systems can have simultaneous access to the remote contingency server at any time, with their respective data and is able to get the contingency ranking based on their performance indices. An EJB (Enterprise Java Beans) based distributed environment has been implemented in such a way that each power system client can access the remote contingency EJB server through JNDI (Java Naming and Directory Interface) naming service with its system data. The server conducts the contingency analysis and it provides the continuous automated critical contingency ranking list based on performance index to all the registered power system clients. EJB server inherently creates a new thread of control for every client request and hence a complete component based distributed environment has been achieved.

The present article describes a new concept to detect the cephalic position. This concept conceives a methodology of low cost computational and provisional that it allows a man-machine communication, based on the localization of the voluntary cephalic position. The program works with image processing and the cephalic position has a rate of 1/50 of second. The system does not require calibration and the user just requires an emitter which has a weight smaller to 2 grams to interact.

The performance of a quasi-optimum distance based downlink power control model is evaluated for high altitude platform station (HAPS) W-CDMA systems using 19 cells model. We have generalized a previous model proposed by Gejji. The downlink capacity using our model is higher than the capacity evaluated using the old model.

The downlink power control problem in WCDMA is studied using two new models. The downlink cell capacity is given for the old given by Gejji and our new models. A capacity increase of 6.8% for the special case j= 0 (no orthogonality between users) and a generalization of the old model are obtained using the second new model.

The demand for mobile communication has been increasing rapidly from day to day. Resulting from this interest, many researches and studies have been conducted for the prediction of the effects of mobile communication on the human health. In this research, mobile propagation measurements are carried out in both side-base stations and mobile phones at 900 MHz. Using the results obtained from these experiments, some statistical properties such as averages and standard deviations of the electric field for various mobile phones are determined. Measurements are repeated for different base stations and mobile phones to obtain more realistic data to calculate important statistical parameters in the mobile systems. The widely used mobile phones in Turkey are selected in the experiments. Risk probabilities for human health are calculated using the standard values existing in the literature. It is not any risk on idle mode but some mobile phones have 100% risk on call setup and active modes for human health.

This commentary discusses the reasons for the very large variation in exposure limits for radiofrequency energy that are in effect throughout the world, which reflect deep philosophical differences about managing risk. There are important practical and philosophical reasons to harmonize exposure limits, but this goal will not be easily achieved.

This paper develops a flux-linkage estimator using voltage model in stator reference based on an improved integrator with DC-offset PI-correction loop having the reference flux magnitude in the correction error. The DCoffset and drift from acquisition channels and the flux-vector initial error are canceled. A phase locked-loop state estimator extracts the speed and position from the estimated rotor flux. This robust solution can be applied in all AC drives with sinusoidal flux distribution in wide speed range, including sensorless control. A sensorless DTC is investigated for both PMSM and IM drives. Simulation results for PMSM drive and also experimental results for IM drive prove highdynamic performances in large speed range step reversal, for zero to rated load-torque step.

A teacher of Computer Science and Mathematics has two options: use precious classroom time in routine operations and boring formulas, thus killing the interest of students and hampering their intellectual development, or challenge their curiosity by formulating interesting and stimulating questions giving them a taste for independent thinking. The teacher need only provide the building blocks and let students themselves form more complex structures, providing them timely hints when needed. In this paper we demonstrate how a very simple procedure can be used, with minor modifications, as a building block to solve a variety of seemingly unrelated problems in the field of graph algorithms.