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Volume 15, Issue 2, 2008
Electrical and Computer Engineering


An 8-Bit Current-Mode Folding ADC with Optimized Active Averaging Network
 
        M. Azin (PhD.)
  • M. Sharif Bakhtiar [PhD.]

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In this paper, an 8-bit CMOS current-mode folding-interpolating ADC is presented. A new active averaging-interpolating network is described, which results in a better error correction factor compared to its resistive counterpart. Using novel circuits for fast settling and careful transistor sizing, a fast (>160 Msps) and low power (70 mW in 2.5 V supply voltage) 8-bit ADC, with a total chip area of 1  1:4 mm in a 0.25 micron CMOS process, is demonstrated.


A New, Publicly Veri able, Secret Sharing Scheme
 
        T. Eghlidos (PhD.)
  • A. Behnad [PhD.]

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A Publicly Veri able Secret Sharing (PVSS) scheme, as introduced by Stadler, has a feature where anyone, besides the participants, can verify the validity of the shares distributed by the dealer. Schoenmakers added a new feature, by providing a proof of correctness of the shares released by the players in the reconstruction process. This protocol is claimed to be an improvement on Stadler's and Fujisaki-Okamoto's, both in eciency and in the type of intractability assumptions. However, Young-Yung improved Schoenmakers' PVSS, using a Discrete-Log instead of a Decision Die-Hellman. In this paper, a new PVSS is presented, having an intrinsic di erence with its predecessors, that is, the participants can prove the validity of their given shares, implicitly, proving their membership by a zero-knowledge protocol. This feature prevents cheaters from participating in the reconstruction process to gain valid shares. Hence, the new proposed PVSS is more secure than previous ones. Besides, the dealer only sends the amount of commitments limited to the threshold value, regardless of the number of shareholders

    this leads to a more dynamic protocol.


Analytical Mode Distributions and Resonant Frequencies in Ladder Networks Used in Power Combining Oscillator Arrays
 
        F. Farzaneh (Professor)
  • M.H. Akbarpour [PhD.]
  • A. Banai [PhD.]

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An analysis of resonant modes in ladder networks is performed using di erence equations. Linear and loop con gurations are studied and analytical relations are derived for the mode distributions and resonant frequencies of these networks, having arbitrary elements. Furthermore, it is shown that a) Modes with an exponential distribution along network nodes may exist in some cases and b) The mode distributions in loop networks are independent of network elements. Finally, a simple criterion is obtained for a loop structure to control the spacing between resonant frequencies.


Direct Introduction of Semicon Layers in a Cable Model
 
        M. Hasheminezhad (PhD.)
  • M. Vakilian [PhD.]

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The detection and location of any Partial Discharge (PD) signal requires an accurate frequency dependent cable model to correctly simulate the PD signal attenuation during its propagation in the cable. This model should be capable of simulating the semiconducting layers, which have signi cant e ects on PD signal attenuation and its propagation velocity. There is a substantial need for improvements in the exibility of the transient cable model through direct introduction of the two semiconducting layers in the cable model. This can be employed in the next step to develop a 3-phase cable model for ATP. This paper has derived an impedance formula for the semiconducting layers. The propagation characteristics of the PD signal, in a cable having two semiconducting layers, are evaluated by applying the derived formula and are compared with the related characteristics in a cable with no semiconducting layer. The propagation of a PD signal applied to the sending end of the core conductor is investigated. In the application of the semicon pick-up sensor in the cable joint, there would be a considerable high frequency voltage across each semiconducting layer, which can be used for the study of PD phenomenon.


A Variational Iteration Method for Solving Systems of Partial Di erential Equations and for Numerical Simulation of the Reaction-Di usion Brusselator Model
 
        Y. Jalilian (PhD.)

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In this work, systems of linear and nonlinear partial di erential equations and the reactiondi usion Brusselator model are handled by applying the variational iteration method. The Variational iteration method has the advantage of being more concise for analytical and numerical purposes. The results reveal that the method is very e ective and convenient.


A Two-Class M/M/1 System with Preemptive Non Real-Time Jobs and Prioritized Real-Time Jobs under Earliest-Deadline-First Policy
 
        M. Kargahi (PhD.)
  • A. Movaghar [PhD.]

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This paper introduces an analytical method for approximating the performance of a two-class priority M=M=1 system. The prioritized class-1 jobs are real-time, served either with the preemptive or non-preemptive Earliest-Deadline-First (EDF) policy and can preempt the non real-time class-2 jobs. The preempted service of the class-2 job is resumed from the time in instances where no class-1 job is in the system. The service discipline of class-2 jobs is FCFS. The required mean service times may depend on the class of the jobs. The real-time jobs have exponentially distributed relative deadlines until the end of service. The system is approximated by a Markovian model in the long run, which can be solved numerically, using standard Markovian solution techniques. The performance measures of the system are the loss probability of the class-1 jobs and the mean sojourn (waiting) time of the class-2 jobs. Comparing numerical and simulation results, it is found that the existing errors are relatively small.


Principal Color and its Application to Color Image Segmentation
 
        S. Kasaei (PhD.)
  • A. Abadpour [PhD.]

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Color image segmentation is a primitive operation in many image processing and computer vision applications. Accordingly, there exist numerous segmentation approaches in the literature, which might be misleading for a researcher who is looking for a practical algorithm. While many researchers are still using the tools which belong to the old color space paradigm, there is evidence in the research established in the eighties that a proper descriptor of color vectors should act locally in the color domain. In this paper, these results are used to propose a new color image segmentation method. The proposed method searches for the principal colors, de ned as the intersections of the cylindrical representations of homogeneous blocks of the given image. As such, rather than using the noisy individual pixels, which may contain many outliers, the proposed method uses the linear representation of homogeneous blocks of the image. The paper includes comprehensive mathematical discussion of the proposed method and experimental results to show the eciency of the proposed algorithm.


The E ect of an Interline Power Flow Controller (IPFC) on Damping Inter-area Oscillations in Interconnected Power Systems
 
        A. Kazemi (PhD.)
  • E. Karimi [PhD.]

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The e ect of an Interline Power Flow Controller (IPFC) on damping low frequency oscillations has been implied in some papers, but has not been investigated in detail. This paper investigates the damping control function of an interline power ow controller installed in a power system. For this purpose, a single machine-in nite bus model, integrated with IPFC, is used and the linearized model is established. Using this model, the Phillips-He ron model of the system for steady state digital simulations is derived. In this paper, the numerical results are presented using the MATLAB simulink toolbox, which shows the signi cant e ect of IPFC on damping inter-area oscillations.


On Domination and its Forcing in Mycielski's Graphs
 
        D.A. Mojdeh (PhD.)
  • N. Jafari Rad [PhD.]

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In this paper, for a given graph, G, some domination parameters and the forcing domination number of the graph, M(G), obtained from G arising in Mycielski's construction, are studied.


New Wavelet-Based Approach for Internal Fault Current Identi cation in Power Transformers
 
        H. Monsef (PhD.)
  • S. Lotfifard [PhD.]

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This paper demonstrates a novel approach for the di erential protection of power transformers. This method uses the Wavelet Transform (WT) and the Adaptive Network-based Fuzzy Inference System (ANFIS) to detect a fault current from an inrush current. The proposed method has been designed, based on the di erences between the amplitudes of wavelet transform coecients in a special band of frequency that is caused by faults and inrush currents. The performance of this algorithm has been simulated and tested under di erent conditions of the switching on of power transformers, using the PSCAD/EMTDC environment software.


Variable, Step-Size, Block Normalized, Least Mean, Square Adaptive Filter: A Uni ed Framework
 
        S.Z. Moussavi (PhD.)
  • M. Shams Esfand Abadi [PhD.]
  • A. Mahlooji Far [PhD.]

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Employing a recently introduced framework, within which a large number of classical and modern adaptive lter algorithms can be viewed as special cases, a generic, variable step-size adaptive lter has been presented. Variable Step-Size (VSS) Normalized Least Mean Square (VSSNLMS) and VSS Ane Projection Algorithms (VSSAPA) are particular examples of adaptive algorithms covered by this generic variable step-size adaptive lter. In this paper, the new VSS Block Normalized Least Mean Square (VSSBNLMS) adaptive lter algorithm is introduced, based on the generic VSS adaptive lter. The proposed algorithm shows the higher convergence rate and lower steady-state mean square error compared to the ordinary BNLMS algorithm.


Design of an Automatic Alignment System for Video Displays Using an Adaptive Alignment Algorithm
 
        A. Peiravi (PhD.)
  • S. Toosizadeh [PhD.]

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One of the critical stages in a display production line is the image alignment of displays that includes the precise adjustment of the geometric parameters and the color of the image. The mutual in uences of the parameters of the display's image necessitate a complex and interactive alignment process. In this paper, the e ect of the mutual in uences of geometric parameters on the alignment process of a display's image are shown, a suitable model for the geometric characteristics of a display's image are suggested and, then, the unknown parameters of the proposed model are estimated by the RLS estimator. Using an o -line estimator, an initial measure of the values of the unknown parameters of the display model is obtained. To modify the model parameters of the consecutive video displays on the production line, an on-line estimator is applied. Variations of the parameters of the display model on a production line are traced using on-line estimation. This model estimation is used to implement an adaptive alignment algorithm. Both the adaptive and the proportional alignment processes have been experimentally implemented under similar working conditions. Experimental results show that the use of the adaptive alignment process considerably increases the speed and reliability of convergence of geometric parameters to their desired values. An IA-32, 3.4 GHz Pentium P4 processor has been used in this research. Considering the rapid developments in UDSM technology and the IA-64 architecture, the application of the proposed adaptive alignment algorithm in an auto-alignment system has the potential for real-time implementation in the near future.


A Programmable GPS Receiver with Test Circuits in 0.18 m CMOS
 
        N. Riahi (PhD.)
  • M. Jenabi [PhD.]
  • A. Fotowat Ahmady [PhD.]

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A 0.18 m single chip GPS receiver, with 19.5 mA current consumption, is implemented in 6.5 mm2. Low-IF architecture was used for a high level of integration and low power consumption. A serial input digital control, with additional testing structure, not adding more than 4% to the Si area, is used in the actual RF circuits, in case of problems, minimizing the number of Si runs.


On the Existence of Periodic Solutions for Nonlinear Ordinary Di erential Equations
 
        D. Shadman (PhD.)
  • B. Mehri [Professor]

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In this paper, the existence of periodic solutions of autonomous ordinary di erential equations of a 4th and 5th order is investigated. The method used is based on the Brower's degree theorem using the homotopy invariant a property of a topological degree.


GLR Detector for Coded Signals in Noise and Interference
 
        A.A. Tadaion (PhD.)
  • M. Derakhtian [PhD.]
  • M.M. Nayebi [PhD.]
  • M.R. Aref [PhD.]

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In this paper, the detection of a coded signal in additive white Gaussian noise and the interference is studied, where there is no knowledge about the correlation between the received symbols and about the noise and interference parameters. The Maximum Likelihood (ML) estimates of the unknown parameters are found, they are substituted in the probability density functions of the observation and the Generalized Likelihood Ratio (GLR) detector is derived. This detector can also be used for the activity detection of a signal in unknown Inter-Symbol Interference (ISI). In this case, the interference is modeled as the unknown correlation between the received symbols. Simulation examples are performed to evaluate the performance of the proposed detector.