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Volume 11, Issue 3, 2004
Electrical and Computer Engineering


On Routing Architecture for Hybrid FPGA
 
        M. Nadjarbashi (PhD.)
  • S.M. Fakhraie [PhD.]
  • A. Kaviani [PhD.]

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In this paper, the routing architecture for an FPGA with hybrid clusters built from a mixture of LUT-based and PLA-like blocks is investigated. The implemented CAD flow that is used to place and route a number of MCNC benchmark circuits in a comparative fashion is discussed. The experimental results demonstrate that cluster sizes of two (2 LUT blocks and 2 PAL blocks) to four (4 LUT blocks and 4 PAL blocks) are appropriate in terms of area and speed. A comparison between hybrid and LUT-based FPGA architectures is also presented, showing that hybrid FPGA has some considerable advantages over a uniform LUT-based architecture.


Designing a Communication Network Using Simulation
 
        S.T. Akhavan Niaki (PhD.)
  • Z. Besharati-Rad [PhD.]

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In this paper, a private telephone communication network of an electrical energy distribution company has been studied analytically and through discrete event system simulation. Considering the pitfalls and difficulties associated with the analytical approach in designing such a network and the power and


Periodic Solution of a Certain Non-Linear Third Order Differential Equation
 
        B. Mehri (PhD.)
  • D. Shadman [PhD.]

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In this paper, the third order differential equation x'''+\psi(x')x''+(k^2+\phi(x))x'+f(t,x)=e(t) is considered. Under certain conditions on the functions appearing in the differential equation, the existence of periodic solutions is proved. Similar problems have been treated by authors in [4,6,7]. However, the method employed here is used by Reissig [1] and the results obtained are, in fact, a generalization of those in [1-3]. The conditions imposed on the nonlinear terms do not require the ultimate boundedness of all solutions.


Optimal Planning of Equipment Maintenance and Replacement on a Variable Horizon
 
        F. Kianfar (PhD.)

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In maintenance and replacement planning of an industry, the purchasing of new equipment on the market with some kind of technological improvement over existing equipment should be taken into account. Because of operating cost, ordinary and preventive maintenance expenses may be lower, production rate may be higher and the quality of output may be better, etc. The industry to be considered in this paper is the mining industry and the replaced equipment is the mine shovel. It is assumed that, at most, one new shovel can be purchased before the mine is exhausted. It is possible that the mine is given up before exhausted, because of the disadvantage of the expense and loss of the salvage value of the shovel compared with the value of the remaining mine. There are four decision variables in this problem, as follows: the aintenance policy in each period, the purchase time of the new shovel, the end of the planning horizon or the time to stop the mining and the value of production during each period. The objective is to determine the values of the decision variables so as to maximize the overall discounted profit of the mine over the planning horizon.


Performance Comparison of Admission Control Policies for New Calls in Soft-Handoff Regions for CDMA Cellular Networks
 
        F. Ashtiani (PhD.)
  • M.R. Aref [PhD.]
  • J.A. Salehi [PhD.]

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In this paper, two basic new call admission control policies in soft-handoff regions in Code-Division Multiple-Access (CDMA) cellular networks are compared. The two policies are Independent Decision Policy (IDP), which is, approximately, equivalent to a directed retry policy proposed for non-CDMA cellular networks and Collective Decision Policy (CDP). The merits in this comparison include the tradeoff between carried traffic and quality loss probability while maintaining other traffic parameters (such as blocking and dropping (handoff failure) probabilities) sufficiently low. Using numerical results, it is deduced that the CDP leads to a better overall performance. Another important issue considered in this paper reverts to spatial fairness. In this respect, the necessary modification for the above admission policies is proposed. In these analyses, a modified reverse link dynamic traffic model is employed, built upon Interference-based Call Admission Control (ICAC), by including the shadowing effect in soft-handoff regions.


Simplification of Boolean Functions Using Boolean Differences
 
        M.B. Ghaznavi-Ghoushchi (PhD.)
  • A.R. Nabavi [PhD.]

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This paper presents a new method for simplification of Boolean functions based on Boolean differences. The proposed method is applicable to various forms of Boolean functions, including truth tables and Binary Decision Diagrams (BDDs). The Boolean differences are extended to cover the truth tables with don't-care components and cutset graphs in BDDs. The results of simplification agree with Quine-McCluskey and ESPRESSO methods. Experimental tests on MCNC and Berkeley PLA benchmarks show that the proposed method gains a performance of 1.5-10 times faster than ESPRESSO. The algorithms of the proposed method are implemented in Java/Perl/C++, and a toolset for logic function simplification is developed.


Syllable Duration Prediction for Farsi Text-to-Speech Systems
 
        B. Nazari (PhD.)
  • K. Nayebi [PhD.]
  • F. Sheikholeslam [PhD.]

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In this paper, two different statistical approaches are used for duration prediction of the Farsi language. These two statistical models are Neural Networks (NN) and Classification And Regression Trees (CART). The first step in this work was to create a database and develop a flexible feature extraction and selection module. In the next step, the output of the feature selection module was used to train both models. The results of the trained models are further studied to determine the most important parameters affecting the syllable duration in Farsi. The model accuracy is evaluated by using separate training and test data. In the third step of this work, an automatic rule generator module was added to the CART model. These duration prediction rules can be easily applied in a rule-based speech synthesis system.


Power System Frequency Estimation Based on Simulated Annealing: A Variable Frequency Model
 
        S.A. Soliman (PhD.)
  • R.A. Alammari [PhD.]
  • A.H. Mantaway [PhD.]
  • M.E. El-Hawary [PhD.]

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This paper presents a new technique for measuring power system frequency, rate of change of frequency and the voltage amplitude and phase angle using the Simulated Annealing (SA) based optimization algorithm. The algorithm uses the digitized samples of the voltage signal at the relay location and minimizes a cost function of the sum of the absolute error between the actual estimated signal samples. The proposed algorithm does not need any filter or model for the system frequency before and during the estimation process. The effects of the number of samples, sampling frequency and harmonics contamination on the estimated parameters are tested and discussed in the paper.


Analysis and Compensation of Receiver Non-Idealities in Wireless OFDM Transceivers
 
        H. Shafiee (PhD.)
  • S. Fouladifard [PhD.]

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High rate wireless communication systems require the design of low-cost radio transceivers with low power consumption. Various architectures for the down conversion of the radio frequency signal to baseband exist. But, with varying degrees, all radio receivers introduce certain non-ideal characteristics of their own, including DC offset, IQ mismatch, frequency offset and phase noise. In this paper, the impact of such non-ideal receiver effects on the performance of an OFDM wireless communication system are investigated. Techniques for compensation or mitigation of such phenomena are discussed and novel methods are proposed.


Iterative Interference Cancellation for a Coded Multicarrier Frequency-Hopping CDMA (MC-FH-CDMA) System
 
        M. Nasiri-Kenari (PhD.)
  • M. Ebrahimi T.M. [PhD.]

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In this paper, a low complexity iterative multi-user receiver for the coded MC-FH-CDMA system, is considered, which has been introduced in [1]. The structure of the proposed receiver consists of a Multi-User Likelihood Calculator (MULC) and a bank of SISO channel decoders, one for each active user. Based on the received signal and a priori information about code bits, provided by SISO decoders in the previous iteration, MULC computes the extrinsic information of the coded symbols of active users in the form of a Log-Likelihood Ratio (LLR). This information is used by channel decoders as a priori information to compute an update of LLRs. The processing proceeds in an iterative manner, similar to the decoding of turbo codes. The performance of the proposed receiver is evaluated in AWGN channels. The numerical results show that the new receiver significantly improves system performance, compared to the conventional single user receiver.


Extended Energy Approach to Propagation Problems in General Anisotropic Media
 
        B. Rashidian (PhD.)
  • S. Khorasani [PhD.]

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In this article, a new general approach has been presented for exact and efficient extraction of eigenpolarizations in anisotropic electromagnetic media with arbitrary constitutive relations. It is shown that the plane wave propagation eigenpolarizations in a linear homogeneous time-independent anisotropic media without free sources, can be obtained through extremizing the difference between stored electric and magnetic energies as a variational functional. It is demonstrated that at these stationary points the wave equation is satisfied by showing that each of the Maxwell curl equations may be obtained by using the other equation as a constraint. Furthermore, it is proven that the theorem holds for extrema of the stored electric energy independently, when the medium is magnetically isotropic. It is concluded that when at least one of the permittivity and permeability tensors are scalar, both the total of and the difference between electric and magnetic energies are extremized simultaneously. As an example, the eigenpolarizations in a non-magnetic anisotropic medium with optical activity are obtained.


Capacity Analysis of a CDMA Cellular System with Mixed Cell Sizes and Imperfect Power Control
 
        H. Rohi (PhD.)
  • M.R. Aref [PhD.]
  • M.E. Kalantary [PhD.]

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The demands for mobile communication services are growing rapidly. In heavily populated areas, cell splits are necessary to increase the capacity of cellular systems. Cell splitting causes a cellular system to have mixed cell sizes. Calculation of the reverse link capacity of CDMA cellular systems with mixed cell sizes and imperfect power control is presented in this paper. When a macro cell is split into micro cells, the capacity of a non-uniform cellular system has been calculated, together with the calculation of micro and neighboring macro cell capacity. The computer simulation results show that with the reduction in radius of a micro cell, its capacity increases, while that of the neighboring macro cells decreases.