IRANIAN JOURNAL OF ELECTRICAL AND COMPUTER ENGINEERING (IJECE)
Year:2006 | Volume:5 | Issue:1|Papers Count:11

Large volumes of fingerprints are collected and stored every day in a wide range of applications, including forensics, access control etc., and are evident from the database of Federal Bureau of Investigation (FBI) which contains more than 70 million finger prints. Wavelet based Algorithms for image compression are the most successful, which result in high compression ratios compared to other compression techniques. Even though wavelet bases are providing good compression ratios, they are not optimal for representing images consisting of different regions of smoothly varying grey-values, separated by smooth boundaries. This issue is addressed by the directional transforms, known as contourlets which have the property of preserving edges. This paper focuses mainly on the new fingerprint compression using contourlet transform (CT), which includes elaborated repositioning algorithm for the CT coefficients, and Modified set partitioning in hierarchical trees (SPIHT) which is applied to get better quality, i.e., high peak signal to noise ratio (PSNR). The results obtained are tabulated and compared with those of the wavelet based ones.

Wireless communications and networking have had tremendous developments in recent years. Recently, some proposals are presented in the literature to build hybrid structures out of different wireless systems. Also, architectures have been proposed for co-operating cellular and WLAN systems. Due to high complexity of mobile networks, proposed protocols and algorithms are usually evaluated by simulations. In these simulations, when real mobility is considered, a certain mobility model must be used. A number of mobility models have been proposed for ad hoc networks. Different mobility models have different properties in terms of node distribution, stability and reality. In a cellular system, hotspots are locations with a large number of subscribers. In hybrid WLAN/Cellular systems, WLANs are used to cover the hotspots. Evaluation of the performance of these hybrid networks should be performed through simulations or analytical modeling. Therefore, special mobility models are needed for this purpose. In this paper, we propose a mobility model based on the original version of random waypoint. This model is applicable for the simulating of the hybrid WLAN/Cellular systems. The proposed strategy is analyzed through simulations and analytical modeling.

In this paper, we develop a new error-resistant secure lossless source coding scheme for discrete sources. Recent results indicate that the same turbo principle that provides sub-optimal strategy for channel coding, can be used to obtain efficient source coding schemes. We extend the source turbo-coding idea to include security for transmission of the compressed data and also to ensure the lossless recovery of information at the receiver. Compression and security are achieved by adapting the random puncturing strategy to the statistics of the source. Lossless compression is guaranteed by finely puncturing the encoded data of a parallel-concatenated turbo code while verifying the integrity of the source information at the source encoder. Simulation results show that the proposed scheme can obtain a compression rate close to the source entropy. For the same block length, this scheme yields better compression rates in comparison with the Lempel-Ziv universal source coding. The proposed scheme has a robust and error-resistant performance over noisy channels for Eb/N0>5 dB.

A high-Q time-variant (TV) band-pass filter (BPF) is analyzed in this paper. N parallel identical low-pass RC filters make this BPF, in which each of these N filters is sequentially switched on for an equal time interval, periodically. The resulting BPF provides a stable frequency response and is insensitive to element variations. Through mathematical analysis, equations are derived for the frequency response and the bandwidth of the BPF. Moreover, the validity of these equations is confirmed by experimental results. These equations make the design of the above high-Q BPF an easy task.

This paper proposes to use variable time steps in circuit envelope simulation. The circuit envelope is a general-purpose simulation technique for the transient and steady state analysis of microwave communication systems and circuits. When a microwave circuit is excited with a time variant envelope signal as digital modulated signal, circuit envelope simulation method may be used. In this paper a new technique is proposed to improve the efficiency of the circuit envelope simulation. Using this technique, a millimeter wave power amplifier is simulated and its results are presented. The evaluation of the results with the existing literature proves the accuracy and efficiency of the new technique.

Transient visual evoked potential (TVEP) has been used as one of the valuable diagnostic tool in clinical environment. Various types of analyze have been performed on TVEP recordings for identifying diagnostically significant information. Conventional methods of detection of visual anomalies, based on TVEP require long periods of testing and averaging. Hence the problem of patient fatigue affects the accuracy of the results. This paper presents an approach to analysis TVEP latency using spectral components. This new approach was successfully tested on 300 normal and 450 abnormal subjects with certain disorders to identify the change in latency.

In this paper, the authors have proposed a 3×3 planar array of water-loaded box-horns for hyperthermia treatment of tumor. The box-horn consists of a TE10 mode H-plane sectoral-horn coupled to a length L of rectangular waveguide of same E-plane height but whose H-plane width is large enough to support the TE30 mode. Thus box-horn supports TE10 and TE30 modes resulting in relatively uniform amplitude distribution over the H-plane of the aperture to prevent steep heating gradient in bio-medium. Expression for electric field in muscle due to planar array of box-horns is derived using two different techniques, i.e., Fresnel-Kirchhoff scalar diffraction field theory and plane wave spectral technique. SAR distributions in different planes of heating medium due the array applicator are evaluated at 2.45 GHz using these techniques. The results for SAR distribution of the planar array of box-horns are also compared with those for single box-horn. The results for SAR distribution in z-direction demonstrate that tumor at greater depth can be heated with the planar array of box-horns due to increased penetration depth in comparison to a single box-horn. Also planar array has wider area of illumination and higher peak value of SAR in both x- and y-directions as compared with a single box-horn. It is shown that the results obtained by these two techniques are in agreement with each other.

A method for estimating cardiac dynamic performance through temporal sequences of X-ray coronary angiograms is proposed. The given data are 3D vessel skeletons, reconstructed from angiogram sequences on two approximately orthogonal views, and correspondences of these skeleton points over consecutive instants. 3D cardiac surface in terms of an extended superquadrics (ESQ) is constructed from vascular skeletons to estimate cardiac deformation. According to actual characteristic of cardiac dynamics that have been confirmed by medical observations and non-rigid motion theory, complex cardiac performances are decomposed into global and local components. Parameters of all components are estimated through motion decomposition as well as compensation. Experimental results on clinical data are illustrated and discussed in terms of expected benefits and potential limitations.

Power line signal are normally subjected to disturbance and noise which degrade the overall performance of power quality monitoring system. This paper proposes a modified approach for denoising by combining an algorithm known as Stein’s Unbiased Risk Estimator (SURE) algorithm incorporated with phaselet transform (PT). This algorithm is chosen particularly, as it not only performs denoising but also tends to optimally smooth the noisy signal. Since the algorithm is incorporated with phaselet, this leads to increase the coefficients obtained. Hence this method is found to be effective for application for denoising of power line signals. The different types of power quality signals simulated using the proposed method is found to be efficient and provide better results with increased Signal-to-Noise ratio (SNR) when compared with the results obtained by applying wavelet transform (WT).

Self-excited induction machines seem to be the most suitable generators for wind energy conversion in remote and windy areas. Steady state analysis for such machines is essential to estimate the behavior under actual operating conditions. This paper presents a new technique for the steady-state analysis of a three-phase self-excited induction generator feeding balanced unity power factor load. Iterative technique has been used to find the generated frequency and Artificial Neural Network (ANN) has been applied to capture the nonlinear magnetization characteristics of induction machine in place of piecewise linear approximation as used by other research persons. The results have been compared with experimental results. The comparison confirms the validity and accuracy of the ANN based modeling of induction generator.

Numerical and experimental results for a double excited synchronous drive are presented in this paper. The finite element method is used to study the performances of a double excited synchronous motor in order to avoid the recurrence. The speed gain in transient operating regime is simulated by coupling the Flux2Dز and Matlab Simulink software. In order to validate the results obtained via numerical magnetic field computation (2D FEM) some of them are compared with the test bench obtained results for a generator regime.