Journal of Communication EngineeringJournal of Communication Engineering
http://jce.shahed.ac.ir/
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Feed provided by Journal of Communication Engineering. Click to visit.Mitigating Node Capture Attack in Random Key Distribution Schemes through Key Deletion
http://jce.shahed.ac.ir/article_566_93.html
Random Key Distribution (RKD) schemes have been widely accepted to enable low-cost secure communications in Wireless Sensor Networks (WSNs). However, efficiency of secure link establishment comes with the risk of compromised communications between benign nodes by adversaries who physically capture sensor nodes. The challenge is to enhance resilience of WSN against node capture, while maintaining the flexibility and low cost features of RKD schemes. We address this problem by proposing an effective technique, namely KDel, which dont require any special-purpose hardware or expensive computations. We demonstrate that our approach significantly increases the resilience of RKD schemes against node capture at the cost of a little communications, while maintaining network connectivity at the same level. Moreover, our scheme is generally applicable as it can improve the resilience of any RKD scheme.Fri, 30 Jun 2017 19:30:00 +0100Design and fabrication of a high-Q near-field probe for subsurface crack detection
http://jce.shahed.ac.ir/article_586_0.html
Non-destructive detection and evaluation of invisible cracks in metal structures is an important matter in several critical environments including ground transportation, air transportation and power plants. In this paper, a high-Q near-field Microwave probe is designed and fabricated using defected ground structures for surface and subsurface crack detection in metal structures. For this purpose, several near-field probes with different DGSs are designed and probe with the highest quality factor is selected for subsurface detection. Experimental results show that the proposed probe is able accurately detect invisible crack of a size 1mm with at least 20dB magnitude and more than 300 degrees phase contrast. It has also been demonstrated that the proposed device can efficiently used for detection and imaging of small failure and crack in dielectric and metallic structures. Also, it is noted that if the probe dimensions scale down, spatial resolution for crack detection of size in micro and nanometer is achieved at millimeter waves.Sun, 04 Feb 2018 20:30:00 +0100A compact stacked Quasi-fractal microstrip antenna for RFID applications
http://jce.shahed.ac.ir/article_551_93.html
In this paper, we propose a new compact quasi-fractal shaped microstrip antenna that consists of a hexagonal patch as the main radiator and a complementary stacked patch as the parasitic element. The overall surface of the proposed quasi-fractal patch is about 55% lower than the conventional hexagonal patch. Using of stacked technique, the gain reduction of compression technique is almost compensated for the proposed antenna while the total gain is reduced only about 1 dBi. Experimental results show that the operation frequency of the microstrip antenna is about 2.5 GHz which covers the microwave frequency band of radio-frequency identification systems.Fri, 30 Jun 2017 19:30:00 +0100A Novel Circularly polarized dielectric resonator antenna with Branch-Line Coupler and ...
http://jce.shahed.ac.ir/article_587_0.html
A new shaped circularly polarized dielectric resonator antenna (CP DRA) is studied with branch-line coupler and log-periodic balun for the GPS application. Since the coupler and balun are located under the DRA, it does not increase the footprint of the antenna, as a result the system is very compact. Two configurations are considered in this paper. In the first configuration, an external 50Ω load is used for the matching port of the branch-line coupler. For the second one, a three-resonator log-periodic balun is used instead of branch-line coupler, thus, no lumped elements are required in this configuration. Moreover, two modes HEM11δ of the cylindrical DRA are utilized to design the wide band circular polarization. The reflection coefficient, axial ratio, antenna gain, and radiation pattern are studied for each configuration. These first and the second configurations offer an impedance bandwidth (S11Sun, 04 Feb 2018 20:30:00 +0100Compensation of Doppler Effect in Direct Acquisition of Global Positioning System using ...
http://jce.shahed.ac.ir/article_555_93.html
Because of the very high chip rate of global positioning system (GPS), P-code acquisition at GPS receiver will be challenging. A variety of methods for increasing the probability of detection and reducing the average time of acquisition have been provided, among which the method of Zero Padding (ZP) is the most essential and the most widely used. The method using the Fast Fourier Transform (FFT), searches phase codes of the uncertainty region in a parallel method to find the desired code for correct acquisition. ZP method is sensitive to Doppler frequency so that the increase in Doppler frequency drastically reduces the probability of detection and consequently the average time of acquisition increases. The presented method in this paper, that called Segmented Zero Padding (SZP), reduces the Doppler effects on probability of detection at the acquisition of GPS receiver. Also, it will be shown that using the proposed algorithm proper mean acquisition time at high Doppler frequencies is achievable. Based on the comparisons made in this paper, we prove that the proposed algorithm in comparison to ZP algorithm, maintains the capability of parallel search and finally has a lower average acquisition time.Fri, 30 Jun 2017 19:30:00 +0100A Data Focusing method for Microwave Imaging of Extended Targets
http://jce.shahed.ac.ir/article_588_0.html
This paper presents a data focusing method (DFM) to image extended targets using the multiple signal classification (MUSIC) algorithm. The restriction on the number of transmitter-receiver antennas in a microwave imaging system deteriorates profiling an extended target that comprises many point scatterers. Under such situation, the subspace-based linear inverse scattering methods, like the MUSIC algorithm, fail to image the extended targets. In proposed method, the DFM divides imaging region into several sections and maps the scattered data to each section by applying a linear transformation. Being weakened clutters from other sections, the resultant focused data contains, mostly, the responses of scatterers inside the desired section. In this way, the number of scatterers is reduced comparing to the number of transmitter-receiver antennas and the requirement for the MUSIC is satisfied. Using experimental data, we show that the DFM in conjunction with the MUSIC is successful in microwave imaging of extended targets.Sun, 04 Feb 2018 20:30:00 +0100Physical Optics Calculation of Electromagnetic Scattering From Haack Series Nose Cone
http://jce.shahed.ac.ir/article_544_93.html
In this paper, the physical optics method is used to study the problem of electromagnetic scattering from Haack series nose cone. First, a meshing scheme is introduced which approximates the curvature of the surface by piecewise linear functions in both axial and rotational directions. This results in planar quadrilateral patches and enables efficient determination of the illuminated region and application of closed-form expression for computing physical optics integral. Then the ray-surface intersections are obtained using the implicit surface equation of Haack series nose cone. The equation obtained by the intersection test does not have analytical solution. Hence, the Steffensen's method is applied to solve this equation numerically. To find the initial point for Steffensen method's iterations, a bounding cylinder is used. It provides high precision evaluation of initial point, fast convergence and short computation time. Moreover, if the ray does not intersect the bounding volume, it certainly misses the bounded object and hence does not need to be tested in the Steffensen's method. The ray-cylinder intersection test has a simple analytical solution, which results in fast rejection of missed rays.Fri, 30 Jun 2017 19:30:00 +0100Power Control and Scheduling For Low SNR Region in the Uplink of Two Cell Networks
http://jce.shahed.ac.ir/article_589_0.html
In this paper we investigate the sub-channel assignment and power control to maximize the total sum rate in the uplink of two-cell network. It is assumed that there are some sub-channels in each cell which should be allocated among some users. Also, each user is subjected to a power constraint. The underlying problem is a non-convex mixed integer non-linear optimization problem which does not have a trivial solution. To solve the problem, having fixed the consumed power of each user, and assuming low co-channel interference region, the sub-channel allocation problem is reformulated into a more mathematically tractable problem which is shown it can be tackled through the so-called Hungarian algorithm. Then, the consumed power of each user is reformulated as a quadratic fractional problem which can be numerically derived. Numerical results demonstrate the superiority of the proposed method in low SNR region as compared to existing works addressed in the literature.Sun, 04 Feb 2018 20:30:00 +0100Evaluation Performance of OFDM Mutlicarrier Modulation over Rayleigh and RicianStandard ...
http://jce.shahed.ac.ir/article_553_93.html
Last years, Wavelet Packet Modulation (WPM) or Wavelet Packet Transform based Orthogonal Frequency Division Multiplexing (WPT-OFDM) have been introduced to wired and wireless communication fields as efficient Multicarrier Modulation (MCM) techniques. The wavelets have interesting features such as flexibility, compatibility and localization in both time and frequency domains with no need to use rectangular window function. As a result, the transmitted signal is naturally less sensitive to inter-symbol and inter-carrier interferences (ISI and ICI). Also, it is possible to implement OFDM modulation without adding cyclic prefix (CP) and it is enough only to use time domain or overlap frequency domain equalization (TEQ or overlap FEQ) in order to shorten the effective channel impulse response length with the purpose of avoiding the ISI and decreasing the ICI. In this paper, we compare BER performance for FFT-OFDM and WPT-OFDM in the presence of two types of channels defined by ETSI (i.e. Rayleigh P1 and Rician F1 channels). In our simulation Haar, Daubechies6, Symlet5 and Coiflet5 wavelets and overlap frequency domain equalization (overlap FEQ) are used for WPT-OFDM in contrast with FFT-OFDM which uses FEQ equalization. Simulation results show that the performance of OFDM will be improved by using WPT transform and due to no need of CP, the power/bandwidth efficiency of OFDM modulation will be improved as well.Fri, 30 Jun 2017 19:30:00 +0100Wideband Dispersion Compensation in Square Lattice Photonic Crystal Fibe
http://jce.shahed.ac.ir/article_610_0.html
In this paper, a new structure is provided for the dispersion compensating photonic crystal fibers in order to broaden the chromatic dispersion and increase the dispersion compensating capability in a wide wavelength range. In the structure, putting a combination of circular holes and a star structure in the inner core clad causes the dispersion coefficient profile to be broadened, and additionally causes the fiber to have a negative dispersion coefficient in the whole S to U telecommunication bands. In this fiber, the minimal dispersion coefficient will be -653ps/(nm.km). Furthermore, with the diameter of the circular holes of the inner clad in this structure increased, a relatively flat dispersion profile will be obtained in the whole E to U telecommunication bands with a dispersion variation equal to 46ps/(nm.km). In the S to C telecommunication bands, the dispersion variation is 17ps/(nm.km). The simulations are all done using the finite difference time domain numerical (FDTD) method.Sun, 18 Feb 2018 20:30:00 +0100CPW-Fed Circularly Polarized Slot ANTENNA with Elliptical-Shaped Patch for UWB Applications
http://jce.shahed.ac.ir/article_554_93.html
A new design of coplanar waveguide (CPW)-fed antenna with circular polarization (CP) and excellent impedance matching is presented. In this design a pair of circular-shaped slits is applied to opposite corners of the slot for enhancing the impedance matching and realizes bandwidth of 134.43% across 2.98-15.20 GHz for VSWR≤2. Furthermore this structure exhibits axial ration bandwidth (ARBW) of 36.22% across 4.43-6.39 GHz by embedding two inverted-L shaped ground arms in the slot. The total dimension of the proposed antenna is 25×25×0.8 mm3. This new design has advantages of, supporting the ultra-wideband (UWB) systems and covering the WLAN spectrums with 3dB CP radiation and VSWR≤2 simultaneously. The numerical and experimental results of the antenna explain the superiority of the proposed antenna performance with comparison to recent similar works.Fri, 30 Jun 2017 19:30:00 +0100Groove Gap Waveguide (GGW) H-plane Horn Antenna and a Method for Its Back lobe Suppression
http://jce.shahed.ac.ir/article_619_0.html
recently a new structure called groove gap waveguide (GGW) is ‎introduced to implement low loss microwave component devices ‎especially for millimeter wave applications. This paper presents a ‎new type of H-plane horn antenna making use of this new technology ‎in which backward radiation is significantly suppressed by ‎introducing a high impedance surface at the antenna aperture. The ‎high impedance surface that we used as the back lobe suppressor is a ‎corrugated surface. The designed antenna is simulated by HFSS and ‎its radiation performance is compared with an ordinary GGW H-‎plane horn in which no back lobe suppression mechanism is used. ‎Results show a significant improvement in back lobe suppression and ‎gain enhancement by the proposed structure.‎Sat, 03 Mar 2018 20:30:00 +0100BLIND PARAMETER ESTIMATION OF A RATE k/n CONVOLUTIONAL CODE IN NOISELESS CASE
http://jce.shahed.ac.ir/article_636_0.html
This paper concerns to blind identification of a convolutional code with desired rate in a noiseless transmission scenario. To the best of our knowledge, blind estimation of convolutional code based on only the received bitstream doesn’t lead to a unique solution. Hence, without loss of generality, we will assume that the transmitter employs a non-catastrophic encoder. Moreover, we consider a complete synchronous scenario in which one can extract separate codewords from received sequence. This assumption is valid in many practical communication systems because, the frame preambles allow us to identify the beginning of each codewords.In this paper, we examine the blind identification problem for rate1/n and rate k/n convolutional codes, respectively. For rate 1/n, we propose an iterative method that uses three steps in each iteration to test the validity of a possible value of n. We show that this method can identify the parameters of a rate 1/n convolutional code from only two different noiseless received codewords. Afterwards, we generalize this method for a rate k/n convolutional code in which each iteration is composed of seven successive steps. We show that this method requires at least k+1 different codewords to identify all parameters of a rate k/n code.Mon, 30 Apr 2018 19:30:00 +0100Design and Implementation of a Compact Super-Wideband Printed Antipodal Antenna Using Fractal ...
http://jce.shahed.ac.ir/article_637_0.html
A compact printed fractal antipodal bow-tie antenna is designed and implemented to simultaneously cover the operations in the C, X, and Ku-bands. It is demonstrated that by addition of small fractal elements at the sides of hexagonal arms of the bow-tie, a wide operating frequency range of 3.3 to 19.1 GHz can be covered while antenna size is only 30×34×1.2 mm3. In order to match the antenna to the 50Ω SMA connector, a multi-section microstrip line of different widths is designed. The simulation results obtained from HFSS simulator package are verified by experimental measurements. Measured data are in good agreement with the simulated results. The frequency- and time-domain characteristics of the antenna including impedance matching, far-field patterns, radiation efficiency, gain, and fidelity factor are presented and discussed. The proposed antenna features 141% impedance bandwidth (defined by -10-dB reflection coefficient), small size, and desirable radiation patterns that make it excellent candidate for integration in broadband array systems.Sun, 06 May 2018 19:30:00 +0100