Journal of Communication EngineeringJournal of Communication Engineering
http://jce.shahed.ac.ir/
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http://jce.shahed.ac.ir/
Feed provided by Journal of Communication Engineering. Click to visit.Sum-Rate Maximization Based on Power Constraints for Cooperative AF Relay Networks
http://jce.shahed.ac.ir/article_449_93.html
In this paper, our objective is maximizing total sum-rate subject to power constraints on total relay transmit power or individual relay powers, for amplify-and-forward single-antenna relay-based wireless communication networks. We derive a closed-form solution for the total power constraint optimization problem and show that the individual relay power constraints optimization problem is a quadratic programming which does not have a closed-form solution. To solve it, we propose a closed-form and low-complex technique which introduces suboptimal solution as an upper bound of system sum-rate. The performance of two new proposed algorithms are evaluated in terms of average achievable sum-rate and energy efficiency in different signal to noise ratios (SNRs). Considering the effect of the number of relays, the effect of channel gains of the source-relay as well as the relay-destination, and also the impact of the level of imperfect CSI are investigated. According to simulation results, higher sum-rate can be achieved in total power constrained scenario for all SNRs but energy efficiency is approximately the same for both of them. In addition, higher sum-rate is achievable by increasing the number of relays and/or improving the quality of uplink and downlink channels as well as decreasing uncertainty of channels.Sat, 31 Dec 2016 20:30:00 +0100Physical Optics Calculation of Electromagnetic Scattering From Haack Series Nose Cone
http://jce.shahed.ac.ir/article_544_0.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.Sun, 01 Oct 2017 20:30:00 +0100Closed-Form Solutions for Broad-Band Equivalent Circuit of Vertical Rod Buried in Lossy Grounds ...
http://jce.shahed.ac.ir/article_456_93.html
Abstract— In this paper, input impedance of a vertical rod under lightning stroke is first computed by applying the method of moments (MoM) on the Maxwell’s equations. The circuit model is then achieved through applying modified vector fitting (MVF) on the computed input impedance. After then the equivalent circuit is again extracted for a few values of soil conductivity and rod radius. Finally using a new fuzzy-based model namely spatial membership functions, closed form solutions for all lumped elements of the equivalent circuit are achieved. Index Terms— Closed-form, lossy ground, lightning stroke, vertical rod, MVF. Index Terms— Closed-form, lossy ground, lightning stroke, vertical rod, MVF.Sat, 31 Dec 2016 20:30:00 +0100A compact stacked Quasi-fractal microstrip antenna for RFID applications
http://jce.shahed.ac.ir/article_551_0.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.Sun, 15 Oct 2017 20:30:00 +0100Miniaturized High-Pass Filter Based on Balanced Composite Right-Left Handed Transmission Line ...
http://jce.shahed.ac.ir/article_457_93.html
In this paper, a compact high-pass filter (HPF) with a sharp rejection response based on the balanced composite right-left handed (CRLH) transmission line (TL) concept is proposed. A series LC resonator using an interdigital capacitor and meander lines is designed. Also, a meander spiral complementary split ring resonator (MSCSRR) is used to realize the parallel LC resonator. The high-pass filter is implemented in microstrip technology by etching MSCSRR, in the ground plane, and series interdigital capacitor with meander lines, in the signal strip. Because of a smaller electrical size of the proposed MSCSRR and also by using meander lines instead of conventional transmission lines, the total physical dimension of the proposed high-pass filter has been reduced. A detailed analysis of the structure, based on the equivalent circuit model is provided. The structure exhibits a balanced CRLH behavior and by properly tuning the geometry of the elements, a high-pass response with a sharp transition band is obtained. To validate the design concept, the proposed high-pass filter has been fabricated and tested. Experimental verification is provided and a good agreement has been found between the simulation and measurement results. To our knowledge, the size of proposed HPF is more compact in comparison with known similar filters.Sat, 31 Dec 2016 20:30:00 +0100Evaluation Performance of OFDM Mutlicarrier Modulation over Rayleigh and RicianStandard ...
http://jce.shahed.ac.ir/article_553_0.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.Sun, 05 Nov 2017 20:30:00 +0100A Deterministic Multiple Key Space Scheme for Wireless Sensor Networks via Combinatorial Designs
http://jce.shahed.ac.ir/article_458_93.html
The establishing of a pairwise key between two nodes for encryption in a wireless sensor network is a challenging issue. To do this, we propose a new deterministic key pre-distribution scheme which has modified the multiple key space scheme (MKSS). In the MKSS, the authors define two random parameters to make better resilience than existing schemes. Instead of a random selection of these parameters, our proposal provides a combinatorial framework by substituting appropriate parameters to satisfy certain properties. We show that the proposed scheme enhances storage memory and improves performance or security by carefully choosing a combinatorial design. In addition, we propose a new key agreement mechanism by using derivative operation on univariate polynomials to aim a desired computational overhead. In this case, the computational overhead of our approach lower than the general case of the MKSS’s. If we choose the primitive element in our general formula as the special case of the MKSS, this new process has the same computational overhead as the MKSS.Sat, 31 Dec 2016 20:30:00 +0100CPW-Fed Circularly Polarized Slot ANTENNA with Elliptical-Shaped Patch for UWB Applications
http://jce.shahed.ac.ir/article_554_0.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.Sun, 05 Nov 2017 20:30:00 +0100New UWB Shielding with Frequency Selective Surfaces
http://jce.shahed.ac.ir/article_459_93.html
In this paper a Frequency Selective Surface (FSS) as a UWB electromagnetic shield is introduced. The proposed FSS comprises a quasi-J.C-Jerusalem Cross- and a copper ring, which are located at both sides of a FR4 substrate and can represent a S.E -Shielding Effectiveness- better than 20dB in 90% bandwidth of Ultra Wide Band frequency. This structure is compact and thin. Each cell comprises J.C elements and a ring at two sides of a FR4 board with 3.2mm thickness, dielectric constant of 4.4, and loss tangent of 0.02. The structure has a 24×36 elements with dimensions of 288×432mm. Also the simulation and measurement results are in good agreement.Sat, 31 Dec 2016 20:30:00 +0100Compensation of Doppler Effect in Direct Acquisition of Global Positioning System using ...
http://jce.shahed.ac.ir/article_555_0.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, 10 Nov 2017 20:30:00 +0100Attack-Aware Cooperative Spectrum Sensing in Cognitive Radio Networks under Byzantine Attack
http://jce.shahed.ac.ir/article_516_93.html
Cooperative Spectrum Sensing (CSS) is an effective approach to overcome the impact of multi-path fading and shadowing issues. The reliability of CSS can be severely degraded under Byzantine attack, which may be caused by either malfunctioning sensing terminals or malicious nodes. Almost, the previous studies have not analyzed and considered the attack in their models. The present study introduces a new issue named attack-aware CSS where the objective is to analyze the occurred attack against CR ad hoc network to ameliorate the performance of data fusion schemes. The novelty includes the modification of Weighted Sequential Probability Ratio Test (WSPRT) algorithm which resulted in Attack-Aware WSPRT (A2WSPRT). The findings indicated considerable reduction in cooperation overhead and enhancement in correct sensing ratio, especially in severe attacks.Sat, 31 Dec 2016 20:30:00 +0100