Abstract in English:Abstract A good wireless network design depends on technical and financial viability and a number of other criteria that must be met. Following the emergence of new technologies and services, such as 5G transmission and the reuse of frequencies, new work is being carried out to ensure a better design for a particular area. This study examines a discrete radio propagation model which employs the K nearest neighbors classifier. The model takes into account the different characteristics of the environment. This article presents a case study for the optimum positioning of base stations in Federal University of Pará (Belém – Brazil), representing a typical Amazon environment. The mentioned scenario is heterogeneous, presenting edifications and considerable forest area. Measurement campaigns were conducted in three different frequencies for the design features of the model: 521 MHz (Brazilian digital TV system), 2100 MHz (Enhanced Data Rates for GSM Evolution), and 2600 MHz (Long Term Evolution). A study of the fading phenomenon in these frequencies was carried out to generalize the frequencies of application for the propagation loss model. When this model was ready, tests (computing simulations) were conducted in two scenarios to optimize the positioning of the radio base stations being studied.
Abstract in English:Abstract In this paper, a novel hybrid algorithm on beam pattern synthesis of sparse arrays is proposed, which aims at minimizing the peak sidelobe level (PSLL). Sparse arrays can provide higher spatial resolution and relatively lower sidelobe than general arrays, but it is necessary to solve the multi-constraint problem of nonconvex nonlinear. Thus, we propose a Convex Improved Genetic Algorithm (CIGA) that can adjust the positions and the excitation coefficients of arrays to achieve the minimum PSLL. The CIGA is an effective two-step approach to the synthesis of sparse array. Firstly, Improved Genetic Algorithm is proposed, which is suitable for beam pattern synthesis of sparse arrays. The Improved Genetic Algorithm is adopted to adjust the positions of arrays to achieve the local optimum PSLL, and then convex optimization method is used to calculate the excitation coefficients in expectation of reaching the minimum PSLL. Simulation results show that the PSLL obtained by CIGA is about 5dB better than the published methods in sparse linear arrays and prove that the CIGA is superior to the published methods.
Abstract in English:Abstract This paper analyzes multi-step-ahead spectrum prediction for Cognitive Radio (CR) systems using several future states. A slot-based scenario is used, and prediction is based on the Support Vector Machine (SVM) algorithm. The aim is to determine whether multi-step-ahead spectrum prediction has gains in terms of reduced channel-switching and increased network throughput compared with short-term prediction. The system model is simulated in software using an exponential on-off distribution for primary-user traffic. A classical energy detector is used to perform sensing. With the help of simplifications, we present new closed-form expressions for the detection probability under AWGN and Rayleigh fading channels which allows the appropriate number of samples for these scenarios to be found. The performance of the proposed predictor is thoroughly assessed in these scenarios. The SVM algorithm had low prediction error rates, and multi-step-ahead idle-channel scheduling resulted in a reduction in channel switching by the SU of up to 51%. An increase in throughput of approximately 4% was observed for multi-step-ahead prediction with three future states. The results also show channel-switching savings can be achieved in a CR network with the proposed approach.
Abstract in English:Abstract The longitudinal, flexural, and torsional modes of acoustical resonances are presented for a long and small thickness cylindrical fiber spool. The fiber spool is built using a monomode optical fiber tightly wound in a helix form around a cylindrical Styropor. The acoustical resonance values are obtained using a Mach Zehnder interferometer with the fiber spool in the long (2 km) arm and a small linewidth laser. To reduce spurious signals, the interferometer was placed inside a vacuum chamber. The measured and theoretical results reasonably agree up to the first fifteen resonant longitudinal modes and for the first five flexural and torsional resonant modes, with a span from 10 Hz up to 200 Hz.
Abstract in English:Abstract In this paper, a compact elliptic-response microstrip low pass filter (LPF) is presented with a wide stop-band using stepped impedance resonators. With high attenuation in the stop-band, the overall size reduction of the proposed filter is achieved using a novel defected ground structure technique using an interdigital capacitor and complementary split ring resonator (CSRR). A 4.2 GHz LPF is designed and simulated on FR4 substrate and a stop band of 8.8 GHz is obtained by utilizing interdigital and complementary split ring resonator. Results further show that the use of U-shaped high impedance line on the top layer of filter enhances the stop-band bandwidth by 2.2 GHz. In the final design, the passband insertion loss is found below 0.5 dB, and –10 dB is obtained over a band from 5.06 GHz to 17.06 GHz between input and output ports. The normalized circuit size of the filter is 0.417× 0.202 and the figure of merit is calculated about 55 at the cut-off frequency. These proposed LPFs have promised significant advantages in the stop-band characteristics with an acceptable roll-off rate for spurious-free communications.
Abstract in English:Abstract In this paper, the authors present a proposal for an application of electromagnetic bandgap (EBG), for suppression of grating lobes, in frequency selective surfaces (FSS), not yet studied in the literature. An alternative type of EBG with square holes was proposed to reduce the computational effort in simulations. The study consists of an application of a rectangular periodic array of cylindrical and square holes in FSS dielectric substrate to create rejection bands and suppress specific resonant frequency modes. We built four prototypes and compared measured results with simulated results obtained with ANSYS HFSS. Simulations and measurements show suppression levels up to 6 dB. A good agreement between the results is observed. The FSS with EBG with square holes allows a simulation time 70 % lower than FSS with EBG with cylindrical holes.
Abstract in English:Abstract In this paper, a novel method is proposed to increase the gain and radiation efficiency of a compact patch antenna. By employing a combination of three efficient techniques, we have developed a multi-resonance L-DGS antenna with a high gain of 5 dB and an efficiency of 99.6%. Furthermore, a novel compact Double Negative metamaterial unit cell and its equivalent circuit are investigated, to achieve high miniaturization of 30×30 mm2 and multi-band wireless applications (2.8 GHz, 4.1-4.45 GHz, 5.6 GHz). Koch snowflake fractal is introduced along radiation patch edges to improve the antenna matching. The antenna is designed using commercially available package CST software, printed on Rogers RT5880, and the probe feed mechanism is adopted for the antenna excitation. Then, to prove the validation of the antenna design, the equivalent circuit is presented and simulated using ADS of Agilent software. The compared simulation results given by CST, HFSS and ADS software have confirmed the antenna use for WIMAX, C-band and WLAN applications.