Resumo em Inglês:
Abstract The accelerated data and apps growth represents significant challenges to the next generation of mobile networks. Amongst them, it is highlighted the necessity for a co-existence of new and old patterns during the transition of architectures. Thus, this paper has investigated solutions for offloading into a hybrid architecture, also known as H-CRAN (Heterogeneous Cloud Radio Access Network Architecture), that centralizes processing and searches a better use of the network resources. The strategy of optimization was analyzed through the evolutive algorithm PSO (Particle Swarm Optimization), in order to find a suboptimal solution to the TLA (Two-Level Allocation) in the H-CRAN architecture and another one based on FIFO (First In, First Out), for benchmarking purposes. SNR (Signal-to-noise ratio) average, Maximum Bit Rate, the number of users with or without connections and number of connections in RRHs and macro were used as performance measurements. Through the results, it was noticed an improvement of approximately 60% in the Maximum Bit Rate when compared to the traditional approach, enabling better service to the users.Resumo em Inglês:
Abstract This paper describes a new design methodology for reconfigurable printed circuits with limited size, using an improved hybrid particle swarm optimization (HPSO) algorithm, reducing the search space by the definition of negative zones (NZ), regions where the swarm of particles should not travel. The proposed design methodology (HPSO-NZ) is used in the development of reconfigurable frequency selective surfaces (RFSSs), restricted to a limited overall size, resulting in entirely new frequency selective surface (FSS) geometries. Two FSS prototypes are designed, fabricated, and measured for comparison purpose. A good agreement is observed between simulation and measurements results, confirming the efficiency and accuracy of the HPSO-NZ algorithm. Also, the performance of the HPSO-NZ algorithm is compared to the ones of genetic algorithm (GA) and particle swarm optimization (PSO) algorithm, showing good consistency results.Resumo em Inglês:
Abstract This paper presents a novel printed monopole antenna for quad-band operation in four WLAN bands: ISM 2.4 GHz, 5.2 GHz, 5.6 GHz, and ISM 5.8 GHz. This antenna is compact, thin, lightweight, easy to manufacture, and suitable for portable devices. It is composed of a folded strip radiator and two parasitic strips printed on a partially grounded substrate. The folded strip radiator interacts with the parasitic strips, which are connected to the ground plane, in such a way as to produce the resonant modes that originate the radiation bands of the antenna. An additional open-ended strip connected to the radiator is used to adjust the antenna input impedance in the upper operation band. A parametric study on several geometrical dimensions of the antenna is carried out in order to analyze their influence on the antenna performance. The fabricated prototype of the proposed printed monopole antenna has overall dimensions of 22 × 48 × 1.6 mm3, and the measured 10-dB return-loss bands exhibited by the antenna are 2149-2660 MHz and 5120-6035 MHz.Resumo em Inglês:
Abstract We investigate a three-dimensional (3D) reciprocal invisibility cloak with a multilayered structure based on coordinate transformation theory and complementary media. There has been considerable research on invisibility cloaks such as the external cloak, which requires complex “anti-objects”, and closed cloaks of different shapes, in which the object enclosed is blind. Because all these are hard to realize in actual application, we apply a uniform layer to the whole construct into several parts in efforts to replace the ideal cloak with the aim to reduce complexity in actual fabrication. This multilayered cloak allows exchange of information without requiring “anti-objects”. All results were simulated and calculated in the Cartesian coordinate system and with the Comsol Multiphysics software. Electrical field simulations verified the efficiency of the designed cloak and the computed radar cross section (RCS) to illustrate the validity of this method and its efficiency in replacing the ideal cloak.Resumo em Inglês:
Abstract In this work, we introduce a new concept of frequency interleaving applied to passive optical networks based in Dense Wavelength Division Multiplexing (DWDM). In order to explore colorless ONUs approach, a single and centralized optical source is used to create the interleaved wavelengths for the downstream and upstream path. In this case, frequency comb generation implemented by recirculating frequency shifting technique allowed the creation of all the wavelengths used in each path. The reception operation is accomplished by introducing, at the ONU side, a combination of a set of optical passive elements. The system with 4 × 12.5 Gbit/s NRZ-OOK (Not Return to Zero - On-Off Keying) modulation format were simulated through 20 km of standard single mode fiber link in both transmission paths. In order to guarantee a high quality optical frequency comb source, the optical carrier-to-noise-ratio (OCNR) was evaluated as well as BER (bit error rate), to analyze the system performance. All devices models and simulations were performed in Matlab environment.Resumo em Inglês:
Abstract A new technique is presented for designing microstrip patch antennas with very good input impedance matching. The analysis is carried out for 1.78 GHz, 2.42 GHz and 3.46 GHz rectangular patch antennas printed on low-cost fiberglass substrates (FR-4), mounted on a ground plane and fed by a microstrip line. The antenna impedance matching is obtained using a slotted microstrip line feeder. The use of the proposed impedance matching technique showed considerable improvement from the reflection coefficient point of view, with reduction of about 20 dB at the resonant frequency, without modifying the original dimensions of the antenna patch elements or the width of the feeding microstrip line. Numerical characterization is carried out using Ansoft Designer software and iterative method WCIP. Prototypes are fabricated and measured, for validation purpose, showing good agreement when compared to simulated results.Resumo em Inglês:
Abstract Here we present a numerical analysis and the optimization of a multi-pump discrete Raman amplification system based on the use of a Tellurite optical fiber as the gain media. By using previously reported optimization techniques we were able to exploit the high Raman gain of Tellurite optical fibers and its multipeak spectrum to achieve amplification over an amplification band from 1520 to 1600 nm. Average gains around 10 dB with ripples in the region of 3 dB were achieved using only 3 pumps with less than 800 mW each. Optimized systems were obtained for different lengths of fiber showing that discrete Raman amplifiers based on tellurite fibers with lengths as short as 100 meters can provide high gains and low ripples in a broad wavelength band. Lower cost systems using only 2 pumps were also analyzed in this study providing 5.8 dB of gain with only 2.4 dB of ripple for an 80 nm signal bandwidth.Resumo em Inglês:
Abstract This paper describes an investigation of the possibility of using a new conductive ink, insted of copper clad laminates, in the manufacturing of microstrip patch antennas on glass and fiberglass substrates and of bioinspired frequency selective surfaces (FSSs) on fiberglass substrates for wireless communication systems. The new conductive ink is developed using synthesized nitrocellulose which, in ethyl acetate solution, works as a bonding agent and carrier for the formation of a conductive film. The load used in the fabrication process is silver metallic powder. Simulation and analysis are performed using Ansoft Designer and HFSS softwares. Microstrip antenna and FSS prototypes are fabricated and measured for comparison purpose. An agreement is observed between simulation and measurements results.Resumo em Inglês:
Abstract A Hexagonal Microstrip Antenna (HMSA) is an approximation to a Circular MSA (CMSA), which is not symmetrical over two principal planes, unlike a CMSA. Consequently, two types of feed positions are feasible for each X and Y-axes. When a quarter-wave transformer or inset feed is used to match the edge impedance of the HMSA, it becomes asymmetrical over the feed axis (E-plane), which leads to increase in the crosspolarization level in the H-plane. In this paper, to reduce the crosspolarization level of HMSA along H-plane and to match the edge impedance of the HMSA on each X and Y-axes with the 50Ω-Microstrip (MS)-line-feed, a single and a pair of shorting posts have been used. The current distribution of the shorted HMSA is changed due to the loading of shorting posts into the patch, which in-turns help to match the edge input impedance. A detailed investigation on the characteristics of the shorted HMSA with modified fundamental mode frequencies has been presented. The co-polarization to crosspolarization ratios (CTCR) in H-plane of the HMSA with a pair of shorting posts has been reduced substantially by more than 20 dB at the broadsight direction in comparison with that of an HMSA with a single shorting post or with an inset. The simulated results of the HMSA with direct 50Ω-MS-line-feed are in good agreement with measured ones.Resumo em Inglês:
Abstract In this study are analyzed horn antennas to operating at X band (8 – 12 GHz) and manufactured by additive manufacturing method (AM). To construct the antennas using AM method was necessary made the structure with acrylonitrile butadiene styrene (ABS) thermoplastic using a 3D printer, and then coated the antennas with conductive surfaces. Were fabricated three antennas with different coated techniques: the first antenna with conductive silver paint, the second antenna using copper tape and the third antenna using copper plated. It is investigated the performances of these antennas in terms of the input reflection coefficient, gain, radiation pattern, weight and compared with the conventional aluminum horn antenna with same dimensions.Resumo em Inglês:
Abstract A pattern reconfigurable antenna array with two elements is designed in this paper. The antenna element is made up of a printed Yagi and feed structure with variable phase. By changing the states of diodes in the feed structure of these two elements, the far-field radiation phase of both elements can be changed. That is, the pattern reconfigurable function of the array is realized. In this way, the impedance bandwidth of array is 75.9% (2.7~6.0 GHz), in which the peak gain direction can be switched between -θ, 0 and +θ (θ = 10°~16° at different frequencies). With the simple reconfigurable structure, the peak gain direction can be adjusted according to demands. It can be applied to broadband investigation systems. To verify the feasibility, a prototype is fabricated, measured, and reasonable agreement between the simulated and measured results is obtained.Resumo em Inglês:
Abstract In this paper, a new multiband fractal frequency selective surface (MF-FSS) is proposed. The work presents a new fractal design methodology for FSSs with Swastika fractal patch elements. The proposed MF-FSS includes periodic arrays of metallic patches, printed on a single layer substrate. The structure parametric analysis is carried out in terms of fractal iterations, geometry elements, and unit-cell size. The simple controllable feature of the proposed structure lets us tune the given parameters of FSS geometry to achieve adjustable bandstop filter. The fractal geometry allows us to design compact structures (CP = 54%) that behave like dual-polarized bandstop filters. The designed structure is validated by means of an excellent agreement between the simulation and measurement results. Also, results show the proposed structure presents the most desirable features like fractal compactness, multiband response, dual polarization, excellent angular stability, and controllability. This work presents a fundamental structure that can be applied into the more complex and sophisticated designs in future.Resumo em Inglês:
Abstract The difference between phase velocities of the odd and even modes in inhomogeneous microstrip coupled lines makes the microstrip directional coupler a poor device regarding directivity. In this work, this issue is successfully compensated by the addition of a matching network at the ports of coupled lines. Furthermore, the proposed matching network, composed of a single segment of microstrip line, was extensively studied providing significant insights for the design of a compact and broadband device. As result, simple design equations based on coupled lines S-parameters are obtained, as well as the achievable operation limits of the proposed matching network. Finally, in order to validate the proposed design methodology, a compact microstrip directional coupler is constructed to operate with directivity higher than 30 dB and coupling of 17 dB over a 600-MHz bandwidth.Resumo em Inglês:
Abstract The interference in adjacent cells and the control of the boundaries have being vastly investigated since the conception of the first cell phone networks. A very large number of small cells are required for new 5G mobile networks, and therefore it is even more important to determine the correct mobile station positioning as well as the control boundaries. In order to minimize these problems, this paper proposes a simple and efficient system that improves the control of the Mobile Management Entity (MME) defined in the Release 8 of 3GPP. The system uses a tracking arrangement capable of determining the direction of the mobile station in the cell area. This information can be used to predict handover between adjacent nodes (changing of cell) minimizing a great problem, the high traffic in the backhaul network. In order to reach these goals, two or more receiver antennas are used as a Radio Direction Finder (RDF) and phase controlled directional antennas or massive multiple-input and multiple-output antennas pointing to different irradiation channels towards different directions. The theoretical section developed in this study was successfully confirmed by the experimental setup with results very closed to the developed formulation.Resumo em Inglês:
Abstract An axicon-frustum basin-type Bessel resonator is designed for generating non-diffraction vortex beams with opposite propagation directions under different conditions. Based on the theory of geometric optics, the principle of creating vortex beams is analyzed in this axicon-frustum basin-shaped resonant cavity. It is shown that a non-diffraction vortex beam can be produced in the cavity under high-order beam stimulation. In the terahertz wavebands, the dyadic Greens function algorithm is used to numerically evaluate the electromagnetic characteristics in the cavity, and the numerical results demonstrate that the conclusion of the principle analysis is valid. Finally, the application of nondiffraction vortex beams in digital communication is explored.