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In this paper, we present a comparison between OFDM and STDCC sounding techniques used to wide band channel characterization in suburban environments at 3.5 GHz band. Measurements of the received signal's power delay profile and power level for each of the sounding techniques were obtained. These experimental results are presented and compared. For this comparison, important wide band characterization information are obtained and the performances of each one of used techniques are observed.Resumo em Inglês:
An optimized design for the spanner shape regular hexagonal monopole (RHM) patch antennas has been reported to yield ultra wide band (UWB) impedance bandwidth. Impedance and radiation characteristics are presented and discussed. From the results, it has been observed that, the impedance bandwidth, defined by 10 dB return loss, can reach a value of 8.63GHz. A rectangular slit in the radiating patch is used to reduce the lower-edge frequency resulting in improved bandwidth. This technique yields the ability to construct a smaller antenna in comparison to a simple printed planar monopole antenna for a given frequency range. The printed metallic patch is defected for increasing the operating bandwidth. The antennas considered in this paper operate between 2.95 GHz to 11.58 GHz, making them suitable for numerous DECT, WLAN, remote sensing, radar, imaging, localization and medical applications. The etched area of the antenna can be used for communication circuit components.Resumo em Inglês:
Narrow band is the major inconvenient of the microstrip antenna. However, various multiband techniques are proposed towards several applications. A simple configuration of the rectangular microstrip antenna allows operating a system of satellite communication in two bands. The configuration consists of a single radiant element and substrate with low dielectric constant. The antenna is fed by a micro-strip line attached in the corner of the patch. This antenna covers two bands, the K and Ku bands, simultaneously. With the same parameters as simple antenna, other shapes are compared with rectangular array antenna, to improve the performances of the antenna and vary their operating frequencies. The designated configurations of the antenna arrays contain 2, 4 and 8 radiating elements.Resumo em Inglês:
The induction planar actuator, i.e. IPA, proposed in this study presents an electromagnetic structure formed by a static ferromagnetic core with an aluminium plate that corresponds to the secondary, and a mover, also called primary. The latter comprehends two three-phase windings, mounted in an armature core, which are orthogonal to each other. When they are fed by three-phase AC excitations, a moving magnetic field takes place, and can travel along the x-axis and the y-axis direction simultaneously. The travelling magnetic field induces electrical currents in the secondary. The interaction between the moving magnetic field from the primary and the magnetic field originated by the induced current in the secondary produces a planar force. That explains the primary movement over the working area defined by the secondary. The 3D flux density distribution of the actuator suggests the employment of a grain-insulated soft magnetic composite to reduce eddy currents and losses on the core of the primary armature core. Magnetic flux density, induced current and planar traction forces are studied.Resumo em Inglês:
A compact coplanar waveguide (CPW)-fed ultra-wideband (UWB) antenna is proposed with band-notched characteristic. The antenna has compact size of 29 x 31 mm². A novel wide polygon-slot is inserted on the antenna to obtain good impedance matching and wide bandwidth. A tapered radiating patch is placed inside the polygon-slot. An embedded C-slot in the radiating patch avoids potential interference from WLAN band. The antenna is fabricated and measured. The measured results confirm that the antenna has operating frequency band of 3.1-10.6 GHz with notched band of 5.1-5.9 GHz. The antenna has stable radiation patterns and consistent gain over operating band. The time domain group delay of antenna is with in 1 ns except in notched band, which indicates good linear phase response. The results indicate that the antenna is good for portable UWB systems.Resumo em Inglês:
In this paper, field measurements carried out in a suburban SFN network with two synchronized transmitters are reported. It is found that the radio signal coverage of the distributed transmission scheme is distinctly improved when compared to a single transmitter system. The path loss gain and improvement associated to the SFN scheme are obtained as well as the multipath channel parameters including the mean and RMS delay spread. A tapped delay line is used to model the average power delay profile (PDP) in the distributed transmission cases and shows rather different features than the single transmission case.Resumo em Inglês:
Frequency-shift-free all-optical amplitude regenerators based on fiber-four-wave mixing were investigated by means of simulations. These regenerators, comprised of two stages of highly nonlinear dispersion-shifted fiber, were designed using a heuristic procedure that implements a routine based on a genetic algorithm to optimize the device performance. A bit error rate improvement of up to four orders of magnitude was found as compared to a previous design approach discussed in the literature. It was due to a proper choice of the pump signal frequency regarding to the input signal that brings about a trade-off between four-wave mixing optical reshaping and four-wave mixing crosstalk leading to optimal optical regeneration. The proposed design method might be applied to other parametric devices that rely on four-wave mixing.Resumo em Inglês:
The use of wireless local area networks, called WLANs, as well as the proliferation of the use of multimedia applications have grown rapidly in recent years. Some factors affect the quality of service (QoS) received by the user and interference is one of them. This work presents strategies for planning and performance evaluation through an empirical study of the QoS parameters of a voice over Internet Protocol (VoIP) application in an interference network, as well as the relevance in the design of wireless networks to determine the coverage area of an access point, taking into account several parameters such as power, jitter, packet loss, delay, and PMOS. Another strategy is based on a hybrid approach that considers measuring and Bayesian inference applied to wireless networks, taking into consideration QoS parameters. The models take into account a cross layer vision of networks, correlating aspects of the physical environment, on the signal propagation (power or distance) with aspects of VoIP applications (e.g., jitter and packet loss). Case studies were carried out for two indoor environments and two outdoor environments, one of them displaying main characteristics of the Amazon region (e.g., densely arboreous environments). This last test bed was carried out in a real system because the Government of the State of Pará has a digital inclusion program called NAVEGAPARÁ.Resumo em Inglês:
We present a holey fiber (HF) with elliptical air-holes located in the center core area that ensures high birefringence, near-zero ultra-flattened chromatic dispersion and very low confinement losses in a wide wavelength range. The finite element method with perfectly matched boundary layer is used to investigate the guiding properties. It is demonstrated that it is possible to design a low-loss dispersion-flattened HF with a high birefringence of 0.0033 at a 1.55 µm wavelength. According to simulation, near-zero ultra-flattened dispersion of 0 ± 0.5 ps/nm/km is obtained in a 1.25 to 1.65 µm wavelength range with low confinement losses of 0.0008 dB/km in the entire band of interest.Resumo em Inglês:
A novel transformation of band pass- to low pass filter is introduced in this paper. First a compact microstrip band pass filter designed, optimized and realized by combining a simple multilayer method with magnetically coupled microstrip U-shaped DGS resonators is proposed. The DGS- and DMS-techniques demonstrated the ability to suppress the undesired harmonic response. The proposed band pass filter is transformed to a new structure with low pass characteristics using a simple strip connection between the neighboring microstrip resonators. The designed compact filters have low insertion loss, sharp transition regions due to the presence of two-transmission zeros at both edges of the pass bands. The measured resonance frequency, bandwidth and insertion loss are 3.4 GHz, 40%, and 0.5 dB respectively. The compact transformed low pass filter offers a wide stop band with a rejection higher than 20 dB up to more than 10 GHz. The undesired harmonic has been successfully suppressed. The simulated and measured results show good agreement and validate the proposed approach.Resumo em Inglês:
In this paper an improved version of zeroth order resonator (ZOR) using Left Handed Metamaterial (LHM) is reported, and its performance is compared with the earlier published ZOR. The resonator is designed based on microstrip technology using composite right left handed transmission line (CRLH TL) approach. The conventional ZOR is designed based on the CRLH TL along with two coupling slots at the input and output ports, whereas the proposed design of ZOR is based on coupling capacitors. Use of coupling capacitor in place of coupling slot improves resonance characteristic of ZOR in terms of return loss and insertion loss and also increases the operational bandwidth. The measured resonant frequency, return loss, insertion loss and fraction bandwidth of the proposed 1.5- unit cell ZOR are 1.5 GHz, -26.31 dB, -0.42 dB and 20.66% respectively, whereas for the conventional 1.5-unit cell ZOR these measured parameters are 1.8 GHz, -6.63 dB, -9.09 dB and 0.77% respectively. The frequency parameter and performance of the resonators are evaluated by full-wave electromagnetic simulator, IE3D, based on method of moments (MoM) and all these results are verified by measurements.Resumo em Inglês:
This paper proposes an approach to estimate the probable location of maximum exposure to electromagnetic fields associated with a radiocommunication station, based only on information of antenna's height, half-power angle and tilt. This approach can be implemented when simulation tools are absent, or/and few basic information on radiating system is available. The proposed analytical expression is compared with simulated and real measured data, showing the good accuracy of the proposed technique. The focus of the work are base stations, however the results may be applicable to any radiocommunication station. As far as the authors know, this is the first study to present a mathematical formulation in closed form under the considered constraints.Resumo em Inglês:
This paper presents the design of a nano-arm fractal antenna suitable for ultra wide band applications. The CPW-feed and fractal concept have been used to achieve the ultra wide bandwidth. The shape of the fractal geometry, the number of iterations and the number of nano-arms are the deciding factors for achieving wider impedance bandwidth. The experimental result of the fractal antenna exhibits ultra wideband characteristics in the frequency range of 2.55 GHz to 11.84 GHz corresponding to an impedance bandwidth of 131.77%. The measured radiation patterns of the proposed antenna are nearly omni-directional in the H - plane and bidirectional in the E-plane. The antenna can be useful for modern wireless communication, medical imaging and ground penetrating radar.Resumo em Inglês:
This paper presents a power-efficient RF differential receiver front-end supporting transmitted-reference (TR) communication in a 90 nm CMOS technology. Particularly, it addresses the issues of designing the frontend amplifier with low-noise and passive matching circuits on a silicon process and integrating a low-power delay unit in the front-end with wideband characteristics. The proposed architecture includes a differential high simulated gain (11 dB) amplifier which is centered at 21.6 GHz (in the K-Band) with a 6.2 GHz bandwidth (18.1~24.3 GHz). The input and output reflection parameters have centered values around -26 and -18 dB, respectively. With noise matching, the amplifier achieves 2.6~2.9 dB bandwidth noise-figure and 2 dBm input power limit for linear coverage. To interface the amplifier with a following RF mixer, a submicron delay-block (DB) is proposed with provision of adjusting number of stages in the delay chain. The branched DB architecture achieves monotonic delays covering a range of 70-800 ps (including group-dispersion). Tweaking of delay is possible through four design parameters and the set-up is analyzed by extending the number of cascaded stages up to eight. Driven from a 1.2 V supply, the amplifier and the DB consume 13.9 and 8.52- 10.61 mW power, respectively, and realize the circuits for the TR front-end. When compared with simulated results of reported CMOS receivers, the proposed design delivers higher performance in terms of a microwave figure-of-merit.Resumo em Inglês:
A distribution-free model is presented for the cumulative distribution function of the differential rain attenuation between two co-channel converging terrestrial links operating at frequencies above 10 GHz. This is accomplished through an extension of the Misme and Fimbel model, which determines the cumulative distribution of the rain attenuation on an isolated link from its parameters and data for the radio climatic region, as well as concepts from probability theory. Next, model predictions and experimental results are compared and effects from variations of the angle between the links and of the path length are studied. Finally, rain effects on the cumulative distribution of the C/I ratio between the desired and interference powers at the same receiver are analyzed, considering the angular discrimination of the receiving antenna.Resumo em Inglês:
A novel approach to design Multiple Function Antenna (MFA) arrays using Artificial Neural Networks is suggested. A planar array with uniform current excitations which can generate different beam widths and gains is designed using Artificial Neural Networks. The desired beam width, gain and number of elements are given as input to the neural network. The output of the neural network is the current excitations in the form ON/OFF state of the array. Radial Basis Function Neural Network (RBFNN) is initially trained with the input-output data pairs and tested. The network showed 98% high success rate.Resumo em Inglês:
An analytical study to quantify the substrate parasitic effects on SiGe HBT amplifiers in both common-base and common-emitter configuration is presented. The power gain relations and stability factors are derived from the modelled S-parameters which are computed at a fixed bias point from the small-signal hybrid-∏ model of SiGe HBT in both configurations. It has been shown that the power gains of SiGe HBT amplifiers in both configurations are degraded when extrinsic and substrate parasitics are taken into account. The degradation in power gains is found to be more pronounced for CB configuration, which makes the design of HBT amplifiers, particularly in the CB mode, difficult. Close matching of the modelled data with the reported experimental results validates the proposed methodology.Resumo em Inglês:
We present and analyze a 17.6-Tb/s DWDM optical transmission composed of 79 channels with 224-Gb/s RZ-DP-16QAM modulation format per-channel and coherent detection. A maximum reach of 678 km is obtained with an optical recirculation loop composed by 226 km of pure-silica core fibers and EDFA amplification only in a 50-GHz grid system with spectral efficiency of 4.2-b/s/Hz. Also, a 25-GHz Gaussian optical pre-filter is applied to each channel and the same reach of 678 km is obtained in a 37.5-GHz channel grid system with spectral efficiency of 5.6-b/s/Hz. These results demonstrate a 33% system capacity improvement without transmission penalties.