Hasil untuk "Cellular telephone services industry. Wireless telephone industry"

Di Wu, Yang Qiu, Guoliang Yu et al.

In this paper, a low profile and high-efficiency decoupling antenna pair for multiunit smartphones is proposed using a similar π-shaped feed structure that can excite the dipole radiation mode of microstrip antenna. Ordinarily, symmetrical single-port T-shaped microstrip antennas can only excite monopole modes of bilateral radiation. This paper changes the vertical feeding microstrip structure into two oblique, similar π-shaped feeding structures. This oblique feeding structure can excite the dipole mode of unilateral radiation of the microstrip antenna. Using this method, the antenna design can be simplified, and the low-coupling independent radiation on both sides of the microstrip antenna can be freely controlled without the need for additional structures. Considering the ultra-thin characteristics of 5G smartphone devices, the parameters of the antenna are further optimized: the optimized antenna profile is only 3.7 mm. The measured results show that the 2 × 2 microstrip antenna pairs can effectively cover the 3.5 GHz band (3.4–3.6 GHz), with a coupling that varies from −16.14 dB to −11.01 dB and an efficiency that varies from 80% to 94.1%. The 8 × 8 MIMO smartphone antenna results show that the coupling varies from −20.1 dB to −12.17 dB, the efficiency varies from 79.72% to 93.7%, and the envelope correlation coefficient (ECC) is lower than 0.05. The microstrip antenna decoupling pair with a similar π-shaped feed structure proposed in this paper has high efficiency and low-profile characteristics have important application value in the decoupling design of 3.5 GHz 5G ultra-thin smartphone antennas.

Haokai Jia, Jinjun Mo, Lin Peng

An ultra-wideband dual-polarized antenna covering multiple communication standards such as LTE700/GSM850/GSM900 is proposed in this paper. The antenna consists of two dipoles that are perpendicularly placed to each other. The two dipoles can generate +45°/−45° linear polarizations, respectively. Dual-loop structure is utilized as the arm of the dipole, while four parasitic patches with shorting walls are coupled to the dipoles to extend the operating bandwidth. The measured results show that the antenna has an impedance bandwidth of 101.4% (0.54 GHz–1.65 GHz) with a reflection coefficient less than −10 dB. The isolation between the two ports is larger than 22 dB, and the cross-polarization is less than −20 dB over the band. Good unidirectional radiation patterns are obtained.

Yanbo Mai, Zheng Sheng, Hanqing Shi et al.

Atmospheric refraction is a special meteorological phenomenon mainly caused by gas molecules and aerosol particles in the atmosphere, which can change the propagation direction of electromagnetic waves in the atmospheric environment. Atmospheric refractive index, an index to measure atmospheric refraction, is an important parameter for electromagnetic wave. Given that it is difficult to obtain the atmospheric refractive index of 100 meters (m)–3000°m over the ocean, this paper proposes an improved extreme gradient boosting (XGBoost) algorithm based on comprehensive learning particle swarm optimization (CLPSO) operator to obtain them. Finally, the mean absolute percentage error (MAPE) and root mean-squared error (RMSE) are used as evaluation criteria to compare the prediction results of improved XGBoost algorithm with backpropagation (BP) neural network and traditional XGBoost algorithm. The results show that the MAPE and RMSE of the improved XGBoost algorithm are 39% less than those of BP neural network and 32% less than those of the traditional XGBoost. Besides, the improved XGBoost algorithm has the strongest learning and generalization capability to calculate missing values of atmospheric refractive index among the three algorithms. The results of this paper provide a new method to obtain atmospheric refractive index, which will be of great reference significance to further study the atmospheric refraction.

Gang Liu, Ming Zhang, Yaming Bo

The actions of a person holding a mobile device are not a static state but can be considered as a stochastic process since users can change the way they hold the device very frequently in a short time. The change in antenna inclination angles with the random actions will result in varied received signal intensity. However, very few studies and conventional channel models have been performed to capture the features. In this paper, the relationships between the statistical characteristics of the electric field and the antenna inclination angles are investigated and modeled based on a three-dimensional (3D) fast ray-tracing method considering both the diffraction and reflections, and the radiation patterns of an antenna with arbitrary inclination angles are deducted and included in the method. Two different conditions of the line-of-sight (LOS) and non-line-of-sight (NLOS) in the indoor environment are discussed. Furthermore, based on the statistical analysis, a semiempirical probability density function of antenna inclination angles is presented. Finally, a novel statistical channel model for stochastic antenna inclination angles is proposed, and the ergodic channel capacity is analyzed.

Bancha Luadang, Rewat Senathong, Chuwong Phongcharoenpanich

This research presents a miniaturized wideband meander line antenna (MLA) using a magneto dielectric (MD) material for mobile device applications. The proposed MLA attached the lower and upper ground planes of the folder-type chassis, connected electrically by grounding strip. The MD material (ECCOSORB MF-124) was subsequently loaded onto the coupling element area of the MLA. The MD-laden MLA was ultracompact (10 mm × 25 mm × 1 mm), with the electrical size of 0.015λ × 0.039λ × 0.0015λ at 470 MHz. The surface current distribution was simulated to determine the optimal parameters of the MD-laden MLA. To verify, a prototype antenna was fabricated and the experiments were performed. The measured impedance bandwidth (S11<−6 dB) covered the frequency range of 467–1012 MHz (73.6%), with an omnidirectional radiation pattern. The radiation efficiency was in excess of 90%, rendering it suitable for the DVB-H/LTE13/GSM850/900 applications.

E. Carr, A. Worth

Bin Deng, Xin-yun Wang, Cheng-guang Wu et al.

Target vibration bears important information for target recognition, and terahertz, due to significant micro-Doppler effects, has strong advantages for remotely sensing vibrations. In this paper, the imaging characteristics of vibrating targets with THz-SAR are at first analyzed. An improved algorithm based on an excellent Bayesian approach, that is, the expansion-compression variance-component (ExCoV) method, has been proposed for reconstructing scattering coefficients of vibrating targets, which provides more robust and efficient initialization and overcomes the deficiencies of sidelobes as well as artifacts arising from the traditional correlation method. A real vibration measurement experiment of idle cars was performed to validate the range model. Simulated SAR data of vibrating targets and a tank model in a real background in 220 GHz show good performance at low SNR. Rapidly evolving high-power terahertz devices will offer viable THz-SAR application at a distance of several kilometers.

Antoine Gademer, Loïca Avanthey, Laurent Beaudouin et al.

Les dernières années ont montré l'intérêt croissant de la télédétection basse altitude (TBA) pour l'étude de zones na- turelles. Mais au-delà de la problématique d'accès au milieu, la cartographie de ces zones à grande échelle pose de nombreuses contraintes sur la partie capteurs d'acquisition. En effet, ce sont des milieux difficiles pour les algorithmes classiques de traitement d'images : intrinsèquement en mouvement (aux échelles d'observations des individus), com- posés d'objets difficilement discernables, ces milieux présentent des conditions météorologiques variables, voir hostiles (éclairage, humidité, température, etc.). Cette cartographie se place généralement dans une étude thématique qui ra- joute ses propres contraintes opérationnelles (besoin d'information 3D comme le relief ou la rugosité, signature spectrale spécifique, prises de vues obliques pour simplifier l'identification visuelle par les experts, etc.). Par ailleurs, l'utilisation en télédétection basse altitude de porteurs légers, comme les micro-drones, limite fortement les ressources disponibles pour les capteurs : puissance de calcul embarquée, encombrement, poids, etc.. Nous présenterons dans cet article deux capteurs : le capteur tri-caméras et le banc stéréoscopique uEye. Le capteur tri-caméras a été développé en 2009 pour l'ac- quisition d'images stéréoscopiques ou obliques à basse altitude. En analysant l'expérience tirée des campagnes terrains effectuées, nous soulignerons l'importance cruciale de la synchronisation précise des prises de vues. Nous présenterons alors notre nouveau banc stéréoscopique amphibie en développement depuis 2013, et qui vise la possibilité d'acquisitions stéréoscopiques parfaitement synchronisées, ce qui en fait un outil idéal pour l'étude des zones littorales (pour la télédé- tection basse altitude ou in situ à faible profondeur). Nous terminerons par une présentation des premiers résultats obtenus avec ce nouveau banc.

Yuming Zeng, Hao Zhou, Hugh Roarty et al.

Wind speed is an important sea surface dynamic parameter which influences a wide variety of oceanic applications. Wave height and wind direction can be extracted from high frequency radar echo spectra with a relatively high accuracy, while the estimation of wind speed is still a challenge. This paper describes an artificial neural network based method to estimate the wind speed in HF radar which can be trained to store the specific but unknown wind-wave relationship by the historical buoy data sets. The method is validated by one-month-long data of SeaSonde radar, the correlation coefficient between the radar estimates and the buoy records is 0.68, and the root mean square error is 1.7 m/s. This method also performs well in a rather wide range of time and space (2 years around and 360 km away). This result shows that the ANN is an efficient tool to help make the wind speed an operational product of the HF radar.

Xiaoli Zhou, Hongqiang Wang, Yongqiang Cheng et al.

Radar coincidence imaging (RCI) is a high-resolution staring imaging technique without the limitation of the target relative motion. To achieve better imaging performance, sparse reconstruction is commonly used. While its performance is based on the assumption that the scatterers are located at the prediscretized grid-cell centers, otherwise, off-grid emerges and the performance of RCI degrades significantly. In this paper, RCI using frequency-hopping (FH) waveforms is considered. The off-grid effects are analyzed, and the corresponding constrained Cramér-Rao bound (CCRB) is derived based on the mean square error (MSE) of the “oracle” estimator. For off-grid RCI, the process is composed of two stages: grid matching and off-grid error (OGE) calibration, where two-dimension (2D) band-excluded locally optimized orthogonal matching pursuit (BLOOMP) and alternating iteration minimization (AIM) algorithms are proposed, respectively. Unlike traditional sparse recovery methods, BLOOMP realizes the recovery in the refinement grids by overwhelming the shortages of coherent dictionary and is robust to noise and OGE. AIM calibration algorithm adaptively adjusts the OGE and, meanwhile, seeks the optimal target reconstruction result.

Yun Zhou, Shaojun Fang, Hongmei Liu et al.

R. Wilding, Rein Juriado

Asheeta Bhavnani, Rowena Won-Wai Chiu, Subramaniam Janakiram et al.

Byeonggwi Mun, Yonghyun Yoon, Hyunwoo Lee et al.

A compact (50 × 50 × 4 mm3) dual-band radio frequency identification (RFID) tag antenna mountable on metallic objects is proposed for the ultra-high frequency (UHF) band (917∼923.5 MHz) and the microwave (MW) band (2.4∼2.45 GHz). With the proximity-coupled feed loop, the proposed antenna consists of two symmetric planar inverted-F antenna (PIFA) elements for the UHF band passive tag and a meander microstrip patch antenna for the MW band active tag. The performance of the proposed antenna is verified by mounting it on the different sizes of the metallic object. Furthermore, the passive tag antenna in the UHF band furthermore may be used for energy harvesting techniques to improve the lifetime of the active tag in the MW band. The measured maximum read range is 5.50 m in the UHF band and 14.15 m in the MW band when the proposed tag antenna is mounted on the metallic objects. The total efficiency for all operating frequency bands is higher than 50%. High isolation (>12 dB) between tag antennas in the UHF band and the MW band is achieved.

Shiqi Wang, Ngai Lok Chong, Johanna Virkki et al.

We investigate the impact of washing on the performance of passive UHF RFID tags based on dipole antennas fabricated from copper fabric and coated with protective epoxy coating. Initially, the tags achieved read ranges of about 8 meters, under the European RFID emission regulation. To assess the impact of washing on the performance of the tags, they were washed repeatedly in a washing machine and measured after every washing cycle. Despite the reliability challenges related to mechanical stress, the used epoxy coating was found to be a promising coating for electrotextile tags in moist conditions.

Juhee Kwon, Eric Johnson

Antonio Ferraz, Clément Mallet, Stéphane Jacquemoud et al.

Dans le cadre des politiques de lutte contre le réchauffement climatique (programme UN-REDD des Nations Unies), les techniques de télédétection sont désormais utilisées pour extrapoler des estimations de la biomasse aérienne à l'échelle locale (dérivées à partir des mesures terrain obtenues via des inventaires forestiers) sur des grandes surfaces où aucune donnée de référence n'est disponible. Néanmoins, la communauté scientifique signale encore une grande incertitude concernant la quantification du CO2 stocké dans les forêts. Cela est dû au nombre insuffisant d'échantillons terrains sur des grandes zones de forêt de la planète, notamment dans des pays qui n'ont pas de pratiques régulières d'inventaires forestiers. Dans cet article, nous investiguons la fiabilité de la technologie lidar aéroporté (airborne laser scanning, ALS) pour estimer la biomasse aérienne des forêts sans nécessiter d'importantes mesures terrain. D'abord, des métriques forestières clés qui sont couramment obtenues via les inventaires forestiers traditionnels sont dérivées par analyse des donnés lidar. Il s'agit notamment de la densité d'arbres, leur hauteur individuelle, l'épaisseur de la couronne, la hauteur moyenne de chaque strate, et le taux de couverture de canopée de chacune de celles-ci. Puis, des équations allométriques sont utilisées pour estimer la biomasse à partir des mesures terrain ainsi que des mesures lidar. Enfin, les résultats sont évalués pour chaque strate de végétation sur 40 parcelles d'une forêt portugaise à plusieurs strates de végétation. La biomasse aérienne est dérivée à l'échelle de la placette forestière avec une erreur de 0,4% comparée aux estimations terrain, ce qui prouve que notre approche est un outil efficace pour estimer la biomasse aérienne avec précision. Le développement de techniques similaires fondées sur le lidar aéroporté, capables de traiter forêts de différents biomes, avec l'utilisation conjointe de mesures obtenues par télédétection satellitaire, serait une avancée significative pour l'estimation de la biomasse sur de vastes régions à l'échelle mondiale.

Chung-Liang Chang, Guo-Shing Huang

A compressive sensing based array processing method is proposed to lower the complexity, and computation load of array system and to maintain the robust antijam performance in global navigation satellite system (GNSS) receiver. Firstly, the spatial and temporal compressed matrices are multiplied with array signal, which results in a small size array system. Secondly, the 2-dimensional (2D) minimum variance distortionless response (MVDR) beamformer is employed in proposed system to mitigate the narrowband and wideband interference simultaneously. The iterative process is performed to find optimal spatial and temporal gain vector by MVDR approach, which enhances the steering gain of direction of arrival (DOA) of interest. Meanwhile, the null gain is set at DOA of interference. Finally, the simulated navigation signal is generated offline by the graphic user interface tool and employed in the proposed algorithm. The theoretical analysis results using the proposed algorithm are verified based on simulated results.

Maria Cecilia Brandalize, Alzir Felippe Antunes

Le Conseil du Service Géographique (DSG), en collaboration avec l'Institut Brésilien de Géographie et de Statistique (IBGE), sont responsables de la cartographie systématique du territoire brésilien (échelle 1/1.000.000 au 1:25.000) depuis leur création, respectivement en 1890 et 1934. Compte tenu de la longue histoire dans l'établissement d'un système cartographique national, comprenant plusieurs projets de cartographie topographique au cours du siècle dernier, la plupart d'entre eux reposent sur une couverture photogrammétrique. Le territoire relevé n’a pas été mis à jour étant donné que le cartes les plus récentes datent des années 80. Le manque d’une politique de mise à jour des cartes topographiques indique la situation chaotique que les planificateurs et les gestionnaires en général connaissent actuellement au Brésil. Ainsi, bien que le territoire brésilien soit complètement couvert, depuis 1922, à l'échelle du 1 :1.000.000 (46 feuilles au total), la gamme de produits la plus courante pour cette échelle date de 1998, lorsque sa dernière mise à jour s’est appuyée sur des images de télédétection. D'autre part, des échelles plus grandes telles que 1:100.000, 1:50.000 et 1:25.000, couvrant respectivement 75%, 14% et 1% du territoire brésilien proviennent de la période entre 1908 et 1985, la plupart datant de 30 ans et sans un mise à jour périodique. Le manque de données cartographiques à des échelles aussi importantes pénalise le développement local et régional, ainsi que la planification et la surveillance de l'environnement, des plans et des actions basées sur des informations peu fiables et inexactes. Les initiatives prises par le gouvernement afin de résoudre certains problèmes de surveillance et de gestion de l'environnement, en particulier dans la région amazonienne, culminent dans des projets fondés uniquement sur les techniques de télédétection, comme les projets RADAM (Radar de l'Amazonie) et SIVAM (Système de Surveillance de l’Amazonie). D'autres initiatives sont remarquées, depuis 2006, pour la coopération entre l'IBGE et l'Alaska Satellite Facility (ASF), visant à la distribution des images de télédétection à des organismes du Gouvernement Fédéral, à des institutions de recherche et à d’autres usagers non commerciaux au Brésil. Ces images visent à accélérer le processus de cartographie du territoire et de ses mises à jour ultérieures, ce qui permet une planification plus efficace de l'action gouvernementale. Dans un pays où le développement et la diffusion des produits cartographiques sont plus avancés que le développement social et économique, de telles initiatives doivent être discutées et analysées de façon critique.

Deshuang Zhao, Yifei Han, Feng Liang et al.

A novel compact beam-reconfigurable patch antenna based on light control of no more than 30 mW optical powers is successfully demonstrated. It consists of one T-shape driven patch and one slot-etched parasitic patch. A silicon dice is employed as the photoconductive switch that is bridged across the slot center for optical control of reconfigurable beams. The antenna greatly reduces the total optical powers required for reconfigurable beams. Such design is based on the fact that the current phase change of the parasitic patch is sensitive to the conductivity of the silicon dice. A few conductivity changes of the silicon dice induced by the optical light can lead to a big phase change of the parasitic patch currents, eventually resulting in reconfigurable beams with low optical power requirement.