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

Qi Guo, Daozong Sun, Zhen Li et al.

In this article, the inverse diffraction parabolic equation (IDPE) model based on the finite difference method is proposed, which is first applied in the multiple nonradiation targets orientation technology. In principle, the electromagnetic signal propagating in the transmission path will produce a reflected signal back to the source end while encountering the discontinuous objects. The distribution of the reflection or refraction intensity is directly associated with the distances and heights of the objects, so the location can be determined by means of analyzing the distribution. Here, according to the profile data of field intensity at the source end, the distribution of backward propagating electromagnetic waves are calculated rapidly by the IDPE. Then, the local extreme searching method is applied to search the coordinate of the convergence point of field intensity and the positions of multiple objects are finally determined. The piecewise linear function is used to model the irregular terrain. The influence of discontinuous terrain slopes on the false alarm probability of objects localization is also analyzed. The results show that the localization accuracy of the IDPE algorithm is affected by multiple factors, such as the radio frequency and sampling interval of field intensity. It is proved that the IDPE is a novel and efficient algorithm for multiple nonradiation targets orientation technology in long-range complicated terrain environment.

Wei Li, Fengshuo Zhang, Ying Suo et al.

In this paper, we propose a miniaturized 2.5-dimensional (2.5D) frequency selective surface (FSS) structure with high angular stability. A novel closed-loop FSS is formed by combining the Jerusalem cross (JC) structure with the conventional rectangular closed loop using vias. This approach further enhances the coupling performance of the FSS and thus achieves miniaturized design. The unit cell size of the proposed FSS is 0.019λ0 × 0.019λ0 at the resonant frequency, and the metal is printed on a dielectric substrate with a thickness of 0.003λ0. The proposed FSS has a resonant frequency of 850 MHz and exhibits band-stop characteristics. It is insensitive to the incident angle with a good operating performance in both the TE and TM wave modes. Therefore, it can be well used as an electromagnetic shield for the GSM 850 band. In order to facilitate the rapid analysis and design of the FSS, the equivalent circuit model is further analyzed and established, and values of the corresponding lumped components are derived. In addition, a prototype FSS is fabricated using printed circuit board technology and is tested in a microwave anechoic chamber. The full-wave analysis simulation, equivalent circuit model simulation, and practical measurement results reflect a high level of consistency.

Haibin Jiang, Zhiyong Yu, Jian Yang et al.

Full-duplex cooperative spectrum sensing (FD-CSS) is an important research field in the field of spectrum sensing. In the FD-CSS network, the secondary user (SU) senses the usage status of the authorized spectrum by the primary user (PU) through the sensing channel and then reports the perceived data to the fusion center (FC) through the reporting channel. The FC makes a comprehensive judgment after summarizing the data through the fusion algorithm. In the secondary network with SU, throughput is an important index to measure the performance of the network. Taking throughput as the optimization goal, this paper theoretically deduces and verifies the optimal data fusion algorithm in cooperative spectrum sensing (CSS), the threshold of optimal energy detection, and the optimal transmission power of SU in the secondary network. The simulation results show the correctness of the results in this paper.

Xinhuan Yang, Yanzhu Qi, Bo Yuan et al.

A miniaturized high-gain flexible unmanned aerial vehicle (UAV) antenna is presented in this study. The proposed antenna basically comprised of three parts of printed patch in series, etched on dielectric substrate. And, a flexible cable is loaded on the bottom of dielectric substrate. A coplanar waveguide (CPW) with asymmetric ground feeding structure is employed to provide good impedance matching. The surface current can achieve the same phase for the straight-line patch and the flexible cable, through adjusting the dimensions of the meander line patch, which increases radiation gain while maintaining the compact size. As an important merit to be highlighted, the flexible cable can greatly reduce the volume and aerodynamic drag of the antenna. It has a low-profile compact size of 196 × 15 × 0.8 mm3 (excluding flexible cable). The results show that the omnidirectional gain fluctuates within 4.5 ± 0.1 dBi in the desired band (902 MHz–928 MHz), which is high enough for the UAV application. Details of the antenna design and experimental results are presented and discussed.

Junchang Sun, Shuai Ma, Hui Zhou et al.

Compared with the line-of-sight (LOS) condition, the multipath effect is more serious in the non-line-of-sight (NLOS) condition. Therefore, the LOS and NLOS identification is necessary for the multipath analysis of signal propagation. The commonly used method is the support vector machine (SVM) method with high computational complexity. To tackle this problem, this paper adopts the SVM classifier based on fewer selected features of the normalized power delay profile (PDP). Therein, the PDP can be obtained using the sliding correlation method. The results show that the SVM-based classifier can achieve high accuracy on LOS and NLOS identification. We then analyze the impact of the signal-to-noise ratio (SNR) and transmitting-receiving (Tx-to-Rx) distance on distinguishable multipaths under LOS and NLOS conditions. According to statistical measurement results, a function of distinguishable multipath numbers is established. Finally, we investigate the multipath power and delay parameters of average delay spread and root mean square (RMS) delay spread based on multipath results. The outcomes of this paper provide a useful support for analyzing signal propagation characteristics.

Longhe Wang, Bo Ai, Jingya Yang et al.

With the development of the vehicular network, new radio technologies have been in the spotlight for maximizing the utilization of the limited radio spectrum resource while accommodating the increasing amount of services and applications in the wireless mobile networks. New spectrum policies based on dynamic spectrum access technology such as flexible access common spectrum (FACS) have been adopted by the Korea Communications Commission (KCC). 23 GHz bands have been allocated to FACS bands by the KCC, which is expected extensively for vehicular communications. The comprehensive knowledge on the radio channel is essential to effectively support the design, simulation, and development of such radio technologies. In this paper, the characteristics of 23 GHz vehicle-to-infrastructure (V2I) channels are simulated and extracted for the urban environment in Seoul. The path loss, shadow factor, Ricean K-factor, root-mean-square (RMS) delay spread, and angular spreads are characterized from the calibrated ray-tracing simulation results, and it can help researchers have a better understanding of the propagation channel for designing vehicular radio technologies and a communication system in a similar environment.

Jun Hu, Tong-Tong Qiu, Xue Lan et al.

With the development of Multiple-Input Multiple-Output technologies, researches on radio vortex wave with orbital angular momentum have become active. At the same time, generators of miniaturized planar antennas have become very interesting. Considering multilayer package, we proposed a uniform circle array consisting of four double-layer patch antennas with microstrip backfeeds. The antenna can generate three modes of vortex waves, which works at frequency 7.6GHz with a bandwidth 8.5%. Compared with orbital angular momentum antennas of phased uniform circular array with other cells, this proposed structure can be easily integrated with planar feeding networks and decoupling networks.

Qian Li, Chong Ding, Ruichao Yang et al.

Meander lines (MLs) in two configurations are presented to reduce the mutual coupling (MC) between two microstrip patch antenna elements. Inserting a slot in the ground plane between the antenna elements is a simple method to reduce the MC, while adding the MLs in the slot of the ground can further reduce the MC. In the first configuration, one ML is inserted in the slot of the ground and a maximum MC reduction of 39 dB throughout the −10 dB bandwidth is achieved. What’s more, the radiation patterns are not changed compared with the dual-element microstrip antenna array with a slotted ground. For the second configuration, two MLs are added in the slot of the ground. It is found that a maximum isolation of 53 dB can be obtained. However, the radiation patterns are slightly changed compared with the dual-element microstrip antenna array with a slot in the ground. Meanwhile, the measured peak gain and efficiency of the dual-element microstrip antenna array in the two configurations are given. Along with this paper, several prototypes have been fabricated and measured. The simulated results are in good accordance with the measurements, which are presented to verify that MC reduction can be achieved between microstrip antenna elements by adding the MLs in the slotted ground.

Muhannad Almutiry, Lorenzo Lo Monte, Michael C. Wicks

We proposed an improved solution to two problems. The first problem is caused by the sidelobe of the dominant scatterer masking a weak scatterer. The proposed solution is to suppress the dominant scatterer by modeling its electromagnetic effects as a secondary source or “extra dependent transmitter” in the measurement domain. The suppression of the domain scatterer reveals the presence of the weak scatterer based on exploitation of multipath effects. The second problem is linearizing the mathematical forward model in the measurement domain. Improving the quantity of the prediction, including multipath scattering effects (neglected under the Born approximation), allows us to solve the inverse problem. The multiple bounce (multipath) scattering effect is the interaction of more than one target in the scene. Modeling reflections from one target towards another as a transmitting dipole will add the multiple scattering effects to the scattering field and permit us to solve a linear inverse problem without sophisticated solutions of a nonlinear matrix in the forward model. Simulation results are presented to validate the concept.

Jian Zhang, Xiaoxing Zhang, Song Xiao

In recent years, extensive research has been conducted on the ultrahigh-frequency (UHF) method. Considering that acquiring a partial discharge UHF signal is the first step in a series of tasks, such as fault diagnosis and defect location, the UHF sensor plays an important role in the UHF method. An antipodal Vivaldi antenna installed at a transformer’s joint is designed in this study according to the structural features of 750 kV transformers in China. Several effective structures, such as linear gradient microstrip and slot edge, are employed to improve the return loss and radiation characteristics. A metal box is designed after analyzing the influence of the metal around the antenna. The metal box can effectively shield against electromagnetic interference and does not deteriorate the performance of the antenna significantly. Experimental data show that this antenna is much more sensitive than the rectangular plane spiral antenna. The proposed antipodal Vivaldi antenna is suitable for detecting partial discharge in large transformers.

Giovanni Cappelletti, Diego Caratelli, Renato Cicchetti et al.

An improved low-profile printed antipodal drop-shaped dipole antenna for wide-band wireless applications is presented. The proposed radiating structure is integrated with a planar metal reflector useful to enhance antenna gain up to 5.5 dBi and the front-to-back ratio up to 21 dB. The geometry of reflector, feeding line, and dipole arms is optimized in order to achieve a broad operating bandwidth useful to meet the requirements of modern wireless communication protocols. Furthermore, the particular shape of the metal reflector and the adoption of a thin low-permittivity dielectric substrate result in a low distortion of the radiated field and a limited back radiation which makes the antenna suitable for UWB applications as well. These features, together with the low profile and the limited occupation area, make the antenna well adapted to mobile terminals as well as radio base stations. A locally conformal FDTD numerical procedure has been adopted to design and analyse the radiating structure, while a SEM technique has been employed to highlight the field perturbation caused by the antenna reflector as well as to extract the characteristics underlying the transient behaviour of the antenna. The experimental measurements performed on an antenna prototype are found to be in good agreement with the numerical computations.

Shuang Li, Wei Liu, Daqing Zheng et al.

Source localization using sensor array in the near-field is a two-dimensional nonlinear parameter estimation problem which requires jointly estimating the two parameters: direction-of-arrival and range. In this paper, a new source localization method based on sparse signal reconstruction is proposed in the near-field. We first utilize l1-regularized weighted least-squares to find the bearings of sources. Here, the weight is designed by making use of the probability distribution of spatial correlations among symmetric sensors of the array. Meanwhile, a theoretical guidance for choosing a proper regularization parameter is also presented. Then one well-known l1-norm optimization solver is employed to estimate the ranges. The proposed method has a lower variance and higher resolution compared with other methods. Simulation results are given to demonstrate the superior performance of the proposed method.

Cheng-Nan Hu, Dau-Chyrh Chang, Chung-Hang Yu et al.

This paper presents a high gain millimeter-wave (mmW) low-temperature cofired ceramic (LTCC) microstrip antenna array with a compact, simple, and low-profile structure. Incorporating minimum mean square error (MMSE) adaptive algorithms with the proposed 64-element microstrip antenna array, the numerical investigation reveals substantial improvements in interference reduction. A prototype is presented with a simple design for mass production. As an experiment, HFSS was used to simulate an antenna with a width of 1 mm and a length of 1.23 mm, resonating at 38 GHz. Two identical mmW LTCC microstrip antenna arrays were built for measurement, and the center element was excited. The results demonstrated a return loss better than 15 dB and a peak gain higher than 6.5 dBi at frequencies of interest, which verified the feasibility of the design concept.

Seok-hwan Min, Hayeon Kim, Haengseon Lee et al.

Indoor millimeter wave propagation at the frequency of 24 GHz is studied by experimental methods. Measurements are performed to obtain temporal and spatial channel model using a channel sounder and rotating antennas in a corridor. The measured impulse responses are processed to obtain compact channel model following Saleh-Valenzuela’s model. The responses are compared with those of 5.3 GHz for the same test sites. Angular spread of 24 GHz is found to be smaller than that of 5.3 GHz, while echoes of 24 GHz are found to be longer than those of 5.3 GHz.

Ben Bacque, T. Gachovska, R. Orr et al.

Français Français

L’utilisation des données LiDAR aéroporté pour modéliser, caractériser et cartographier la ressource forestière est effective depuis une dizaine d’années dans les pays d’Amérique du Nord ou d’Europe du Nord. Néanmoins, en France, il existe peu d’exemples d’applications forestières du LiDAR sur de grandes surfaces, dans des contextes forestiers souvent plus complexes et hétérogènes que les forêts boréales et les grandes pinèdes du nord de l’Europe. Dans cette étude, la méthode dite « surfacique », qui consiste à calibrer des modèles empiriques de régression mettant en relation des paramètres dendrométriques mesurés sur le terrain avec des métriques dérivées des données LiDAR, est évaluée sur trois sites forestiers français. Les modèles de prédiction se basent sur les métriques usuelles dérivées du nuage de points LiDAR, ainsi que sur des métriques calculées à partir d'une individualisation préalable des houppiers des arbres dominants. Une validation indépendante, à l’échelle du peuplement, a permis d’évaluer la fiabilité des modèles de prédiction sur des surfaces de l'ordre d’un hectare, pertinentes pour le gestionnaire. Les résultats montrent qu’il est possible de caractériser la ressource forestière dans différents peuplements, allant des hêtraies ou pinèdes régulières de plaine aux sapinières-pessières hétérogènes de montagne. L'erreur des modèles (RMSE) estimée par validation croisée à l'échelle de la placette est de 14 à 22 % (R² de 0,75 à 0,90) pour la surface terrière, de 7 à 8 % (R² de 0,76 à 0,96) pour le diamètre dominant et de 17 à 32 % (R² de 0,50 à 0,88) pour la densité de tiges. La validation indépendante à l’échelle du peuplement montre une bonne fiabilité des modèles quel que soit le paramètre forestier étudié, et tant qu’ils sont utilisés dans leur domaine de validité. Les écarts entre les moyennes des prédictions et les mesures de référence terrain sont de l’ordre de 10 à 15 % pour la surface terrière, de 6 à 8% pour le diamètre dominant et de 10 à 33% pour la densité de tiges. Ces résultats démontrent, sur des surfaces unitaires d’environ un hectare, que l'inventaire par LiDAR aérien peut atteindre une précision équivalente à celle des méthodes traditionnelles de terrain, y compris pour des forêts complexes.

Wei-Qiang Pan, Xiao-Lan Zhao, Yao Zhang et al.

This paper presents a novel method to design dual-band bandpass filters with tunable lower passband and fixed upper passband. It utilizes a trimode resonator with three controllable resonant modes. Discriminating coupling is used to suppress the unwanted mode to avoid the interference. Varactors are utilized to realize tunable responses. The bandwidth of the two bands can be controlled individually. Transmission zeros are generated near the passband edges, resulting in high selectivity. For demonstration, a tunable bandpass filter is implemented. Good agreement between the prediction and measurement validates the proposed method.

Wei Fan, Pekka Kyösti, Jesper Ø. Nielsen et al.

This paper discusses over the air (OTA) testing for multiple input multiple output (MIMO) capable terminals with emphasis on modeling bidirectional spatial channel models in multiprobe anechoic chamber (MPAC) setups. In the literature, work on this topic has been mainly focused on how to emulate downlink channel models, whereas uplink channel is often modeled as free space line-of-sight channel without fading. Modeling realistic bidirectional (i.e., both uplink and downlink) propagation environments is essential to evaluate any bidirectional communication systems. There have been works stressing the importance of emulating full bidirectional channel and proposing possible directions to implement uplink channels in the literature. Nevertheless, there is no currently published work reporting an experimental validation of such concepts. In this paper, a general framework to emulate bidirectional channels for time division duplexing (TDD) and frequency division duplexing (FDD) communication systems is proposed. The proposed technique works for MPAC setups with arbitrary uplink and downlink probe configurations, that is, possibly different probe configurations (e.g., number of probes or their configurations) in the uplink and downlink. The simulation results are further supported by measurements in a practical MPAC setup. The proposed algorithm is shown to be a valid method to emulate bidirectional spatial channel models.

Ngoc Phuc Le, Le Chung Tran, Farzad Safaei

The use of per-subcarrier antenna subset selection in OFDM wireless systems offers higher system capacity and/or improved link reliability. However, the implementation of the conventional per-subcarrier selection scheme may result in significant fluctuations of the average power and peak power across antennas, which affects the potential benefits of the system. In this paper, power efficiency of high-power amplifiers and energy efficiency in per-subcarrier antenna selection MIMO-OFDM systems are investigated. To deliver the maximum overall power efficiency, we propose a two-step strategy for data-subcarrier allocation. This strategy consists of an equal allocation of data subcarriers based on linear optimization and peak-power reduction via cross-antenna permutations. For analysis, we derive the CCDF (complementary cumulative distribution function) of the power efficiency as well as the analytical expressions of the average power efficiency. It is proved from the power-efficiency perspective that the proposed allocation scheme outperforms the conventional scheme. We also show that the improvement in the power efficiency translates into an improved capacity and, in turn, increases energy efficiency of the proposed system. Simulation results are provided to validate our analyses.

Michelangelo Villano, Fabiola Colone, Pierfrancesco Lombardo

We consider the selection of an antenna array configuration, composed of a small number of omnidirectional elements, to be exploited for passive radar sensors. Based on properly identified pattern characteristics and design criteria for practical applications, a suitable planar configuration is selected that allows both angular selectivity and direct signal attenuation. The selected configuration is further optimized in terms of sidelobe level by resorting to appropriate amplitude tapering. Moreover, three different approaches are investigated for antenna-based adaptive disturbance cancellation, and a comparative performance analysis is carried out. Simulation results show that an effective clutter suppression is obtained if the direct signal from the transmitter is attenuated by means of spatial adaptive cancellation, and the multipath echoes from stationary obstacles are removed by means of temporal adaptive cancellation. In particular, the approach based on the Sidelobe Canceller is shown to yield good performance while requiring a limited system complexity.