共查询到20条相似文献,搜索用时 15 毫秒
1.
If you asked people 20 years ago what they could do with their phone, they would have simply said, "Call people". Today, a reply would not be that short and easy. The transformations this device has undergone over the last two decades are tremendous. The mobile phone has evolved into a sleek multifuncational marvel. However, the versatile new models are not as good as the old ones when it comes to clear reception. Also, mobile phones' additional functions eat up battery life, so there is less talk time. The author looks at how mobile telephoning has turned into mobile media-based information exchange and the turmoil this transformation has caused. 相似文献
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A new technique of synthesis of near-field (NF) amplitude and phase patterns of linear, planar, of volume arrays of finite size or arrays located on a planar contour of finite size is presented. The array could consist of point dipoles or directive elements. The criterion for prescribing the NF (amplitude and phase) pattern information in the synthesis problem for unique determination of array excitation currents is also stated. The proposed near-field synthesis technique is based on the potential integral solution of source currents, Nyquist sampling of the near-field data and the technique of linear least square approximation (LLSA). The NF pattern synthesis technique is illustrated to synthesize a variety of NF patterns with a number of array configurations. Application of the proposed NF pattern synthesis technique to minimize distortion in far-field patterns of arrays mounted on a conducting platform and to realize array antennas with low sidelobes in the near and far field is also presented. 相似文献
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A unified method for the optimization of receiving arrays is presented. The optimization is performed by a linear transformation (coordinate transformation) method. Arrays of lossless arbitrarily arranged in space, but uniformly oriented, elements are analyzed. 相似文献
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Application of antenna arrays to mobile communications. II.Beam-forming and direction-of-arrival considerations 总被引:5,自引:0,他引:5
Godara L.C. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1997,85(8):1195-1245
Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing 相似文献
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Giacomazzi P. Musumeci L. Caizzone G. Verticale G. Liggieri G. Proietti A. Sabatini S. 《IEEE network》2006,20(1):12-20
IP telephony over mobile ad hoc networks is a topic of emerging interest in the research arena as one of the paths toward the fixed-mobile convergence in telecommunications networks. To investigate the performance characteristics of this service, we propose a complete system architecture, which includes a MAC protocol, a routing protocol, and the treatment of voice packets. The telephone system is analyzed in the case of point-to-point calls inside the ad hoc network, and the end-to-end performance is assessed in terms of the percentage of blocked and dropped calls, packet loss and packet delay. The analysis takes into account network scalability by investigating how; the size of the multihop ad hoc network impacts the quality of service. Moreover, the synthetic mean opinion score of the telephone service is evaluated according to the ITU-T E-model. 相似文献
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Bolomey J.-C. Cown B.J. Fine G. Jofre L. Mostafavi M. Picard D. Estrada J.P. Friederich P.G. Cain F.L. 《Antennas and Propagation, IEEE Transactions on》1988,36(6):804-814
Key results are summarized of efforts to significantly reduce the near-field measurement time by utilizing one- or two-dimensional arrays of modulated scattering probes in lieu of the single probe ordinarily used in conventional near-field measurement techniques. Results of analytical, numerical, and experimental investigations show that the modulated-scattering technique (MST) using arrays of hundreds or even thousands of modulated scattering probes can be used to map the complex near-field of antennas or scatterers in a few seconds or minutes. The results also strongly indicate that classical (nonmodulated) receiving/transmitting arrays can be adapted for rapid near-field data collection. Major factors affecting the accuracy and speed of probe arrays for near-field measurement are delineated and discussed. Experimental results obtained using laboratory prototype MST systems are also presented and discussed 相似文献
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Bucci O.M. Capozzoli A. D'Elia G. 《Antennas and Propagation, IEEE Transactions on》2004,52(1):132-141
A conformal array power pattern synthesis technique is presented which makes it possible to take into account near-field constraints and to reconfigure the radiated pattern by controlling only the phases of the excitation coefficients. Far-field pattern specifications are given by masks while near-field constraints are given by prescribing the maximum allowable field intensity at points arbitrarily located in a given near-field region. The amplitude of the excitations, common to all radiated beams, and the phases corresponding to each one are obtained as a result of the synthesis algorithm. 相似文献
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The analysis of a Y-junction laser array is presented. It is shown that the lowest-order cavity mode of this array has the lowest threshold gain and is thus preferentially excited. This mode has a uniform near-field distribution. Compared with the sinusoidal near-field distribution of the supermodes of the evanescently coupled laser arrays, this uniformity not only can delay the onset of the spatial-hole burning, which is the source of unstable far-field characteristic at high power level, it also allows for higher total power output before catastrophic mirror damage. 相似文献
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It is generally accepted that the Dolph-Pritchard technique for computing optimum or Chebyshev radiation patterns for single-lobe endfire arrays is valid for any array element spacing less than one-half wavelength. However, it can be shown that multiple-lobe radiation patterns will be obtained using this technique for element spacing less than one-half wavelength. A maximum element spacing for single-lobe radiation patterns can be derived, and this spacing is a function of the major-lobe-to-sidelobe amplitude ratio as well as the order of the Chebyshev polynomial. In general, for large amplitude ratios this maximum spacing approaches one-quarter wavelength. 相似文献
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为了实现对室内声源定位的目的,文中对其中的两个关键技术:时延估计、定位算法做了深入的研究.通过使用高保真监听拾音器、多功能信号采集器MPS010602,以及结合简单的数据采集图形化编程软件LabVIEW,搭建了软硬件设计系统,讨论了五元十字阵列在不同条件下的定位精度.实验应用表明:该系统可以创新性的对多个声源判决定位,并且提高了声阵列定位成像系统在细节上的分辨能力. 相似文献
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The optimum directivity of various types of uniformly spaced broadside arrays of dipoles is investigated theoretically in this paper. The formulation is processed with the aid of an array matrix. The expression for the optimum directivity and the corresponding excitation are expressed directly in terms of the elements of the array matrix. The computed values are assembled in several sets of curves, and the results are compared with the directivity of uniformly excited arrays. 相似文献
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圆形口径平面天线阵列的多约束稀布优化方法 总被引:1,自引:0,他引:1
针对圆形口径平面稀布阵列的多约束优化设计问题,以均匀同心圆环阵列的阵元位置分布特性为基础,构造了稀布圆阵的满足多个优化约束的可行初始解.提出了一种个体元素的间接表示法,设计了一种新的交叉算子和变异算子,运用改进的实数遗传算法优化设计天线阵的阵元位置.优化约束包括阵元数约束、口径约束和最小阵元间距约束,优化目标是使阵列响应的峰值旁瓣电平最小.运用这种改进实数遗传算法可以充分利用阵元布阵的自由度,同时能减小搜索空间,提高计算效率。仿真试验证实了算法的稳健性和有效性. 相似文献
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Simple unified algorithm for estimating and tracking location of desired talker by microphone arrays
In this paper, we discuss a unified approach and its simple algorithm for estimating and tracking the location of the desired talker in the far field and the near field by microphone arrays. The approach is unified for the far field and the near field and can enhance the effective power of the talker's signal. The simple algorithm further avoids singular-value decomposition (SVD) computations and is suitable for real-time processing. Computer simulations and experiments using actual array data support the techniques.Financial support from National Science and Technology Board of Singapore.On leave from the Department of Electronic Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China. 相似文献
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The paper introduces a new development of an existing technique for channel sounding waveform generation. The signal is based on an optimized low crest factor signal which is pre-equalized and predistorted to compensate for the linear and nonlinear elements in the transmitter. The generated signal is such that, at the power amplifier's output, the power spectrum over the bandwidth of interest is uniform and such that there are no out-of-band components. In this way best utilisation is made of the available bandwidth and power. No bandpass filters are required 相似文献
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This paper is an examination of the diffusion of mobile telephony in Norway, and particularly among teens. There has been a near saturation of this social group. Because of this situation, it is of interest to know what this can tell us regarding the mechanisms of adoption. Given this focus I look into the work of Rogers ’ and that of Silverstone and Haddon and their domestication perspective. The positive and the negative sides of these approaches are examined in the light of the recent experience with the mobile telephone. Rogers’ discussion of the social mechanisms behind diffusion and his work on the critical mass of communication equipment are of interest. On the other hand his basis in the world of marketing and perhaps simplistic diffusion progression are questioned. Another approach is that of domestication is seen to be a more of a global analysis of adoptions ex post facto. The approach provides one with an understanding of how innovations change and are changed by their social contexts. Finally, several areas of further research are outlined. 相似文献
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Microwave diagnosis of antennas is considered as a viable tool for the determination of reflector surface distortions and location of defective radiating elements of array antennas. A hybrid technique based on the combination of the spherical near-field measurements and holographic metrology reconstruction is presented. The measured spherical near-field data are first used to construct the far-field amplitude and phase patterns of the antenna on specified regularized u -v coordinates. These data are then utilized in the surface profile reconstruction of the holographic technique using a fast-Fourier-transform (FFT)/iterative approach. Results of an experiment using a 156-cm reflector antenna measured at 11.3 GHz are presented for both the original antenna and the antenna with four attached bumps. Several contour and gray-scaled plots are presented for the reconstructed surface profiles of the measured antennas. The recovery effectiveness of the attached bumps has been demonstrated. The hybrid procedure presented is used to assess the achieved accuracy of the holographic reconstruction technique because of its ability to determine very accurate far-field amplitude and phase data from the spherical near-field measurements 相似文献