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141.
C. M. Peter Ho Prof. Theodore S. Rappaport M. Prabhakar Koushik 《International Journal of Wireless Information Networks》1994,1(1):61-76
In this paper, the effects of antenna pattern and antenna polarization on indoor obstructed (OBS) wireless channels are investigated experimentally. Our results show that linearly polarized (LP) directional antennas are more effective in combating multipath components than other types of antennas in OBS channels. The measurement results are verified with a deterministic wide-band propagation model based on image theory that takes into account the effects of building geometry, antenna pattern, and antenna polarization. Preliminary prediction results show that the propagation model holds promise for accurate and efficient in-building wireless channel prediction. 相似文献
142.
偏振干涉法用于偏振器消光比的测量 总被引:2,自引:0,他引:2
提出一种偏振器消光比测量的新方法。由于采用了高消光比偏振分光系统和相干探测技术,使得消光比的测量方便和准确。 相似文献
143.
B. L. Ulich 《International Journal of Infrared and Millimeter Waves》1981,2(2):293-310
The basic gain and pointing characteristics of millimeter-wave radio telescopes are described in this paper. Formal definitions of relevant telescope parameters are given. Performance limits set by conventional technology are discussed and compared with measurements of existing telescopes. Methods are also suggested for minimizing pointing errors. 相似文献
144.
Radio pulses from extensive air showers (EAS) at 30, 44, and 60 MHz frequencies have been studied, using wide band broad-side
arrays of half-wave dipole antenna systems. The experimental results support the theoretical prediction that the field strength
of radio emission depends on the shower size. An asymmetry has been noticed in the pulse height distributions of radio pulses
detected by North-South and East-West directed arrays. These observations are in agreement with the theory that the charge
separation mechanism is predominant in generating radio pulses from EAS and radio emission is polarised in the East-West direction.
Experimental data are compared with those of earlier workers. 相似文献
145.
Chihiro J. Uchibori Masayuki Okunishi T. Oku A. Otsuki Naoki Ono Masanori Murakami 《Journal of Electronic Materials》1994,23(9):983-989
The formation mechanisms of InAs/Ni/W ohmic contacts to n-type GaAs prepared by radio-frequency (rf) sputtering were studied
by measuring contact resistances (Rc) using a transmission line method and by analyzing the interfacial structure mainly by x-ray diffraction and transmission
electron microscopy. Current-voltage characteristics of the InAs/Ni/W contacts after annealing at temperatures above 600°C
showed “ohmic-like behavior.” In order to obtain the “ohmic” behavior in the contacts, pre-heating at 300°C prior to high
temperature annealing was found to be essential. The contacts showed ohmic behavior after annealing at temperatures in the
range of 500∼850°C and contact resistance values of as low as ∼0.3Ω-mm were obtained. By analyzing the interfacial structures
of these contacts, InxGa1−xAs layers with low density of misfit dislocations at the InxGa1−xAs and GaAs interface were observed to grow epitaxially on the GaAs substrate upon heating at high temperatures. This intermediate
InxGa1−xAs layer is believed to divide the high energy barrier at the contact metal and GaAs interface into two low barriers, resulting
in reduction of the contact resistance. In addition, Ni was found to play a key role to relax a strain in the InxGa1−xAs layer (introduced due to lattice mismatch between the InxGa1−xAs and GaAs) by forming an intermediate NixGaAs layer on the GaAs surface prior to formation of the InxGa1−xxAs layer. 相似文献
146.
利用近红外光谱(Near infrared spectrum,NIRS)测量技术进行射频损毁术中实时监测技术研究,探讨立体定向术中损毁疗效评估的可行性.在进行丘脑腹外侧核(Ventrolateral Thalamus,Vim)毁损术射频损毁的同时,使用近红外光谱实时采集系统检测在损毁过程中吸收系数(μa)与优化散射系数(μ's)的变化情况.结果表明: 44℃射频损毁过程中吸收系数和优化散射系数增大,停止掀毁后逐步恢复,稳定后μa和μ's稍高于初始值; 70℃射频损毁时μz和μ's增大,停止损毁且稳定后保持不变.根据μa和μ's的变化规律进行立体定向毁损过程实时监测是非常有可能的. 相似文献
147.
148.
We consider a multi‐cell (MC) code division multiple access (CDMA) system that supports multiple service classes, including peak rate allocated and elastic ones. Peak rate allocated sessions—when admitted into the system—transmit at a constant bit rate, while elastic sessions can be slowed down at the expense of increasing their residency time. Admitted sessions cause an instantaneous bit rate‐dependent interference in neighbour cells. In this rather general setting, we propose a method to calculate the class‐wise blocking probabilities as the functions of the estimated so‐called inter‐cell coupling factors. In the paper this coupling factor is the ratio between the uplink path gains to different Node‐B:s (that can be easily obtained in a CDMA system from pilot measurement reports), but our model could include other coupling measures as well. We find that when these coupling factors are underestimated, the system may get into false states (FSs) or false rate states (FRSs) that lead to violating the noise rise threshold. As traffic becomes increasingly elastic, the probability of FSs decreases, but the probability of FRSs increases. Based on numerical results, we make the point that as the traffic becomes more elastic, avoiding the underestimation of these coupling factors as well as exercising MC admission control plays an increasingly important role in guaranteeing proper service quality. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
149.
Christos S. Koukourlis 《International Journal of Communication Systems》2008,21(4):405-418
The implementation of a contemporary method that enables the transmission of digital information at a rate of 2 Mbps over TV signal using the existing broadcasting infrastructure is described. Detailed information on the prototype hardware is given along with experimental results that prove the validity of the proposed method. Finally, a concept for including the method to the existing TV broadcasting network is proposed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
150.
《Digital Communications & Networks》2018,4(4):287-295
This paper focuses on potential issues related to the random selection of a sensing channel that occurs after the prediction phase in a Cognitive Radio Network (CRN). A novel approach (Approach-1) for improved selection is proposed, which relies on the probabilities of channels by which they are predicted idle. Further, closed-form expressions are derived for the throughput of Cognitive Users (CUs) in the conventional and proposed approaches. In addition to this, a fundamental approach for computing the prediction probabilities is also proposed. Moreover, a new challenging issue named “sense and stuck” was observed in the conventional approach. The proposed approach is validated by comparing the results achieved with the results of the conventional approach. However, to achieve the prediction probabilities, the pre-channel-state-information is a prerequisite, but it may be unavailable for particular scenarios; therefore, a modified selection method is introduced to avoid the sense and stuck problem. An algorithm to evaluate the throughput using the random, improved, and modified selection methods is presented with its space and time complexities. Furthermore, for additional improvement in the throughput of the CU, a new frame structure is introduced, in which the spectrum prediction and sensing periods are exploited for simultaneous transmission of data via the underlay spectrum access technique (Approach-2). The simulated results of Approach-2 are compared with our pre-obtained results of Approach-1, which confirm significant improvement in the throughput. 相似文献