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51.
A closed-form conditional probability density function (PDF) of the Nakagami-faded-interference-to-signal power ratio, given the exact location of the tagged mobile, is derived for integer values of Nakagami (1960) fade parameter m. The conditional PDF, whose coefficients can be computed efficiently in a recursive manner, significantly reduces the computational complexity of forward-link bit error rate (BER) evaluation of a direct-sequence code-division multiple-access (DS-CDMA) cellular system over a fading channel, BER curves reveal that the performance improvement of increasing m is not significant for m>4. Performance results for noninteger values of m can be estimated using the linear interpolation technique. With the derived BER expressions, a more realistic cellular model that takes into account the effects of nonidentical m and path-loss exponent is proposed and analyzed. By substituting appropriate values of m, the BER performance for a class of fading distributions such as Rayleigh and Ricean fading can be evaluated or approximated. In particular, the Nakagami approximation may be treated as a tight lower bound to the corresponding mathematically involved Ricean case 相似文献
52.
A growing application area in mobile communications is mobile teleconferencing, in which a group of mobile users collaborate in an interactive procedure, such as a board meeting, a task force, a scientific discussion, or even a virtual classroom. Wireless communications transmit conversations via radio, making them more susceptible to eavesdropping and unauthorized access than are conversations carried via wires. Therefore, it is crucial to ensure confidentiality and authenticity in mobile teleconferencing. When deploying secure services in mobile teleconferences, it has to be taken into account that the mobility of users is usually built on portable devices with limited computing capability. A secure conference scheme for mobile communications needs to be executed efficiently on portable devices. We propose a new secure and efficient conference scheme for mobile communications. Based on a modular square root technique, this scheme is secure against eavesdropping, impersonating, and tracking attacks and allows a participant to join or quit a mobile teleconference dynamically. In addition, the scheme is particularly efficient on the mobile user's portable device because the mobile user needs to perform only single modular multiplication plus encryptions and decryptions of a secret key cryptosystem. 相似文献
53.
有源声学结构:概念、实现及应用 总被引:12,自引:2,他引:10
有源声学结构是近10年来在有源控制和功能结构基础上,发展起来的一项用于噪声控制的新型声学结构,具有低频响应好、通用性强、工程应用前景好的特点。本文就有源声学结构的基本概念、组成结构、实现方法及工程应用等方面的问题给予了深入研究。 相似文献
54.
During the Japanese Occupation of Singapore (1942-1945), Singapore was renamed Syonan (or Syonanto). The Japanese Military Administration established The Medical College on 27 April 2603 (1943) and it was known as The Marei Ika Daigaku or Syonan Medical College. It was sited at the Tan Tock Seng Hospital (Hakua Byoin). The Ika Daigaku relocated to the General Hospital, Malacca in February 2604 (1944) where it functioned till the end of the Japanese Occupation in September 1945. About 200 students from Singapore, Malaya, Sumatra and Java attended the Syonan Medical College; the students were taught mainly Japanese language and culture. 相似文献
55.
56.
In conventional setpoint control problem of robots, the desired position is specified as a point. However, it is interesting to observe from most human reaching movements that the desired targets are regions rather than points. In fact, when the desired region is specified arbitrarily small, it reduces to a point. In this paper, we propose a new control concept called region reaching control for robots. In this new control concept, the desired objective can be specified as a region instead of a point. Since the desired region can be specified arbitrarily small, the region control concept is also a generalization of setpoint control problem. Experimental results are presented to illustrate the performance of the proposed controllers. 相似文献
57.
If you work in the same technical field long enough, you start to see history repeat itself: The more things change, the more they stay the same. 相似文献
58.
This article describes a new approach to fabricate various embedded ceramic microstructures. Design geometries of the microstructures are replicated onto a soft reusable polydimethylsiloxane (PDMS) mold. Rapid consolidation of ceramic suspension on the molds using gel‐casting technique produces structured ceramic layers. 85% aqueous glycerol solution has been identified as suitable adhesive agent to laminate the ceramic layers. Capability of the approach in fabricating embedded microstructures of 3‐dimensional and aspect ratio as high as 20 and 50 has been demonstrated. Ceramic microthruster and Y‐shaped microfluidic reactor are fabricated using this new approach to show its potential to construct various ceramic microdevices. 相似文献
59.
Xizu Wang Jian Wei Ho Qingyi Yang Hoi Lam Tam Gui Xin Li Kok Wai Cheah Furong Zhu 《Organic Electronics》2011,12(11):1943-1947
In this work, Ag nanoparticles were modified by an ultra-thin plasma-polymerized fluorocarbon film (CFX) to form a composite CFX-modified Ag nanoparticles/indium tin oxide (ITO) anode for application in organic photovoltaic (OPV) devices. A CFX-modified Ag nanoparticles/ITO anode exhibited a superior surface work function of 5.4 eV suited for application in OPV devices. The performance of zinc phthalocyanine:fullerene-based OPV devices showed a significant improvement when the structural identical cells are made with the CFX-modified Ag nanoparticles/ITO. This work yielded a promising power conversion efficiency of 3.5 ± 0.1%, notably higher than that with a bare ITO anode (2.7 ± 0.1%). 相似文献
60.
Adams J.A. Thayne I.G. Beaumont S.P. Wilkinson C.D.W. Johnson N.P. Kean A.H. Stanley C.R. 《Electron Device Letters, IEEE》1993,14(2):85-87
MESFETs with gate lengths in the range of 40 to 300 nm with GaAs and AlGaAs buffer layers were characterized by high-frequency transit-time measurements. The total carrier transit time is interpreted as being composed of an intrinsic part, a drain delay, and a channel charging delay. The drain field's effect on the geometry of the gate depletion region, and the injection of carriers into the buffer layer are used to describe the origin of these delays and their limiting effect on the high-frequency performance of sub-0.1-μm gate-length MESFETs 相似文献