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991.
Performance of ultra-wideband communications with suboptimal receivers in multipath channels 总被引:26,自引:0,他引:26
The performance of a single-user ultra-wideband (UWB) communication system employing binary block-coded pulse-position modulation (PPM) and suboptimal receivers in multipath channels is considered. The receivers examined include a RAKE receiver with various diversity combining schemes and an autocorrelation receiver, which is used in conjunction with transmitted reference (TR) signaling. A general framework is provided for deriving the performance of these receivers in multipath channels corrupted by additive white Gaussian noise (AWGN). By employing previous measurements of indoor UWB channels, we obtain numerical results for several cases which illustrate the tradeoff between performance and receiver complexity. 相似文献
992.
Jianjun Gao Choi Look Law Hong Wang Aditya S. Boeck G. 《Microwave Theory and Techniques》2003,51(10):2079-2089
A new method for determining the four noise parameters of pseudomorphic high electron-mobility transistors (pHEMTs) based on a 50-/spl Omega/ noise measurement system without a microwave tuner is presented. The noise parameters are determined based on the noise correlation matrix technique by fitting the measured noise figure of the active device. On-wafer experimental verification up to 26 GHz is presented and a comparison with a tuner-based method is given. The scaling rules for noise parameters have also been determined. Good agreement is obtained between simulated and measured results for 2/spl times/20 /spl mu/m, 2/spl times/40 /spl mu/m, and 2/spl times/60 /spl mu/m gatewidth (number of gate fingers /spl times/ unit gatewidth) 0.25-/spl mu/m double-heterojunction /spl delta/-doped pHEMTs. 相似文献
993.
Yong-Joon Jeon Hyung-Wook Kim Min-Seok Kim Young-Sik Ahn Jong-Won Kim Ji-Youn Choi Doo-Chan Jung Jin-Ho Shin 《Microwave and Wireless Components Letters, IEEE》2003,13(3):102-104
An HBT amplifier with a "post-distortion"-type linearizer utilizing a base-collector junction diode shows more than 8-dB improvement of adjacent channel power ratio, and the collector linearizer comprising a reverse biased base-collector junction diode requires no additional dc power consumption and has no deterioration of RF performance. The linearization technique of post-distortion compensates the nonlinearity of HBTs, which arises from the C/sub bc/ variation due to a large-signal swing. 相似文献
994.
Hyun-Jun Choi Young-Ho Seo Ji-Sang Yoo Dong-Wook Kim 《Optics and Lasers in Engineering》2008,46(4):343-348
A digital holography interference pattern generated by a computer calculation (computer generated hologram, CGH) is one of the most expensive contents and its usage is being expanded. Thus, it is highly necessary to protect the ownership of a digital hologram. This paper introduces a watermarking scheme, a method to protect the ownership of digital holograms using the DCT domain data as the ones to be watermarked. This scheme shows very high imperceptibility and strong robustness against the anticipated attacks. We expect that the conclusions of this paper will be a very useful basis for further work in the area of electronic watermarking schemes for the digital holograms. 相似文献
995.
This paper investigates the influence of uncertainties in geometrical coordinates on calculated torso and epicardial potentials. Two types of sources, spherical epicardial and multipolar, are both considered. A concentric sphere model with the epicardial surface represented by a unit sphere and the torso surface represented by a spherical surface of radius 1.4 is utilized. While the representation of biological surfaces with spheres is a highly idealized situation, the dimensions chosen and the approximations utilized are such that the results should be indicative of those using measured biological coordinates. 相似文献
996.
B. S. Choi 《Annals of the Institute of Statistical Mathematics》1985,37(1):535-539
Summary It is shown that a normal probability density can be characterized as a limit of conditional probability densities of i.i.d.
uniform random variables. 相似文献
997.
998.
Il Kim Hong Ki Choi Taek Kyu Han Seong Ihl Woo 《Journal of polymer science. Part A, Polymer chemistry》1992,30(10):2263-2271
A series of monoester catalysts has been studied, each catalyst prepared by the reaction of magnesium diethoxide with benzoyl chloride [BzCOCl, to produce ethyl benzoate (EB) in situ] in the presence of excess titanium tetrachloride. Solid product and catalysts obtained by subsequent treatments with titanium tetrachloride were characterized by elemental analysis, IR spectroscopy, x-ray diffraction, BET measurement, and thermal gravimetric analysis. The catalysts yielded very high activity (above 20 kg polymer/g Ti h atm) for the polymerization of propylene in slurry reactions. From the results of polymerization as well as catalyst characterization, the effects of internal and external Lewis bases on the isospecificity and stability of catalysts are discussed in detail. © 1992 John Wiley & Sons, Inc. 相似文献
999.
Sei-Jin Oh Chul-Jin Choi Soon-Ju Kwon Sang-Ho Jin Byoung-Kee Kim Jin-Soo Park 《Journal of magnetism and magnetic materials》2004,280(2-3):147-157
The magnetic properties of Fe–Co nanoparticles synthesized by chemical vapor condensation (CVC) process were investigated. Effect of CVC processing variables on the magnetic properties was analyzed in detail, using Mössbauer spectroscopy, XRD, BET and HRTEM. The synthesized particles were nearly spherical, and their surfaces were identified to be -FeOOH, γ-FeOOH and Fe3O4, but not -Fe2O3. The magnetic properties were strongly influenced by CVC processing parameters. The increase of cobalt content had changed the magnetic property of the sample. However, when the decomposition temperature and the oxygen content in the carrier gas (Ar) were increased, the magnetic property reduced with decreasing the average particle size. Increasing the vacuum pressure in the chamber resulted in that the magnetic field reinforced with the increase of average particle size. 相似文献
1000.
Novel zero-voltage and zero-current-switching (ZVZCS) full-bridge PWM converter using coupled output inductor 总被引:2,自引:0,他引:2
Hang-Seok Choi Jung-Won Kim Bo Hyung Cho 《Power Electronics, IEEE Transactions on》2002,17(5):641-648
A novel zero-voltage and zero-current-switching (ZVZCS) full-bridge pulse-width-modulated (PWM) converter is proposed to improve the previously proposed ZVZCS full-bridge PWM converters. By employing a simple auxiliary circuit with neither lossy components nor active switches, soft-switching of the primary switches is achieved. The proposed converter has many advantages such as simple auxiliary circuit, high efficiency, low voltage stress of the rectifier diode and self-adjustment of the circulating current, which make the proposed converter attractive for the high voltage and high power applications. The principles of operation and design considerations are presented and verified on the 4 kW experimental converter operating at 80 kHz. 相似文献