Browsing by Author "Hung, CJ"

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Combining adaptive smoothing and decision-directed channel estimation schemes for OFDM WLAN systems
(2003)
Liu, HY
;
Yu, YH
;
Hung, CJ
;
Hsu, TY
;
Lee, CY
In this paper, a new channel estimation method for OFDM WLAN systems is proposed. This proposal mainly consists of smoothing filtering and decision-directed tracking loop schemes, where the former is used to enhance performance at low SNR and the latter is exploited to enhance performance at high SNR respectively. Together with an adaptive channel management, better performance in terms of MSE and PER can be achieved. Simulation shows the proposed method (1) achieves better 9.0dB similar to 13.0dB gain in MSE than zero forcing criterion and better 2.0dB gain in MSE than conventional approaches in BPSK transmission, and (2) contributes 0.8dB similar to 2.0dB gain in SNR for 10% PER in different transmission modes.
Polymer blends of poly(ethylene-2,6-naphthalate) with polystyrene compatibilized by styrene-glycidyl methacrylate copolymers. I. Rheology, morphology, and mechanical properties
(2003-02-07)
Huang, JM
;
Ju, MY
;
Hung, CJ
;
Luoh, WC
;
Chang, FC
The compatibilization of blends of poly(ethylene-2,6-naphthalate) (PEN) with polystyrene (PS), through the styrene-glycidyl methacrylate copolymers (SG) containing various glycidyl methacrylate (GMA) contents, was investigated in this study. SG copolymers are able to react with PEN terminal groups during melt blending, resulting in the formation of desirable SG-g-PEN copolymers in the blend. These in situ formed copolymers tend to reside along the interface preferentially as the result of interfacial reaction and thus function as effective compatibilizers in PEN/PS blends. The compatibilized blends exhibit higher viscosity, finer phase domain, and improved mechanical properties. It is found that the degree of grafting of the in situ formed SG-g-PEN copolymer has to be considered as well. In blends compatibilized with the SG copolymer containing higher GMA content, heavily grafted copolymers would be produced. The length of the styrene segment in these heavily grafted copolymers would be too short to penetrate deep enough into the PS phase to form effective entanglements, resulting in the lower compatibilization efficiency in PEN/PS blends. Consequently, the in situ formation of SGg-PEN copolymers with an optimal degree of grafting is the key to achieving the best performance for the eventually produced PEN/PS blends through SG copolymers. (C) 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 967-975, 2003.
Spatial distributions of elastically backscattered electrons from copper and silver
(1999-12-21)
Kwei, CM
;
Hung, CJ
;
Su, P
;
Tung, CJ
;
電子工程學系及電子研究所
We investigated the spatial distributions regarding the pathlength, the penetration depth, and the lateral displacement of 200-2000 eV electrons elastically backscattered from copper and silver We calculated these distributions by the Monte Carlo method using elastic scattering cross sections and inelastic inverse mean free paths for volume and surface excitations. in our approach, we applied the partial wave expansion method and the finite difference technique to calculate electron elastic cross sections by the Hartree-Fock-Winger-Seitz scattering potential for solid atoms. We employed the extended Drude dielectric function to estimate electron inelastic mean free paths inside the solid and electron surface excitation parameters outside the solid. Our study was focused on the energy dependence of the pathlength distribution, the maximum depth distribution and the radial distribution. We found that both the radial displacement and the maximum depth of backscattered electrons were on the order of a few angstroms. The maximum depth and the pathlength distributions obeyed the exponential attenuation form. The ratio of the attenuation lengths for the pathlength and the maximum depth distributions saturated to a value somewhat greater than two. Considering the back and forth trajectories of backscattered electrons, it revealed that mast electrons were backscattered from the solid through a single elastic scattering or a few elastic scatterings. As electron energy decreases, this ratio became larger, indicating that the probability for smaller scattering angles increases.