Browsing by Author "Liu, WS"

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A novel and efficient hybrid model of radio multipath-fading channels in indoor environments
(2003-03-01)
Tarng, JH
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Liu, WS
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Huang, YF
;
Huang, JM
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電信工程研究所
This paper presents a novel and efficient hybrid model combining a two-dimensional (2-D) site-specific model and a statistical model to characterize multipath fading in indoor environments. The site-specific, model describes the propagation effects of interior walls and building walls. The latter model characterizes the effect of scattering due to rough surface boundaries and/or randomly positioned scatterers such as furniture and personnel, which significantly affects small-scale fading. The hybrid model is computationally efficient since only the 2-D site-specific model is needed. In addition to Accurately predicting mean field strength, the model can effectively quantify the relative mean contribution of diffused scattering with a factor r. The factor is also an effective index to quantify the cluttering strength of the propagation environment: 1) light-cluttering situation r less than or equal to 0.35 and 2) heavy-cluttering situation r greater than or equal to 0.65. Some blind tests validate the effectiveness of the model. A large amount of experimental data for 2.44-GHz radio at many different sites shows that a Nakagami distribution describes the fading distribution well.
Separated-transport-recombination p-i-n photodiode for high-speed and high-power performance
(2005-08-01)
Shi, JW
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Hsu, HC
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Huang, FH
;
Liu, WS
;
Chyi, JI
We demonstrate a novel p-i-n photodiode (PD) structure, the separated-transport-recombination PD, which can greatly relieve the tradeoffs among the resistance-capacitance bandwidth limitation, responsivity, and output saturation power performance. Incorporating a short carrier lifetime (less than 1 ps) epitaxial layer to serve as a recombination center, this device exhibits superior speed and power performance to a control PD that has a pure intrinsic photoabsorption layer. Our demonstrated structure can also eliminate the bandwidth degradation problem of the high-speed photodetector, whose active photoabsorption layer is fully composed of short lifetime (similar to 1 ps) materials, under high dc bias voltages.