Browsing by Author "Chen, Ko-Feng"

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On Composite Channel Estimation in Wireless Massive MIMO Systems
(2013-01-01)
Chen, Ko-Feng
;
Liu, Yen-Cheng
;
Su, Yu T.
;
傳播研究所
;
Institute of Communication Studies
A multiuser MIMO (MU-MIMO) TDD system in which the base station (BS) uses a large scale antenna array to communicate with single-antenna mobile users is considered. We present novel schemes to estimate both large-scale and small-scale fading coefficients by uplink pilot sequences. The large-scale fading coefficients (LSFCs) are usually ignored or assumed perfectly known and almost all MIMO channel state information (CSI) estimation studies deal solely with small-scale fading coefficients (SSFCs). We propose low complexity algorithms that give reliable estimates for both FCs. The LSFC estimator takes advantage of the excess spatial samples received and the channel hardening effect while the SSFC estimator is based on a rank-reduction approach. Our estimators require a low training overhead and both analysis and numerical experiments prove that they offer superior mean-squared error performance.
Valence state map of iron oxide thin film obtained from electron spectroscopy imaging series
(2007)
Chen, Ko-Feng
;
Lo, Shen-Chuan
;
Chang, Li
;
Egerton, Ray
;
Kai, Ji-Jung
This paper demonstrates the applicability of electron-spectroscopic imaging (ESI) for valence-state mapping of the iron oxide system. We have previously developed a set of signal-processing methods for an EST series, to allow mapping Of sp(2)/sp(3) ratio, dielectric function and energy bandgap. In this study, these methods are applied to generate a valence-state map of an iron oxide thin film (Fe/alpha-Fe2O3). Two problems, data undersampling and a convolution effect associated with extraction of the image-spectrum from the core loss image series, were overcome by using cubic-polynomial interpolation and maximum-entropy deconvolution. As a result, the reconstructed image-spectrum obtained from the EST series images has a quality as good as that of conventional electron energy-loss spectra. The L-3/L-2 ratio of the reconstructed EST spectrum is determined to be 3.30 +/- 0.30 and 5.0 +/- 0.30 for Fe and alpha-Fe2O3, respectively. Our L-3/L-2, ratio mapping shows an accurate correspondence across the Cu/Fe/alpha-Fe2O3 region. The effect of delocalization and chromatic aberration on the EST resolution is discussed and estimated to be about 2 nm for the case of L-3/L-2, ratio mapping. (c) 2006 Published by Elsevier Ltd.