Browsing by Author "Chien, FT"

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Blind recursive tracking of carrier frequency offsets in MC-CDMA systems
(2005)
Chien, FT
;
Kuo, CCJ
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A blind recursive algorithm to effectively update the carrier frequency offset (CFO) vector in a multicarrier code-division multiple-access (MC-CDMA) system is studied in this research. The recursive relation is developed based on the expectation maximization (EM) algorithm with a quadratic constraint. This new perspective enables the use of linear estimation theory to deal with the blind CFO estimation problem, leading to an analytic CFO estimate in closed-form. The multiple access interference (MAI) is mitigated using the second order statistics of the interference-plus-noise vector, which can also be updated in a recursive manner under the EM formulation. Finally, we verify the effectiveness of the proposed algorithm with computer simulation.
Performance analysis of multicarrier CDMA systems with frequency offsets and random spreading under optimum combining
(2006-04-01)
Chien, FT
;
Hwang, CH
;
Kuo, CCJ
;
傳播研究所
;
電子工程學系及電子研究所
The carrier-frequency offset effect on the performance of asynchronous multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) systems with aperiodic random spreading and correlated Rayleigh fading is studied in this paper. We obtain the optimum combining filter that maximizes the signal-to-interference-plus-noise ratio (SINR) of the combined statistics and exploits correlated information among subchannels. A closed-form expression for the unconditional covariance matrix of the interference-plus-noise vector, which forms the basis of our theoretical analysis of the maximum SINR and the average bit error probability formula, is derived by averaging several random parameters including asynchronous delays, correlated Rayleigh fading, and signature sequences. The analytic results obtained are applicable to MC-CDMA with appropriate modifications. Furthermore, we show that the MC-CDMA system with a common random signature sequence over all subcarriers for a given user outperforms that with distinct sequences over different subcarriers. Finally, the performance of MC-CDMA systems using the optimum combining technique is compared with that of different combining filters in the simulation.
Stability investigation of single-wafer process by using a spin etcher
(2003-07-01)
Kang, TK
;
Wang, CC
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Tsui, BY
;
Yang, WL
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Chien, FT
Etch rate instability was found in a spin etcher. When chemical was pumped to the spin etcher, the flow rate became unstable; possibly resulting in a chemical deficiency due to low mass transport at the wafer edge. Consequently, the etch rate and etch uniformity are unstable. The detailed etch mechanism has been investigated and the mass transport deficiency can be avoided. Less than 2% of etch nonuniformity and a stable process can be achieved by achieving a stable flow rate and control of the surface reaction over the whole wafer in spin etching. (C) 2003 The Electrochemical Society.