Browsing by Author "Chang, Wei-Chieh"

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CMA adaptive equalization in subspace pre-whitened blind receivers
(2019-05-01)
Chang, Wei-Chieh
;
Yuan, Jenq-Tay
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電信工程研究所
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Institute of Communications Engineering
In blind channel equalization, the use of whitening transformation (WT) preceding the constant modulus algorithm (CMA), referred to as the pre-whitened CMA, may accelerate the rate of convergence of using the CMA alone. In this work, we develop a novel subspace pre-whitened CMA (SP-CMA) using the subspace WT. By allowing the channel matrix to be non-square, this approach for the subspace WT offers greater flexibility in the design of the WT than the conventional per-whitened CMA does. The similarities and differences between the SP-CMA and the conventional CMA were first examined and analyzed in terms of their convergence behaviors from a theoretical viewpoint. The convergence behavior of the SP-CMA was analyzed under the whiteness assumption in which the input of the blind equalizer has been whitened beforehand by the subspace WT. The upper bound of the improvement in convergence of the SP-CMA over its CMA counterpart was developed. This analysis can be readily extended to other existing pre-whitened CMA schemes. Computer simulations using two highly dispersive multipath channels confirmed the superior convergence of the SP-CMA. (C) 2019 Elsevier Inc. All rights reserved.
Intramolecular Locked Dithioalkylbithiophene-Based Semiconductors for High-Performance Organic Field-Effect Transistors
(2017-09-20)
Vegiraju, Sureshraju
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Chang, Bo-Chin
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Priyanka, Pragya
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Huang, Deng-Yi
;
Wu, Kuan-Yi
New 3,3-dithioalkyl-2,2-bithiophene (SBT)-based small molecular and polymeric semiconductors are synthesized by end-capping or copolymerization with dithienothiophen-2-yl units. Single-crystal, molecular orbital computations, and optical/electrochemical data indicate that the SBT core is completely planar, likely via S(alkyl)S(thiophene) intramolecular locks. Therefore, compared to semiconductors based on the conventional 3,3-dialkyl-2,2-bithiophene, the resulting SBT systems are planar (torsional angle <1 degrees) and highly -conjugated. Charge transport is investigated for solution-sheared films in field-effect transistors demonstrating that SBT can enable good semiconducting materials with hole mobilities ranging from approximate to 0.03 to 1.7 cm(2) V-1 s(-1). Transport difference within this family is rationalized by film morphology, as accessed by grazing incidence X-ray diffraction experiments.
Linear, mixed-valent homocatenated tri-tin complexes featuring Sn-Sn bonds
(2020-06-25)
Chang, Wei-Chieh
;
Raj, Ankit
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Hiramatsu, Hirotsugu
;
Li, Han-Jung
;
Ziegler, Micah S.
A series of tri-tin complexes((LSn)-Sn-Ph)(3)Xwith triple-decker structures (L-Ph= 2,5-di(o-pyridyl)-3,4-diphenylpyrrolate; X = Cl, AlCl4, OTf, and PF6) was synthesized by reducingL(Ph)SnClwith (LiBBu3H)-Bu-s and subsequent reactions. Structural characterization of((LSn)-Sn-Ph)(3)Clrevealed a Sn-Sn-Sn core, and DFT calculations suggest that its HOMO is primarily sigma-bonding along the tri-tin framework.((LSn)-Sn-Ph)(3)Clreacts with W(CO)(5)THF to afford((LSn)-Sn-Ph)(2)(W(CO)(5))(2)andL(Ph)SnCl, implying that((LSn)-Sn-Ph)(3)Clmay exhibit dynamic behavior in solution.