Browsing by Author "Li, Wen-Hsuan"

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A Low-Complexity Direction-of-Arrival Estimation Algorithm for Full-Dimension Massive MIMO Systems
(2014)
Yang, Kai-Yu
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Wu, Jwo-Yuh
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Li, Wen-Hsuan
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電機工程學系
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Department of Electrical and Computer Engineering
Full dimension (FD) MIMO, whereby a 2-dimensional (2D) antenna array is placed at the base station, has been known as a promising solution to economize spatial size of practical massive MIMO systems. To exploit such spatial resource for system performance enhancement, e.g., via three-dimensional beamforming, accurate estimation of the direction-of-arrival (DoA) of the signal sources is necessary. Existing DoA estimation methods using 2D arrays typically resorted to joint search over the 2D angular domain; however, the required algorithmic complexity would be prohibitively large, especially in the massive MIMO scenario. This paper proposes a two-stage low-complexity DoA estimation scheme, in which two MUSIC algorithms are performed for estimating, respectively, the elevation and azimuth angles of the impinging sources. Detailed flop count analyses are provided for justifying the low-complexity advantage. Various numerical simulations are also used to illustrate the performance of the proposed scheme.
Alteration of the Substrate's Prefolded Conformation and Cyclization Stereochemistry of Oxidosqualene-Lanosterol Cyclase of Saccharomyces cerevisiae by Substitution at Phenylalanine 699
(2010-02-05)
Wu, Tung-Kung
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Chang, Cheng-Hsiang
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Wen, Hao-Yu
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Liu, Yuan-Ting
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Li, Wen-Hsuan
The Saccharomyces cerevisiae ERG7(Phe699) mutants produced one chair-chair-chair (C-C-C) and two chair-boat-chair (C-B-C) truncated tricyclic compounds, one tetracyclic 17 alpha-exocyclic unrearranged intermediate, and two 17 beta-exocyclic truncated rearranged intermediates. These results provided direct evidence for the importance of the residue in affecting mechanistic transitions between C-B-C and C-C-C substrate conformation and between the 17 alpha- and 17 beta-exocyclic side chain stereochemistry as well as in stabilizing the 6 -6-5 tricyclic and the protosteryl C-17 cations.
BER-Improved Quantization of Source-to-Relay Link SNR for Cooperative Beamforming: A Fixed Point Theory Approach
(2019-07-01)
Li, Wen-Hsuan
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Wu, Jwo-Yuh
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交大名義發表
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電信工程研究所
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National Chiao Tung University
Cooperative beamforming is a potentially useful technique for enhancing link reliability in modern wireless relay communications. To aid the beamforming design, the signal-to-noise ratio (SNR) of the source-to-relay (S-R) channel links must be known at the destination node. Abdallah and Papadopoulos in IEEE Trans. Signal Processing, vol. 56, no. 10, 2008, proposed a beamforming system with relay-assisted SNR acquisition; that is, the S-R link SNR is first quantized at each relay and is then forwarded to the destination. An optimal quantizer design problem was proposed in that paper, aiming at reducing the system bit error rate; however, only the binary quantization case was considered therein, with the quantization threshold computed by a suggested rule of thumb. In this paper, we study the aforementioned quantizer design problem in the general multiple-bit setting. We show that the solutions to the first-order necessary condition for optimality can be obtained as a fixed point of a certain nonlinear map over the feasible threshold set. The existence and uniqueness of the fixed point are established by using, respectively, the Brouwer's and Schauder's fixed point theorems. Finally, we show that the fixed point thus obtained yields the globally optimal set of quantization thresholds. To the best of our knowledge, this paper is the first which leverages fixed point theories to rigorously solve SNR quantization problems in the context of wireless relay communication.
Differential Stereocontrolled Formation of Tricyclic Triterpenes by Mutation of Tyrosine 99 of the Oxidosqualene-Lanosterol Cyclase from Saccharomyces cerevisiae
(2009-11-01)
Wu, Tung-Kung
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Li, Wen-Hsuan
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Chang, Cheng-Hsiang
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Wen, Hao-Yu
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Liu, Yuan-Ting
The function of the Tyr99 residue from Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase (ERG7) was analyzed by constructing deletion and site-saturated mutants. Two truncated intermediates, (13 alpha H)-isomalabarica-14Z,17E,21-trien-3 beta-ol and (13 alpha H)-isomalabarica-14E,17E,21-trien-3 beta-ol, were isolated from the ERG7(Y99X) mutants. These results suggest that the functional role of ERG7(Y99) is to affect both chair-boat 6-6-5 tricyclic Markovnikov C-14 cation stabilization and the stereochemistry of the protons at the C-15 position for subsequent deprotonation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Least-Squares Pilot Sequence Design for TDD Massive MIMO Systems under Inter-Cell Timing Misalignment
(2018-01-01)
Li, Wen-Hsuan
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Wu, Jwo-Yuh
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Hsu, Chia-Kang
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Wang, Li-Chun
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電機工程學系
Pilot contamination (PC) is known as a dominant factor for the performance of time-division duplex massive MIMO systems. Most of the existing studies of PC assumed perfect inter-cell synchronization, which is too costly to achieve or even impossible in practice. In this paper, we consider the unsynchronized scenario, in which the reused pilot signals from other cells are subject to timing misalignment, and propose a method for pilot sequence design for reducing the mean square error (MSE) of the linear least squares (LS) channel estimation. An analytic MSE formula is first derived, which is a very complicated function of the pilot coefficients. To ease analysis, an upper bound on the MSE is then derived. Through minimization of this upper bound, an analytic solution is obtained. Computer simulations are used to illustrate the performance of the proposed pilot sequence.
Mutation of isoleucine 705 of the oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae affects lanosterol's C/D-ring cyclization and 17 alpha/beta-exocyclic side chain stereochemistry
(2011)
Wu, Tung-Kung
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Chang, Yi-Chun
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Liu, Yuan-Ting
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Chang, Cheng-Hsiang
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Wen, Hao-Yu
Site-saturated substitution in Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase at Ile705 position produced three chair-boat-chair (C-B-C) truncated tricyclic compounds, two 17 alpha-exocyclic protosteryl intermediates, two protosteryl C-17 truncated rearranged intermediates and the normal biosynthetic product, lanosterol. These results indicated the importance of the Ile705 residue in affecting lanosterol's C/D ring stabilization including 6-6-5 tricyclic and protosteryl C-17 cations and 17 alpha/beta-exocyclic side chain stereochemistry.
ORGN 610-Identification of a putative active site residue within oxidosqualene-lanosterol cyclase from saccharomyces cerevisiae that influences B/C ring cyclization
(2006-09-10)
Li, Wen-Hsuan
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Wu, Tung-Kung
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生物科技學系
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Department of Biological Science and Technology
Protein engineering of oxidosqualene-lanosterol cyclase into triterpene monocyclase
(2013)
Chang, Cheng-Hsiang
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Wen, Hao-Yu
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Shie, Wen-Shiang
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Lu, Ching-Ting
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Li, Meng-Erh
A computational modeling/protein engineering approach was applied to probe H234, C457, T509, Y510, and W587 within Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase (ERG7), which spatially affects the C-10 cation of lanosterol formation. Substitution of Trp587 to aromatic residues supported the "aromatic hypothesis" that the pi-electron-rich pocket is important for the stabilization of electron-deficient cationic intermediates. The Cys457 to Gly and Thr509 to Gly mutations disrupted the pre-existing H-bond to the protonating Asp456 and the intrinsic His234 : Tyr510 H-bond network, respectively, and generated achilleol A as the major product. An H234W/Y510W double mutation altered the ERG7 function to achilleol A synthase activity and generated achilleol A as the sole product. These results support the concept that a few-ring triterpene synthase can be derived from polycyclic cyclases by reverse evolution, and exemplify the power of computational modeling coupled with protein engineering both to study the enzyme's structure-function-mechanism relationships and to evolve new enzymatic activity.
The cysteine 703 to isoleucine or histidine mutation of the oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae generates an iridal-type triterpenoid
(2012-11-01)
Chang, Cheng-Hsiang
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Chen, Yi-Chi
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Tseng, Sheng-Wei
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Liu, Yuan-Ting
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Wen, Hao-Yu
The Cys703 to Ile or His mutation within Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase ERG7 (ERG7(C7031/H)) generates an unusual truncated bicyclic rearranged intermediate, (8R,9R,10R)-polypoda-5,13E,17E,21-tetraen-3 beta-ol, related to iridal-skeleton triterpenoid. Numerous oxidosqualene-cyclized truncated intermediates, including tricyclic, unrearranged tetracyclic with 17 alpha/beta exocyclic hydrocarbon side chain, rearranged tetracyclic, and chair chair chair tricyclic intermediates (compounds 3-9), were also isolated from the ERG7(C703X) site-saturated mutations or the ERG7(F699T/C7031) double mutation, indicating the functional role of the Cys703 residue in stabilizing the bicyclic C-8 cation and the rearranged intermediate or interacting with Phe699, and opened a new avenue of engineering ERG7 for producing biological active agents. (C) 2012 Elsevier Masson SAS. All rights reserved.