Browsing by Author "Chang, YM"

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A new channel equalizer for OFDM-based wireless communications
(2005)
Chang, YM
;
Kuang, CW
;
Lin, CC
;
Sang, TS
;
Chang, HC
This paper presents a new channel equalizer for OFDM-based communication systems. The channel equalizer consists of the adaptive estimation of channel frequency response (CFR) and the signal recovery. CFR is obtained by the two-dimensional linear interpolation of pilots from the frequency axis and the time axis. To avoid the noise enhancement in signal recovery, maximum-likelihood sequence estimation (MLSE) is applied to improve 1.5dB in SNR while using Rayleigh fading channel model with 30Hz Doppler frequency shift. As compared to the linear equalizer without feedback, the division free approach provides more accurate signal recovery in circuit implementation.
Effects of ammonia plasma treatment on the surface characteristics of carbon fibers
(2006-02-24)
Wen, HC
;
Yang, K
;
Ou, KL
;
Wu, WF
;
Chou, CP
Carbon fibers were grown from cobalt catalysts with larger size (> 100 nm), and the size distribution can be controlled by pretreatment. Pretreated cobalt catalytic-layers were observed as islands, which can enhance the growth of carbon fibers. The carbon fibers were treated by ammonia plasma in a PECVD system. High-energy ammonia plasma not only can cause damage but also adsorb on carbon fibers. The ammonia plasma treatment resulted in the etching effect. It is also observed that the more treatment time, the more disorder in structures of carbon fibers. The N-H functional groups were found on the surfaces of ammonia plasma treated carbon fibers and this observation can be further investigated to develop chemical sensor application. (c) 2005 Elsevier B.V. All rights reserved.
Performance evaluation of ring-structure register file in multimedia applications
(2003)
Lin, TJ
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Chang, CC
;
Yang, TH
;
Chang, YM
;
Lin, CH
As the concurrent functional units in media processors increase continuously to meet the performance needs, the required access (i.e. read or write) ports of the centralized register file (RF) multiply rapidly and cannot be efficiently implemented. We propose a novel ring-structure RF, which is composed of register sub-blocks identical to the RF for a single functional unit. Data exchanges among functional units occur on the switch network of the ring registers. The proposed RF has been integrated into a four-way VLIW DSP processor successfully that demonstrates its effectiveness in DSP kernels. The synthesis result shows that our proposed ring-structure RF saves 91.88% silicon area of the centralized one, while reducing its access time by 77.35%.
Synthesis and characterization of segmented copolymers of aromatic polyether sulfone and thermotropic liquid crystalline poly(oxy-1,4-phenylenecarbonyl-co-oxy-2,6-naphthaloyl)
(1996-03-01)
Chang, YM
;
Hsu, CS
;
Liu, MC
;
應用化學系
;
Department of Applied Chemistry
The synthesis of segmented copolymers of aromatic polyether sulfone and thermotropic liquid crystalline poly(oxy-1,4-phenylenecarbonyl-co-oxy-2,6-naphthaloyl) is presented. The segmented copolymers were prepared by solution polycondensation of hydroxy-terminated polyether sulfone with 4-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid in a mixture of triphenylphosphine, pyridine and hexachloroethane. The obtained polymers were fractionated to isolate the pure segmented copolymers. All of the segmented copolymers reveal two glass transitions. The first glass transition at about 75 degrees C belongs to the segmental motions of liquid crystalline polyester blocks. The second glass transition at about 140 degrees C belongs to the segmental motions of polyether sulfone blocks. Optical polarizing microscopy and X-ray diffraction measurements verify the presence of a nematic liquid crystalline phase for the segment copolymers. The experimental results indicate that the segmental copolymers have a microphase-separated morphology, i.e., both amorphous and liquid crystalline properties are shown by the polyether sulfone and liquid crystalline polyester segments, respectively.
Universal switch blocks for three-dimensional FPGA design
(2004-02-01)
Wu, GM
;
Shyu, M
;
Chang, YM
;
資訊工程學系
;
Department of Computer Science
The authors consider the switch-block design problem for three-dimensional FPGAs. A three-dimensional switch block M with W terminals on each face is said to be universal if every set of nets satisfying the dimension constraint (i.e. the number of nets on each face of M is at most K) is simultaneously routable through M. A class of universal switch blocks for three-dimensional FPGAs is presented. Each of the switch blocks has 15 W switches and switch-block flexibility 5 (i.e. F-S=5). It is proved that no switch block with less than 15W switches can be universal. The proposed switch blocks are compared with others of the topology associated with those used in the Xilinx XC4000 FPGAs. Experimental results demonstrate that the proposed universal switch blocks improve routabilty at the chip level. Further, the decomposition property of a universal switch block provides a key insight into its layout implementation with a smaller silicon area.