Browsing by Author "Chang, WS"

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Construction of error resilient synchronization codeword for variable-length code in image transmission
(2000)
Lee, YS
;
Chang, WS
;
Ho, HH
;
Lee, CY
;
電子工程學系及電子研究所
Variable length code ( VLC ), also called Huffman code [1], is the most popular data compression technique used for image compression and transmission. But, it is vulnerable to loss of synchronization under transmission in a noisy channel. It will result in large drops in video transmission quality. For stopping error propagation, synchronization codeword ( SC ) is mostly used to localize error propagation effect. However, most of the SC cannot tolerate noise errors. We propose an iterative and efficient algorithm to construct error-resilient and variable-length SC for any application defined VLC table. They can be sed for synchronization of packet ( ERVL-SOP ). It can be appended at the end of certain number of symbols to form a packet. Thus, channel noise error can be localized. With using constructed SC as SOP, the result shows that it can achieve high signal-to-noise ratio ( PSNR=26dB ) compared to use normal VLC code as SOP at bit error rate ( BER ) of 10(-3) environment. In addition, the incorrect ERVL-SOP detection rate can be decreased to less than 0.0013% effectively.
Electrical properties of amorphous silicon films with different thicknesses in metal/insulator/semiconductor structures
(1996-05-01)
Tai, YH
;
Su, FC
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Chang, WS
;
Feng, MS
;
Cheng, HC
The density of states (DOS) of hydrogenated amorphous silicon (a-Si:H) is an important issue in the study of the physics of amorphous semiconductors. In many earlier reports concerning the analysis of the field-effect conductance metal/insulator/ a-Si:H structures, namely, thin-film transistors (TFTs), the potential at the semiconductor surface apart from the gate insulator/a-Si:H interface, i.e., the rear interface, was assumed to be zero. However, in principle, as the thickness of the semiconductor film is smaller than the theoretically expected width of the space charge region, this assumption no longer holds. Hence, it is necessary to reconsider the band-bending phenomena of the a-Si:H active layers. It was found that the DOS, which was extracted previously from the field-effect conductance of the TFTs based on the assumption of the zero-potential rear interface, was appropriate only for the thick a-Si:H films. As for the thin semiconductor films, the accurate DOS can be obtained by fitting the calculated field-effect conductance, with a surmised possible DOS, to the experimentally measured data via the method developed.
HVLC: Error correctable hybrid variable length code for image coding in wireless transmission
(2000)
Lee, YS
;
Yu, CM
;
Chang, WS
;
Lee, CY
;
電子工程學系及電子研究所
Variable length code (VLC), also called Huffman code [1] is the most popular data compression technique used for solving transmission channel bandwidth bottleneck in image compression standards such as JPEG, MPEG, and H263. But, it is vulnerable to loss of synchronization if they are transmitted consecutively through a noisy wireless channel. It will result in large drops in video transmission quality. We propose a novel Hybrid VLC (HVLC) coding scheme to provide high tolerances to random and burst errors in worsening channel conditions. It exhibits high synchronization, error correction capability and low redundancy. For erroneous HVLC bitstream, it is able to self-synchronize within one codeword. The result shows that it achieves high signal-to-noise ratio (PSNR=30dB) compared to existing VLC schemes at bit error rate (BER) of 10(-3) environment. With efficient memory mapping, HVLC requires low memory spaces and achieves high throughput rate. It is very suitable for VLSI implementation in wireless application.