Browsing by Author "Sun, Yu-Chen"

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Conductivity and tunneling density of states in granular Cr films
(2010-08-12)
Sun, Yu-Chen
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Yeh, Sheng-Shiuan
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Lin, Juhn-Jong
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電子物理學系
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物理研究所
We have measured the tunneling differential conductances, G(V), of four Al/AlOx/Cr planar tunnel junctions as well as the conductivities, sigma(T), of the Cr electrodes at liquid-helium temperatures. The Cr electrodes were made to be granular with dimensionless intergrain tunneling conductance spanning from g similar or equal to 1 to g >> 1, and the dimensionality of the granular array d=3. For the samples with g >> 1, we found that the measured G(V) curves display large zero-bias singularities which obey a ln V law at low bias voltages (less than or similar to a few millielectron volt) while crossing over to a root V law at high bias voltages. Simultaneously, the conductivities of the Cr electrodes reveal ln T dependence below a characteristic temperature. These results are explained in terms of the recent theory of granular metals. In a sample with g similar or equal to 1, in addition to the conductivity dependence sigma proportional to ln T, we observed a universal scaling behavior of the normalized differential conductance [G(V, T) -G(0, T)]/root T with the combined parameter root e vertical bar V vertical bar/k(B)T in a wide temperature interval of 2.5-32 K. This result is not yet understood.
ERROR-RESILIENT VIDEO CODING USING MULTIPLE REFERENCE FRAMES
(2013-01-01)
Tsai, Wen-Jiin
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Sun, Yu-Chen
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資訊工程學系
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Department of Computer Science
An error-resilient scheme based on multiple reference frames is proposed, which employs error-resilient frames (ER-frame) as part of reference frames and adopts a rate-distortion optimized (RDO) technique to choose the blocks referring to ER-frames. To reduce the computational cost, two techniques are further proposed. Experimental results show that adopting ER-frames enhances error-resilient performance; using RDO makes the scheme adaptive to various packet loss rates and video sequences; and applying time reduction techniques reduces computational cost significantly with neglectable performance loss.
Perceptual-based distributed video coding
(2012-04-01)
Sun, Yu-Chen
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Tsai, Chun-Jen
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資訊工程學系
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Department of Computer Science
In this paper, we propose a perceptual-based distributed video coding (DVC) technique. Unlike traditional video codecs, DVC applies video prediction process at the decoder side using previously received frames. The predicted video frames (i.e., side information) contain prediction errors. The encoder then transmits error-correcting parity bits to the decoder to reconstruct the video frames from side information. However, channel codes based on i.i.d. noise models are not always efficient in correcting video prediction errors. In addition, some of the prediction errors do not cause perceptible visual distortions. From perceptual coding point of view, there is no need to correct such errors. This paper proposes a scheme for the decoder to perform perceptual quality analysis on the predicted side information. The decoder only requests parity bits to correct visually sensitive errors. More importantly, with the proposed technique, key frames can be encoded at higher rates while still maintaining consistent visual quality across the video sequence. As a result, even the objective PSNR measure of the decoded video sequence will increase too. Experimental results show that the proposed technique improves the R-D performance of a transform domain DVC codec both subjectively and objectively. Comparisons with a well-known DVC codec show that the proposed perceptual-based DVC coding scheme is very promising for distributed video coding framework. (C) 2012 Elsevier Inc. All rights reserved.
PRIORITIZED SIDE INFORMATION CORRECTION FOR DISTRIBUTED VIDEO CODING
(2009)
Sun, Yu-Chen
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Lian, Shiau-Yu
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Tsai, Chun-Jen
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資訊工程學系
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Department of Computer Science
In this paper, a distributed video coding technique with prioritized channel coding of W-Z frames is presented. In the proposed framework, W-Z frame macroblocks are classified into different groups based on the estimated quality of the side information. The information is transmitted via uplink channel back to the encoder so that macroblocks with similar error statistics can be grouped tighter in same coding blocks for channel coding. With this approach, decoder can request more parity bits to correct macroblocks whose side information quality is worse and request less parity bits for macroblocks with smaller side information errors. Initial experimental results show that the proposed technique call improve the R-D performance of both pixel-domain and transform-domain DVC codecs considerably.
Rate-distortion optimized mode selection method for multiple description video coding
(2014-09-01)
Sun, Yu-Chen
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Tsai, Wen-Jiin
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資訊工程學系
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Department of Computer Science
Multiple description coding (MDC) is a potential solution for video transmission over error-prone networks because it shows promising enhancement of error resilient capability. The MDC systems encode a single video stream into two or more equally important independent sub-streams, called descriptions. Therefore, if some of the descriptors get lost, remaining descriptors can be used to recover the video. Much research has proposed different information distribution methods. Since each method has different characteristic, we proposed a general rate-distortion optimization framework for MDC systems in this paper. By sophisticated rate-distortion analysis and optimization, the framework enables MDC systems to adaptively encode video considering contents and channel variation. Experimental results showed that, by comparing with the work in Tsai and You (IEEE Trans Circ Syst Video Technol 22(2):309-320, 2012), the proposed technique improves the R-D performance significantly. The improvement can be up to 2.4 dB for the channels with 0 % similar to 20 % packet loss rates, and it can be even more if the loss rate increases. The proposed framework is not restricted to specific MDC tools. Ones can easily integrate their proposed coding tools into the framework and achieve better performance as long as the macroblock\'s bitrate and distortion information can be measured.
Resource-aware Replication Strategies in P2P VoD Services with Scalable Video Streams
(2012)
Ho, Chien-Peng
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Sun, Yu-Chen
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Yu, Jen-Yu
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Lee, Suh-Yin
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資訊工程學系
This article aims to discuss the replication principle that underlies correlations between peer-network conditions and video quality impacts over unstructured peer-to-peer (P2P) video-on-demand (VoD) overlay networks. In particular, the conditions of a network path among peers, such as communication latencies, packet buffer status, and upload bandwidth, can be used to develop failover mechanisms that enable recovery from a failure in part of the P2P VoD system. The failure recovery can be accomplished by using the resource-aware replication strategy, which can deploy high video quality impacts and popular media-data replicas to the movie time-scale of low averaged resource rate and discontinuous area. The simulation results demonstrate that replicas of popular and high video-distortion data are significant and reflect physical demands. In addition, the averaged visual quality of video can be enhanced, and the load imposed on a VoD server can be reduced, through facilitating proper progression of replication strategy.
Robust Video Coding Based on Hybrid Hierarchical B Pictures
(2014-05-01)
Tsai, Wen-Jiin
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Sun, Yu-Chen
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Chiu, Po-Jui
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資訊工程學系
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Department of Computer Science
Compressed video streams transmitted over error-prone environments are usually corrupted by transmission errors. Error-concealment techniques can be used to recover the lost information. In this paper, a hybrid model is proposed to improve the error-concealment performance. The model combines two hierarchical B-picture coding structures such that key-frames, reference B frames, or even nonreference B frames have buddy frames to serve as their data recovery frames when they are lost. With buddy frames, the distance between a lost frame and its recovering frame can be substantially reduced. In addition, an improved estimation method is also proposed to further increase the accuracy of recovering motion. Error-concealment performance can thus be significantly improved with little bitrate redundancy. We have conducted experiments to compare its performance with other methods, and the results show that the proposed hybrid model outperforms these competed methods. The advantages of the proposed hybrid model are demonstrated in error-free and packet-loss environments.