• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2563-2578
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• 1996

In this paper, channel error characteristics are investigated to alleviate the channel error propagation problem of the digital TV transmission systems. First, error propagation problems, which are mainly caused by the inter-frame dependancy and variable length coding of the MPEG-2 baseline encoder, are intensively analyzed. Next, existing channel resilient schemes are systematically classified into two kinds of schemes; one for the encoder and the other for the decoder. By comparing the performance and implementation cost, the encoder side schemes, such as error localization, layered coding, error resilience bit stream generation techniques, are described in this paper. Also, in an effort to consider the parcticality of the real transmission situation, an efficient error detection scheme for a decoder system is proposed by employing a priori information of the bit stream syntas, checking the encoding conditions at the encoder stage, and exploiting the statistics of the image itself. Finally, subsequent error concealment technique based on the DCT coefficient recovery algorithm is adopted to evaluate the performance of the proposed error resilience technique. The computer simulation results show that the quality of the received image is significantly improved when the bit error rate is as high as 10$^{-5}$ .

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.193-198
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• 2006

멀티미디어 데이터를 이종의 수신자에게 안정적으로 전달하고자 하는 것은 인터넷에서 중요한 주제 중의 하나이다. 특히, 최근에 소개된 계층형 MDC(Layered Multiple Description Coding) 기법은 오버레이 멀티캐스트에서 이 문제를 효율적으로 해결하는데 중요한 접근방법이다. 그러나, 이 과정에서 저속 수렴(slow convergence)과 참가 실험(join experiment) 동안에의 손실과 같은 문제가 새롭게 발생하게 되었다. 본 논문에서는 비디오 스트리밍 서비스에서 위의 문제를 해결할 수 있는 효율적인 계층형 멀티캐스트 혼잡 제어 기법을 소개한다. 여기서 제시하는 기법의 가장 특징적인 점은 사용자가 수신할 계층(layer)의 수를 결정하기 위하여 패킷페어(packet-pair)방식에 기반한 수신률 조절 메커니즘을 사용하는 것이다. 결과적으로 본 논문에서는 수신자가 최적의 전송률에 빠르게 수렴하면서도 손실을 최소화할 수 있는 종단-대-종단간 혼잡 제어 기법을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.11
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• pp.1054-1063
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• 2012

In this paper, we introduce basic theories, effects and applications of the unequal error protection (UEP) system that is expected to play a major role in the future multi-layered broadcast system. Also we show results of surveys on the various previous studies and standards about the UEP systems, and we give prospects of standardizations and future applications of UEP based on the surveys.

• Information and Communications Magazine
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• v.32 no.2
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• pp.63-72
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• 2015

최근 디지털방송의 화두는 단연 UHD 이다. 케이블방송, 위성방송, IPTV 등 유료방송을 중심으로 2014년부터 UHD 방송 상용서비스 경쟁이 본격화 되었다. 지상파에서도 2009년 9월 표준 제정된 DVB-T2를 기반으로 HEVC(High Efficiency Video Coding)을 적용한 실험방송이 진행되고 있으며, ATSC에서는 HEVC를 적용하여 UHD 방송의 고정수신과 HD 방송의 이동수신 동시서비스를 목표로 ATSC 3.0 표준화가 빠르게 진행되고 있다. 특히, ATSC 3.0 표준화는 국내 가전사와 ETRI가 주도하고 있으며, 유럽의 DVB와 중국의 NERC-DTV, 일본의 NHK, Sony 등도 참여하고 있는 등 전 세계 방송 관련 기관들로부터 차세대 지상파 방송표준으로 주목을 받고 있다. 본고에서는 지상파 UHD 고정수신 및 이동방송서비스 관련 기술개발과 표준화 동향을 살펴보고, 최근 ATSC 3.0에서 주목받고 있는 LDM(Layered Division Multiplexing) 기술의 장점 대해서 소개하고자 한다.

• Journal of Broadcast Engineering
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• v.20 no.1
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• pp.16-25
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• 2015

Even if the demands for ultra-high-quality multimedia contents are increasing, it is difficult to produce, encode, play and transport ultra-high-quality contents under the existing broadcasting environment. By the reason, various technologies for the UHD contents have been developed in order to satisfy the user's needs. In this paper, we propose a design methodology of a broadcasting system, which consists of two parts, for UHD services with two parts. At the transmit part of the proposed system can encode a video into several layered-bitstreams hierarchically, and then transport each bitstream over heterogeneous networks. The receiver part can play the received video by composing the separated bitstreams. The proposed system can adaptively provide both HD and UHD contents according to user's reception conditions by using the heterogeneous networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.435-446
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• 2014

Even if it is important to transmit high rate multimedia information without any transmission errors for surveillance systems, it is difficult to achieve error-free transmission due to infra-less adhoc networks. In order to reduce the transmission errors furthermore, additional signal overheads or retransmission of signals should be required, but they may lead to transmission delay. This paper represents a study on low delay and adaptive video transmission for the unmanned surveillance systems by developing system protocols. In addition, we introduce an efficient and adaptive control algorithm using system parameters for exploiting unmanned surveillance system properly over multi-channels.

• Journal of Digital Contents Society
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• v.8 no.4
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• pp.441-449
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• 2007

In video coding, motion estimation is a process to estimate the pixel of the current frame from the reference frame, which affects directly the predictive quality and the encoding time. This paper is related to AHHS(Adaptive Hierarchical Hexagon Search) using spatio-temporal motion activity for fast motion estimation. The proposed method defines the spatio-temporal motion activity of the current macroblock using the motion vectors of its spatio-temporally adjacent macroblocks, and then conventional AHS(Adaptive Hexagon Search) is performed if the spatio-temporal motion activity is lower, otherwise, hierarchical hexagon search is performed on a multi-layered hierarchical space constructed by multiple sub-images with low frequency in wavelet transform. In the paper, based on computer simulation results for multiple video sequences with different motion characteristics, the performance of the proposed method was analysed and assessed in terms of the predictive quality and the computational time. Experimental results indicate that the proposed method is both suitable for (quasi-) stationary and large motion searches. The proposed method could keep the merit of the adaptive hexagon search capable of fast estimating motion vectors and also adaptively reduce the local minima occurred in the video sequences with higher spatio-temporal motion activity.