• Journal of Broadcast Engineering
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• v.16 no.1
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• pp.144-154
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• 2011

In this paper, we propose a parallel LDPCA encoding method for fast transform-domain Wyner-Ziv video encoding which is suitable in an ultra fast and low power video encoding. The conventional transform-domain Wyner-Ziv video encoding performs LDPCA channel coding of quantized transform coefficients in bitplane-serial fashion, which takes about 60% of total encoding time, and this computational complexity becomes severer as the bitrate increases. The proposed method binds several bitplanes into one packed message and carries out the LDPCA encoding in parallel. The proposed LDPCA encoding method improves the encoding speed by 8 ~ 55 times. In the experiment, the proposed Wyner-Ziv encoder can encode 700 ~ 2,300 QCIF size frames per second with GOP=64. The method can be applied to the pixel-domain Wyner-Ziv encoder using LDPCA, and has a wide scope of application.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.8
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• pp.1675-1685
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• 2012

DVC (Distributed Video Coding) technique plays an essential role in providing low-complexity video encoder. But, in order to achieve the better rate-distortion performances, most DVC systems need feedback channel for parity bit control. This causes the DVC-based system to have high decoding latency and becomes as one of the most critical problems to overcome for a real implementation. In order to overcome this problem and to accelerate the commercialization of the DVC applications, this paper analyzes an effect of LDPCA frame size for adaptive LDPCA frame-based parity bit request estimations. First, this paper presents the LDPCA segmentation method in pixel-domain and explains the temporal-based bit request estimation method and the spatial-based bit request estimation method using the statistical characteristics between adjacent LDPCA frames. Through computer simulations, it is shown that the better performance and fast decoding is observed specially when the LDPCA frame size is 3168 in QCIF resolution.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.136-137
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• 2010

본 논문에서는 고속, 저전력 비디오 부호화에 적합한 변환영역 Wyner-Ziv 분산비디오부호화기를 더욱 고속화하기 위한 병렬처리 방법을 제안한다. 기존에는 변환영역 Wyner-Ziv 분산비디오부호화를 위해 양자화 정보를 비트플레인단위로 분해후 이를 순차적으로 LDPCA 부호화하여 전체 부호화기 연산량에서 LDPCA의 복잡도가 약 54% 정도 차지하였고, 이는 고비트율로 부호화 할수록 더욱 증가하였다. 제안방법은 이를 개선하기 위해 여러 개의 비트플레인을 하나의 심벌 (symbol)로 묶어서 LDPCA 부호화를 수행하여 한 번의 연산으로 여러 개의 데이터를 동시에 처리할 수 있게 한다. 일종의 단일 명령 복수 데이터 처리 (SIMD, Single instruction, multiple data)에 의한 고속화 방법이다. 이를 통해 제안방법은 기존의 순차적 처리 방법에 비해 저비트율에서는 8배, 고비트율에서는 55배까지 LDPCA의 부호화 속도를 향상시켰다. 결과적으로 전체 부호화에서 LDPCA의 상대적인 복잡도 비율은 4%정도로 낮아지게 되었으며 Wyner-Ziv 영상의 부호화 속도도 약 1.5 ~ 2배까지 향상되었다. 제안방법은 LDPCA를 사용하는 다른 Wyner-Ziv 분산비디오부호화 구조에도 적용 가능할 것으로 기대한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4C
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• pp.329-336
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• 2010

Distributed source coding (DSC) system moves computational burden from encoder to decoder, so it takes higher decoding complexity. This paper explores the problem of reducing the decoding complexity of practical Slepian-Wolf coding using low-density parity check accumulate (LDPCA) codes. It is shown that the convergence of mean magnitude (CMM) stopping criteria for LDPC codes help reduce the 85% of decoding complexity under the 2% of compression rate loss, and marginal initial rate request reduces complexity below complexity minimum bound. Moreover, inter-rate stopping criterion, modified for rate-adaptable characteristic, is proposed for LDPCA codes, and it makes decoder perform less iterative decoding than normal stopping criterion does when channel characteristic is unknown.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.132-135
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• 2010

LDPCA 부호는 부호율-적응적인 특성과 함께 뛰어난 압축률을 가지고 있어 분산 소스 부호화 시스템에서 사용되는 오류정 정부호로서 많이 사용되고 있다. 하지만 소스와 보조정보 사이의 상관관계가 낮은 영역에서는 급격한 성능열화가 일어나게 된다. 본 논문에서는 기존 LDPCA 부호에 특정 압축률 이상의 단계에서 추가 누적 신드롬 대신 변수노드와 일대일로 연결되어 있는 차수-1 신드롬을 전송하는 방식을 적용하여 이 영역에서 급격하게 발생하는 성능열화를 줄였다. 또한 차수-1 신드롬과 연결할 변수노드 집합을 선택할 때 복호화기에서 사용하는 LDPCA 부호의 검사노드 차수 분포를 집중시키는 알고리즘을 제안하여 성능을 더욱 향상시켰다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.259-265
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• 2012

Recently, many research works are focusing on DVC (Distributed Video Coding) system for low complexity encoder. Most DVC systems need feedback channel for parity bit control to achieve the good RD performances, however, this causes the system to have high decoding latency and is considered as one of the most critical problems for real implementation. In order to overcome this problem, this paper proposes an effective distributed video decoding method using adaptive LDPCA frame-based parity bit request estimation. The proposed method applies for the pixel-domain Wyner-Ziv system and exploits the statistical characteristics between adjacent LDPCA frames to estimate adaptively the parity bit request. Through computer simulations, it is shown that the proposed method achieves about 80% of latency reduction compared to the conventional no-estimation DVC system.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2011.07a
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• pp.133-134
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• 2011

본 논문에서는 소스코딩에 활용되고 있는 LDPCA 부호를 가변 부호율을 얻는 채널코딩 목적으로써의 사용 가능성을 타진한다. 컴퓨터 성능 실험의 결과로 가변 부호율과 어느 정도의 BER 성능을 확인하였지만, 체크노드 머징기법이 여타의 LDPC 부호에 비해 성능을 크게 떨어뜨리는 것으로 나타났다. 향후 체크노드 머징이 가능하면서도 좀 더 개선된 성능을 가지는 LDPCA 를 설계하는 일이 중요할 것으로 생각된다.

• The Journal of the Korea Contents Association
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• v.12 no.4
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• pp.31-39
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• 2012

DVC(Distributed Video Coding) techniques have been attracting a lot of research works since these enable us to implement the light-weight video encoder and to provide good coding efficiency by introducing the feedback channel. However, the feedback channel causes the decoder to increase the decoding complexity and requires very high decoding latency because of numerous iterative decoding processes. So, in order to reduce the decoding delay and then to implement in a real-time environment, this paper proposes several parity bit estimation methods which are based on the temporal correlation, spatial correlation and spatio-temporal correlations between LDPCA frames on each bit plane in the consecutive video frames in pixel-domain Wyner-Ziv video coding scheme and then the performances of these methods are compared in fast DVC scheme. Through computer simulations, it is shown that the adaptive spatio-temporal correlation-based estimation method and the temporal correlation-based estimation method outperform others for the video frames with the highly active contents and the low active contents, respectively. By using these results, the proposed estimation schemes will be able to be effectively used in a variety of different applications.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.6
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• pp.66-74
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• 2010

Recently distributed video coding (DVC) is spotlighted for the environment which has restriction in computing resource at encoder. Wyner-Ziv (WZ) coding is a representative scheme of DVC. The WZ encoder independently encodes key frame and WZ frame respectively by conventional intra coding and channel code. WZ decoder generates side information from reconstructed two key frames (t-1, t+1) based on temporal correlation. The side information is regarded as a noisy version of original WZ frame. Virtual channel noise can be removed by channel decoding process. So the performance of WZ coding greatly depends on the performance of channel code. Among existing channel codes, Turbo code and LDPC code have the most powerful error correction capability. These channel codes use stochastically iterative decoding process. However the iterative decoding process is quite time-consuming, so complexity of WZ decoder is considerably increased. Analysis of the complexity of LPDCA with real video data shows that the portion of complexity of LDPCA decoding is higher than 60% in total WZ decoding complexity. Using the HDA (Hard Decision Aided) method proposed in channel code area, channel decoding complexity can be much reduced. But considerable RD performance loss is possible according to different thresholds and its proper value is different for each sequence. In this paper, we propose an adaptive HDA method which sets up a proper threshold according to sequence. The proposed method shows about 62% and 32% of time saving, respectively in LDPCA and WZ decoding process, while RD performance is not that decreased.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.107-108
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• 2012

For low complexity encoder, the parity bit transmission through a feedback channel is an essential part of DVC. But feedback channel-based parity bit control is a major cause for the high decoding time latency. In this paper, we propose a fast distributed video decoding by parity bit request estimation using rate-distortion model. Through computer simulations, it is shown that the proposed method can achieve complexity reduction compared to other methods.