LDPCA code construction for Slepian-Wolf coding

Error correcting codes used for Distributed Source Coding (DSC) generally assume a random distribution of errors. However, in certain DSC applications, prediction of the error distribution is possible and thus this assumption fails, resulting in a sub-optimal performance. This letter considers the construction of rate-adaptive Low-Density Parity-Check (LDPC) codes where the edges of the variable nodes receiving unreliable information are distributed evenly among all the check nodes. Simulation results show that the proposed codes can reduce the gap to the theoretical bounds by up to 56% compared to traditional codes.peer-reviewe

Selective reconstruction of low motion regions in distributed video coding

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union - European Social Fund. (ESF 1.25).The Distributed Video Coding (DVC) paradigm offers lightweight encoding capabilities which are suitable for devices with limited computational resources. Moreover, DVC techniques can theoretically achieve the same coding efficiency as the traditional video coding schemes which employ more complex encoders. However, the performance of practical DVC architectures is still far from such theoretical bounds, mainly due to the inaccurate Side Information (SI) predicted at the decoder. The work presented in this paper shows that the soft-input values predicted at the decoder may not correctly predict the Wyner-Ziv coefficients, even for regions containing low motion. This generally degrades compression efficiency. To mitigate this, the proposed system predicts the quality of the SI for regions with low motion and then employs a technique which avoids correcting mismatch at locations where the SI and WZ falls within different quantization intervals but the prediction error is within an acceptable range. The experimental results demonstrate that the average Peak Signal-to-Noise Ratio (PSNR) is improved by up to 0.39dB compared to the state-of-the-art DVC architectures, like the DISCOVER codec.peer-reviewe

Reducing correlation noise in Wyner-Ziv video coding

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union – European Social Fund. (ESF 1.25).Over the past few decades, Distributed Video Coding (DVC) has been considered as a compression paradigm suitable for applications which require simple encoding. Yet, the performance obtained with practical architectures is still far from the theoretical bound, mainly due to the inaccurate Side Information (SI) predicted at the decoder. The work presented in this paper tries to improve the correlation between the bit-planes of the SI and the corresponding bitplanes of the Wyner-Ziv (WZ) frame. The proposed algorithm uses the adjacent key frames to predict the quantization intervals for the SI and for the WZ frame. It then chooses whether the quantization module should use the floor or the ceiling operationsuch that theindices generated for the two frames differ by the smallest number of bits possible. Experimental results show that, for a given target quality, the proposed method can reduce the WZ bit-rate by up to 8.4% compared to the traditional coding schemes.peer-reviewe

Improved rate-adaptive codes for distributed video coding

The research work is partially funded by the STEPS Malta.This scholarship is partly financed by the European Union - European Social Fund (ESF 1.25).Distributed Video Coding (DVC) is a coding paradigm which shifts the major computational intensive tasks from the encoder to the decoder. Temporal correlation is exploited at the decoder by predicting the Wyner-Ziv (WZ) frames from the adjacent key frames. Compression is then achieved by transmitting just the parity information required to correct the predicted frame and recover the original frame. This paper proposes an algorithm which identifies most of the unreliable bits in the predicted bit planes, by considering the discrepancies in the previously decoded bit plane. The design of the used Low Density Parity Check (LDPC) codes is then biased to provide better protection to the unreliable bits. Simulation results show that, for the same target quality, the proposed scheme can reduce the WZ bit rates by up to 7% compared to traditional schemes.peer-reviewe

Adaptive rounding operator for efficient Wyner-Ziv video coding

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union – European Social Fund. (ESF 1.25).The Distributed Video Coding (DVC) paradigm can theoretically reach the same coding efficiencies of predictive block-based video coding schemes, like H.264/AVC. However, current DVC architectures are still far from this ideal performance. This is mainly attributed to inaccuracies in the Side Information (SI) predicted at the decoder. The work in this paper presents a coding scheme which tries to avoid mismatch in the SI predictions caused by small variations in light intensity. Using the appropriate rounding operator for every coefficient, the proposed method significantly reduces the correlation noise between the Wyner-Ziv (WZ) frame and the corresponding SI, achieving higher coding efficiencies. Experimental results demonstrate that the average Peak Signal-to-Noise Ratio (PSNR) is improved by up to 0.56dB relative to the DISCOVER codec.peer-reviewe

Improved Wyner-Ziv video coding efficiency using bit plane prediction

The research work is partially funded by STEPS-Malta and partially by the European Union - ESF 1.25.Distributed Video Coding (DVC) is a coding paradigm where video statistics are exploited, partially or totally, at the decoder. The performance of such a codec depends on the accuracy of the soft-input information estimated at the decoder, which is affected by the quality of the side information (SI) and the dependency model. This paper studies the discrepancies between the bit planes of the Wyner-Ziv (WZ) frames and the corresponding bit planes of the SI. The relationship between these discrepancies is then exploited to predict the locations where the bit plane of the SI is expected to differ from that of the original WZ frame. This information is then used to derive more accurate soft-input values that achieve better compression efficiencies. Simulation results demonstrate that a WZ bit-rate reduction of 9.4% is achieved for a given video quality.peer-reviewe

Improving decoding speed for parallel distributed video coding architectures

The research work disclosed in this publication is partially funded by the Strategic Educational Pathways Scholarship Scheme (Malta). The scholarship is part-financed by the European Union – European Social Fund. (ESF 1.25).The Distributed Video Coding (DVC) paradigm is suitable for devices which have limited encoding capabilities. However, it is characterized by excessive decoding delays which compromise their application for time constrained services. This limitation can be mitigated by adopting parallel DVC architectures. Yet, the traditional Gray-code or binary-code representations have a non-uniform distribution of mismatch across bit-planes, resulting in uneven decoding times which hinder parallel decoding. This work proposes an alternative indexing scheme, where mismatch is distributed more uniformly amongst bit-planes and thus comparable decoding delays are expected, facilitating parallel implementations. This method reduces decoding time by up to 32% compared to architectures using simple parallel techniques, with a slight loss of 0.06dB in RD performance.peer-reviewe

Modified distribution of correlation noise for improved Wyner-Ziv video coding performance

This research work was partially funded by the Strategic Educational Pathways Scholarship Scheme (STEPS-Malta) and by European Union - European Social Fund (ESF 1.25).Despite theorems predicting that Distributed Video Coding can achieve the same performance as traditional predictive video coding schemes, the coding efficiency of practical architectures is still far from these bounds. This is attributed to the poor Side Information (SI) estimated at the decoder and to the inability of the channel codes to recover the source at the Slepian-Wolf (SW) limits. This paper tackles the latter issue by recovering the SI bit-planes starting from the most unreliable bit of each coefficient. Most of the mismatch in SI is thus accumulated within the first decoded bit-planes, leaving the last bit-planes with very few or no mismatch. Low-Density Parity-Check Accumulate (LDPCA) codes can then benefit from such compact distribution of correlation noise since they offer a smaller percentage error, from the SW bounds, when mismatch is accumulated in few higher entropy bit-planes. Furthermore, with this setup, most of the last bit-planes can be recovered very effectively using just 8-bit or 16-bit Cyclic Redundancy Codes. Experimental results show that the proposed scheme can reduce the Wyner-Ziv bit-rates by up to 21% compared to the DISCOVER codec.peer-reviewe

Low-density parity-check codes for asymmetric distributed source coding

The research work is partially funded by the Strategic Educational Pathways Scholarship Scheme (STEPS-Malta). This scholarship is partly financed by the European Union - European Social Fund (ESF 1.25).Low-Density Parity-Check (LDPC) codes achieve good performance, tending towards the Slepian-Wolf bound, when used as channel codes in Distributed Source Coding (DSC). Most LDPC codes found in literature are designed assuming random distribution of transmission errors. However, certain DSC applications can predict the error location within a certain level of accuracy. This feature can be exploited in order to design application specific LDPC codes to enhance the performance of traditional LDPC codes. This paper proposes a novel architecture for asymmetric DSC where the encoder is able to estimate the location of the errors within the side information. It then interleaves the bits having a high probability of error to the beginning of the codeword. The LDPC codes are designed to provide a higher level of protection to the front bits. Simulation results show that correct localization of errors pushes the performance of the system on average 13.3% closer to the Slepian-Wolf bound, compared to the randomly constructed LDPC codes. If the error localization prediction fails, such that the errors are randomly distributed, the performance is still in line with that of the traditional DSC architecture.peer-reviewe