Browsing by Author "Hornansky, Martin"

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Customizing short-length LT codes with evolution strategies for video streaming protection
(2017-07-01)
Hornansky, Martin
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Zao, John K.
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資訊工程學系
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Department of Computer Science
Designing short-length Luby Transform (SLLT) codes to best protect video streaming and multicasting over lossy communication remains largely an empirical exercise. In this paper, we present a systematic approach to customize the decoding performance of these codes so that the protected video bitstreams may have the best playback quality over a wide range of channel loss rates. Our approach begins with the proposal of a new SLLT decoding performance model based on three parameters: decoding overhead, symbol decoding failure rate and tail probability of symbol decoding failure rate. We then formulate the design of SLLT codes as a multi-objective optimization problem, specify the design objectives in terms of goal program, and search for the most suitable codes using an augmented weighted Tchebycheff method implemented with the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). Two design examples are provided to illustrate the effectiveness of our approach: (1) an SLLT postcode of a short-length raptor code that provides erasure protection to H.264 AVC bitstreams, and (2) an SLLT post-code of a rateless UEP code that supports graceful degradation of H.264 SVC playback quality. Empirical results demonstrate that the proposed method is capable of producing SLLT codes with customized decoding performance, whereas, the customized codes enable the playback pictures to attain significantly higher PSNR values at different stages of the decoding process than the pictures recovered under the protection of conventionally optimized codes.
Design of Optimal Short-Length LT Codes Using Evolution Strategies
(2012)
Zao, John K.
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Hornansky, Martin
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Diao, Pei-lun
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資訊工程學系
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Department of Computer Science
Luby Transform (LT) and its companion Raptor codes are the most popular implementations of digital fountain codes. Performance of these rateless forward erasure correction codes is determined mainly by the degree distributions of their encoded symbols. Although the asymptotic behaviors of LT codes with large (>10(5)) symbol blocks have been deduced analytically, a proficient method for finding the optimal degree distributions of short length (<10(3)) LT codes is still absent. In this paper, we propose a practical approach to employ evolution strategies in finding the degree distributions of optimal short-length LT codes for different applications. Our approach begins with the development of a new performance model for LT codes based on three measurements: coding overhead epsilon, failure ratio r and failure occurrence probability p. Three evolution strategies (DE, CMA-ES and NES) were then employed to minimize these performance measurements separately with careful design of fitness functions and necessary transformations of decision variables. Throughout the evolution process, the performance of individual LT code in the population was evaluated with numerical simulations. Our experiments showed that the optimal degree distributions can be found using all three evolution strategies but with different convergence rates and the (r, p, epsilon) values of these optimized codes are all distributed on a smooth concave surface.
OPTIMIZED RATELESS UEP CODES FOR SCALABLE VIDEO STREAMING
(2012)
Zao, John K.
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Hornansky, Martin
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Diao, Pei-Lun
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Wang, Bo-Wei
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Wang, Chung-Hsuan
Wireless video streaming often suffers from heavy and varying amount of packet loss. Short-length Luby Transform (SLLT) codes are often employed to offer necessary rateless or universal erasure protection. Nevertheless, a proficient method for finding the optimal degree distributions of SLLT codes is still missing although the asymptotic behaviors of infinite-length LT codes have long been deduced. In this paper, we propose a practical approach to find the optimal degree distributions of LT codes with arbitrary input block lengths. Our approach starts with a new fitness model for the LT codes based on three performance measurements: their coding overhead e, decoding failure ratio r and failure probability p. We then employed the exponential natural evolution strategy (xNES) along with a suitable choice of initial degree distribution and a proper transformation between the genotypes and the phenotypes to search for the optimized degree distributions. The optimized SLLT codes designed using this approach far outperforms the ones obtained through asymptotic approximation. As an example application, we constructed a family of rateless convolutional UEP codes using these optimized SLLT codes as the rateless postcodes. These codes offer superb universal unequal erasure protection to wireless H.264/SVC broadcasting with only 16%-20% coding overhead. This design exercise, however, made clear the necessity of matching the rateless erasure correction capability of the SLLT postcode with the error-rate sensitive UEP capability of the convolutional precode. The effect of code matching was demonstrated clearly in the improvement of rate-distortion performance of video playback.