Browsing by Author "Yen, Kuo-Kuang"

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Adjusted Robust Soliton Distribution (ARSD) with Reshaped Ripple Size for LT Codes
(2013)
Yen, Kuo-Kuang
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Liao, Yen-Chin
;
Chen, Chih-Lung
;
Chang, Hsie-Chia
;
電子工程學系及電子研究所
In this work, we improve the performance of robust Soliton distribution (RSD) for LT codes by reshaping its expected ripple size. Our goal is to make the ripple size as close to a constant theta k as possible during BP decoding process, where 0 < theta <= 1 is called ripple size ratio (RSR) and k is the total number of input symbols. We only adjust the proportion of degree 1, degree 2 and the maximum existing degree in RSD to minimize the mean squared error between the expected ripple size and the constant theta k. In addition, we develop upper and lower bounds of RSR as well as an indicator for choosing RSD. Simulation results show that by carefully choosing RSR, the adjusted RSD (ARSD) is able to outperform RSD in terms of successful decoding rate. Compared to RSD, ARSD also reduces the average overhead needed to decode all k input symbols.
An Improved LT Encoding Scheme with Extended Chain Lengths
(2012-01-01)
Yen, Kuo-Kuang
;
Chen, Chih-Lung
;
Chang, Hsie-Chia
;
交大名義發表
;
National Chiao Tung University
The BP decoding terminates frequently during the early stage for LT codes with the robust Soliton distribution. Generally, more than 90% of undecoded input symbols result from decoding termination within the range 0 <= n <= k/2, where n and k are the decoded and total number of input symbols, respectively. This study focuses on reducing the symbol loss probability by preventing early decoding termination. Input symbols can be divided into decoding chains with respect to the connectivity of degree-2 encoding symbols such that neighbors of a degree-2 encoding symbol belong to the same decoding chain. The number of input symbols in a decoding chain is called the chain length. It is found that the average chain length is shorter if the decoding termination occurs within 0 <= n <= k/2. We propose an encoding scheme which increases the chain length to avoid early decoding termination. Each code block is divided into two groups - the first one contains tau randomly selected input symbols, while the rest k - tau symbols form the second group. Neighbors of any degree-2 encoding symbol are restricted from different groups of input symbols. The probability that two degree-2 encoding symbols have a neighbor in common is increased, leading to longer decoding chain on average. Simulation results show that the symbol loss probability of the proposed encoding scheme is always lower than that of the LT encoding. The improvement by our scheme in the symbol loss probability increases with k. In comparison with the LT encoding, when the overhead is sufficiently large, the proposed scheme also achieve higher probability of successful decoding.
An Improved LT Encoding Scheme with Extended Chain Lengths
(2012-01-01)
Yen, Kuo-Kuang
;
Chen, Chih-Lung
;
Chang, Hsie-Chia
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The BP decoding terminates frequently during the early stage for LT codes with the robust Soliton distribution. Generally, more than 90% of undecoded input symbols result from decoding termination within the range 0 <= n <= k/2, where n and k are the decoded and total number of input symbols, respectively. This study focuses on reducing the symbol loss probability by preventing early decoding termination. Input symbols can be divided into decoding chains with respect to the connectivity of degree-2 encoding symbols such that neighbors of a degree-2 encoding symbol belong to the same decoding chain. The number of input symbols in a decoding chain is called the chain length. It is found that the average chain length is shorter if the decoding termination occurs within 0 <= n <= k/2. We propose an encoding scheme which increases the chain length to avoid early decoding termination. Each code block is divided into two groups - the first one contains tau randomly selected input symbols, while the rest k - tau symbols form the second group. Neighbors of any degree-2 encoding symbol are restricted from different groups of input symbols. The probability that two degree-2 encoding symbols have a neighbor in common is increased, leading to longer decoding chain on average. Simulation results show that the symbol loss probability of the proposed encoding scheme is always lower than that of the LT encoding. The improvement by our scheme in the symbol loss probability increases with k. In comparison with the LT encoding, when the overhead is sufficiently large, the proposed scheme also achieve higher probability of successful decoding.
Design of LT Code Degree Distribution with Profiled Output Ripple Size
(2015)
Yen, Kuo-Kuang
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Liao, Yen-Chin
;
Chang, Hsie-Chia
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
LT codes, a candidate for next-generation forward error correction (FEC) scheme, draws great attention due to its low encoding/decoding complexity and capacity-approaching properties. Especially for wireless applications in fast-changing environments, adaptive degree distribution is a possible solution to balance the trade-off between LT codes\' efficiency and robustness. A fast mapping from attributes in the decoding process to degree distribution is required for realizing adaptive degree distribution. This study presents a reverse mapping from the expected ripple size to degree distributions. The basic idea is to minimize the error between a predetermined curve mu (rho) and the expected ripple size R (Omega (x); rho) of a target degree distribution Omega (x), where rho is the number of decoded input symbols. By converting the code degree design into a pure optimization problem, it is possible to design LT codes with constraints from performance requirements to complexity issues. Applying sequential quadratic programming, a ripple-based distribution (RBD) is presented as a feasible design example. Simulation results show that, as compared to robust Soliton distribution (RSD) and previous studies, RBD is able to reduce the transmission overhead as well as the encoding and decoding complexity by at least 31.2% and 25.4%, respectively.(1)
Integrating Non-Repetitive LT Encoders With Modified Distribution to Achieve Unequal Erasure Protection
(2013-12-01)
Yen, Kuo-Kuang
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Liao, Yen-Chin
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Chen, Chih-Lung
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Zao, John K.
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Chang, Hsie-Chia
The performance of LT code is highly related to the code length. A decoder is more likely to deplete degree-1 encoding symbols and terminate during early stage when the code length is short. In this work, we modify the robust Soliton distribution (RSD) and increase the degree-1 proportion. More degree-1 encoding symbols can be generated to relieve early decoding termination. The proportion of low degrees, except for degree-1, is also reduced. Therefore, receivers collect less encoding symbols carrying redundant information. In addition, Non-Repetitive (NR) encoding scheme is proposed to avoid producing repeated degree-1 encoding symbols. To improve video transmission quality, previous studies redesign LT codes to provide Unequal Error Protection (UEP) for different Scalable Video Coding (SVC) layers. Unlike those studies to modify the code structure, we integrate multiple NR encoders to achieve UEP ability. Experimental results show that our UEP scheme outperforms previous studies in terms of the PSNR.
Modified Robust Soliton Distribution (MRSD) with Improved Ripple Size for LT Codes
(2013-05-01)
Yen, Kuo-Kuang
;
Liao, Yen-Chin
;
Chen, Chih-Lung
;
Chang, Hsie-Chia
;
電子工程學系及電子研究所
In this letter, we propose a scheme to modify robust Soliton distribution (RSD) with respect to the expected ripple size. We only adjust the proportion of degree 1, degree 2 and the maximum degree to derive the modified RSD (MRSD). Thus the proposed scheme contains only two variables and its complexity does not increase with the code length. Our objective is to increase the mean of the expected ripple size while decreasing its variance at the same time. Furthermore, sequential quadratic programming is introduced to maximize the objective function under certain constraints. Simulation results show that, with different code lengths, MRSD saves 2% to 5.8% overhead to decode entire input symbols, compared to RSD.
Non-Repetitive Encoding with Increased Degree-1 Encoding Symbols for LT Codes
(2012)
Yen, Kuo-Kuang
;
Liao, Yen-Chin
;
Chen, Chih-Lung
;
Chang, Hsie-Chia
;
電子工程學系及電子研究所
For LT codes with robust Soliton distribution, the ripple size is relatively small in the beginning of BP decoding process. Therefore, most of decoding termination occurs due to lack of ripple at early stage. In this study, we aim at reducing early decoding termination for low symbol loss probability. First, given k input symbols, the degree-1 proportion is increased to enlarge the average ripple size within the range 0 <= n <= k/2, where n is the number of decoded input symbols. Second, we propose Non-Repetitive (NR) encoding scheme to avoid generating repeated degree-1 encoding symbols. An NR encoder forces the first k degree-1 encoding symbols to connect to different input symbols. Simulation results show that NR encoding outperforms LT encoding in terms of symbol loss probability. Besides, less encoding symbols is needed to achieve high successful decoding probability when our scheme is applied. With k = 2000, NR encoding reaches a successful decoding probability of 99.6 % when overhead is 0.2, while LT encoding requires an overhead of 0.3 2 to reach the same probability.