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Optimizing the Parallel Tree-Search for Finding Shortest-Span Error-Correcting CDO Codes

IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 2014年第11期25卷 2992-3001页

作者： Kowarzyk, Gilbert Belanger, Normand Haccoun, David Savaria, Yvon Ecole Polytech Montreal Montreal PQ Canada

Finding optimal/short-span Convolutional Self-Doubly Orthogonal (CDO) codes and Simplified-CDO (S-CDO) codes for a specified order J is computationally very challenging. This paper describes several optimizations that were applied to an implicitly-exhaustive search algorithm in order to reduce the time required for finding these types of codes. The resulting high-performance parallel implementation provides an impressive speedup that is greater than 16 300 (CDO, J - 7) and 6300 (S-CDO, J - 8) over the reference implicitly-exhaustive search algorithm, and greater than 2000 (J - 17) over the fastest published CDO validation function used in high-performance pseudorandom search algorithms. These speedups are achieved through enhancements in the deterministic search-space reduction, and a vastly improved validation function that makes use of a novel data structure for enabling data-reuse and incremental computations. The resulting validation function speedup is greater than 60 000 (S-CDO, J = 17) and 190 000 (CDO, J = 17) when compared to its reference implementation. The combination of optimizations and load-balancing techniques allowed us to leverage hundreds of processor cores in order to complete an exhaustive search over a search space that is some 10(14) times larger than what was previously possible.

关键词： Convolutional code self-doubly orthogonal code parallel tree-traversal data-reuse systematic encoder threshold decoder

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Search and determination of convolutional self-doubly orthogonal codes for iterative threshold decoding

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IEEE TRANSACTIONS ON COMMUNICATIONS 2005年第5期53卷 802-809页

作者： Haccoun, D Cardinal, C Gagnon, F Ecole Polytech Dept Elect Engn Montreal PQ H3C 3A7 Canada Ecole Technol Super Dept Elect Engn Montreal PQ H3C 1K3 Canada

In this paper, we present new results on the search and determination of wide-sense convolutional self-doubly orthogonal codes ((CSOC)-C-2-WS) which can be decoded using a simple iterative threshold decoding algorithm without interleaving. For their iterative decoding, in order to ensure the independence of observables over the first two iterations without the presence of interleavers, these (CSOC)-C-2 must satisfy specific orthogonal properties of their generator connections. The error performances of (CSOC)-C-2, depend essentially on the number of taps J of the code generators but not on the code memory length. Since the overall latency of the iterative threshold decoding process is proportional to the memory length of the codes, therefore, when searching for the best (CSOC)-C-2-WS of a given J value, the memory length of the codes should be chosen to be as small as possible. In this paper, we present a code-searching technique based on heuristic computer searching algorithms which have yielded the best known (CSOC)-C-2-WS. The construction method for (CSOC)-C-2-WS has provided the best known r = 1/2 codes with the shortest memory length having J ≤ 30. Although not very complex to implement, the search method presented here is quite efficient especially in reducing very substantially the execution time required to determine the codes with the shortest spans. Furthermore, in addition to presenting the search results for the codes, error performances obtained by simulation are also provided.

关键词： convolutional code convolutional self-doubly orthogonal code ((CSOC)-C-2) span of the code systematic encoder threshold decoder

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Convolutional self-doubly orthogonal codes and their iterative threshold decoding

Convolutional self-doubly orthogonal codes and their iterati...

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15th IEEE International Symposium on Personal, Indoor, Mobile, Radio Communications (PIMRC 2004)

作者： Cardinal, C Haccoun, D Ecole Polytech Dept Elect Engn Montreal PQ H3C 3A7 Canada

ISBN: (纸本)0780385233

An extension of convolutional self-orthogonal codes called convolutional self-doubly orthogonal codes which are decoded using an iterative threshold decoding algorithm with no interleaver is presented. These new codes allow good error performances in addition to providing attractive trade-off between complexity and latency. Some code searching results yielding new codes are provided together with their error performance evaluation. Puncturing techniques for systematic convolutional codes that allows to obtain high-rate R = b/(b + 1) punctured convolutional self-doubly orthogonal codes in the wide sense are also investigated. Some punctured convolutional self-doubly orthogonal codes are presented and their bit error probabilities are evaluated using computer simulations.

关键词： convolutional self-orthogonal codes threshold decoder iterative decoding convolutional self-doubly orthogonal codes

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Searching for short-span Convolutional Doubly Self-Orthogonal Codes: A parallel implicitly-exhaustive-search algorithm

Searching for short-span Convolutional Doubly Self-Orthogona...

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Canadian Conference on Electrical and Computer Engineering

作者： Kowarzyk, G. Savaria, Y. Haccoun, D. Ecole Polytech Dept Elect & Comp Engn Montreal PQ H3C 3A7 Canada

ISBN: (纸本)9781424416424

In this paper we present an efficient algorithm to search for optimal/short-span Convolutional Self-Doubly Orthogonal Codes ((CSOC)-C-2) using a novel parallel exhaustive-search algorithm. The error correcting codes are used in the new (CSOC)-C-2 encoding/iterative threshold decoding technique that was introduced as an alternative to Turbo Codes. Since the iterative threshold decoding algorithm does not use interleaving, the generator connections in these codes must satisfy specific orthogonality properties to ensure the independence of observables over the first two iterations. The code constraint length (or "span" of the code) corresponds to the latency of each decoding iteration, and minimizing it for a given error-correcting capability is important when building high-performance, low-latency codecs. The proposed algorithm drastically speeds up the implicitly-exhaustive search for shorter-span codes and scales well on today's multi-core computer systems. On a 16-core server, the computational time for obtaining optimal J=6 and J=7 (CSOC)-C-2 was reduced by 93%.

关键词： convolutional code convolutional self-doubly orthogonal code ((CSOC)-C-2) multithreaded search parallel search span of the code systematic encoder threshold decoder

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