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arXiv cs/0601113cs.ITcond-mat.dis-nnmath.IT
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LDPC码线性规划译码的一种有效伪码字搜索算法

An Efficient Pseudo-Codeword Search Algorithm for Linear Programming Decoding of LDPC Codes

Michael Chertkov, Mikhail G. Stepanov

摘要:

在低密度奇偶校验(LDPC)码的线性规划(LP)解码中,在由码字\cite{03FWK}跨越的多面体的松弛上最小化具有与对数似然比相关的系数的线性泛函。为了量化LP解码,从而描述在中等和大信噪比(SNR)下的纠错方案的性能,重要的是研究松弛多面体以更好地理解其顶点,所谓的伪码字,特别是那些是零码字的邻居的顶点。在这份手稿中,我们提出了一种技术,以启发式地创建这些邻居和他们的距离列表。我们的伪码字搜索算法通过随机选择噪声的初始配置开始。通过离散数量的步骤来修改配置。每个步骤由两个子步骤组成。首先,将LP解码器应用于噪声配置,导出伪码字。其次,找到与伪码字和零码字等距的噪声的配置。生成的噪声配置用作下一步的条目。迭代快速收敛到与零码字相邻的伪码字。重复多次,该过程的特征在于伪码字有效距离的分布函数(频谱)。编码方案的有效距离近似于频谱中的最短距离伪码字。Tanner $[155,64,20]$码和Margulis $p=7$和$p=11$码(分别为672和2640位长)在加性白高斯噪声(AWGN)信道上操作的示例上证明了该过程的效率。

英文摘要:

In Linear Programming (LP) decoding of a Low-Density-Parity-Check (LDPC) code one minimizes a linear functional, with coefficients related to log-likelihood ratios, over a relaxation of the polytope spanned by the codewords \cite{03FWK}. In order to quantify LP decoding, and thus to describe performance of the error-correction scheme at moderate and large Signal-to-Noise-Ratios (SNR), it is important to study the relaxed polytope to understand better its vertexes, so-called pseudo-codewords, especially those which are neighbors of the zero codeword. In this manuscript we propose a technique to heuristically create a list of these neighbors and their distances. Our pseudo-codeword-search algorithm starts by randomly choosing the initial configuration of the noise. The configuration is modified through a discrete number of steps. Each step consists of two sub-steps. Firstly, one applies an LP decoder to the noise-configuration deriving a pseudo-codeword. Secondly, one finds configuration of the noise equidistant from the pseudo codeword and the zero codeword. The resulting noise configuration is used as an entry for the next step. The iterations converge rapidly to a pseudo-codeword neighboring the zero codeword. Repeated many times, this procedure is characterized by the distribution function (frequency spectrum) of the pseudo-codeword effective distance. The effective distance of the coding scheme is approximated by the shortest distance pseudo-codeword in the spectrum. The efficiency of the procedure is demonstrated on examples of the Tanner $[155,64,20]$ code and Margulis $p=7$ and $p=11$ codes (672 and 2640 bits long respectively) operating over an Additive-White-Gaussian-Noise (AWGN) channel.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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