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arXiv 1004.4882cs.ITmath.IT
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Johnson方案中码的性质

Properties of Codes in the Johnson Scheme

Natalia Silberstein

摘要:

达到球填充界的码被称为完美码。编码理论中定义完美码的最重要的度量是汉明度量和约翰逊度量。对于Hamming度量,有限域上的所有完美码都是已知的,而在Johnson度量中,Delsarte在20世纪70年代证明了不存在非平凡的完美码。一般不存在性的证明仍然是一个悬而未决的问题。在这项工作中,我们研究等重码以及双重等重码,并减少完美的代码可能存在于这两种情况下的参数范围。我们从等重码开始。利用Johnson图J(n,w)中的完美码与块设计之间的联系,对单完美码的Roos界进行了改进,并给出了一些新的可除性条件.接下来,我们考虑完美码的二项式矩。我们展示了哪些参数可以排除一完美码。我们研究了J(2 w,w)中的两个完美码,并提出了存在这样的代码的必要条件。证明了在J(2 w,w)中不存在长度小于2.5*10^{15}的二完美码。接下来,我们研究完美双等重码。本文提出了一种码的参数族,其码的球的大小能整除整个空间的大小。然后,我们证明了这样的码的长度的一个界,类似于Roos的约翰逊图中的完美码的界。最后,我们描述了Steiner系统和双Steiner系统,它们分别与等重码和双等重码强连通。给出了Steiner系统长度上界的一个基于反码的证明,证明了双Steiner系统是直径完美码,并给出了双Steiner系统长度上界的一个估计。

英文摘要:

Codes which attain the sphere packing bound are called perfect codes. The most important metrics in coding theory on which perfect codes are defined are the Hamming metric and the Johnson metric. While for the Hamming metric all perfect codes over finite fields are known, in the Johnson metric it was conjectured by Delsarte in 1970's that there are no nontrivial perfect codes. The general nonexistence proof still remains the open problem. In this work we examine constant weight codes as well as doubly constant weight codes, and reduce the range of parameters in which perfect codes may exist in both cases. We start with the constant weight codes. We introduce an improvement of Roos' bound for one-perfect codes, and present some new divisibility conditions, which are based on the connection between perfect codes in Johnson graph J(n,w) and block designs. Next, we consider binomial moments for perfect codes. We show which parameters can be excluded for one-perfect codes. We examine two-perfect codes in J(2w,w) and present necessary conditions for existence of such codes. We prove that there are no two-perfect codes in J(2w,w) with length less then 2.5*10^{15}. Next we examine perfect doubly constant weight codes. We present a family of parameters for codes whose size of sphere divides the size of whole space. We then prove a bound on length of such codes, similarly to Roos' bound for perfect codes in Johnson graph. Finally we describe Steiner systems and doubly Steiner systems, which are strongly connected with the constant weight and doubly constant weight codes respectively. We provide an anticode-based proof of a bound on length of Steiner system, prove that doubly Steiner system is a diameter perfect code and present a bound on length of doubly Steiner system.

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