7,395 research outputs found
On the complete weight enumerators of some linear codes with a few weights
Linear codes with a few weights have important applications in authentication
codes, secret sharing, consumer electronics, etc.. The determination of the
parameters such as Hamming weight distributions and complete weight enumerators
of linear codes are important research topics. In this paper, we consider some
classes of linear codes with a few weights and determine the complete weight
enumerators from which the corresponding Hamming weight distributions are
derived with help of some sums involving Legendre symbol
Near MDS poset codes and distributions
We study -ary codes with distance defined by a partial order of the
coordinates of the codewords. Maximum Distance Separable (MDS) codes in the
poset metric have been studied in a number of earlier works. We consider codes
that are close to MDS codes by the value of their minimum distance. For such
codes, we determine their weight distribution, and in the particular case of
the "ordered metric" characterize distributions of points in the unit cube
defined by the codes. We also give some constructions of codes in the ordered
Hamming space.Comment: 13 pages, 1 figur
On the binary codes with parameters of triply-shortened 1-perfect codes
We study properties of binary codes with parameters close to the parameters
of 1-perfect codes. An arbitrary binary code ,
i.e., a code with parameters of a triply-shortened extended Hamming code, is a
cell of an equitable partition of the -cube into six cells. An arbitrary
binary code , i.e., a code with parameters of a
triply-shortened Hamming code, is a cell of an equitable family (but not a
partition) from six cells. As a corollary, the codes and are completely
semiregular; i.e., the weight distribution of such a code depends only on the
minimal and maximal codeword weights and the code parameters. Moreover, if
is self-complementary, then it is completely regular. As an intermediate
result, we prove, in terms of distance distributions, a general criterion for a
partition of the vertices of a graph (from rather general class of graphs,
including the distance-regular graphs) to be equitable. Keywords: 1-perfect
code; triply-shortened 1-perfect code; equitable partition; perfect coloring;
weight distribution; distance distributionComment: 12 page
Bounds on the size of codes
In this dissertation we determine new bounds and properties of codes in
three different finite metric spaces, namely the ordered Hamming space, the
binary Hamming space, and the Johnson space.
The ordered Hamming space is a generalization of the Hamming space that
arises in several different problems of coding theory and numerical
integration. Structural properties of this space are well described in the
framework of Delsarte's theory of association schemes. Relying on this
theory, we perform a detailed study of polynomials related to the ordered
Hamming space and derive new asymptotic bounds on the size of codes in this
space which improve upon the estimates known earlier.
A related project concerns linear codes in the ordered Hamming space. We
define and analyze a class of near-optimal codes, called near-Maximum
Distance Separable codes. We determine the weight distribution and provide
constructions of such codes. Codes in the ordered Hamming space are dual to
a certain type of point distributions in the unit cube used in numerical
integration. We show that near-Maximum Distance Separable codes are
equivalently represented as certain near-optimal point distributions.
In the third part of our study we derive a new upper bound on the size of
a family of subsets of a finite set with restricted pairwise intersections,
which improves upon the well-known Frankl-Wilson upper bound. The new bound
is obtained by analyzing a refinement of the association scheme of the
Hamming space (the Terwilliger algebra) and intertwining functions of the
symmetric group.
Finally, in the fourth set of problems we determine new estimates on the
size of codes in the Johnson space. We also suggest a new approach to the
derivation of the well-known Johnson bound for codes in this space. Our
estimates are often valid in the region where the Johnson bound is vacuous.
We show that these methods are also applicable to the case of multiple
packings in the Hamming space (list-decodable codes). In this context we
recover the best known estimate on the size of list-decodable codes in
a new way
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