27,390 research outputs found
Quasi-Cyclic Codes
Quasi-cyclic codes form an important class of algebraic codes that includes
cyclic codes as a special subclass. This chapter focuses on the algebraic
structure of quasi-cyclic codes, first. Based on these structural properties,
some asymptotic results, a few minimum distance bounds and further applications
such as the trace representation and characterization of certain subfamilies of
quasi-cyclic codes are elaborated. This survey will appear as a chapter in "A
Concise Encyclopedia of Coding Theory" to be published by CRC Press.Comment: arXiv admin note: text overlap with arXiv:1906.0496
Hierarchical and High-Girth QC LDPC Codes
We present a general approach to designing capacity-approaching high-girth
low-density parity-check (LDPC) codes that are friendly to hardware
implementation. Our methodology starts by defining a new class of
"hierarchical" quasi-cyclic (HQC) LDPC codes that generalizes the structure of
quasi-cyclic (QC) LDPC codes. Whereas the parity check matrices of QC LDPC
codes are composed of circulant sub-matrices, those of HQC LDPC codes are
composed of a hierarchy of circulant sub-matrices that are in turn constructed
from circulant sub-matrices, and so on, through some number of levels. We show
how to map any class of codes defined using a protograph into a family of HQC
LDPC codes. Next, we present a girth-maximizing algorithm that optimizes the
degrees of freedom within the family of codes to yield a high-girth HQC LDPC
code. Finally, we discuss how certain characteristics of a code protograph will
lead to inevitable short cycles, and show that these short cycles can be
eliminated using a "squashing" procedure that results in a high-girth QC LDPC
code, although not a hierarchical one. We illustrate our approach with designed
examples of girth-10 QC LDPC codes obtained from protographs of one-sided
spatially-coupled codes.Comment: Submitted to IEEE Transactions on Information THeor
A tight upper bound on the number of non-zero weights of a quasi-cyclic code
Let be a quasi-cyclic code of index . Let be the
subgroup of the automorphism group of generated by and
the scalar multiplications of , where denotes the standard
cyclic shift. In this paper, we find an explicit formula of orbits of on
. Consequently, an explicit upper bound on
the number of non-zero weights of is immediately derived and a
necessary and sufficient condition for codes meeting the bound is exhibited. In
particular, we list some examples to show the bounds are tight. Our main result
improves and generalizes some of the results in \cite{M2}
Construction of Quasi-Cyclic Product Codes
Linear quasi-cyclic product codes over finite fields are investigated. Given
the generating set in the form of a reduced Gr{\"o}bner basis of a quasi-cyclic
component code and the generator polynomial of a second cyclic component code,
an explicit expression of the basis of the generating set of the quasi-cyclic
product code is given. Furthermore, the reduced Gr{\"o}bner basis of a
one-level quasi-cyclic product code is derived.Comment: 10th International ITG Conference on Systems, Communications and
Coding (SCC), Feb 2015, Hamburg, German
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