190 research outputs found
Problems on q-Analogs in Coding Theory
The interest in -analogs of codes and designs has been increased in the
last few years as a consequence of their new application in error-correction
for random network coding. There are many interesting theoretical, algebraic,
and combinatorial coding problems concerning these q-analogs which remained
unsolved. The first goal of this paper is to make a short summary of the large
amount of research which was done in the area mainly in the last few years and
to provide most of the relevant references. The second goal of this paper is to
present one hundred open questions and problems for future research, whose
solution will advance the knowledge in this area. The third goal of this paper
is to present and start some directions in solving some of these problems.Comment: arXiv admin note: text overlap with arXiv:0805.3528 by other author
Decoding Reed Solomon and BCH codes beyond their error-correction radius: an euclidean approach
In questo lavoro viene presentato un algoritmo alternativo per il list decoding di codici Reed-Solomon e BCH
basato sull'algoritmo di divisione euclidea. Fissato un numero e, e data una parola ricevuta, l'obiettivo e' quello di dare in output una lista di parole del codice che abbiano distanza al piu' e da essa. Per i codici BCH la decodifica avviene attraverso
la ricerca del polinomio locatore dell'errore, un particolare polinomio che si trova nel nucleo della matrice delle sindromi e che ha tutte le radici nel campo di partenza. Utilizzando queste proprieta', e attraverso l'algoritmo di divisione euclidea, siamo in grado di elencare tutti i possibili polinomi locatori dell'errore, e quindi tutte le parole del codice che abbiano la distanza desiderata.
Vengono poi analizzati gli aspetti computazionali di tale algoritmo, nel caso generale e in alcuni casi particolari.
Infine vengono fatti dei confronti con gli algoritmi gia' esistenti, e vengono studiati dei bound sul numero massimo di parole che l'algoritmo restituisce
Self-Dual Codes
Self-dual codes are important because many of the best codes known are of
this type and they have a rich mathematical theory. Topics covered in this
survey include codes over F_2, F_3, F_4, F_q, Z_4, Z_m, shadow codes, weight
enumerators, Gleason-Pierce theorem, invariant theory, Gleason theorems,
bounds, mass formulae, enumeration, extremal codes, open problems. There is a
comprehensive bibliography.Comment: 136 page
Locally Recoverable Codes From Algebraic Curves
Locally recoverable (LRC) codes have the property that erased coordinates can be recovered by retrieving a small amount of the information contained in the entire codeword. An LRC code achieves this by making each coordinate a function of a small number of other coordinates. Since some algebraic constructions of LRC codes require that , where is the length and is the size of the field, it is natural to ask whether we can generate codes over a small field from a code over an extension. Trace codes achieve this by taking the field trace of every coordinate of a code. In this thesis, we give necessary and sufficient conditions for when the local recoverability property is retained when taking the trace of certain LRC codes.
This thesis also explores a subfamily of LRC codes with hierarchical locality (H-LRC) which have tiers of recoverability. We provide a general construction of codes with 2 levels of hierarchy from maps between algebraic curves and present several families from quotients of curves by a subgroup of automorphisms. We consider specific examples from rational, elliptic, Kummer, and Artin-Schrier curves and examples of asymptotically good families of H-LRC codes from curves related to the Garcia-Stichtenoth tower
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