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Title	On the structure of Hermitian codes
Author(s)	Chris Heegard, John B. Little, Keith Saints
Type	Article in Journal
Abstract	Let X_m denote the Hermitian curve x^{m 1} = y^m y over the field F_m^2. Let Q be the single point at infinity, and let D be the sum of the other m^3 points of X_m rational over F_m^2, each with multiplicity 1. X_m has a cyclic group of automorphisms of order m^2 - 1, which induces automorphisms of each of the one-point algebraic geometric Goppa codes C_L(D, aQ) and their duals. As a result, these codes have the structure of modules over the ring F_q[t], and this structure can be used to good effect in both encoding and decoding. In this paper we examine the algebraic structure of these modules by means of the theory of Groebner bases. We introduce a root diagram for each of these codes (analogous to the set of roots for a cyclic code of length q - 1 over F_q), and show how the root diagram may be determined combinatorially from a. We also give a specialized algorithm for computing Groebner bases, adapted to these particular modules. This algorithm has a much lower complexity than general Groebner basis algorithms, and has been successfully implemented in the Maple computer algebra system. This permits the computation of Groebner bases and the construction of compact systematic encoders for some quite large codes (e.g. codes such as C_L(D, 4010Q) on the curve X_{16}, with parameters n = 4096, k = 3891).
Length	22
Copyright	Elsevier Science B.V.
File
URL	dx.doi.org/10.1016/S0022-4049(96)00067-9
Language	English
Journal	Journal of Pure and Applied Algebra
Volume	121
Number	3
Pages	293-314
Publisher	Elsevier Science
Year	1997
Month	October
Edition	0
Translation	No
Refereed	No