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On the concept of code-isomorphy
Authors:Ioana Constantinescu  Werner Heise
Institution:(1) Mathematisches Institut, Technische Universität, D-80290 München, Germany
Abstract:LetF be a finite set of cardinality ¦F¦ =q ge2,n ge 1 an integer and rhov:F n×FnrarrNopf0 theHamming metric. Acode isomorphism C rarr D between two block codesC,D 
$$ \subseteq$$
Fn is defined as an isometry which can be extended to an isometry of the whole space Fn. Any permutation pgr isinS n of the positions canonically induces a so-calledequivalence map 
$$\tilde \pi$$
isin Aut Fn; any system kappa colone (kappa1,kappa2,...,kappan) ofn permutations of the character setF induces a so-calledconfiguration 
$$\tilde \kappa$$
isin Aat Fn. The group Aut Fn of all isometries of Fn turns out to be semidirect product of the configuration group with the symmetric group of degreen. The codeword estimating failure probability of a maximum likelihood codeword estimator for aq-nary symmetric channel does not depend on the transmitted codeword, if the automorphism group of the code acts transitively on the set of codewords. When using a systematic (n, k)-encoder, the symbol decoding failure probability does not depend on the transmitted symbol or on the time of transmission if the configuration group and the automorphism group act transitively on the set of codewords resp. on the set of thek information positions.In memoriam Giuseppe Tallini
Keywords:
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