Abstract

In this paper, we study convolutional codes with a specific cyclic structure. By definition, these codes are left ideals in a certain skew polynomial ring. Using that the skew polynomial ring is isomorphic to a matrix ring we can describe the algebraic parameters of the codes in a more accessible way. We show that the existence of such codes with given algebraic parameters can be reduced to the solvability of a modified rook problem. It is our strong belief that the rook problem is always solvable, and we present solutions in particular cases.

Highlights

  • Convolutional codes (CC’s, for short) form an important class of error-correcting codes in engineering practice

  • It is easy to see that the existence of (n − 1)-dimensional σ-CCC’s with arbitrarily prescribed Forney indices implies the solvability of Problem 4.5 for any given numbers r1, . . . , rn−1 ∈ {0, . . . , n − 1}

  • We have studied σ-CCC’s in F[z]n where n | (q − 1) and where the automorphism σ induces a cycle of length n on the primitive idempotents of A

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Summary

Introduction

Convolutional codes (CC’s, for short) form an important class of error-correcting codes in engineering practice. In the 1970s, a lot of effort has been made to construct powerful CC’s with the aid of good block codes, see [14, 13] This idea has been resumed in the papers [24, 7]. In that case the skew polynomial ring A[z; σ] turns out to be isomorphic to a matrix ring over a commutative polynomial ring This allows us to construct generator polynomials of CCC’s with prescribed algebraic parameters. The existence of such codes reduces to a combinatorial problem followed by a problem of constructing polynomial matrices with certain degree properties. We close the paper with a short section illustrating how to generalize the results to codes that are cyclic with respect to a general automorphism

Preliminaries on Cyclic Convolutional Codes
The Matrix Ring M
Construction and Existence of σ-CCC’s
The Modified Rook Problem
Extension to General Automorphisms — An Example
Concluding Remarks
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