Hadamard Full Propelinear Codes of type Q. Rank and Kernel

TL;DR

This paper studies Hadamard full propelinear codes of type Q, establishing their properties, equivalences, and providing a construction method to generate larger codes with specific kernel and rank characteristics.

Contribution

It introduces the concept of HFP-codes of type Q, proves their equivalence with Hadamard groups, and presents a construction method for larger codes with desired kernel and rank properties.

Findings

Kernel dimension is always 1 or 2.

When kernel dimension is 2, the transposed code's kernel dimension is 1.

A method to construct larger HFP-codes with specified kernel and rank.

Abstract

Hadamard full propelinear codes (HFP-codes) are introduced and their equivalence with Hadamard groups is proven (on the other hand, it is already known the equivalence of Hadamard groups with relative $(4n,2,4n,2n)$-difference sets in a group and also with cocyclic Hadamard matrices). We compute the available values for the rank and dimension of the kernel of HFP-codes of type Q and we show that the dimension of the kernel is always 1 or $2$. We also show that when the dimension of the kernel is 2 then the dimension of the kernel of the transposed code is 1 (so, both codes are not equivalent). Finally, we give a construction method such that from an HFP-code of length $4n$, dimension of the kernel $k=2$, and maximum rank $r=2n$, we obtain an HFP-code of double length $8n$, dimension of the kernel $k=2$, and maximum rank $r=4n$.