Linear Size Constant-Composition Codes Meeting the Johnson Bound

TL;DR

This paper establishes the minimal length for constant-composition codes meeting the Johnson bound across various alphabet sizes, using new combinatorial constructions and refined methods.

Contribution

It provides a tight lower bound on the minimal length for such codes and determines exact values for all q-ary cases under certain conditions.

Findings

Lower bound on N_{ccc}({ar{w}}) established

Exact values of N_{ccc}({ar{w}}) determined for all q-ary codes

New combinatorial constructions used to achieve bounds

Abstract

The Johnson-type upper bound on the maximum size of a code of length $n$, distance $d=2w-1$ and constant composition ${\overline{w}}$ is $\lfloor\dfrac{n}{w_1}\rfloor$, where $w$ is the total weight and $w_1$ is the largest component of ${\overline{w}}$. Recently, Chee et al. proved that this upper bound can be achieved for all constant-composition codes of sufficiently large lengths. Let $N_{ccc}({\overline{w}})$ be the smallest such length. The determination of $N_{ccc}({\overline{w}})$ is trivial for binary codes. This paper provides a lower bound on $N_{ccc}({\overline{w}})$, which is shown to be tight for all ternary and quaternary codes by giving new combinatorial constructions. Consequently, by refining method, we determine the values of $N_{ccc}({\overline{w}})$ for all $q$-ary constant-composition codes provided that $3w_1\geq w$ with finite possible exceptions.