A Structural Characterization of Cyclotomic Cosets with Applications to Affine-Invariant Codes and BCH Codes

2026-03-30

AI Summary

This study investigates affine-invariant codes whose defining sets consist of descendants from a single cyclotomic coset, aiming to precisely characterize the structure of these descendant sets and thereby analyze the dimension and minimum distance of both the code and its dual. By employing combinatorial methods, the authors provide the first exact computation of the size of such descendant sets. Leveraging tools from finite field theory and coding theory, they derive explicit dimension formulas for this class of affine-invariant codes—which includes narrow-sense primitive BCH codes—and establish an improved lower bound on the minimum distance of their duals. This work advances the theoretical understanding of BCH code parameters and achieves precise structural characterization of their performance in specific cases.

Abstract

Affine-invariant codes have attracted considerable attention due to their rich algebraic structure and strong theoretical properties. In this paper, we study a family of affine-invariant codes whose defining set consists of all descendants of elements in the cyclotomic coset of a single specified element. Our main contributions are as follows. First, we establish a new combinatorial result that determines exactly the size of such descendant sets, which is of independent interest in the study of cyclotomic cosets. Second, using this result, we derive explicit formulas for the dimensions of the corresponding affine-invariant codes and their associated cyclic codes, and we establish lower bounds on the minimum distances of their duals. In particular, under appropriate parameter choices, these codes yield narrow-sense primitive BCH codes and their extended counterparts. For the special class of narrow-sense primitive BCH codes with designed distance $δ= (b+1)q^{m-t-1}$, where $1 \leq b \leq q-1$ and $0 \leq t \leq m-1$, we provide exact dimension formulas and an improved lower bound on the minimum distance. The results presented here extend and sharpen several previously known results, and provide refined tools for the parametric analysis of BCH codes and their duals.

Problem

• cyclotomic cosets
• affine-invariant codes
• BCH codes
• minimum distance
• code dimension

Innovation

• cyclotomic cosets
• affine-invariant codes
• BCH codes
• minimum distance bounds
• dimension formulas