Homecs.ITarXiv:2605.29439

On the Maximal Length of MDS Elliptic Codes

cs.ITmath.IT2026-05v1license

Abstract

The determination of the maximal length of maximum distance separable (MDS) codes arising from elliptic curves is a central problem in coding theory. For an elliptic curve EE over Fq\mathbb{F}_q, let MEC(k,q)\operatorname{MEC}(k,q) denote the maximal length of a qq-ary MDS elliptic code of dimension kk. It was recently shown that MEC(k,q)q+12+q\operatorname{MEC}(k,q)\le\frac{q+1}{2}+\sqrt{q} for q289q\ge289 and 3k(q+12q)/103\le k\le(q+1-2\sqrt{q})/10, with equality for odd kk when qq is an odd square. This paper investigates the remaining open cases, namely even dimension kk, non-square qq and fields of characteristic 22, and provides a complete resolution of the tightness question for the two natural parity regimes of q+1+2qq+1+\lfloor 2\sqrt{q}\rfloor. We prove that if the support of GG (used to define the code) consists of Fq\mathbb{F}_q-rational points, the bound decreases to q+12+q1\frac{q+1}{2}+\sqrt{q}-1 for even kk. Without this restriction, we construct MDS codes attaining q+12+q\frac{q+1}{2}+\sqrt{q} for even kk. More generally, we establish MEC(k,q)=q+1+2q2\operatorname{MEC}(k,q)=\frac{q+1+\lfloor2\sqrt{q}\rfloor}{2} when q+1+2qq+1+\lfloor2\sqrt{q}\rfloor is even, and MEC(k,q)=q+2q2\operatorname{MEC}(k,q)=\frac{q+\lfloor2\sqrt{q}\rfloor}{2} when it is odd.

Cite

@article{arxiv.2605.29439,
  title  = {On the Maximal Length of MDS Elliptic Codes},
  author = {Haojie Chen and Chuangqiang Hu and Junjie Huang and Chang-An Zhao},
  journal= {arXiv preprint arXiv:2605.29439},
  year   = {2026}
}