Self-Dual Near MDS Codes from Elliptic Curves

In recent years, self-dual MDS codes have attracted a lot of attention due to theoretical interest and practical importance. Similar to self-dual MDS codes, self-dual near MDS (NMDS for short) codes have nice structures as well. From both theoretical and practical points of view, it is natural to study self-dual NMDS codes. Although there has been lots of work on NMDS codes in literature, little is known for self-dual NMDS codes. It seems more challenging to construct self-dual NMDS codes than self-dualMDS codes. The only work on construction of self-dual NMDS codes shows existence of q-ary self-dual NMDS codes of length q - 1 for odd prime power q or length up to 16 for some small primes q with q <= 197. In this paper, we make use of properties of elliptic curves to construct self-dual NMDS codes. It turns out that, as long as 2 vertical bar q and n is even with 4 <= n <= q + left perpendicular 2 root q right perpendicular - 2, one can construct a self-dual NMDS code of length n over Fq. Furthermore, for odd prime power q, there exists a self-dual NMDS code of length n over Fq if q >= 4(n+3) x (n + 3)(2).