Improved asymptotic bounds for codes using distinguished divisors of global function fields

Abstract

For a prime power $q$, let $α_q$ be the standard function in the asymptotic theory of codes, that is, $α_q(δ)$ is the largest asymptotic information rate that can be achieved for a given asymptotic relative minimum distance $δ$ of $q$-ary codes. In recent years the Tsfasman-Vlăduţ-Zink lower bound on $α_q(δ)$ was improved by Elkies, Xing, and Niederreiter and Özbudak. In this paper we show further improvements on these bounds by using distinguished divisors of global function fields. We also show improved lower bounds on the corresponding function $α_q^{\rm lin}$ for linear codes.