On the automorphism groups of some AG-codes based on C_{a,b} curves

We study Ca,b curves and their applications to coding theory. Recently, Joyner and Ksir have suggested a decoding algorithm based on the automorphisms of the code. We show how Ca,b curves can be used to construct MDS codes and focus on some Ca,b curves with extra automorphisms, namely y ³ = x⁴ + 1, y ³ = x⁴ −x, y ³ −y = x⁴. The automorphism groups of such codes are determined in most characteristics.