Hermitian codes from higher degree places

Matthews and Michel (2005) [29] investigated the minimum distances of certain algebraic-geometry codes arising from a higher degree place P. In terms of the Weierstrass gap sequence at P, they proved a bound that gives an improvement on the designed minimum distance. In this paper, we consider those of such codes which are constructed from the Hermitian function field Fq2(ℋ). We determine the Weierstrass gap sequence G(P) where P is a degree 3 place of Fq2(ℋ), and compute the Matthews and Michel bound with the corresponding improvement. We show more improvements using a different approach based on geometry. We also compare our results with the true values of the minimum distances of Hermitian 1-point codes, as well as with estimates due to Xing and Chen (2002) [33].