Orthogonal sets of vectors over Z_m

The theory of Hadamard matrices is concerned with finding maximal sets of orthogonal vectors whose components are +1's and -1's. A natural generalization of this problem is to allow entries other than ±1's or to allow entries from some fixed field or ring. In the case of an arbitrary field or ring there may be "orthogonal" sets of "vectors" whose cardinality exceeds the "dimension" of the space. The purpose of this paper is to obtain an explicit formula for the maximum cardinality of such an orthogonal set when the ring involved is Z_m, the integers modulo m.