An important question in the construction of orthogonal arrays is what the minimal size of an array is when all other parameters are fixed. In this paper, we will provide a generalization of an inequality developed by Bierbrauer for symmetric orthogonal arrays. We will utilize his algebraic approach to provide an analogous inequality for orthogonal arrays having mixed levels and show that the bound obtained in this fashion is often sharper than Rao's bounds. We will also provide a new proof of Rao's inequalities for arbitrary orthogonal arrays with mixed levels based on the same method. Key words. Mixed-level orthogonal array, group character, adjacency operator. AMS Subject Classification: Primary 05B15, Secondary 62K15
Wiebke S. Diestelkamp