Mean square error optimality of orthogonal space-time block codes

Linear space-time block coding (STBC) is a conceptually simple transmission technique for channels with multiple transmit and receive antennas. In this paper, we study a subclass of linear STBC, namely orthogonal STBC (OSTBC), with the primary goal of contributing towards a complete understanding of OSTBC. In particular, we prove that OSTBC is optimal in an important minimum mean-square error (MSE) sense. As a by-product, we also obtain a concise characterization of linear and orthogonal STBC's as well as the relationship between them. The MSE optimality of OSTBC shown herein can be used as a way of introducing this coding scheme in a formal manner.