Fading-Resilient Super-Orthogonal Space-Time Signal Sets: Can Good   Constellations Survive in Fading?
  In this correspondence, first-tier indirect (direct) discernible constellation expansions are defined for generalized orthogonal designs. The expanded signal constellation, leading to so-called super-orthogonal codes, allows the achievement of coding gains in addition to diversity gains enabled by orthogonal designs. Conditions that allow the shape of an expanded multidimensional constellation to be preserved at the channel output, on an instantaneous basis, are derived. It is further shown that, for such constellations, the channel alters neither the relative distances nor the angles between signal points in the expanded signal constellation. 
Dumitru Mihai Ionescu and Zhiyuan Yan