Optimal rotation angles for quasi-orthogonal space-time codes with PSK modulation

Abstract

Full diversity of quasi-orthogonal space-time block codes with complex signals could be achieved by constellation rotation. In this letter, we derive the optimal rotation angle in the sense of maximizing coding gain for quasi-orthogonal codes with phase-shift keying (PSK) modulation using a geometry-based approach. We also prove that the rotated PSK signals with an even constellation size have higher coding gains (or diversity products) than those with an odd constellation size.