Signal Constellations for Orthogonal Space-Time Block Codes

Orthogonal space-time block codes (OSTBCs) have recently attracted considerable attention due to their properties of full diversity and low implementation complexity. However, most works in this area simply employ classic phase-shift keying (PSK) or quadrature amplitude modulation (QAM) constellations, which are not necessarily optimal for OSTBCs. In this paper, we consider the problem of designing signal constellations for communication systems using OSTBCs, where the channel state information (CSI) available at the receiver is an estimate of the time variant channel gains with a specific estimation error. We perform an asymptotic symbol error probability (SEP) analysis and derive a criteria to design constellations that match well with the level of the channel estimation error. New signal constellations are found by means of a gradient search over a continuous alphabet. Simulation results show that the obtained constellations outperform not only the conventional QAM constellation, but also other well-known constellations used for efficient data communications.