An optimal two transmit antenna space-time code and its stacked extensions

A space-time code is proposed that exhibits the highest coding gain between competing full rate full transmit diversity space-time codes for the two transmit antenna wireless channel. The proposed code is derived from a layered architecture with real rotation of QAM information symbols in two dimensions. The existing codes of similar architecture concentrate on application of complex full modulation diversity rotations or asymmetric real rotations for the two layers. An analytic evaluation illustrates the significant improvement in coding gain achieved with the proposed code. Moreover, the value of the unnormalized coding gain for the new code is independent of the rate of the code. A stacked extension of the proposed code offers a reduced complexity capacity optimal alternative to the full diversity codes for larger number of transmit antennas. Performance enhancement in several scenarios is verified through simulations.