Combining beamforming and quasi-orthogonal space-time block coding using channel mean feedback

Recently, Jongren-Skoglund-Ottersten and Zhou-Giannakis proposed new design criterion and algorithm that combine the space-time block coding with linear beamforming. This method is very successful when it is applied to the orthogonal space-time block code (STBC). However, the same method cannot be directly applied to the more advanced quasi-orthogonal STBCs due to the non-orthogonal nature of the quasi-orthogonal designs. In this paper, based on the same design criterion, we consider the quasi-orthogonal codes as beamforming candidates. Through asymptotic analysis, we dramatically simplify the design criterion and construct the beamforming matrix for the quasi-orthogonal designs. The proposed quasi-orthogonal STBC beamformer can be presented as a novel full rate eigen-beamformer that works for any systems with four or more transmit antennas. Simulation results for a system with channel mean feedback demonstrate that the new beamforming scheme has significant gains over the orthogonal STBC based beamforming schemes.