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

Recently, G. Jongren et al., (see IEEE Trans. Inform. Theory, vol.48, p.611-27, 2002) and S. Zhou and G.B. Giannakis (see IEEE Trans. Sig. Process., vol.50, no.10, p.2599-613, 2002) proposed a new design criterion and algorithm that combine 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. 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 system 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.