Re-configurable linear precoders to compensate for antenna correlation in orthogonal and quasi-orthogonal space-time block coded systems

High fading correlations reduce multiple input multiple output (MIMO) channel capacity and system performance (Shiu, D. et al., 2000; Bolcskei, H. and Paulraj, A.J., 2000). Nevertheless, considerable performance gains can be obtained by transmission on the eigenmodes of the transmit antenna correlation matrix (Brunner, C. et al., 2000). H. Sampath and H. Paulraj (see IEEE Commun. Lett., vol.6, no.6, p.239-41, 2002) propose an optimal linear precoder that assumes knowledge of the transmit antenna correlations and improves performance of a space-time coded system by forcing transmission on the nonzero eigenmodes of the transmit antenna correlation matrix. The main advantage of this precoder is that it does not have to track fast fading, but only the slowly varying antenna correlations. The latter can be fed back to the transmitter using a low-rate feedback link or can be based on uplink channel estimation. We investigate the application of linear precoders to space-time block coded systems. The system model and the design criterion for re-configurable precoders are presented and applied to orthogonal and quasi-orthogonal space-time block coding schemes with N transmit antennas. Simulation results illustrate the achieved performance enhancements.