Transmit beamforming techniques for space-frequency coded MIMO-OFDM systems in a correlated Ricean fading channel

In highly spatially correlated channels the diversity gain achieved by space-frequency (SF) coding is significantly low. Nevertheless, when full or partial channel state information is available at the transmitter, improved performance can be obtained by combining transmit beamforming with SF coding. In this paper we propose two novel transmit beamforming techniques based on the minimum pair-wise error probability (PEP) criterion for SF-coded MIMO-OFDM systems in frequency-selective Ricean fading channels. The proposed beamforming techniques (referred to as Technique 1 and Technique 2) require only the channel mean and spatial correlation statistics. Technique 1 optimally distributes the total transmit power among all the eigenmodes of the channel, whereas Technique 2 allocates the total transmit power only to the strongest eigenmodes of the channel. The simulation results demonstrate that Technique 1 and 2 offers considerable performance improvements over a system using only SF coding in low and highly spatially correlated channels, respectively. When compared with Technique 1, Technique 2 is more appealing due to the facts that it has less computational complexity, and that it offers better performance in highly correlated channels for all values of the Ricean-K factor.