Joint transmit diversity and downlink beamforming by using a minimum BER criterion

In this work, we propose a novel criterion to find the optimum precoder for joint transmit diversity and downlink beamforming. This precoder is an extension of the purely spatial downlink beamforming and can be seen as a transformation that transforms K real antennas into L virtual antennas, with L les K. The proposed criterion is based on the minimization of the received BER and extends the previous technique [1] (Eigen- Beamforming) to any type of channel distribution, not only Rayleigh. Simulation results show that the proposed technique is equivalent to Eigen-Beamforming for Rayleigh channel, but outperforms the latter for Rician channels, providing substantial improvement. This makes the proposed technique an attractive solution for the general application, where the channel type is not known a priori.