Hybrid transmit waveform design based on beamforming and orthogonal space-time block coding

In this paper, we derive a hybrid of Beam-Forming (BF) and Space-Time Block Coding (STBC), where the space-time code is transmitted over the beams generated by the steering vectors corresponding to the channel path directions. This is for the practical case where the transmit array may have adequate information on the departure angles of the dominant paths between transmitter and receiver, but unreliable information on the associated complex path gains. We compute analytically the Signal-to-Noise Ratio (SNR) of the proposed hybrid for the specific case of a two-path channel model and using the orthogonal Alamouti code, and compare the result to the SNR of optimal Linear Precoding (LP) and the theoretically possible SNR of Orthogonal STBC (OSTBC). To improve the performance, power loading schemes are also considered. Simulation results show that the performance of the BF/STBC hybrid with and without power loading can be very close to LP - under certain conditions - or even better in the practical case where there are phase estimation errors in the path gain estimates employed at the transmitter.