Hybrid transmit waveform design in outdoor channels

Outdoor channels can be modelled as as a sum of array response vectors of varying gain at different Angles of Departure (AoDs) from different point sources. Based on this characteristics, 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 array response vectors. 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. In the case where the transmitter has knowledge on the associated complex path gains, a power loading scheme is designed when. 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 Preceding (LP) and the theoretically possible SNR of Orthogonal STBC (OSTBC). 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.