Double-Directional Beamforming MIMO: A Simulation Study

Beamforming (BF) and MIMO (multi-input, multi-output) improve coverage and capacity in radio communication. However, they are applied for different goals. BF is used when the channel rank is low and MIMO when the rank is high. Theoretical MIMO studies concentrate on the radio channel capacity limits and usually ignore the effect of actual antennas. This study shows first bit-error-rate (BER) simulation results for a combined BF and MIMO scheme. The Butler matrix (BM) is applied at the transmitter and receiver to create parallel channels and to bring BF gain. Parallel data streams are transmitted via parallel orthogonal beams and the received signals are processed in the beam domain. In the BF MIMO the SINR level is increased and interference between data streams is reduced. Simulation results show remarkable gains in outage capacity. However, preliminary CDMA BER studies reveal that the method suffers from the lack of diversity if no coding over beams is applied.