Combining beamforming and transmit diversity for closed-loop downlink transmission

Multi-antenna technique is an effective means for improving performance of the downlink transmission. Both beamforming (BF) and transmit diversity (TD) which exploit multiple antennas are attractive candidates for increasing channel capacity. In this paper, an adaptive downlink transmission approach combining beamforming with transmit diversity in the closed-loop mode is presented, and the transmitter can adaptively change the transmission mode between two methods according to actual channel states. The first method combines BF with space-time block coding (STBC), while the second one combines BF, STBC and selection transmit diversity (STD). Both of them exploit the feedback information from the mobile terminal to aid the downlink transmission. Simulation results in terms of bit error rate (BER) performance are presented, which show the high performance over conventional STBC scheme.