Relation between beamforming and diversity in feedback MIMO system

In mobile communication, frequency domain and time domain have been used adequately, then, space domain is an important domain to use. This paper studies feedback MIMO system, investigates the relation between beamforming and space diversity. In FDD regime, we use codebook known to both transmitter and receiver to decide either beamforming or space diversity to increase reliability. Both methods can guarantee full diversity order. Since MIMO system with two antennas at mobile station is applicable, we compare performances of beamforming and diversity, which shows that beamforming is better at low SNR and space diversity is better at high SNR on perfect channel estimation. When diversity order is four, their performances are not increased so fast as diversity order increases; therefore, there is a diminishing gain.