Practical Multiuser MIMO Beamforming Using the Strongest Eigenmodes

In multi-user MIMO systems, coordinated beam- forming can be used to relax the dimensional constraint of block diagonalization and accommodate more users. However, coor- dinated beamforming and other similar beamforming schemes require coordination of information from the base station to the users, which requires user specific reference signals. Moreover, coordinated beamforming methods have high feedback overhead in general. In this paper, a simple and practical linear beamforming algorithm called Strongest Eigenmode Beamforming (SEB) is proposed based on the strongest eigenmodes. The proposed method is sub-optimal; however, the performance loss is not significant especially in the presence of receive correlation. More importantly, SEB does not require coordination of information from transmitter to receivers. In addition, the sufficient informa- tion required at the base station for the proposed SEB scheme is only the strongest eigenvector of each user's channel. As a result, SEB has lower feedback requirement than coordinated beamforming schemes and conventional limited feedback algorithms can be used. It is shown using simulations that SEB has better performance than coordinated beamforming schemes for the same feedback overhead.