Beamforming in multiuser MIMO downlink systems: Non-cooperative and cooperative approaches

In this paper, joint transmitter and receiver beamforming algorithms are proposed for downlink in multiuser multi-input multi-output (MIMO) communication systems. The proposed beamforming algorithms are developed based on non-cooperative and cooperative utility functions. In non-cooperative approach, utility function of each user is defined based on the performance of the user without considering the impact of the user´s action on the others. However in cooperative approach, in addition to the performance of the user, the impact of user´s action on the other users is considered in the user´s utility function. Two iterative algorithms are derived by maximizing the utility function of the user in order to estimate transmitter and receiver beamforming vectors. The performances of the proposed algorithms are evaluated by computer simulations and compared with that of the duality method-based minimum mean square error (DM-MMSE) beamforming algorithm. Simulation results show the superiority of our proposed cooperative beamforming algorithm regarding the bit error rate (BER) performance and convergence rate.