Closed-loop pre-equalization for multiuser multicarrier MIMO systems under QoS restrictions

In this paper, a closed-loop pre-equalization approach for multiuser multicarrier code division multiple access (MC-CDMA) systems under a multiple-input multiple-output (MIMO) framework is presented. This work investigates the impact and limitations of combining the robustness of a feedback scheme with the degrees of freedom available in the system, given in terms of the number of subcarriers and multiple antennas, while satisfying the quality of service (QoS) requirements. Simulation results show that the derived closed-loop pre-equalization scheme takes advantage of the spatial diversity, induced by the transmit antennas, to yield a notable power reduction while achieving the objective QoS under a severe system operation. Further investigations are required to identify the impact of the receive antennas in the MIMO system.