Non-cooperative feedback control game under a sum feedback-rate constraint in MIMO broadcast channels

Abstract

Channel state information (CSI) is known to play crucial role for downlink transmissions of multi-user multiple-input multiple-output (MU-MIMO) systems. To acquire CSI at the base station, feedback from users is necessary. Since the optimal feedback-rate to maximize the total throughput is possibly changed by the channel condition, the conventional equal-sized feedback can be inefficient in MU- MIMO system. Therefore, in this thesis, we first investigate the effect of different-sized feedback-rate and propose the non-cooperative feedback-rate control game for improving total throughput in MU-MIMO system with multiple frequency bands. Based on the game theory, the utility function of each user is defined as the downlink throughput minus a linear price function of the CSI feedback-rate. Moreover, we suggest a simple algorithm to find the proper pricing factors for the proposed game considering multiple users and multiple frequency bands. Simulation results show that the total throughput of the proposed game yields better performance than that of the conventional equal-sized feedback-rate scheme. With limited available radio resources, system throughput and fairness are usually in conflict with each other, balancing system throughput and fairness with high resource efficiency is necessary. Also, the analysis of feedback-rate allocation considering these two performance measures is needed. Therefore, in this thesis, we also propose the non-cooperative feedback-rate control game for improving throughput fairness in MU-MIMO system. Based on the game theory, the utility function of each user is considered both throughput fairness and total throughput. Moreover, we investigate the existence of the Nash-equilibrium of the proposed game and outage probability in terms of CSI feedback-rate. Simulation results show that the proposed game improves throughput fairness, and thus achieves better outage performance, as compared to the conventional equal-sized feedback scheme.