Opportunistic Beamforming for Multiuser MIMO Downlink Employing Rateless Codes with Delay Constraint

In this paper, a framework of opportunistic beamforming for multiuser MIMO downlink employing rateless codes is considered. By exploiting the benefits of a combination of opportunistic beamforming and rateless codes, the system performance is obviously improved while guaranteeing QoS requirement, such as maximum average delay. It is proved that, in order to satisfying delay constraint, the maximum number of admissible users is bounded. With the purpose of achieving a balance between throughput and feedback, a novel concept of netput is introduced accordingly. Through maximizing the netput, the optimal feedback threshold in terms of the number of user, the maximum delay constraint, transmit power and the arrival rate of user data at the base station (BS) is derived. Moreover, the impact of feedback delay on the netput is investigated in detail and the corresponding feedback threshold is given. Finally, our theoretical claims are validated by the numerical results.