Dynamic bit allocation and differential quantization in feedback link for robust power allocation in multiuser opportunistic beamforming

Multi-antenna systems provide advantages in terms of link quality and multiuser access capabilities, which can be achieved by using schemes as multibeam opportunistic beamforming. This scheme only requires partial channel state information at the transmitter (CSIT) in terms of the equivalent channel moduli. This paper deals with the problem of feeding back the CSI from the multiple receivers to the base station (BS) transmitter through limited capacity feedback links. This involves a quantization and a delay that produces errors in the CSIT. In this sense, the proposed scheme in this paper is based on a robust design that takes into account these errors. Additionally, a dynamic bit allocation in the feedback among the users is derived, and combined with differential quantization to minimize the transmit power. It considers both the userspsila sensitivities to the quantization errors and the Doppler frequencies due to the mobility. Simulation results show the benefits from using such schemes.