Dynamic Feedback Bits Allocation in Distributed Antenna Systems with Limited Feedback

Efficient channel state information (CSI) feedback can simplify the signal preprocessing at the transmitter and improve the performance of a distributed antenna system (DAS). In order to maximize the feedback utility efficiency, we propose to dynamically allocate feedback bits across multiple remote antenna units (RAUs) according to the instantaneous channel condition for a given total feedback constraint. We first derive an upper bound and a lower bound on the spectral efficiency of the DAS. Then, by maximizing the bounds while satisfying the feedback bits constraint respectively, we derive two adaptive feedback allocation schemes. Furthermore, the impact of imperfect CSI at the mobile user (MU) is analyzed and the corresponding feedback bits allocation scheme is given. Numerical results show that the proposed adaptive schemes have obvious performance gains over the traditional uniform feedback allocation.