Adaptive CQI Feedback and Efficient CQI Update Scheme for Codebook Based MU-MIMO in E-UTRA

Codebook based multiple-input multiple-output (MIMO) preceding can significantly improve the system spectral efficiency with limited feedback and has been accepted as one of the most promising techniques for the Evolved UTRA (E-UTRA). Compared with single-user (SU) MIMO, multi-user (MU) MIMO can further improve the system spectral efficiency due to increased degree of freedom in transmission. In order to reduce the feedback overhead, feedback of single channel quality indicator (CQI), e.g. rank 1 CQI, is required in E-UTRA currently. Then, the main challenge is how to obtain CQIs of other ranks at node B for rank adaptation with single CQI feedback. Therefore, in this paper, an efficient CQI update scheme at node B based on statistical characteristics of CQI of various ranks is firstly proposed. To further increase the accuracy of CQI at node B for data transmission, an adaptive CQI feedback scheme is then proposed in which single CQI with the rank same as previously scheduled is fed back. Simulation results show that our proposed CQI update scheme can achieve some performance gain compared with conventional method with fixed backoff. Moreover, with proposed adaptive feedback scheme, much additional performance gain can be obtained and the performance can approach the upper bound.