Efficient CQI update scheme for codebook based MU-MIMO with single CQI feedback in E-UTRA

Codebook based multiple-input multiple-output (MIMO) precoding 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 and computational complexity, feedback of single rank 1 (corresponding to transmission of single stream) channel quality indicator (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 arising from statistical characteristics of CQI of various ranks is proposed. Simulation results show that our proposed scheme can yield significant improvement on spectral efficiency compared with conventional CQI update schemes.