Research On Multi-user Channel Feedback Technology In Massive MIMO

With the development of multi-antenna technology,the research on MIMO has gradually evolved from single-user SU-MIMO to multi-user massive MIMO.At the same time,changes in antenna structure have extended this technology from a two-dimensional plane to a three-dimensional plane,forming the representative 3D-MIMO.In multi-user massive MIMO systems,the process of link adaptation is critical,and feedback of channel state information is an integral part of it.Therefore,this thesis focuses on the Multi-user Channel Feedback Technology in Massive MIMO.The details of our research are as follows:1.In order to obtain more accurate multi-user channel quality information at the base station,this thesis proposes a multi-user CQI recomputation method.This method is implemented in a codebook-based channel feedback scheme.The multi-user CQI recalculated using single-user CQI is mainly based on the statistical characteristics of the codebook.The method has been proved by simulation to have a good sum rate performance.The difference between perfect CQI and the proposed CQI is small in the case of a large number of antennas.2.In order to better reduce the codebook calculation and search overhead of large-scale 3D-MIMO,this thesis proposes a separate codebook feedback scheme with different codebook combinations in horizontal and vertical dimensions.With the help of existing representative codebooks,the codebook selection and feedback of this scheme are processed respectively in the horizontal and vertical directions.Compared with the common non-separate codebook feedback scheme,this scheme greatly reduces the complexity of codebook search.Based on the simulation of different separate codebook combinations,this thesis points out the optimal combination of horizontal codebook and vertical codebook.3.Concerned about the possibility of total feedback limitation under massive MIMO,this thesis proposes a channel feedback scheme based on fixed total feedback.The scheme fixes the total feedback bits of the system and explores the system performance under different user numbers and various single-user feedback bits.This thesis also introduces the concept of optimal single-user feedback bits.The simulation results show that the channel feedback scheme based on fixed total feedback in large-scale MIMO can achieve the compromise between feedback accuracy and the number of multi-user.The best number of single-user feedback bits derived in this thesis is consistent with the simulation results in the actual scene,which verifies rationality of the theoretical derivation of this thesis.