Key Techniques Of Codebook Design And Selection For Massive MIMO

With the popularization of intelligence and the rapid development of the Internet,5G will be officially put into commercial use in 2020.By the means of diversified application scenarios and various communication services,people propose higher technological expectations to mobile communication systems.As one of the key technologies in the 5G physical layer,massive MIMO technology deploys a large number of antenna arrays to achieve greater diversity gains with limited system bandwidth,which not only improves the system capacity and spectrum utilization,but also effectively reduces multiuser interference and inter-symbol interference to achieve high-speed,high-stability communication transmission.However,there are still some problems lied in some aspects of massive MIMO,such as high-dimensional matrix inversion,large feedback overhead,codebook design,pilot pollution,and codebook selection accuracy.Based on codebook design and codebook selection,this thesis focuses on the following innovations:This thesis studies how to design a large-scale codebook space that can be directly applied to a large-scale multi-antenna MIMO precoding system with limited feedback overhead,where the codeword resolution is flexible and variable while quantization precision of the codeword is guaranteed.Therefore,a block DFT codebook using variable parameters is designed in order to adapt to the user's uniform or non-uniform distribution scenes,which is generated to maximize the average correlation with the multi-dimensional channel matrix by adjusting the parameters of the optimal solution.When tested over the 3GPP spatial channel model,the new codebook exhibits significant gains over existing ones,outperforming the DFT based codebook in different user azimuths,different numbers of feedback bits,and different numbers of antennas.The advantages are more obvious with the increase in the number of base station antennas.Aiming at the problem that user distribution features are not considered in codebook design for three-dimension multiple-input multiple-output(3D MIMO)system,a 3D MIMO limited feedback transmission scheme based on the user distribution is proposed,which not only enhances the vertical dimension freedom,but also matches the limited feedback precoding system under the non-uniform usedistribution.After modeling the non-uniform user distribution and constructing the corresponding design model of vertical domain partition,a non-uniform codeword allocation algorithm is established.Furthermore,a modified MMSE selection criterion is adopted.The proposed scheme obtains a higher system gain compared to the ones without considering user distribution,thereby making more flexible use of codeword resource with limited overhead.