Research On Limited Feedback Based On3D MIMO Systems

As the research project of Active Antenna System had been established in the3rd Generation Partnership Project (3GPP), the three dimension (3D) multiple input multiple output (MIMO) technology, which is the most pressing concerns for new wireless technologies, has gained great attentions. Compared to the traditional MIMO,3D MIMO can sufficiently use the spatial degree of freedom in vertical dimension, and can be helpful in improving the transport performance of LTE/LTE-A, eliminating the inter-cell interference, and increasing spectral efficiency.Considering the enormous information flows between base station (BS) and user equipment (UE) brought by sophisticated antenna configurations, the limited feedback can be adopted in the3D MIMO systems. How to allocate the feedback bits to two dimension channel quantization properly and optimally becomes more important. Also, the research of the feedback compression is of great help in promoting the application of3D MIMO. Efficient use of feedback resource, high performance can be assured.This thesis focuses on3D MIMO technology, and makes research on the optimal allocation of feedback resource and feedback compression. This thesis builds the optimization model of bits allocation in the form of minimizing the differences between limited feedback and ideal feedback. The feedback compression scheme is also proposed by combining the strong channel correlation of3D MIMO system.This thesis summarizes the research status of3D MIMO technology and3D channel model. In the research of bits allocation, the configuration of channel state information reference signal (CSI-RS) ports is given based on the analysis of channel correlation of3D MIMO system. Then, the optimization model of bits allocation is built. By analyzing the differences between the horizontal dimension and vertical dimension, the optimal allocation results are carried out under the certain conditions of antenna numbers and polarization mode. Lastly, the result that3D MIMO system with optimal feedback bits allocation has better spectral efficiency performance than the system with equal feedback bits allocation scheme. In the research of feedback compression, the reducing feedback scheme is proposed based on dynamic adjustment of feedback period. Based on the principle that average feedback period in dynamic adjustment mode of feedback period must be larger than that of fixed period mode, the theoretical derivation of channel correlation threshold is carried out. The simulation results indicate that this reducing feedback scheme can decrease feedback largely under the premise of guaranteeing the spectral efficiency.