Feedback Technology In LTE 3D-MIMO System

Multiple-input multiple-out-put (MIMO) technology can greatly improve system capacity and spectrum efficiency in limited, bandwidth by using multiple antennas on both sides of the transmitter and receiver. In conventional MIMO system, 2D channel model is widely used, which ignores the distinction of users'vertical dimension distribution and limits the system performance. Moreover,MIMO system performance highly depends on the accuracy of the channel state information (CSI) obtained by base station (BS). In FDD mode, CSI is obtained by user equipment' s (UE) feedback. With the increase of antenna ports, the feedback overhead increases synchronously. When the user is in high speed, the timeliness of feedback becomes the main factor that affects the performance of MIMO system.Based on the CAICT LTE-A tsandardiziation project, this thesis mainly researches 3D-MIMO channel model and the feedback mechanism in 3D-MIMO system. The main work of this thesis includes:(1) According to 3GPP TR 36.873 standard, 3D-MIMO channel model is built in this thesis. To verify the veracity of 3D-MIMO channel model,parameters' calibration are implemented. In addition, several key modules in system level simulation platform are designed, including: business model, user scheduling module, precoding module and codebook selection module.(2) Based on exact 3D-MIMO channel model, this thesis proposes a new type of "semi-open loop" feedback mechanism based on dual-codebook cyclic precoding in high speed mobile state. The simulation results show that the"semi-open loop" feedback mechanism can effectively improve the timeliness of feedback, optimize the coverage performance of the system, and reduce the feedback overhead.(3) To solve the problem that the codebook design complexity increases rapidly with the increase of the antenna port, explicit feedback based on the maximum singular value and implicit feedback based on dual-codebook are studied in the multi-user MIMO system. The simulation results show that,explicit feedback can bring about 50% gain of the average cell throughput, and doesn't need complex codebook design.