Research On Channel Propagation Characteristic And Acquisition Technology Of Millimeter Wave MIMO Systems

With the popularization of smart portable terminal, wireless communication systems that operate in bands below 6 GHz are unable to satisfy the rapidly growing demand for data traffic. Millimeter wave band has become the key band to realize 10 Gbps throughput in indoor Wireless LAN and the fifth generation mobile communication (5G) system because of its abundant bandwidth resources, which has arisen attention of academic experts and scholars. In order to further increase systems' throughput and support multi-stream transmission, millimeter wave communication will adopt multiple input multiple output (MIMO) technology. Therefore, determining channel characteristic of millemeter wave MIMO system and accordingly investi-gating channel acquisition technology is the precondition of utilize large bandwidth effectively to achieve high spectral efficiency and wide coverage. The main work and innovations of this thesis are summarized as follows:Firstly, the physical layer and MAC layer of IEEE 802.11 aj(45 GHz), which is the first millimeter wave MIMO WLAN standard, is elaborated. Particularly, data packet structure, launchs process and key modules of SC PHY and OFDM PHY, basic frame structure and channel access mechanism of MAC layer are introduced, which lays foundation of following research.Secondly, channel characteristic is deeply analyzed. In detail, Propagation loss of millimeter wave and MIMO channel model in 45 GHz is introduced. The SNR and capacity of LOS and NLOS channel varies with the transmit distance, the sparsity and characteristic of channel are deeply researched. Further, the char-acteristic of LOS MIMO system's effective channel is analyzed from condition number and effective degrees of freedom. The simulation results show that the subarray spacing can be a little bigger than the optimal value, and increasing the number of subarray antennas can effectively improve effective degrees of freedom of equivalent channel.Thirdly, the feedback mechanism of channel state information in IEEE 802.11aj(45 GHz) is designed. In particular, the formats of feedback and reconstruction of channel state information is developed according to channel characteristic. Then, the packet structure for channel sounding and the format of feedback report frame is formulated based on feedback kinds. At last, the parameters for angle quantization and subcarrier grouping feedback are determined through system level simulation, which can effectively reduce the overhead for CSI feedback.Finally, hybrid beamforming in multi-user millimeter MIMO system is researched. Based on the analysis of hybrid beamforming structure, multi-user hybrid beamforming with split subarray which is suitable for the transmission in short-range WLAN, is proposed. Furthermore, a new hybrid beamforming algorithm based on channel reciprocity and the DFT codeword training method of its' analog part are proposed. The simulation results show that the proposed scheme is superior to the schemes presented in published literature, and can approach the performance of the optimal unconstrained digital beamforming scheme. The DFT codeword training method of its' analog part converges quickly, and the total training overhead is much lower than the methods presented in literature.