Research On The Key Technology For 3D MIMO System Based On The Limited Feedback Scheme

As the number of intelligent mobile terminal exponentially increases, the demand of high data rate and spectrum resource become more urgent. So, the 3D MIMO technology, which increases the number of antennas in base station and exploits the degrees of freedom in vertical dimension to improve the spectral efficiency, has become one of the key technology enabling the 5G communication system come true in the future.With the deployment of massive antennas at the base station (BS) in the 3D MIMO system, the precoding beams become narrower and the system is more sensitive to the accuracy of the channel information. As a result, the size of the codebook and the overhead of the reference signal increases, which leads to the increased channel state information (CSI) feedback overhead, and seriously affects the uplink throughput. Furthermore, the computational complexity for terminals to handle data increases at the same time, which put forward the higher request for the development of hardware. Eventually, the 3D MIMO transmission performance seriously decreased. Hence, the existing configuration of reference signal and the feedback mechanism cannot meet the high demand of 3D MIMO system. From the above, the research on the new 3D MIMO technology should be with the goal of reducing the cost of reference signal and feedback overhead,and a better transmission scheme with limited feedback should be put forward.In order to reduce the resource overhead and improve the whole system performance, in this paper, we investigated the 3D MIMO downlink transmission system and proposed a new transmission scheme of CSI-RS, along with the channel state information feedback. Our specific research work in this paper can be summarized as follows.-First, we investigate multiple technologies in the CSI-RS design,codebook design and feedback schemes for 3D MIMO system on the basis of a large number of documents. We have also investigated multiple options for 3D MIMO codebook scheme and finally adopt the Kronecker product-based codebook (KPC) for precoding operation at the base station (BS).-Then, we proposed a hierarchical CSI-RS scheme based on the properties of the 3D spatial channel. According to the long-term and instantaneous characteristics of 3D spatial channel mode, we divide the CSI-RS into two components: long-term CSI-RS and short-term CSI-RS. The long-term CSI-RS coarsely detects the channel's main direction imformation of the UE. The short-term CSI-RS is used for fine positioning. In order to conduct efficient transmission in FDD system, a low-overhead channel information feedback scheme is proposed based on the design of the CSI-RS.-Furthermore, we propose a multi-user pairing and scheduling criteria evolved from the best companion cluster(BCC) approach based on the hierarchical CSI-RS scheme to achieve the multiuser transmission.Finally, we carry out the in-depth analysis of the proposed and existing schemes, which includes an assessment of their throughput performance and resource overhead in both SU-MIMO system and MU-MIMO system.Simulation results show that our proposed scheme achieves better tradeoff between resource overhead and throughput performance.