Research On Key Techniques Of3D MIMO

Faced with the challenges of spectrum shortage, energy consumption and capacity deficiency brought by the development of mobile internet, how to make the most of the limited resources to improve the spectrum efficiency and transmission rate has become the key problem of future communication system.3D MIMO, which combines the communication in both horizontal and vertical dimensions unlike traditional MIMO, offers the system another way to improve the performance. Therefore, this new topic has drawn much attention of researchers all over the world, and become an important issue of3GPP Release12. In this paper, we will focus on the key transmission techniques of3D MIMO, and mainly study the impacts of three-dimensional beamforming and base station downtilt on the system performance. The research of this paper includes but not limited to:Firstly, this paper gives a systematic introduction of the rationales, application scenarios and key transmission techniques for3D MIMO. The transmission techniques involve three-dimensional channel model, vertical antenna gain, beamforming and interference management. As a basis for subsequent study, the relationship between3D MIMO and massive MIMO is also demonstrated.Secondly, using ZF receiving algorithm, we study the user-specific beam steering technique, which is one category of three-dimensional beamforming, to analyze the uplink performance of single-cell and multi-cell3D MIMO system. Simulation results indicate that, when the users are concentrated in the cell center, the user-specific beam steering can increase received signal to inference and noise ratio, and consequently improve the performance. However, when the users are distributed on the cell edge, too large received power will lead to a severe interference, and therefore degrade the performance. This conclusion has some reference meaning for the application for3D beamforming.Thirdly, this paper extends current scenarios of3D MIMO to the situations of high-rise building and large scale of base station antennas. In detail, impact of base station downtilt on the system performance is analyzed here. Besides, we discuss the performance in cases of high SNR regime and three-dimensional user distribution. Simulation shows that, base station downtilt plays an important role in3D MIMO system performance, especially when users are vertically distributed. Increasing of SNR, user distribution and user number within a specific range also improve the performance. These research results can be used as a reference for the infrastructure.