Research On3D MIMO Beamforming Algorithms

For current mobile communication systems, to increase system capacity and reduce interference is still the most important development objective. In the existing cellular system, the base station transmitter beam can only be adjusted in horizontal dimension, and the vertical dimension downtilt is fixed for each user. Therefore, all kinds of beamforming/precoding technologies are based on the horizontal dimension channel information. Conventional2D MIMO beamforming is made on only two-dimensional direction, i.e., the user data can only be processed in the horizontal dimension channel information, thereby forming a small beam radiation pattern in the antenna in real time for prospective users.In fact, due to the3D (three-dimensional) character of the real channel, the downtilt-fixed model cannot achieve optimal system throughput.3D MIMO Beamforming technology can fully explore the three-dimensional space degrees of freedom, to track user channel phase information on horizontal and vertical dimensions effectively. It can also improve service user SINR, reduce inter-cell interference and improve system throughput and frequency efficiency. It is one of the promising directions of future MIMO technology.Based on traditional2D MIMO beamforming algorithm, this thesis will investigate the3D MIMO beamforming algorithms which introducing the vertical dimension. According to the estimated3D channel information, we adjust the3D beamforming weight in antenna terminal, to make the beam main lobe align the target user in three-dimensional space. It can increase the received signal power and improve the signal to interference noise ratio, thereby enhancing the throughput of the entire system. In this thesis, our research and innovation are as follows:In this thesis, the following two3D MIMO beamforming schemes are mainly discussed. In3D beamforming system, the design of3D codebook is a critical step, which determines the beam control accuracy of the antenna system and the implementation complexity of system feedback mechanism. So these two schemes are based on two different codebook design mechanisms for research.Option I:3D MIMO beamforming scheme based on independent horizontal and vertical codebook. Horizontal and vertical dimensions are designed independently. Based on these two independent codebooks, user feedback two separate2D PMIs. The base station make3D MIMO beamforming based on the feedback horizontal and vertical PMIs. Numerical results showed that our proposed3D MIMO beamforming scheme can reasonably improve the overall system capacity performance compared with conventional2D MIMO beamforming. The performance gain can be13%.Option II:3D MIMO beamforming scheme based on unified3D codebook. The unified3D MIMO codebook is constructed by combining horizontal and vertical codebook using a certain algorithm design, in which the existing2D codebook is reused. UE feedback a3D PMI based on this3D codebook. The base station makes3D MIMO beamforming using the3D PMI reported by the UE. Numerical results showed that3D MIMO beamforming scheme based on unified3D codebook can further improve the system performance compared with conventional2D MIMO beamforming and3D MIMO beamforming scheme based on independent horizontal and vertical codebook.Finally, a summary of the full text is made and future research directions are discussed.