Research On Hybrid Beamforming In Millimeter Wave Communications

The millimeter wave?mmwave?communication is the frontier for wireless communication.Mmwave has been receiving tremendous interest by academia and industry,because of the limitation of spectrum available in sub-6GHz bands.Large scale MIMO and beamforming can make up the huge path loss of mmwave signal and become the key technology of mmwave mobile communication.In addition,it is impossible to realize the all digital processing of traditional MIMO systems in mmwave communication due to the constraints such as implement complexity,hardware cost,and power consumption.Therefore,the analog and digital hybrid beamforming technology in mmwave MIMO system has become a research focus.In this thesis,millimeter wave propagation characteristics,channel model and hybrid beamforming technology are studied,the main work and achievements are as follows:1.The fixed beamforming and CSI-based precoding in mmwave single user MIMO system is studied.Due to the large difference in sub-channel gain obtained by SVD decomposition in FBCP hybrid beamforming,the overall performance of the system is degraded.In order to solve this problem,we apply the LDL^H decomposition precoding in traditional MIMO to the digital processing part of FBCP algorithm and the hybrid beamforming based on LDL^H decomposition is proposed.The proposed hybrid beamforming can acquire more uniform sub-channel gain,thus improving the system's bit error rate performance.Computer simulation shows that the proposed algorithm reduces the bit error rate of the system without increasing the computational complexity compared with the FBCP algorithm.2.In the multiuser MIMO downlink at millimeter wave communication,an improved algorithm of hybrid block diagonalization based on QR decomposition and LDL^H decomposition is proposed.The proposed hybrid beamforming algorithm replaces the two singular value decomposition in the hybrid block diagonalization algorithm with QR decomposition and LDL^H decomposition respectively.Compared with the original algorithm,the acquired algorithm not only improves the bit error rate performance of the system,but also reduces the computational complexity.3.A hybrid multi-stream diversity beamforming algorithm for mmwave multiuser MIMO systems is proposed.In the multiuser MIMO system,the traditional block diagonalization operation is achieved by solving the null space of the interference matrix formed by other users'channel matrices.In this thesis,we propose a new method to construct the interference matrix,and the user's own channel information is also included.The resulting precoding can not only eliminate multiuser interference,but also eliminate the interference between the equivalent receiving antennas,so as to obtain better system performance.The simulation results show that the proposed hybrid beamforming algorithm can obtain better bit error rate performance and spectral efficiency compared with the hybrid block diagonalization algorithm.