Research On Beamforming Technology Robust To Beam Pointing Error

As the key technology of the fifth-generation mobile communication system,beamforming technology can form the beam with high gain and strong directivity by adjusting the antenna array,so that the energy can be concentrated in a certain direction to compensate the path loss in transmission effectively,and then the received signal-to-noise can be improved.However,in practical applications,due to the influence of equipment or complex communication environment,beam pointing errors may exist,especially when the beam energy is very concentrated,even a small deviation will have a great impact on system performance.Hence,in order to overcome the problem of unstable beam pointing,this paper studies the beamforming technology robust to pointing error.The main works are as follows:First,the beamforming technology with stable beam gain within a certain pointing error range is studied.According to the robust transmission and antenna power efficiency issues,the constraints satisfied by the beamforming vector are deduced.According to these constraints,the codebook search algorithm based on spherical decoding and the iterative algorithm based on manifold optimization are studied for beamforming design.The two algorithms are simulated and analyzed.Both algorithms can achieve robustness to pointing errors,but due to the limitation of the codebook,the stability of the former algorithm is not as good as that of the iterative algorithm.Then,the robust beamforming technology based on the principle of the maximum signal-to-noise ratio in single-user system is studied.The traditional Maximum Ratio Combining(MRC)algorithm and the Maximum Ratio Transmission(MRT)algorithm are improved respectively.Considering the impact of beam pointing error,the MRC and MRT criteria are used to design the beamforming vector.To obtain the optimal beamforming weighted vector,the Augmented Lagrange Method(ALM),the Alternating Direction Method of Multipliers(ADMM)and the steepest descent method are used.Then the simulation results are given.Compared with traditional MRC and MRT,the improved algorithm takes the pointing error factor into account in modeling,and the system error performance is robust to the angle error.Finally,the beamforming technology robust to angle error for multi-user systems is studied,including the robust receiving beamforming in the multi-user uplink communication system and the robust transmitting beamforming in the multi-user downlink communication system.Based on the Minimum Mean Square Error criterion(MMSE),the robust algorithms RMMSE algorithm and MO-RMMSE algorithm based on manifold optimization are proposed to overcome the angle error.At the same time,simulation verification is carried out in four scenarios,including the uplink and downlink communication systems within single-path channel and multi-path channel.The simulation diagrams of bit error performance of the four systems are given.Compared with the traditional MMSE algorithm and the Sphere Decoding(SD)receiving algorithm,the system bit error performance under the RMMSE and MO-RMMSE algorithms will not be affected by the angle error when there is an angle error.As for the robust minimum variance(RMVB)algorithm,the proposed algorithms show better robust performance.And with the angle error increasing,the number of users increasing,or the number of antennas increaseing,the gap of the robust performance between the RMVB algorithm,the RMMSE algorithm and the MO-RMMSE algorithm is more obvious.