| Beamforming is one technology that transmits or receives signal in specific direction.It is widely applied in multiple antenna communication system.By combining collaborative communication and beamforming,the cooperative beamforming greatly improves energy and frequency spectrum utilization efficiency of multiple antenna system.At the same time it also enhances the reliability of the signal and expands the cooperation communication distance.So it has great application prospects in the wireless sensor network.The thesis focuses on cooperative beamforming technology.First of all,we comprehensively introduce cooperative beamforming.On the basis of geometric model,probability function can be used to analyze the beam pattern.At the same time,the article illustrates the four key technologies of cooperative beamforming,especially the synchronization technology.Then the thesis mainly studies the carrier phase synchronization.For two cases of flat fading channel and time-varying channel,the article respectively establishes system model,introduces the existing classic algorithms,and proves the feasibility of the algorithm in theory.Finally,the thesis puts forward the corresponding improved algorithms.The system convergence performance of the existing one-bit algorithms is not really good.The thesis proposes an improved one-bit algorithm named variable directional perturbation based one-bit feedback algorithm.The proposed algorithm adjusts the step of random perturbation and the step of direction of perturbation to improve the convergence speed by utilizing limited feedback information fully.The cooperative beamforming must overcome the negative effects of channel phase drift under time-varying channel,so random perturbation step needs to control more effectively.The thesis proposes an impoved time-varying algorithm named signal monitoring based two-bit feedback algorithm.Compared with the existing algorithms,the proposed algorithm has more advantages in tracking time-varying channel. |
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