Codebook Design And Beam Squint Research In Hybrid Beamforming

As a new type of array signal processing technology,hybrid beamforming can achieve a compromise between cost and performance in a higher operating frequency band,and has great research value in the fields of 5G technology evolution,6G preresearch,and military and civilian radar.In recent years,due to the rapid development of beam alignment technology,codebooks have become an important working method for hybrid beamforming,and how to design codebooks for hybrid beamforming is a key issue.In addition,higher frequency bands correspond to larger bandwidths,which will produce the beam squint phenomenon and affect the effectiveness of the codebook work.Therefore,it is necessary to study the beam squint suppression method in hybrid beamforming.Based on the above situation,this thesis has carried out investigations on codebook design and beam squint suppression in hybrid beamforming,which can be stated as follows:Firstly,this thesis studies two types of representative codebook design methods in planar array hybrid beamforming,namely the codebook design method based on gradient descent algorithm and the codebook design method based on geometric decomposition algorithm.Starting from different technical routes,the two methods both obtain relatively flat and concentrated patterns and generate the required codebooks.At the same time,two decomposition methods of rank-1 matrix are also studied,namely the eigenvalue decomposition method and the random decomposition method.After simulation comparison,it can be seen that random decomposition method has great advantages over the eigenvalue decomposition method,and this method can be extended to various scenarios where rank-1 decomposition is required.Secondly,through theoretical analysis and simulation,this thesis has found that in the broadband system,the beam generated by the hybrid beamforming will produce beam squint,resulting in the attenuation of the target direction gain and the fluctuation of the concentration index.Therefore,a beam squint suppression method is studied for narrow beams to reduce the gain attenuation in the target direction;at the same time,the codebook design method based on geometric decomposition is improved to further improve of the concentration index on different subcarriers the codebook at the expense of acceptable flatness loss;Simulation analysis proves the effectiveness of the above two methods in suppressing beam squint.Finally,in view of the broad engineering application prospects of conformal arrays,this thesis has proposed a codebook design method for conformal array hybrid beamforming.The main work includes: Adjusting the basic structure of hybrid beamforming to make it suitable for conformal arrays;Using Euler rotation to overcome the difficulty that the pattern product theorem does not apply in conformal arrays;Formulating a non-convex optimization problem and applying a cross-polarization constraints;Solving the optimization problem after relaxation.It is verified by simulation experiments that the proposed algorithm can obtain excellent directivity coefficients in the target area of the main polarization pattern,and at the same time obtain a lower maximum main polarization level in the non-target direction area and the maximum cross-polarization level in the whole space.As the first algorithm considering cross-polarization suppression in the hybrid beamforming codebook of conformal arrays,the algorithm proposed in this thesis is shown to be feasible and can produce good performance results.