Research On Hybrid Beamforming Technique In MmWave Massive MIMO Wireless Communication System

As one of the key techniques in millimeter-wave massive multiple input multiple output(MIMO)system,the hybrid beamformer(HBF)is composed of high-dimension analog beamformer(ABF),network of phase shifters,a small number of radio frequency(RF)chains,and low-dimension digital beamformer(DBF).Owing to its reduced cost and approximation of full-DBF's performance,the hybrid beamforming becomes one of the hotspots in recent years.However,at present,there are some problems in the research of hybrid beamforming technique,such as high complexity and almost abandoning the traditional full-digital algorithms.Therefore,this paper first deeply studies the traditional hybrid beamforming technology,and then proposes improved schemes based on specific problems.The specific work and innovations are as follows:1.The related contents of millimeter-Wave massive MIMO system and beamforming technique are described,including research background,domestic and foreign research status,etc.;based on several typical connectivities of phase shifters network,the theories of typical hybrid beamforming are demonstrated,and preliminary MATLAB simulations are performed to illustrate the estimation performance of all schemes.The beam pattern of different numbers of array,the performance of different digital algorithms and the beam pattern of different codebooks are simulated and analyzed by MATLAB.2.A low complexity hybrid beamforming scheme based on codebook combined with adaptive algorithm is proposed.Firstly,in analog domain,beam scanning operation is performed with the Discrete Fourier Transform(DFT)codebook to find out the beam vector which is closest to the direction of the target signal to be as the analog beam weight-vector,and the vector performs ABF operation on received signals for output operation.Through RF chains,the output signals flow into the digital domain.Subsequently,in digital domain,the adaptive algorithm is used to obtain the optimal digital beamforming vector.The results show that,combined with codebook,the adaptive algorithm can steer the main beam to the direction of the target,and steer deep“NUlls” to the direction of interferences;besides,the estimation and the singular value decomposition(SVD)of the channel matrix in traditional hybrid beamforming scheme can be avoided,owing to the introduction of the beam search and the adapative algorithms,thus the complexity is reduced.The proposed scheme can be close to the optimal performance in the aspects of signal to interference plus noise ratio(SINR)and spectral efficiency(SE).3.Based on the coherent multipath environment,another hybrid beamforming scheme is proposed.Firstly,the DFT codebook is still utilized in analog domain to scan all the signals;then a set of codebook beams which are the closest to the direction of all signals,forms the analog beamforming matrix,and the analog beamformer performs analog beamforming on the received signal for output.Subsequently,in digital domain,before the operation of digital beamforming,the proposed scheme based on recovering the dimension of the digital beamformer,adds a step of signal reconstruction,which improves degree of freedom(DOF)of the digital beamformers.Finally,operating traditional decoherence algorithm,the optimal digital beamforming vector is generated.The proposed scheme significantly improves the performances of SINR and spectral SE,which are almost close to those of full digital beamforming.