Research On The Direction-of-Arrival Estimation For Massive MIMO Beamforming

Massive MIMO(Multi-input-multi-output,MIMO)system is one of the candidate technologies of the future fifth-generation mobile communication system.Thanks to the beamforming technique,which performs weighting process before the data being transmitted at the base station,the large-scale antenna array can form a narrow transmitting beam.The main energy is thus aligned with the target user at the receiving end,which improve greatly the multiplexing capability of the spectrum resource as well as the spectral efficiency.One of the keys to successful beamforming is to obtain accurate direction of arrival(DoA)information of the source.However,when the base station antenna deployment changes from MIMO to massive MIMO,the DoA estimation algorithms present new challenges.Although there are many available methods for DoA,the system models used are mostly limited to uniform linear array or simple rectangular array.In the case of massive antenna array system,the two-dimension DoA estimation,joint estimation of elevation and azimuth,still remains unstudied.In this thesis,a DoA estimation algorithm for beamforming is proposed for massive antenna array system,which is capable of joint estimation of elevation and azimuth angle.The algorithm has low complexity and high estimation accuracy.The main innovations of this thesis are summarized as follows:The system modeling of three kinds of large-scale antenna arrays is conducted,and the coverage ability and angle resolution of different array configurations are analyzed and compared.Then,the new characteristics of beamforming technology appeared in the massive MIMO systems are analyzed,such as the dimension expansion of directional beam,the enhancement of beam resolution and the increase of computational complexity.The relationship between the beamforming technique and the DoA estimation is clarified by the conduction of three constraint criteria for the optimal weight vector formation.Two typical algorithms,Multiple Signal Classification(MUSIC)and Estimation of Signal Parameters via Rotational Invariance Techniques(ESPRIT),are conducted to the DoA estimation for beamforming technique.The factors affecting the performance of the algorithm are analyzed comprehensively.With the help of mathematical theory derivation and practical indoor measurement data,the performance evaluation of the algorithm is carried out and the design criterion for DoA estimation in massive MIMO beamforming is proposed.Unitary EPSRIT is adopted to realize the joint estimation of elevation angle and azimuth angle in the massive uniform rectangular array(URA).Because the algorithm owns high precision,low complexity,de-coherence function,and it can automatically match the two-dimensional angle,its estimation performance in the massive MIMO is really good.With the help of Monte Carlo simulation,the influence of antenna array,source number and element number on the angle estimation algorithm of large-scale antenna array is studied.According to performance analysis,azimuth angle is more vulnerable to antenna configuration than elevation angle in massive MIMO systems.Array resolution is proposed to analyze the differences in the estimation performance between elevation and azimuth.Finally,the thesis presents that how the characteristics of the DoA estimation studied could provide a possible solution for the large-scale antenna array deployment.