Research On Millimeter-wave Large-scale Antenna Technology

At present,most of the wireless communication systems are deployed below 3GHz,the increasing number of wireless devices in the access network leads to an increase in the order of the amount of mobile data.The ever-increasing demand for network capacity causes a spectrum crunch for the low frequency band.The millimeter-wave band has a large amount of spectrum resources for wireless communication,which can greatly improve the wireless network capacity to meet the growing demand for data services.Millimeter-wave signal experience a high path loss while the large-scale antenna technology can provide sufficient link gain in the communication transceiver to establish a solid connection.In the millimeter-wave band,the signal wavelength is short which make it suitable for large-scale antenna array deployment.Millimeter-wave large-scale antenna technology can obtain gains from several aspects by the combination of millimeter wave spectrum resource and array antenna technology.This technology can significantly improve the performance of wireless communication systems in the future of broadband wireless communications applications and will play an important role.The practical application of millimeter-wave large-scale antenna technology still faces many challenges.The research content of this dissertation is the analog beamforming method in millimeter-wave large scale array and the beamforming method for the one-bit antenna array.The concrete research contents are as follows:In order to solve the problem of limited precision of phase shifter in analog beamforming,this dissertation analyses the gain loss caused by the quantization error of RF phase shifter for the single stream beamforming.The influence from millimeter wave channel is considered during the analysis.The theoretical model between phase shifter quantization error and the gain loss of the array is established and the theoretical result is verified by simulation.At the same time,the error of the phase shifter will deviate the beam pointing.The influence of the quantization error on the single stream beam pointing is analysed.The theoretical relationship between the pointing error and the quantization error of the phase shifter is established.The simulation results show that in the case of a large-scale millimeter-wave array,the error is limited.In the millimeter-wave system,the linear antenna array and the planar antenna array have suitable application scenarios.In this dissertation,the above analysis extended from the linear array to the planar array.Relationship between the gain loss,pointing error and the phase shifter error is derived and theoretical results are verified through simulation.Millimeter-wave array has a large number of antenna elements,conventional beamforming method take channel estimation to establish the connection in the practical application has a great cost and complexity.In this dissertation,we propose a low-complexity analog beamforming method.This method obtains the array response of the largest path in the millimeter-wave channel as a beamforming vector in several iterations by using power iteration method,the approximate orthogonal property between the different paths in the millimeter-wave channel are derived.This iteration method can avoid channel estimation procedure.Beam alignment between the two sides of the communication is achieved thropugh multiple iterations.This method can obtain the performance close to the traditional SVD beamforming method and has a fast convergence,it reduce the system overhead in the process of establishing the wireless communication connection.In practical application,the planar antenna array not only provide more gain but also has a better point resolution,in the future broadband communications planar antenna array will have a great application potential.In this dissertation,the beamforming method based on power iteration for linear array is extended to planar array and a method of obtaining the received signal of each element in the two-dimensional array under the condition of single RF link is proposed.In the iteration,array response vector for the strongest millimeter wave path is obtained as the beamforming vector.Simulation results show that the proposed method can obtain the channel capacity near that obtained by SVD method and can converge fastly.In the current millimeter-wave large-scale antenna array technology,many papers are related to narrowband channel beamforming.In this dissertation,we propose an iterative beamforming method for linear phased-array in frequency-selective channel.The method extracts the phase of the singular vector of the channel matrix as the beamforming vector.The principle of method is to use the power iteration method to obtain the approximate optimal beamforming coefficient.This method avoids the channel estimation under the condition of large-scale antenna array and reduces the overhead in the millimeter-wave wireless communication system and with a fast convergence.Millimeter-wave large-scale array antenna using full-precision DAC for data sampling will bring greater system power consumption.In order to solve this problem,this dissertation proposes a receiver beamforming method for one-bit multi-antenna array.The method firstly uses a grid based method to reach the rough estimate of DOA,it select the grid with the highest received power as the rough DOA.Then it is taken as the initial value of the adaptive algorithm LMS and finally beamforming vector is found by LMS algorithm.The method can obtain near-accurate performance and has a faster convergence.