Investigations On Millimeter Wave Massive MIMO Array Technologies

With the increasing demand of data service in mobile communication,the fourth generation mobile network(4G)is unable to meet the requirements of increasingnetwork capacity,transmission rate and low latency,etc.As a comparison,the fifth generation mobile network(5G)communication system has higher user experience rate better mobility and lower end-to-end latency.Hitherto,5G technologies in sub-6GHz band have come into the stage of commercial application.In order to obtain more spectrum resources and achieve greater communication bandwidth and higher speed,5G mobile communication is developing towards millimeter-wave frequency.Millimeter-wave 5G systems are developed under the framework of hybrid multi-beam array based on phased sub-arrays,in which the complexity,power consumption and cost is reduced while the system performance is greatly limited.The research work of this paper mainly focuses on full digital millimeter wave massive MIMO array technologies for B5 G and 6G communications.The main research works of this paper are as follows:(1)For the application of millimeter wave B5G/6G massive MIMO array,a 64 channel full digital multi beam array working in 37-42.5GHz band is developed and realized for the first time.Different from conventional T/R module,a TDD architecture with separate transmitter and receiver is adopted in this array,which makes more flexible channel configuration and hardware distribution possible.The transmitting module,receiving module,local oscillator generating circuit,antenna array and other key components of millimeter wave RF front-end have achieved good performance,which can meet the requirements of realizing array beamforming and high-speed high-quality communication in millimeter wave band.At the same time,based on the features of millimeter-wave large-scale array,the use of feedlines with unequal lengths between each antenna unit and its corresponding transmitting / receiving module is proposed to realize a compact and space-efficient interconnection.The developed full digital Q-band millimeter wave massive MIMO array can be used in some scenarios such as millimeter wave communication base station,millimeter-wave channel sounding,millimeter-wave measurement platform,etc.(2)In this paper,the influence of unequal length feedline on the beam performance of wideband modulated signal in massive MIMO array is studied,and the phase offset caused by unequal length cable for signal deviating from calibration frequency is analyzed.The Q-band5 G millimeter wave massive MIMO array is taken as an example to calculate the phase difference between different array elements at the edge frequency of upper and lower sidebands of wideband modulated signal.At the same time,the far-field pattern of the array is simulated and tested under different direction of beams.The simulation and test results show that the proposed feeding scheme has little influence on the radiation characteristics of the array.Also,by utilizing this scheme,the interconnection between antennas and RF modules can be realized in a more space-efficienct way which hardly sacrifices beam characteristics.(3)The calibration methods of massive MIMO transmitting array and receiving array are studied.Based on the proposed method,4 × 16 element-5G millimeter wave massive MIMO transmitting array and receiving array in the Q-band of are calibrated separately.Then,the experiments of single beam steering and multiple concurrent beam forming are performed on the transmitting and receiving arrays respectively,to verify the correctness of the proposed array calibration method and the beamforming ability of the Q-band 5G millimeter wave massive MIMO array.The communication quality of Q-band 5G massive MIMO array under 5G NR signal is tested.The test results show that the calibrated Q-band 5G massive MIMO array has excellent over-the-air(OTA)performance and is capable of achieving higher modulation and demodulation quality for wideband modulated signals.(4)Analysis and studies on the radiation characteristics of arrays with different numbers of failed elements under different electrical status are performed.The reliability of analytical formula for failed array without mutual coupling is proved through systematic computation,simulation and experiments.In this paper,the probability model of pattern parameters for massive MIMO array with failed elements is proposed.Also,the comparison between the results derived from probabilistic model and statistical results is made to validate the correctness and effectiveness of the proposed probabilistic model.The proposed probabilistic model can be a substitute for the statistical analysis based on large numbers of samples to get expectations and variations of main radiation parameters directly.And it can be used for the fast evaluation of the radiation characteristics of arrays with different percentage of failed elements under different electrical status.In addition,the probability distribution of main radiation characteristics of arrays with different percentage of failed elements under different electrical status is also analyzed.(5)For Wifi application based on IEEE 802.11aj(45 GHz),the RF front-end for short range access under this standard is designed and realized.The RF front-end can be configured to TDD/FDD mode flexibly according to application scenarios.And detailed measurements of its RF performance are performed.The measurement results show that the RF front-end of IEEE 802.11aj(45 GHz)short range access system achieves good performance,which can meet the requirements and applications of RF front-end for high-speed short range access under IEEE 802.11 aj standard.