Research On Channel Characteristics And Modeling Of Millimeter-wave Massive MIMO Outdoor Scenario

With the development of wireless communication to today's 4G,the key to technological optimization or innovation is to solve the limited and scarce frequency resources and the increasing demand for data traffic.For 5G,which is in the upsurge of research,increasing system capacity and spectrum efficiency are still important indicators for us to develop wireless communication technologies.Massive Multiple-Input Multiple-Output(Massive MIMO)technology is to set up hundreds of antennas(128,256 or more)at the base station,so as to realize hundreds of antennas to send data at the same time.Based on the succession of MIMO technology,it makes full use of space diversity and multiplexing technology to make communication have a significant improvement in energy efficiency,safety,robustness and spectrum utilization.Millimeter-wave band,that is,the wavelength of the electromagnetic wave at the millimeter level.Because it effectively alleviates the frequency occupancy of the low frequency band which tends to be saturated,and has the characteristics of wide bandwidth,narrow beam,good anti-interference and high security,it has been widely concerned in recent years.Moreover,millimeter-wave communication equipment required for the small size,the use of small size antennas will be able to get high directivity,so that we can effectively combine Massive MIMO technology for wireless communication.However,it is found that the millimeter-wave signal has a large fading,which makes the study of it more in the indoor environment.But the combination of beamforming technology and millimeter-wave Massive MIMO technology can theoretically achieve communication with strong directivity,long range and high power,which is suitable for outdoor scenarios.Therefore,based on the above theories,the main research contents and innovative contributions are as follows:Firstly,the theories and methods of wireless channel modeling are deeply researched,the principles of MIMO channel modeling and Ray-tracing(RT)simulation are analyzed.Secondly,based on the idea of ray tracing simulation modeling,a method of calibrating the parameters of the ray tracing simulator based on genetic algorithm is proposed.The actual calibration is carried out at 28 GHz.Compared with the measured data,it is verified that calibration reliability and accuracy,so we successfully set up a millimeter wave communication channel simulation platform.Thirdly,the calibrated simulation platform is used to analyze and summarize the parameters of path loss,multipath,Rice K factor,delay spread and angle spread of millimeter-wave channel.Fourthly,the subchannel characteristics of Massive MIMO are simulated and analyzed by ray tracing simulator.At the same time,the parameters of delay spread and angle spread are statistical modeled.Finally,considering the characteristics of millimeter-wave and Massive MIMO,we propose that beamforming technology,combined with both,can be used in downtown or main street in urban outdoor scenarios.The simulation results show that the directivity of the antenna to the target user is stronger and the channel capacity of the system is significantly improved.Therefore,the antenna can be effectively used to solve the communication quality in the densely populated area under outdoor environment.