Research On Channel Measurement And Channel Fading Characteristics For Massive MIMO System

With the development of social society and the improvement of people's living standard,the demand for mobile communications,which is not just content with the voice,SMS and other basic services,has gradually transformed into multimedia communications and all things interconnection.Compared with the traditional mobile communication,the 5th generation(5G)mobile communication system needs to not only meet the requirements of the scenarios of mobile Internet and Internet of Things(IoT),but also handle the extreme performance challenge.For the mobile Internet scenarios,5G mobile communication system can provide faster experience speed and greater bandwidth access capability;for the IoT scenarios,5G mobile communication system can provide higher connection density and lower end-to-end delay.Massive MIMO technology,as an important candidate technology for 5G,can make full use of channel resources,suppress inter-user interference,greatly improve the spectral efficiency and channel capacity by equipping hundreds of antennas at the base station.Meanwhile,with the huge array gains that can effectively enhance the signal to noise ratio,the massive MIMO system can simultaneously serve more users in the same time-frequency resources,which satisfy the requirements of green communication.As the communication medium of wireless communication,the wireless channels play a basic role in the field of wireless communication.The research of wireless channels can provide important reference for the application,design,simulation and deployment of communication system.In this thesis,the wireless channel measurement and channel fading characteristic analysis for Massive MIMO system is studied.In this thesis,we first introduce the fading characteristics of wireless channels and the processing method of the measurement data.Then we introduce our channel sounder used in wireless channel measurement in realistic scenario,and propose a frequency domain method to eliminate the system response of the channel sounder in order to obtain the objective channel impulse response.By using numerical simulation and measured data,the effect of eliminating the system response is verified.Under the premise of eliminating the system response of the measurement equipment,a Massive MIMO wireless channel measurement and channel characteristic analysis work is carried out.In particular,we use two kinds of Massive MIMO array structures with linear and circular shapes with different propagation scenes and different measurement frequencies.Based on the measured data,the fading characteristics of the channel angle domain and the time domain are analyzed specifically.Compared with the conventional MIMO systems,the massive MIMO systems with 128 antennas can not only comprehensively illustrate the distribution of angle-of-arrivals in the angle domain,but also show that the root mean square delay in the time domain is stationary at high frequencies and non-stationary at low frequencies.This is due to the fact that the low frequency has lower path losses and larger obstacle reflection coefficients.At last,the channel orthogonality of the Massive MIMO system is further discussed by using the channel singular value decomposition.We show that with the increase of the number of antennas,the realistic channel singular value spreading cumulative distribution function curve is closer to the ideal independent and identically distributed channel,and the channels with bad conditions can be largely avoided,which implies that the orthogonality of the user channel is enhanced.The above studies provide a reference for the research and commercialization of Massive MIMO technology.