Design And Implementation Of Physical Random Access Channel In Massive MIMO System

With the popularization of intelligent mobile terminals and the continuous growth of new mobile ser-vices brought by Internet of Everything(IoE),the 5th generation of mobile communication systems(5G)needs to meet the needs of higher date rate,spectral efficiency and power efficiency,as the 4th generation of mobile communication systems(4G),which can only support a Gigabit per second transmission rate,will hardly meet the application requirements of the future mobile communication.This requires new wireless commu-nication technologies to be supported.At the same time,with the wireless resources increasing,the core issues in 5G are to reduce the energy consumption of mobile communication networks and to improve the spectral efficiency and power efficiency.Among them,massive MIMO wireless transmission technology has become one of the most promising directions in the field of 5G mobile communications as it can deeply exploit space resources.However,massive MIMO will introduce some new problems,such as massive MIMO wireless channel model,channel status information acquisition,multi-user data transmission and initial access.In recent years,researchers in academia transfer the massive MIMO channel from the antenna domain to the beam domain,effectively solving the data chanel transmission problems with beam domain channel model,massive MIMO pilot reuse method and beam division multiple access(BDMA)transmission scheme.How-ever,for the initial access process,massive MIMO introduces some new problems which need further study when communications have not yet established.For downlink synchronization,researchers have proposed an omnidirectional transmission scheme,which solves the problem that the beam angle is narrow and needs to be scanned frequently.However,the research on the uplink Physical Random Access Channel(PRACH)still remain a gap.In this thesis,we focus on the problem of PRACH when the beam angle is narrow and the number of users in the cell is large.Based on the massive MIMO beam domain channel,the Massive MI-MO PRACH design is studied,and based on the massive MIMO prototype system,the algorithm has been designed and implemented.First of all,We analyze the massive MIMO beam domain channel comprehensively and systematically.The flat fading beam domain channel,wideband OFDM beam domain chanel and millimeter-wave beam domain chanel are modeled respectively.The relationship between the antenna domain channel and the beam domain channel is studied.Also,we demonstrate the channel sparsity in the beam domain,which is the basis of the massive MIMO beam domain uplink synchronization method.The channel sparsity in the beam domain is verified by simulation experiments.Then based on the characteristics of beam domain,we look at the massive MIMO multi-user uplink synchronization method in beam domain.Firstly,for flat fading channel,we prove that massive MIMO beam domain synchronization has anti-MUI(Multi-User interference)performance.Then the temporal synchro-nization method has been studied when the angle of arrival(AoA)is unknown at the base station.Based on this,the massive MIMO-OFDM PRACH detection algorithm is proposed.The theoretical interpretation of massive MIMO-OFDM random access tuning estimation in antenna domain and beam domain is given.The antenna domain and beam Domain random access receiver diversity method is studied,and the performance comparison of different combining methods under the beam domain is given,and a SC/EGC beam domain combining method which is convenient for hardware implementation is proposed.The simulation results show that the performance of the massive MIMO-OFDM random access detection algorithm proposed in this thesis is significantly better than the traditional random access antenna domian detection algorithm.Finally,Based on the massive MIMO-OFDM random access detection algorithm,we design and imple-ments the hardware based on the massive MIMO prototype verification system on the national key experi-ment of mobile communication.Firstly,the architecture of massive MIMO prototype verification system and the USRP platform are introduced.Based on the core functions of random access,MAC layer protocol is simplified.Based on this,a low complexity beamforming scheme on USRP is designed.The DFT hybrid time-frequency transmitter is used at the transmitting end and the down-sampling frequency-domain receiver is used at the receiving end,which greatly reduces the computation and resource consumption.Then fixed-point simulation is carried out.And our design is implemented in hardware on the USRP.Combined with the features of 5G prototyping system,a USRP development scheme based on UHD and RFNoC is proposed,which improves the efficiency of prototype verification system development.