Research On Key Technology Of Millimeter-wave Wireless Communication System

In recent years,with the rapid development of wireless communication,people are increasingly demanding data traffic.Wireless data traffic is projected to skyrocket 10000 fold within the next 20 years.To tackle this incredible increase in wireless data traffic,a approach is to move up in frequency,into an unused nontraditional spectrum where enormous bandwidths are available,such as at millimeter wave(mmWave).The availability of huge bandwidth coupled with the use of large antenna arrays with as many as 8 to 256 elements at both transmitter and receiver have attracted considerable attention for people.There are many technologies that need to be improved and improved in millimeter-wave wireless communication systems.In this paper,we will conduct in-depth research on two key technologies-signal synchronization and beamforming.Firstly,this thesis introduces the millimeter wave cluster delay line channel model from two aspects: large-scale fading and small-scale fading.Large-scale channel characteristics are described by average path loss and shadow fading.Small-scale channel characteristics appear as clustering and angular domain expansion.Then,this thesis presents the block diagram of the transmitter and receiver of the OFDM system,introduces the basic theory of OFDM technology,and briefly describes the two key technologies of the millimeter wave wireless communication system,namely signal synchronization and beamforming.The thesis mainly analyzes the influence of symbol timing deviation in OFDM system,and then discusses the signal synchronization technology.At the same time,the thesis also outlines the classification and main methods of beamforming.Additionally,this thesis proposes a synchronization algorithm based on Golay complementary sequence and compares it with the classical synchronization algorithm.The classical synchronization algorithms mainly include S&C algorithm,Minn algorithm and cross-correlation-based synchronization algorithm.The advantages and disadvantages of the algorithms are analyzed from the perspectives of implementation complexity,timing accuracy and applicable scenarios.Starting from the aperiodic autocorrelation property and fast correlation structure of Golay sequence,we further improve the Golay correlator,design the synchronization training symbol,and give the timing synchronization method.Through simulation,from three aspects of the acquisition probability under the constant false alarm criterion,the timing mean square error and the channel estimation performance,the thesis verifies that the proposed synchronization method can not only perform accurate timing synchronization,but also has excellent channel estimation performance.Furthermore,we give the FPGA implementation of the synchronization based on Golay complementary sequence.By introducing the functions and design ideas of data caching,energy calculation,peak detection and other modules,the overall architecture and design outline of the timing synchronization module are described.This thesis focuses the design of the Golay correlator,and gives the RTL schematic and timing simulation waveforms.The thesis highlights the advantages of the Golay correlator by comparing with the performance of the traditional correlator.On this basis,we combine theoretical analysis with actual simulation to verify the final implementation of the timing synchronization module.Finally,this thesis studies the millimeter wave beamforming technology,and proposes a greedy hybrid beamforming algorithm based on orthogonal codebook and a power iterative hybrid beamforming scheme based on beam selection.By describing the system model of hybrid beamforming,the paper gives the joint optimization problem in hybrid beamforming.Review three classical beamforming algorithms-codebook-based analog beamforming,SVD-decomposed digital beamforming,and hybrid beamforming based on orthogonal matching pursuit.By comparing the spectral efficiency of each algorithm under different data streams,the paper verifies that our design approximates the optimal unconstrained beamforming in performance,and the implementation complexity is lower than the hybrid beamforming based on orthogonal matching pursuit.