Research And Verification Of Synchronization In Massive MIMO Systems Based On Omnidirectional Precoding

To cope with the development trend of diverse and differentiated business needs in the future mobile communication system and meet the multidimensional requirements of ultra-high speed,ultra-low latency,high-speed mobility,high energy efficiency and ultra-high connection,5G new radio technology will depend on a series of key technologies,such as more flexible frame structure,multi-antennas,beamforming and ef-ficient coding,to tackle the challenge.Among them,massive multiple-input-multiple-output(MIMO)plays crucial roles in improving the spectral efficiency and transmission reliability through mining space resources deeply with flexible waveform algorithms.This dissertation mainly focuses on 5G-NR and investigates the research on the approaches of synchronization signals omnidirectional transmission in massive MIMO sys-terms.Meanwhile,the method of synchronization signal detection in the process of the cell search are proposed and implementation scheme is completed on the FPGA platform.First of all,this dissertation investigates the synchronization signal in 5G-NR system,the channel trans-mission characteristics and the channel model of massive MIMO system.Based on the series of NR Release 15 protocols,the 5G wireless frame structure and the ways of synchronization sequence generation and re-source mapping are studied.For the signal transmission scenario in massive MIMO system,the transmission characteristics of wireless channels and the channel model are given under the one-ring scattering model.Then,we investigates the omnidirectional precoding for synchronization signal transmission and down-link synchronization algorithm in massive MIMO system.Due to the large number of antennas,there are problems of excessive pilot overhead in channel estimation.We propose omnidirectional precoding based transmission,where the high-dimensional signal vector is decomposed into the product of omnidirectional matrix and low-dimensional vector that is independent of channel.The terminals only need to estimate the equivalent channels to reduce the pilot overhead significantly.For omnidirectional precoding matrix design,two basic condition are proposed that must be satisfied to meet the requirement for reliable cell-wide cover-age of signal power in angle domain and equal power on each antenna at any instant time.By utilizing ZC sequence and Alamouti coding,we give some examples of joint design about omnidirectional precoding ma-trix and low-dimensional signal vector not only in uniform linear array but also in uniform planar array.On this basic,aiming at the limitations of the classical methods of transmitting synchronization signals,a scheme of omnidirectional transmission of synchronization signals for massive MIMO systems is presented.Based on the maximum likelihood criterion of joint timing and frequency offset channel estimation,the method of detecting synchronization signal through segmented cross-correlation are deduced.Depending on dividing the synchronization sequence into multiple segments,computing cross-correlation respectively and accumu-lating them together,this algorithm can effectively combat the impact of frequency offset on the detection of the synchronization signal.Meanwhile,correlation-based detection method based on multi-path windows filtering is proposed in multi-path environment,and in the case of multi-stream synchronization sequences the performance can be further improved by using space-time coding to obtain diversity gain.Numerical simu-lation results show that omnidirectional transmission and synchronization signal detection using dual-stream sequences based on omnidirectional precoding are significantly superior to single-stream sequences,and the detection algorithm is robust.Finally,on the basis of the above research,we design the specific implementation process of omnidi-rectional transmission and downlink synchronization detection.First of all,the overall hardware platform architecture and the design scheme of the prototype verification system are given.Afterwards,fix-point implementation scheme of omnidirectional precoding and downlink synchronization are designed,and the performance comparison between fixed-point and floating-point is provided.Then we design the modules of the circuit,interface and the timing and implement the transmitter and receiver by Verilog based on Xilinx Kintex-7 and Virtex-7 series FPGA.At last,the test results and hardware resource consumption are provided.