Research On Downlink Synchronous Detection Technology Of 5G Communication Signal

5G is a new generation of mobile communication technology based on LTE,which has the technical advantages of wide coverage,high capacity and high rate.Similar to the process of LTE system accessing the network,5G mobile terminal accesses the network after completing the cell search process.As an important part of the physical layer,cell search is the first step for signal exchange and transmission between mobile terminal and base station.Improving the cell search performance is the key to improving the communication system.The configuration of synchronization signal and wireless frame architecture of 5G communication system is more flexible than that of LTE system,so it is necessary to study the downlink synchronization detection technology of 5G communication signal.This paper studies the cell search in the downlink synchronization process.The main research contents are as follows:Firstly,this paper summarizes the 5G downlink synchronous cell search process,then puts forward improved algorithms for PSS synchronization,SSS synchronization and frequency offset estimation in cell search,simulates and analyzes the algorithms in each stage under AWGN channel.In PSS synchronization,an improved frequency domain differential accumulation algorithm is proposed.The received PSS sequence is segmented according to the local PSS sequence after superposition segmentation.Superposition can reduce the amount of blind detection calculation at the receiving end,and the anti-noise of PSS sequence can be improved through differential accumulation.Compared with the improved frequency domain difference algorithm,the sliding cross-correlation algorithm has a high amount of computation,the anti-noise of the segmented cross-correlation algorithm is limited,and the peak to average ratio of the symmetrical autocorrelation algorithm is reduced.The simulation analysis shows that the improved frequency domain difference accumulation algorithm has good anti frequency offset and anti-noise,and the computational complexity is 55.8%lower than that of the sliding cross-correlation detection algorithm.Aiming at the high computational complexity of SSS synchronization algorithm,an SSS synchronization detection algorithm based on Hadamard operation is proposed.After one Hadamard product operation,the cell group ID can be detected quickly.Compared with the traditional SSS detection algorithm,the synchronization time is shortened by 46.2%and the synchronization detection efficiency of 5G NR system is improved.Secondly,the fractional frequency offset estimation algorithm is usually used to estimate the frequency offset of terminal communication instruments.According to the difference of symbol index value between PSS sequence and SSS sequence in time domain,a fractional frequency offset estimation algorithm based on joint synchronization sequence is proposed.Compared with the three fractional multiple frequency offset estimation algorithms:CP based frequency offset estimation,PSS based segmented frequency offset estimation and PSS based image correlation frequency offset estimation,the frequency offset estimation algorithm based on joint synchronization sequence has the best performance.When SNR is 10 d B,MSE reaches the order of 10^-7.Finally,the online test of synchronization detection algorithm is completed on 5G base station comprehensive tester 5252D.Build a test environment with carrier frequency of 2.6GHz,bandwidth of 100M,SCS30kHz and PCI 3.When the frequency offset is 0Hz,30Hz,300Hz and 350Hz,the 5252D can accurately demodulate PCI.The detectable Freq error indexes are-0.08Hz,29.99Hz,300.02Hz and 327.07Hz respectively.When the frequency offset value set by the signal source is 0Hz?300Hz,the difference between the frequency offset measured by the 5252D and the frequency offset of the signal source is within±1Hz,and the frequency offset error meets the acceptance requirements of the instrument.