| Millimeter wave communication has become one of the key technologies of 5G(5th Generation of Mobile Communication System,5G)mobile communication system due to its ability to meet the spectrum bandwidth requirements for future mobile communication broadband transmission.Cell search is the first step for 5G terminals to access the 5G network.Due to severe path loss in the millimeter wave frequency band,the cell synchronization/physical broadcast channel block(Synchronization/Physical broadcast channel block,SS/PBCH)is transmitted in a beam mode.If the terminal cannot obtain the SS/PBCH,it cannot communicate.In addition,compared with the traditional microwave communication,millimeter wave communication has a larger frequency offset,which will have a serious impact on the time and frequency synchronization of receiving SS/PBCH beam,resulting in inaccurate detection of physical cell identification.Therefore,it is necessary to design a reasonable and efficient 5G millimeter wave initial synchronization process.The research work of this thesis is as follows:1.The search process of 5G millimeter wave beam is studied.According to the 3GPP protocol for transmission time slot of 5G millimeter wave synchronization signal,the codebook is used to transmit the synchronization beam,so that the synchronization beams have different amplitudes after passing through the 5G millimeter wave channel.The terminal selects a suitable beam for the subsequent synchronization process,but the beam search is not accurate due to noise and other effects.So the power spectrum of the received beam is calculated by using the power spectrum periodogram method.,The fixed power threshold value and the slope threshold value of the beam are designed as the method to determine the threshold of beam.Compared with the traditional single algorithm,the dual threshold beam search method has better performance.2.Study the time and frequency synchronization process of receiving beam.Firstly,it is proved by simulation that 5G primary synchronization signal has good correlation in the time domain and the secondary synchronization signal has good correlation in the time and frequency domain.The tolerance of the two synchronization signals against frequency offset is ±0.5 subcarrier spacing.Aiming at the problem that the carrier frequency offset may exceed the integer multiple of the subcarrier spacing in 5G millimeter wave,which makes the traditional detection algorithm invalid.A timing synchronization method of the primary synchronous signal with frequency offset is proposed,and integral frequency offset is estimated and compensated.The timing synchronization is carried out again,according to the two segment cross-correlation algorithm of primary synchronization signal.This algorithm can effectively reduce the detection error of timing synchronization and physical cell group identification when frequency offset is too large.In the detection of the secondary synchronization signal,a simplified detection algorithm based on the Hadamard product is proposed according to the characteristics of the Gold sequence,compared with the traditional secondary synchronization signal detection algorithm,it can save a lot of computation.Finally,the detection accuracy of the physical cell identification is verified in different 5G millimeter wave channel environments.The results show that the 5G millimeter wave initial synchronization scheme is reliable. |
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