| 5G is the fifth-generation mobile communication technology developed on the basis of the LTE system.Its purpose is to realize ultra-low latency,low power consumption,high reliability,and high transmission rate performance of mobile communications to promote the development of emerging industries such as the Internet of things and artificial intelligence.Currently,the 5G new air interface standard of non-Standalone has been frozen.The key technology exploration for the 5G standard has become one of the hot topics in the current communication technology research.The cell search and random access process,as two important parts of the physical layer,is the key to improving system performance.By using the synchronization sequence to complete the cell search,the terminal can correctly demodulate the downlink data and obtain the key system information to open the communication connection with the base station.By using the preamble sequence to implement the random access procedure,the terminal can establish uplink initial synchronization with the base station and obtain the time-frequency resources required for uplink data transmission.Therefore,designing some reasonable and efficient uplink and downlink synchronization sequence and synchronization detection schemes can satisfy the user's demand for high-quality communication process.The main research work for this issue is as follows:Firstly,the downlink synchronization process is studied.By comparing and analyzing the time-frequency ambiguity of Zadoff-Chu(ZC)and m-sequences,the reason why the m-sequence is selected as the downlink synchronization sequence in the 5G standard is demonstrated.Based on the in-depth analysis of traditional detection algorithms for each key module in the cell search,a low-complexity differential correlation detection algorithm is proposed based on the characteristics of the central complex conjugate symmetry of the primary synchronization sequence in the 5G standard.The conjugate multiplication between adjacent symbols reduces the sensitivity to frequency offsets.Simulations show that the algorithm has good robustness to low SNR and large frequency offset.In addition,based on the structural characteristic of the secondary synchronization sequence scrambled by two-level m-sequences,a frequency domain detection scheme based on FWHT method is proposed.Under the condition of excellent detection performance,the detection complexity of the secondary synchronization sequence is reduced by 92.8%.Secondly,aiming at the problem of degraded demodulation performance in random access process due to frequency offset in high-speed scenario,a preamble sequence design and detection scheme is proposed.This scheme combines the two conjugate symmetrical preamble sequences into a new preamble sequence by using the relationship between the peak offset distance of the correlation function and the ZC sequence root index caused by the frequency offset,and implements two-stage joint detection for the new sequence.The proposed scheme avoids the disadvantages of using limited sets in LTE,improves the number of available preamble sequences in one cell,and weakens the influence of integer frequency offset on the process of synchronization detection,which provides an efficient solution support for the random access process in high-speed scenario.Finally,to achieve the process of cell search,the downlink physical layer link level simulation platform is built by Matlab simulation software.The simulation results show that the overall module algorithm has a good convergence.At the same time,through the modeling and analysis of the preamble sequence and detection scheme designed in this paper in the high-speed scenario,the reliability of the scheme is verified. |
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