Research On 5G Random Access Technology In High-speed Mobile

5G is a new generation of mobile communication technology,which is widely used in various industries and fields of society because of its high speed and low delay.In the field of high-speed rail,5G also plays a huge role.With the rapid development of high-speed railway,its running speed is faster and faster,making 4G unable to meet the requirements.5G supports ultra-high speed movement up to 500km/h,and has made more optimization to combat Doppler frequency shift,which greatly improves the performance in high-speed mobile scenes.Random access is the first step of establishing connection between user terminal and base station,and it is the most basic processing mechanism of mobile communication system.The random access process sends the random access preamble for the user equipment and receives it at the base station,so as to realize uplink synchronization and uplink data transmission.The research focuses on the design of Doppler frequency shift algorithm to achieve more efficient communication quality.Firstly,this dissertation introduces the key technologies of 5G physical layer.Compared with LTE technology,5G is optimized on its basis,including frame structure and resource allocation.The channel design of 5G random access is summarized,including the application scenario of 5G random access and the complete process of random access,and the format type and resource configuration of random access preamble sequence are described in detail.Then the generation process of random access preamble sequence is given,the characteristics of ZC sequence and the function of measuring time offset are introduced in detail,and the random access preamble sequence at UE and its baseband signal generation are introduced.Secondly,this dissertation puts forward the system model of preamble detection,and explains the interference between signal subcarriers caused by frequency offset.Then,it compares and analyzes the preamble demodulation method,the influence of power combination on performance during multi antenna reception,and the setting mode of noise power.In the high-speed mobile scene,the three detection windows generated by the detection sequence are mainly analyzed and determined.Based on the three window detection algorithm,this paper sets two threshold thresholds to detect the three search windows,and then determines the threshold after superimposing the dispersed power.Through simulation analysis,the preamble detection performance in high-speed mode is improved.Finally,this chapter mainly analyzes and studies the preamble detection of ultra-high speed mobile scene.The influence of frequency offset on random access in ultra-high speed mobile scene is deduced by formula,and the signal energy is dispersed into five search windows.5G NR is used to propose the restriction set B in the ultra-high speed scene,so that the five search windows of the preamble will not overlap.In this dissertation,an ultra-high speed mode detection algorithm using restriction set B is proposed to detect the secondary threshold of five search windows,and an adaptive random access algorithm is further proposed,which can reduce the computational complexity and increase the success rate of preamble detection,which provides a new scheme support for random access detection in ultra-high speed mobile scene.The reliability of the algorithm proposed in this paper is verified by simulation analysis.