Research On Physical Random Access Technology In 5G System

5G is a next-generation mobile communication technology developed on the basis of the LTE system.It will significantly improve the system spectrum efficiency and access capability in a variety of scenarios,such as hotspot high-capacity scenarios,low-power large-connection scenarios,low-latency,high-reliability scenarios,and continuous widecoverage scenarios,to meet the user experience in a variety of regional scenarios for the future.As the speed of high-speed rail has become faster and faster,the research on random access technology in high-speed scenes and ultra-high-speed scenes has become a hot spot in the field of communication.Random access is the first step in establishing a connection between a user terminal and a wireless network,and plays a key role in improving system performance.Better design performance,efficient detection algorithms can meet the user's demand for high-quality communication.For the related problems of random access in 5G new air interface,the main research contents of this paper are as follows:Firstly,we study the random access demodulation algorithm and the sequence correlation algorithm.By simulating the complexity and performance of the algorithm,we find a better performance algorithm.We study the detection algorithms in low-speed scenes,including noise power estimation,peak power calculation and multi-antenna power combining algorithm,and give the complexity comparison and performance analysis and conclusions of the proposed scheme.Secondly,this paper focuses on the detection algorithm of random access preamble in highspeed scenes and ultra-high-speed scenes.In the high-speed scene,when the Doppler frequency offset is less than 1.25 k Hz,the peak detection algorithm is improved based on the characteristics of the correlation peak power offset caused by the frequency offset.We propose a quadratic threshold decision algorithm based on noise power estimation,which can effectively solve the problem of high false alarm probability caused by false peaks under high SNR.For high speed scenes,when the Doppler frequency offset is less than 1.25 k Hz spacing,we propose a detection algorithm for the new restricted set preamble in the 5G new air interface.This algorithm uses the five detection windows to jointly detect the random access preamble sequence according to the characteristics of the new limit set frequency offset leading to power dispersion.The new algorithm can effectively avoid the impact of the majority of the Pulse frequency offset on the detection of the random access preamble sequence,and provides an effective solution for the detection of the random access preamble in the ultra-high speed scenario.Finally,the Matlab simulation tool is used to build the physical layer link simulation platform.On the simulation platform,the detection algorithm of the random access preamble under high-speed scene and super-high speed scene is simulated and verified.The simulation results show that the proposed algorithm performs better than the existing detection algorithm in the Doppler frequency offset of one unit subcarrier interval(frequency offset is less than 1.25KHz).When there are more Pule frequency offsets(frequency offset greater than 1.25 k Hz less than 2.5 k Hz),the existing detection algorithm can not meet the detection performance requirements,and the preamble detection algorithm can still effectively detect the preamble sequence.The results verify the reliability of the proposed algorithm.