Research And Simulation Of Random Access In 5G NR Communication System

With the continuous development of mobile communications,4G has long been unable to meet people’s daily needs,and more and more people have invested in the research of 5G construction.Random access is the first step to establish the connection between the User Equipment(UE)and the generation Node B(g NB),which directly affects the performance of the communication system.Therefore,it is necessary to conduct in-depth research on random access.Firstly,through the R15 version protocol released by 3GPP and the interaction analysis between the base station and the terminal in the random access process,this paper gives the processing flow of the random access physical channel link in the 5G communication system and the content of the bearer data information.Secondly,a Physical Random Access Channel(PRACH)link,Physical Downlink Control Channel(PDCCH)link,Physical Downlink Share Channel(PDSCH)link and Physical Uplink Shared Channel(PUSCH)link are built,from the perspective of physical layer link,the data interaction in the random access process is expounded,and the construction of a link-level random access simulation platform is completed.The platform uses C++ language and adopts a modular design.For the contention-based random access,two modules of synchronization and competition are designed,which are divided into the base station side and the terminal side,which can realize the transmission and reception of data,and complete the basic functions of the random access process.Finally,the detection of the preamble signal in the random access process is studied,and a set of preamble detection scheme is designed.Aiming at the phenomenon that the false alarm rate generated by the detection of the preamble sequence is high when the user’s moving speed is high at medium and low speeds,compensation for the Doppler frequency offset caused by the terminal movement is added to the receiving end.Aiming at the problem that the dual-threshold detection algorithm does not estimate the noise in real time,the detection algorithm is improved,and a dualthreshold preamble detection algorithm based on noise power estimation is proposed by combining the semi-dynamic threshold idea.At the same time,the traditional preamble detection process is also optimized.The simulation results show that the detection performance of the preamble detection scheme designed in this paper has been improved.