Study Of Enhancements Technologies For PRACH In High Speed Scenarios

With the development of high-speed lines and vehicles,communication in high-speed scenarios has become an important part of our lives.As a new generation wireless communication system,5G(the 5th Generation)can support UEs(User Equipments)with the moving speeds up to 500km/h.PRACH(Physical Random Access Channel)carries the PRACH preamble signal,which plays an important role in the initial random access,radio link reconstruction and timing synchronization,and is an important part of the physical layer of the mobile communication system.PRACH preamble sequences are generated with the ZC(Zadoff-Chu)sequence.The receiver performs the PRACH preamble detection and the timing synchronization according to the correlation calculation results of PRACH preamble sequences.In the high-speed mobile environment,the correlation calculation results of PRACH preamble sequences are affected by the Doppler frequency offset,which affect the communication quality of the mobile communication system.Firstly,this thesis studies the PRACH access performance in high-speed scenarios.The Doppler frequency offset affects the orthogonality among sub-carriers of the OFDM(Orthogonal Frequency Division Multiplexing)system,thereby affecting the PRACH access performance.This thesis analyzes the inter-subcarrier interference characteristics caused by the frequency offset,then the influence of the frequency offset on correlation calculation results of PRACH preamble sequences is analyzed.Compared with the conventional PRACH access performance research,this thesis not only quantitatively analyzes the PRACH preamble detection performance,but also studies its timing performance.The correctness of theoretical derivation and PRACH access performance analysis conclusions are verified by simulation.Secondly,this thesis proposes an enhanced frequency offset estimation algorithm,which makes full use of the amplitude,position and phase of the peak of correlation calculation results at the receiver.Compared with the conventional frequency offset estimation algorithm,it can estimate the frequency offset in a larger range.Combining the previous analysis,this thesis analyzes the performance of the enhanced frequency offset estimation algorithm.Based on the analysis of the enhanced frequency offset estimation algorithm performance,this thesis studies the performance of enhanced receiver,and the performance gain brought by the enhanced receiver is demonstrated by simulation results.Furthermore,the ZC sequences used in the 5G NR(New Radio)system have the characteristics of low PAPR(Peak-to-Average Power Ratio)and good correlation,but the peaks of their correlation calculation results are greatly affected by the frequency offset,which will affect the PRACH access performance in high-speed scenarios.The design requirements that the PRACH preamble needs to meet in the high-speed scenario are summarized and an access sequence against the frequency offset is proposed in this thesis.In addition,considering that the PAPR of the time domain PRACH preamble sequence should be as low as possible,PRACH root sequence suitable for high-speed scenarios is proposed,based on the anti-frequency offset access sequence and the method of sequence splicing.Then,based on the PRACH root sequence,the PRACH preamble generation mode and related parameters as well as the PRACH preamble formats are defined,and the PRACH preamble design suitable for high?speed scenarios is finished.Finally,simulation and analysis prove that the PRACH access performance is significantly improved with the proposed PRACH preamble design in high-speed scenarios.