| Random access is the first process before the start of communication.Only after the UE accesses successfully,the uplink data can be transmitted.For the LTE system,even if the speed reaches 350km/h or even 500km/h,the network can still maintain the link,but when the speed is greater than 250km/h,such as ground high speed moving scenarios,the access performance will deteriorate,so research new random access plan has a certain significance.This article mainly studies the LTE random access algorithm,The first chapter explains the research background and significance and analyzes the research status and existing problems at home and abroad.Studies the transmission and reception of the LTE PRACH signal in detail,and deeply analyzes the impact on the random access performance when the UE moves at high speed.Deduces and verifies by simulation that the received signal changes in the presence of Doppler frequency offset,the threshold of the noise detection algorithm for peak detection is improved.An improved semi-dynamic threshold setting algorithm is proposed.It solves the problem when the noise power estimation inaccurate on detection performance.When the signal to noise ratio is high,the others peak near the correlation peak begins to rise and gradually submerge the noise.The false alarm caused by the increase of others peaks when the two times threshold decision algorithm is improved to limit the high signal to noise ratio is proposed.The PRACH physical link layer simulation is set up.Under the simulation platform,the improved algorithm is verified.For the sequence of preamble format 0~3 in high-speed mode,the simulation and result analysis are performed under two different channel models of AWGN/ETU70.The simulation results show that the improved algorithm has a certain improvement on the performance of random access.The related research work of the dissertation has certain reference value for further research on the random access algorithm in the ground high-speed moving scene. |
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