Analysis And Realization Of Cell Search Algorithm Of LTE System

LTE(Long Term Evolution,LTE)project is an evolution of the third generation mobile communications,which is a next generation standard for wireless communications on the basis of the third generation of mobile communications technology which is most widely used.Cell search is an important physical layer procedure by which a user equipment(UE)acquires downlink synchronization.UE will obtain the downlink system information by demodulating the received physical layer broadcast channel,and achieve uplink synchronization between UE and base station through the random access procedure to obtain uplink resources needed,so as to realize the normal communication between the base station UE.Cell search procedure is consisted of two basic parts : to achieve time and frequency synchronization,to get the Physical Cell Indicator(PCI).While,UE can acquire the time and frequency synchronization,detect cycle prefix(CP)mode and obtain frequency/time division duplexing(FDD/TDD)system identity.Firstly,on the basis of surveying on the research status at home and abroad of LTE –TDD cell search and studying the principle of OFDM(Orthogonal Frequency Division Multiplexing),this paper his thesis analyses the ICI(Inter-Carrier Interference)and ISI(Inter-Symbol Interference)caused by synchronization error,and verify the importance of synchronization techniques for OFDM system through simulation.Secondly,Primary Synchronization Signal(PSS),secondary synchronization signal(SSS),the reference signal(RS)generating mode and mapping in the frequency domain location are introduced in the next part.This paper discusses the downlink coarse and fine timing synchronization and frequency synchronization,analysis and verifies the coarse timing synchronization including that based cross-correlation of PSS sequence,M-part cross-correlation of PSS sequence autocorrelation of PSS,accumulate-correlation of PSS,fine timing synchronization and the secondary synchronization methods.This paper Focuses on how to get the cell ID through the reference signals,CRS-method is compared with traditional method to verify advantage of the former to the latter.Downlink frequency synchronization is another important part in this paper.This paper analyzes the original fractional frequency offset estimation methods include taking use of a cyclic prefix(cycle prefix,CP)repeats estimate,the cost function algorithm and PSS fitting algorithm.Aiming at the CP algorithm has the shortcomings which are high speed but low accuracy and cost function algorithm high accuracy but slow speed,an improved cost function algorithm is proposed and to be verified through simulation.