| As a green and efficient centralized architecture,C-RAN(Cloud Random Access Network)is an important direction for the evolution from LTE to 5G.The centralized base station processing mode,which is the new trend of wireless communications in the future,has drawn attention since its launch.With the increase of the number of subscribers and base stations,how to reduce inter-user interference becomes the focus.LTE uplink reduce the interference between users by ensuring the synchronization between users and base stations.Therefore,accurate uplink synchronization plays an important role in ensure the communications process.This article focuses on how to achieve more accurate and efficient uplink synchronization in the C-RAN’s centralized architecture and user-centric model.1.Studied the features,advantages and application scenarios of C-RAN architecture.The comparison between the two merging modes of CoMP(Coordinated Multipoint)technology under C-RAN architecture is also provided,which also provides the idea for the joint estimation of TA(Timing Advance).2.Simulated different timing synchronization algorithm.The ML algorithm based on CP(Cyclic Prefix),the S&C algorithm based on training sequence,the improved Minn algorithm and the Park algorithm are all estimated by the redundancy characteristics of the sequence.The DMRS algorithm is based on the reference signal phase-shift from the DFT transformation of the shift in time domain.The DMRS algorithm is used as a basis for subsequent consolidation algorithms without the additional introduction of sequence occupancy resources and the estimation range is not limited by the sequence length.3.Proposed a new algorithm for joint uplink synchronization and TA estimation for multiple base stations by a user under the user-centric model.The algorithm estimates the TA value separately by each base station,and performs joint TA estimation according to the power and the rate of change of power of the received signal,to ensure that the user keeps the synchronization with the base station cluster all the time by updating the TA estimation.Compared with the traditional algorithm that only synchronizes with the main base station,the joint synchronization algorithm reduces the synchronization error of the whole system.Through the study of the relationship of the distance between base stations and the signal coverage,it can be seen that the accuracy of timing estimation of joint TA estimation improves obviously when base stations have similar distance with UE.Finally,the thesis summarizes all the work,including the work done,the results,the deficiencies and the next work plan. |
