Research On Downlink Synchronization In LTE System

LTE uses the OFDM modulation technology in the physical layer, OFDM technology can effectively improve the system throughput and spectrum utilization. But at the same time, it faces the problem of high precision synchronous demand technologh. Therefore, the research on downlink synchronization has a good theoretical significance and practical value.This paper focuses on the process of downlink synchronization in LTE system and the corresponding synchronization algorithm, including the capture stage and the tracking stage. The capture stage is mainly based on the detection of PSS and SSS signal to achieve the initial timing synchronization and coarse frequency offset estimation. The coarse timing position, coarse frequency offset estimation and ID value within the cell group are obtained by PSS detection. The algorithm for obtaining the position of the coarse timing synchronization is the time domain cross correlation algorithm, partial correlation modulus accumulation algorithm and “PMF+FFT” algorithm. The SSS detection can obtain the cell group ID and frame synchronization, the corresponding algorithm has the frequency domain cross correlation algorithm and parity sequence correlation detection algorithm. The tracking stage is based on the channel estimation of the reference signal. The residual time and frequency synchronization error information are obtained by the time tracking algorithm and the frequency synchronization tracking algorithm. It can correct the time and frequency for the current subframe.In this paper, a link level simulation platform is set up according to the standard of LTE physical layer, and the simulation of various algorithms is carried out. The simulation results show that, in the capture stage, the timing synchronization performance of the “PMF+FFT” algorithm in the coarse timing synchronization detection is the best under the condition of large frequency offset and low signal to noise ratio. The performance of the frequency domain cross correlation algorithm is better than the parity sequence correlation detection algorithm. However, the parity sequence correlation detection algorithm is better than the frequency domain correlation algorithm in the implementation complexity, and it is widely used in practice. In the tracking stage, the time and frequency synchronization error is further reduced, and the synchronization state is maintained by the time tracking algorithm and the frequency synchronization tracking algorithm. Simulation results and theoretical analysis of various algorithms are consistent. In this paper, a set of downlink synchronization algorithm in LTE system can meet the performance requirements.