Research On LTE Downlink Synchronization Algorithm

3GPP initiated research projects of Long Term Evolution(LTE) for satisfied the demandsof next-generation wireless mobile broadband services.OFDM is a technology of multi-carriermodulation as one of the key technologies of the LTE physical layer. It is very important forOFDM system to obtain more accurate time and frequency synchronization, because OFDMis very sensitive to time and frequency offset.Downlink synchronization procedure and the corresponding synchronization algorithmsin TDD-LTE are researched in this paper. LTE downlink synchronization procedure includessynchronous capture procedure and synchronous tracking procedure. In the synchronouscapture stage, terminal obtain the regular position, the frequency offset estimation and sectorID by using primary synchronization signal (PSS). Commonly used timing algorithmsincludes correlation algorithm, cross-correlation algorithm and algorithm integratedautocorrelation and cross-correlation algorithm. Coarse frequency offset estimation algorithmincludes three algorithms. Frame synchronization and cell ID are obtained by using secondarysynchronous signals SSS, SSS detection algorithm includes coherent detection algorithm andnon-coherent detection algorithm. In the synchronous tracking stage, terminal obtain theamount of time and frequency adjustment by using Cyclic prefix (CP) or pilot (RS), therelated estimation algorithms include frequency offset estimation algorithms of time domainand frequency domain.In this paper, TDD-LTE link simulation platform is constructed and a variety ofalgorithms in downlink synchronization process are simulated. The result of simulation showsthat in the synchronous capture stage, cross-correlation algorithm achieves the bestperformance in three kinds of synchronization algorithms of PSS coarse timing, PSS coarsefrequency offset estimation algorithm1and algorithm2are drop in performance affected bytiming, coarse frequency offset estimation algorithm3can improve the performance in caseof larger frequency offset, but the disadvantage of this algorithm is that it can only completeinteger times frequency offset estimation. In the secondary synchronization signal detection algorithm, we can find that the performance of coherent detection is better than thenon-coherent detection by simulation in case of small frequency offset. In the case of largefrequency offset, with the increase of SNR, the performance of coherent detection algorithmis worse than partial coherence algorithm of non-coherent detection algorithms, theperformance of differential coherent detection algorithm is worse than partial coherencedetection algorithm. In the synchronous tracking stage, firstly, frequency offset estimationalgorithm of frequency domain is simulated, and the performances of frequency offsetestimation algorithms under several kinds of pilot symbols combination are compared bysimulation. Finally, frequency offset estimation algorithms of time domain and frequencydomain are simulated, and the performances of frequency offset algorithm before and afterjoining the smoothing algorithm are compared. According to the simulation, we can find that,whether smoothed or not, time domain（TTI）algorithm is better than time （symbol）domainalgorithm, and frequency domain algorithm is better than time domain algorithm.