Research And Implementation On Synchronization Technology Of LTE Physical Layer Downlink

LTE is a Long Term Evolution launched by3GPP in March2005. Compared with the third generation mobile communication technology, LTE has some unique features including its high transmission rate and short transmission delay. OFDM multiple access is mainly used in LTE downlink, which is very sensitive for carrier frequency and phase deviation. If carrier frequency and phase deviation is large, Orthogonality between subcarriers will be destroyed, which causes subcarriers and symbols interference and reduces the reliability of the mobile communication system. So Synchronization plays an important role in OFDM system.The paper has introduced the cross-correlation detection algorithm which is based on the primary synchronization sequence, This algorithm completes the cell search process that user terminals can access to the base station. Synchronization in LTE downlink is composed by cell ID search and frequency offset estimation. Cell ID search algorithm is a process that a user terminal in an initial access or cell switching state can acquire cell ID. The paper has made a detailed study on the specifications of the self-correlation of the PSS sequence in the time domain and frequency domain by Matlab simulation platform.The cross-correlation detection algorithm and differential detection algorithm used in frame synchronization are compared, it turns out a result by analyzing the comparison. In addition, the paper find out the periodic distribution phenomenon of differential detection algorithm according to the way of generating PSS sequences, obtained the differential correlation detection algorithm for the main causes of the decrease of LTE downlink synchronization performance.The paper gives the design ideas of carrier frequency offset estimation algorithm for LTE downlink. In a wireless communication system, Frequency offset estimation needs to be done because crystal oscillation has some errors in frequency when receiving the signal, and user terminal generate Doppler shift in High speed mobile environment, which causes Larger receiver frequency shift. The frequency offset estimation is divided into an integer multiple of the frequencyoffset estimation (IFO), a small multiple of the frequency offset estimation (FFO) and the residual frequency offset estimation (RFO). Frequency offset estimation and compensation has a direct impact on the accuracy of each channel’s demodulation, which is very important.The paper has made a research on the design of FFO estimation method assisted with polar based on the CP(Cyclic Prefix) and PSS differential correlation estimation method to calculate IFO considering the characteristic of channel correlation.The design process of the synchronization of LTE downlink receiver have been analyzed in the paper. The paper introduces graphical programming platform Lab VIEW and Lab VIEW FPGA module.The PSS detection and CP type detection module in sychronization part have been finished. The hardware design of FPGA is realized By FIFO(First Input First Output)and Pipeline technology, the hardware program is optimized, which signiticantly reduced the consumption of resources, leave more resources for demodulation and MIMO detection.