Research And Implementation Of Synchronization Algorithm In Multi-path And Fast Time-varying Environment

With the rapid development of 4G mobile communication technologies,LTE-A standard has been widely used in more and more fields.Owing to the use of SC-FDMA,the uplink of LTE-A standard has many advantages in supporting high-speed,high spectrum efficient and high mobile data transmission.SC-FDMA has the characteristics of low peak-to-average power ratio(PAPR),high spectral efficiency and strong anti-fading performance.Under the circumstance of the fast time-varying channel,however,the orthogonality among subcarriers is destroyed by the doppler frequency offset,which impacts the amplitude and phase of the received signal.Moreover,in the multi-path channels,different timing offset between the base station and users could lead to the signal distortion.Therefore,in order to ensure the orthogonality between the carriers in the SC-FDMA system,the receiver and the transmitter need to keep synchronization in both frequency and time.Focusing on the frequency offset and timing offset in multi-user scene of multi-path fast time-varying channel,we propose an improved algorithm,and simulate the classical algorithms and the proposed algorithm in multi-user scenario.In addition,an efficient hardware platform is built for the potential studies of frequency offset and timing synchronization problem in the future.The main contributions of this paper can be summarized as follows:Firstly,we introduce the basic principles of SC-FDMA,which includes its generation methods,mapping scheme,advantages and disadvantages.In addition,we introduce the basic concepts of the LTE uplink including the system model,the uplink frame structure and the demodulation reference signal used for synchronous estimation.Secondly,the frequency offset estimation under fast time-varying channel is investigated.We introduce several classical frequency offset estimation algorithms,elaborately derive the formulas in multiuser scenarios,give the estimated range of each algorithm,and finally obtain the performance of each algorithm at different speeds by Monte Carlo simulations.Considering performance and resources,we give the optimal choice under specific circumstances,which is beneficial for the hardware implementation of frequency offset estimation.Then,we study the symbol synchronization under multipath fast time-varying channel,introduce several classical symbol timing estimation algorithms,and summarize the disadvantages and applicable scope according to the performance analysis.Based on the traditional pilot-based symbol timing estimation algorithm,a novel block iteration algorithm for symbol timing estimation is proposed.The algorithm can be divided into four steps.Firstly,the most suitable pilot symbol is selected.Secondly,the segmented correlation and timing estimation are performed on the selected pilot.Thirdly,the frequency domain correction is performed on the received pilot by using the first estimate.Finally,the final timing estimate is obtained via iterative computations.The simulation results show that,the proposed algorithm improves the estimation accuracy by 20%-40% and reduces the implementation complexity compared with the traditional first-path search algorithm.Finally,in order to track and monitor the frequency offset and timing offset,and to give the statistical analysis,we give the hardware implementation of a frequency offset estimation algorithm and a timing estimation algorithm respectively,which is frequency offset estimation algorithm based on CP and the proposed timing estimation algorithm in this paper.And in order to improve the efficiency of the research,we design a distributed transmission protocol based on automatic identification of MAC address in the structure of Ethernet frame.With the use of protocol,the FPGA implementation of Ethernet communication is realized.With the assistance of the laboratory hardware modules and the upper computer platform,we can simulate the synchronization algorithm.