Research And Improved Design On Synchronization Algorithms For OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) has become the key technique in broadband wireless access and the next generation mobile communication system.It is an attractive transmission scheme for telecommunication systems due to its high spectral efficiency, high data rate and well anti-multipath ability and so on. But OFDM system is very sensitive to the synchronization errors than single carrier system. The timing synchronization errors will introduceinter-symbol interference (ISI), while the carrier frequency errors will introduce sub-channel interference (ICI). It is important for OFDM system to obtain accurate symbol timing and carrier frequency synchronization. This paper analyses some typical symbol synchronization algorithms and the carrier frequency synchronization algorithms in depth. It analyses and compares their performances, and proposed a novel synchronization method based on the down-sampling of the received signal and local sequence for the OFDM system. The main thesis is as follows:Firstly, a brief introduction about the present situation of the mobile communications, which tells the important role of the OFDM technology played in the future mobile communication.The paper elaborates the basic structure of the OFDM system, the basic principles of OFDM system, critical applications, and its key technology, focuses on that the synchronization technology is critical in OFDM systems, the main principle of synchronization errors, variety of synchronization algorithms,and their performances on OFDM system.Secondly,it discusses the synchronization algorithms based on training sequences, analyses the synchronization technology in OFDM systems, the impact on system performances in depth, as well as several typical algorithms.The main work of this part is that the analysis of several typical algorithms,such an SC,Moose PH and PC algorithm,simulates these algorithms on Matlab,compares the probability of error, mean square error performances with each other, analyses their advantages and disadvantages in the synchronization performance.Finally, according to the original SC algorithm analysis above, summed up its inadequacy, that is, the judgment function has a platform effect, which seriously affects the symbol timing estimation and frequency offset estimation’s accuracy. For this reason, a new joint symbol timing and carrier frequency synchronization method for this system is proposed based on the down-sampling of the received signal and local sequence, and then implements it on Matlab simulation platform, and compare it with the original SC algorithm. Simulation result shows that compared to the original SC algorithm, the proposed novel synchronization algorithm based on the down-sampling of the received signal with the local sequences has a better estimation performance, the estimated value is more accurate, much closer to the theoretical value.