Research On Algorithm Of Synchronization In OFDM System

In the wireless mobile channel, Extensive attentions have been paid to Orthogonal Frequency Division Multiplexing (OFDM) due to its high spectral efficiency, high data rate and well anti-multipath ability. It is regarded as one of the best transmission method in the future wireless broadband communication, it is the key technique of the fourth generation mobile communication. However, OFDM systems are extremely sensitive to synchronization error. When synchronization error exits, Serious Inter-Carrier Interference and Inter-Symbol Interference are introduced and the systems performance will be degraded greatly. So keep accurate is essential to OFDM systems. Accomplishments to timing synchronization problem of OFDM in this paper were done as follows:Firstly, the maximum likelihood estimation algorithm based on cyclic prefix and the maximum correlation estimation algorithm are introduced, and the results are described in detail by computer simulation.Secondly, in-depth research on serial symbol timing synchronization algorithms based on training sequence, towarding the shortcomings of the phantom which result in ambiguity of timing estimation and multi-peak in the conventional methods, an improved method based on new training sequence is proposed. The real-valued PN sequence are interposed only in the even number of the subcarriers in frequency domain, the length of the PN sequence is half of the OFDM signals, After IDFT we can get the new training sequence with character of symmetric and conjugate. By finding the maximum value of the timing metric to estimate the starting point of the OFDM signal. The performances of several algorithms are analyzed by computer simulation, at the same time, the advantages and disadvantages are pointed out about the several algorithms. Finally, To improve the efficiency of bandwidth, this paper proposes a method of frame synchronization applying parallel mismatch sequence.That makes use of the auto-correlation property of the mismatched sequence and the effective sidelobes suppression in the wireless mobile communication systems, the received sequence at the receiver is correlated with the sequence of the mismatched filter coefficient to find the largest part of the relevant points to estimate the starting point of the OFDM frame synchronization. Through the MATLAB simulation, it compared with the m sequence of the same length in multipath fading channels, the results of simulation by MATLAB verified the feasibility of this paper, and provided the direction of the further research aspects.