Research On Symbol Synchronization Technology Of Broadband OFDM Systems

OFDM(Orthogonal Frequency Division Multiplexing) is a kind of multi-carrier modulation (MCM) technologies.It has a lot of advantages which are strong anti-multipath fading, anti-ISI, anti-narrowband interference and high frequency efficiency, etc.Therefore, it is concerned widely.However, OFDM systems are very sensitive to symbol timing error.Therefore, as an important part of this system the symbol timing synchronization has become the research focus in the modern communication field.The task of the timing synchronization is determining the starting position of each OFDM symbol in receiver, which is the starting position of each FFT window.The wrong timing will result in the FFT window contains two consecutive OFDM symbols in demodulation process, reducing the system performance.Therefore, the research of symbol synchronization for OFDM system is essential.This paper calculates parameters of OFDM transmission system based on the indicator of project, then simulates and compares some typical symbol synchronization algorithm based on two ways of assisted on the data-aided and non-data-aided symbol synchronization algorithm.At last, a new optimal timing synchronization algorithm is proposed to achieve the indicators of project.The algorithm use the CAZAC sequence which has the excellent correlation as training sequence, and use both the structure of the new training sequence and method which is the cross-correlation of the received signal and the local training sequence to determine the timing synchronization position, and use Matlab to simulate. The peak of the timing measurement function of this algorithm is extremely sharp, so the symbol timing synchronization position only needs one step to be determined according to the estimate value and the frame structure.This algorithm is more simple and convenient compared to traditional timing synchronization method having two steps of frame synchronization and symbol timing synchronization.Meanwhile, the algorithm uses the relationship between the integer frequency offset and the correlation characteristics of training sequence, and then estimates the integral frequency offset directly combining with the timing position in time domain, which reduces the computational complexity of synchronization.In multi-path channel, the algorithm can makes the synchronization timing of strongest path of received signal to correct to the first path accurately.The simulation results show that the algorithm has a very good synchronization performance at AWGN channel with low SNR and multipath fading channel, and the indicator can be completed.