Study Of Frame Synchronizationalgorithms And Related Technologies For OFDM Systems

Nowadays Orthogonal Frequency Division Multiplexing(OFDM) has become a key technology for 4G systems for its high spectral efficiency and robust capability of resisting multipath interference. But OFDM system is very sensitive to the timing and frequency offset because of its high requirement for the subcarriers'orthogonality. So synchronization is the key problem for OFDM system. In lack of necessary synchronizer, the orthogonal property of subchannels will be destroyed, it will introduce intercarriers interferences ( ICI). Therefore it must be of practical significance to research on synchronization algorithm..First of all, this thesis depicts the main principle of OFDM system and the affect of wireless fading channel on OFDM signal. then it describes the effect of the timing offset and frequency offset on the system in detail, and then analyses two classic frequency and timing synchronization algorithms, i.e., the ML(maximum likelihood)algorithm based on the CP and the Schmidl's algorithm based on the PN training sequence.The thesis systematically analyzes the frame timing synchronization algorithm suitable for IEEE802.11a and the modified method of frame timing estimation which is suitable to IEEE802.11a is proposed. In IEEE 802.11a system , the data are transmitted in burst frames and there exists a preamble, which is composed of ten repeated short training sequences and two repeated long training sequences in front of each frame. A modified method of frame timing estimation is proposed. This algorithm is based on the conjugate symmetry feature. It can reduce computation amount but for exchange of real and imaginary parts while in sampling, which is of good practical values.