Research Of OFDM Synchronization Technologies Based On Training Symbol

In the recent years, Orthogonal Frequency Division Multiplexing (OFDM) has gained much interest of researchers. This technique has high spectral efficiency and is an effective transmission scheme for counteracting multipath fading, and it has been widely used in Digital Video Broadcasting for Terrestrial(DVB-T), Integrated Service Digital Broadcasting for Terrestrial(ISDB-T), and Asymmetric Digital Subscriber Line(ADSL). Now it is thought to be a major technique for the fourth generation communication system. As a multi-carrier modulation technique, OFDM is very sensitive to synchronization error, so the synchronization method for OFDM is a very important task.This paper discusses on OFDM synchronization technologies based on training symbol. The main creativities are the followings:1. Research on the synchronization method for OFDM in Wireless Channel. An improved joint time and frequency synchronization algorithm for OFDM is proposed. The improved algorithm can get high accuracy for both frequency offset estimation and timing estimation, and can solve the problem of timing synchronization when the first path is not the strongest path in Wireless Channel. A joint algorithm with high frequency offset acquisition probability is also proposed for OFDM in the timing-variant multipath Channel, in which equal power paths may occur. It can not only solve the problem of timing synchronization when the first path is not the strongest path, but also get high probability of frequency offset acquisition.2. Research on the one-training-symbol fast synchronization method for OFDM. When the first path is the strongest path in the channel, only one training symbol is needed for joint synchronization. An improved one-training-symbol fast synchronization method is proposed, which can get high accuracy of frequency offset estimation and fast synchronization speed. The performance of the algorithm which uses conjugated-symmetrical-structured training symbol in multipath is also analyzed, and the channel environment where this kind of algorithm works well is given. Finally, by introducing the coarse synchronization process into the algorithm which uses the symmetrical-repeated-structured training symbol, the computational complexity of the algorithm is reduced.3. Research on the synchronization method for OFDM based on time domain PN training symbol. The synchronization algorithm which can design the training symbol freely is studied and a conclusion is drawn: In AWGN channel, this kind of algorithm can choose the PN training symbol freely, so it can be extended flexibly to any other method that a known training symbol is used for timing synchronization, channel estimation, equalization and other purposes. But in multipath channel, the performance of frequency offset estimation is affected by the training symbol itself, the weighted factors, correlation length and channel delay, so it cannot choose the training symbol as freely as in AWGN Channel. Otherwise, the accuracy of estimation will be reduced or the algorithm will fail. Finally, by introducing the differential relations into a kind of orthogonal PN sequence, a joint algorithm using the PN sequence as the training symbol can be got, and it can find the timing position accurately.