Timing Synchronization Algorithm In OFDM System Under Multipath Fading Channel

Nowadays Orthogonal Frequency Division Multiplexing (OFDM) is regarded as a promising solution for the next generation wireless communication systems operating in frequency-selective fading environments with their ability of enhancing the data rate in limited spectrum.The thesis will focus on timing synchronization algorithms designed for OFDM receivers with the support by the national 863 project of China, including the algorithm and the performance.Firstly, the development of mobile communication system is traced back. The background of the thesis and projects is introduced. The wireless channel is analyzed in detail. We build up the math model of fading channel, and then research the characters of fading Channel. Then the principal of OFDM system is introduced, with many concerns of its inborn advantage in supporting high-speed wireless transportation.Synchronization is the key technology in OFDM system. In chapter three, the SNR lost in OFDM system due to synchronization errors is studied and we introduce different kinds of the synchronization algorithms of OFDM.In chapter four, the synchronization algorithms in B3G project are introduced. We analyze the performance of different synchronization algorithms and do some changes to the algorithms in the practical operation.In chapter five, we focus on the environment of complex multi-path channel, and we find that exist timing synchronization algorithms are not applied in this environment. In the complex multi-path channel environment, the exist timing synchronization algorithms cause really bad timing error, and it brings difficulties to the signal recovery. Because in this environment, the strongest path is not the first path, and all the timing synchronization algorithms are based on searching the strongest path, so the symbol start position is delayed. The OFDM symbol now lost some data in the beginning part, and in the end it includes some data of the next OFMD symbol, so ISI and ICI are introduced after FFT. The system needs new timing synchronization algorithms. Firstly, we introduce some new timing synchronization algorithms in complex multi-path channel, and we analyze their performances. Secondly, based on the B3G system, we propose a new timing synchronization algorithm using the concept of"sliding sum". In the new algorithm, we do not search the strongest path, but calculate the sliding energy sum of the different path and search the peak of the sum. We find the peak is a plateau, and the last position of the plateau is just the position of the first path, so we get the first path. The new algorithm has a good performance in the B3G simulation system.