The Research On Symbol Synchronization And Channel Estimation In OFDM System

The future wireless mobile communication systems are expected to provide ubiquitous, high-quality, and high-rate mobile multimedia transmission.However, hostile multipath fading radio conditions give rise to serious inter-symbol interference (ISI); even worse, wireless channel are often time varying, which makes the system more vulnerable and more difficult to track the channel state.Orthogonal Frequency Dvision Multiplexing (OFDM), which is inherently resistant against ISI, has invoked a popular research interest in recent years, and has been a promising candidate technology of the physical layer for future weideband high-date-rate wireless communications.Notwithstanding,OFDM is much more vulnerable to errors of both time and frequency synchronization and to that of channel estimation, and how to obtain correct timing and channel estimation efficiently is highly critical to OFDM systems.The dissertation will focus on both of the aspects of OFDM systems mentioned above.Firstly, in this dissertation,two types of symbol start time estimation schemes for Orthogonal Frequency Division Multiplexing (OFDM) systems are evaluated and analyzed.Simulation results suggest that:pilot symbol based synchronization has better performance over cyclic prefix based schemes,and it performances improved when the length of pilot symbol increases;cyclic prefix based synchronization method has a high spectrum efficiency in spite of its relative low acquisition of synchronization rate;and the former is more suitable to bursting symbol based information systems,such as IEEE802.11a,while the later can be used in broadcasting systems for continuous media streams,such as digital video broadcasting systems,digital audio broadcasting systems.Secondly, the dissertation proposes a novel blind symbol-timing scheme for OFDM systems based on cyclostationarity feature of received symbols.The proposed schemes also exploits the periodicity of OFDM symbol introduced by cyclic prefix, by applying 2-dimentional Fourier transformation and choosing the appropriate correlation peak value as the symbol start location, the precision of this scheme is higher than previous conventional method.Thirdly, the dissertation presents analysis with regard to channel estimation of OFDM systems.Several interpolation algorithm in OFDM systems which based on pilot sequence have been analyzed in the first instance,and the influence of the channel noise on interpolation precision has discussed.The theoretic analysis and simulation results show that:the interpolation error induced by the precision of interpolation procedure itself has out weight...