Studies On Synchronization Technique In OFDM Systems

Because of its advantages of high spectrum utilization rate, powerful capability of resisting multi-path interference and others, OFDM technique has been used in many fields of wired and wireless wide band data communication. It is also been regarded as one of the core technologies for the fourth generation mobile communication. But symbol timing error and carrier frequency offset are main factors restricting application of OFDM system. This paper researches some classical symbol synchronization algorithms and carrier frequency offset synchronization algorithms both at home and abroad, and put a rigorous demonstration and deep research on the performance of these algorithms in high–speed multi-path fading environment ,thus to seek a sort of synchronization scheme which is applicable in high–speed multi-path fading environment. Main works and innovation of this paper include:Firstly, through theoretical analysis of characteristics of wireless channel, this paper summarizes the characteristics of wireless channel in high–speed multi-path fading environment and its effect on signal, introduces and simulates the wireless channel model used in this paper.Secondly, via simulation, this paper places emphasis on analyzing the effect of symbol synchronization error and frequency synchronization offset on system's performance based on deep analysis and research on OFDM system's principles. Then, it compares and analyses some kinds of symbol synchronization algorithms and frequency offset estimation algorithms in high–speed multi-path fading environment. Toward symbol synchronization algorithm, it mostly compares and analyses the performance of Maximum Likelihood symbol timing synchronization algorithm based on cyclic prefix, symmetric algorithm based on conjugate symmetric training sequence, Schmidl & Cox algorithm, Minn & Letaief algorithm and Park & Cheon algorithm and so on. Toward frequency synchronization algorithm, it mostly compares and analyses the performance of time-domain coherence algorithm based on training sequence, frequency offset estimation algorithm based on pilot, integer frequency offset estimation algorithm based on pilot, integer frequency offset estimation algorithm based on repeated PN sequence and so on. Moreover, analyses and indicates their advantages, disadvantages and applied areas through simulation.Finally, a synchronization scheme is proposed for solving OFDM system's synchronization realization problem in high–speed multi-path fading environment based on analyzing and comparing all kinds of algorithms. This scheme combines symbol synchronization,decimal frequency offset synchronization,integer frequency offset synchronization ,channel estimation ,etc. Via simulation and analysis, it indicates that this scheme can control frequency offset estimation error in a small range based on getting symbol fine synchronization, its calculation quantity is little and estimation precision is high, it can realize symbol synchronization, frequency offset capture, frequency offset tracking and other synchronization tache in high–speed multi-path environment effectively. The interrelation of frequency offset estimation and channel estimation can also be got from the result.