Based On The Frequency Of The Ofdm System To Capture And Tracking Algorithm

Orthogonal frequency division multiplexing (OFDM) is researched more and more in recent years.OFDM divide a channel to a serial of sub-channel with a approximate plat frequency spectrum feature . The receiver resisted multi-path fading by combining all the signals in the sub-channels.Compared to the single carrier system,OFDM system has more restricts on synchronization precision. In high dynamic circumstance, there is Doppler frequency, and its various order derivation in which one order derivation is called Doppler rate .All of the uncertainty about the frequency increased the complexty of estimation. This paper researched the effection of system performance in high dynamic circumstance,and improved a frequency synchronization method by estimation not only form time domain but also frequency domain instead of the traditional ones only capture and track from time domain. Then the simulation result is given.Considering the special place of high dynamic mobile circumstance, this paper analyzed the typical algorithm of estimation Doppler frequency and Doppler rate:LS ,ML and Extended Kalman Algorithm,and gave the simulation result.In chapter one, this paper introduced the history of OFDM ,the application of OFDM, and the research actuality, described the frame of OFDM systems first, analyzed the impact of system performance due to synchronization error.Chapter three and four researched several synchronization algorithm , which can be applied in plat circumstance or high dynamic circumstance .At last, chapter five summarized the work of the paper and discussed the future of frequency synchronization.The improvements of the paper are as follows: First, chapter three gived a design of frequency estimation loop with not only the time domain but also the frequency domain. The simulation result indicated that the impoved loop can both keep a low RMSE performance and enlarge the scale of frequency estimation compared to the loop only with time domain capture.Second, chapter four improved the pahse estimate method in LS algorithm. The old method will give a wrong phase when the move acceleration is a negative value or a changed one. The improved method avoid these instances and give a precise phase recovery result.