中文摘要：

正交频分复用（OFDM）作为未来移动通信的主导技术,研究将OFDM应用于铁路环境下的相关技术———在铁路无线衰落信道下的同步和信道联合估计具有重要意义。由于在OFDM系统中,定时同步、频率同步和信道估计之间存在着密切的联系,本文对此进行研究,建立了频率选择性衰落信道下的OFDM系统模型,设计估计帧结构和基于最大似然准则的定时同步、载波同步和信道参数联合估计的代价函数,进而提出联合估计算法。通过仿真验证所提算法,并得到如下结论：联合同步与信道估计,可以使系统整体性能得到优化;精确估计会改善系统性能,但多次迭代改善有限,特别是在低信噪比的情况下,所以建议采用粗估计和一次精确估计以达到较好的效果。

英文摘要：

As the dominant technology in future mobile communication,Orthogonal Frequency Division Multiplexing（OFDM） is studied for its application in the field of railways.Synchronization and combined channel estimation in wireless fading channels are the most significant correlated technology.In this paper, timing synchronization,frequency synchronization and channel estimation are studied,which have intimate relationships in OFDM systems;the OFDM system model i n frequency selective fading channels is set up;the frame structure for estimation and the cost function of combined estimation of timing synchronization,carrier synchronization and channel estimation based on the Maximum Likelihood Criterion are designed;and then,a combined estimation algorithm is proposed.Simulation results show as follows： Combined synchronization and channel estimation are able to optimize the integrated capacity of the system;accurate estimation is able to improve the performance of the system,but the improvement is limited through multiple iteration,especially when the SNR is very low.Coarse estimation and accurate estimation for one time are suggested so as to achieve better effect.