利用循环前缀的OFDM系统定时同步算法

Novel time synchronization algorithm using the cyclic prefix for OFDM systems

在频率选择性衰落信道下,由于符号间干扰(ISI)的存在,利用循环前缀(CP)的最大似然正交频分复用(OFDM)系统同步算法性能较差.首先,通过改善循环前缀"集相关"特性存在的缺陷,提出了一种新的定时度量函数.利用无符号间干扰区间内的采样点,对相隔OFDM符号长度的两个数据块进行相关运算.其次,提出新的检测函数,在由定时度量函数最大值和循环前缀长度确定的区间内,搜索检测函数的最大值,得到定时偏移估计值,完成定时同步.仿真结果表明,在频率选择性衰落信道下,与已有算法相比,本算法定时偏移估计值期望更接近理想值,均方差更小,复杂度更低.

Due to the intersymbol interference（ISI）,the Maximum Likelihood（ML） algorithm using the cyclic prefix（CP） in orthogonal frequency division multiplexing（OFDM） systems performs poorly in frequency selective fading channels.Firstly,a novel timing metric is presented,which avoids the disadvantage of ensemble correlation.Using the sample data that is not affected by the ISI,the novel algorithm performs correlation operations between two data blocks which are a distance of an OFDM symbol length apart from each other.Secondly,we propose a novel detection function.By searching its maximum in a search range decided by the maximum of the timing metric and the length of CP,the timing offset is gained and the time synchronization can be obtained.Simulation results show that the novel algorithm has more accurate time offset estimation,smaller Mean Square Error（MSE） and lower complexity in frequency selective fading channels.