OFDM中基于CP的最大似然估计同步技术

Maximum likelihood estimation synchronization technology based on CP at OFDM system

在OFDM系统中,实现符号定时和载波频率同步是实现OFDM技术的关键。一种盲同步算法是基于CP(循环前缀)的最大似然估计,该算法利用CP与该符号尾部数据的相关关系来实现符号定时和载波同步。然而使用这种算法当信号在时变多径信道中传输时,系统性能会明显降低。提出一种新型的CP结构,把CP分为两部分,其中一部分是复制前一个符号开头,另一部分是复制当前符号的尾部。CP的个数不变,所以CP的两部分个数各占CP的一半。利用这种新型的CP结构,FFT的起始时刻就可以落到有效数据段内(符号定时误差的绝对值应该小于CP/2)。OFDM的系统性能也能得到明显的改善。

The symbol timing and carrier frequency synchronization is the key issue of OFDM system. A blind synchronization algorithm is the maximum likelihood estimation based on CP, the algorithm makes use of the correlation between CP and the symbol tail data to realize the symbol timing and carrier synchronization, When the algorithm is used in the signal trausmission at the time varying multipath channel, the performance of the system is decreased obviously. This paper presents a new structure of CP; the CP is divided into two parts one part is copied the symbol header, the other part is the tail to copy the carrent symbol; the numbers are unchanged, the two part of the CP numbers accounted for half of the CP. Using this novel CP structure, the starting time of FFT can fall into the data segment（ the absolute value of the symbol timing error is less than CD/2. The performance of the OFDM system is improved significautly.