基于ES-CAZAC序列的CO-OFDM系统定时同步算法  

Timing synchronization method based on ES-CAZAC sequences for CO-OFDM systems

作　　者：李莉[1] 吴迪[1] 韩力[2] 胡贵军[1] 

机构地区：[1]吉林大学通信工程学院,吉林长春130012 [2]吉林大学物理学院,吉林长春130012

出　　处：《光电子．激光》2015年第9期1692-1699,共8页Journal of Optoelectronics·Laser

基　　金：国家自然科学基金(61177066)资助项目

摘　　要：针对传统基于复伪噪声(PN)序列的定时同步算法在相干光正交频分复用(CO-OFDM)系统中存在定时度量函数模糊和峰均功率比(PAPR)高的问题,提出了基于偶对称恒振幅零相关(ESCAZAC,even symmetry constant amplitude zero auto-correlation)序列的定时同步算法。改进算法训练序列包含两部分,并将这两部分看作两个窗口,利用偶数长度的CAZAC序列具有偶对称特性分别计算两个窗口的相关度,通过两个窗口同时得到最大相关度来确定正确定时点。分别在高斯白噪声信道和10Gbit/s的CO-OFDM系统上进行仿真。结果表明,改进算法在不增加算法复杂度的情况下,能得到十分尖锐的定时度量函数,并且几乎没有旁瓣的干扰。在CO-OFDM系统下,改进算法的旁瓣模糊度较Park算法减少26.7%,在色散常数较大的情况下定时均方误差(MSE)仍在10-5左右,定时精准。同时,ES-CAZAC训练序列具有理想的PAPR值。Since the traditional timing synchronization algorithms based on complex pseudo noise （PN） sequence have ambiguity timing estimation and a high peak to average power ratio （PAPR） ,we propose a timing synchronization algorithm based on even symmetry constant amplitude zero auto--correlation （ES-CAZAC） sequences for coherent optical othogonal frequency division multiplexing （CO-OFDM） system. This algorithm relies on the good properties of CAZAC sequence .. low PAPR and even symmetry of even length sequence. The training sequence consists of two different CAZAC sequences, which are re- garded as two windows respectively. After using the even symmetry property to calculate the correlation degree of the two windows,we can get the correct timing point only when the two windows have a maxi- mized correlation degree simultaneously. The modified algorithm is tested both in a Gaussian white noise channel and 10 a Gbit/s CO-OFDM system. The results show that the modified algorithm gives a sharp timing metric function without increasing any complexity. In the CO-OFDM system, compared with Park＇s,the degree of side lobe ambiguity for modified algorithm decreases by 26.7%. In a large disper- sion system,the mean square error （MSE） of the modified algorithm maintains 10-5 ,which means a correct timing estimation. At the same time,the ES-CAZAC sequence has an ideal PAPR value of 0 dB. The modified algorithm with a low complexity, an ideal PAPR and a high accuracy is suitable for the high speed CO-OFDM system.

关 键 词：相干光正交频分复用(CO-OFDM) 定时同步 恒振幅零相关(CAZAC)序列 

分 类 号：TN913.7[电子电信—通信与信息系统]