摘要
研究了基于多像素光子计数器的光脉冲位置调制(PPM)通信系统开环同步及数据恢复技术。首先,对PPM异步采样信号进行快速傅里叶变换;然后,用Quinn、Jacobsen和MacLeod算法分别估计信号的初始频偏及时延偏差;其次,由频偏和时延偏差估计值及相关运算恢复PPM信号的光子数,进而求得三种算法对应的三组时隙对数似然比序列;最后,从三组时隙对数似然比序列中选择标准差最大的序列作为纠错译码器的输入。仿真及实验结果表明,该时隙同步方法在极低的光功率下同步精度高、运算速度快、鲁棒性强且易于实现;对于64PPM调制信号,本算法平均每信号时隙只需要探测1.33个光子,就能使误码率小于10^(-5)。
Objective Because of the extremely long communication link in deep space,the detection signal is easily affected by channel characteristics such as background light noise and delay jitter,and the output signal-to-noise ratio(SNR)is very low,which leads to the poor synchronization performance of a receiver.Therefore,it is very important to achieve precise synchronization at low SNR.In general,pulse position modulation(PPM)slot synchronization is mainly in the form of closed-loop tracking,such as phase-locked loop and early-late gate,and the system design is complex.According to the estimation of timing error of the training sequence inserted periodically,the open-loop synchronization is realized,which will waste certain transmitting power.Using the maximum likelihood synchronization method of the guard slot,this method can reduce the computational complexity effectively,however,the bit error rate(BER)will be obvious when the signal power is high.The slot synchronization method of a photon detector array based on photon arrival time measurement requires complexity that is still high.The clock synchronization method based on the fast Fourier transform(FFT)has fast computing speed and the support of underlying hardware.It is suitable for real-time signal processing and has been widely used in wireless communication and optical fiber communication.However,the error of the signal parameters obtained directly from the FFT line spectrum is sometimes very large,which requires frequency correction.However,the single frequency correction method is not robust.We will apply the classical FFT algorithm to the photon-detected PPM communication system in slot synchronization.A method of PPM open-loop synchronization is proposed by selecting the optimal value from the Quinn,Jacobsen,and MacLeod algorithms.To solve the problem that the existing data recovery methods are inaccurate,a data recovery method based on correlation detection is proposed.Methods The optical PPM signal is sampled asynchronously more than twofold and passed
作者
向劲松
张少华
Xiang Jinsong;Zhang Shaohua(School of Communication and Information Engineering,Chongqing University of Posts and Telecommunications,Chongqing 400065,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第9期143-152,共10页
Chinese Journal of Lasers
基金
国家自然科学基金(61571072,61371096)。
关键词
光通信
脉冲位置调制
多像素光子计数器
时隙同步
数据恢复
optical communications
pulse position modulation
multipixel photon counter
slot synchronization
data recovery
