Timing Synchronization Technology Of Asynchronous Clock Sampling Signal Based On PPM Modulation Optical Communication

In the deep-space optical communication,the pulse position modulation(PPM)technology has been widely concerned because of its high power utilization.Since the asynchronous clock sampling does not need closed-loop clock tracking,it has simple system structure and and easy for realization.So it has been widely applied in digital receiver.However,there also exists timing error during the process of asynchronous clock sampling,which can cause the actual sampling point position to deviate from the best sampling point position,and thus reduces the synchronization performance of the described system.So it is necessary to accurately predict the clock error to correct the timing error.After PPM modulation,when the light pulse signal passes through the photon detector detection in the channel transmission,there will be time slot broadening phenomenon due to the impact of delay jitter.The digital receiver often only has the corrective effect on the timing error of the signal interpolation without considering the broadening phenomenon.So,the performance of the described system fails to be optimized.Therefore,it is worthy of studying the PPM modulated asynchronous sampling signal in the accurate estimation of timing synchronization parameters and signal recovery.In this thesis,two kinds of data recovery schemes are proposed for the data recovery problem of asynchronous sampling signal under the condition of PPM modulation pulse broadening.The first scheme is based on the incorporation of interpolation of pulse broadening waveform and broadening effect compensation.In the first scheme,the interpolation and pulse broadening effect compensation are realized according to the weight coefficient.The second is based on the separation of interpolation and pulse broadening effect compensation.In the second scheme,the standard interpolation formula is used for interpolation according to the clock error,and then the broadening effect compensation is performed.The simulation results show that the two schemes can effectively solve the problems of slot sampling error and pulse broadening effect,and complete the data recovery of PPM modulation signal.Compared with the second scheme,the combined data recovery scheme has better performance and small calculating amount,and can realize the data recovery of the PPM-modulated asynchronous sampling signal.In addition,aiming at the estimation of the timing error of the PPM modulated asynchronous sampling signal,the scheme of SCPPM code-aided iterative timing synchronization has been studied in this thesis.Since the general maximum-likelihood criterion is relatively complicated,the EM algorithm iteration is used to estimate the timing synchronization parameters.However,the simulation results show that the SCPPM code-aided iterative timing synchronization scheme based on EM algorithm has smaller effective synchronous ranges,and its synchronization performance is poor in the condition of relatively large timing error.Therefore,the scheme of SCPPM code-aided iterative timing synchronization in the condition of large timing error has been proposed in this thesis.The scheme firstly constructs the evaluation function through the soft information of the SCPPM decoded output to carry out the coarse synchronization in the relatively large ranges,and then carries out the fine synchronization of timing error in the small ranges through the EM iterative algorithm.The simulation results show that the synchronization scheme proposed in this thesis can greatly improve the effective range of timing synchronization.