Clock Synchronization Technology For Optical PPM Signal With One Sample Per Slot In Deep Space Optical Communication

In deep-space optical communications,the power of the airborne terminals is extremely limited and the resource is very valuable.It's widely recognized that the photon detection array and the pulse position modulation(PPM)are two key technologies in enhancing the energy exchange efficiency at the launch terminal.However,the deep-space optical communication is mainly featured with extremely remote communication link with large energy consumption,which may bring about heavy signal attenuation at the receiver and low SNR ratio.It is difficult for the receiver to realize accurate clock synchronization and data recovery.It becomes more difficult to complete the clock synchronization of the PPM signal and reliable data recovery especially when the asynchronous clock sampling is conducted at single PPM slot frequency for the rather less data collected and weak ability of anti-delay jitter.Therefore,this thesis conducts research on the clock synchronization and data recovery of the data signal at single PPM slot frequency.The data collected is rather less and the signal is easily to be damaged and being affected by the pulse displacement error caused by the delay jitter when the sampling frequency signal is single sample per slot.To resolve the above problems,this thesis proposes the data recovery technology of delay sampling based on single PPM slot frequency.In the plan,the output signal of the photon detection array is divided into two groups.The signal sampling of the even group will be carried out half a slot time later than the odd group,then the two sets of sampling data are merged and interpolated are conducted respectively in order to complete the data recovery.The simulation result shows that the delay sampling can effectively reduce the signal loss in traditional sampling and restrain the pulse misplacement error caused by the delay jitter when the sampling frequency is one sample per slot.Aiming at the photon detected optical PPM communication system of asynchronous sampled with one sample per slot,this thesis proposes a clock synchronization scheme based on guard slots.One or more guard slots are inserted into each PPM symbol in the transmitter.Due to the fact that there are only background photons in these guard slots,while in the other slots there are both background photons and signal photons.Depending on these features,we can achieve clock synchronization.Clock synchronization is mainly divided into two parts: timing coarse synchronization and timing fine synchronization.The sampling data of the receiver are cyclically accumulated with the numbers of slots in PPM symbol.We achieve the coarse timing synchronization based on the statistical characteristics of photon in guard slots.After completing the timing coarse synchronization,three fine synchronization scheme is proposed in this thesis.The interpolation search method is used for one of the fine timing synchronization.The other two fine synchronization schemes are joint precision estimating combined with code-aided,which are based on the guards slot and interpolation matching search.The simulation results show that the proposed method can achieve effective synchronization within the scope of large timing offset,and the synchronization performance is effectively improved when we select the appropriate timing fine synchronization scheme based on the number of guard slots,characteristics of channel,and amount of statistics in the actual optical communication system.