Research On Time Delay Alignment And Synthesis Technology Of Photon Detector Array In Deep Space Optical Communication

Pulse Position Modulation(PPM)combined with photon detection arrays have been widely used in deep space optical communication systems due to its high energy conversion efficiency,strong anti-interference ability and high surveying frequency.Because of the deep-space communication link is far away,the transmitted optical signals are susceptible to the influence of background light noise,time delay jitter and other photon detection channel characteristics,and the signal-to-noise ratio of each unit in the optical array receiver extremely low.Therefore,in order to ensure the effective alignment and synthesis of each array unit signal,it is very important to study the time-delay alignment and synthesis technology of photon detection array signal suitable for this scene.Aiming at the problem of time-delay alignment between signals of photon detection array,a time-delay estimation method based on photon position matching was proposed in this thesis.Considering the influence of delay jitter,the relationship between photon position values can be utilized,and the pulse broadening waveform function is used to calculate the matching degree of two photon positions.After matching all the photons detected by each detector,the similarity degree between the photon detector signals can be obtained,and the delay value is determined according to the total matching degree.Based on the photon position matching principle,two photon detection array delay estimation schemes are designed: The first is to align each signal with the maximum signal intensity path as a reference,and then align each signal with it separately.The second method uses a step-by-step composite signal as a reference,and each branch signal is sequentially aligned with the reference signal.The simulation results show that the two array delay estimation schemes based on photon position matching can achieve the time delay alignment of photon detection array signals.Aiming at the problem of signal synthesis of photon detection array,in order to make full use of the effective information of each branch signal,a joint reference time-delay estimation scheme of multi-channel signals is selected as the basic scheme of system synthesis.After the time-delay estimation is completed,the advantages of the existing time error estimation methods based on protection slot and two-dimensional search are combined to deal with large time error.The method of timing error estimation based on protection slot is used,and the method of timing error estimation based on two-dimensional search is used when dealing with small timing error.In addition,the complexity of two-dimensional search is high.In order to speed up the search,an improved method of variable step search is proposed.Finally,after the synchronization operation of each branch signal is completed,the likelihood ratio is weighted according to the reliability of signal photons in different intervals of time slot affected by delay jitter.The simulation results show that the photon detection array synthesis technology based on multi-channel joint reference can synthesize more effective photon information,and ultimately achieve better system synthesis performance.