Slot Synchronization Technology For Photon Detected PPM Signals Based On Early-late Gate Tracking

The laser communication system combining the Pulse Position Modulation(PPM)and photon-counting detector arrays has attracted extensive attention in the deep space optical communication because of its high energy efficiency and strong anti-interference ability.The deep space optical communication features harsh communication environment.The influence of background light noise,delay jitter and other photon detection channel characteristics imposes serious interference on the detector arrays signal,resulting in unsatisfactory synchronization performance of the receiver.In this sense,realizing accurate synchronization is an urgent issue to be solved.The closed loop synchronization method,due to its need for closed loop tracking,can adjust and synchronize the received signal in real time,which features high tracking accuracy and good dynamic adaptability.Therefore,in the deep space optical communication system,it is worth studying deeply to achieve deep space optical PPM slot synchronization through the early-late gate.Considering the photon offset in the PPM slot under the Poisson channel when using the existing early-late gate to perform timing error detection,which results in not necessarily accurate timing error detected by timing error device.In this thesis,according to the photon offset,the optimization processing technology for the error signal is proposed.The existing timing error calculation formula is corrected by using the integral value of the photon pulses of the photon offset part.Simulation results show that the closed loop synchronization scheme after optimization of the error signal can effectively achieve PPM slot synchronization and has fast capture tracking speed in worse deep space environment(large jitter and background),and the bit error rate performance of the system is also superior to the closed loop synchronization scheme that is not optimized.In addition,the atmospheric turbulence will cause serious interference to optical signal,resulting in deep fading of optical signal,or even causing communication interruption.So,in this thesis,a method of Kalman filter for the sampling location is considered to replace the loop filter in the deep space optical PPM closed-loop system.At the same time,considering the parameters such as jitter and background noise,the expression of observed noise covariance under this filter model under Poisson channel is deduced.Simulation shows that the expression has certain reliability.Then by comparing and simulating the optimized closed loop synchronization scheme based on different filters in Poisson channel,the effectiveness of Kalman filter is verified.Finally,it is applied to the fading channel.Simulation results show that the optimized closed loop synchronization scheme based on the Kalman filter can be well adapted to the great-fading channel environment.