Research On Digital Reception Technology And Experimental Of Optical PPM Communication Based On MPPC Detection

Pulse Position Modulation(PPM)is the key technology of space optical communication,which has the advantages of high energy efficiency and strong anti-jamming capability.Multi-Pixel Photon Counter(MPPC)has many advantages such as high gain,excellent Photon counting ability,simple structure and low cost.It has been widely studied and applied in laser ranging,laser communication,underwater optical communication and other fields in recent years This thesis mainly carries on the optical PPM communication digital receiving technology and experimental research based on MPPC detection.Firstly,the hardware experiment platform of optical PPM communication based on MPPC detection is built.The whole scheme of the experimental system is given.The transmitter and receiver of the experimental system and the main instruments used in the system are introduced in detail.The transmitter outputs data-modulated optical PPM pulse,which is transmitted through the channel to the receiver,where the optical signal is detected and sampled,and the sampled signal is transmitted to the computer for slot synchronization and data recovery,final decoded output.Secondly,as to the existing photon number recovery method based on MPPC detection,the thesis proposes a data recovery method based on correlation detection from the view of MPPC output pulse area.which does not require photons to be detected at the same time and the pulse amplitude to be superimposed at the maximum.First,the frequency and time delay deviation of the asynchronous sampled PPM signal are estimated by using the Fast Fourier Transform(FFT)Algorithm,then the sampling signal is correlated with the standard single-photon impulse response waveform to detect the number of photons in each PPM slot.Experimental results show that the bit error rate performance of the proposed correlation detection Algorithm is better than that of the traditional photon number recovery method.Finally,in view of the complex closed-loop slot synchronization method and the slow operation speed of the existing open-loop slot method.In the this thesis,the ratio method is applied to the slot synchronization of optical PPM communication system from the perspective of frequency domain.Due to the poor robustness of single ratio method,an optical PPM slot synchronization method based on multiple ratio method is proposed.After the asynchronous sampling signal passes through FFT,the optimal value of Quinn,Jacobsen and Mac Leod methods is selected to realize the open-loop synchronization of PPM slot by the maximum standard deviation criterion of the logarithmic likelihood ratio of slot.Simulation and experimental results show that this method does not need to insert training sequence,the system structure is simple,and accurate slot synchronization can be achieved at lower optical power.Compared with the single ratio method,the proposed slot synchronization method is more robust.