Research On The Design Method Of Multi-aperture Coherent Optical Receiver

Free space optical communication(FSOC)has higher transmission rate and longer transmission distance than microwave communication,and has the advantages of small terminal size,rich spectrum resources and strong confidentiality,so it can play a huge role in inter-satellite communication and satellite-ground communication.In the satellite-ground FSOC system,the beams are greatly expanded due to the long transmission distance;in addition,the signal light intensity flicker due to atmospheric turbulence,which makes the power of the optical signal received by the ordinary single aperture optical receiver low,and the dynamic range of signal-to-noise ratio is large,which limits the performance of the receiver.Multi-aperture coherent optical receivers use multiple optical antennas to receive space diversity optical signals with independent transmission paths,which can effectively increase the optical signal receiving area,and greatly improve the receiver signal-to-noise ratio through coherent combination,and effectively suppress the effect of atmospheric turbulence,so as to greatly improve the performance of the satellite-ground FSOC system.This paper focuses on the design of multi-aperture digital coherent optical receivers.A method for receiving and demodulating and recovering free-space optical communication signals is proposed.The specific research contents are as follows: 1)An atmospheric channel model is established for the satellite-earth space optical communication link,and the influence of free space transmission and atmospheric turbulence on the received optical power is analyzed,and then the analysis model of the signal-to-noise ratio and bit error rate of the coherent optical receiver is established.The relationship between the signal-to-noise ratio and the bit error rate of the multi-aperture coherent optical receiver under the maximum ratio combining,equal gain combining and selecting combining are studied,which lays a theoretical foundation for the design of the receiver.Finally,according to the specific channel conditions,the corresponding receiving system and parameters are given.2)The digital coherent combining algorithm including time alignment and phase alignment algorithm is studied,focusing on the optimization design of the phase alignment algorithm,the effect of ASE noise on the error of phase alignment is analyzed,and the relationship between the error of phase alignment and the combining loss are established,a general method for optimizing the computational complexity of the phase alignment algorithm is provided and verified by a large number of numerical simulations.Finally,according to the specific received signal conditions,based on the equal gain combining,the corresponding algorithm solution and coherent combination optimization method are given.3)The carrier recovery algorithm is studied,and the performance and computational complexity of various blind algorithms and data-aided algorithms are compared.Finally,the algorithmic solution is given for the specific combined signal conditions.Numerical simulations show that the performance of the designed DSP algorithm system including coherent combining algorithm and carrier recovery algorithm has reached the expected demand.