Abstract: Aiming at the great influence of atmospheric turbulence on the performance of space optical
communication system，a scheme of atmospheric turbulence compensation based on mode diversity combined with
MRC ( Maximum Ratio Combining) algorithm is proposed． Different modes are used as independent channels for
spatial diversity reception，and the maximum ratio combining algorithm is used to realize the diversity and union
of multi-mode channels． In the aspect of MRC algorithm implementation，the phase and signal-to-noise ratio
measurement in different branch weighting coefficients are transformed into the same frequency and phase
adjustment in digital domain and the calculation of signal-to-noise ratio weight coefficients，which simplifies the
hardware implementation difficulty． Applying VPItransmissionMaker simulation platform and combining with
Matlab programming，a simulation system is built to verify the feasibility of this method． The simulation results
show that this method can compensate the effect of atmospheric turbulence on the performance of air-optical
communication system，and the compensation effect for strong turbulence is slightly better than that for weak
turbulence． The more the number of mode diversity，the better the compensation effect．

Key words: optical communications, mode division multiplexing, atmospheric turbulence, few mode fiber