Research On Spatial Modulation Of Satellite-Terrestrial Laser Communication Uplink

Satellite-terrestrial laser communication uses laser instead of microwave as a communication carrier to transmit information between satellites and ground optical stations,and has the characteristics of no spectrum limitation and wide bandwidth.However,when the laser beam passes through the atmosphere,the refractive index fluctuation caused by the near-ground turbulence will affect the transmission quality of the beam and destroy the coherence of the laser beam,thereby causing a series of atmospheric turbulence effects such as beam wander,angle of arrival fluctuation and light intensity scintillation.Beam wander is caused by random deflection of the beam propagation direction due to the influence of vortices larger than the beam diameter.When the transmission beam in the downlink reaches the near-ground turbulence,the beam diameter is already much larger than the vortex size of the turbulence,so the impact of beam wander on the downlink is smaller.Therefore,this paper mainly analyzes the situation of the satellite-terrestrial laser communication uplink.At present,the methods to reduce the impact of atmospheric turbulence on the performance of satellite-terrestrial systems mainly include modulation technology,coding technology,and multiple-input multiple-output(MIMO)technology.In this paper,the spatial modulation method is used to alleviate the effect of atmospheric turbulence,and an uplink system of MIMO satellite-terrestrial laser communication with combined modulation of optical spatial modulation(OSM)and OSM-media-based modulation(OSM-MBM)is proposed.The Málaga(M)distribution is used to characterize the combined effects of near-surface turbulent beam wander,angle of arrival fluctuations,and light intensity scintillation.Using the equal gain combining receiver,the bit error rate(BER)closed expression of MIMO satellite-terrestrial laser communication uplink with OSM modulation and OSM-MBM joint modulation is derived.The influence of laser communication parameters on the system BER is simulated and analyzed,including: signal-to-noise ratio,receiving aperture,emission radius,and the unique parameters of satellite-terrestrial laser communication: beam divergence angle and zenith angle.And compared with minimum shift keying modulation,differential phase shift keying modulation and optical spatial shift keying modulation.Finally,a monte carlo(MC)simulation is used to compare the analysis results.The research results show that both OSM modulation and OSM-MBM joint modulation can significantly improve the performance of the satellite-terrestrial laser communication uplink system.Based on modulation,the system performance is improved from the perspective of coding,and a MIMO satellite-terrestrial laser communication uplink system with space-time block code(STBC)coding and space-frequency block code(SFBC)coding is proposed.The near-surface turbulence is simulated using the M-distribution,using an equal gain combining receiver.Considering the combined effects of uplink beam wander,arrival angle fluctuation and light intensity scintillation,the closed expression of BER for the uplink system of MIMO satellite-terrestrial laser communication with two encoding methods is derived.The influence of satellite-terrestrial laser communication parameters on the system bit error rate is simulated and compared with the uncoded scheme.The research results show that STBC coding and SFBC coding can further improve the performance of the satellite-terrestrial laser communication uplink system and reduce the communication cost.This research provides a theoretical basis for the engineering realization of satellite-terrestrial laser communication.