| Blue-green laser communication has become the splendid technology in submarine wireless communication,due to the strong penetration ability.It provides technology support of information transmission for underwater equipment with its higher communication rate.Compared with the downlink channel of satellite submarine,the uplink channel not only needs to consider the scattering of sea water and atmosphere,but also the spot convergence and drift caused by the fluctuation of the air-sea interface have more severe effect on the communication performance.The challenge of dynamic change with sea wave puts forward much higher demands of receiving performance in the satellite communication system.This makes it harder for study on the uplink communication than that of downlink communication.The study of uplink transmission characteristics is carried out in satellite-submarine communication channels utilizing blue-green laser,so as to satisfy communication requirements from satellite platforms and underwater equipment.The analysis on characteristics of transient distribution and long-term statistics from submarine laser uplink communication is performed with the three-dimensional dynamic sea surface model utilizing Monte Carlo method.Based on the analysis of PM wave spectrum,a three-dimensional sea surface model is established that varies with wind speed,wind direction and time by using the linear superposition method of equal division frequency,and here it verifies the validity.Aiming at the time-varying characteristics of the sea surface,the distribution of laser spot is calculated by Monte Carlo method.The spots pass through the air sea interface and reach the receiving surface at different times.The temporal and spatial characteristics of the spot shape,energy attenuation and the dynamic change of the spot centroid are analyzed.The results show that the spot centroid changes from tens of kilometers to hundreds of kilometers for Low Earth Orbit(LEO)satellite platform.The larger spot centroid drifting is,the smaller the receiving number of photons reaches the receiving surface due to the total reflection caused by the air-sea interface.Besides,the effects on the transient light spot distribution are simulated and analyzed from different sea surface wind speeds,underwater transmission distances,water quality types,light source divergence angles and emission angles.The simulations show that these factors will cause the change of spot shape,channel attenuation and spot centroid coordinate,but there has little influence with the change of divergence angle of light source.The expansion effects overall uplink link have been analyzed with spatial and time distribution through long-term statistics of the receiving surface signal.It has been found that the increase of wind speed and sea water transmission distance,the deterioration of water quality will result in the augment of spatial expansion and time delay.For example,the spatial expansion radius is 300 ? 400 km and the time delay is 200 ? 350?s;There is little change in spatial expansion and time delay of light field with different divergence half angle of light source;When the laser elevation increased to 15o,there is no obvious effect on spatial expansion.However,the time delay increases by about 80?s.The performance of communication system with a certain receiving aperture at receiver has been analyzed.And the total number of photons received by the receiver under different wind speed and underwater transmission distance has been given.Increasing the size of aperture can effectively improve the receiving efficiency,and the number of received photons increases with the square of the effective receiving aperture.At last,the research results can provide a theoretical reference for the design and implementation of satellite submarine communication. |
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