| In recent years,cross-media communication has been widely concerned as a research hotspot.The main application scenarios are the interconnection between underwater platforms and land-based,aerial platforms and satellites.With the increase of data volume and the development of cloud computing,cross-media communication has put forward higher requirements on transmission rate,security and stability.At present,the main means of cross-media communication is using radio to transmit data at home and abroad.However,seawater absorbs radio very strongly,and energy loss during transmission is large,which seriously affects communication quality.Studies have confirmed that there is also an atmospheric window similar to that present in the sea,and the attenuation of blue-green light in seawater is much smaller than in other bands.Therefore,blue-green laser communication begins playing an important role in cross-media communication.It is worth noting that most of the existing literature research focuses on the downlink communication of blue-green laser,and there is relatively little research on uplink communication.The channel of the blue-green laser uplink transmission is more complicated,especially at the sea/air boundary.The laser propagates from the optically denser medium to the optically thinner medium.With resulting in Changes of communication performance,the random fluctuation of the sea surface will cause the expansion,flicker and drift of the receiving surface spot,and bad sea conditions may even interrupt the communication process.In this paper,a systematic model of cross-media blue-green laser uplink communication is firstly established in the study of blue-green laser communication.Secondly,the composition of seawater and atmospheric channels and the effects of various suspended particles on laser scattering and absorption are analyzed in depth.The geometrical optical properties at the sea/air interface were investigated.The theoretical calculation of the spot diameter of the receiving surface and the center shift of the beam at the ideal sea surface tilt angle are calculated.A three-dimensional random sea surface model was simulated using the P-M spectrum and the direction function suggested by ITTC.The three-dimensional random model of sea surface is simulated by using the PM spectrum and the direction function suggested by ITTC.In the third chapter,by analyzing the channel attenuation of the cross-media blue-green laser uplink communication,the calculation expression of the system path loss is obtained,and the influence of system parameters on the path loss is analyzed in detail.By studying the receiver noise,it is determined that the background light noise and the receiver thermal noise are the main noise sources of the system.The normalized SNR expression is obtained,and the optimal receiving angle of view of the system is determined.The OOK modulation mode is selected,and the influence of link rate and transmission power on the bit error rate is analyzed based on the link characteristics of the system.The system is verified to be viable by reversing the average transmit power of the system.The channel delay of the system is theoretically calculated for different waters.At last,the Monte Carlo method is used to simulate the uplink transmission of the cross-media blue-green laser,and the simulation algorithm is improved for the cross-media transmission.The transmission characteristics of the system are studied.For the transmission distance and the wind speed of sea surface,it is analyzed that the distribution of the light field and the delay spread of the blue-green laser transmission.The research work in this paper will provide a theoretical basis for the development of cross-media blue-green laser communication test prototype.It provides a long-distance communication method across media,and adds a possible communication means for uplink communication between underwater platform and air platform. |
