Experimental Research On High Speed Underwater Wireless Communication Based On Blue/Green Laser

At present,the development of marine resources has become one of the development strategies of all countries in the world.In order to cope with the exploitation of marine resources,research on effective high-speed communication method has become an important task.So far,there are two traditional underwater communication methods,namely underwater electromagnetic wave communication and underwater acoustic communication.Although the technology is mature,the capacity and delay cannot meet the future needs.In contrast,the research and application on high-speed underwater wireless communication based on blue/green laser is particularly important,and it has become the most feasible solution for short-and medium-range underwater communication.Universities and reseairch institutes at home and abroad are working on the research of related technologies and the production of prototypes.Although the bandwidth of underwater blue/green laser communication is greatly improved compared with traditional underwater wireless communication,the bandwidth of this band is basically maintained at around 1 GHz,which limits the further expansion of communication capacity.This makes it even more important to further increase the communication rate by the DSP algorithm.In this paper,the transmission limit rate is experimentally studied using the devices with a bandwidth of the order of GHz.And because it is a kind of free-space light transmission,the angle of the incident light,the aperture of the receiving end and solar background noise also affect the actual transmission quality,so the reseairch iin this aspect cannot be ignored.The main achievements and innovations of this thesis include:First,the underwater blue-green high-speed transmission in indoor clean water link is achieved,which based on intensity Modulation and direct detection with OFDM technology.By using higher-order Quadrature Amplitude Modulation(QAM)using 1 GHZ bandwidth photoelectric device,reached the transmission rate of 6.23 Gb/s in 128 QAM-OFDM Modulation.Second,In view of the high Peak to Average Power Ratio(PAPR)required for OFDM modulation,the relationship between nonlinear distortion of the signal and the modulation depth of the laser is analyzed,and the effectiveness of the Volterra series based recursive least square algorithm(VRLS)for the nonlinear compensation of the laser operating in the saturated region and with high modulation depth is verified by experiments.Third,the link performance analysis model of underwater optical communication under the different receiving condition is constructed,the theoretical derivation and simulation analysis show that the model can be used to analysis including Photodiode(Photodiode,PD)type,PD core diameter and viewing angles,different receiving conditions such as sun background noise effect the performance of the system effectively,which provides the reference to define the underwater optical communication scenarios of different types of PD be used in.What's more,In the case of extreme requirements on system performance,the performance improvement effect of undeirwater optical communication system using homodyne detection and liquid nitrogen refrigeration is analyzed.