| In recent years,with the increasing demand in the fields of marine resource development and marine environmental monitoring,designing an efficient and reliable data transmission technology to support real-time communication between submarine equipment has become a hot and difficult topic in current research.Underwater optical communication is gaining increasing attention as a promising technology due to its advantages over traditional underwater acoustic and radio frequency communication.These advantages include high data rates,large bandwidth,low power consumption,and small equipment size.However,it should be noted that underwater optical communication also has some shortcomings.On the one hand,due to the existence of water absorption effects,the signal transmission distance is limited;On the other hand,when light propagates in water,it will undergo backscattering,leading to the occurrence of self interference,which will seriously affect the performance of full duplex optical communication systems.In order to effectively alleviate the difficulties faced by underwater optical communication,this paper conducts a comprehensive study on the underwater optical forward communication links and underwater backscattering characteristics.Firstly,the spatial diversity structure of Multiple Input Single Output(MISO)is utilized to improve the transmission distance of full duplex communication systems;Secondly,a digital time domain self-interference suppression scheme is proposed using the modeling results of underwater optical backscattering as a priori condition to address the backscattering problem of the full-duplex optical communication terminal.Finally,complete the software and hardware construction of the communication system and conduct relevant tests.The main work of this article is as follows:(1)The overall framework of underwater visible light full duplex communication systems is analyzed,and the attenuation characteristics of visible light transmission in complex underwater channel environments are deeply discussed.The widely used optical modulation techniques and channel coding techniques in various underwater optical communication systems are compared and analyzed,providing a basis for selecting the final design scheme of the communication system.(2)Two theoretical performance evaluation methods for underwater optical communication systems were studied,which are the attenuation equation of the underwater optical forward link and the formula for calculating the bit error rate of the optical communication system.The advantages of MISO spatial diversity architecture in extending the forward link distance of underwater optical communication systems are compared and analyzed quantitatively from the aspects of communication link distance,system error rate,and signal light source radiation.(3)The Monte Carlo simulation algorithm and underwater light backscattering theory are studied.Based on this,a new modeling method for underwater visible light backscattering is proposed.Based on the modeling results,a new digital time domain self interference suppression scheme is proposed,and its effectiveness is verified from both the steady-state mean square error of the algorithm and the system error rate.(4)Taking underwater sensor node data acquisition as the system application scenario,a set of underwater visible light full duplex MISO communication system based on self interference suppression scheme is designed.At the same time,to meet the system functional requirements,a communication protocol suitable for underwater data acquisition was designed,and the performance of the communication system was tested.The results show that the full duplex optical communication system designed in this paper has complete data acquisition functions,with a transmission distance more than 20 m in free space,and a transmission rate of 20 M.The system error rate test results show that the self interference suppression scheme proposed in this paper can significantly reduce the error rate of communication systems,achieving the goal of improving the performance of full duplex communication systems. |
