Underwater High-speed Wireless Optical Communication System Based On OFDM

With the deepening of marine exploration research,underwater wireless optical communication becomes more and more important.In order to combat frequency selective fading and improve frequency band utilization,it is a general trend to apply orthogonal frequency division multiplexing(OFDM)technology to underwater wireless optical communications.However,OFDM also has its shortcomings.Due to the multi-carrier modulation,the system will inevitably have a problem of excessive peak-to-average power ratio(PAPR).This peak power may exceed the linear bandwidth of the system and cause nonlinear distortion,which will affect the system Communication performance.Therefore,the use of an effective PAPR suppression algorithm is particularly important for the realization of OFDM-based underwater wireless optical communication systems.In this paper,based on the statistical characteristics of the DC bias optical orthogonal frequency division multiplexing(DCO-OFDM)PAPR,the relationship between the PAPR of the DCOOFDM system and the autocorrelation of the input signal is elaborated in detail.Then,the PAPR suppression algorithm of the traditional radio frequency OFDM system is improved,and a time-frequency domain interleaving-selective mapping method(TFI-SLM)PAPR suppression joint algorithm is designed.The algorithm first uses time-frequency domain interleaving to reduce the autocorrelation of the input signal,and then further reduces the PAPR of the DCO-OFDM system through the selection mapping method(SLM).Finally,this paper designs an underwater wireless visible light communication system based on DCO-OFDM,the main work is as follows:(1)Introduce three kinds of visible light OFDM modulation technology in detail,explain the difference of the positive real number signal that they need in obtaining visible light communication through the system schematic diagram,analyze and compare their advantages and disadvantages,and finally choose DCO-OFDM modulation technology as Research content of this article.(2)The definition of PAPR is introduced,and the impact of excessive PAPR on the OFDM system is described.The statistical characteristics of traditional radio frequency OFDM system PAPR and DCO-OFDM system PAPR are analyzed,and their PAPR is simulated and compared to provide a theoretical basis for the subsequent PAPR suppression algorithm.(3)Analyze and discuss several classic PAPR suppression algorithms,elaborate their principles in detail,and compare the advantages and disadvantages of these classic algorithms.Finally,the issues that should be considered when designing the PAPR suppression algorithm are proposed.(4)A TFI-SLM joint algorithm is designed to suppress the excessive PAPR of the DCOOFDM system.Then elaborate the DCO-OFDM wireless optical communication system based on TFI-SLM joint algorithm in detail,and focus on describing and analyzing TFI,SLM and DC modules.Finally,the PAPR suppression effect of other traditional algorithms is simulated and compared.(5)Using FPGA hardware platform,an underwater wireless optical communication system based on DCO-OFDM is designed,and then the system is tested,and the test results meet the expected requirements.