Study On Key Techniques Of LED-Based Underwater Optical Wireless Communication

In recent years,with the explosive growth of human population and the depletion of resources,the marine environment with abundant resources,including biological and mineral resources,has aroused great interest of many countries and regions in devel-opment and utilization of the marine environment.In the exploration of the ocean,underwater communication technology will become more and more important.This dissertation focuses on theoretical and experimental study of.First of all,a digital domain equalization method is applied to realize the off-line 400Mbps transmission through a 10-meter underwater channel in this dissertation,in or-der to overcome the data rate limitation.A pre-equalization filter is then derived to deal with the LED exponential response based on the characteristics of the LED frequency response.Afterwards,the optimal receiver and matched filter are designed.The rela-tionship between transmission rate and distance is further analyzed theoretically.The maximum transmission distance at a given rate under different water quality conditions is obtained.Finally,the methods are verified by an indoor off-line experimental system.Secondly,in view of the low receiver sensitivity of traditional underwater wave-form detection,a photomultiplier tube(PMT)is used to perform photon counting recep-tion of weak underwater signals.For the discrete photon counting receiving model of an underwater weak light channel,a receiving algorithm is proposed to mitigate inter-symbol interference.In particular,for the photon counting process with inter-symbol in-terference,linear detection and maximum likelihood detection algorithms are proposed to mitigate inter-symbol interference.During analysis,the linear detection algorithm under the waveform channel and the linear receiving criterion under the photon count-ing channel are compared.It is found that signal under the photon counting channel has self-interference characteristics,due to the fact that the photon counting process is a Poisson process.The influence of different received optical signal to noise ratios and different average received photon numbers on the signal-to-interference and noise ratio(SINR)is analyzed.Finally,the above-mentioned photon detection algorithms for un-derwater weak signals are verified in an off-line experimental system.The differences between experimental and simulation results are compared,and the feasibility of the algorithms are experimentally demonstrated.