Performance Analysis Of Underwater Wireless Optical Communication Systems Based On Partially Coherent Beams

Underwater wireless optical communication(UWOC)system as a key technology,which has the characteristics of higher data rate,lower time delay and better security,has received widespread attention in the military and industrial fields.However,UWOC also has many problems.When the beam propagates through the underwater channel,it will be seriously attenuated by the combined effects of seawater absorption,scattering effects,and ocean turbulence effects.In order to improve the communication quality and extend the transmission distance,technologies such as spatial diversity and channel coding can be used,as well as partially coherent optical transmission technologies.However,compared with the research on the atmospheric turbulence,the research on the propagation of partially coherent beams through the underwater channels still needs to be in-depth.In addition,in practical applications,an avalanche photodiode(APD)is usually used to improve the sensitivity of a receiver.However,high temperature and other factors will reduce the performance of the detector,which will further deteriorate the performance of the UWOC system.Therefore,we mainly study the transmission characteristics of underwater wireless optical communication based on partially coherent Gaussian beams.The main works are shown as follows:(1)We study the effects of partially coherent optical parameters and oceanic turbulence parameters on the average capacity and average bit error rate(ABER)of UWOC system.Firstly,a single-input single-output underwater wireless optical communication(SISOUWOC)system with polar codes based on On-Off keying(OOK)modulation is established.Then,the Gauss-Schell model(GSM),beam spread function(BSF)and log-normal(LN)distribution model are adopted to establish an underwater joint channel model.On this basis,the expressions of the average capacity and average bit error rate of UWOC system in the weak oceanic turbulence are derived.The effects of partially coherent beam parameters and oceanic turbulence parameters on the average capacity of the SISO-UWOC system are then studied by numerical calculations.In addition,the theoretical bit error rate of the SISOUWOC system is verified by the Monte Carlo(MC)method and the effect of polar codes on the system performance is also studied.(2)The average bit error rate performance of UWOC system in the weak oceanic turbulence based on avalanche photodiodes(APD)and orthogonal frequency division multiplexing(OFDM)modulation considering different noises is analyzed.Firstly,an APD-based OFDMUWOC system with partially coherent beam is established,in which every subcarrier using M-ary quadrature amplitude modulation(M-QAM).Then based on the Gaussian-Shell model,BSF and LN distribution model,the analytical expressions of OFDM-UWOC system are derived considering both thermal noise and shot noise.Then,the effect of polar codes on the system performance with thermal noise limited is studied.Subsequently,the influence of different APD parameters,partially coherent beam parameters and oceanic turbulence parameters on the ABER performance of UWOC system considering both thermal noise and shot noise is investigated.This thesis provides some reference for the design of partially coherent optical underwater wireless communication system.