Research On UWOC Communication System In Ocean Turbulent Channel

The increasingly frequent exploration and development of the ocean has put forward higher requirements for underwater wireless communication.Compared with the traditional underwater acoustic communication technology,underwater wireless optical communication(UWOC)technology has received extensive attention because of its high rate and low delay.However,uwoc technology also faces many challenges.The absorption scattering effect and turbulence effect of seawater will lead to beam diffusion,power loss and light intensity fluctuation,which will affect communication.Due to the directivity of light propagation and the influence of water flow,the alignment error between transceivers will also affect the system performance.The marine environment is different from the atmospheric environment,and its absorption and scattering effects and turbulence effects are also different from those of the atmosphere.Therefore,it is of great significance to study the channel model of underwater wireless optical communication in combination with beam diffusion,power loss and alignment error,and further study the performance of the communication system according to the channel model.Based on this,the research of the thesis mainly includes the following points:(1)The light intensity distribution model,the alignment error model and the turbulent light intensity fluctuation model of the channel are studied,and the joint channel gain model is derived based on the above three factors.Among them,for the light intensity distribution model,the beam spread function model under absorption and scattering and the average light intensity distribution model under turbulence are studied,and the two models are combined and compared with the photon Monte Carlo simulation;In the thesis,the alignment error is divided into position error and angular error.Based on the beam spread function model,the alignment error power loss model is constructed to study the influence of transceiver position and angular error on power loss.At the same time,according to the random power variation caused by the random jitter of the receiver,the probability density distribution model of power attenuation caused by alignment error is studied;For the random fluctuation model of light intensity caused by turbulence,i.e.turbulence intensity fluctuation model,the thesis studies the classical lognormal fluctuation model under the condition of weak turbulence and the new mixed exponential generalized gamma(EGG)distribution model which has a wider application range;Finally,when the turbulence intensity fluctuation model obeys the lognormal distribution,combined with the beam spread function model and the alignment error model,the lognormal distribution joint channel gain model is constructed.When the turbulence intensity fluctuation model obeys the EGG distribution,the EGG distribution joint channel gain model is constructed.(2)Combined with the constructed joint channel gain model,this paper studies the bit error rate performance of the communication system using asymmetric clipped optical orthogonal frequency division multiplexing(ACO-OFDM)modulation and demodulation technology when the receiver obtains ideal channel state information(CSI),The closed form expressions of the theoretical bit error rate of the system under the two channel models are derived and compared with the simulation results.At the same time,the influence of turbulence intensity fluctuation and alignment error on the bit error rate performance of the system is studied.In order to mitigate the adverse effects of turbulence intensity fluctuation and alignment error on the system,this paper further studies the system performance under the single input multiple output(SIMO)diversity reception technology at the receiver,and studies the improvement of SIMO diversity reception compared with single input single output(SISO)under the turbulence intensity rise and alignment error.(3)Based on the field programmable gate array(FPGA),the intellectual property(IP)core module of ACO-OFDM transceiver with the functions of frame detection,timing synchronization,channel estimation and equalization is designed.The logarithm normal distribution is simulated with the MATLAB software of personal computer(PC),and the turbulence intensity fluctuation of egg distribution is combined with the alignment error channel,The thesis studies the bit error performance of the system when the receiver does not obtain the non ideal CSI,that is,there is timing synchronization error and channel estimation error,and compares it with the system bit error rate when the receiver obtains the CSI.At the same time,it runs on the FPGA development board to verify the feasibility of the aco-ofdm transceiver system.