Study On NLOS Underwater Optical Wireless Channel Modeling

With the increase of marine scientific research activities,people have put forward higher requirements for the effectiveness and reliability of underwater communication.Compared with traditional underwater acoustic communication,underwater optical wireless communication(UOWC)with light wave as the carrier is favored for its advantages of large optical signal capacity,high data rate and low time delay.However,the widely studied line-of-sight(LOS)UOWC is vulnerable to plankton in seawater.Non-line-of-sight(NLOS)transmission reduces the system’s tracking and aiming requirements,and ensures stable connection in the scene with obstacles,thus becomes a new solution for the realization of UOWC.As key factors affecting the system performance of UOWC,underwater wireless optical channel characteristics have also got attention,and establishing a reasonable channel model has become the significant premise to obtain accurate channel characteristics.Consequently,NLOS UOWC channel modeling research has attracted high attention in recent years.NLOS UOWC channel can be divided into reflective type and scattering type according to the different physical mechanism causing the deflection of light propagation direction.This thesis proposes more overall and accurate model for two kinds of channel respectively,and studies their channel characteristics by combining theoretical analysis and simulation experiments,so as to provide reference for the design of NLOS UOWC system.Firstly,for reflective NLOS UOWC channel,we take comprehensively the random slope of sea surface,the random receiver pointing orientation and the motion characteristics of transceiver in practical ocean into account,and propose a new reflective random time-varying channel model.The expressions of channel impulse response(CIR)and path loss are derived in the prolate spherical coordinate(PSC)system.Then,for four different reflective channel scenarios,the effects of receiving field of view(FOV),transmitting beam divergence angle and seawater types on path loss under different transceiver spacing are evaluated,the CIR characteristic under different sea surface slope variances,transceiver depths and times is investigated.The accuracy of the theoretical analysis results are verified by Monte Carlo Simulation(MCS).Secondly,for the scattering NLOS UOWC channel,the scattering effect of the rough sea surface on the propagating beam is solved based on the scattering cross section in this thesis.Combined with the particle scattering of water described by Henyey-Greenstein phase function,a rough sea surface and water particle joint scattering channel model is proposed,and the MCS algorithm for solving the channel characteristics is also designed.Compared with the traditional particle scattering channel,it is concluded that the proposed joint scattering channel has better path loss and CIR characteristics.In addition,the effects of typical transceiver configuration parameters,including transceiver azimuth angle and zenith angle,FOV and beam divergence angle,as well as channel parameters,including transceiver spacing,seawater type and statistical parameters of rough sea surface on CIR and path loss characteristics are studied in detail based on MCS algorithm.The simulation results provide guidance for the design of ocean multiple scattering system.