Research On Underwater High-speed Visible Light Communications

With further exploration into the ocean,much attention is paid to sea territory and marine resource,and the need of underwater optical wireless communications is growing rapidly,which make it an important research area.Unfortunately,the underwater optical channel suffers from numerous factors such as water absorption and scattering,making the research on underwater optical communication be always restricted with complicated underwater optical channel,and there is no universal effective theoretical model to describe the various environment underwater.The main research contents and results in this paper are focused on underwater channel model,signal design and communicating simulations of complicated environment,which are summarized as follows:1.Aiming at the current situation that the diverse and complicated underwater optical channel lack valid theoretical model,a numerical simulation system of underwater optical channel based on Monte Carlo is implementated.The MCNS(Monte Carlo numerical simulation)for underwater optical channel target tracing the properties of a single traveling photon,and massive independent repeated trials could produce a stable and smooth curve which approximate the impulse response.According to the characteristics of UWOC,we modified the MC method,and for the first time designed and integrated a series of function modules,including multiple light source models,the offset model of non-aligned transceivers,the model of real-time motion of transceivers and dynamic 3D display,which improved the performance at simulating the communication in various underwater enrionment.Compared to the measurements of literature,the validity of our system is verified.2.Aiming at the problem that traditional OOK signal is inefficient underwater,a zero-padding(ZP)based block-transmission scheme of 4PAM-ZP signals is presented to reduce the influence of inter-symbol-interference.Simulation results show that 4PAM-ZP system is effective especially for serious dispersive channel with high data rates.The communication performance is improved further with optimal power allocation and reasonable length of block and padded zeros.3.Aiming at studying visible light communications in practical complicated underwater,a massive photons based MCNS system is developed.Numerical simulation reults suggest that the type of light source,optical power,water type and transmission rate should all be took into account for reliable communication when refer to various link ranges,and the motion of transceivers may seriously affect the temporal dispersion of channel impulse response and received power,which depend on the velocities of motion and initial distances.