Analysis Of Time Delay Characteristics Of Underwater Laser Time Service Channel

Underwater laser timing is a way to achieve high-precision underwater time service by replacing radio wave or acoustic wave with wireless laser,which effectively making up many defects such as serious attenuation of underwater radio wave,large transmission delay and low transmission rate of acoustic wave.It has shown infinite potential in marine survey,underwater wireless communication as well as navigation and positioning,and it is becoming a new trend in the future research of underwater time service technology.Firstly,this paper introduces the background and significance of the application of the existing timing technology,and highlights the key points and difficulties of underwater timing through its development status and characteristics.In addition,based on the advantages of huge information carrying capacity,fast transmission speed,confidentiality and strong anti-interference performance of UWOC(Underwater wireless optical communication),an underwater laser timing model is proposed.Secondly,the delay characteristics of underwater laser pulse are simulated and analyzed.Finally,the pulse response of seawater channel in underwater laser timing is modeled.The main research contents of the paper are as follows:(1)The optical properties of seawater are studied,the absorption and scattering effects of underwater laser transmission and several scattering phase functions are analyzed,and compared with the measured data,the FF phase function with higher fitting degree is selected for the subsequent simulation.In addition,by comparing the small-angle approximation method and Monte-Carlo method,which are commonly used to analyze the time-domain broadening characteristics of underwater laser pulse transmission,MC method has been chosen as the core of the simulation scheme,for it is more suitable for underwater laser transmission physical process without too many approximations.(2)By considering the relationship between UWOC normalized receiving power and transmission distance,the angular-field-of-view(AFOV)by the receiver and the receiving optical aperture of the receiver,the channel delay characteristics of laser pulses transmitted in three typical sea areas are simulated and analyzed.(3)Several methods commonly used in UWOC channel impulse response modeling are introduced,and on this basis,a multi-gamma function(MGF)model is improved.The accuracy and superiority of MGF modeling were verified by comparing with the existing functional model,and the model was used to model the impulse response of underwater laser transmission.In this paper,the channel delay characteristics of the underwater optical link in the underwater laser timing model are studied,and an MGF model is optimized and improved,whose simple closed expression provides a useful reference for the link design of the UWOC system and the time dispersion study of the underwater optical link.The purpose of this paper is to provide some theoretical basis and reference value for the underwater laser timing system designed to realize accurate tracking of sea surface and high precision positioning of underwater equipment in the future.