Performance Analysis Of Multi-hop Based UOWC System

Underwater Wireless Optical Communication(UOWC)can effectively realize underwater high-speed,low-latency communication.Compared with two traditional methods,underwater acoustic communication and Radio Frequency(RF)communication,UOWC not only can transmit more information every time,and the rate of dispatching information bits is faster,but also it consumes much less energy,and the expense to set up is also quite low.However,the complicated marine environment severely hinders the spread of light underwater.Various components in the sea water absorb light power more or less,and light will also be scattered due to these particles,as well as the power fluctuations caused by underwater turbulence and alignment problems.These factors reduce the nature of communication and the communication distance is significantly shortened.Therefore,we adopt a Multi-hop solution in UOWC,which can not only extend the communication distance of the link,but also reduce the interference of interferences such as underwater turbulence by shortening the distance between each hop link.The system can display better to appease the growing pressure for transmitting more and faster,and ensure the reliability of the system.This paper discusses the Multi-hop UOWC system under different detection methods:heterodyne coherent detection and direct detection(DD).What’s more,DD could be separated into two types: input-independent DD and cost-dependent DD.Besides,relay includes channel state information(CSI)-assisted relay and fixed-gain(FG)relay.At the same time,the scenarios without pointing error and with pointing error are also considered.So as to accurately simulate the underwater wireless optical communication environment,we established the corresponding mathematical model of the Multi-hop UOWC system.In this system model,we use the mixed Exponential-Gamma distribution to simulate the underwater channel conditions,which can accurately describe the underwater complex channel environment that takes scattering,absorption and turbulence into account.Secondly,this paper derives several closed-form performance expressions for evaluating system ability.For example,outage probability,channel capacity and likewise the average bit error rate using different modulation methods.Through a series of analysis and research,the CSI-assisted relay formula presents better outage probability and average error rate performance,but it is also more sensitive to turbulence.But the channel capacity of fixed-gain relay scheme shows better performance.Input independent DD detection has the best outage probability performance,followed by heterodyne coherent detection and cost-dependent DD detection.Although the performance degradation caused by turbulence is not small,the multi-hop technology can remarkably let the system capability make strides,and performance is positively related to the number of hops.The pointing error also affects the performance of the system,but only the number of hops matters.Turbulence intensity,relay scheme,and detection method are not related to pointing error.In spite of the fact that the increase in the number of hops will also increase the pointing error,the multi-hop scheme gives the performance more benefits.Finally,the results were tested by Monte Carlo simulation to ensure correctness.