Research On Non-ideal Transmission Characteristics Of Underwater LED Wireless Optical Communication System

The ocean is an important area for economic development and military security in the 21 st century.With the continuous development of our country's ocean development and the continuous advancement of the ocean power strategy,underwater communication technology plays a key role in ocean exploration and development.Underwater wireless optical communication(UWOC),an emerging underwater high-speed data transmission method,has the advantages of low latency,high bandwidth,low power consumption,small size,and high confidentiality compared to traditional electromagnetic wave communication and underwater acoustic communication.However,in the current research on UWOC,there are still many challenges that limit the application of UWOC technology.In this paper,the theoretical research and technical improvement of the UWOC system based on light emitting diodes(LEDs)are carried out.In underwater LED wireless optical communication systems,non-ideal transmission characteristics are the bottlenecks that limit its development.Aiming at the non-ideal transmission characteristics in underwater LED wireless optical communication,the baseline wander caused by the nonlinearity of the system,the low signal-to-noise ratio caused by the absorption of optical signals by seawater channels,and the inter-symbol interference caused by the bandwidth limitation of LED devices,this paper proposes two solutions to overcome the non-ideal transmission characteristics in underwater LED wireless optical communication systems.Firstly,a solution combining limited length coding and energy detection is proposed for the problem of baseline wander and low signal-to-noise ratio.Based on the receiving circuit of UWOC system using OOK modulation,this paper deduces the formation mechanism of baseline wander,establishes the corresponding mathematical model,adopts the limited length coding to match the transmission characteristics of the system,and proposes energy detection Algorithm to improve the detection performance under low signal-to-noise ratio.The simulation results show that the combination of length-limit coding and energy detection can effectively improve the stability of communication.Secondly,in order to solve the problem of low communication speed of underwater LED wireless optical communication system,a soft-switching dual-mode blind equalization algorithm is proposed.In this paper,the latest advances in filter combination in the adaptive filtering literature are used.The outputs of the parallel constant modulus algorithm(CMA)and the decision-directed(DD)algorithm are convexly combined by the mixed parameters,and the mixed parameters are iteratively updated to achieve two Automatic switching between equalization algorithms without artificially setting switching thresholds.In addition,a mathematical model of the steady-state mean square error of the soft-switching dual-mode blind equalization algorithm in a non-stationary environment is derived.Simulation results show that the steady-state performance of the algorithm is consistent with theoretical calculations,and has better performance than other equalization algorithms.Finally,an experimental platform was set up,and the conclusions obtained from the simulation were verified experimentally.The differences between the experimental results and the simulation are analyzed and compared,which proves that the proposed anti-ideal transmission characteristic scheme has good performance and can provide a reference for the subsequent design of underwater LED wireless optical communication systems.