Underwater laser communication technology plays an important role in wireless data transmission in underwater research and exploration missions.underwater wireless optical communication(UWOC)system needs to rely on the APT(acquisition,Pointing and Tracking)system to achieve accurate alignment between transceiver and receiver.However,due to the interference of the complex underwater environment,the laser beam is easy to be attenuated and distorted,resulting in the deformation of imaging light spot,which makes the APT system unable to accurately align the laser beam,and thus causes the communication anomaly of the UWOC system.In order to solve this problem,a high-bandwidth underwater laser communication system based on deformable spot positioning APT is developed in this paper.The system can smoothly track and accurately alignment under the condition of deformable spot,so as to achieve high-speed and stable underwater laser communication.The characteristics of underwater laser communication channel are important factors affecting the communication performance of UWOC system.Through the quantitative analysis and simulation of the hardware parameters of the UWOC system,it is concluded that the UWOC system designed in this paper can operate stably in the underwater environment where the total attenuation coefficient of water quality is between the coastal seawater and the harbor turbid water.At the level of system hardware design,this paper selects appropriate electronic and optical components according to the design indexes,and completes the circuit design of point-to-point laser communication driver and receiving unit in LOS(Line Of Sight)mode.In the circuit design of receiving unit,AGC(Automatic Gain Control)circuit is introduced.The circuit can automatically adjust the circuit gain according to the amplitude of the input signal,so that the output signal is always kept at a stable amplitude.In order to improve the data processing speed,this paper uses the FPGA core board to realize 4-PPM(Pulse Position Modulation)modulation and demodulation method to reduce the power consumption of the system.At the same time,the Ethernet communication board realizes the high-speed data transmission between the upper computer and the FPGA main control board.The test results show that the system can achieve the maximum communication distance of 10 meters,the maximum communication rate of 10Mbps(Megabits per second)performance indicators.APT system can automatically locate the imaging coordinates of laser spot,control the pinhead tracking laser according to the coordinate data of the spot,and complete the alignment operation required for laser communication.However,the interference of the complex underwater environment will cause deformation of laser spot imaging,resulting in the failure of the APT system to track smoothly and accurately.Therefore,an APT system with deformation spot positioning function is developed in this paper.In terms of the hardware design of APT system,this paper adopts a two-degree-of-freedom cradle head equipped with OPENMV image processing board to realize the image acquisition,positioning of light spots and control of cradle head.In terms of software design of APT system,a control algorithm based on KCF(Kernel Correlation Filter)for locating and tracking deformation light spots is designed and deployed on OPENMV board.The algorithm can effectively suppress the positioning error caused by the deformation of light spot,and make the APT system track path smoother.The test results show that the algorithm proposed in this paper can control the average alignment error within 8 pixels when the image pixel is 320×240.At the same time,with a maximum communication distance of 10 meters,it can achieve smooth tracking of deformed spot and fast alignment within 6.5 seconds. |