Research on underwater wireless dynamic optical communication system based on PPM modulation

Abstract

In order to achieve underwater wireless dynamic optical communication, a laser communication system is proposed based on Pulse Position Modulation (PPM). In order to achieve underwater laser communication accurately, the mathematical model of underwater laser communication was constructed with small angle analysis. The pulse position modulation demodulation algorithm is designed, and the workflow of modulation and demodulation is given in the transmit module and the receive module. In the experiment, Lumileds-470 nm light source was selected for data communication for testing at a communication rate of 15 Mbp/s. In the servo control process, the square wave signal used for stepping motor drive had a stable amplitude output and a stable time width. It can well simulate the testing process of underwater dynamic scanning. In the experiment, laser light spots were obtained under different attenuation states, and the characteristics of the light spot distribution were analyzed. The numerical reconstruction of the light spot energy was completed in MATLAB. Three types of light attenuators, 1.0%, 0.1%, and 0.01%, were used to simulate different light attenuations underwater. The test results show that the system error rate is better than 10−6 when attenuation chip is 1.0%. When attenuation chip is 0.1%, the error rate of the system is reduced to 10−4. When attenuation chip is 0.01%, a valid signal cannot be obtained by the system. The feasibility of the system is verified.