The Underwater High-speed LED Optical Communication Technology Research

As land resources are gradually reduced, people are no longer limited to make exploration of land resources which is only 29% of the earth’s surface. They have turned to the abundant marine resources, and the exploration of marine resources is considered as the primary resource access to human beings. Due to the rugged environment of seabed, underwater robot(ROV) is now playing an irreplaceable role in marine resources exploration. In order to use ROV better, networking technology between the ROVs is indispensable. It can be divided into two ways: wired and wireless. The wireless networking is more widely used than cable networking for it is more convenient used in the complicated seabed environment and the structure is simpler.From a technical point of view, some technologies are successfully communicated on land. However, the seawater is a special medium. Therefore, those technologies can not be directly transplanted into underwater working. Underwater wireless communication mode can be divided into underwater acoustic communications, underwater electromagnetic wave communication and underwater optical communication. Comparing with underwater acoustic communications and underwater electromagnetic wave communication, underwater optical communication has advantages of small volume, low consumption and high bandwidth.This paper proposed a high-speed underwater LED optical communication system. This system should achieve the following goals: the speed will reach 100 kbit/s when the BER(Bit Error Rate) is zero and the distance will be up to 10 meters. In this paper, topic background, research significance,present situation and development trend in the future ofunder water optical communication are introduced and then the main content of this topic is detailed elaborated.This paper mainly completed the following sections: detailed introduction of underwater transmission attenuation effect of light, LED code modulation technology and link access protocol, design of underwater LED optical communication system control and selection of power supply module, design of light send circuit, design of light receive circuit, system softwore and system debugging.From the perspective of the optical properties of the sea-water, the transmission absorption and scattering effect and energy model, the underwater light transmission attenuation effect can be elaborated. LED code modulation technology mainly includes OOK modulation technology and PPM, PWM modulation technology.In the optical communication system control module, STM32F407 is as microcontrollers and MCP2150 is as codec chip. And in Power supply module, TI chip is selected to design a circuit of ±5V and 3.3V.For the optical communication send system module, it made a complete comparison with semiconductor laser and semiconductor light-emitting diodes and then design the LED driver circuit.For the optical communication receive system module, it emphatically expounds the working principle and characteristic parameters of light detector. Then I-V conversion circuit and filter amplifier circuit are designed. Finally, system decision circuit is completed according to the BER principle and also optical block device of the receive system is completed.The software design of the optical communication system becomes much easier because of the support of MCP2150 chip to IrDA protocol standard. The paper analyzes the connection establishment of the master-slave node and the process of the data transmission.And it also completes the software design of data receiving and transmitting as well as the Broadcast ID set.For system debugging, it first introduced the overall level of optical communication system hardware structure, and then the distance of underwater optical communication was under test when BER is zero. The result shown that the distance was more than 10 meters and the speed reached more than 100kb/s, which means the system reached the expected design goal.At the end of this paper, the review and summary of this study were given and also the deficiency at present and improvement in the future were pointed out.