Research On Underwater Wireless Digital Transceiver System

Underwater wireless communication is mainly used in the information exchanging between submerged devices, divers, and the controlling of autonomous vehicles (AUV), as well as data transmission in underwater sensor network and other fields. The continuous developing needs of audio and video transmission, and the real-time data exchanging between underwater units put forward higher requirement for the communication capability of underwater communication technology. Traditional acoustic communication is vulnerable to the environment noise; and the rate is low; bandwidth is limited. It can’t meet the new requirements. Due to the scattering and absorption constraints and the high-precision alignment requirements blue-green laser communication technologies are also difficult to achieve practical application. Because of the huge size of antennas and high energy consumption and low communication rate, the super long wave communication system is only applied in the communication between land-base and submarines.In recent years, it is a main issue to apply the digital signal processing technology to improve the capabilities of the underwater communication system and develop high-performance, small size underwater antenna. At present, some foreign institutions have researched underwater communication in short rang, and achieved certain results. And some of domestic colleges also earried out the relative research, while it needs further work.In the previous period of this paper, our laboratory has implemented the study of the underwater antenna. Considered the heave attenuation of the electromagnetic transmission underwater, we designed the loop antenna used for underwater close-up radio frequency communication. The main content of this paper is to build digital underwater RF communication transceiver system, including applying the digital signal processor (DSP); the realization of the digital modulation and demodulation functions; and the design of corresponding power amplifier module for the subsequent research of final digital transceiver.First we introduced the current research of the underwater wireless communication, compared and analyzed several existing underwater communication technologies, and discuss the advantages and the applications of the underwater RF communication technology. In the second chapter, we introduced the main parameters of the underwater antenna, and improved the design of the antenna’s impedance matching and power amplifier. In the third chapter, several digital signal processing technologies are introduced, including:digital filtering design, digital small signal detection technology and digital modulation and demodulation principle. Also we analyzed the advantages of digital signal processing technology.In the forth chapter, overall structure of digital communications system is discussed, we design a complete digital transceiver system:in the transmitter we use direct digital frequency synthesizer (DDS) chip to achieve the basic digital modulation process; in the receiving end, we have achieved analog/digital conversion at the rate of5M/s and the digital demodulation process. In addition, we have tested the designed system’s communication capability in different ranges and in air and water environment respectively. The test results showed that the system can achieve underwater communication process at40cm range with rate of30kbit/s. Finally, summarized the content of the work, and give some suggestions of the optimal design in the future.