The Study Of The Key Technologies And Applications For OFDM In High-Speed UWA Communication

UWA (Underwater Acoustic) communication technology is of great strategic significance in national defense, but also increasingly being applied to the marine environment inspection, resource development and other civilian areas. High-speed data transmission has become one of the hot research topics in the forefront of UWA communication technologies, is also an urgent task.The most difficult problem in high-speed UWA communication is multi-path interferences, which cause the decline of the receive signals and inter symbol interference (ISI); coupled with high background noise, low frequency carrier, extremely limited bandwidth and transmission conditions of the time-space-frequency characteristics, UWA channel becomes the most difficult wireless communication channel so far. So, reliable high-speed UWA communication has become a worldwide problem.In recent years, as orthogonal frequency division multiplexing (OFDM) technology with high spectrum efficiency, strong ability of overcoming multi-path and impulse noise, the ability of high-speed transmission in the case of efficient utilization of bandwidth and simple method, it becomes one of the focuses in high-speed UWA communication.The paper mainly studies the key technologies and system applications for OFDM in high-speed UWA communications, the main content of this paper are as follows:1. The study of the key technologies for OFDM in high-speed UWA communication: In this paper, parts of the technologies for OFDM in high-speed UWA communication have been studied by simulations, and tested by the data collected on the lake and sea. The major key technologies studied as follows:a) Guard Interval (GI): The effect of the GI for OFDM systems has been analyzed in the paper; considered the characteristics of the deep sea channel, a structure of the GI is proposed, which is suitable for UWA communications in deep sea; simulation results show that the structure has good results.b) Channel Estimation: this paper discussed the channel estimation method of PSAM (Pilot Symbol Assisted Modulation), and inserted a special study of the effect on OFDM system by different pilot interval.c) Frequency Synchronization: the effect of frequency synchronization on OFDM systems has been analyzed. A frequency estimation method is proposed, which has high estimation accuracy, the simulation and experimental results show that the method is feasible and effective.d) Phase Noise: In this paper, a theoretical analysis of the phase rotation has been done, especially the phase noise caused by the deviation of the sampling clock. A method of phase compensation for the deviation of the sampling clock is proposed, and it has been proved by lake experiments.2. The experimental study of high-speed UWA communications based on OFDM: In the paper, the experiments have been done respectively in the lake and the sea, the experimental results show that it is feasible to achieve high-speed UWA communication by using the OFDM technologies, and it can reach higher data rate with lower BER.3. Application study of OFDM systems in high-speed UWA communication: Two high-speed UWA communication systems based on OFDM have been discussed in the paper:a) Underwater repeater system based on OFDM: This paper introduced the system design and implementation of the system. The experiment of the system in the lake achieved good results. Suggestions for improvement have been proposed in view of the inadequacies of the existing system.b) Super-speed UWA communication system based on OFDM for images transmission: The system is mainly used for underwater high-resolution images transmission or even video transmission. In the paper, hardware and software design and system debugging issues are discussed, and the system test has been completed.