Design And Realization Of Hydro-acoustic Communication System Based On Automatic Detection And FDMA

With the rapid development of modern communication technology, theapplication field of communication is more and more widely, which increasinglyimpacts on the human. At present, wired and wireless communications over the waterhave developed quite mature, but underwater wireless communication is still in theresearch and development. The oceans occupy a large area with rich resources andhuge development and utilization of value and a great demand for underwatercommunication is needed in both military and civil field, so there is an increasingemphasis on research and development of underwater communication systems. In thelong-distance underwater wireless communication systems, acoustic wave is the mosteffective transfer form to transmit information. Under this background, the research ofcommunication systems in the ocean has become a hot spot.In this paper, the modulation and demodulation parts of underwater acousticcommunication systems are studied and an automatic signal-detection of modulationand demodulation system is designed, which makes the system more adaptive.The paper firstly introduces the research and progress at home and abroad, thebasic principles and structure of the underwater acoustic communication. Thenaccording to modulation and demodulation part of the structure of the underwateracoustic communication system, the basic principles of the related technology torealize the modulation and demodulation system are introduced and analyzed, whichprovides the theoretical basis for the design of automatic detection of modulation anddemodulation system in underwater acoustic communication.Next, this paper introduces the design of the general structure of the modulationand demodulation system, and focus on the circuit design of the system and thebuilding of the hardware platform. At last the three main function modules of the design system are analyzed in detail. The basic structure, principle and characteristicsof the direct digital frequency synthesize technology is introduced briefly, and thenthe scheme of modulating circuit with the DDS technology is presented. According tothe requirements of the design system and the advantages of energy detectionalgorithms, the scheme of using energy detection algorithm to realize theautomatically-detected function which meets the design of the system. And a newmethod to set threshold is proposed. The principle of DFT demodulation technique isintroduced and analyzed, and then the scheme of realizing the demodulation circuitwith DFT technology is presented.In the paper, the modulation and demodulation system with automaticallysignal-detection based on FPGA is designed and realized. The software developmentplatform used to achieve the system functions is described. Then the FPGAimplementations of the functional modules in the system parts are analyzed in detail,and finally the system is tested. The test result shows that the system works normaland stably, which meets the design requirement.