Research On Underwater Target Detecting Technology Using Variable-frequency Signal Based On Spectrum-cognition

Since the beginning of21st century, human beings pay more and more attention to theexploration of ocean, which has abundant resources such as power and minerals, along withthe development of social economic. Underwater target detecting technology plays animportant role in the development of ocean economics and in military and civiliandevelopment also. Furthermore, the rapid development of modern digital signal processingtechnology and integrated electronic technology provide greater research and developmentspace for underwater target detecting technology.Underwater target detection refers to detecting, observing and identifying the underwatertarget by the use of sonar, underwater television or magnetic detection equipment and so on,which transmit the signals in acoustic, optic and electromagnetic wave respectively. Radiowave and optical wave suffer large attenuation when propagating in underwater channel,which is the most complicated wireless channel of all. Acoustic wave is the only one that hasgood performance when propagating in underwater channel, therefore the acoustic detectingmethod is the most widely used underwater target detecting technology currently.Aimed at researching and making some improvements on the basis of traditionalunderwater target detecting technologies which have a few drawbacks such as low accuracy,complicated echo-wave processing, poor real-time capability and so on, this thesis design aprecise and highly real-time underwater target detecting method-Underwater target detectingtechnology using variable-frequency signal based on spectrum-cognition.1. By introducing the cognitive radio technology used on the land into underwateracoustic channel, the problem of poor quality of underwater channel is solved by the use ofspectrum-sensing. And the energy detection method is pointed out suitable for underwateracoustic channel, based on which a novel active and passive combined underwater spectrum-cognitive approach is put forward in this thesis. Simulation experiments verify that theintroduction of spectrum-cognitive technology into the underwater target detection canimprove the signal-to-noise ratio of transmitted signal, thereby enhancing the resolution of echo wave.2. Theoretical analysis and simulation experiment in the thesis show that chirp signal,when used as the detection signal, can obtain good time resolution and frequency resolution atthe same time, and that the output of the matched filter of chirp signal after propagating instrong Doppler-shift underwater acoustic channel has the pulse-compression characteristic.On this basis, a novel modulation method using variable-frequency signal is proposed, and itsworking principle and characteristics are analyzed.Finally, an integrated underwater target detection system and its simulation analysis areput forward. Simulation results verify the effectiveness of this system, and show that, theproposed underwater target detection system has higher resolution compared with thetraditional one without spectrum-cognition or single-frequency pulse signal detection system.