Mobile Underwater Acoustic Communication Based On FH-FSK

In recent years,the underwater mobile platform represented by Autonomous Underwater Vehicle has developed rapidly.The mobile underwater platform needs to communicate with the mother ship,but the complexity of the underwater environment and the Doppler Effect caused by its own motion,will affect the performance of the communication.Therefore,it is important to study the robust and reliable communication of underwater mobile platforms.Shannon's theorem shows that when the rate of information transmission is constant,the signal-to-noise ratio and signal bandwidth are interchangeable.And the system bandwidth can be increased to ensure that the signal is transmitted with a lower information error probability at a lower signal-to-noise ratio,which is the basic idea of spread spectrum communication.As a kind of spread spectrum communication,frequency hopping communication is often combined with FSK modulation to form FH-FSK,which spreads information bits in the channel with specific hopping rules,and spreads the spectrum to improve the anti-jamming of the system,and to ensure reliable communication over long distances under complex channel conditions.This thesis studies mobile FH-FSK communication to achieve stable and reliable communication in underwater acoustic channel.The paper mainly includes the following contents:1.Study the relevant theories of FH-FSK communication modeling and simulation.Based on the mathematical model and communication model of FH-FSK communication,the FH-FSK communication flow is briefly analyzed.Then,the three generation methods of the frequency hopping pattern are simulated and analyzed.Then,the modulation and demodulation method in communication is studied.Finally,parameter simulation and communication performance analysis of FH-FSK communication are performed.2.Study channel coding techniques in FH-FSK communication.Communication performance is improved by using LDPC codes and polarization codes.In this paper,the check matrix of LDPC code is constructed by Mackay method,the generator matrix is generated by Gaussian elimination method,and the BP algorithm is decoded.When performing polarization code simulation,the position of the information sequence is selected by Gaussian approximation,and the generator matrix is determined by recursive expression,and decoded by CA-SCL algorithm.Finally,the two channel coding methods are combined with FH-FSK to verify the communication performance through simulation and river test.3.Study the doppler estimation techniques in mobile FH-FSK communication.Since the FH-FSK communication sequence is composed of a wake-up sequence,a synchronization sequence,and an information sequence.Therefore,when studying the Doppler effect,the effects of three methods,namely,the matched filter method,the fast correlation method and the Goertzel energy detection,are applied to the wake-up signal detection and the self-synchronization method based on the frequency hopping sequence.In order to eliminate the influence of Doppler effect,Doppler estimation is performed on multiple chips based on DFT interpolation.After obtaining multiple frequency shift factors,Kalman filtering is proposed to select parameters and optimize and improve the processing.Finally,the performance of mobile FH-FSK communication is verified by simulation and experiment.4.Study the implementation of FH-FSK communication system visualization software.Firstly,the overall design of the FH-FSK communication interface and the specific implementation of each module are introduced.Total,the visual design can be divided into a parameter setting module,a transmitting end module,a receiving end module,and a waveform display module.Finally,the implementation process of each module is introduced in detail,and the corresponding results are shown.