Research On Synchronization And Equalization Of Underwater Acoustic Communication Sweep-spread Carrier System

In a shallow water acoustic channel,the phenomenon of severe time-space-frequency varying exists due to the spread of multiple path,dispersive phenomena,which may lead to signal distortion and the decreasing of the system reliability.To construct a high-rate and reliable underwater acoustic communication system,this paper utilized Sweep-Spread Carrier(SSC)system based on de-chirp demodulation.However,the increasing of the communication rate meant the Anti-interference processing would be ever more challenging.Therefore,this paper had a research on two of the key technologies of the SSC system to improve the reliability,which are synchronization detection and channel equalization.Synchronization detection plays the most important role in the underwater acoustic communication systems.It is discovered that the STLFM signal has double energy peaks in their 'optimal' fractional Fourier transform domain and these two peaks have symmetry in their amplitude if the STLFM signal is captured in the accurate time windows for the synchronizing.By taking its unique feature into account,a synchronization detection method based on the STLFM(Symmetrical Triangular Linear Frequency Modulation)is proposed in this paper.Also,channel equalization and SSC system was combined to improve the anti-inter-symbol-interference,avoiding the frequency selective fading brought from rate increasing.In this paper,the three equalization schemes are combined with time domain equalization,frequency domain equalization and fractional Fourier domain equalization respectively.Finally,the performance simulation is carried out in Bellhop channel model,Raytracing channel model and Wu-yuan Bay test channel respectively.The main work of this paper is summarized as follows:1.Firstly,the research background,the status of synchronous technology and the research of equalization technology are introduced systematically.2.The basic principle of the sweep spread carrier system is introduced,and its advantages and disadvantages and performance improvement space are expounded.Then discuss the first improvement point-synchronization.Based on the symmetric trigonometric frequency modulation signal,a synchronization algorithm based on symmetric trigonometric frequency fractional symmetry is proposed,and the simulation performance is simulated under three model channels.3.Research on channel equalization techniques.The basic principle of time domain equalization,frequency domain equalization is introduced,and the basic scheme of equalization scheme is realized by linear equalization structure.In the simulation channel simulation performance,analysis of the basic characteristics of various programs.4.On the basis of realizing the linear equalization,the equalization structure is transformed into a nonlinear structure,and the equalization ability of the inter-code crosstalk is further improved.Time domain,frequency domain equalization using turbo equalization structure,and fractional domain equalization using linear structure.