The Applications Of Hilbert-Huang Transform In Underwater Acoustic Communication System

The Hilbert-Huang Transform (HHT) is a new theory, which is first developed by Huang with other professors in 1998, for nonlinear and non-stationary signal analysis. The key part of this method is the empirical mode decomposition (EMD) method with which any complicated signal can be decomposed into a finite and often small number of intrinsic mode function (IMF). With the Hilbert transform, the meaningful instantaneous frequencies of every IMF which give precise description of the varying frequency are obtained.As a new signal analysis theory, the HHT has been widely used on nonlinear system, biomedicine, earthquake, bridge monitoring, error diagnosis, gravity wave, ocean circulation, environment engineering, and signal processing. However, there is no report about the application of this theory in communication field. In this paper, HHT has been applied to underwater acoustic communication. Feasibility study on this method is the focus of this paper.Firstly the paper states the main idea of the HHT and also some problems which are faced on application. Then it compares the FFT with the HHT in signal processing by using several practical examples in order to revealing the advantage of the HHT in signal processing. With the characteristics that the instantaneous frequencies of non-stationary signal can be given by HHT method, a new approach to modem is proposed——HHT modem. The merit of this modem has good secrecy.Using the new method proposed in the paper as modem, combining with RAKE receivers and Reed-Solomon (RS) code, we proposed the HHT underwater acoustic communication system. On the base of MATLAB simulation, we got the emulation of the HHT underwater acoustic communication system. We discussed its performance by error rate figure, and analyzed the improvement of environmental interference by RAKE receivers and RS code, finally, gave the environment which the system can suit. In order to validate the validity and stability of HHT underwater acoustic communication system in real communication environment, we have done the experiments in channel cistern and lake. The paper analyzed data we have got in the experiments. By researching the theory, analyzing the simulation and disposing the experimental data, we validated applying HHT method into underwater acoustic communication is feasible.Finally, the realization steps of the HHT modem based on the fixed-point digital signal processor (DSP) is provided. Considering with the memory and real-time of the DSP, we reasonably chose the methods such as end disposal, curve-fitting, ending condition, and summarized the DSP optimization methods. In the end, the simulator results of the method are given on the chip TMS320VC5509A in the CCS software.