A Study For Voice Coding On Marine VHF Communication

At present, voice communication of Marine VHF uses analog, and the technology of voice communication system is easy to realize. But the bandwidth of the modulated signal is wide, and the quality and process of communication is hard to control. For this circumstance, on the basis of all digital VHF communication system, this paper puts forward a project of speech coding. The voice signal is dealt with MELP (Mixed Excitation Linear Prediction) coder and QPSK modulation. It can decrease the bandwidth and increase the transportation efficiency.MELP is a speech coding. It is based on traditional LPC parametric model, and applies five additional features. They are: mixed excitation, aperiodic pulses, adaptive spectral enhancement, pulses dispersion and Fourier magnitude modeling. It can simulate speech characteristics more naturally. The paper mainly develops the theory of MELP, including the procedure of coding and decoding, and some special formulas and methods. After it is dealt with by MELP coder, the voice signal is modulated. Therefore the application of the QPSK modulation enhances the efficiency of transportation. After studies on the theory of QPSK, the QPSK modulation is simulated with MATLAB tools, which confirms the feasibility of the project theoretically.The paper introduces the hardware including TMS320VC5416DSP and software programming in the project. We modify the algorithm of C language with the principles of DSP. It shows the procedure of software processing of algorithm and different parts of the algorithm. In this paper, with TMS320VC5416 DSK as hardware development platform and C language and assembly language as software tools, the realization of the MELP and QPSK has been initially achieved.