| The technology of modulation and demodulation is the key technology in the shipping information transmission . It is one of the most advanced technologies in the current communication field that realizing modulation and demodulation by software. This paper has studied and realized the Soft-Modulation and Soft-Demodulation taking sonic card of the computer as basic hardware platform on the basis of the thought of the software radio.This paper starts with studying digital modulation and demodulation theory at first, and analyses basic principle of three kinds of important modulation and demodulation way ( FSK, MSK, GMSK ). Then it puts forward the scheme of soft modulation-demodulation system based on sonic card on this basis: transforming from digital file to modulated audio file via algorithm by the use of computer. It also studies the algorithms of FSK, MSK, GMSK modulation and demodulation mode, and summarizes the general the software modulation and demodulation algorithm. Also, man-machine interactive interface for modulation-demodulation is preliminary designed and studied.The research method is using VC programming to realize the modulation and demodulation of the signal by audio-card.The significance for this paper is to realize digitized modulation and demodulation by means of the software. It is based on the audio-card of PC. The audio card of PC is the development platform, and it has convenience and practicability enormously. The content of this paper adapts the development and updating of current science and technology,having research value in a sense.
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