The Fully Digital MSK Modulation-Demodulation System Based On DSP

Now it is information society. In the all of information technologies, the transmission and communication of information take an important effect. And to the information's transmission, digital communication has been an important means. So the way of signal's modulation was converted from analog to digital continually and widely. This thesis studied MSK modulation scheme which is a kind of digital method depending on the development of today's communication technologies.This thesis mainly discusses the method of MSK modulation and demodulation. The traditional way of modulation and demodulation is using the way of analog. But in this thesis, a digital method of accomplishing MSK modulation and demodulation was put up and realized. The function of digital modulation and demodulation has been realized on the basis of DSP (Digital Signal Processor) system. And the mainly content of this thesis are presented as follows:1. Studying the method of MSK modulation. This thesis studied and introduced the method of MSK modulation. It is a special type of constant envelope-continuous phase FSK. Because MSK phase is continuous, the rolloff velocity of the MSK spectrum to the PSK was improved greatly. On the other hand, if the channel's bandwidth is presented, the data transmission rate of MSK is better than that of BPSK.2. Realization of signal's digital MSK modulation. The thesis used a fully digital method that employed the principle of direct digital frequency synthesis to realize the modulation based on DSP. This method only modulates digital signals. If the signal is analog, it must be filtered and sampled to be the digital signal.3. Realization of MSK modulated signals' digital demodulation. The digital MSK demodulation based on the DSP system employed the theory of power spectral analysis to demodulate the digital MSK modulated signal.The significance of this thesis is that it employs the most advanced digital technology in the field of communication to realize MSK modulation and demodulation. It is based on DSP system to finish all kinds of functions and it is a "SOFT" way. The "SOFT" way used in this thesis is not same as the traditional analog way. It is a fully digital method and has more flexibility:1. It is not necessary to design more involved hardware circuits. It focuses on the design of digital signal processing program.2. It can change some performance if some parameter was altered or the software was upgraded on the same hardware platform. For example, different data transmission rate was realized if the sampling frequency was changed in this thesis.3. In the same system, the software's modification can realize modulation of different ways, such as FSK and PSK.4. It isn't easy to be influenced and has strongly credibility, because the digital system only has two tones (high and low).5. It is easy to realize modularization.So this method has some practice meaning to the research of nowadays communication technology.