Digital Modulation Recognition And Multipurpose Digital Demodulation On The Basis Of SDR

The SDR, Software Defined Radio, is a kind of new architecture which was first proposed in 90's in last century. Its primary idea is to realize all kinds of functions on an opening expanded and simple hardware platform by loading related software programs, without changing the structure of hardware circuit. It is the important parts of SDR that are the automatic digital modulation recognition and the methods of multipurpose digital demodulation. The technique of modulation recognition is the precondition with which the demodulation and communication can successfully carry out under the complex situation of many modulation types in future. Moreover, the technology of modulation and demodulation is the basis of modern communication. The ideal methods of digital demodulation should be a multipurpose one that can demodulate many types of digital modulation signal in the environment of SDR.This work has been carried out as a part of project, named design of experiment platform of mobile communication based on SDR. According to the development trend and applied request of SDR, we concentrate our study on digital modulation recognition and methods of multipurpose digital demodulation.This paper firstly introduces the experiment platform of mobile communication based on SDR that is regarded as hardware basis of our research. The platform is made up of ADC, DAC, transmitter, receiver and high-speed digital signal processing board. And the board's core is the DSP chip TMS320C6713 produced by TI Company. All of our works, including simulation, real-time emulation and downloading, are able to be completed on the platform because of its characters of high-speed processing ability and strong function. Two new character parameters, N_Z and E_a, are picked up with inheriting the research fruits of twotheories, judgment theory by signal envelope and decision theory by instantaneous parameters. The two parameters respectively are the zero-crossing amount of envelope-layering sequence and the mean of envelop to instantaneous amplitude, via detailed analysis of sequence of envelope-layering amplitude of modulation signal. Using this method, 4 classes of modulation signal, including 8 types, can be recognized with 6 selected character parameters. And it only needs at most to calculate 4 parameters to identify a single modulation type. So it is very helpful to improve the ability of real-time processing of modulation recognition because of decreasing the number of character parameters. On the other hand, multipurpose methods of digital demodulation with envelope-layering also are studied and discussed in detail. Many experiments are made to test the methods' applicable effect, and the result proves that the methods are very effective and efficient to demodulate 4 classes of modulation signal, including ASK, FSK, PSK and QAM.With the situation of carrying out the project, this work is greatly useful and credible for the engineering applicability with its advantages of wide adaptability and simple calculation. So it is very applicable in the field of teaching and research. The methods of digital modulation recognition and multipurpose digital demodulation on the bases of SDR not only adapt the project of communication platform, but also have spreading value to applying in other wide-band SDR project and system of wireless communication.