The Realization And Research Of Software Radio Receiver Based On Direct Mid-frequency Sampling

With the occurrence of multi-standards and poly-systems in wireless communication system, the increase of the requirement of intercourse and the lacking of radio frequency spectrum resource, the traditional wireless communication system cannot be adapted to the relative development. Software radio technology offers a feasible method to solve this problem so as to become a focus of research. Whereas, the deficiency both in electronic device and technology results in that the ideal software radio can hardly be realized and people have to seek a compromising and feasible method. Software radio receiver system based on direct mid-frequency sampling, which is researched in this paper, is one of the feasible software radio system nowadays.Firstly, the paper presents the basic principles of software radio, introduces the origin, the concept, the features, the research status quo domestically and abroad and the developing direction of the software radio, analyzes the different basic structures of software radio system in terms of different sampling methods, including software radio structure with broadband and low-pass sampling, software radio structure with direct band-pass sampling and the software structure with broadband mid-frequency sampling, and analyzes some key technologies in software radio.Consequently, through the full comparison of several signal sampling modes, the broadband sampling mode is centered out in adaptation to present application. Combining the software radio system with the idea of broadband mid-frequency sampling, the paper puts forward the feasible structure plot of software radio receiver system based on direct mid-frequency sampling nowadays. Then the working principle of each module is analyzed, including radio frequency processing, middle frequency processing and base-band processing. In the pre-procession of front radio frequency, the super-heterodyne technology which get proper A/D sampling rate through choosing a proper frequency and bandwidth is adopted.Furtherly, the paper analyses and studies the realization of the mid-frequency processing. According to the requirement of system property, AD6640 and HSP50214B are selected functioning as A/D switcher and specific programming digital downconverter, thenthe paper highlights the structures, functions, applications, designs and outer interface circuit connect of the AD6640 and HSP50214B.Finally, the paper presents the realization of the base-band processing. GMSK is selected as demodulating method for its excellent frequency spectrum characteristics and permanent envelope property. The paper introduces in detail the GMSK demodulation principle, different demodulating algorithm and realizing principle. Through the analysis of advantages of several GMSK arithmetic and requirement of system processing, the base-band time lag demodulating algorithm based on quadrature demodulation and TMS320VC5402 are selected for base-band processing. Furthermore, the paper introduces the basic development of DSP and hardware frame of TMS320VC5402, and provides the program flow chart of GMSK demodulation which realizes with TMS320VC5402 and emulational wave with CCS software.The theory analysis and emulation research prove that software radio receiver based on direct mid-frequency sampling is feasible, and possesses the strong flexibility and expansibility.