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

In the past 20 years, wireless communication has advanced rapidly in the world,which provides kinds of services to the people, and satisfies various requirements of our society.Whereas, most of the wireless communication systems are not compatible with each other, and it has already become a great difficulty to overcome nowadays. Software radio (SR) emerged as the times require, and provides a thought of solving this problem. SR is based on a versatile programmable platform to realize all kinds of communications criterions, to meet requirements of many increasing new molds and functions. The agility of systems is highly improved. As another revolution in wireless communication area, SR has become one of the most important research fields. This paper aimed at studying the principle, architecture and features of SR, and the result shows that the ideal SR can hardly be realized now because of the deficiency of the electronic devices and technology in present day. As a compromising method, a SR receiver platform based on direct mid-frequency band-pass sampling is researched in this paper, which is one of the feasible software radio systems nowadays. This paper explores how to make use of ADC(Analog to Digital Converter), DDC(Digital Down Converter), DSP(Digital Signal Processor) devices to build the SR platform. Almost all kinds of functions of SR are realized by software, and demodulation can be realized based on the same hardware platform only by software too. The theory of demodulation algorithms for SR has been analyzed in this paper, and digital quadrature demodulation for IF receiver system is adopted because of excellent characteristic prior to analog correlation demodulation. Finally, the demodulation courses of AM(Amplitude Modulation) and FM(Frequency Modulation) are simulated with SIMULINK. The theory analysis and emulation research prove that SR system based on direct mid-frequency sampling is feasible, and possesses the flexibility and expansibility.