The Implementation Of RF Signal Demodulation In Baseband And Spectrum Analysis Based On Software Radio

Communication technology, especially wireless communication technology, is developing rapidly. The shortage of spectrum resource, the increasing complexity of electromagnetic environment, the growing denseness of RF signals and the RF signal interference are becoming the main problems in the development of wireless communication. The spectrum resource is one of the most important strategic resources for a country. So, in order to protect, manage and utilize the limited spectrum resource efficiently, we must strengthen the spectrum resource management. The frequency assignment and the spectrum daily maintenance are the two main tasks of spectrum resource management. Both of their executions depend on the result of radio monitoring, which relies on radio receivers. As a result, the radio receiver plays an important part in the spectrum management.Nowadays,the manufacture of monitoring receivers is mainly monopolized by the multinational companies belong to the developed countries such as Germany, France, America and so on. The receivers made by these companies are so expensive that we almost can't offer for them. Today, the requirements in radio monitoring field change rapidly, the monitoring system is necessary to updates frequently. But the update of the imported monitoring products is very expensive and the procedure is complicated. So, to make radio monitoring receivers by ourselves has important significance to the development of our country's communication technology. The receivers must accords with our national condition, with independent intellectual property, update conveniently and with low costThe development of software radio solves the problems that the traditional analog receiver can not solve. Radio receivers based on software radio can monitor in wide-band, high speed and complicated electromagnetic environment. The receivers have the characteristic of high-compatibility. The development of software radio made the study of digital receiver with higher-speed, wider-band, higher-compatibility and more conveniently characteristic becoming possible. There has been many high performance digital radio receivers based on software radio soled in the radio monitoring market. But, in our country, the development of digital radio monitoring receivers is nearly at the starting stage.The paper realized some key functions in the digital receivers that based on software radio. Baseband demodulation, ITU measurement and spectrum analysis are implemented in the paper. The paper introduces the demodulation process of amplitude modulation, frequency modulation, phase modulation signals in detail. Also, the paper realized the measurement of some signal characteristics suggested by ITU such as modulation depth, frequency deviation and signal-occupancy-bandwidth. At the end of the paper, spectrum analysis for RF signals was implemented. During the process of baseband demodulation of FM signal, the rule of phase fuzzy was found and the ambiguity resolution was exposed. Then the demodulation for signals that demodulated by frequency was achieved successfully. During the realization of ITU measurement, the method to calculate signals'modulation depth from signal envelope, which was computed by software, was exposed, the method to compute the frequency deviation using the instantaneous frequency, which was demodulated in FM demodulation process, was exposed too.Besides the realization of demodulation, the paper analyses the performance of anti-frequency offset and anti- phase offset characteristics of the baseband demodulation. Also, the application scope of various demodulation methods was analyzed. Meanwhile, many methods to measure the ITU signal characteristics were implemented. The application scopes of the methods were also studied. In the process of spectrum analysis, various methods were adopted and the results were compared. The measured results of the baseband demodulation, ITU measurement and spectrum analysis are accords with the real signals'character tics. The functions in the paper performance good. It's proved that they can be part functions of digital radio receiver. The system described in this paper meets the original requirements.