| Spectrum monitoring is one of the key technologies of radio spectrum management. The main tasks of spectrum monitoring are as follows. a) Monitoring the interest of bands or frequencies and providing information available for frequency assignment and electromagnetic environment evaluation. b) Monitoring the spectrum of the built stations to determine whether they operate on the authorized status or range. c) Finding and locating harmful interferences.The traditional methods of spectrum monitoring are mainly to utilize a spectrum analyzer /receiver (e.g. HP8563E) to receive and collect the interest of signal (IOS) and realize the spectrum measurement and statistic by spectrum analysis. But the traditional spectrum analysis methods have some limitations. The main reason is that the Fourier transform represents signal as the sum of sine waves which have entire property. But the actual signals carrying information usually have the time-varying spectrum and local property. So the signal can not be characterized well, and the spectrum will be not monitored well in precision and particularity. With the rapid development of radiocommunication service, the number of stations and the density of high buildings are increasing rapidly, especially the mobile stations, so the electromagnetic environment becomes badly day after day. The methods of radio-determination and radiolocation are limited in finding the harmful interferences and stations. Therefore, some parameters of the inferences need be estimated, such as center frequency, bandwidth, code rate, et al. It is useful to capture the characteristics of interferences and find them.With the above reasons, besides the traditional spectrum analysis, this paper utilizes the time-frequency analysis tool to estimate the parameters of signals and provides a new radio spectrum monitoring system based on software-defined radio. The system has some merits as follows. a) The system can more precisely and particularly monitor the signal spectrum with the method of time-frequency analysis introduced. b) With the estimation of the signal parameters, the system can catch some characteristics of the interferences and find the interferences effectively. c) Based on the software-defined radio, the level of automation of the system is high. Finally, the paper discusses the problems of system realization in actual engineering. |
