Research And Simulation For GNSS Intermediate Frequency Signals

With the development of modern science and technology, the global satellitenavigation system has been used widely, and been closely linked to everyday lives. As thesatellite navigation system is able to provide fast and accurate positioning, velocity andtiming services, navigation and positioning technology has been widely used in variousindustries, such as national defense, air shipping and life rescuing. The current globalsatellite navigation system includes the U.S. GPS system, Russia’s GLONASS system, theEuropean Galileo system and China’s Compass system. Among them, GPS andGLONASS systems have been built and are being modernized, while the Galileo andCompass systems are being constructed and improved, and soon will be able to startproviding the navigation and positioning services.With the growing number of global navigation system built and used, the users havemore option of navigation system than before. In order to avoid duplication ofdevelopment and waste of resources, it is necessary to design a suitable receiver with goodperformance, that is, through which users can receive signals of a variety of navigationsystem and can complete navigation. To develope this kind of system which can receivedifferent types of navigation signals of GNSS systems and can successfully completenavigation and positioning services and to meet users’ requirements for a multi-purposewill become the future development direction for the receiver. The research anddevelopment of receiver is inseparable from the test of signal, which requires signalsimulator capable of generating close to the real environment navigation signals, and allthis start from the research of digital IF signal. In this paper, we take the U.S. GPS systemand European Galileo system as examples, and do research on the IF signal.First, the structures, thesignal composition and the signal generating of these twonavigation systems were studied, and the characteristics of these two navigation systemswere analyzed. Second, the digital IF signal generation principle by the signalgeneration process were further analysed to derive the mathematical model of digital IFsignal. For the navigation signal transduction in real environment, the paper discusses thevarious sources of error signal and derives their mathematical model and gives a digital IFsignal simulator structure. Finally, in order to achieve the IF signal simulation in theMatlab software environment, we set up an simulation platform close to the real digital IFsignal. Using the simulation platform, the error mathematical model and digital IF signal model were simulated. The results show that each mathematical model is right.