Study On Simulation Of Gps Software Receiver Technology

GPS software receiver technology, which is based on Software Defined Radio, can be used to process GPS IF (intermediate frequency) digital signal in the general software environment, and to implement GPS signal acquisition, tracking, demodulation and so on, with the aim of realizing navigation and positioning. The technology uses less peripheral hardware, and can handle more signals processing in the programmable software environment. And it has many advantages over the traditional hardware-based receiver technology in the flexiblility, economical consideration, modulization, visualization and so on. Therefore, it will meet GNSS rapid development so well that it is becoming an important study focus as well as a promising direction. The dissertation mainly focus on the the key algorithm of signal acquisition and tracking involved in the GPS software receiver.First of all, beginning with the definition of SDR, the advantages of receiver based SDR over traditional GPS receiver are simply summed. Then the general architecture of GNSS receiver based SDR is described, and so is the basic theory of the signal processing in GPS software receivers.Secondly, the spread spectrum modulation of GPS signal is introduced, and the correlation properties of C/A code, as the basis of the algorithm involved in the paper, are studied in detail. Then Doppler effects upon the carrier and code in the GPS signal is analyzed. Based on the above analysis, IF digital signal is simulated as the data source.Thirdly, the fast acquisition method based on FFT in frequency-field is mainly studied. The results of the comparison experiment with the real raw signal show that the frequency-field method can much more effectively reduce the acquisition time than the traditional method. Based on the frequency-field method, two ways of weak signal acquisition are presented: coherent integration and non-coherent integration. The test results with the raw signal reveal that non-coherent integration acquisition has better performance.Finally, the principle and realization of the Early-Late Delay Lock Loop (DLL) used to track code and the Costas Phase Lock Loop (PLL) used to track carrier are studied. The test results verified the feasibility and validity of the tracking algorithms.