Simulate GPS Intermediate Frequency Signals By Software

GPS is a new generation system of satellite guiding and orientation. The system is global, all time active and based on radio wave. Plus it has the ability of accurate three-dimensional guiding and orientation. With the purpose of analyzing the entire GPS system's function and structureand, testing the performance of GPS signal simulator is needed that can be used to simulate the real GPS signals under all kinds of the conditions. This paper studies single channel GPS Intermediate Frequency (IF) signals generator which is based on software radio. It is necessary to simulate GPS Intermediate Frequency (IF) signals under all kinds of conditions by software.In this article, I first introduce the background and aim of entire subject to give the readers a main recognition. Then we start from the prototypes of the signal blocks and analyzing the subject theoretical foundation in detail. The analysis includes the techniques for Direct Sequence Spread Spectrum (DSSS) communication and the definition and generation of Pseudonoise Sequence. Further we discuss the mathematical model of physical blocks in order to process the software simulation. It includes the generator of C/A Code and the model of GPS Intermediate Frequency signals. It is ought to figure out that I discuss the influence the noise caused on this system. We use the C++ language to archive the simulation in the Microsoft Visual C++ circumstance. The entire generating system is divided into three parts, including C/A Code, Signal Generating and Quantizer. After writing codes and checking and confirming, I archive the basic functions. If you input the guiding codes and control data like satellite selecting signal, Doppler frequency movement, sampling period, at last you can get the digital middle frequency signals with gauss distributing noise.In the end, I summarize the entire subject and figure out some existing defects. It is making a definite direction for the deeper analysis and research of the GPS Intermediate Frequency (IF) signals's system in the future.