Key Technology Study And Implementation Of The Baseband System Of Satellite Position Receiver

The paper study the structure and principle of the baseband system of satellite position receiver based on Direct Sequence Spread Spectrum (DSSS), analyze the key technology.The paper presents the structure of Digital Down Converter (DDC), discuss how to achieve Direct Digital Frequency Synthesizer (DDFS) on FPGA efficiently. Discuss slippage correlation acquisition and point out the its disadvantage, present an improved method of acquisition by two stop and two threshold and analyze the improvement in theory. Study the application of Digital Match Filter (DMF) in PN code synchronization, against the disadvantage of slippage correlation acquisition. Analyze how to achieve DMF on FPGA efficiently. Introduce the guide acquisition based on distributed sample acquisition with good future. Focus on discussing the trace loop based on Delay Lock Loop (DLL), improve the accuracy of phase detecting by Least Squares. Fast Fourier Transformation is used in DMF to detect frequency shift fast and accurately in the condition of large Doppler Shift. Then the application structure diagram is present.Simulation is also present with theory analysis in the paper. The simulation result of DDFS is identical with mathematic compute and proves the correction of the method. The simulation and experiment of two stop and two threshold slippage correlation acquisition show that the acquisition time falls by 10%. The simulation of pipeline adder proves that the compute speed is improved and it can be used in DMF.The key technology of baseband system which is mentioned in this paper is based on FPGA, so the selection is a part of the paper. The algorithm is optimized according to the characteristic of FPGA.A part of methods which are mentioned in the paper is applied in BD-I satellite position receiver successfully. The other is prepared for another DSSS receiver, more details will be optimized and improved in application.