Design And Implementation Of The Front-end For Navigation Receiver Based On RF Sampling

For recent years,the four main global satellite navigation systems are developing at the same time with the ascending dependence for global Satellite navigation technology from high-technology military and human-being's daily life.The monitoring navigation receiver,which is compatible with multiple frequency points and systems,becomes highly significant as the new institution signal is developing.In consideration of the development trend of satellite navigation receiver having multiple frequency points and systems,it is very essential to come up with the digital radio frequency(RF)front end.The satellite navigation receiver based on the direct RF sampling technology adopts the digital down conversion(DDC)technology,so that it can ensure the consistency between each two frequency points and more acceptable distortion of the signal.The front end of the receiver would easily disturbed by many kinds of radio frequency signal because of the long distance between the satellite and the ground,so the interference restraint and the parameter estimate are also the important.This paper introduces a design method of the double channels DDC based on the RF sampling,and comes up with a program of DDC based on six frequency points and nine channels of signal through the research of the band-pass sampling theorem,the mixing technology,the multiphase pumping filtering and the CIC and FIR filter,and some essential simulation and FPGA realization are undertaken.In the design process,processing of optimizing according to the performance of filters are used to save the hardware resource.The time domain processing and the frequency domain processing are respectively used before and after the DDC processing to restrain the impulse interference and narrow band interference and the estimation of parameters.One kind of method for acquiring the estimation of the impulse width and period of impulse interference,along with the frequency point and bandwidth and the JSR of narrow band interference,is come up with through energy accumulation and the threshold iteration to restrain the interference.The researches above are undertaken based on the same platform,and realized by a FPGA after the simulation through MATLAB and MODELSIM.They are assembled to become the digital front-end of the navigation receiver.It is a bridge between the signals from antenna and the tracking and capture of the receiver.