Design and Validation of Direct Digitization Scheme for GNSS Receiver Front-Ends

Traditional global navigation satellite system(GNSS) receiver front-ends is very complex and inflexible when receiving multi-system signals.To solve such a problem,a digitized radio frequency(RF) front-end design was proposed based on the direct RF sampling.Considering that GNSS signals primarily concentrate on low frequency band and high frequency band,like two integral band-pass signals,the sampling rate of such signals can’t be low due to the wide band.In this paper,firstly,the sampling rate selection algorithm for multiple band-pass signals was discussed.Then the direct RF sampling rate for such two GNSS band-pass bands was determined.For the purpose of lowering the aforementioned high sampling rate,a decimation and filtering network was designed.Finally,based on the fact that analog to digital converter(A/D) specially designed for direct RF sampling is capable of outputting the data at half the sampling rate,the digital down-conversion of the signal of interest as well as its separation from the entire band was realized.Thus multi-frequency signal receiving can be achieved by software implementation of the design and the system flexibility will be greatly improved.Experiments have proved the effectiveness of the design.