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.