A direct RF sampling multifrequency GPS receiver

The future satellite positioning/navigation systems (both GPS and Galileo) will provide civil signals on multiple frequencies, similar to that currently available only for military use. The multiple distinct frequencies will provide many advantages to users of the navigation systems. This paper presents a direct RF sampling front end design well suited for multiple frequency satellite navigation receiver design. No frequency down conversion is necessary, rather the particular frequency bands of interest are intentionally aliased using a wide band ADC. The resulting samples are passed, via a doubling buffering FPGA design, to the memory space of a host PC for storage as well as eventually processing of the multiple frequency transmissions. This paper describes the design of the front-end, validates its concept with collected data, and discusses the variations on the design of a generic multiple frequency GPS front end.