Direct sampling global positioning system (GPS) receiver

摘要

A direct sampling technique for use in global positioning system (GPS) receivers, in which received signals are separated into two frequency bands centered at frequencies L1 and L2, respectively, and are then digitally sampled using analog-to-digital converters (24.1 and 24.2) controlled by sampling clock signals derived from a common clock signal generator (26). The clock signal generator frequency and the digital sampling frequencies are selected to provide a sampled carrier frequency that is as low as possible without resulting in a spread spectrum with components in both a positive and a negative frequency region of the spectrum, thereby preserving the real-valued nature of the signal samples. For L1 at 308F and L2 at 240F , where F=5.115 , a common clock frequency of 8.5F satisfies these requirements by providing aliasing sampling rates of 306F and 238F, respectively, with L1 and L2 both having sampled carrier frequencies of 2F.