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 bandscentered atfrequencies L1 and L2, respectively, and are then digitally sampled usinganalog-to-digitalconverters (24.1 and 24.2) controlled by sampling clock signals derived from acommon clock signal generator (26). The clock signal generator frequency andthe digitalsampling frequencies are selected to provide a sampled carrier frequency thatis as lowas possible without resulting in a spread spectrum with components in both apositive anda negative frequency region of the spectrum, thereby preserving the real-valued natureof the signal samples. For L1 at 308F and L2 at 240F, where F=5.115, a commonclock frequency of 8.5F satisfies these requirements by providing aliasingsampling ratesof 306F and 238F, respectively, with L1 and L2 both having sampled carrierfrequenciesof 2F.