Smoother-Based GPS Signal Tracking in a Software Receiver

Global Positioning System (GPS) signal tracking algorithms have been developed using the concepts of Kalman filtering and smoothing. The goal is to improve phase estimation accuracy for non-real-time applications. A bit-grabber/software-receiver has been developed for the GPS L1 coarse/acquisition signal. The bit grabber down-converts, digitizes, and stores the raw RF signal. The software receiver tracks each signal using a 2-step process. The first step uses phase-locked and delay-locked loops. The second step refines the tracking accuracy through the use of linear smoothing techniques. These techniques make optimal use of after-the-fact data.