Gps Signal Acquisition, Tracking Algorithm

Although originally developed for the military, the GPS (Global Positioning System) has proven invaluable for a multitude of civilian applications. Each application demands specific performance from the GPS receiver, and the associated requirements often vary widely. The pursuit of market-admitted GPS receivers with high precise and low-cost make more people do research on GPS receivers.The receiver is consisted of RF front-end, signal acquisition, signal tracking, bit synchronization, sub-frame synchronization and the navigation solution modules. Signal acquisition and tracking is critical for a GPS receiver, for their speed and sensitivity decide the receiver performance. Since the ability of the GPS receiver to work under weak signal and various dynamic conditions is required nowadays, signal acquisition and tracking algorithm should be modified for higher sensitivity and less complicated.The paper is organized as follows. First, GPS signal simulation. GPS signal is simulated by NCO based algorithm and look-up table method, which can be used in algorithm verification. Second, signal acquisition. A new acquisition algorithm with high sensitivity based on the combination of coherent and non-coherent integration is proposed. This is followed by a description of three other algorithms. Finally, after analyzing the general tracking method, a new method based on PLL/FLL is introduced.All algorithms are demonstrated using simulated GPS signals and real GPS signals. The results have shown the coherent/non-coherent integration acquisition algorithms ability to reliably work with 33dB/Hz signals, the PLL/FLL tracking algorithms ability to reliably work with acceleration over 10g.