Abstract: The signal quality of navigation satellites is the essential factor to the positioning performance. When the interferences occur  on the satellite′s hardware or on the space propagation signals, the corresponding waveforms will be  distorted, and the correlation peaks generated by the receivers become biased, hence degrade the positioning resolution, moreover, the positioning ability of users may also lost. Through  monitoring  the space signals, it may further assure the system′s service performance. The  causes of the distortion for GPS signals were concluded  based on current signal quality monitoring techniques.The modeling of distorted signals was completed based on digital fault model, analog fault model, digital/analog fault model.  The methods of multi-correlators GPS signal monitoring were presented and verified by applying the above three models.

Key words: Signal quality monitoring, Multi-correlators, Signal distortion, Global positioning system, Navigation satellite