Final answer:
Assisted GPS (A-GPS) enhances GPS signal acquisition speed by using additional network resources, whereas Differential GPS (DGPS) increases accuracy by correcting GPS signal errors with ground-based reference stations. Both systems aim to improve upon standard GPS technologies, which must also consider relativistic effects for maintaining accuracy.
Step-by-step explanation:
Assisted GPS (A-GPS) and Differential GPS (DGPS) are both technologies that enhance the accuracy and reliability of standard GPS systems, but they function in different ways. A-GPS utilizes both satellite signals and assistance from network resources to quickly obtain the user's position, especially in environments where GPS signals may be weak or obstructed, like urban canyons. This greatly speeds up the time to first fix (TTFF) when acquiring satellite signals. In contrast, DGPS improves accuracy by using a network of fixed ground-based reference stations that transmit the difference between the positions indicated by the GPS satellites’ signals and the known fixed positions. This information is used to correct the GPS signal errors and can improve accuracy to within a few centimeters to a few meters.
GPS navigation systems must account for the effects of both special and general relativity to maintain precision and accuracy. Satellites orbiting the Earth at high speeds and altitudes experience time differently due to these relativistic effects, which must be corrected to prevent GPS units from losing their accuracy within minutes.