Difference Between GPS and AGPS

GPS vs AGPS

The Global Positioning System or GPS was a technology developed by the military to provide an edge in the battlefield. The GPS device receives information from any four of the 32 satellites that orbit the earth. It then calculates the distances from the satellites and derives its location by trilateration. Assisted GPS or AGPS is another type of GPS that relies on an assistance server, aside from the satellites. The assistance server provides additional information to the device that can aid it in the calculation of the location. This can be very helpful when the signal from the satellite is pretty weak.

GPS receivers have been around a lot longer than AGPS and standalone GPS navigation devices are being used in planes, boats, and most recently in cars. AGPS are common on mobile phones where the data link is already in place. The information from the assistance server can allow the device to provide the correct location where a standalone GPS receiver would otherwise no work. AGPS is also able to arrive to a fix much faster compared to GPS, especially the first time the device is booted. These desirable features make AGPS somewhat superior to GPS in terms of performance.

The data link required by AGPS can result in extra charges to your mobile phone if you do not have an unlimited data plan. These charges can vary depending on the pricing structure that the mobile phone company follows as some charge based on the amount of data while others charge based on the length of time that it is connected. Another problem with AGPS is the coverage of the mobile phone company. Although some AGPS receivers are capable of functioning as a GPS receiver, most are unable and would stop functioning once you go beyond the coverage area. GPS receivers are not restricted to the range of cellular sites and you can get a fix just about anywhere on the surface of the earth.

Summary:
1. GPS relies on the satellites alone to calculate its position while AGPS relies on both the satellites and an assistance server
2. AGPS receivers are mostly equipped on mobile phones while most standalone devices have GPS
3. AGPS can be more reliable than GPS in certain situations
4. AGPS can be faster in calculating the actual location than GPS
5. GPS is generally free while AGPS can incur additional charges
6. Some AGPS devices are capable of working as stand-alone GPS receivers once they go beyond network coverage

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