Updated 26 May, 2012, 4:18 pm IST

What is A-GPS? How Does it Work?

18 Mar, 2010, 4:08 pm IST | by Kamakshi S

With the help of A-GPS, the GPS (Global Positioning System) technology has been brought to your cell phones too.

With the help of A-GPS, the GPS (Global Positioning System) technology has been brought to your cell phones too. Let us understand what it is and how it works.

A-GPS is an acronym for Assisted Global Positioning System. It addresses signal and network problems by using assistance from other services. Such technology in your cell phone can help you in various ways like tracking your current location, receiving turn-by-turn direction instructions, location based tracking, etc. The working of a GPS and an AGPS is similar apart from this minor detail. Let us first understand how GPS signals are received and monitored.

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Working of a GPS system:
GPS uses 27 satellites (24 currently working, 3 are meant for backup, in case of failure) to enable a person to pin-point his current location. The calculation to ascertain the location is based on a simple arithmetic theory known as trilateration.

Since the Earth is a sphere, each satellite generates a specific part of the sphere it hovers and revolves with. An intersection of three such spheres which is closest to the GPS device’s location is done and the location is thus identified. This technique of trilateration is known as 3D trilateration. To gather the requesting device’s current location and provide accurate response, the GPS receiver requires two vital details, i.e. the location of at least three satellites above it and the distance the device and each of those satellites. These details are usually provided using low-frequency radio signals.

Hence more expensive GPS devices tend to have multiple sensors for better reception. This information is then relayed back to the receiver device, via radio waves or other such technique.

Working of an A-GPS system:
GPS devices can plot absolute directions based on your current position or they can give you directions through a map device irrespective of your current position. Thus a good GPS system with high-sensors can cost you quite a lot.

As a step further, A-GPS technology helps to overcome these glitches. Suited for mobile devices, A-GPS takes assistance from GPRS and at times, the service provider network information, to pin-point the current location accurately. Moreover the amount of CPU and programming required for a GPS phone is reduced by diverting most of the work to the assistance server instead.

A typical A-GPS enabled Cell phone uses a GPRS or other such Internet based data connection to build a contact with the assistance server for A-GPS. This exercise usually is a bit slow if you are connecting with the server for the first time. As this technique does not take into account the cell phone service provider network completely, you only pay the GPRS usage charges and nothing else. The only down-side to this technology is that an A-GPS server cannot utilize any of the three standby satellites available for GPS connections.