Understanding AGPS (Assisted GPS)
Almost all smartphones out in market has inbuilt AGPS chip and if you are wondering what is AGPS and how its different from regular GPS then here is my attempt to help you understand.
Before we start, here is my analogy.
If GPS is Byke, then aGPS is a Byke with Choke.
Yes, Role of Choke in Byke and ‘A’ in AGPS are similar, both help to reduce start time. In simple language it helps to speed up.
So What is AGPS?
AGPS is Assisted Global positioning system, which takes assistance from mobile tower to reduce time to fix position. Mobile towers has GPS Receivers which will continuously receive signals from GPS satellites and powerful servers to process the received information.
AGPS in mobile device can access this information available in mobile tower servers to increase time to fix first location. Following are some of the advantages of using AGPS
- Faster location acquisition
- Less processing power thus saves battery.
- Indoors location acquisition
Is AGPS sending mobile tower location instead of actual user location?
No, it will take information from mobile tower to just fix initial position. So that AGPS will return updated user location faster. To understand what information AGPS use from mobile tower and how its increasing startup time, then we need to understand how GPS works. Understanding it will also helps us to get answers for below
- Why GPS not works at indoor?
- Why GPS takes more time to provide location?
- Why GPS consumes more battery?
OK, How GPS Works?
I have avoided all jargons and tried my best to simplify as much as possible so that everyone will understand it better
There are around 32+ satellites circling earth at an altitude of 12k miles to and sends precise orbital information like distance, time at 50bps. Receiver needs to receive this information and process it to find important information like distance and time.
Step one is finding right satellites, not all satellites are visible from user location because of the shape of the earth but we still need to find and receive distance information from 3 or more satellites from available satellites to calculate and find user location.
Time taken to find this information is what we call as TTFF(Time To Fix First). This initial TTFF is often called a cold start, it can take anywhere from 18 seconds to few minutes to acquire a signal. Again time varies on user location and amount of interference. Open fields are faster than buildings because buildings can interfere with the satellite-receiver line of site.
Step two is triangulation, if we get distance information from three or more satellites then we can start calculating user location.
Finding right satellites, receiving signals , processing it and finally triangulating it are time consuming tasks.
Here comes A-GPS, which will help use to find right satellites and signal processing.
Will AGPS work without mobile network?
Yes, Almost all A-GPS chips available in mobile will fall back and work as regular GPS when there is no connectivity to mobile network.
If you think any other information on A-GPS can add value to above article then comment to improve.
