I found some interesting material in the WMExperts about GPS and aGPS.

GPS stands for Global Positioning System, as aGPS stands for Assisted Global Positioning System.

What is "Assisted" and who is the assistant, you ask?

Here's the answer:

Ever noticed that when you first start a route it sometimes takes a long while for the navigation software to find your location?

Well, it's not a problem in the software of course, it's a problem caused by the way GPS works:

Your GPS device needs to find orbit and clock data for the relevant satellites - this process is called TTFF (Time To First Fix) or "Cold Start" and it takes a while (sometimes few seconds, with my bad luck it usually takes few minutes - after I already took the wrong exit...).

This is where the 'a' gets into action:

When you use assisted GPS this process is much faster because the device is pulling the satellite information from a cellular network, which usually gets this information much faster. This process saves time and battery life, but it can also cause problems as described by Tariq Bamadhaj at MyTodayScreen:

"When aGPS is turned on, it relies on data from your carrier to fix your position. So if your carrier did not have those data, as in my case with T-Mobile USA, aGPS is just a glorified feature on your device..."


So, to summarize:

aGPS gives:

  • Faster location acquisition
  • Less processing power is required by the device
  • Saves battery life
  • Location acquisition indoors or in non-optimal environmental settings

But if the Cellular carrier does not hold the relevant information, bugs and problems may occur.

Read more about it in here: Quick Tip- You May Not Want aGPS On

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Ran said…
you mean 'cold start', not 'called start', right?
Gil Bouhnick said…
Thanks for the correction.