Assisted GPS, A-GPS, AGPS

GPS and A-GPS work together to supply fast and accurate location information

SiRF A-GPS Chip
SiRF A-GPS chip. SiRF

Assisted GPS, also known as A-GPS or AGPS, enhances the performance of standard GPS in smartphones and other mobile devices connected to the cellular network. Assisted GPS improves the location performance in two ways:

  • A-GPS helps the phone obtain a faster "Time to First Fix," (TTFF) which significantly improves startup performance. Assisted GPS acquires and stores information about the location of satellites using the cellular network so the information does not need to be downloaded by satellite.
  • Assisted GPS positions a phone or mobile device when GPS signals are weak or not available. GPS satellite signals may be impeded by tall buildings, and they don't penetrate building interiors well. Assisted GPS uses proximity to cellular towers to calculate position when GPS signals are not available.

How GPS and Assisted GPS Work Together

A GPS system needs to make satellite connections and find the orbit and clock data before it knows its location. This is the Time to First Fix. The process can take from 30 seconds to a couple of minutes before your device can acquire a signal—exactly how long depends on the surroundings and amount of interference. Wide-open areas are easier to acquire a signal in than a city with tall buildings.

When your device uses assisted GPS, the time to signal acquisition is much faster. Your phone pulls information about the location of satellites from the nearest cellular tower, which saves time.

As a result, you:

  • Get faster signal acquisition
  • Save battery life
  • Get location information even when GPS can't get a signal

By itself, assisted GPS doesn't position the mobile device as closely as GPS, but working together, the two cover all the bases. All modern phones have an A-GPS chip in them, but not all phones use it.

When you are looking for a new smartphone, ask if it has full, autonomous assisted GPS that is user accessible. This is the best configuration for users, although only some phones support it. Some phones may offer only limited A-GPS or assisted GPS that is not accessible to users at all.