Editing Assisted GNSS (section)

=== Modes of operation ===
Assistance falls into two categories:
; Mobile Station Based (MSB)
: Information used to acquire satellites more quickly.
:* It can supply [[ephemeris|orbital data]] or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases.
:* The network can provide precise time.
; Mobile Station Assisted (MSA)
: Calculation of position by the server using information from the GPS receiver.
:* The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position.
:* The assistance server has a good satellite signal and plentiful computation power, so it can compare fragmentary signals relayed to it.
:* Accurate, surveyed coordinates for the [[cell site]] towers allow better knowledge of local [[ionospheric]] conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position.

Not every A-GNSS server provides MSA mode operation due to the computational cost and the declining number of mobile terminals incapable of performing their own calculations. Google's SUPL server is one that doesn't.

A typical A-GPS-enabled receiver uses a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on [[time to first fix]], but does not depend on the network, and therefore can work beyond network range and without incurring data-usage fees.<ref name="cnet">{{cite web|last=Low |first=Aloysius |url=http://www.cnet.com.au/mobilephones/phones/0,239025953,339281483,00.htm |title=Phones |publisher=CNET |access-date=2017-04-02}}</ref> Some A-GPS devices do not have the option of falling back to standalone or autonomous GPS.