Editing Assisted GNSS (section)

== Operation ==
In A-GPS, the [[List of mobile network operators|network operator]] deploys an A-GPS [[Server (computing)|server]], a [[Web cache |cache server]] for GPS data. These A-GPS servers download the orbital information from the satellite and store it in the database. An A-GPS-capable device can connect to these servers and download this information using mobile-network radio bearers such as [[GSM]], [[CDMA]], [[WCDMA]], [[3GPP Long Term Evolution|LTE]] or even using other radio bearers such as [[Wi-Fi]] or [[LoRa]]. Usually the data rate of these bearers is high, hence downloading orbital information takes less time. Utilizing this system can come at a cost to the user. For billing purposes, network providers often count this as a [[data access]], which can cost money, depending on the [[Telecommunications tariff|tariff]].<ref name="cnet"/>

To be precise, A-GPS features depend mostly on an Internet network or connection to an [[Internet service provider|ISP]] (or CNP, in the case of CP/mobile-phone device linked to a cellular network provider data service). A mobile device with just an [[Global Positioning System#Satellite frequencies|L1 front-end radio receiver]] and no GPS acquisition, tracking, and positioning engine only works when it has an internet connection to an ISP/CNP, where the position fix is calculated offboard the device itself. It doesn't work in areas with no coverage or internet link (or nearby [[base transceiver station]] (BTS) towers, in the case on CNP service coverage area). Without any of those resources, it can't connect to the A-GPS servers usually provided by CNPs. On the other hand, a mobile device with a GPS chipset requires no data connection to capture and process GPS data into a position solution, since it receives data directly from the GPS satellites and is able to calculate a position fix itself. However, the availability of a data connection can provide assistance to improve the performance of the GPS chip on the mobile device. 

=== 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.