What is A-GPS? How does it work?

Assisted GPS or Augmented GPS (commonly abbreviated as A-GPS or aGPS) is a system to help reduce the boot time and start positioning of GPS devices.

A-GPS is now common in phones, computers, tablets with GPS, especially the use is even more after the US requires 911 calls (police call, emergency call) to be located. Caller to support as quickly as possible.

Normal GPS devices only rely on information from satellites to operate. They will take 30-40 seconds to be able to locate you the first time you start up because the data transmission speed of the security signal is only about 50 bits / s, very slow, causing the download to lose a lot of information. . Not to mention that if the satellite signal is lost during positioning, the device will have to do this from the beginning, and then into the urban area, the signal will weaken because of buildings, not to mention that weather events, meteorology, and even trees on the head.

How A-GPS works.

That's why people make A-GPS, it will work thanks to the A-GPS servers deployed by the mobile network operator. These servers can be considered as a cache of GPS data, it will take data from satellites and store it on the ground database. When your phone accesses these servers, they get information much faster using 3G, 4G, or even Wi-Fi connections. These connections are much faster than satellite links.

As such, your phone will get information about its location in an approximate way, though not as accurate as retrieving data directly from GPS satellites, but locating a narrow area in a short time. very short is very good already. Slowly, when the GPS signal is more stable, the phone will calculate the exact location.

This support data is divided into 2 types:

1. Mobile Station Based (MSB) : Phones that use a support server to help find satellites faster because the server already has satellite flight trajectory information and the exact time. The phone then calculates its location.
2. Mobile Station Assisted (MSA): The phone records the time and location of GPS satellites, sends this data to the ground server so it can calculate it (in combination with some other data stored by the server). stocked). Once done, return to the current location for the phone.
   One advantage of MSA is that the server will perform location calculations so the phone will be lighter, the location will be calculated faster.

As you can see above, A-GPS requires Internet to work , so when you go into weak signal areas or the network connection is broken, A-GPS no longer works. And in theory, you also spend a little money on 3G, 4G network capacity, though not much. Meanwhile, the GPS connection is not dependent on the Internet at all.

Most phones today not only use GPS or A-GPS, it also combines with the system of positioning using Wi-Fi, the system of positioning with mobile stations to calculate out your location. That's why iOS and Android both now announce that when you turn on Wi-Fi, your location will be more accurate than using GPS.