GPS IN MOBILE PHONES

•In 1999 Mobile phone manufacturer Benefon launched the first commercially-available GPS phone, a safety phone called the Benefon Esc! The GSM phone was sold mainly in Europe, but many other GPS-enabled mobile phones would follow.

• The Esc! was featured a large, greyscale LCD. Esc! allowed for users to load maps onto the phone, to trace their position and movement, and to call or send their coordinates via SMS to a list of set numbers by setting an "Emergency Key". It also featured a "Friend Find" service, whereby users with Esc! handsets could track each other's locations directly on their handset display.

•A normal GPS receiver listens to a particular frequency for radio signals. Satellites send time coded messages at this frequency. Each satellite has an atomic clock, and sends the current exact time as well.• The amount of information needed to operate well, it can take 30-60 seconds to get a location on a regular GPS

AGPS

The lowest form of GPS does the following:

• Get some information from the cell phone company to feed to the GPS receiver - some of this is gross positioning information based on what cellular towers can 'hear' your phone, so by this time they already phone your location to within a city block or so.

• Switch from cellular to GPS receiver for 0.1 second (or some small, practically unoticable period of time) and collect the raw GPS data (no processing on the phone).

• Switch back to the phone mode, and send the raw data to the phone company

• The phone company processes that data (acts as an offline GPS receiver) and send the location back to your phone.

AGPSThis saves a lot of money on the phone design, but it has a heavy load on cellular bandwidth, and with a lot of requests coming it requires a lot of fast servers. Still, overall it can be cheaper and faster to implement.

More recent designs include a full GPS chip. They still get data from the phone company - such as current location based on tower positioning, and current satellite locations - this provides sub 1 second fix times.

This information is only needed once, and the GPS can keep track of everything after that with very little power. If the cellular network is unavailable, then they can still get a fix after awhile. If the GPS satellites aren't visible to the receiver, then they can still get a rough fix from the cellular towers.