GPS takes a long time to get its position

Mon, 2013-07-29 15:36 by admin · Forum/category:

The first question is whether you had an Internet connection. Without Internet it takes much longer for the GPS to get a position.

To get a position fix, the GPS needs the satellite orbit data first. There are two ways to get these:

  1. Over the Internet
  2. From a GPS satellite

With an Internet connection a typical time to the first fix is 15 s. Even without an Internet connection the time for a subsequent fix, less than 4 h after the phone already had one, is also around 15 s.

Without an Internet connection things are getting a bit more awkward. The satellites do transmit their own orbit data (ephemeris), but they transmit the data only once every 30 s. Any interruption in the reception will destroy the data block. It's an all-or-nothing situation. If the reception keeps getting interrupted, like when you are in a city canyon or in a forest, it can take any time until the device is lucky enough to receive the entire ephemeris block from each satellite.

If your phone is clear of obstacles—and your own body counts as an obstacle as well, so hold it high—it may get its first position fix in less than one minute. But it can also take up to 15 min, or much longer under unfavorable conditions, until the GPS receiver can determine its position.

Things get even worse if the GPS has no Internet connection and is moving fast or has been moved more than 100 km or has not been used for half a year. In this case the time to first fix is around 15 min even under the best of conditions.

For a more elaborate, more precise explanation, please read Time to first fix.

Just remember: A smartphone without Internet is like a car without wheels.

I've had clueless people complain about bad GPS functionality, only to find that they had switched off their Internet connection.