How does GPS work

When you turn on your GPS unit or GPS enabled mobile phone for the first time, it starts to search for satellites, usually it needs at least three satellites to determine your current location, however it needs signal from four satellites to acquire more accurate position. This process is called satellites acquisition and may take from a few minutes to over ten minutes depending on where you are.

When the GPS receiver needs to acquire the serial number, orbit and frequency of each satellites and store them. Then the GPS chip will use the signal received from the satellites to calculate your coordinates.

While determine your position, the GPS chip will store two types of data:

– The serial number, orbit and frequency of each satellite and their positions in four hours for future use (the data expires after four hours).
-The coordinates of your last place.

So next time you start your gps cell phone, it does not need to search the satellites again, it can use the information stored previous and needs less time to acquire your current position. That is why when you go through a tunnel or pull out of a garage, you can get your current coordinates quickly

However if you use GPS four hours after your last navigation or moved to another place, the data stored will not be valid and you need another cold start which is time consuming.