Cell phones: Free GPS

The reality of a-GPS

Most of these phones are sold with what is called "a-GPS" which effectively stands for 'assisted GPS'. What happens is that they reduce the size and power of the GPS antenna as well as the processing power of the phone by using remote carrier hardware. The service intervenes when you make a connection in order to speed up the hardware, it will generally be something as follows:

You request directions with normal GPS:
1. You make the request with your phone
2. Phone acquires satellite signals
3. Your phone uses the data to figure out where you are, where you want to go, and how you can get there.
4. Your phone displays the results

When you make a request using the carrier service:
1. You make the request with your phone
2. Your phone connects to cell towers to figure out where you are (within a few blocks or miles)
3. Your phone connects with satellite towers, but sends the data to the carrier; they tell you where you are
4. You phone submits the data about where you are and where you want to go to the carrier; they do the data and return the best route to you.
5. Your phone displays the result

What happens is that a-GPS may, or may not be able to be configured to run without assistance. Nearly all phones CAN run without the carrier program assuming you can download a local program and stet it up. Google Maps and TomTom6 are both good examples available for Windows Mobile. You will nearly always find that connecting to satellites and finding routes will take longer, but for $180 a year those few seconds each time could be worth it.