Method and device to determine out of coverage for mobile devices

1. A method, in a mobile device configured to obtain position information from a position broadcast system, the position broadcast system comprising a plurality of transmitters that each broadcast a respective signal containing position information for the respective transmitter, the method comprising:

measuring signal strengths of signals from each of a plurality of the transmitters of the position broadcast system;

determining that the mobile device is out of range of the position broadcast system if the measured signal strengths satisfy an out of range criterion;

if the mobile device is determined to be out of range, operating the mobile device according to an out of range profile for conservation of power; and

if the mobile device is not determined to be out of range, attempting to lock on to a position using the position broadcast system,

wherein the out of range criterion differs from criteria used to determine whether or not it is possible to lock on to a position, and wherein determining that the mobile device is out of range based on the out of range criterion comprises at least one of:

determining that fewer than a predetermined number of the measured signal strengths are above a threshold value;

determining that a sum of highest measured signal strengths of signals from each of a predetermined number of transmitters is below a threshold value; and

determining that the signal strength of fewer than a predetermined number of visible transmitters is above a threshold value; and

wherein operating the mobile device according to an out of range profile for conservation of power comprises turning off a position broadcast receiver in the mobile device.

2. The method of claim 1 , wherein the position broadcast system is a Global Positioning System (GPS), and measuring the signal strengths comprises measuring signal strengths of a plurality of signals from satellites of the Global Positioning System (GPS).

3. The method of claim 1 , further comprising attempting to obtain position information from the position broadcast system after a predetermined period of time after the mobile device is determined to be out of range has expired.

4. The method of claim 1 , wherein measuring the signal strengths comprises averaging a plurality of measurements for each signal.

5. The method of claim 1 , further comprising indicating with a user interface that the mobile device is out of range if the mobile device is determined to be out of range.

6. A mobile device comprising:

a receiver for measuring signal strengths of signals from each of a plurality of transmitters of a position broadcast system;

an out of range determination module configured to determine that the mobile device is out of range of the position broadcast system if the measured signal strengths satisfy at least one out of range criterion; and

a processor configured to:

if the mobile device is determined to be out of range, operate the mobile device according to an out of range profile for conservation of power; and

if the mobile device is not determined to be out of range, attempt to lock on to a position using the position broadcast system;

wherein the out of range determination module is configured to perform at least one of the method steps comprising:

determining that fewer than a predetermined number of the measured signal strengths are above a threshold value;

determining that a sum of highest measured signal strengths of signals from each of a predetermined number of transmitters is below a threshold value; and

determining that the signal strength of fewer than a predetermined number of visible transmitters is above a threshold value,

wherein determining that the mobile device is out of range based on the at least one out of range criterion uses criteria that differ from criteria used to determine whether or not it is possible to lock on to a position; and

wherein operating the mobile device according to an out of range profile for conservation of power comprises turning off a position broadcast receiver in the mobile device.

7. The mobile device of claim 6 , wherein the plurality of transmitters are satellites.

8. The mobile device of claim 6 , wherein the receiver is a Global Positioning System (GPS) receiver.

9. The mobile device of claim 8 , wherein the out of range determination module is implemented by firmware for controlling a GPS chipset.

10. The mobile device of claim 8 , wherein the out of range determination module is implemented by a GPS chipset.

11. One or more non-transitory computer readable media having computer readable instructions stored thereon that when executed implement a method for determining if a mobile device is out of range of a position broadcast system, the position broadcast system comprising a plurality of transmitters that each broadcast signals containing position information for the respective transmitter, the method comprising:

measuring signal strengths of signals from each of a plurality of the transmitters of the position broadcast system;

determining that the mobile device is out of range of the position broadcast system if the measured signal strengths satisfy an out of range criterion;

if the mobile device is determined to be out of range, operating the mobile device according to an out of range profile for conservation of power; and

if the mobile device is not determined to be out of range, attempting to lock on to a position using the position broadcast system,

wherein the out of range criterion differs from criteria used to determine whether or not it is possible to lock on to a position, and wherein determining that the mobile device is out of range based on the out of range criterion comprises at least one of:

determining that fewer than a predetermined number of the measured signal strengths are above a threshold value;

determining that a sum of highest measured signal strengths of signals from each of a predetermined number of transmitters is below a threshold value; and

determining that the signal strength of fewer than a predetermined number of visible transmitters is above a threshold value; and

wherein operating the mobile device according to an out of range profile for conservation of power comprises turning off a position broadcast receiver in the mobile device.

12. The method of claim 1 , wherein operating the mobile device according to an out of range profile further comprises at least one of instructing all applications on the mobile device that rely on location information to use the last position received, and displaying an indication on a user interface of the mobile device that the device is out of range.

13. The method of claim 4 , wherein the plurality of measurements for each signal are taken over a predetermined period of time.

14. The method of claim 1 , wherein operating the mobile device according to an out of range profile further comprises presenting an option on a user interface to attempt to obtain position information, the option being presented when a predetermined period of time after the mobile device is determined to be out of range has expired.