Patent ID: 8199051

Claim:
A mobile device, comprising: a global navigation satellite system (GNSS) receiver configured to receive GNSS signals; a second receiver configured to receive a terrestrial beacon signal; and a controller operatively coupled to the GNSS receiver and the second receiver; wherein the controller is configured to detect when GNSS signals are unavailable due to signal blockage and, in response thereto, to use a received terrestrial beacon signal to determine whether a previous GNSS location update is valid; and wherein the mobile device is configured to perform the following steps to determine whether a previous GNSS location update is valid: the GNSS receiver is employed to develop a first valid GNSS position including latitude, longitude, altitude, and timing; in parallel, the second receiver is employed to detect and identify one or more radio beacons in predefined transmission bands; the first valid GNSS position and a first list of beacons are stored locally within the mobile device; GNSS position information is passed to a location-consuming application; the GNSS receiver enters a low power sleep mode until a next required update time as determined by the location-consuming application; the second receiver enters a low power sleep mode until the next required update time; upon determining that the GNSS receiver has failed to produce a valid GNSS location fix, the second receiver produces a current list of detectable, identifiable beacons; the current beacon list is compared to a prior beacon list associated in time with a last valid GNSS location fix; and upon determining the presence of a limited-range beacon in both the current and prior beacon lists, the mobile device reuses a last valid GNSS position, and then switches the GNSS receiver off and sets triggering conditions to reactivate and retry GNSS location at a later time when those triggering conditions are met.