Femtocell fingerprinting

1. A method comprising:

providing a central fingerprint database operable to store a fingerprint for proximity detection, the fingerprint characterizing proximity of a femtocell;

executing a fingerprint manager in communication with the fingerprint database for:

creating the fingerprint, and storing, for the fingerprint, a fingerprint component that characterizes proximity of the femtocell; and

executing a proximity detector in communication with the fingerprint database, and, with the proximity detector:

obtaining an environmental measurement;

analyzing the fingerprint to find that the fingerprint is a matching fingerprint with respect to the environmental measurement; and

initiating a cell search for a specific femtocell that corresponds to the matching fingerprint.

2. The method of claim 1 , further comprising:

determining a particular femtocell for enhanced fingerprinting, and in response:

creating multiple fingerprints in the central fingerprint database for that particular femtocell.

3. The method of claim 2 , where determining comprises:

determining the particular femtocell responsive to frequency of selection of that particular femtocell.

4. The method of claim 2 , where determining comprises:

determining the particular femtocell responsive to recency of selection of that particular femtocell.

5. The method of claim 1 , further comprising:

obtaining the fingerprint component from radio resource control measurements of neighboring macrocells.

6. The method of claim 1 , further comprising:

obtaining the fingerprint component from positioning system measurements of location.

7. The method of claim 1 , further comprising:

obtaining the fingerprint component from wireless network measurements of visible access points.

8. The method of claim 1 , where creating the fingerprint comprises:

creating multiple different fingerprints corresponding to multiple different physical approaches to a particular femtocell among the femtocells.

9. The method of claim 1 , further comprising:

determining when the fingerprint has triggered more than a threshold number of failed cell searches, and in response:

deleting the fingerprint from the central fingerprint database.

10. The method of claim 1 , where creating the fingerprint comprises:

creating the fingerprint responsive to successful connections to the femtocells.

11. The method of claim 1 , further comprising:

selectively updating the fingerprint component.

12. The method of claim 1 , further comprising:

deleting the fingerprint.

13. A system comprising:

a central fingerprint database operable to store a fingerprint of a femtocell;

a fingerprint manager in communication with the fingerprint database, the fingerprint manager configured to:

create the fingerprint in the fingerprint database, and store, for the fingerprint, a fingerprint component that represents a proximity characteristic of the femtocell; and

a proximity detector in communication with the fingerprint database, the proximity detector configured to:

obtain location information applicable to a device;

compare the fingerprint to the location information to determine whether to trigger a cell search; and

initiate a current attempt to connect the device to the femtocell when the cell search is triggered.

14. The system of claim 13 , where:

the proximity detector is further configured to:

increase time between subsequent attempts as remaining power supply energy decreases.

15. The system of claim 13 , where:

the proximity detector is further configured to:

determine when the fingerprint has triggered more than a threshold number of failed connection attempts, and in response:

increase a time interval until initiation of a subsequent attempt to connect the device.

16. The system of claim 13 , where:

the fingerprint manager is further configured to:

determine a reliability criterion for the fingerprint; and

delete the fingerprint when the reliability criterion fails a reliability threshold.

17. The system of claim 13 , where:

the proximity detector is further configured to:

increase time between subsequent attempts when a prior attempt has failed.

18. The system of claim 13 , where:

the fingerprint manager is further configured to:

create an additional fingerprint for the femtocell, where the additional fingerprint characterizes a different physical approach to the femtocell.

19. The system of claim 13 , where:

the fingerprint component comprises a macrocell identity for a macrocell visible from the femtocell.

20. The system of claim 13 , where:

the fingerprint manager is further configured to:

update the fingerprint when an update criterion is met.

21. The system of claim 20 , where:

the update criterion comprises an updated frequency configuration of the femtocell, a neighboring cell, or both.

22. The system of claim 20 , where:

the update criterion comprises a changed physical cell identity or a changed primary scrambling code.

23. A system comprising:

a non-volatile fingerprint memory;

a fingerprint database;

a fingerprint manager in communication with the fingerprint database, the fingerprint manager configured to:

obtain, after power-up, a fingerprint of a local cell for a restricted subscriber group from the non-volatile fingerprint memory;

store the fingerprint in the fingerprint database, and store, for the fingerprint, a fingerprint component comprising a proximity characteristic of the local cell;

update the fingerprint when an update criterion is met;

determine a reliability criterion for the fingerprint; and

delete the fingerprint when the reliability criterion fails the reliability threshold;

a proximity detector in communication with the fingerprint database, the proximity detector configured to:

obtain an environment characteristic applicable to a device;

compare the fingerprint to the environmental characteristic to determine whether to trigger a cell search; and

initiate an attempt to connect the device to the local cell when the cell search is triggered; and

where the fingerprint manager is operable to obtain the fingerprint component from any set of one or more of:

a radio resource control input operable to convey a macrocell measurement as the fingerprint component to the fingerprint manager;

a positioning system input operable to convey physical location information as the fingerprint component to the fingerprint manager; and

a wireless network input operable to convey wireless access point information as the fingerprint component to the fingerprint manager.

24. The system of claim 23 , where:

the proximity detector is further operable to:

perform a phased comparison to the fingerprint, including a coarse match that triggers a subsequent acquisition of additional environment characteristics; and

confirm identity of the local cell by acquiring system information.