Phased search for femtocells
View Patent ↗User equipment (UE) includes an architecture for locating femtocells. The architecture implements a phased search approach. The phased search helps the UE find the correct femtocells in a time and power efficient manner, by performing the search in a way that matches the likely changes to femtocell configurations.
1. A method comprising:
determining that a device is within a redefined distance threshold of a femtocell; and
executing a phased search for the femtocell, the phased search comprising:
a first phase that searches an expected femtocell frequency and expected femtocell identifier; and
a second phase executed when the first phase fails, the second phase comprising searching for the femtocell by modifying the first phase according to a first expected behavior of the femtocell; and
setting a search timer for searching the expected femtocell frequency and expected femtocell identifier to a shorter time period than used when the device is not determined to be within the predefined distance threshold.
2. The method of claim 1 , where:
the expected behavior comprises a change in cell identifier.
3. The method of claim 2 , where:
the cell identifier comprises a physical cell identifier.
4. The method of claim 2 , where:
the cell identifier comprises a primary scrambling code.
5. The method of claim 2 , further comprising:
attempting reselection to the femtocell using the change in cell identifier and expected femtocell frequency.
6. The method of claim 1 , where the phase search further comprises:
a third phase that searches for the femtocell by modifying the second phase according to a second expected behavior of the femtocell.
7. The method of claim 6 , where:
the second expected behavior compress a change in frequency.
8. The method of claim 7 , further comprising:
obtaining system information from a currently camped cell; and
limiting the change in frequency to a set of frequencies obtained from the system information.
9. The method of claim 8 , further comprising:
executing the third phase over the set of frequencies and allowable cell identifiers for the frequencies in the set of frequencies.
10. A system comprising:
a radio frequency (RF) communication interface; and
circuitry in communication with the RF communication interface, the circuitry configured to:
match environmental measurements to a fingerprint for a femtocell;
determine an expected frequency and cell identifier for the femtocell;
obtain location information that locates the system to within a predefined distance threshold of the femtocell;
initiate a phase one search for the femtocell on the expected frequency and cell identifier; and
responsive to the location information, set a search timer for the phase one search by setting the search timer for a shorter time period than the location information does not locate the system to within the predefined distance threshold; and
if the phase one search fails, execute a phase two search comprising a search modification to the phase one search, responsive to expected behavior of the femtocell.
11. The system of claim 10 , where:
the search modification to the phase one search comprises a change in the cell identifier.
12. The system of claim 10 , where the circuitry is further configured to:
if the phase two search fails, execute a phase three search comprising a search modification to the phase two search, responsive to expected behavior of the femtocell.
13. The system of claim 12 , where:
the search modification to the phase two search comprises a change in the expected frequency.
14. The system of claim 13 , where the circuitry is further configured to:
obtain system information from a currently camped cell; and
limit the change in expected frequency to a set of frequencies obtained from the system information.
15. The system of claim 10 , where:
the location information comprises macrocell measurements.
16. The system of claim 10 , where:
the location information comprises satellite positioning information or wireless network location information, or both.
17. The system of claim 10 , where the circuitry is further configured to adjust, relative to a complete match, a duration of the search timer responsive to a partial match between the environmental measurements and the fingerprint.
18. A system comprising:
a radio frequency (RF) communication interface;
a fingerprint database comprising:
a frequency fingerprint component for a femtocell;
a cell identifier fingerprint component for the femtocell; and
macrocell measurements for the femtocell;
a proximity detector in communication with the fingerprint database and operable to:
obtain environmental macrocell measurements from the RF communication interface;
responsive to the environmental macrocell measurements, determine that the system is located within a predefined distance threshold of the femtocell; and
initiate a search for the femtocell; and
circuitry in communication with the RF communication interface, the circuitry configured to:
receive the frequency fingerprint component and cell identifier fingerprint component for the femtocell;
initiate a first search phase that attempts to locate the femtocell as specified by the frequency fingerprint component and cell identifier fingerprint component;
set a search timer for the first search phase by setting the search timer for a shorter time period than when the system is not located within the predefined distance threshold;
if the first search phase fails, execute a second search phase that attempts to locate the femtocell at a different cell identifier;
if the second search phase fails, execute a third search phase that attempts to locate the femtocell at a different frequency; and
when there is a positive search result, attempt to camp onto the femtocell according to search parameters giving rise to the positive search result.
19. The system of claim 18 , where the circuitry is further configured to:
obtain system information from a currently camped cell; and
limit the different frequency to a frequency specified in the system information.
20. The system of claim 18 , where the environmental macrocell measurements comprise a signal strength measurement for a neighbor macrocell.