Maintaining and searching sets of cells in a wireless communication system

• US 20050272425A1
• Filed: 09/21/2004
• Published: 12/08/2005
• Est. Priority Date: 05/19/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Amerga, Messay, Emani, Chalapathi Rao
• Granted Patent: US 7,286,801 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04B 1/70735 Code identification H04B1/7083 takes precedence
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 52/0206 in access points, e.g. base stations access point devices per se H04W88/08
• CPC Class Codes: H04W 52/0245 according to signal strength
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

For cell measurement, a wireless device categorizes cells whose identities are known to the device into multiple sets. The wireless device may obtain these cells from the system via signaling and/or detect these cells via searches. Different sets of cells may be associated with different levels of importance (e.g., for handoff), require different amounts of processing for measurements, and so on. Each set is associated with a particular measurement rate. Cells deemed to be more important (e.g., for handoff) are measured more frequently. Cells deemed to be less important and/or require more processing for measurements (e.g., cells with unknown timing) are measured less frequently. The wireless device performs searches and makes measurements for the cells in each set at the measurement rate selected for that set.

Claims

1. An apparatus in a wireless communication system, comprising:

a controller operative to categorize a plurality of cells into a plurality of sets, each set being associated with a particular rate for performing measurements for cells in the set, and wherein the plurality of sets are associated with a plurality of different measurement rates; and

a demodulator operative to perform measurements for the cells in each set at the measurement rate for the set.

2. The apparatus of claim 1, wherein the cells in the system are operated asynchronously, and wherein at least one set includes cells with unknown timing.

3. The apparatus of claim 1, wherein the plurality of sets include a first set with at least one serving cell, a second set of neighbor cells with known timing, and a third set of neighbor cells with unknown timing.

4. The apparatus of claim 3, wherein the controller is further operative to initiate measurements for the at least one serving cell at a first rate, initiate measurements for the neighbor cells with known timing at a second rate that is less frequent than the first rate, and initiate measurements for the neighbor cells with unknown timing at a third rate that is less frequent than the second rate.

5. The apparatus of claim 4, wherein the plurality of sets further include a fourth set with candidate cells deemed to be good candidates for handoff, and wherein the controller is further operative to initiate measurements for the candidate cells at a fourth rate that is more frequent than the second rate.

6. The apparatus of claim 5, wherein the candidate cells include neighbor cells in the second set with high received signal quality.

7. The apparatus of claim 5, wherein the candidate cells include cells recently removed from the first set.

8. The apparatus of claim 5, wherein the plurality of sets further include a fifth set with detected cells that are not identified as neighbor cells by the system, and wherein the controller is further operative to initiate measurements for the detected cells at a fifth rate that is more frequent than the third rate.

9. The apparatus of claim 8, wherein the controller is further operative to limit the fifth set to a predetermined number of detected cells and to purge cells in the fifth set, as needed, based on detection time and received signal quality for the cells in the fifth set.

10. The apparatus of claim 1, wherein the measurement rate for each set is selected based on likelihood of the cells in the set being assigned for communication.

11. The apparatus of claim 10, wherein the measurement rate for each set is further selected based on amount of processing required to perform measurements for the cells in the set.

12. A method of performing measurements for cells in a wireless communication system, comprising:

categorizing a plurality of cells into a plurality of sets, each set being associated with a particular rate for performing measurements for cells in the set, and wherein the plurality of sets are associated with a plurality of different measurement rates; and

performing measurements for the cells in each set at the measurement rate for the set.

13. The method of claim 12, wherein the plurality of sets include a first set with at least one serving cell, a second set of neighbor cells with known timing, and a third set of neighbor cells with unknown timing, and wherein measurements for the at least one serving cell are made at a first rate, measurements for the neighbor cells with known timing are made at a second rate that is less frequent than the first rate, and measurements for the neighbor cells with unknown timing are made at a third rate that is less frequent than the second rate.

14. The method of claim 13, wherein the plurality of sets further include a fourth set with candidate cells deemed to be good candidates for handoff, and wherein measurements for the candidate cells are made at a fourth rate that is more frequent than the second rate.

15. The method of claim 14, wherein the plurality of sets further include a fifth set with detected cells that are not identified as neighbor cells by the system, and wherein measurements for the detected cells are made at a fifth rate that is more frequent than the third rate.

16. An apparatus in a wireless communication system, comprising:

means for categorizing a plurality of cells into a plurality of sets, each set being associated with a particular rate for performing measurements for cells in the set, and wherein the plurality of sets are associated with a plurality of different measurement rates; and

means for performing measurements for the cells in each set at the measurement rate for the set.

17. The apparatus of claim 16, wherein the plurality of sets include a first set with at least one serving cell, a second set of neighbor cells with known timing, and a third set of neighbor cells with unknown timing, and wherein measurements for the at least one serving cell are made at a first rate, measurements for the neighbor cells with known timing are made at a second rate that is less frequent than the first rate, and measurements for the neighbor cells with unknown timing are made at a third rate that is less frequent than the second rate.

18. The apparatus of claim 17, wherein the plurality of sets further include a fourth set with candidate cells deemed to be good candidates for handoff, and wherein measurements for the candidate cells are made at a fourth rate that is more frequent than the second rate.

19. The apparatus of claim 18, wherein the plurality of sets further include a fifth set with detected cells that are not identified as neighbor cells by the system, and wherein measurements for the detected cells are made at a fifth rate that is more frequent than the third rate.

20. A processor readable media for storing instructions operable in a wireless device to:

categorize a plurality of cells into a plurality of sets, each set being associated with a particular rate for performing measurements for cells in the set, and wherein the plurality of sets are associated with a plurality of different measurement rates; and

initiate measurements for the cells in each set at the measurement rate for the set.

21. An apparatus in a wireless communication system, comprising:

a demodulator operative to perform searches to detect for cells in the system; and

a controller operative to identify cells detected by the searches and not signaled by the system, store the detected cells in a set, and purge cells in the set, if needed, to limit the set to a predetermined number of detected cells.

22. The apparatus of claim 21, wherein the controller is further operative to

determine whether to purge any cells currently stored in the set in order to make room for cells detected in a current measurement period, and

if cells are to be purged from the set, identify at least one cell to purge based on last detection time and received signal quality for the cells currently stored in the set.

23. The apparatus of claim 22, wherein the controller is further operative to

sort the cells currently stored in the set based on last detection time and received signal quality for the cells,

select cells for purging starting with oldest detection time, and

if multiple cells have equal detection time, select cells for purging starting with lowest received signal quality.

24. A method of maintaining cells in a wireless communication system, comprising:

performing searches to detect for cells in the system;

identifying cells detected by the searches and not signaled by the system;

storing the detected cells in a set; and

purging cells in the set, if needed, to limit the set to a predetermined number of detected cells.

25. The method of claim 24, further comprising:

determining whether to purge any cells currently stored in the set in order to make room for cells detected in a current measurement period; and

if cells are to be purged from the set, identifying at least one cell to purge based on last detection time and received signal quality for the cells currently stored in the set.

26. An apparatus in a wireless communication system, comprising:

means for performing searches to detect for cells in the system;

means for identifying cells detected by the searches and not signaled by the system;

means for storing the detected cells in a set; and

means for purging cells in the set, if needed, to limit the set to a predetermined number of detected cells.

27. The apparatus of claim 26, further comprising:

means for determining whether to purge any cells currently stored in the set in order to make room for cells detected in a current measurement period; and

means for, if cells are to be purged from the set, identifying at least one cell to purge based on last detection time and received signal quality for the cells currently stored in the set.