Method and apparatus for performing inter-system searches in idle mode

1. An apparatus for wireless communication, comprising:

at least one processor configured to determine received signal level for a first radio access technology (RAT), to determine received signal level for a second RAT, to determine a difference between the received signal level for the first RAT and the received signal level for the second RAT, and to determine a rate of searches for the second RAT based on the difference between the received signal levels for the first and second RATs, the rate identifying a repetition period for performing the searches; and

a memory coupled to the at least one processor;

wherein the at least one processor is configured to select one of multiple possible rates based on the difference, and to use the selected rate as the rate of searches for the second RAT.

2. The apparatus of claim 1 , wherein the at least one processor is configured to select a first rate if the difference is less than a threshold, to select a second rate slower than the first rate if the difference is greater than the threshold, and to use the selected first or second rate as the rate of searches for the second RAT.

3. The apparatus of claim 1 , wherein the at least one processor is configured to compare the difference against multiple thresholds for multiple ranges, each range being associated with a different search rate, and to select a search rate associated with a range within which the difference falls as the rate of searches for the second RAT.

4. The apparatus of claim 1 , wherein the at least one processor is configured to determine the rate of searches for the second RAT based on a function of the difference.

5. The apparatus of claim 1 , wherein the at least one processor is configured to select a predetermined rate as the rate of searches for the second RAT until at least one condition is satisfied, and to select one of multiple possible rates based on the difference as the rate of searches for the second RAT after the at least one condition is satisfied.

6. The apparatus of claim 5 , wherein the at least one condition is satisfied if a predetermined number of most recent searches for the second RAT is unsuccessful, or if cell reselection is not performed within a predetermined number of seconds, or both.

7. The apparatus of claim 1 , wherein the at least one processor is configured to select a fastest rate among all possible rates for searches for the second RAT if the received signal level for the first RAT is below a low threshold.

8. The apparatus of claim 1 , wherein the at least one processor is configured to operate in an idle mode with a serving cell in the first RAT, and to use received signal level of the serving cell as the received signal level for the first RAT.

9. The apparatus of claim 1 , wherein the first RAT is Global System for Mobile Communications (GSM) and the second RAT is Wideband Code Division Multiple Access (WCDMA).

10. A method for wireless communication, comprising:

determining received signal level for a first radio access technology (RAT);

determining received signal level for a second RAT;

determining a difference between the received signal level for the first RAT and the received signal level for the second RAT; and

determining a rate of searches for the second RAT based on the difference between the received signal levels for the first and second RATs, the rate identifying a repetition period for performing the searches;

wherein the determining the rate of searches comprises selecting one of multiple possible rates based on the difference, and using the selected rate as the rate of searches for the second RAT.

11. The method of claim 10 , wherein the determining the rate of searches comprises

comparing the difference against at least one threshold for multiple ranges, each range being associated with a different search rate, and

selecting a search rate associated with a range within which the difference falls as the rate of searches for the second RAT.

12. The method of claim 10 , wherein the determining the rate of searches comprises

selecting a predetermined rate as the rate of searches for the second RAT until at least one condition is satisfied, and

selecting one of multiple possible rates based on the difference as the rate of searches for the second RAT after the at least one condition is satisfied.

13. The method of claim 10 , further comprising:

selecting a fastest rate among all possible rates for searches for the second RAT if the received signal level for the first RAT is below a low threshold.

14. An apparatus for wireless communication, comprising:

means for determining received signal level for a first radio access technology (RAT);

means for determining received signal level for a second RAT;

means for determining a difference between the received signal level for the first RAT and the received signal level for the second RAT; and

means for determining a rate of searches for the second RAT based on the difference between the received signal levels for the first and second RATs, the rate identifying a repetition period for performing the searches;

wherein the means for determining the rate of searches comprises means for comparing the difference against at least one threshold for multiple ranges,

each range being associated with a different search rate, and means for selecting a search rate associated with a range within which the difference falls as the rate of searches for the second RAT.

15. The apparatus of claim 14 , further comprising:

means for selecting a fastest rate among all possible rates for searches for the second RAT if the received signal level for the first RAT is below a low threshold.

16. A non-transitory computer program product, comprising:

a computer-readable medium comprising:

code for causing at least one computer to determine received signal level for a first radio access technology (RAT);

code for causing at least one computer to determine received signal level for a second RAT;

code for causing the at least one computer to determine a difference between the received signal level for the first RAT and the received signal level for the second RAT; and

code for causing the at least one computer to determine a rate of searches for the second RAT based on the difference between the received signal levels for the first and second RATs, the rate identifying a repetition period for performing the searches;

the computer-readable medium further comprising:

code for causing the at least one computer to compare the difference against at least one threshold for multiple ranges, each range being associated with a different search rate; and

code for causing the at least one computer to select a search rate associated with a range within which the difference falls as the rate of searches for the second RAT.

17. The non-transitory computer program product of claim 16 , the computer-readable medium further comprising:

code for causing the at least one computer to select a fastest rate among all possible rates for searches for the second RAT if the received signal level for the first RAT is below a low threshold.

18. An apparatus for wireless communication, comprising:

at least one processor configured to determine received signal level for a first radio access technology (RAT), and to control searches for a second RAT based on the received signal level for the first RAT and frequency bands for the first and second RATs, the control including a repetition period for performing the searches; and

a memory coupled to the at least one processor;

wherein the at least one processor is configured to select at least one frequency band among multiple frequency bands for the second RAT based on the received signal level and frequency band for the first RAT and the multiple frequency bands for the second RAT, and to perform searches for the second RAT for only the at least one frequency band.

19. The apparatus of claim 18 , wherein the at least one processor is configured to determine a factor indicative of a difference between path loss for the first RAT and path loss for the second RAT based on the frequency bands for the first and second RATs, and to control searches for the second RAT based on the factor and the received signal level for the first RAT.

20. The apparatus of claim 18 , wherein the at least one processor is configured to determine whether to perform or skip searches for the second RAT based on the received signal level for the first RAT and the frequency bands for the first and second RATs.

21. The apparatus of claim 18 , wherein the at least one processor is configured to determine a rate of searches for the second RAT based on the received signal level for the first RAT and the frequency bands for the first and second RATs.

22. The apparatus of claim 18 , wherein the at least one processor is configured to determine an order of multiple frequency bands for the second RAT, and to perform searches for the second RAT for the multiple frequency bands, one frequency band at a time and in accordance with the determined order.

23. A method for wireless communication, comprising:

determining received signal level for a first radio access technology (RAT); and

controlling searches for a second RAT based on the received signal level for the first RAT and frequency bands for the first and second RATs, the controlling including a repetition period for performing the searches;

wherein the controlling searches for the second RAT comprises

selecting at least one frequency band among multiple frequency bands for the second RAT based on the received signal level and frequency band for the first RAT and the multiple frequency bands for the second RAT, and

performing searches for the second RAT for only the at least one frequency band.

24. The method of claim 23 , wherein the controlling searches for the second RAT comprises

determining whether to perform or skip searches for the second RAT based on the received signal level for the first RAT and the frequency bands for the first and second RATs.

25. The method of claim 23 , wherein the controlling searches for the second RAT comprises

determining a rate of searches for the second RAT based on the received signal level for the first RAT and the frequency bands for the first and second RATs.

26. The method of claim 23 , wherein the controlling searches for the second RAT comprises

determining an order of multiple frequency bands for the second RAT, and

performing searches for the second RAT for the multiple frequency bands, one frequency band at a time and in accordance with the determined order.