WLAN system scanning and selection
Techniques for performing WLAN system scanning and selection are described. A terminal performs multiple iterations of scan to detect for WLAN systems. A scan list containing at least one WLAN system to detect for is initially determined. For each scan iteration, a scan type may be selected from among the supported scan types. The selected scan type may indicate passive scan or active scan, frequency channels to scan, etc. A scan may be performed based on the selected scan type. Signal strength measurements are obtained for access points received during the scan and used to identify detected access points. After all scan iterations are completed, candidates access points are identified based on the scan results, e.g., based on the signal strength measurements for the detected access points and a detection threshold. The best candidate access point may be selected for association by the terminal.
1. An apparatus comprising:
a processor configured to select a number of scan iterations that vary with a received signal strength indicator, to perform the number of scan iterations to detect for access points and to identify candidate access points for association based on results of performing the number of scan iterations;
the processor further configured to select a scan type for each of the number of scan iterations, to perform each scan iteration based on the scan type selected for the scan iteration, and to wait for a wait-scan time between each scan iteration;
wherein the wait-scan time at a current scan iteration is a maximum of a wait minimum time and a wait-scan time for a scan iteration previous to the current scan iteration provided a decision is made not to reduce wait time after the current scan iteration; and
wherein the wait-scan time at the current scan iteration is a maximum of the wait minimum time and the wait-scan time for the scan iteration previous to the current scan iteration reduced by a step size time provided a decision is made to reduce wait time after the current scan iteration.
2. The apparatus of claim 1 , wherein the selected scan type for each scan iteration indicates passive scan or active scan.
3. The apparatus of claim 1 , wherein the selected scan type for each scan iteration indicates at least one frequency channel to scan.
4. The apparatus of claim 1 , wherein the processor is configured to perform active scan for at least one of the number of scan iterations if active scan is permitted for current location of the apparatus, and to perform passive scan for all of the number of scan iterations if active scan is not permitted for the current location.
5. The apparatus of claim 4 , wherein the processor is configured to determine whether active scan is permitted for the current location based on a beacon frame received from an access point.
6. The apparatus of claim 4 , wherein the processor is configured to determine whether active scan is permitted for the current location based on a transmission received from a base station in a cellular network.
7. The apparatus of claim 1 , wherein for each scan iteration the processor is configured to obtain signal strength measurements for received access points and to identify detected access points based on the signal strength measurements for the received access points.
8. The apparatus of claim 7 , wherein for each scan iteration the processor is configured to declare a received access point as a detected access point if a signal strength measurement obtained for the received access point in the scan iteration exceeds a detection threshold.
9. The apparatus of claim 7 , wherein for each scan iteration the processor is configured to filter signal strength measurements obtained for each received access point for current and prior scan iterations, and to declare a received access point as a detected access point if a filtered signal strength measurement for the received access point exceeds a detection threshold.
10. The apparatus of claim 7 , wherein for each scan iteration the processor is configured to determine a variable detection threshold for the scan iteration and to identify the detected access points based on the signal strength measurements for the received access points and the variable detection threshold.
11. The apparatus of claim 1 , wherein the processor is configured to obtain signal strength measurements for access points detected in the number of scan iterations, and to identify the candidate access points based on the signal strength measurements for the detected access points.
12. The apparatus of claim 11 , wherein the processor is configured to declare a detected access point as a candidate access point if signal strength measurements obtained for the detected access point exceed a detection threshold for at least a predetermined number of scan iterations.
13. The apparatus of claim 11 , wherein the processor is configured to filter signal strength measurements obtained for each detected access point in the number of scan iterations, and to declare a detected access point as a candidate access point if a filtered signal strength measurement for the detected access point exceeds a selection threshold.
14. The apparatus of claim 11 , wherein the processor is configured to determine a variable selection threshold for each detected access point based on number of scan iterations in which the detected access point has sufficiently strong signal strength measurements, and to determine whether each detected access point is a candidate access point based on signal strength measurements and the variable selection threshold for the detected access point.
15. The apparatus of claim 1 , wherein the processor is configured to select the number of scan iterations further based on signal strength measurements for the detected access points.
16. The apparatus of claim 1 , wherein the processor is configured to wait a particular time duration between scan iterations.
17. A method comprising:
selecting a number of scan iterations that vary with a received signal strength indicator;
using a controller to perform the number of scan iterations to detect for access points;
identifying candidate access points for association based on results of the number of scan iterations;
selecting a scan type for each of the number of scan iterations;
performing each scan iteration based on the scan type selected for the scan iteration;
waiting for a wait-scan time between each scan iteration, wherein the wait-scan time vary with scan iteration;
wherein the wait-scan time at a current scan iteration is a maximum of a wait minimum time and a wait-scan time for a scan iteration previous to the current scan iteration provided a decision is made not to reduce wait time after the current scan iteration; and
wherein the wait-scan time at the current scan iteration is a maximum of the wait minimum time and the wait-scan time for the scan iteration previous to the current scan iteration reduced by a step size time provided a decision is made to reduce wait time after the current scan iteration.
18. The method of claim 17 , wherein the controller performs the number of scan iterations by:
performing active scan for at least one of the number of scan iterations if active scan is permitted for current location of a terminal, and
performing passive scan for all of the number of scan iterations if active scan is not permitted for the current location.
19. The method of claim 17 , wherein the controller performs the number of scan iterations by:
obtaining signal strength measurements for received access points, and
identifying detected access points based on the signal strength measurements for the received access points.
20. The method of claim 17 , wherein the identifying the candidate access points comprises:
obtaining signal strength measurements for access points detected in the number of scan iterations, and
identifying the candidate access points based on the signal strength measurements for the detected access points.
21. An apparatus comprising:
means for selecting a number of scan iterations that vary with a received signal strength indicator;
means for performing the number of scan iterations to detect for access points;
means for identifying candidate access points for association based on results of the number of scan iterations;
means for waiting a wait-scan time between each scan iteration, wherein the wait-scan time at a current scan iteration is a maximum of a wait minimum time and a wait-scan time for a scan iteration previous to the current scan iteration provided a decision is made not to reduce wait time after the current scan iteration; and
wherein the wait-scan time at the current scan iteration is a maximum of the wait minimum time and the wait-scan time for the scan iteration previous to the current scan iteration reduced by a step size time provided a decision is made to reduce wait time after the current scan iteration.
22. The apparatus of claim 21 , wherein the means for performing the number of scan iterations comprises:
means for selecting a scan type for each of the number of scan iterations, and
means for performing each scan iteration based on the scan type selected for the scan iteration.
23. The apparatus of claim 21 , wherein the means for performing the number of scan iterations comprises:
means for obtaining signal strength measurements for received access points, and
means for identifying detected access points based on the signal strength measurements for the received access points.
24. The apparatus of claim 21 , wherein the means for identifying the candidate access points comprises:
means for obtaining signal strength measurements for access points detected in the number of scan iterations, and
means for identifying the candidate access points based on the signal strength measurements for the detected access points.
25. A non-transitory computer-readable medium for storing instructions to:
select a number of scan iterations that vary with a received signal strength indicator;
perform the number of scan iterations to detect for access points, and identify candidate access points for association based on results of the number of scan iterations;
select a scan type for each of the number of scan iterations;
perform each scan iteration based on the scan type selected for the scan iteration;
wait a wait-scan time between each scan iteration;
wherein the wait-scan time at a current scan iteration is a maximum of a wait minimum time and a wait-scan time for a scan iteration previous to the current scan iteration provided a decision is made not to reduce wait time after the current scan iteration; and
wherein the wait-scan time at the current scan iteration is a maximum of the wait minimum time and the wait-scan time for the scan iteration previous to the current scan iteration reduced by a step size time provided a decision is made to reduce wait time after the current scan iteration.
26. The non-transitory computer-readable medium of claim 25 , and further for storing instructions to:
obtain signal strength measurements for received access points, and
identify detected access points based on the signal strength measurements for the received access points.
27. The non-transitory computer-readable medium of claim 25 , and further for storing instructions to:
obtain signal strength measurements for access points detected in the number of scan iterations, and
identify the candidate access points based on the signal strength measurements for the detected access points.