Method of scanning for beacon transmissions in a WLAN
A wireless station ( 114 ) is within range of more than one access point ( 120, 124 ) transmitting on the same channel. The wireless station is associated with one access point and not the other. Consequently the wireless station may receive undesired beacons ( 304 ) and desired beacons ( 302 ) on the channel. To optimize power save operation the wireless station arbitrates between a scan and shut down scanning procedure ( 708 ) and a timed window channel scanning procedure ( 724 ), depending on whether the desired beacon is the first received beacon upon waking up from a low power state at a target beacon time.
1. A method of scanning for a beacon from a wireless local area network (WLAN) access point by a wireless station, comprising:
performing a scan and shut down procedure, including:
waking up a WLAN radio subsystem of the wireless station at a scan start time;
receiving a beacon from one of at least two access points operating on the same channel in the vicinity of the wireless station, the beacon including beacon data including an access point identifier;
passing the beacon data to a host processor of the wireless station;
placing the WLAN radio subsystem into a low power state immediately after receiving and passing;
comparing the access point identifier with a desired access point identifier, performed by the host processor;
if the access point identifier is the same as the desired access point identifier, continuing with the scan and shut down procedure for receiving a next beacon transmission; and
if the access point identifier is not the same as the desired access point identifier, discarding the beacon data and using a timed window scanning procedure for receiving the next beacon transmission.
2. A method of scanning for a beacon as defined in claim 1 , wherein receiving the beacon data includes receiving a basic service set identifier as the access point identifier.
3. A method of scanning for a beacon as defined in claim 1 , wherein receiving the beacon transmission is receiving a full beacon.
4. A method of scanning for a beacon as defined in claim 3 , wherein receiving the full beacon includes receiving the full beacon at a substantially 102.4 millisecond interval.
5. A method of scanning for a beacon as defined in claim 1 , wherein receiving the beacon is receiving a supplemental beacon, the supplemental beacon having less beacon data than a full beacon.
6. A method of scanning for a beacon as defined by claim 1 , wherein waking up the WLAN radio subsystem at the scan start time is performed with timing information received in a previously received beacon.
7. A method of scanning for a beacon from a wireless local area network (WLAN) access point by a wireless station, comprising:
performing a timed window scanning procedure, including:
waking up a WLAN radio subsystem of the wireless station at a scan start time;
receiving a first beacon and a second beacon, the first and second beacons transmitted by first and second access points, respectively, transmitting on the same channel, the first and second beacons including beacon data including an access point identifier;
passing the beacon data to a host processor of the wireless station;
placing the WLAN radio subsystem into a low power state after the end of a timed window interval;
comparing the access point identifier of the first beacon with a desired access point identifier, performed by the host processor;
if the access point identifier of the first beacon is the same as the desired access point identifier, using a scan and shut down procedure for receiving a next beacon transmission; and
if the received access point identifier of the first beacon is not the same as the desired access point identifier, discarding the beacon data and using the timed window procedure for receiving the next beacon transmission.
8. A method of scanning for a beacon as defined in claim 7 , wherein receiving the beacon data includes receiving a basic service set identifier as the access point identifier.
9. A method of scanning for a beacon as defined in claim 7 , wherein receiving the first beacon transmission is receiving a full beacon.
10. A method of scanning for a beacon as defined in claim 9 , wherein receiving the full beacon includes receiving the full beacon at a substantially 102.4 millisecond interval.
11. A method of scanning for a beacon as defined in claim 7 , wherein receiving the first beacon transmission is receiving a supplemental beacon, the supplemental beacon having less beacon data than a full beacon.
12. A method of scanning for a beacon as defined by claim 7 , wherein waking up the WLAN radio subsystem at the scan start time is performed with timing information received in a previously received beacon.