Enhanced passive scanning

• US 20050128988A1
• Filed: 09/10/2004
• Published: 06/16/2005
• Est. Priority Date: 09/30/2003
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wilson, Timothy J., Emeott, Stephen P., Smith, Brian K., Simpson, Floyd D.
• Granted Patent: US 7,675,878 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

The invention provides an enhanced passive scanning method for a wireless local area network, including the steps of transmitting at least one of a beacon signal or a gratuitous probe response in a WLAN channel by an access point. The gratuitous probe response is a supplemental beacon signal that is transmitted at intervals between the occurrence of regular beacon signals, but contains only essential information to allow mobile station manage roaming and timing.

Claims

1. An enhanced passive scanning method for a wireless local area network, comprising:

transmitting beacon signals at a beacon interval, each beacon containing a beacon information set;

transmitting gratuitous probe response signals at a gratuitous probe response interval containing a subset of the beacon information, the gratuitous probe response signals transmitted at a gratuitous probe response interval, the gratuitous probe response interval being shorter than the beacon interval such that a plurality of gratuitous probe response signals are transmitted between successive beacon signals, and containing a subset of the beacon information.

2. The method of claim 1 wherein the beacon signal or the gratuitous probe response is transmitted from one of a mobile station or an access point.

3. The method of claim 1 wherein the beacon signal is transmitted from an access point, the beacon signal including an access-point timestamp, a beacon interval, a basic service set identifier, and a traffic indication map element.

4. The method of claim 1 wherein the gratuitous probe response signal is transmitted from an access point, the gratuitous probe response including an access-point timestamp, a gratuitous probe response interval, and a basic service set identifier.

5. The method of claim 1 wherein the beacon interval is 100 milliseconds.

6. The method of claim 3 wherein the beacon signal further comprises delivery traffic information message count for indicating how many beacons, including a present beacon, appear before the next delivery traffic information message.

7. The method of claim 3 wherein a delivery traffic information message is included in each beacon signal wherein the corresponding delivery traffic information message count has a zero value.

8. A method for facilitating enhanced passive scanning by mobile stations in a WLAN by an access point, comprising:

determining the occurrence of one of a target beacon transmit time and an target gratuitous probe response time;

transmitting a beacon signal if the target beacon transmit time occurs; and

transmitting a gratuitous probe response signal if the target gratuitous probe response time occurs.

9. A method for facilitating enhanced passive scanning as defined in claim 8, wherein transmitting the beacon signal comprises acquiring the channel using a high priority transmission.

10. A method for facilitating enhanced passive scanning as defined in claim 8, wherein determining the occurrence of the target beacon transmit time when the modulo of the TSFtimer and the beacon interval is zero.

11. A method for facilitating enhanced passive scanning as defined in claim 8, wherein determining the occurrence of the target gratuitous probe response time when the modulo of the TSFtimer and the supplemental beacon interval is zero.

12. A method for facilitating enhanced passive scanning as defined in claim 8, wherein the beacon signal includes an access-point timestamp, a beacon interval, a basic service set identifier, and a traffic indication map.

13. A method for facilitating enhanced passive scanning as defined in claim 8, wherein the gratuitous probe response signal includes an access-point timestamp, a gratuitous probe response interval, and a basic service set identifier.

14. A method for facilitating enhanced passive scanning as defined in claim 8, wherein both the beacon signal and gratuitous probe response signals contain a supplemental information element including an element identifier field, length field, and supplemental beacon interval field.

15. A method of indicating to a mobile wireless local area network device that an access point supports supplemental beaconing, comprising:

transmitting from the access point a beaconing signal selected from one of a beacon signal and a gratuitous probe response signal, and including a supplemental beacon field in the beaconing signal; and

receiving the beaconing signal at the mobile wireless local area network device.