Intelligent roaming in AGV application

• US 6,332,077 B1
• Filed: 07/29/1999
• Issued: 12/18/2001
• Est. Priority Date: 07/29/1999
• Status: Expired due to Fees

• Current Assignee: National Datacomm Corp. (Usi Corporation)
• Original Assignee: National Datacomm Corp. (Usi Corporation)
• Inventors: Hsu, Yi-Shou, Wu, Chi-Kai
• Primary Examiner(s): Nguyen, Lee
• Application Number:
  US09/363,548
• Time in Patent Office: 873 Days
• Field of Search: 455/432, 455/435, 455/436, 455/441, 455/440, 455/434, 370/331, 370/338, 375/132
• US Class Current: 455/432.1
• CPC Class Codes: H04W 8/08 Mobility data transfer

Abstract

A roaming algorithm for associating a mobile station (STA) with an access point in a wireless LAN system used in an automatic guidance vehicle (AGV) application. Fast roaming is achieved by eliminating a STA'"'"'s scanning time during the search of the next AP to associate with. To eliminate the scanning time, each AP is pre-configured with its adjacent APs in advance. Whenever an AP is associated with, a mobile station (STA) gets the information of neighboring APs from the currently associated AP. Then, the STA continuously monitors the signal strength of APs in its neighborhood. During roaming, the STA chooses the best AP to associate with without having to scan all the APs.

Claims

1. A method for associating a mobile station (STA) with an access point (AP) in a wireless LAN having a plurality of APs, comprising the steps of:

pre-configuring each AP with its adjacent APs in advance according to relative locations of said plurality of APs;

downloading wireless hopping information of the adjacent APs of a currently associated AP whenever an AP is associated; and

selecting a best AP for said STA to associate with when roaming is activated, using a method including the steps of;

a. determining if a roaming direction exists for said STA;

b. selecting an AP from the adjacent APs as the best AP if a roaming direction exists and by associating with the selected AP the same roaming direction can be continued;

otherwise

c. scanning the adjacent APs and selecting an AP that has a highest received signal strength as the best AP.

2. The method for associating a mobile station with an access point as claimed in claim 1, wherein if the selected AP in step b is hung up or can not be associated with, step c is used to select a best AP.

3. The method for associating a mobile station with an access point as claimed in claim 1, wherein each AP continuously broadcasts a Beacon frame to an Ethernet in the wireless LAN, said Beacon frame comprising hopping set and hopping pattern that are parameters of wireless hopping information.

4. The method for associating a mobile station with an access point as claimed in claim 1, wherein the received signal strength of an AP is the value of the received signal strength indicator (RSSI) of a Beacon frame broadcast by an AP.

5. The method for associating a mobile station with an access point as claimed in claim 4, wherein after said STA has downloaded wireless hopping information of the adjacent APs of a currently associated AP, said STA continuously sniffs the Beacon frames of the adjacent APs and saves the RSSI values of the received Beacon frames.

6. The method for associating a mobile station with an access point as claimed in claim 5, wherein a hopping dwell period is a multiple of Beacon intervals and an AP broadcasts its Beacon frame at the start of each hopping dwell period, said STA being synchronized to each AP for hopping directly to an adjacent AP and staying for a short period to listen for the Beacon frame of the adjacent AP.

7. The method for associating a mobile station with an access point as claimed in claim 5, wherein said STA keeps the RSSI values of the received Beacon frames for last four sniffs corresponding to each adjacent AP.