System and method for reducing packet collisions in wireless local area networks

• US 20080101308A1
• Filed: 10/26/2006
• Published: 05/01/2008
• Est. Priority Date: 10/26/2006
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Gaur, Sudhanshu
• Granted Patent: US 7,801,104 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A system (e.g., an AP or a STA) in a WLAN comprises slot information (e.g., slot association or slot bias information); a counter for counting slot numbers; and a medium access controller operative to monitor a wireless medium and to initiate transmission of a MAC frame during a current slot based on a distributed wireless access protocol (e.g., DCF or EDCA), on a current slot number (t) corresponding to the current slot as counted by the counter, and on the slot information. The medium access controller may initiate frame transmission when a backoff counter is zero and when t mod N=n_i (such that N=number of STAs, and n_i=assigned slot number). Alternatively, the medium access controller may initiate frame transmission when a backoff counter is zero and when a slot bias mechanism effecting a probability of access to the wireless medium is satisfied.

Claims

1. A system in a wireless local area network, comprising:

slot information;

a counter for counting slot numbers; and

an access controller operative to monitor a wireless medium and to initiate transmission of a MAC frame during a current slot based on a distributed wireless access protocol, on a current slot number corresponding to the current slot as counted by the counter, and on the slot information.

2. The system of claim 1, wherein the slot information includes one of slot association information or slot bias information.

3. The system of claim 1, operative in an access point, and further comprising a server module operative to communicate the slot information to wireless stations in the wireless local area network.

4. The system of claim 1, operative in a wireless station.

5. The system of claim 1, wherein the slot information is updated in a beacon frame.

6. The system of claim 1, wherein the distributed wireless access protocol includes one of DCF or EDCA.

7. The system of claim 1, wherein the distributed wireless access protocol includes EDCA, wherein the slot information corresponds to a particular access class, and wherein the slot information corresponding to the particular access class is rotated dynamically among predetermined slot information values.

8. The system of claim 1, wherein the access controller initiates the transmission of the MAC frame when a backoff counter is zero and when t mod N=n_i, where t is the current slot number, N is the total number of wireless stations in the wireless local area network, and n_i is a slot number assigned to a wireless station as the slot information.

9. The system of claim 1, wherein the access controller initiates the transmission of the MAC frame when a backoff counter is zero and when a slot bias mechanism is satisfied, the slot bias mechanism operative to effect a probability of access to the wireless medium.

10. The system of claim 9, wherein the slot bias mechanism generates a random number and compares the random number against a high probability value when t mod N=n_i, where t is the current slot number, N is the total number of wireless stations in the wireless local area network, and n_i is a slot number assigned to a wireless station as the slot information, and compares the random number against a lower probability value when t mod N≠

n_i.

19. The system of claim 9, wherein the slot bias mechanism generates a random number and compares the random number against a high probability value when t mod N=n_i, where t is the current slot number, N is the total number of wireless stations in the wireless local area network, and n_i is a slot number assigned to a wireless station as the slot information, and compares the random number against a lower probability value when t mod N≠

n_i.

11. A method in a wireless local area network, comprising:

identifying a MAC frame intended for transmission on a wireless medium;

monitoring the wireless medium;

counting slot numbers; and

initiating transmission of the MAC frame during a current slot based on a distributed wireless access protocol, on a current slot number corresponding to the current slot as counted by the slot counter, and on slot information.

12. The method of claim 11, wherein the slot information includes one of slot assignment information or slot bias information.

13. The method of claim 11, operative in an access point, and further comprising communicating the slot information by the access point to wireless stations in the wireless local area network.

14. The method of claim 11, operative in a wireless station.

15. The method of claim 11, further comprising using a beacon frame to update the slot information.

16. The method of claim 11, wherein the distributed wireless access protocol includes EDCA and the slot information corresponds to a particular access class, and further comprising rotating dynamically the slot information corresponding to the particular access class among predetermined slot information values.

17. The method of claim 11, wherein the initiating of the transmission of the MAC frame occurs when a backoff counter is zero and when t mod N=n_i, where t is the current slot number, N is the total number of wireless stations in the wireless local area network, and n_i is a slot number assigned to a wireless station as the slot information.

18. The method of claim 11, wherein the initiating of the transmission of the MAC frame occurs when a backoff counter is zero and when a slot bias mechanism is satisfied, the slot bias mechanism operative to effect a probability of access to the wireless medium.

20. A system in a wireless local area network, comprising:

an access point (AP) including

a server module for generating slot information for the AP and stations (STAs);

an AP counter for counting slot numbers; and

an AP medium access controller for monitoring a wireless medium and for initiating transmission of a MAC frame during a current slot based on a distributed wireless access protocol, on a current slot number corresponding to the current slot as counted by the AP counter, and on the slot information; and

at least one STA including

a client module for receiving the slot information generated by the server module;

a STA counter for counting slot numbers; and

a STA medium access controller for monitoring a wireless medium and for initiating transmission of a MAC frame during a current slot based on a distributed wireless access protocol, on a current slot number corresponding to the current slot as counted by the STA counter, and on the slot information.