HYBRID COORDINATION FUNCTION (HCF) ACCESS THROUGH TIERED CONTENTION AND OVERLAPPED WIRELESS CELL MITIGATION

• US 20080019329A1
• Filed: 10/01/2007
• Published: 01/24/2008
• Est. Priority Date: 07/05/2001
• Status: Active Grant

• Current Assignee: AT&T Intellectual Property II LP (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: BENVENISTE, MATHILDE
• Granted Patent: US 8,130,770 B2
• Time in Patent Office: Days
• US Class Current: 370/337
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 72/541 using the level of interference
• CPC Class Codes: H04W 72/542 using measured or perceived quality
• CPC Class Codes: H04W 74/02 Hybrid access
• CPC Class Codes: H04W 74/06 using polling
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method and system reduce interference between overlapping first and second wireless LAN cells in a medium. Each cell includes a respective plurality of member stations and there is at least one overlapped station occupying both cells. An inter-cell contention-free period value is assigned to a first access point station in the first cell, associated with an accessing order in the medium for member stations in the first and second cells. The access point transmits a beacon packet containing the inter-cell contention-free period value, which is intercepted at the overlapped station. The overlapped station forwards the inter-cell contention-free period value to member stations in the second cell. A second access point in the second cell can then delay transmissions by member stations in the second cell until after the inter-cell contention-free period expires. The beacon packet sent by the first access point station also includes an inter-cell contention-free period value, which causes the member stations in the first cell to delay accessing the medium until polled by the first access point. After the expiration of the intra-cell contention-free period, member stations in the first cell may contend for the medium based on the quality of service (QoS) data they are to transmit, using the Tiered Contention Multiple Access (TCMA) protocol.

Claims

1. A method for reducing interference between overlapping first and second wireless cells in a medium, each cell including a respective plurality of member stations and an overlapped station occupying both cells, comprising:

assigning an inter-cell contention-free period value to a first member station in the first cell, associated with an accessing order in the medium for member stations in the first and second cells;

transmitting by the first member station in the first cell, a beacon packet containing the inter-cell contention-free period value;

receiving the beacon packet at the overlapped station and forwarding the inter-cell contention-free period value to member stations in the second cell; and

delaying transmissions by member stations in the second cell until after said inter-cell contention-free period.

2. The method of claim 1, wherein a duration of the inter-cell contention-free period is deterministically set.

3. The method of claim 1, wherein a duration of the inter-cell contention-free period is a function of a tag value that represents said accessing order in which a cell with a given tag value will access the medium in a transmission frame.

4. The method of claim 3, wherein a first tag value is assigned to the first cell and a second, different tag value is assigned to the second cell.

5. The method of claim 4, wherein said first and second tag values are reassigned for each transmission frame, to enable each cell to have a chance at accessing the medium.

6. The method of claim 5, wherein the first and second tag values are permuted.

7. The method of claim 5, wherein the first and second tag values are reassigned based on at least one traffic condition in the medium.

8. The method of claim 5, wherein the first and second tag values are reassigned based on at least one traffic priority in the medium.

9. The method of claim 4, wherein a delay corresponding to two consecutive tag values is one time slot in a transmission frame.

10. The method of claim 1, which further comprises:

transmitting in the beacon packet to member stations in the first cell, an intra-cell contention-free period value, during which they will delay accessing the medium.

11. The method of claim 10, which further comprises:

transmitting by the first member station in the first cell during the intra-cell contention-free period, a polling packet to a second member station in the first cell authorizing the second station to transmit data.

12. The method of claim 11, wherein member stations in said first cell wait to be polled with a polling packet from said first station, before transmitting data during said intra-cell contention-free period.

13. The method of claim 11 wherein said intra-cell contention-free period value is deterministically set.

14. The method of claim 10 which further comprises:

assigning to member stations in the first cell, a first shorter backoff time value for high Quality of Service (QoS) data and a first longer backoff time value for lower QoS data, a backoff time being an interval that a member station in the first cell waits after expiration of the intra-cell contention-free period, before the member station contends for access to the medium.

15. The method of claim 14, wherein the backoff time for a particular one of said member stations in the first cell is deterministically set.

16. The method of claim 14, wherein the backoff time for a particular one of said member stations in the first cell is randomly drawn from a contention window range of possible values between a minimum delay interval to a maximum delay interval.

17. The method of claim 16, wherein transmission of packets within the first cell gives preference to high QoS data over low QoS data, to insure that a required quality of service is maintained for each type of data.

18. The method of claim 16, wherein the inter-cell contention-free period terminates when the maximum delay interval for backoff time terminates in the first cell for transmission of the high Quality of Service (QoS) data in the first cell, for giving member stations in the second cell an opportunity to transmit high Quality of Service (QoS) data in the second cell before the lower QoS data is transmitted in the first cell.

19. The method of claim 3, wherein tag values can be reused for non-overlapping cells in a region sharing the medium.

20. A wireless communications system having reduced interference between overlapping first and second wireless cells in a medium, each cell including a respective plurality of member stations and an overlapped station occupying both cells, comprising:

a first access point station in the first cell having an inter-cell contention-free period value associated with an accessing order in the medium for member stations in the first and second cells;

said first access point station transmitting a beacon packet containing the inter-cell contention-free period value;

an overlapped station occupying both cells receiving the beacon packet and forwarding the inter-cell contention-free period value to member stations in the second cell; and

a second access point station in the second cell receiving the inter-cell contention-free period value and delaying transmissions by member stations in the second cell until after said inter-cell contention-free period.

21. The system of claim 20, wherein a duration of the inter-cell contention-free period is a function of a tag value that represents said accessing order in which a cell with a given tag value will access the medium in a transmission frame.

22. The system of claim 21, wherein a first tag value is assigned to the first cell and a second, different tag value is assigned to the second cell.

23. The system of claim 22, wherein said first and second tag values are reassigned for each transmission frame, to enable each cell to have a fair chance at accessing the medium.

24. The system of claim 22, wherein the first and second tag values are permuted.

25. The system of claim 22, wherein the first and second tag values are reassigned based on at least one traffic condition in the medium.

26. The system of claim 22, wherein the first and second tag values are reassigned based on at least one traffic priority in the medium.

27. The system of claim 22, wherein a delay corresponding to two consecutive tag values is one time slot in the transmission frame.

28. The system of claim 20, which further comprises:

said first access point station transmitting in the beacon packet to member stations in the first cell, an intra-cell contention-free period value, during which they will delay accessing the medium.

29. The system of claim 28, which further comprises:

said first access point station transmitting in the first cell during the intra-cell contention-free period, a polling packet to a second member station in the first cell authorizing the second station to transmit data.

30. The system of claim 29, wherein member stations in said first cell waits to be polled with a polling packet from said first access point station, before transmitting data during said intra-cell contention-free period.

31. The system of claim 28, which further comprises:

high Quality of Service (QoS) member stations in the first cell, having a first shorter backoff time value for high Quality of Service (QoS) data and a first longer backoff time value for lower QoS data, a backoff time being an interval that a member station in the first cell waits after expiration of the intra-cell contention-free period, before the member station may contend for access to the medium.

32. The system of claim 31, wherein the backoff time for a particular one of said member stations in the first cell is deterministically set.

33. The system of claim 31, wherein the backoff time for a particular one of said member stations in the first cell is randomly drawn from a contention window range of possible values between a minimum delay interval to a maximum delay interval.

34. The system of claim 33, wherein transmission of packets within the first cell gives preference to high QoS data over low QoS data, to insure that a required quality of service is maintained for each type of data.

35. The system of claim 33, wherein the inter-cell contention-free period terminates when the maximum delay interval for backoff time terminates in the first cell for transmission of the high Quality of Service (QoS) data in the first cell, thereby giving member stations in the second cell an opportunity to transmit high Quality of Service (QoS) data in the second cell before the lower QoS data is transmitted in the first cell.

36. The system of claim 21, wherein tag values can be reused for non-overlapping cells in a region sharing the medium.

37. A method for reducing interference between overlapping wireless cells, each cell including an access point station and a plurality of member stations, comprising:

assigning to a first access point station in a first wireless cell, a first contention-free period value;

assigning to first member stations in said first cell, a first shorter backoff value for high QoS data and a first longer backoff value for lower QoS data;

assigning to a second access point station in a second wireless cell that overlaps said first cell, a second contention-free period value longer than said first contention-free period value;

assigning to second member stations in said second cell, a second shorter backoff value for high QoS data and a second longer backoff value for lower QoS data;

transmitting a first beacon packet including said first contention-free period value, from said first access point to said first member stations in said first cell;

transmitting a second beacon packet including said second contention-free period value, from said second access point to said second member stations in said second cell;

transmitting a first contention-free time response frame containing said first contention-free period value, from said first member stations, for alerting said second access point and said second member stations in said second cell, that the medium has been seized by said first access point;

waiting for said first contention-free period at said first member stations to begin counting down said first shorter backoff for high QoS data and then transmitting first high QoS data;

waiting for said second contention-free period at said second member stations to begin counting down said second shorter backoff for high QoS data and then transmitting second high QoS data;

waiting for said first contention-free period at said first member stations to begin counting down said first longer backoff for low QoS data and then transmitting first low QoS data; and

waiting for said second contention-free period at said second member stations to begin counting down said second longer backoff for lower QoS data and then transmitting second lower QoS data.

38. The method of claim 37, wherein an Inter-Cell Network Allocation Vector at each access point indicates a contention-free period value when the medium will be free.

39. The method of claim 37, wherein the access point will decrease its backoff value only after the expiration of the Inter-Cell Network Allocation Vector.

40. The method of claim 37, wherein potential collisions between different access points are resolved by using deterministic backoff delays.