Hybrid coordination function (HCF) access through tiered contention and overlapped wireless cell mitigation
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.
1. A method for reducing an interference between overlapping first and second wireless cells in a medium, each wireless cell including a respective plurality of member stations and an overlapped station occupying both wireless cells, comprising:
assigning an inter-cell contention-free period having a value to a first member station in the first wireless cell, associated with an accessing order in the medium for member stations in the first and second wireless cells; and
transmitting by the first member station in the first wireless cell, a beacon packet containing the value, wherein the beacon packet is transmitted to the overlapped station for allowing the overlapped station to forward the value to the member stations in the second wireless cell.
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 the accessing order in which a wireless 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 wireless cell and a second, different tag value is assigned to the second wireless cell.
5. The method of claim 4 , wherein the first and second tag values are reassigned for each of a plurality of transmission frames, to enable each wireless 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 3 , wherein the tag values are reused for non-overlapping wireless cells in a region sharing the medium.
10. The method of claim 4 , wherein a delay corresponding to two consecutive tag values is one time slot in a transmission frame.
11. The method of claim 1 , which further comprises:
transmitting in the beacon packet to the member stations in the first wireless cell, a second value representing an intra-cell contention-free period, during which the member stations in the first wireless cell will delay accessing the medium.
12. The method of claim 11 , which further comprises:
transmitting by the first member station in the first wireless cell during the intra-cell contention-free period, a polling packet to a second member station in the first wireless cell authorizing the second station to transmit data.
13. The method of claim 12 , wherein the member stations in the first wireless cell wait to be polled with a polling packet from the first member station, before transmitting data during the intra-cell contention-free period.
14. The method of claim 12 wherein the value of the intra-cell contention-free period is deterministically set.
15. The method of claim 11 which further comprises:
assigning to the member stations in the first wireless cell, a first backoff time value for high quality of service data and a second backoff time value for low quality of service data, a backoff time being an interval that a member station in the first wireless cell waits after an expiration of the intra-cell contention-free period, before the member station contends for access to the medium.
16. The method of claim 15 , wherein the backoff time for a particular one of the member stations in the first wireless cell is deterministically set.
17. The method of claim 15 , wherein the backoff time for a particular one of the member stations in the first wireless cell is randomly drawn from a contention window range of values between a minimum delay interval to a maximum delay interval.
18. The method of claim 17 , wherein a transmission of packets within the first wireless cell gives preference to the high quality of service data over the low quality of service data, to insure that a required quality of service is maintained for each type of data.
19. The method of claim 17 , wherein the inter-cell contention-free period terminates when the maximum delay interval for a backoff time terminates in the first wireless cell for transmission of the high quality of service data in the first wireless cell, for giving the member stations in the second wireless cell an opportunity to transmit high quality of service data in the second wireless cell before the low quality of service data is transmitted in the first wireless cell.
20. A wireless communications system for reducing an interference between overlapping first and second wireless cells in a medium, each wireless cell including a respective plurality of member stations and an overlapped station occupying both wireless cells, comprising:
a first access point station in the first wireless cell having an inter-cell contention-free period having a value associated with an accessing order in the medium for the member stations in the first and second wireless cells, wherein the first access point station transmits a beacon packet containing the value, wherein the beacon packet is transmitted to the overlapped station for allowing the overlapped station to forward the value to the member stations in the second wireless cell.