“Shield”: protecting high priority channel access attempts in overlapped wireless cells
A method and system reduce interference between overlapping first and second wireless LAN cells contending for the same medium. Each cell includes a respective plurality of member stations. 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 in the first cell transmits an initial shield packet to deter other stations from contending for the medium. The access point then transmits a beacon packet containing 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 intra-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.
1. A method for reducing interference between overlapping first and second wireless local area network cells in a medium, each cell including a respective plurality of member stations, comprising:
assigning an inter-cell contention-free period value to an access point station in the first wireless local area network cell, associated with an accessing order in the medium for member stations in the first and second wireless local area network cells;
transmitting by the access point station in the first wireless local area network cell, a shield packet to deter other member stations from contending for the medium; and
transmitting by the access point station in the first wireless local area network cell, a beacon packet containing the inter-cell contention-free period value.
2. The method of claim 1 , further comprising:
receiving the beacon packet at the member stations in the second wireless local area network cell; and
delaying transmissions by the member stations in the second wireless local area network cell until after the inter-cell contention-free period.
3. The method of claim 2 , further comprising:
transmitting in the beacon packet to the member stations in the first wireless local area network cell an intra-cell contention-free period value, during which the member stations in the first wireless local area network cell will delay accessing the medium.
4. The method of claim 3 , further comprising:
transmitting by the access point station in the first wireless local area network cell during the intra-cell contention-free period a polling packet to a second member station in the first wireless local area network cell authorizing the second member station to transmit data.
5. The method of claim 4 , wherein the member stations in the first wireless local area network cell wait to be polled with a polling packet from the first member station before transmitting data during the intra-cell contention-free period.
6. The method of claim 3 , further comprising:
assigning to the member stations in the first wireless local area network cell a first shorter backoff time value for high quality of service data and a first longer backoff time value for lower quality of service data, a backoff time being an interval that a member station in the first wireless local area network cell waits after an expiration of the intra-cell contention-free period before the member station contends for access to the medium.
7. A wireless communications system having reduced interference between overlapping first and second wireless local area network cells in a medium, each cell including a respective plurality of access point stations, comprising:
a first access point station in the first wireless local area network 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 wireless local area network cells, wherein the first access point station transmits a shield packet to deter other member stations from contending for the medium, and wherein the first access point station transmits a beacon packet containing the inter-cell contention-free period value.
8. The wireless communications system of claim 7 , further comprising:
a second access point station in the second wireless local area network cell receiving the inter-cell contention-free period value and delaying transmissions by member stations in the second wireless local area network cell until after the inter-cell contention-free period.
9. The wireless communications system of claim 8 , further comprising:
the first access point station transmitting in the beacon packet to member stations in the first wireless local area network cell an intra-cell contention-free period value, during which member stations delay accessing the medium.
10. The wireless communications system of claim 9 , further comprising:
the first access point station transmitting in the first wireless local area network cell during the intra-cell contention-free period a polling packet to a second member station in the first wireless local area network cell authorizing the second member station to transmit data.
11. The wireless communications system of claim 10 , wherein member stations in the first wireless local area network cell wait to be polled with a polling packet from the first access point station before transmitting data during the intra-cell contention-free period.
12. The wireless communications system of claim 9 , further comprising:
wherein member stations in the first wireless local area network cell are assigned a shorter backoff time value for a back off time for high quality of service data and a longer backoff time value for the back off time for lower quality of service data, wherein the back off time being a time interval that the member stations in the first wireless local area network cell wait after an expiration of the intra-cell contention-free period before the member stations in the first wireless local area network cell contend for access to the medium.