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. 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 enabling a plurality of overlapped wireless LAN cells to have contention-free access to a medium, each cell including a respective plurality of member stations, comprising:
assigning a first inter-cell contention-free period value to a first access point station in a first cell, associated with an accessing order in the medium for member stations in first and second cells of the plurality of cells during a transmission frame;
transmitting by the first access point station in the first cell, a beacon packet containing the first inter-cell contention-free period value;
receiving the beacon packet at an overlapped station occupying the first cell and the second cell, and forwarding the inter-cell contention-free period value to member stations in the second cell, to delay transmissions by member stations in the second cell until after said first inter-cell contention-free period;
assigning a second inter-cell contention-free period value to a second access point station in the second cell, associated with said accessing order;
transmitting by the second access point station in the second cell, a second beacon packet containing the second inter-cell contention-free period value;
receiving the second beacon packet at an overlapped station occupying said first cell and said second cell, and forwarding the second inter-cell contention-free period value to member stations in the first cell to delay transmissions by member stations in the first cell until after said second inter-cell contention-free period;
receiving the first inter-cell contention-free period value and the second inter-cell contention-free period value at a third access point station in a third cell overlapped with said first cell and said second cell;
selecting a backoff time for said third access point station following the second inter-cell contention-free period, to begin transmission by the third access point station in the third cell of a third beacon packet containing a third inter-cell contention-free period value; and
receiving the third beacon packet at an overlapped station occupying said first cell and an overlapped station occupying said second cell, and forwarding the third inter-cell contention-free period value to member stations in the first and second cells to delay transmissions by member stations in the first and second cells until after said third inter-cell contention-free period.
2. The method of claim 1 , which further comprises:
transmitting in the first beacon packet to member stations in the first cell, an intra-cell contention-free period value, during which they will delay accessing the medium.
3. The method of claim 2 , which further comprises:
transmitting a peg packet by the third access point station in the third cell to deter member stations in said overlapped first cell from contending for the medium.
4. A method for enabling a plurality of overlapped wireless LAN cells to have contention-free access to a medium, each cell including a respective plurality of member stations, comprising:
assigning a first inter-cell contention-free period value to a first access point station in a first cell, associated with an accessing order in the medium for member stations in first and second cells of the plurality of cells during a transmission frame;
transmitting by the first access point station in the first cell, a beacon packet containing the first inter-cell contention-free period value;
assigning a second inter-cell contention-free period value to a second access point station in the second cell, associated with said accessing order;
transmitting by the second access point station in the second cell, a second beacon packet containing the second inter-cell contention-free period value;
receiving the first inter-cell contention-free period value and the second inter-cell contention-free period value at a third access point station in a third cell overlapped with said first cell and said second cell;
selecting a backoff time for said third access point station following the second inter-cell contention-free period, to begin transmission by the third access point station in the third cell of a third beacon packet containing a third inter-cell contention-free period value; and
receiving the third inter-cell contention-free period value at member stations in the first and second cells to delay transmissions by member stations in the first and second cells until after said third inter-cell contention-free period.
5. The method of claim 4 , which further comprises:
transmitting in the first beacon packet to member stations in the first cell, an intra-cell contention-free period value, during which they will delay accessing the medium.
6. The method of claim 5 , which further comprises:
transmitting a peg packet by the third access point station in the third cell to deter member stations in said overlapped first cell from contending for the medium.