'Shield': protecting high priority channel access attempts in overlapped wireless cells

• US 20030156553A1
• Filed: 09/27/2002
• Published: 08/21/2003
• Est. Priority Date: 11/02/2001
• 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 7,248,600 B2
• Time in Patent Office: Days
• US Class Current: 370/317
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02
• CPC Class Codes: H04W 74/06 using polling
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02
• 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 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.

Claims

1. A method for reducing interference between overlapping first and second wireless LAN cells in a medium, each cell including a respective plurality of member stations, 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 during a transmission frame;

transmitting by the first member station in the first cell, a shield packet to deter other stations from contending for the medium;

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 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, 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.

3. The method of claim 2, 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.

4. The method of claim 3, wherein member stations in said first cell must wait to be polled with a polling packet from said first station before transmitting data during said intra-cell contention-free period.

5. The method of claim 2, 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 must wait after expiration of the intra-cell contention-free period before the member station may contend for access to the medium.

6. A wireless communications system having reduced interference between overlapping first and second wireless LAN cells in a medium, each cell including a respective plurality of member stations, 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 during a transmission frame;

said first access point station transmitting a shield packet to deter other stations from contending for the medium;

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

7. The system of claim 6, 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.

8. The system of claim 7, 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.

9. The system of claim 8, wherein member stations in said first cell must wait to be polled with a polling packet from said first access point station before transmitting data during said intra-cell contention-free period.

10. The system of claim 7, 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 must wait after expiration of the intra-cell contention-free period before the member station may contend for access to the medium.

11. A method for reducing interference between overlapping wireless LAN 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 LAN 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 LAN 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 by the first access point station in the first cell a shield packet to deter other stations from contending for the medium;

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, thereby 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.