Access method for periodic contention-free sessions

• US 7,773,625 B2
• Filed: 02/19/2007
• Issued: 08/10/2010
• Est. Priority Date: 11/02/2001
• Status: Expired due to Fees

• Current Assignee: AT&T Intellectual Property II LP (AT&T, Inc.)
• Original Assignee: AT&T Intellectual Property II LP (AT&T, Inc.)
• Inventors: Benveniste, Mathilde
• Primary Examiner(s): Qureshi; Afsar M.
• Application Number:
  US11/676,475
• Publication Number:
  US 20070211749A1
• Time in Patent Office: 1,268 Days
• Field of Search: 370229-254, 370317-468, 455/422.1, 455/434, 455/450, 455/825.5, 340/825.5
• US Class Current: 370/445
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 74/02 Hybrid access
• CPC Class Codes: H04W 74/0808 using carrier sensing, e.g. carrier sense multiple access [CSMA]
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

An access method for periodic contention-free sessions (PCFS) reduces interference between overlapping first and second wireless LAN cells contending for the same medium. Each cell includes a respective plurality of member stations and an access point (AP) station. The access method for periodic contention-free sessions (PCFS) includes a fixed cycle time that reduces conflicts with PCFS from other cells. The PCFS from several cells are repeated in cycles of cycle period (CP), which is the contention-free period (CFP) of an access point times a factor that is a function of the number of overlapping cells. Periodic contention-free sessions (PCFSs) are generated, one from each overlapping cell. PCFS transmission attempts occur at the fixed specified time spacing following the start of the previous cycle. Each active AP sets a timer at CP and a PCFS is initiated when the timer expires. The timer is then reset and starts a new cycle.

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:

coordinating by a first member station in the first cell a sequence of first periodic contention-free sessions, each said first periodic contention-free session including multiple bursts with other member stations in the first cell, and retaining control of the medium by said first member station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

setting a fixed cycle time by the first member station to repeat transmitting said first periodic contention-free sessions, the cycle time being a cycle period (CP), which is a contention-free period (CFP) of a member station times a factor which is a function of a number of overlapping cells;

transmitting said first periodic contention-free sessions by the first member station;

coordinating by a second member station in the second cell a sequence of second periodic contention-free sessions, each said second periodic contention-free session including multiple bursts with other member stations in the second cell, and retaining control of the medium by said second member station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

setting said fixed cycle time by the second member station to repeat transmitting said second periodic contention-free sessions following said first periodic contention-free sessions; and

transmitting said second periodic contention-free sessions by the second member station.

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

coordinating by a third member station in a cell a non-periodic contention-free session, said non-periodic contention-free session including multiple bursts with other member stations, and retaining control of the medium by said third member station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

transmitting by said third member station an updated Network Allocation Vector (NAV) to member stations, said updated NAV being an increment in a length of said non-periodic contention-free session, said increment being an inter-BSS contention period (IBCP); and

transmitting by said third member station said non-periodic contention-free session to interleave said periodic contention-free sessions with said non-periodic contention-free session.

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

coordinating by a third member station in a cell a non-periodic contention-free session, said non-periodic contention-free session including multiple bursts with other member stations, and retaining control of the medium by said third member station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

transmitting by said third member station an updated Inter-BSS Network Allocation Vector (IBNAV) to member stations, said updated IBNAV being an increment in a length of said non-periodic contention-free session, said increment being an inter-BSS contention period (IBCP); and

transmitting by said third member station said non-periodic contention-free session to interleave said periodic contention-free sessions with said non-periodic contention-free session.

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

maintaining quality of service (QoS) of transmissions from member stations by interleaving periodic contention-free sessions with a non-periodic contention-free session having a QoS requirement;

scheduling traffic to be transmitted from selected member stations;

scheduling periodic traffic to be transmitted in periodic contention-free sessions;

scheduling non-periodic traffic in a non-periodic contention-free session according to a traffic priority; and

scheduling delay-sensitive traffic first, followed by traffic having lower priorities.

5. 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;

said first access point station coordinating in the first cell a sequence of first periodic contention-free sessions, each said first periodic contention-free session including multiple bursts with other member stations in the first cell, and retaining control of the medium by said first access station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

said first access point station setting a fixed cycle time to repeat transmitting said first periodic contention-free sessions, the cycle time being a cycle period (CP), which is a contention-free period (CFP) of a member station times a factor which is a function of a number of overlapping cells;

said first access point station transmitting said first periodic contention-free sessions;

a second access point station in the second cell;

said second access point station coordinating in the second cell a sequence of second periodic contention-free sessions, each said second periodic contention-free session including multiple bursts with other member stations in the second cell, and retaining control of the medium by said second access station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

said second access point station setting said fixed cycle time to repeat transmitting said second periodic contention-free sessions following said first periodic contention-free sessions; and

said second access point station transmitting said second periodic contention-free sessions.

6. The system of claim 5, which further comprises:

a third member station in a cell;

said third member station coordinating a non-periodic contention-free session, said non-periodic contention-free session including multiple bursts with other member stations, and retaining control of the medium by said third member station by using interframe spaces between the bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

said third member station transmitting an updated Network Allocation Vector (NAV) to member stations, said updated NAV being an increment in a length of said non-periodic contention-free session, said increment being an inter-BSS contention period (IBCP); and

said third member station transmitting said non-periodic contention-free session to interleave said periodic contention-free sessions with said non-periodic contention-free session.

7. The system of claim 5, which further comprises:

a third member station in a cell;

said third member station coordinating a non-periodic contention-free session, said non-periodic contention-free session including multiple bursts with other member stations, and retaining control of the medium by said third member station by using interframe spaces between the bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session until an end of a session;

said third member station transmitting an updated Inter-BSS Network Allocation Vector (IBNAV) to member stations, said updated IBNAV being an increment in a length of said non-periodic contention-free session, said increment being an inter-BSS contention period (IBCP); and

said third member station transmitting said non-periodic contention-free session, to interleave said periodic contention-free sessions with said non-periodic contention-free session.

8. The system of claim 5, which further comprises:

a third member station;

said third member station maintaining quality of service (QoS) of transmissions from member stations by interleaving periodic contention-free sessions with a non-periodic contention-free session having a QoS requirement;

said third member station scheduling traffic to be transmitted;

said third member station scheduling periodic traffic to be transmitted in periodic contention-free sessions;

said third member station scheduling non-periodic traffic in a non-periodic contention-free session according to a traffic priority; and

said third member station scheduling delay-sensitive traffic first, followed by traffic having lower priorities.