Preemptive packet for maintaining contiguity in cyclic prioritized multiple access (CPMA) contention-free sessions

• US 8,068,470 B2
• Filed: 07/13/2007
• Issued: 11/29/2011
• 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): HSU, ALPUS
• Application Number:
  US11/777,736
• Publication Number:
  US 20080013509A1
• Time in Patent Office: 1,600 Days
• Field of Search: 370/338, 370/348, 370/444, 370/448
• US Class Current: 370/338
• CPC Class Codes: H04W 24/04 Arrangements for maintaining operational condition
• 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 point transmits a preemptive peg packet when it has no data to transmit in order to maintain the contiguity of its transmission timing position with respect to the timing position of other contention-free sessions (CFS) transmitted by other access points in an existing, periodic sequence. The cyclic prioritized multiple access (CPMA) method establishes the transmission timing position of contention-free sessions (CFS) between overlapping first and second wireless LAN cells contending for the same medium. Each cell includes a respective plurality of member stations. If an access point has no traffic, it will transmit a short, preemptive pegging packet and reset its backoff timer. In this manner, no gaps longer than the distributed coordination function (DCF) Interframe Space (DIFS) are left idle. This prevents other stations from using DCF contention to seize the channel, until all access points have completed one contention-free session (CFS) per periodic cycle.

Claims

1. A method for reducing interference between overlapping first and second wireless local area network cells in a medium, each of the first and second wireless local area network cells including a respective plurality of member stations, comprising:

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

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

transmitting by the first access point station a preemptive peg packet to maintain a contiguity of a transmission timing position of the first access point station with respect to a timing position of the second contention-free sessions transmitted by the second access point station; and

the preemptive peg packet preventing gaps to be left idle for longer than a distributed coordination function interframe space;

whereby other stations are prevented from using the distributed coordination function interframe space to seize the medium, until the first and second access point stations have completed one contention-free session per periodic cycle.

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

setting by the first access point station a backoff timer to a fixed deterministic post-backoff delay, which has a value of Bkoff times a fixed number of idle time slots, the value of Bkoff being greater than a number of overlapping cells;

counting down the backoff timer by the first access point station;

transmitting another one of the first contention-free sessions by the first access point station when the backoff timer expires; and

resetting the backoff timer to the value of Bkoff to start a new cycle.

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

the backoff timer being counted down using an interframe space.

4. The method of claim 3, wherein the interframe space being a priority interframe space.

5. The method of claim 3, wherein the interframe space being a minimum arbitration interframe space.

6. The method of claim 2, further comprises:

listening by the second access point station in the second wireless local area network cell to the activity in the medium and detecting an end to one of the first contention-free sessions indicated by an interval longer than a priority interframe space idle interval following an end to the activity in the medium;

setting a second post-backoff delay by the second access point station to transmit a minimal interval after the one of first contention-free sessions of the first access point station; and

coordinating by the second access point station in the second wireless local area network cell a second contention-free session of the second contention-free sessions, the second contention-free session including multiple bursts with other access point stations in the second cell, and retaining the control of the medium by the second access point station by using interframe spaces between the multiple bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium.

7. The method of claim 6, wherein the second post-backoff delay being a minimum arbitration interframe space.

8. The method of claim 6, further comprises:

initiating by the second access point station another one of the second contention-free sessions when the second post-backoff delay is counted down to zero; and

resetting the second post-backoff delay to start a new cycle.

9. The method of claim 6, further comprises:

separating consecutive ones of the first and second contention-free sessions by idle gaps which are less than a priority interframe space.

10. The method of claim 9, where the setting the second post-backoff delay further comprises:

detecting an idle period X=priority interframe space +x, x>

0 at time t; and

setting the second post-backoff delay at time t, to a value of Bkoff−

x.

11. A wireless communications system having reduced interference between overlapping first and second wireless local area network cells in a medium, each of the first and second wireless local area network cells including a respective plurality of member stations, comprising:

a first access point station in the first wireless local area network cell, wherein the first access point station coordinates in the first wireless local area network cell a periodic sequence of first contention-free sessions, each of the first contention-free sessions including multiple bursts with other member stations in the first wireless local area network cell, and retaining a control of the medium by the first access point station by using interframe spaces between the multiple bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium;

a second access point station in the second wireless local area network cell, wherein the second access point station coordinates in the second wireless local area network cell a periodic sequence of second contention-free sessions, each of the second contention-free sessions including multiple bursts with other member stations in the second wireless local area network cell, and retaining the control of the medium by the second access point station by using interframe spaces between the multiple bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium;

wherein the first access point station transmits a preemptive peg packet to maintain a contiguity of a transmission timing position of the first access point station with respect to a timing position of the second contention-free sessions transmitted by the second access point station; and

wherein the preemptive peg packet prevents gaps to be left idle for longer than a distributed coordination function interframe space;

whereby other stations are prevented from using the distributed coordination function interframe space contention to seize the medium, until the first and second access point stations have completed one contention-free session per periodic cycle.

12. The system of claim 11, further comprises:

the first access point station setting a backoff timer to a fixed deterministic post-backoff delay, which has a value of Bkoff times a fixed number of idle time slots, the value of Bkoff being greater than a number of overlapping cells;

the first access point station counting down the backoff timer;

the first access point station transmitting another one of the first contention-free sessions when the backoff timer expires; and

the first access point station resetting the backoff timer to the value of Bkoff to start a new cycle.

13. The system of claim 12, further comprises:

the backoff timer being counted down using an interframe space.

14. The system of claim 13, wherein the interframe space being a priority interframe space.

15. The system of claim 13, wherein the interframe space being a minimum arbitration interframe space.

16. The system of claim 12, further comprises:

the second access point station listening in the second wireless local area network cell to the activity in the medium and detecting an end to one of the first contention-free sessions indicated by an interval longer than a priority interframe space idle interval following an end to the activity in the medium;

the second access point station setting a second post-backoff delay to transmit a minimal interval after the one of first contention-free sessions of the first access point station; and

the second access point station coordinating in the second wireless local area network cell a second contention-free session of the second contention-free sessions, the second contention-free session including multiple bursts with other access point stations in the second wireless local area network cell, and retaining the control of the medium by the second access point station by using interframe spaces between the multiple bursts such that the multiple bursts appear to contending stations to be a single instance of activity in the medium.

17. The system of claim 16, wherein the second post-backoff delay being a minimum arbitration interframe space.

18. The system of claim 16, further comprises:

the second access point station initiating another one of the second contention-free sessions when the second post-backoff delay is counted down to zero; and

the second access point station resetting the second post-backoff delay to start a new cycle.

19. The system of claim 16, further comprises:

the second access point station separating consecutive ones of the first and second contention-free sessions by idle gaps which are less than a priority interframe space.

20. The system of claim 19, in which the setting the second post-backoff delay further comprises:

the second access point station detecting an idle period X=priority interframe space +x, x>

0 at time t; and

the second access point station setting the second post-backoff delay at time t, to a value of Bkoff−

x.