STAGGERED STARTUP FOR CYCLIC PRIORITIZED MULTIPLE ACCESS (CPMA) CONTENTION-FREE SESSIONS

• US 20080013515A1
• Filed: 09/28/2007
• Published: 01/17/2008
• Est. Priority Date: 11/02/2001
• Status: Active Grant

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: BENVENISTE, MATHILDE
• Granted Patent: US 7,983,231 B2
• Time in Patent Office: Days
• US Class Current: 370/338
• 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

A staggered startup method and system for a cyclic prioritized multiple access (CPMA) 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. A first member station in the first cell coordinates a periodic sequence of first contention-free sessions. Each contention-free session includes multiple bursts with other member stations in the first cell. The first member station retains control of the medium by using interframe spaces sufficiently short between the bursts so 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. A second member station in the second cell listens to the activity in the medium and detects an end to one of the first contention-free sessions indicated by an interval longer than a PIFS idle interval following an end to the activity in the medium. The second member station then sets a post-backoff delay to periodically transmit a minimal interval after the first contention-free sessions of the first member station. The second member station coordinates in the second cell a periodic sequence of second contention-free sessions. In this manner, contention-free sessions are interleaved on a periodic basis in the first and second cells.

Claims

1. A method for reducing interference between overlapping first and second wireless 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 periodic sequence of first contention-free sessions, each said 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 sufficiently short between the multiple bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session;

listening by a second member station in the second cell to said activity in the medium and detecting an end to one of said first contention-free sessions indicated by an interval longer than an idle interval following an end to said activity in the medium;

setting a post-backoff delay by said second member station to periodically transmit after said first contention-free sessions of said first member station; and

coordinating by said second member station in the second cell a periodic sequence of second contention-free sessions, each said 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 sufficiently short between the multiple bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium.

2. The method of claim 1, wherein said post-backoff delay being a minimum arbitration interframe space (AIFS).

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

initiating a contention-free session when said post-backoff delay is counted down to zero; and

resetting said post-backoff delay to start a new period.

4. The method of claim 1, wherein consecutive ones of said contention-free sessions are separated by idle gaps<

=PIFS.

5. The method of claim 1, in which said setting a post-backoff delay further comprises:

detecting an idle period X=PIPS+x, x>

O at time t;

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

x; and

said value of Bkoff being a fixed deterministic backoff delay, which is greater than a number of overlapping cells.

6. The method of claim 1, wherein said first and second wireless cells are wireless local area network cells.

7. A wireless communications system having reduced interference between overlapping first and second wireless 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 periodic sequence of first contention-free sessions, each said session including multiple bursts with other member stations in the first cell, and retaining control of the medium by said first access point by using interframe spaces sufficiently short between the multiple bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session;

a second access point station in the second cell;

said second access point listening in the second cell to said activity in the medium and detecting an end to one of said first contention-free sessions indicated by an interval longer than an idle interval following an end to said activity in the medium;

said second access point setting a post-backoff delay by to periodically transmit after said first contention-free sessions of said first access point; and

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

8. The system of claim 7, wherein said post-backoff delay being a minimum arbitration interframe space (AIFS).

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

said second access point initiating a contention-free session when said post-backoff delay is counted down to zero; and

said second access point resetting said post-backoff delay to start a new period.

10. The system of claim 7, wherein consecutive ones of said contention-free sessions being separated by idle gaps<

=PIFS.

11. The system of claim 7, wherein said setting a post-backoff delay further comprises:

said second access point detecting an idle period X=PIFS+x, x>

O at time t;

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

x; and

said value of Bkoff being a fixed deterministic backoff delay, which is greater than a number of overlapping cells.

12. The system of claim 7, wherein said first and second wireless cells are wireless local area network cells.

13. A computer-readable medium having stored thereon a plurality of instructions, the plurality of instructions including instructions which, when executed by a processor, cause the processor to perform the steps of a method for reducing interference between overlapping first and second wireless 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 periodic sequence of first contention-free sessions, each said 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 sufficiently short between the multiple bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium during a session;

listening by a second member station in the second cell to said activity in the medium and detecting an end to one of said first contention-free sessions indicated by an interval longer than an idle interval following an end to said activity in the medium;

setting a post-backoff delay by said second member station to periodically transmit after said first contention-free sessions of said first member station; and

coordinating by said second member station in the second cell a periodic sequence of second contention-free sessions, each said 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 sufficiently short between the multiple bursts that the multiple bursts appear to contending stations to be a single instance of activity in the medium.

14. The computer-readable medium of claim 13, wherein said post-backoff delay being a minimum arbitration interframe space (AIFS).

15. The computer-readable medium of claim 13, which further comprises:

initiating a contention-free session when said post-backoff delay is counted down to zero; and

resetting said post-backoff delay to start a new period.

16. The computer-readable medium of claim 13, wherein consecutive ones of said contention-free sessions are separated by idle gaps<

=PIFS.

17. The computer-readable medium of claim 13, in which said setting a post-backoff delay further comprises:

detecting an idle period X=PIPS+x, x>

O at time t;

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

x; and

said value of Bkoff being a fixed deterministic backoff delay, which is greater than a number of overlapping cells.

18. The computer-readable medium of claim 13, wherein said first and second wireless cells are wireless local area network cells.