Fixed deterministic post-backoff for cyclic prioritized multiple access (CPMA) contention-free sessions
First Claim
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 first contention-free session, 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 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;
setting by the first member 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 member station;
transmitting a second contention-free session by the first member station when the backoff timer expires; and
resetting the backoff timer to the value of Bkoff to start a new cycle.
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Abstract
A cyclic prioritized multiple access (CPMA) method is disclosed which includes Fixed Deterministic Post-Backoff. Fixed deterministic post-backoff reduces conflicts between access points of overlapping cells. Contention-free sessions (CFSs) can be generated, one from each overlapping cell. Each active access point engages in a fixed deterministic post-backoff. A fixed deterministic backoff delay (Bkoff times a fixed number of idle time slots) is used by all access points, with the value of Bkoff being greater than the number of overlapping cells. The Bkoff should be large enough to enable the traffic that needs to be accommodated by the channel. Each access point has a backoff timer that is counted down using the shortest interframe space possible, typically the Priority Interframe Space (PIFS). A contention-free session (CFS) is initiated when the backoff timer expires, and it is then reset to the value of Bkoff to start a new cycle. A cycle is measured in terms of idle time slots instead of a fixed time interval. Contention-based transmissions can be attempted by an access point or other stations in the cell using their assigned priority while the access point is counting down its backoff timer. A new access point can get started and resolve possible collisions by a small random backoff. Subsequent contention-free sessions (CFSs) will not conflict, given an existing sequence of non-conflicting CFSs, since the follower access point'"'"'s backoff delay exceeds that of the leader'"'"'s by at least one times the fixed number of idle time slots. In this manner, contention-free sessions can be conducted without interference in the first and second cells.
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Citations
18 Claims
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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:
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coordinating by a first member station in the first cell a first contention-free session, 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 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; setting by the first member 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 member station; transmitting a second contention-free session by the first member station when the backoff timer expires; and resetting the backoff timer to the value of Bkoff to start a new cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 12)
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10. 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:
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a first access point station in the first cell; said first access point station coordinating in the first cell a first contention-free session, 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 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; a backoff timer in said first access point station, which is set 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; said backoff timer counting down said fixed deterministic post-backoff delay; said first access point station transmitting a second contention-free session when the backoff timer expires; and said backoff timer resetting the value of Bkoff to start a new cycle. - View Dependent Claims (11, 13, 14, 15, 16, 17, 18)
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Specification