Methods and devices for coordinating the transmissions of access points in WLANs
View Patent ↗The coordination of transmissions by access points (APs) in a wireless local area network (WLAN) is carried out by allowing APs to transmit during slots of a Contention Free Period (CFP). Prior to transmission, slots are assigned to APs using a 4-approximation technique. This technique allows an AP to transmit using multiple frequencies. The assignment of slots satisfies a maximal, lower bound of an AP slot-to-user ratio.
1. A method for coordinating transmissions of access points in a wireless local area network comprising the steps of:
estimating a number of slots for each access point associated with a contention free period (CFP);
generating estimated slot sequences, slot assignments and a transmission frequency for each access point based on the estimated number of slots and an interference graph associated with every access point;
determining a total number of slots used in the estimated slot assignments;
comparing the total number of slots to an available number of slots;
adjusting a slot-to-user ratio of each access point until said ratios substantially equal a maximum, lower bound of all of the slot-to-user ratios; and
assigning each access point a number of slots and a slot sequence based on the estimated slot assignments and slot sequences and assigning each access point a transmission frequency when the total number of slots equals the available number of slots.
2. The method as in claim 1 wherein the adjustment step further comprises the steps of:
increasing the slot-to-user ratio of each access point when the total number of slots is less than the available number of slots; and
decreasing the slot-to-user ratio of each access point when the total number of slots is greater than the available number of slots.
3. The method as in claim 1 further comprising the steps of:
estimating a next number of slots for each access point based on each access point's adjusted slot-to-user ratio; and
generating next, estimated slot sequences, slot assignments and a transmission frequency for each access point based on the next number of slots and the interference graph.
4. The method as in claim 1 wherein the generation step further comprises generating the estimated slot sequences, slot assignments and frequencies such that no two interfering access points are assigned the same transmission frequency during a given slot and such that a total number of assigned slots is minimized.
5. The method as in claim 1 wherein the method comprises a 4-approximation technique.
6. A system for coordinating transmissions of access points in a wireless local area network operable to:
estimate a number of slots for each access point associated with a contention-free period (CFP);
generate estimated slot sequences, slot assignments and a transmission frequency for each access point based on the estimated number of slots and an interference graph associated with every access point;
determine a total number of slots used in the estimated slot assignments;
compare the total number of slots to an available number of slots;
adjust a slot-to-user ratio of each access point until said ratios substantially equal a maximum, lower bound of all of the slot-to-user ratios; and
assign each access point a number of slots and a slot sequence based on the estimated slot assignments and slot sequences and assigning each access point a transmission frequency when the total number of slots equals the available number of slots.
7. The system as in claim 6 further operable to:
increase the slot-to-user ratio of each access point when the total number of slots is less than the available number of slots; and
decrease the slot-to-user ratio of each access point when the total number of slots is greater than the available number of slots.
8. The system as in claim 6 further operable to:
estimate a next number of slots for each access point based on each access point's adjusted slot-to-user ratio; and
generate next, estimated slot sequences, slot assignments and a transmission frequency for each access point based on the next number of slots and the interference graph.
9. The system as in claim 6 further operable to:
generate the estimated slot sequences, slot assignments and frequencies such that no two interfering access points are assigned the same transmission frequency during a given slot and such that a total number of assigned slots is minimized.
10. The system as in claim 6 wherein the system is operable to coordinate the transmissions using a 4-approximation technique.
11. A system for coordinating transmissions of access points in a wireless local area network comprising:
means for estimating a number of slots for each access point associated with a contention free period (CFP);
means for generating estimated slot sequences, slot assignments and a transmission frequency for each access point based on the estimated number of slots and an interference graph associated with every access point;
means for determining a total number of slots used in the estimated slot assignments;
means for comparing the total number of slots to an available number of slots;
means for adjusting a slot-to-user ratio of each access point until said ratios substantially equal a maximum, lower bound of all of the slot-to-user ratios; and
means for assigning each access point a number of slots and a slot sequence based on the estimated slot assignments and slot sequences and assigning each access point a transmission frequency when the total number of slots equals the available number of slots.
12. The system as in claim 11 further comprising:
means for increasing the slot-to-user ratio of each access point when the total number of slots is less than the available number of slots; and
means for decreasing the slot-to-user ratio of each access point when the total number of slots is greater than the available number of slots.
13. The system as in claim 11 further comprising:
means for estimating a next number of slots for each access point based on each access point's adjusted slot-to-user ratio; and
means for generating next, estimated slot sequences, slot assignments and a transmission frequency for each access point based on the next number of slots and the interference graph.
14. The system as in claim 11 further comprising:
means for generating the estimated slot sequences, slot assignments and frequencies such that no two interfering access points are assigned the same transmission frequency during a given slot and such that a total number of assigned slots is minimized.