System and method for adaptive polling in a WLAN
A method (S 200 ) and system for scheduling data transmissions between a base station ( 110 ) and a plurality of user terminals ( 130 ) in a wireless network. The method and system include transmitting a first poll ( 260 ) from the base station ( 110 ) to a first user terminal traffic stream (Step S 210 ). In response to the first poll ( 260 ) the first user terminal traffic stream transmits a first frame ( 210 ) to the base station ( 110 ), where a queue state of the first user terminal traffic stream is indicated in the header of the first frame ( 210 ) (Step S 220 ). The base station ( 110 ) removes the first user terminal traffic stream from an active list when the first frame ( 210 ) indicates that the queue state is empty (Step S 230 ). The base station ( 110 ) then calculates a deferral window ( 220 ) and schedules transmissions of other data frames ( 240 ) between the base station ( 110 ) and the plurality of user terminal traffic streams that remain on the active list (Steps S 240 and S 250 ). At the expiration of the deferral window ( 220 ) the first user terminal traffic stream is returned to the active list (Step S 260 ).
1. A method of scheduling data transmissions between a base station and a plurality of user terminal traffic streams in a wireless QoS network, comprising:
transmitting a first poll from said base station to a first user terminal traffic stream in an active list of the user terminal traffic streams;
transmitting at least one frame from a group of data frames from said first user terminal traffic stream to said base station in response to said first poll, wherein a queue state of said first user terminal traffic stream is indicated in said frame;
removing said first user terminal traffic stream from said active list when said frame indicates that said queue state is empty;
calculating a deferral window for said first user terminal traffic stream;
scheduling transmissions of data frames between said base station and said plurality of user terminal traffic streams that remain on said active list; and
returning said first user terminal traffic stream to said active list at the expiration of said deferral windows,
wherein said deferral window is calculated using an algorithm based on the following equation:
T
D
=
{
T
i
,
L
i
/
ρ
i
≥
T
db
T
s
,
otherwise
(
1
)
where T i is an interval selected by a deferral window adaptation algorithm, T db is a requested delay bound, L i is a nominal data frame size, ρ i is a mean data transfer rate, T s is a scheduling window, and T D is the duration of said deferral window.
2. The method of claim 1 , wherein T i is calculated using an algorithm based on the following equation:
T
i
=
T
i
-
(
T
W
-
T
Q
)
+
σ
where T W is the average time between a first in line data frame arrival point in a user terminal traffic stream queue and the arrival of a first poll since a previous return of said user terminal traffic stream to said active list, T Q is the average time between the return of said user terminal traffic stream to said active list and the scheduled transmission of a next poll, and σ is a heuristic factor based on the inter-arrival period variance of an uplink traffic stream.
3. The method of claim 1 , wherein said deferral window is calculated based on a defined inter-arrival period of a user terminal traffic stream.
4. The method of claim 3 , wherein said inter-arrival period corresponds to a period between voice or video data frames generated by a codec.
5. A system of scheduling data transmissions comprising:
a plurality of user terminal traffic streams in an active list; and
a base station, wherein said base station is operable to:
transmit a first poll to a first user terminal traffic stream selected from said plurality of user terminal traffic streams;
receive at least one frame from a group of data frames from said first user terminal traffic stream in response to said first poll, wherein a queue state of said first user terminal traffic stream is indicated in said frame;
remove said first user terminal traffic stream from the active list when said frame indicates that said queue state is empty;
calculate a deferral window for said first user terminal traffic stream;
schedule transmissions of data frames between said base station and said plurality of user terminal traffic streams that remain on said active list; and
return said first user terminal traffic stream to said active list at the expiration of said deferral window,
wherein said deferral window is calculated using an algorithm based on the following equation:
T
D
=
{
T
i
,
L
i
/
ρ
i
≥
T
db
T
s
,
otherwise
(
1
)
where T i is an interval selected by a deferral window adaptation algorithm, T db is a requested delay bound, L i is a nominal data frame size, ρ i is a mean data transfer rate, T s is a scheduling window, and T D is the duration of said deferral window.
6. The system of claim 5 , wherein T i is calculated using an algorithm based on the following equation:
T
i
=
T
i
-
(
T
W
-
T
Q
)
+
σ
where T W is the average time between a first in line data frame arrival point in a user terminal traffic stream queue and the arrival of a first poll since a previous return of said user terminal traffic stream to said active list, T Q is the average time between the return of said user terminal traffic stream to said active list and the scheduled transmission of a next poll, and σ is a heuristic factor based on the inter-arrival period variance of an uplink traffic stream.
7. The system of claim 5 , wherein said deferral window is calculated based on a defined inter-arrival period of a user terminal traffic stream.
8. The system of claim 7 , wherein said inter-arrival period corresponds to a period between voice or video data frames generated by a codec.
9. A system of scheduling data transmissions comprising:
a plurality of user terminal traffic streams in an active list;
a base station;
means for transmitting a first poll from said base station to a first user terminal traffic stream selected among said plurality of user terminal traffic streams;
means for transmitting at least one frame from a group of data frames from said first user terminal traffic stream to said base station in response to said first poll;
means for removing said first user terminal traffic stream from the active list when said frame indicates that said queue state is empty;
means for calculating a deferral window for said first user terminal traffic stream using an algorithm based on the following equation:
T
D
=
{
T
i
,
L
i
/
ρ
i
≥
T
db
T
s
,
otherwise
(
1
)
where T i is an interval selected by a deferral window adaptation algorithm, T db is a requested delay bound, L i is a nominal data frame size, ρ i is a mean data transfer rate, T s is a scheduling window, and T D is the duration of said deferral window;
means for scheduling transmissions of data frames between said base station and said plurality of user terminal traffic streams that remain on said active list; and
means for returning said first user terminal traffic stream to said active list at the expiration of said deferral window.
10. The system of claim 9 , wherein T i is calculated using an algorithm based on the following equation:
T
i
=
T
i
-
(
T
W
-
T
Q
)
+
σ
where T W is the average time between a first in line data frame arrival point in a user terminal traffic stream queue and the arrival of a first poll since a previous return of said user terminal traffic stream to said active list, T Q is the average time between the return of said user terminal traffic stream to said active list and the scheduled transmission of a next poll, and σ is a heuristic factor based on the inter-arrival period variance of an uplink traffic stream.