Scheduling depending on quality of service and channel properties
View Patent ↗A method is described for scheduling a plurality of data flows to a plurality of shared channels in a wireless communication system transmitting data packets in time intervals of frames and applying adaptive modulation and coding. The method comprises the steps of determining virtual link adaptation parameters for at least a part of all combinations of data flow and shared channel, based on state information from the respective shared channel, and based on Quality of Service requirements for the respective data flow; calculating potential data rates for said combinations of data flow and shared channel, based on said virtual link adaptation parameters; calculating priority values for said combinations of data flow and shared channel, based on said potential data rates; and selecting, based on the calculated priority values, for at least a part of the shared channels, a data flow for which data is to be transmitted on each of these shared channel during the time interval of one frame.
1. A method for scheduling a plurality of data flows to a plurality of shared channels in a wireless communication system transmitting data packets in time intervals of frames and applying adaptive modulation and coding, the method comprising the steps of:
a) determining virtual link adaptation parameters for at least a part of all combinations of data flow and shared channel, based on state information from the respective shared channel, and based on Quality of Service requirements for the respective data flow;
b) calculating potential data rates for said combinations of data flow and shared channel, based on said virtual link adaptation parameters;
c) calculating priority values for said combinations of data flow and shared channel, based on said potential data rates, using a formula
P s,k ( t n )= D k ·S k ( t n )· G s,k ( t n )· C s,k ( t n ),
wherein
s denotes a shared channel, k denotes a data flow and t n , denotes a particular frame;
P s,k (t n ) is the calculated priority value for data flow k on shared channel s in frame t n ;
D k is a value depending on Quality of Service requirements of data flow k;
S k (t n ) is a weight for flow k during frame t n ;
G s,k (t n ) is a metric reflecting a current buffer status of data flow k, and
C s,k (t n ) is a metric reflecting the current potential data rate calculated in step b), of data flow k on shared channel s; and
d) selecting, based on said priority values, for at least a part of the shared channels, a data flow for which data is to be transmitted on each of the part of the shared channels during the time interval of one frame.
2. The method of claim 1 , wherein step d) selects a data flow having the highest priority value for data transmission on said shared channel during said time interval of one frame.
3. The method of claim 1 , wherein said weight S k (t n ) is depending on at least one of
i) a type of subscription of a user who is served by the respective data flow;
ii) whether said data flow carries user data or signalling information;
iii) a required average data rate associated with the respective data flow.
4. The method of claim 1 , wherein said weight S k (t n ) is increased with increasing traffic load for flows with restrictive Quality of Service requirements and/or decreased with increasing traffic load for flows with non-restrictive Quality of Service requirements.
5. The method of claim 1 , wherein said value depending on Quality of Service requirements of data flow k is calculated using the formula
D k =−log(ε k )/( T k ) δ
wherein
T k and ε k denote the delay threshold and the maximum probability of exceeding it for flow k respectively; and
δ is a real number greater than or equal to zero.
6. The method of claim 1 , wherein said metric reflecting a current potential data rate of data flow k on shared channel s is calculated using the formula
C
s
,
k
(
t
n
)
=
[
DRC
s
,
k
(
t
n
)
]
α
[
R
k
(
t
n
)
]
β
wherein
DRC s,k (t n ) denotes the instantaneous data-rate potentially achievable on shared channel s for flow k at time t n according to current settings of adaptive modulation and coding;
R k (t n ) denotes a potential average data rate for flow k; and
α and β are real constants greater than zero.
7. The method of claim 1 , wherein said metric reflecting a current potential data rate of data flow k on shared channel s is calculated using the formula
C
s
,
k
(
t
n
)
=
[
SIR
s
,
k
(
t
n
)
]
α
[
avrgSIR
k
(
t
n
)
]
β
wherein
SIR s,k (t n ) is a Signal to Interference/Noise Ratio for data flow k on shared channel s;
avrgSIR k (t n ) is either an average Signal to Interference/Noise Ratio for shared channel s or an average Signal to Interference/Noise Ratio over multiple/all shared channels.
8. The method of claim 1 , wherein said metric reflecting a current buffer status of data flow k is calculated using the formula
G
s
,
k
(
t
n
)
=
1
B
k
·
(
J
s
,
k
)
γ
[
∑
j
=
1
J
s
,
k
f
j
,
k
·
b
j
,
k
·
g
j
,
k
(
t
n
)
]
γ
wherein
j is an index of a packet in a buffer of a data flow, with j=1 indicating a packet to be scheduled next;
ƒ j,k is a monotonic decreasing function (ƒ j,k ≧ƒ j+1,k ) in j;
b j,k is a size of packet j;
J s,k is either
i) a value equal to or smaller than a number of packets of flow k which may be transmitted at time t n on shared channel s according to an instantaneous data rate potentially achievable on shared channel s for flow k at time t n according to current settings of adaptive modulation and coding; or
ii) a number of total packets in a buffer of flow k;
B k is defined as
B
k
=
∑
j
=
1
J
s
,
k
b
j
,
k
;
and
g j,k (t n ) is a waiting time of packet j in flow k.
9. The method of claim 1 , wherein
D
k
=
1
/
(
T
k
)
δ
;
S
k
(
t
n
)
=
const
;
C
s
,
k
(
t
n
)
=
[
SIR
s
,
k
(
t
n
)
]
α
[
avrgSIR
k
(
t
n
)
]
β
with
α
=
β
;
G
s
,
k
(
t
n
)
=
1
B
k
·
(
J
s
,
k
)
γ
[
∑
j
=
1
J
s
,
k
b
j
,
k
·
g
j
,
k
(
t
n
)
]
γ
with
J
s
,
k
=
N
s
,
k
;
with parameter settings:
δ=γ=1 . . . 6;
α=β=1 . . . 6.
10. The method of claim 1 , wherein
D
k
=
1
/
(
T
k
)
δ
;
S
k
(
t
n
)
=
const
;
C
s
,
k
(
t
n
)
=
[
SIR
s
,
k
(
t
n
)
]
α
[
avrgSIR
k
(
t
n
)
]
β
;
G
s
,
k
(
t
n
)
=
1
B
k
·
(
J
s
,
k
)
γ
[
∑
j
=
1
J
s
,
k
b
j
,
k
·
g
j
,
k
(
t
n
)
]
γ
with
J
s
,
k
=
N
s
,
k
;
with parameter settings:
δ=γ=1 . . . 6;
α=1 . . . 6;
β=1.
11. The method of claim 1 , wherein
D
k
=
1
/
(
T
k
)
δ
;
S
k
(
t
n
)
=
const
;
C
s
,
k
(
t
n
)
=
[
DRC
s
,
k
(
t
n
)
]
α
[
R
k
(
t
n
)
]
β
G
s
,
k
(
t
n
)
=
1
B
k
·
(
J
s
,
k
)
γ
[
∑
j
=
1
J
s
,
k
b
j
,
k
·
g
j
,
k
(
t
n
)
]
γ
with
J
s
,
k
=
N
s
,
k
;
with parameter settings:
δ=γ=1 . . . 6;
α=1 . . . 6;
β=1.
12. The method of claim 9 , wherein g j,k (t n )=W j,k (t n ).
13. The method of claim 9 , wherein
g
j
,
k
(
t
n
)
=
exp
(
p
k
W
j
,
k
(
t
n
)
-
p
W
tot
_
1
+
p
W
tot
_
)
.
14. A computer-readable storage medium having stored thereon instructions that, when executed in a processor of a base station or a mobile station of a wireless communication system, causes the processor to perform the method of claim 1 .
15. A transmission apparatus for a wireless communication system transmitting data packets in time intervals of frames and applying adaptive modulation and coding, the transmission apparatus comprising:
virtual link adaptation means configured to determine virtual link adaptation parameters for at least a part of all combinations of data flow and shared channel, based on state information from the respective shared channel, and based on Quality of Service requirements for the respective data flow;
means for calculating potential data rates for said combinations of data flow and shared channel, based on said virtual link adaptation parameters; and
a scheduler, configured i)to calculate priority values for said combinations of data flow and shared channel, based on said potential data rates, using a formula
P s,k ( t n )= D k ·S k ( t n )· G s,k ( t n )· C s,k ( t n ),
where s denotes a shared channel, k denotes a data flow and t n denotes a particular frame;
P s,k (t n ) is the calculated priority value for data flow k on shared channel s in frame t n ;
D k is a value depending on Quality of Service requirements of data flow k;
S k (t n ) is a weight for flow k during frame t n ;
G s,k (t n ) is a metric reflecting a current buffer status of data flow k; and
C s,k (t n ) is a metric reflecting the current potential data rate calculated in step b), of data flow k on shared channel s; and
ii) to select, based on said priority values, for at least a part of the shared channels, a data flow for which data is to be transmitted on said shared channel during the time interval of one frame.
16. The transmission apparatus of claim 15 , wherein the scheduler is further configured to select the data flow with the highest priority value for data transmission on said shared channel during said time interval of one frame.
17. A base station for a wireless communication system, the base station comprising the transmission apparatus according to claim 15 .
18. A mobile station for a wireless communication system, the mobile station comprising the transmission apparatus according to claim 15 .