Apparatus and method for controlling inter-cell interference in wireless communication system
A method for controlling inter-cell interference in a wireless communication system includes receiving information about an interference control period from a central controller, performing carrier sensing based activation competition in the interference control period, and scheduling user equipments served by the BS if the BS wins the carrier sensing based activation competition. The carrier sensing based activation competition may be based on a BS-specific back-off value related to a BS-specific weight. The BS-specific weight may be determined as the sum of products of an instantaneous throughput and a differential value of an average throughput based utility function, for all UEs served by the BS.
1. A method for controlling inter-cell interference in a wireless communication system, which is performed by a base station (BS), the method comprising:
receiving information about an interference control period from a central controller;
performing carrier sensing based activation competition in the interference control period; and
scheduling user equipments served by the BS if the BS wins the carrier sensing based activation competition,
wherein the carrier sensing based activation competition is based on a BS-specific back-off value related to a BS-specific weight, and
wherein the BS-specific weight is determined as the sum of products of an instantaneous throughput and a differential value of an average throughput based utility function, for all UEs served by the BS.
2. The method according to claim 1 ,
wherein the BS-specific back-off value is randomly selected in a period having a specific length,
wherein the period having the specific length decreases as the BS-specific weight increases.
3. The method according to claim 1 , wherein the period is (0, 2λ m ) wherein λ m is a BS-specific value, λ m =e −w m (τ) and w(τ) corresponds to the BS-specific weight in a superframe τ.
4. The method according to claim 1 , wherein the BS-specific weight is determined as
w
(
τ
)
=
∑
n
∈
N
U
′
(
R
_
n
)
r
n
,
PS
,
wherein w(τ) denotes the BS-specific weight in a superframe τ, N denotes a set of UEs served by the BS, n represents a UE in the UE set,
U
(
R
_
n
)
=
{
log
(
R
_
n
)
,
if
α
=
1
,
(
1
-
α
)
R
_
n
1
-
α
,
otherwise
,
,
R n represents the average throughput of the UE n, α is a constant and r n,PS is the instantaneous throughput of the UE n in the interference control period.
5. The method according to claim 1 , wherein performing of the carrier sensing based activation competition comprises determining whether the intensity of a reference signal received from at least one neighboring BS exceeds a threshold value,
wherein, if the intensity of the reference signal received from the at least one neighboring BS does not exceed the threshold value for a time corresponding to the BS-specific back-off value, it is determined that the BS wins the activation competition.
6. The method according to claim 1 , wherein if at least one neighboring BS is defeated in the carrier sensing based activation competition, the at least one neighboring BS maintains an idle state.
7. The method according to claim 1 ,
wherein the information about the interference control period is determined based on information about gradients of utility function in a period in which interference control is performed (hereinafter, “control period”) and gradients of utility function in a period in which interference control is not performed (hereinafter, “no-control period”), at each BS in the wireless communication system,
wherein the interference control period is determined such that one having a higher gradient between the control period and the no-control period is set more frequently in the interference control period.
8. The method according to claim 7 ,
wherein information about the gradient of utility function of a BS (m) in the period in which interference control is performed corresponds to Δ m,PS =Σ nεN m U′( R n )r n,PS , and information about the gradient of utility function of the BS (m) in the period in which interference control is not performed corresponds to Δ m,PS =Σ nεN m U′( R n )r n,PS ,
wherein N m denotes a set of UEs served by the BS (m), n denotes a UE in the UE set,
U
(
R
_
n
)
=
{
log
(
R
_
n
)
,
if
α
=
1
,
(
1
-
α
)
R
_
n
1
-
α
,
otherwise
,
,
R n is the average throughput of the UE n, α is a constant, r n,PS is an instantaneous throughput of the UE (n) in the period in which interference control is performed, and r n,PS is an instantaneous throughput of the UE (n) in the period in which interference control is not performed.
9. The method according to claim 8 ,
wherein the period θ in which interference control is performed and the period 1−θ in which interference control is not performed are updated as
θ
←
θ
+
γ
∑
m
Δ
m
,
PS
1
+
γ
∑
m
(
Δ
m
,
NPS
+
Δ
m
,
PS
)
,
1
-
θ
←
1
-
θ
+
γ
∑
m
Δ
m
,
NPS
1
+
∑
m
γ
(
Δ
m
,
NPS
+
Δ
m
,
PS
)
,
wherein γ is a scaling factor and 0<γ<<1.
10. A base station (BS) for controlling inter-cell interference in a wireless communication system, the BS comprising:
a radio frequency (RF) unit; and
a processor configured to control the RF unit,
wherein the processor is configured to receive information about an interference control period from a central controller, to perform carrier sensing based activation competition in the interference control period and to schedule user equipments served by the BS if the BS wins the carrier sensing based activation competition,
wherein the carrier sensing based activation competition is based on a BS-specific back-off value related to a BS-specific weight, and
wherein the BS-specific weight is determined as the sum of products of an instantaneous throughput and a differential value of an average throughput based utility function, for all UEs served by the BS.
11. The BS according to claim 10 ,
wherein the BS-specific back-off value is randomly selected in a period having a specific length,
wherein the period having the specific length decreases as the BS-specific weight increases.
12. The BS according to claim 10 , wherein the period is (0, 2λ m ) wherein λ m is a BS-specific value, λ m =e −w m (τ) and w(τ) corresponds to the BS-specific weight in a superframe τ.
13. The BS according to claim 10 ,
wherein the BS-specific weight is determined as
w
(
τ
)
=
∑
n
∈
N
U
′
(
R
_
n
)
r
n
,
PS
,
wherein w(τ) denotes the BS-specific weight in a superframe τ, N denotes a set of UEs served by the BS, n represents a UE in the UE set,
U
(
R
_
n
)
=
{
log
(
R
_
n
)
,
if
α
=
1
,
(
1
-
α
)
R
_
n
1
-
α
,
otherwise
,
,
R n represents the average throughput of the UE (n), α is a constant and r n,PS is the instantaneous throughput of the UE (n) in the interference control period.
14. The BS according to claim 10 ,
wherein the processor is configured to determine whether the intensity of a reference signal received from a neighboring BS exceeds a threshold value,
wherein, if the intensity of the reference signal received from the neighboring BS does not exceed the threshold value for a time corresponding to the BS-specific back-off value, it is determined that the BS wins the activation competition.
15. The BS according to claim 10 , wherein if at least one neighboring BS is defeated in the carrier sensing based activation competition, the at least one neighboring BS maintains an idle state.
16. The BS according to claim 10 ,
wherein the information about the interference control period is determined based on information about gradient of utility function in a period in which interference control is performed (hereinafter, “control period”) and gradient of utility function in a period in which interference control is not performed (hereinafter, “no-control period”), at each BS in the wireless communication system,
wherein the interference control period is determined such that one having a higher gradient between the control period and the no-control period is set more frequently in the interference control period.
17. The BS according to claim 16 ,
wherein information about the gradient of utility function of a BS (m) in the period in which interference control is performed corresponds to Δ m,PS =Σ nεN m U′( R n )r n,PS , and information about the gradient of utility function of the BS (m) in the period in which interference control is not performed corresponds to Δ m,PS =Σ nεN m U′( R n )r n,PS ,
wherein N m denotes a set of UEs served by the BS (m), n denotes a UE in the UE set,
U
(
R
_
n
)
=
{
log
(
R
_
n
)
,
if
α
=
1
,
(
1
-
α
)
R
_
n
1
-
α
,
otherwise
,
,
R n is the average throughput of the UE (n), α is a constant, r n,PS is instantaneous throughput of the UE (n) in the period in which interference control is performed, and r n,PS is instantaneous throughput of the UE (n) in the period in which interference control is not performed.
18. The BS according to claim 17 ,
wherein the period θ in which interference control is performed and the period 1−θ in which interference control is not performed are updated as
θ
←
θ
+
γ
∑
m
Δ
m
,
PS
1
+
γ
∑
m
(
Δ
m
,
NPS
+
Δ
m
,
PS
)
,
1
-
θ
←
1
-
θ
+
γ
∑
m
Δ
m
,
NPS
1
+
∑
m
γ
(
Δ
m
,
NPS
+
Δ
m
,
PS
)
,
wherein γ is a scaling factor and 0<γ<<1.