Adjusting a power allocation of users in a digital subscriber line environment
A method and a device adjust a power allocation of users in a digital subscriber line environment. An intermediate power allocation is determined for at least one user initializing with the digital subscriber line environment based on a new power allocation determined for the digital subscriber line environment containing the at least one user. The intermediate power allocation provides a predefined minimum signal-to-noise ratio margin for the active users of the digital subscriber line environment. Furthermore, a communication system can contain such a device.
1. A method for adjusting a power allocation of users in a digital subscriber line environment, which comprises the steps of:
determining an intermediate power allocation for at least one user initializing with the digital subscriber line environment based on a new power allocation determined for the digital subscriber line environment containing the at least one user, the intermediate power allocation providing a predefined minimum signal-to-noise ratio margin for active users of the digital subscriber line environment; and
determining the intermediate power allocation such that a distance metric between an actual power allocation and the new power allocation is reduced:
wherein the distance metric comprises a distance function selected from the group consisting of:
Δ
(
s
(
i
)
,
s
new
)
=
∑
n
∑
k
(
s
k
n
(
i
)
s
k
,
new
n
-
1
)
2
;
Δ
(
s
(
i
)
,
s
new
)
=
∑
n
∑
k
α
k
n
(
s
k
n
(
i
)
-
s
k
,
new
n
)
2
;
and
Δ
(
s
(
i
)
,
s
new
)
=
∑
n
∑
k
α
k
n
(
s
k
n
(
i
)
s
k
,
new
n
-
s
k
,
new
a
s
k
n
(
i
)
)
2
;
wherein
s k n denotes a power spectrum density of a transmit signal of a user n;
k denotes a subchannel or tone;
s new is the new power allocation; and
s(i) is the intermediate power allocation at a step i.
2. A method for adjusting a power allocation of users in a digital subscriber line environment, which comprises the steps of:
determining an intermediate power allocation for at least one user initializing with the digital subscriber line environment based on a new power allocation determined for the digital subscriber line environment containing the at least one user, the intermediate power allocation providing a predefined minimum signal-to-noise ratio margin for active users of the digital subscriber line environment;
wherein the intermediate power allocation is determined by solving a following optimization problem:
Δ
(
s
(
i
)
,
s
new
)
s
.
t
.
R
n
(
γ
_
)
❘
s
(
i
)
≥
R
target
n
∀
n
∑
k
s
k
n
(
i
)
≤
P
max
n
∀
n
0
≤
s
k
n
(
i
)
≤
s
k
,
mask
n
∀
n
,
k
wherein
n∈ i ⊂ is the user;
i denotes a group containing the at least one user initializing with the digital subscriber line environment;
denotes the users sharing a same binder;
s k n denotes a power spectrum density of a transmit signal of a user n;
s k,mask n is a PSD mask determined by a band profile used;
k determines a subchannel or tone;
s new is the new power allocation;
s(i) is the intermediate power allocation at a step i;
γ is the predefined minimum SNR margin;
R n is a data rate of the user n;
R target n is a target data rate of user n; and
P max n is a maximum aggregate transmit power of the user n.
3. The method according to claim 2 , which further comprises solving the optimization problem via a dual decomposition combined with a convex relaxation.
4. The method according to claim 3 , which further comprises solving the optimization problem by decomposing a Lagrangian
Λ
=
Δ
(
s
(
i
)
,
s
new
)
+
∑
n
ω
n
(
R
target
n
-
R
n
(
i
)
)
+
∑
n
λ
n
(
∑
k
s
k
n
(
i
)
-
P
max
n
)
wherein
ω n is a dual variable corresponding to a data rate constraint of the user n; and
X n is a dual variable corresponding to a power constraint, into per-tone Lagrangians Λ k according to
Λ
=
∑
k
Λ
k
+
∑
n
ω
n
R
target
n
-
∑
n
λ
n
P
max
n
︸
const
.
in
s
(
i
)
with
Λ
k
=
∑
n
(
s
k
n
(
i
)
s
k
,
new
n
-
1
)
2
+
∑
n
λ
n
s
k
n
(
i
)
-
f
s
∑
n
ω
n
log
2
(
1
+
1
γ
_
Γ
g
k
n
,
n
s
k
n
(
i
)
∑
m
≠
n
g
k
n
,
m
s
k
m
(
i
)
+
σ
k
2
)
.
5. The method according to claim 4 , wherein a dual problem
max
ω
n
,
λ
n
∀
n
∈
𝒢
i
min
s
k
n
(
i
)
∀
n
∈
𝒢
i
,
k
Λ
s
.
t
.
ω
n
,
λ
n
≥
0
∀
n
0
≤
s
k
n
(
i
)
≤
s
k
,
mask
n
∀
n
,
k
of the optimization problem is solved by solving K independent sub-problems
min
s
k
n
(
i
)
∀
n
∈
𝒢
i
Λ
k
s
.
t
.
0
≤
s
k
n
(
i
)
≤
s
k
,
mask
n
∀
n
per Lagrange multiplier search step.
6. The method according to claim 2 ,
wherein at an initial step i=0, it is determined whether the minimum SNR margin γ with 1≦ γ ≦γ target exists so that the optimization problem is feasible for s(0);
wherein in case where the minimum SNR margin γ exists, the value is used to determine the at least one intermediate power allocation;
wherein in case no such minimum SNR margin γ ≧1 exists, a set 0 is augmented by at least one additional user whose power allocation is re-shaped at the time instant t=t 0 .