Method and apparatus for allocating downlink power in an orthogonal frequency division multiplexing communication system
View Patent ↗In an Orthogonal Frequency Division Multiplexing communication system, a radio access network allocates a transmit power for a downlink transmission to a mobile station based on a mean channel quality metric and a channel quality metric second order statistic, in various embodiments a channel quality metric variance or standard deviation, reported by the mobile station.
1. A method for providing channel quality feedback in an Orthogonal Frequency Division Multiplexing communication system wherein a frequency bandwidth is divided into a plurality of sub-bands, the method comprising:
receiving, by a access network element, a mean channel quality metric and one or more of a standard deviation and a variance of the channel quality metric from a mobile station; and
allocating, by the access network element, a transmit power for a downlink transmission to the mobile station based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric wherein allocating the transmit power for a downlink transmission including (a) calculating a desired channel quality metric value based on a predetermined modulation and coding rate and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric (b) determining, based on the predetermined modulation and coding rates and the received mean channel quality metric and the one or more of the standard deviation and a variance of the channel quality metric, a transmit power needed to achieve the desired channel quality metric value wherein the transmit power is determined based on the following equation,
P
tx
=
m
·
β
γ
_
(
ⅇ
SNR
effective
m
·
β
-
1
)
wherein P tx represents the transmit power, SNR effective represents the desired channel quality metric, m and β are gamma distribution parameters, and γ represents the mean channel quality metric.
2. The method of claim 1 , further comprising transmitting a downlink signal to a mobile station based on the allocated transmit power.
3. The method of claim 1 , further comprising estimating a parameter m of the gamma distribution based on the mean channel quality metric and the one or more of the standard deviation and a variance of the channel quality metric.
4. The method of claim 1 , wherein determining a transmit power comprises determining, for an Nth transmission, a minimum transmit power P tx to achieve the desired channel quality metric based on the following equation,
P
tx
=
m
N
β
N
γ
_
N
(
(
ⅇ
-
SNR
effective
,
N
β
N
-
(
L
1
L
1
+
…
+
L
N
(
1
+
γ
_
1
m
1
β
N
)
-
m
1
+
…
+
L
N
-
1
L
1
+
…
+
L
N
(
1
+
γ
_
N
-
1
m
N
-
1
β
N
)
-
m
N
-
1
)
L
N
L
1
+
…
+
L
N
)
-
1
m
N
-
1
)
wherein L i is the number of symbols in transmission i and i=1, . . . , N, representing N transmissions.
5. An access network element operable in an Orthogonal Frequency Division Multiplexing communication system wherein a frequency bandwidth is divided into a plurality of sub-bands, the access network element comprising:
a transceiver to receive a mean channel quality metric and one or more of a standard deviation and a variance of the channel quality metric from a mobile station and
a controller coupled to the transceiver, the controller configured to allocate a transmit power for a downlink transmission to the mobile station based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric, to allocate a transmit power for a downlink transmission based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric by (a) calculating a desired channel quality metric value based on a predetermined modulation and coding rate and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric and (b) determining, based on the predetermined modulation and coding rates and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric, a transmit power needed to achieve the desired channel quality metric value, to assume that the channel quality metric follows a gamma distribution in calculating a desired channel quality metric value and to determine a transmit power by determining the transmit power based on the following equation,
P
tx
=
m
·
β
γ
_
(
ⅇ
SNR
effective
m
·
β
-
1
)
wherein P tx represents the transmit power, SNR effective represents the desired channel quality metric, m and β are gamma distribution parameters, and γ represents the mean channel quality metric.
6. The access network element of claim 5 , wherein the transceiver further to transmit a downlink signal to a mobile station based on the allocated transmit power.
7. The access network element of claim 5 , wherein the controller is configured to estimate a parameter in of the gamma distribution based on the mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric.
8. The access network element of claim 5 , wherein the controller is configured to determine, for an Nth transmission, a minimum transmit power P tx to achieve the desired channel quality metric based on the following equation,
P
tx
=
m
N
β
N
γ
_
N
(
(
ⅇ
-
SNR
effective
,
N
β
N
-
(
L
1
L
1
+
…
+
L
N
(
1
+
γ
_
1
m
1
β
N
)
-
m
1
+
…
+
L
N
-
1
L
1
+
…
+
L
N
(
1
+
γ
_
N
-
1
m
N
-
1
β
N
)
-
m
N
-
1
)
L
N
L
1
+
…
+
L
N
)
-
1
m
N
-
1
)
.
wherein L i is the number of symbols in transmission i and i =1 , . . . , N, representing N transmissions.
9. A method for providing channel quality feedback in an Orthogonal Frequency Division Multiplexing communication system wherein a frequency bandwidth is divided into a plurality of sub-bands, the method comprising:
receiving, by an access network element, a mean channel quality metric and one or more of a standard deviation and a variance of the channel quality metric from a mobile station; and
allocating, by the access network element, a transmit power for a downlink transmission to the mobile station based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric wherein allocating the transmit power for a downlink transmission including (a) calculating a desired channel quality metric value based on a predetermined modulation and coding rate and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric (b) determining, based on the predetermined modulation and coding rates and the received mean channel quality metric and the one or more of the standard deviation and a variance of the channel quality metric, a transmit power needed to achieve the desired channel quality metric value and determining, for an Nth transmission, a minimum transmit power P tx to achieve the desired channel quality metric based on the following equation,
P
tx
=
m
N
β
N
γ
_
N
(
(
ⅇ
-
SNR
effective
,
N
β
N
-
(
L
1
L
1
+
…
+
L
N
(
1
+
γ
_
1
m
1
β
N
)
-
m
1
+
…
+
L
N
-
1
L
1
+
…
+
L
N
(
1
+
γ
_
N
-
1
m
N
-
1
β
N
)
-
m
N
-
1
)
L
N
L
1
+
…
+
L
N
)
-
1
m
N
-
1
)
.
wherein P tx represents the transmit power, SNR effective represents the desired channel quality metric, m and β are gamma distribution parameters, γ represents the mean channel quality metric, L i is the number of symbols in transmission i and i=1, . . . , N, representing N transmissions;
estimating, by the access network element, a parameter m of the gamma distribution based on the mean channel quality metric and the one or more of the standard deviation and a variance of the channel quality metric.
10. An access network element operable in an Orthogonal Frequency Division Multiplexing communication system wherein a frequency bandwidth is divided into a plurality of sub-bands, the access network element comprising:
a transceiver to receive a mean channel quality metric and one or more of a standard deviation and a variance of the channel quality metric from a mobile station and
a controller coupled to the transceiver, the controller configured to allocate a transmit power for a downlink transmission to the mobile station based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric, to allocate a transmit power for a downlink transmission based on the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric by (a) calculating a desired channel quality metric value based on a predetermined modulation and coding rate and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric and (b) determining, based on the predetermined modulation and coding rates and the received mean channel quality metric and the one or more of the standard deviation and the variance of the channel quality metric, a transmit power needed to achieve the desired channel quality metric value, to assume that the channel quality metric follows a gamma distribution in calculating a desired channel quality metric value and to determine, for an Nth transmission, a minimum transmit power P tx to achieve the desired channel quality metric based on the following equation,
P
tx
=
m
N
β
N
γ
_
N
(
(
ⅇ
-
SNR
effective
,
N
β
N
-
(
L
1
L
1
+
…
+
L
N
(
1
+
γ
_
1
m
1
β
N
)
-
m
1
+
…
+
L
N
-
1
L
1
+
…
+
L
N
(
1
+
γ
_
N
-
1
m
N
-
1
β
N
)
-
m
N
-
1
)
L
N
L
1
+
…
+
L
N
)
-
1
m
N
-
1
)
wherein P tx represents the transmit power, SNR effective represents the desired channel quality metric, m and β are gamma distribution parameters, γ represents the mean channel quality metric, L i is the number of symbols in transmission i, and i=1, . . . , N, representing N transmissions.