Method and apparatus for scheduling a controlchannel in an orthogonal frequency division multiplexing communication system
A scheduler capable of operating in an Orthogonal Frequency Division Multiplexing communication system schedules a control channel for a user equipment by determining a channel quality metric associated with the user equipment, calculating a target control channel element quality metric, determining a control channel element utilization rate, wherein the control channel element utilization rate a past rate of utilization of control channel elements, and selecting a control channel element aggregation level for the control channel based on the channel quality metric, the target control channel element quality metric, and the control channel element utilization rate. The scheduler then allocates control channel elements to the control channel based on the selected control channel element aggregation level. The scheduler further may steal power from one or more unused control channel elements and assign the stolen power to control channel elements assigned to the control channel.
1. A method for scheduling a control channel for a user equipment in an Orthogonal Frequency Division Multiplexing communication system, the method comprising:
determining a channel quality metric associated with the user equipment;
calculating a target control channel element quality metric;
determining a control channel element utilization rate, wherein the control channel element utilization rate corresponds to a past rate of utilization of control channel elements; and
selecting a control channel element aggregation level for the control channel based on the channel quality metric, the target control channel element quality metric, and the control channel element utilization rate.
2. The method of claim 1 , wherein calculating a target control channel element quality metric comprises applying an adjustment factor to a calculated target control channel element quality metric.
3. The method of claim 1 , wherein the target control channel element quality metric and the determined channel quality metric each comprises a signal-to-noise ratio.
4. The method of claim 1 , further comprising:
assigning the control channel to the user equipment, wherein the assigned control channel comprises a plurality of control channel elements corresponding, in quantity, to the control channel element aggregation level selected for the control channel; and
transmitting one or more of a downlink grant and an uplink grant to the user equipment over the assigned control channel.
5. The method of claim 1 , further comprising stealing power from one or more unused control channel elements and assigning the stolen power to one or more of the plurality of control channel elements assigned to the control channel.
6. The method of claim 1 , wherein the target control channel element quality metric comprises a signal-to-noise ratio and wherein the target control channel element quality metric is calculated by use of the following equation:
SNR
CCE
=
10
×
log
10
[
1
M
P
R
B
(
2
(
MPR
PDCCH
MPR
A
)
-
1
)
]
+
SNR
PDCCH_offset
(
dB
)
where SNR CCE is the target control channel element quality metric, MPR PDCCH is a Modulation order Product Code Rate for the control channel, MPR A and MPR B are constants, and SNR PDCCH _ offset is a control channel adjustment factor.
7. The method of claim 1 , wherein the control channel element utilization rate is based on one or more of a number of control channel elements and a percentage of control channel elements allocated to control channels in each of one or more past scheduling periods.
8. The method of claim 1 , wherein determining a control channel element utilization rate comprises calculating an average control channel element utilization over a plurality of past scheduling periods.
9. The method of claim 1 , wherein the control channel is a Physical Downlink Control Channel.
10. A scheduler for scheduling a control channel for a user equipment in an Orthogonal Frequency Division Multiplexing communication system, the scheduler comprising a processor that is configured to:
determine a channel quality metric associated with the user equipment;
calculate a target control channel element quality metric;
determine a control channel element utilization rate, wherein the control channel element utilization rate corresponds to a past rate of utilization of control channel elements; and
select a control channel element aggregation level for the control channel based on the channel quality metric, the target control channel element quality metric, and the control channel element utilization rate.
11. The scheduler of claim 10 , wherein the processor is configured to calculate a target control channel element quality metric by applying an adjustment factor to a calculated target control channel element quality metric.
12. The scheduler of claim 10 , wherein the target control channel element quality metric and the determined channel quality metric each comprises a signal-to-noise ratio.
13. The scheduler of claim 10 , wherein the processor is configured to:
assign the control channel to the user equipment, wherein the assigned control channel comprises a plurality of control channel elements corresponding, in quantity, to the control channel element aggregation level selected for the control channel; and
convey one or more of a downlink grant and an uplink grant to the user equipment over the assigned control channel.
14. The scheduler of claim 10 , wherein the processor is configured to steal power from one or more unused control channel elements and assigning the stolen power to one or more of the plurality of control channel elements assigned to the control channel.
15. The scheduler of claim 10 , wherein the scheduler further comprises an at least one memory device coupled to the processor, wherein the target control channel element quality metric comprises a signal-to-noise ratio, and wherein the processor is configured to calculate the target control channel element quality metric by use of the following equation that is maintained by the at least one memory device:
SNR
CCE
=
10
×
log
10
[
1
M
P
R
B
(
2
(
MPR
PDCCH
MPR
A
)
-
1
)
]
+
SNR
PDCCH_offset
(
dB
)
where SNR CCE is the target control channel element quality metric, MPR PDCCH is a Modulation order Product Code Rate for the control channel, MPR A and MPR B are constants, and SNR PDCCH _ offset is a control channel adjustment factor.
16. The scheduler of claim 10 , wherein the control channel element utilization rate is based on one or more of a number of control channel elements and a percentage of control channel elements allocated to control channels in each of one or more past scheduling periods.
17. The scheduler of claim 10 , wherein the control channel is a Physical Downlink Control Channel.
18. An eNodeB comprising the scheduler of claim 10 .