Method and apparatus for determining channel quality and performing adaptive modulation/coding within a multicarrier communication system
View Patent ↗In a multi-carrier communication system employing adaptive modulation and coding, a receiver feeds back channel quality information for a “binned” group of subcarriers instead of sending an individual quality report for each subcarrier. A transmitter will utilize the channel quality information for the bin to determine a set of γ eff values corresponding to a set of modulation and coding scheme candidates, where γ eff is an effective SNR that would yield a same FER in an AWGN channel. The transmitter utilizes the set of γ eff values to aid in determining a modulation and coding scheme, and determine a single modulation and coding scheme for all subcarriers within the channel.
1. A method for performing adaptive modulation and coding of a data stream in a multi-carrier communication system employing a plurality of subcarriers, wherein the plurality of subcarriers are divided into bins of subcarriers, the method comprising the steps of:
receiving a channel-quality report comprising a value related to a mean in channel quality for at least one bin of subcarriers;
determining an expected FER AWGN (γ eff ) for a set of modulation and coding scheme candidates based on the channel-quality report, where γ eff is an effective signal-to-noise ration (SNR) that would yield a same frame error rate (FER) in an adaptive White Gaussian noise (AWGN) channel;
determining a modulation and coding scheme for the data stream based on the expected FER AWGN (γ eff ); and
utilizing the modulation and coding scheme to transmit the data stream over the multi-carrier communication system.
2. The method of claim 1 wherein the step of receiving the channel-quality report comprises the value related to the mean and a mean for at least one bin of OFDM subcarriers.
3. The method of claim 1 wherein the step of receiving the channel-quality report comprises the value related to the mean and a value related to a variance in channel magnitude for the at least one bin of subcarriers.
4. The method of claim 1 wherein the step of receiving the channel-quality report comprises the step of receiving the set of γ eff values corresponding to the set of modulation and coding scheme candidates.
5. The method of claim 1 wherein the step of receiving the channel-quality report comprises the value related to the mean and a value related to a variance in SNR for the at least one bin of subcarriers.
6. The method of claim 1 wherein the step of determining the modulation and coding scheme comprises the steps of:
determining an expected FER for the modulation and coding scheme candidates that can be assigned; and
choosing the modulation and coding scheme that has a highest possible throughput with an expected FER lower than a target value.
7. The method of claim 6 wherein the step of determining the expected FER comprises the step of determining the expected FER AWGN (γ eff ), and
γ
eff
=
-
β
ln
(
1
N
′
∑
k
=
1
N
′
ⅇ
Γ
(
μ
k
,
σ
k
,
β
)
)
,
where N′ is the total number of bins of subcarriers, k represents a bin number, β is an optimization parameter, μ k is a mean value of the channel quality for bin k, σ k is a variance of the channel quality over bin k, and Γ(μ k ,σ k ,β) is a function of μ k , σ k and β.
8. The method of claim 7 wherein
Γ
(
μ
k
,
σ
k
,
β
)
=
(
μ
k
-
f
σ
k
2
)
2
γ
_
β
,
and
ƒ is an optimization parameter based on a bin size, γ is an average received symbol SNR.
9. The method of claim 1 wherein the step of determining the modulation and coding scheme comprises the step of determining the modulation from the group consisting of QPSK and 16-QAM.
10. The method of claim 1 wherein the step of determining the modulation and coding scheme comprises the step of determinipg the coding from the group consisting of ¼, ½, and ¾ rate coding.
11. A method for receiving adaptively modulated and coded data in a multi-carrier communication system employing a plurality of subcarriers, wherein the plurality of subcarriers are divided into bins of subcarriers, the method comprising the steps of:
determining channel quality for at least one bin of subcarriers;
reporting to a transmitter, a set of γ eff values corresponding to a set of modulation and coding scheme candidates, where γ eff is an effective signal-to-noise ratio (SNR) that would yield a same frame error rate (FER) in an adaptive White Gaussian noise (AWGN) channel; and
receiving the adaptively modulated and coded data via a modulation and coding scheme based on the set of γ eff values.
12. An apparatus for performing adaptive modulation and coding of a data stream in a multi-carrier communication system employing a plurality of subcarriers, wherein the plurality of subearriers are divided into bins of subcarriers, the apparatus comprising:
a modulation and coding scheme (MCS) selector receiving a channel-quality report comprising a value related to a mean in channel quality for at least one bin of subcarriers, the MCS selector outputting a modulation and coding scheme for the data stream based on the received channel-quality report and an effective signal-to-noise ratio (SNR) that would yield a same frame error rate (FER) in an adaptive White Gaussian noise (AWGN) channel; and
a modulator/coder receiving the MCS and outputting modulated and coded data based on the modulation and coding scheme.
13. The apparatus of claim 12 further comprising:
a transmitter for transmitting the modulated and coded data over the plurality of subcarriers.
14. The apparatus of claim 12 wherein the channel-quality report additionally comprises a value related to a standard deviation in channel quality for the at least one bin of subcarriers.
15. The apparatus of claim 12 wherein the channel-quality report comprises the value related to the mean and a standard deviation in SNR for the at least one bin of subcarriers.
16. The apparatus of claim 12 wherein the modulation and coding scheme comprises a modulation from the group consisting of QPSK and 16-QAM.
17. An apparatus for receiving adaptively modulated and coded data in a multi-carrier communication system employing a plurality of subcarriers, wherein the plurality of subcarriers are divided into bins of subcarriers, the apparatus comprising:
a bin quality determiner analyzing a received signal from a receiver and determining a set of γ eff values corresponding to a set of modulation and coding scheme candidates, where γ eff is an effective signal-to-noise ratio (SNR) that would yield a same frame error rate (FER) in an adaptive White Gaussian noise (AWGN) channel; and
the receiver for receiving the adaptively modulated and coded data that was modulated and coded via a modulation and coding scheme based on the set of γ eff values.