Stream-based power allocation in multi-stream transmissions
A wireless communications device comprises a transmitter configured to distribute a data stream as a plurality of sub-streams, allocate power to each sub-stream of the plurality of sub-streams, and convert the sub-streams into one or more transmit signals. The wireless communications device also comprises a processor which is configured to obtain channel-quality indicators corresponding to the sub-streams and adjust one or more power allocations of one or more sub-streams to reduce a collective error rate of the data stream based on the channel-quality indicators, subject to a total power limit.
1. A wireless communications device comprising:
a transmitter configured to:
distribute a data stream as a plurality of sub-streams;
allocate power to each sub-stream of the plurality of sub-streams; and
convert the sub-streams into one or more transmit signals; and
a processor configured to:
obtain channel-quality indicators corresponding to the sub-streams; and
adjust one or more power allocations of one or more sub-streams to reduce a collective error rate of the data stream based, at least in part, on the channel-quality indicators,
wherein the one or more power allocations are subject to a total power limit,
wherein the collective error rate of the data stream is a sum of error rate approximations for the sub-streams, the error rate approximation for each sub-stream being expressible as e −p k SNR k , where SNR k is a signal-to-noise ratio value for a kth sub-stream, p k is a power allocation for the kth sub-stream, the total power limit is
∑
k
=
1
K
p
k
,
and k is a sub-stream index.
2. The wireless communications device of claim 1 , wherein the sub-streams are tones of orthogonal frequency-division multiplexing modulation.
3. The wireless communications device of claim 1 , wherein the sub-streams are a collection of spatial streams of tones of orthogonal frequency-division multiplexing modulation.
4. The wireless communications device of claim 1 , wherein the processor is further configured to use orthogonal frequency-division multiplexing (OFDM) and allocate power for each OFDM tone.
5. The wireless communications device of claim 1 , wherein the sub-streams include multiple spatial streams or space-time streams for conversion to the one or more transmit signals.
6. The wireless communications device of claim 1 , wherein the channel-quality indicators are signal-to-noise ratio values for each of the sub-streams.
7. The wireless communications device of claim 1 , wherein the processor is further configured to determine the power allocations based on optimizing for minimizing the collective error rate of the data stream.
8. The wireless communications device of claim 1 , wherein the collective error rate of the data stream is a sum of analytical expressions for an error rate of each sub-stream or as a sum of approximations for the error rate of each sub-stream.
9. The wireless communications device of claim 8 , wherein the collective error rate of the data stream is a collective symbol error rate and the error rate of each sub-stream is a symbol error rate of each sub-stream.
10. The wireless communications device of claim 8 , wherein the collective error rate of the data stream is a collective bit-error rate and the error rate of each sub-stream is a bit-error rate of each sub-stream.
11. The wireless communications device of claim 1 , wherein the processor is further configured to determine the power allocation of each sub-stream according to the relationship:
p
k
=
1
S
N
R
k
(
ξ
-
ln
1
S
N
R
k
)
+
,
wherein
ξ
=
P
+
∑
k
=
1
,
p
k
>
0
K
1
S
N
R
k
ln
1
S
N
R
k
∑
k
=
1
,
p
k
>
0
K
1
S
N
R
k
and
(
x
)
+
=
{
x
0
≤
x
0
x
<
0
.
12. A wireless communications device comprising:
a transmitter configured to:
distribute a data stream as a plurality of sub-streams;
allocate power to each sub-stream of the plurality of sub-streams; and
convert the sub-streams into one or more transmit signals; and
a processor configured to:
obtain channel-quality indicators corresponding to the sub-streams; and
adjust one or more power allocations of one or more sub-streams to reduce a collective error rate of the data stream based, at least in part, on the channel-quality indicators,
wherein the one or more power allocations are subject to a total power limit,
wherein the collective error rate of the data stream is a sum of analytical expressions for a bit-error rate of each sub-stream, the bit-error rate of each sub-stream being expressible as
1
2
erfc
(
p
k
S
N
R
k
)
for BPSK or QPSK, or
2
log
2
M
×
(
1
-
1
M
)
×
erfc
(
3
2
p
k
S
N
R
k
M
-
1
)
for M-QAM, where SNR k is a signal-to-noise ratio value of a kth sub-stream, M is a constellation size of the kth sub-stream, p k is a power allocation of each sub-stream, the total power limit is
∑
k
=
1
K
p
k
,
and k is a sub-stream index.
13. A method of operating a wireless communications device, comprising:
distributing, using a transmitter, a data stream as a plurality of sub-streams;
allocating, using a processor, power to each sub-stream of the plurality of sub-streams;
converting, using the transmitter, the sub-streams into one or more transmit signals;
determining, using the processor, a collective error rate of the data stream by determining a sub-stream error rate corresponding to each sub-stream and summing the sub-stream error rates; and
adjusting, using the processor, one or more power allocations of one or more sub-streams to reduce the collective error rate of the data stream,
wherein the one or more power allocations are subject to a total power limit,
wherein the sub-stream error rate corresponding to each sub-stream is expressible as e −p k SNR k , SN R k being a signal-to-noise ratio value of a kth sub-stream, p k being a power allocation of each sub-stream, the total power limit being
∑
k
=
1
K
p
k
,
and k being a sub-stream index.
14. The method of claim 13 , wherein said adjusting comprises determining a power allocation of each sub-stream according to the relationship:
p
k
=
1
S
N
R
k
(
ξ
-
ln
1
S
N
R
k
)
+
,
wherein
ξ
=
P
+
∑
k
=
1
,
p
k
>
0
K
1
S
N
R
k
ln
1
S
N
R
k
∑
k
=
1
,
p
k
>
0
K
1
S
N
R
k
and
(
x
)
+
=
{
x
0
≤
x
0
x
<
0
.
15. A method of operating a wireless communications device, comprising:
distributing, using a transmitter, a data stream as a plurality of sub-streams;
allocating, using a processor, power to each sub-stream of the plurality of sub-streams;
converting, using the transmitter, the sub-streams into one or more transmit signals;
determining, using the processor, a sub-stream error rate corresponding to each sub-stream and a collective error rate of the data stream therefrom; and
adjusting, using the processor, one or more power allocations of one or more sub-streams to reduce the collective error rate of the data stream,
wherein the one or more power allocations are subject to a total power limit,
wherein the sub-stream error rate of each sub-stream is
1
2
erfc
(
p
k
S
N
R
k
)
for BPSK or QPSK, or
2
log
2
M
×
(
1
-
1
M
)
×
erfc
(
3
2
p
k
S
N
R
k
M
-
1
)
for M-QAM, SNR k is a signal-to-noise ratio value of a kth sub-stream, M is a constellation size of the kth sub-stream, p k is a power allocation of each sub-stream, the total power limit is
∑
k
=
1
K
p
k
,
and k is a sub-stream index.