Method for optimizing the transmit signal in multiple antenna wireless links
View Patent ↗In the method, spatial steering of parallel symbol streams and a transmit power of each symbol stream is determined based on a statistical distribution of a channel. The determined spatial steering and transmit powers may then be applied by a transmitter to optimize the transmit signal.
1. A method of optimizing transmit covariance for a multiple antenna transmitter, comprising:
determining spatial steering of parallel symbol streams and a transmit power of each symbol stream based on a statistical distribution of a channel, the determining step, for each symbol stream, including,
determining a first possible transmission power based on a kth transmission power for the symbol stream, where k represents an interval of time,
determining a second possible transmission power based on the kth transmission power for the symbol stream and the statistical distribution of the channel, and
determining the (k+1)th transmission power for the symbol stream based on the first and second possible transmission powers.
2. The method of claim 1 , wherein the determining the (k+1)th transmission power further comprises:
selecting one of the first and second possible transmission powers; and
scaling the selected transmission powers for the symbol streams so that a sum of the selected transmission powers for the symbol streams does not exceed an available amount of power at a transmitter, the scaled selected transmission powers serving as the (k+1)th transmission powers.
3. The method of claim 2 , wherein the selecting step selects a maximum one of the first and second possible transmission powers.
4. The method of claim 1 , wherein the determining a second possible transmission power step determines the second possible transmission power based on the (k)th transmission power, the statistical distribution of the channel, and an available amount of power at a transmitter.
5. The method of claim 1 , wherein the determining a second possible transmission power step determines the second possible transmission power based on the (k)th transmission power, the statistical distribution of the channel, and a noise power at a receiver.
6. The method of claim 1 , wherein the determining a second possible transmission power step determines the second possible transmission power based on the (k)th transmission power, the statistical distribution of the channel and a number of receive antennas.
7. The method of claim 1 , wherein the determining the (k+1)th transmission powers step determines the (k+1)th transmission powers according to the following expression:
for m=1, . . . , M, where M is the number of transmit antennas,
p
m
′
(
k
+
1
)
=
max
(
p
m
(
k
)
,
E
[
Tr
{
B
-
m
+
P
Mσ
2
H
~
m
H
~
m
A
}
]
-
N
E
[
H
~
m
(
B
-
m
)
2
H
~
m
Mσ
2
+
p
m
(
k
)
H
~
m
B
-
m
H
~
m
]
)
where p′ m (k+1) is a (k+1)th second possible transmission power for the mth symbol stream, H represents the statisitical distribution of the channel, {tilde over (H)}=HV with V computed to be the eigenvectors of E[H H H], N is a number of receive antennas, σ 2 indicates an arithmetic mean of the noise variances at the N receive antennas, matrix A is given by,
A
=
(
I
+
1
Mσ
2
H
~
P
(
k
)
H
~
H
)
-
1
while the M matrices B −m , m=1, . . . , M, are given by
B
-
m
=
[
I
+
1
M
σ
2
H
~
-
m
P
-
m
(
k
)
H
~
-
m
H
]
-
1
where {tilde over (H)} −m and P −m (k) indicate the corresponding matrices without the m-th column, and {tilde over (H)} m denotes the m-th column of H.