Maximum ratio transmission
View Patent ↗An arrangement where a transmitter has a plurality of transmitting antennas that concurrently transmit the same symbol, and where the signal delivered to each transmitting antenna is weighted by a factor that is related to the channel transmission coefficients found between the transmitting antenna and receiving antennas. In the case of a plurality of transmit antennas and one receive antenna, where the channel coefficient between the receive antenna and a transmit antenna i is h i , the weighting factor is h* i divided by a normalizing factor, a, which is ( ∑ k = 1 K h k 2 ) 1 / 2 , where K is the number of transmitting antennas. When more than one receiving antenna is employed, the weighting factor is 1 a ( gH ) H , where g=[g 1 . . . g L ), H is a matrix of channel coefficients, and α is a normalizing factor ( ∑ p = l L ∑ q = l L ∑ k = l K h pk h qk * ) 1 / 2 .
1. A method comprising:
receiving, via L receive antennas, from K transmit antennas, L received versions of a symbol, c, weighted prior to transmission by a transmit weighting vector proportional to [gH] Hermitian , where g is a vector having L components and the superscript Hermitian is the Hermitian operator; and
weighting the L received versions of the symbol, c, by a weighting factor based on g to generate L weighted received versions of the symbol c,
wherein H is a channel estimate matrix having K×L elements h kl , corresponding to channels between the K transmit antennas and the L receive antennas,
wherein K is greater than one, and
wherein L is greater than one.
2. The method as recited in claim 1 , further comprising:
transmitting, using the K transmit antennas, the symbol, c, weighted by the transmit weighting vector.
3. The method as recited in claim 1 , wherein the transmit weighting vector is normalized by a normalization factor, a, equal to
(
∑
p
=
1
L
∑
q
=
1
L
g
p
g
q
*
∑
k
=
1
K
h
pk
h
qk
*
)
1
/
2
.
4. The method as recited in claim 1 , wherein the transmit weighting vector is normalized by a normalization factor, a, equal to
(
∑
p
=
1
L
∑
q
=
1
L
∑
k
=
1
K
h
pk
h
qk
*
)
1
/
2
.
5. The method as recited in claim 1 , wherein the elements of vector g satisfy
(
g
p
g
q
*
)
=
∑
k
=
1
K
h
pk
h
qk
*
∑
k
=
1
K
h
pk
h
qk
*
,
where p=1, 2, . . . , K and q=1, 2, . . . , L.
6. The method, as recited in claim 1 , further comprising:
summing the L weighted, received versions of the symbol c to thereby form an estimated version, ĉ, of the symbol c.
7. The method, as recited in claim 6 , wherein an overall signal-to-noise ratio of the estimated version ĉ is set to a maximum value.
8. The method, as recited in claim 1 , wherein a transmitter coupled to the transmitting antennas outputs the same amount of power regardless of a number of transmit antennas in the K transmit antennas.