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 p k h qk * ) 1 / 2 .
1. A system comprising:
K transmit antennas;
a transmitter configured to weight a symbol c by a vector of K weighting factors, to thereby generate K weighted versions of the symbol c and configured to transmit respective weighted versions of the symbol c on corresponding antennas of the K transmit antennas,
wherein the vector of K weighting factors is proportional to [gH] H , where g is a vector having L components and the superscript H is the Hermitian operator,
wherein at least one of K and L is greater than one.
2. The system, as recited in claim 1 , further comprising:
L receive antennas; and
a receiver configured to receive from the L receive antennas, L received versions of the symbol c transmitted by the K transmit antennas and configured to weight the L received versions of the symbol c by the vector g to generate L weighted, received versions of the symbol c.
3. The system, as recited in claim 2 , wherein K is greater than one and L is greater than one.
4. The system, as recited in claim 2 , wherein the vector of K weighting factors is normalized by a normalization factor, a, equal to
(
∑
p
=
1
L
∑
q
=
1
L
g
p
g
q
*
∑
k
=
1
K
h
p
k
h
qk
*
)
1
/
2
,
wherein h pq is a matrix of coefficients for the channel between the K transmit antennas and the L receive antennas.
5. The system as recited in claim 4 , wherein the normalization factor, a, is
(
∑
p
=
1
L
∑
q
=
1
L
∑
k
=
1
K
h
p
k
h
qk
*
)
1
/
2
.
6. The system as recited in claim 2 , wherein the elements of vector g satisfy
(
g
p
g
q
*
)
=
∑
k
=
1
K
h
p
k
h
qk
*
∑
k
=
1
K
h
p
k
h
qk
*
,
where
p
=
1
,
2
,
…
,
K
and
q
=
1
,
2
,
…
,
L
.
7. The system as recited in claim 2 , wherein the receiver is configured to sum the L weighted, received versions of the symbol c to thereby form an estimated version, ĉ, of the symbol c.
8. The system, as recited in claim 7 , wherein an overall signal-to-noise ratio of the estimated version ĉ is set to a maximum value.
9. The system, as recited in claim 7 , wherein an overall signal-to-noise ratio (SNR) of the estimated version ĉ is
γ
=
a
2
L
γ
o
,
where
a
=
(
∑
p
=
1
L
∑
q
=
1
L
∑
k
=
1
K
h
p
k
h
qk
*
)
1
/
2
and γ o is the average SNR for the case of a single transmitting antenna.
10. A system comprising:
K transmit antennas;
L receive antennas;
a transmitter configured to weight a symbol c and configured to transmit respective weighted versions of the symbol c on corresponding antennas of the K transmit antennas; and
a receiver configured to receive from the L receive antennas, L received versions of the symbol c transmitted by the K transmit antennas and configured to weight the L received versions of the symbol and configured to sum the L weighted, received versions of the symbol to thereby form an estimated version, ĉ, of the symbol c,
wherein K is greater than one and L is greater than one and the overall signal-to-noise ratio (SNR) of the estimated version ĉ is
γ
=
a
2
L
γ
o
,
where
a
=
(
∑
p
=
1
L
∑
q
=
1
L
∑
k
=
1
K
h
p
k
h
qk
*
)
1
/
2
,
γ o is the average SNR for the case of a single transmitting antenna, and
h pq is the element indexed by p and q of a channel estimate matrix H having K×L elements.
11. The system, as recited in claim 10 , wherein the transmitter weights the symbol c by a vector of K weighting factors, the vector of K weighting factors being proportional to [gH] H , where g is a vector having L components and the superscript H is the Hermitian operator.
12. The system, as recited in claim 10 , wherein the receiver weights L received versions of the symbol by the vector g the elements of vector g satisfying
(
g
p
g
q
*
)
=
∑
k
=
1
K
h
p
k
h
qk
*
∑
k
=
1
K
h
p
k
h
qk
*
,
where
p
=
1
,
2
,
…
,
K
and
q
=
1
,
2
,
…
,
L
,
and
h pq is an element indexed by p and q of a channel estimate matrix H having K×L elements.