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 receiving antenna, where the channel coefficient between the receive antenna and a transmit antenna [I] i is h i , the weighting factor is h i * divided by a normalizing factor, α, 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 αis a normalizing factor ( ∑ p = l L ∑ q = l L ∑ k = l K h p k h qk * ) 1/2 .
1. In a wireless communication system comprising transmitter apparatus for use with receiver apparatus wherein the transmitter apparatus comprises more than one antenna, a method of improving a signal to noise ratio of a transmission channel between the transmitter and receiver apparatus comprising:
determining channel coefficients, h i , for each transmission channel between transmitter antennae and said receiver apparatus where i equals the number of transmitting apparatus antennae;
determining a normalization factor from the determined channel coefficients;
weighting each signal delivered to a transmitting antenna by a different weighting factor proportional to the inverse of the normalization factor; and
maximizing signal to noise ratio such that the gain in signal-to-noise ratio by utilizing more than one transmit antenna is proportional to the square of the normalization factor.
2. In a wireless communication system, a method of improving the signal to noise ratio as recited in claim 1 wherein said maximizing signal tom noise ratio further comprises utilizing more than one receive antennae such that the gain in signal-to-noise ratio is proportional to the square of the normalization factor divided by the number of receive antennae.
3. A method as recited in claim 1 where the weighting factor comprises a vector of size equal to the number of transmit antennae.
4. A method as recited in claim 1 where the weighting factor for each transmit antenna is equal to the conjugate of the corresponding channel coefficient, h i *, divided by the normalization factor.
5. A method as recited in claim 1 where the normalization factor α is given by the equation:
a
=
(
∑
k
=
1
K
h
k
2
)
1
2
where K is the number of transmit antennae and h 1 . . . h k represent the channel coefficients.
6. A method as recited in claim 3 wherein the weighting factor is a vector determined according to the equation
v
=
1
a
[
h
1
…
h
K
]
H
,
where α is the normalization factor, K is the number of transmit anntennae and H is the Hermitian operator.
7. A method as recited in claim 2 where the normalization factor α is given by the equation:
a
=
(
∑
p
=
1
L
∑
q
=
1
L
∑
k
=
1
K
h
pk
h
qk
*
)
1
2
where K is the number of transmit antennae and L is the number of receive antennae.
8. A method as recited in claim 1 wherein the channel coefficients are determined via a training session including transmitting pilot signals from each transmitting antenna to the receiving apparatus.
9. A method as recited in claim 2 further comprising transmitting a symbol and estimating a value of the symbol at the receiving apparatus by weighting and summing the received signals by weighting factors for each receive antennae.
10. A transmitter apparatus for use in a wireless communications system comprising:
a source of data symbols to be transmitted,
a source of channel coefficient information for each channel to a receiver apparatus,
first and second multipliers coupled to the data symbol source and to the channel coefficient source,
respective first and second antennae coupled to respective first and second multipliers for transmitting a data signal to said receiver apparatus, and
means for computing a weighting factor for each transmission channel and for use at each of said first and second multipliers, each weighting factor being proportional to the inverse of a normalization factor and proportional to the channel coefficient information for a given transmission channel, the transmitted signal from respective antennae being the result of a multiplication by said multiplier of a data symbol to be transmitted and a respective, computed weighting factor for each transmission channel.
11. A transmitter apparatus as recited in claim 10 , where the weighting factor for each transmission channel is equal to the conjugate of the corresponding channel coefficient, h 1 *, divided by the normalization factor.
12. A transmitter apparatus as recited in claim 11 , the multiplication of each symbol to be transmitted resulting in a gain in signal to noise ratio performance of the transmitter apparatus proportional to the square of the normalization factor.
13. A transmitter apparatus as recited in claim 11 , wherein the weighting factor is represented as α vector determined according to the equation
v
=
1
a
[
h
1
…
h
K
]
H
,
where a is the normalization factor, K is the number of transmit antennae and H is the Hermitian operator and h 1 . . . h k represent the channel coefficients.
14. A transmitter apparatus as recited in claim 10 , the normalization factor α is given by the equation:
a
=
(
∑
k
=
1
K
h
k
2
)
1
2
where K is the number of transmit antennae and h 1 . . . h K represent the channel coefficients.
15. A transmitter apparatus as recited in claim 10 , the transmitter apparatus forming part of a telecommunications system for use with receiver apparatus, said receiver apparatus comprising more than one antenna, the gain in signal-to-noise ratio being proportional to the square of the normalization factor divided by the number of receive antennae.
16. A wireless communication method for transmitting data as symbols to a receiver, the method comprising:
multiplying each symbol to be transmitted at first and second multiplier circuits, the first multiplier circuit for multiplying the each symbol by a different weighting factor than the second multiplier circuit, the distant weighting factor being associated with each multiplier circuit and each multiplier circuit having an associated transmit antenna of a plurality of K transmitting antennae, where K is greater than one; the weighting factor for one multiplier circuit being proportional to a complex conjugate of the channel transfer coefficient for a channel between said associated transmit antenna with said one multiplier circuit and the receiver, and
transmitting the weighted output symbols of said first and second multiplier circuits via its respective associated transmit antenna.
17. A wireless communication method as recited in claim 16 wherein the weighting factor for each of said first and said second multiplier circuits is given by the complex conjugate, h i *, of the channel transfer coefficient for said channel, divided by a normalizing factor, α, which is
(
∑
k
=
1
K
h
k
2
)
1
2
.
18. A method as recited in claim 17 farther comprising determining the channel transfer coefficients for each channel between transmit antenna and receiver antenna via a training session including transmitting pilot signals from each transmitting antenna to the receiver.