US 6,888,809 B1 · Space-time processing for multiple-input, multiple-output, wireless systems

Abstract

In a MIMO system the signals transmitted from the various antennas are processed so as to improve the ability of the receiver to extract them from the received signal even in the face of some correlation. More specifically the number of bit streams that is transmitted simultaneously is adjusted, e.g., reduced, depending on the level of correlation, while multiple versions of each bit stream, variously weighted, are transmitted simultaneously. The variously weighted versions are combined to produced one combined weighted signal. The receiver processes the received signals in the same manner as it would have had all the signals reaching the receive antennas been uncorrelated. The weight vectors may be determined by the forward channel transmitter using the channel properties of the forward link which are made known to the transmitter of the forward link by being transmitted from the receiver of the forward link by the transmitter of the reverse link or the weight vectors may be determined by the forward channel transmitter using the channel properties of the forward link and the determined weight vectors are made known to the transmitter of the forward link by being transmitted from the receiver of the forward link by the transmitter of the reverse link. The channel properties used to determine the weight vectors may include the channel response from the transmitter to the receiver and the covariance matrix of noise and interference measured at the receiver.

Claims22

Dependent claims

A method for transmitting signals in communications system having a transmitter with N transmit antennas transmitting over a forward channel to a receiver having L receiver antennas and a reverse channel for communicating from said receiver to said transmitter, in which there may exist correlation in the signals received by two or more of said L receive antennas, the method comprising the steps of:

determining the number of independent signals that can be transmitted from said N transmit antennas to said L receive antennas;
creating, from a data stream, a data substream to be transmitted for each of the number of independent signals that can be transmitted from said N transmit antennas to said L receive antennas;
weighting each of said substreams with N weights, one weight for each of said N transmit antennas, to produce N weighted substreams per substream;
combining one of said weighted substreams produced from each of said substreams for each of said transmit antennas to produce a transmit signal for each of said transmit antennas.

1 more element

A receiver for use in a MIMO system, comprising:

L antennas;
L downconverters;
an estimator for determining an estimate of an interference covariance matrix for a forward channel being received by said receiver;
an estimator for determining an estimate of a channel response for a forward channel being received by said receiver;
and
a weight calculator for calculating weights for use by a transmitter of said forward channel to transmit data substreams to said receiver, said weights being determined in said weight calculator by
solving a matrix equation H†(KN)H=U†Λ2U where:
H is a channel response matrix;
H† is a conjugate transpose of said channel response matrix H;
KN is the interference covariance matrix;
U is a unitary matrix, each column of which is an eigenvector of H†(KN)H;
Λ is a diagonal matrix defined as Λ=diag(λ1, . . . , λM), where λ1, . . . , λM are each eignevalues of H†(KN)H, M being the maximum number of nonzero eigenvalues, which corresponds to the number of said independent signals;
and
U† is the conjugate transpose of matrix U;
waterfilling said eigenvalues λ by solving the simultaneous equations
λ
~
k
=
(
v
-
1
(
λ
k
)
2
)
+
⁢
⁢
and
⁢
⁢
∑
k
⁢
⁢
λ
~
k
=
P
,
for ν, where:
k is an integer index that ranges from 1 to M;
P is the transmitted power;
+ is an operator that returns zero (0) when its argument is negative, and returns the argument itself when it is positive;
and
each {tilde over (λ)} is an intermediate variable representative of a power for each weight vector;
defining matrix Φ as Φ=U†diag({tilde over (λ)}1, . . . , {tilde over (λ)}M)U, where diag indicates that the various {tilde over (λ)} are arranged as the elements of the main diagonal of matrix Φ;
wherein each column of matrix Φ is used as a normalized weight vector indicated by Φ=[z1, . . . , zN] and said normalized weight vectors are made up of individual normalized weights z, zi=[zi1, . . . , ziN], where i is an integer ranging from 1 to N;
developing unnormalized weight vector wi=[wi1, . . . , wiN], with each of said weights therein being √{square root over({tilde over (λ)})}izij, where j is an integer ranging from 1 to N.

51 more elements

A method for determining weights for use in transmitting signals in communications system having a transmitter with N transmit antennas transmitting over a forward channel to a receiver having L receiver antennas and a reverse channel for communicating from said receiver to said transmitter, in which there may exist correlation in the signals received by two or more of said L receive antennas, the method comprising the steps of:

determining the number of independent signals M that can be transmitted from said N transmit antennas to said L receive antennas through a process of determining weights for substreams derived from data to be transmitted via said N antennas as part of forming said signals, wherein said weights are determined by
solving a matrix equation H†(KN)H=U†Λ2U where:
H is a channel response matrix,
H† is a conjugate transpose of said channel response matrix H,
KN is the interference covariance matrix,
U is a unitary matrix, each column of which is an eigenvector of H†(KN)H,
Λ is a diagonal matrix defined as Λ=diag(λ1, . . . , λM), where λ1, . . . , λM are each eigenvalues of H†(KN)H, M being the maximum number of nonzero eigenvalues, which corresponds to the number of said independent signals, and
U† is the conjugate transpose of matrix U,
waterfilling said eigenvalues λ by solving the simultaneous equations
λ
~
k
=
(
v
-
1
(
λ
k
)
2
)
+
⁢
⁢
and
⁢
⁢
∑
k
⁢
⁢
λ
~
k
=
P
,
for ν, where:
k is an integer index that ranges from 1 to M,
P is the transmitted power,
+is an operator that returns zero (0) when its argument is negative, and returns the argument itself when it is positive, and
each {tilde over (λ)} is an intermediate variable representative of a power for each weight vector,
defining matrix Φ as Φ=U†diag({tilde over (λ)}1, . . . , {tilde over (λ)}M)U, where diag indicates that the various λ are arranged as the elements of the main diagonal of matrix Φ,
wherein each column of matrix Φ is used as a normalized weight vector indicated by Φ=[z1, . . . , zN] and said normalized weight vectors are made up of individual normalized weights z, zi=[zi1, . . . , ziN], where i is an integer ranging from 1 to N,
developing unnormalized weight vector wi=[wi1, . . . , wiN], with each of said weights therein being √{square root over({tilde over (λ)})}izij, where j is an integer ranging from 1 to N.

44 more elements

Dependencies are inferred from the claim text.

Space-time processing for multiple-input, multiple-output, wireless systems

Life of this patent

Space-time processing for multiple-input, multiple-output, wireless systems

Life of this patent

Abstract

Claims22