Method of multiple-antenna wireless communication using space-time codes
View Patent ↗In a method of wireless transmission, space time matrices are used to spread the transmission of data over two or more transmit antennas and/or over two or more symbol intervals. Initially, blocks of data are encoded as symbols, each being a complex amplitude selected from a symbol constellation. A finite set of space-time matrices, referred to as “dispersion matrices,” is predetermined. In transmission, a group of symbols are transmitted concurrently. Each of the symbols to be transmitted is multiplied by a respective dispersion matrix. Thus, a composite matrix, proportional to a sum of dispersion matrices multiplied by their corresponding symbols, is modulated onto a carrier and transmitted. In reception, knowledge of the dispersion matrices is used to recover the transmitted symbols from the received signals corresponding to the composite matrix that was transmitted.
1. A method of transmitting data over a wireless communication channel, wherein data are to be embodied in at least one signal distributed over plural transmit antennas, or over plural time intervals, or both, according to a space-time matrix, the method comprising:
mapping a block of data to a sequence of symbols, each symbol having a scalar value;
defining each element of the space-time matrix as a weighted sum of symbols, wherein weights are assigned to each symbol according to a respective dispersion matrix for that symbol, the dispersion matrices do not lead to an orthogonal design, and at least one dispersion matrix is effective for distributing its associated symbol over two or more transmit antennas; and
transmitting a signal according to the space-time matrix.
2. The method of claim 1 , wherein the symbols are selected from a symbol constellation.
3. The method of claim 1 , wherein the sequence of symbols comprises complex-valued symbols selected from a constellation and further comprises the complex conjugates of the selected symbols.
4. The method of claim 1 , wherein the sequence of symbols comprises real numbers whose amplitudes equal the real parts of elements selected from a constellation, and imaginary numbers whose amplitudes equal the imaginary parts of the selected constellation elements.
5. The method of claim 1 , wherein the dispersion matrices are determined by an optimization procedure directed at making the most efficient use of the channel capacity.
6. The method of claim 1 , wherein the dispersion matrices are determined by an optimization procedure that seeks to maximize a measure of mutual information between transmitted and received signals.
7. The method of claim 6 , wherein the measure of mutual information is derived, in part, from an effective channel matrix {tilde over (H)} that linearly relates a vector {tilde over (s)} of real and imaginary parts of selected symbols to a vector {tilde over (x)} of real and imaginary parts of signals received due to transmission of the selected symbols, the linear relationship having the form {tilde over (x)}=(normalizing factor)×{tilde over (H)}{tilde over (s)}+(additive noise vector).
8. The method of claim 7 , wherein the measure of mutual information is proportional to a statistical expected value of log det
(
I
2
NT
+
ρ
M
H
~
H
~
T
)
,
wherein M is the number of transmit antennas, there are N receiving antennas, there is a measured signal-to-noise ratio of ρ, the signal to be transmitted is distributed over T time intervals, I 2NT is the identity matrix of dimension 2NT, and {tilde over (H)} T is the conjugate transpose of {tilde over (H)}.
9. The method of claim 6 , wherein the measure of mutual information is derived from an effective channel matrix {tilde over (H)}, each element of {tilde over (H)} is a weighted sum of real and imaginary parts of measured channel coefficients, and in each said element, the weights are real and imaginary parts of elements of dispersion matrices.
10. The method of claim 9 , wherein the measure of mutual information is proportional to a statistical expected value of log det
(
I
2
NT
+
ρ
M
H
~
H
~
T
)
,
wherein M is the number of transmit antennas, there are N receiving antennas, there is a measured signal-to-noise ratio of ρ, the signal to be transmitted is distributed over T time intervals, I 2NT is the identity matrix of dimension 2NT, and {tilde over (H)} T is the conjugate transpose of {tilde over (H)}.