Multiple input, multiple output communications systems
View Patent ↗Embodiments of the present invention include systems and methods for optimizing the transmitter and receiver weights of a MIMO system. In one embodiment, the weights are optimized to create and steer beam nulls, such that each transmitted signal is substantially decoupled from all other signals between a MIMO transmitter a MIMO receiver. In another embodiment, the weights are selected such that, the signal strength of each weighted signal transmitted through a communications channel along a respective signal path is substantially equivalent, but for which the weighting vectors are not necessarily orthogonal. In a further embodiment, each transmitted signal is coupled only between its own transmitter and receiver antennas with a gain, or eigenvalue, that is a consequence of the weights, and which is bounded to within a desired range of values while at the same time the weighing vectors are orthogonal. Embodiments employing various decomposition techniques are also provided.
1. A multiple-input, multiple-output signal transmitter comprising:
a plurality of signal inputs, each signal input configured to provide an input signal;
a plurality of multipliers, each multiplier configured to weight an input signal with a respective value of a vector (V);
a plurality of combiners, each combiner configured to combine respective ones of the plurality of weighted input signals; and
a plurality of antennas, each antenna configured to transmit one of the combined weighted input signals;
wherein V comprises a matrix of transmitter weighting coefficients, L comprises a lower triangular matrix, and the inverse of V is designated V −1 such that V −1 L −1 comprises a matrix of receiver weighting coefficients.
2. The transmitter of claim 1 , wherein each of the plurality of antennas is configured to transmit one of the combined weighted input signals through a transmission channel represented by a channel matrix H that is a product of the lower triangular matrix L and a unitary matrix Q, such that H=LQ.
3. The transmitter of claim 2 , wherein V comprises a matrix comprising eigenvectors for the unitary matrix Q.
4. The transmitter of claim 2 , wherein:
at least two of the plurality of antennas comprise a transmit array, the transmit array configured to transmit at least two of the combined weighted input signals along a respective signal paths; and
the value of the vector V is selected such that the signal strength of the at least two combined weighted input signals received at a receive array is substantially equivalent to the at least two weighted input signals transmitted from the transmit array.
5. The transmitter of claim 4 , wherein the transmit array is further configured to receive corresponding transmitted signals from the receive array.
6. The transmitter of claim 2 , wherein the matrix Q is decomposable such that Q=V Λ V −1 , wherein Λ is a diagonal matrix comprising at least one eigenvalue.
7. The transmitter of claim 6 , wherein all eigenvalues have a unit magnitude.
8. The transmitter of claim 6 , wherein the matrix V is orthonormal.
9. A multiple-input, multiple-output signal transmission system comprising:
a plurality of signal inputs, each signal input configured to provide an input signal;
a plurality of multipliers, each multiplier configured to weight a respective input signal with a respective value of a vector (V);
a plurality of transmit combiners, each transmit combiner configured to combine respective ones of the plurality of weighted input signals;
a plurality of transmit antennas, each transmit antenna configured to transmit one of the combined weighted input signals;
a plurality of receive antennas, each receive antenna configured to receive the transmitted signals;
a plurality of receive vector multipliers, each receive vector multiplier configured to weight a respective received signal from a one of the plurality of receive antennas with a respective value of a vector of the form V −1 L −1 , wherein L comprises a lower triangular matrix and the inverse of V is designated as V −1 ;
a plurality of receive combiners, each receive combiner configured to combine a plurality of the weighted received signals; and
a plurality of signal outputs.
10. The system of claim 9 , wherein V −1 L −1 comprises a matrix of receiver weighting coefficients.
11. The system of claim 9 , wherein each of the plurality of transmit antennas is configured to transmit one of the combined weighted input signals through a transmission channel represented by a channel matrix H that is a product of the lower triangular matrix L and a unitary matrix Q, such that H=LQ.
12. The system of claim 10 , wherein V comprises a matrix comprising eigenvectors for the unitary matrix Q.
13. The system of claim 9 , further comprising a plurality of digital-to-analog converters, each digital-to-analog converter configured to convert a one of the combined weighted input signals from digital to analog prior to transmission by the plurality of transmit antennas.
14. The system of claim 13 , further comprising a plurality of analog-to-digital converters, each analog-to-digital converter configured to convert a one of the respective received signals from the plurality of receive antennas from analog to digital.
15. The system of claim 9 , wherein the matrix V is orthonormal.
16. A method of transmitting a signal through a transmission channel comprising:
calculating a transmission matrix H representing the transmission channel;
using a first decomposition technique to decompose the transmission matrix H into a product of a lower triangular matrix L and a unitary matrix Q, such that H=LQ;
orthogonalizing the unitary matrix Q using a second decomposition technique to decompose the unitary matrix Q into a product of:
a matrix V comprising transmitter weighting coefficients;
a diagonal matrix Λ comprising at least one eigenvalue; and
an inverse of matrix V represented as V −1 , such that Q=V Λ V −1 ;
combining the results of the first decomposition and the second decomposition such that the transmission matrix H=L V Λ V −1 ; and
transmitting the signal through the transmission channel using the transmission matrix H.
17. The method of claim 16 , wherein all eigenvalues have a unit magnitude.
18. The method of claim 16 , wherein the matrix V is orthonormal.