Precoding techniques for downlink coordinated multipoint transmission in radio communications system

1. A method for deciding a precoding vector of coordinated multi-point transmission (CoMP) for at least one user equipment in a network, comprising:

receiving channel state information for CoMP from the user equipment, wherein the channel state information includes inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the inter-cell correlation property is represented by a cross-correlation channel matrix which is obtained by correlation between a first transmit channel matrix from the serving cell to the ,equipment and a second transmit channel matrix from the cooperating cell to the user equipment, and

wherein a precoding matrix index (PMI) for the serving cell and the cooperating cell is selected by the user equipment with a joint channel matrix and a joint correlation matrix, wherein the joint channel matrix is constructed b the first transmit channel a matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation matrix is constructed by the cross-correlation channel matrix, the first auto-correlation channel of the serving cell and the second auto-correlation channel matrix of the cooperating cell; and

deciding the precoding vector of CoMP based on the channel state information.

2. The method according to claim 1 , wherein the channel state information further includes first auto-correlation channel property between the serving cell and the user equipment.

3. The method according to claim 2 , wherein the network estimates second auto-correlation channel property between the cooperating cell and the user equipment by using the first auto-correlation channel property and the inter-cell correlation property.

4. The method according to claim 2 , wherein the channel state information further includes second auto-correlation channel property between the cooperating cell and the user equipment.

5. The method according to claim 1 , wherein the user equipment feeds back PMI information and channel matrix information whose term is longer than the PMI information, wherein the channel matrix information includes at least the cross-correlation channel matrix and the auto-correlation channel of the serving cell, wherein the PMI information includes the PMI for the serving cell and the PMI for the cooperating cell.

6. The method according to claim 1 , wherein the user equipment feeds back PMI information and channel matrix information whose bandwidth is wider than the PMI information, wherein the channel matrix information includes at least the cross-correlation channel matrix and the auto-correlation channel of the serving cell, wherein the PMI information includes the PMI for the serving cell and the PMI for the cooperating cell.

7. A system for deciding a precoding vector of coordinated multipoint transmission (CoMP) for at least one user equipment in a network, comprising:

a receiver for receiving channel state information for CoMP from the user equipment, wherein the channel state information includes inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the inter-cell correlation property is represented by a cross-correlation channel matrix which is obtained by correlation between a first transmit channel matrix from the serving cell to the user equipment and a second transmit channel matrix from the cooperating cell to the user equipment, and

wherein a precoding matrix index (PMI) for the serving cell and the cooperating cell is selected by the user equipment with a joint channel matrix and a joint correlation matrix, wherein the joint channel matrix is constructed by the first transmit channel matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation matrix is constructed by the cross-correlation channel matrix, the first auto-correlation channel of the serving cell and the second auto-correlation channel matrix of the cooperating cell; and

a scheduler for deciding the precoding vector of CoMP based on the channel state information.

8. The system according to claim 6 , wherein the channel state information further includes first auto-correlation channel property between the serving cell and the user equipment.

9. The system according to claim 7 , wherein the scheduler estimates second auto-correlation channel property between the cooperating cell and the user equipment by using the first auto-correlation channel property and the inter-cell correlation property.

10. The system according to claim 7 , wherein the channel state information further includes second auto-correlation channel property between the cooperating cell and the user equipment.

11. A base station in a cellular network, comprising the system according to claim 6 .

12. A user equipment in a cellular network, comprising:

a channel estimator for generating channel state information for CoMP, wherein the channel state information includes inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the channel state information further includes second auto-correlation channel property between the cooperating cell and the user equipment, and

wherein a precoding matrix index (PMI) for the serving cell and the cooperating cell is selected by using a joint channel and a joint correlation matrix, wherein the joint channel matrix is constructed by the first transmit channel matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation matrix is constructed by the cross-correlation channel matrix, the first auto-correlation channel of the serving cell and the second auto-correlation channel matrix of the cooperating cell; and

a transmitter for transmitting the channel state information to the serving cell.

13. The user equipment according to claim 11 , wherein the channel state information further includes first auto-correlation channel property between the serving cell and the user equipment.

14. The user equipment according to claim 11 , wherein the inter-cell correlation property is represented by a cross-correlation channel matrix which is obtained by correlation between a first transmit channel matrix from the serving cell to the user equipment and a second transmit channel matrix from the cooperating cell to the user equipment.

15. The user equipment according to claim 12 , wherein the user equipment feeds back PMI information and channel matrix information whose term is longer than the PMI information, wherein the channel matrix information includes at least the cross-correlation channel matrix and the auto-correlation channel of the serving cell, wherein the PMI information includes the PMI for the serving cell and the PMI for the cooperating cell.

16. The user equipment according to claim 12 , wherein the user equipment feeds back PMI information and channel matrix information whose bandwidth is wider than the PMI information, wherein the channel matrix information includes at least the cross-correlation channel matrix and the auto-correlation channel of the serving cell, wherein the PMI information includes the PMI for the serving cell and the PMI for the cooperating cell.

17. A feedback method in a user equipment in a cellular network, comprising:

generating channel state information for CoMP, wherein the channel state information includes inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the channel state information further includes second auto-correlation channel property between the cooperating cell and the user equipment, and

wherein a precoding matrix index (PMI) for the serving cell and the cooperating cell is selected by using a joint channel matrix and a joint correlation matrix, wherein the joint channel matrix s constructed by the first transmit channel matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation matrix is constructed by the cross-correlation channel matrix, the first auto-correlation chat el of the serving cell and the second auto-correlation channel matrix of the cooperating cell; and

transmitting the channel state information to the serving cell.

18. A computer-readable program stored in a recording medium, for functioning a program-controlled processor as a system deciding a precoding vector of coordinated multipoint transmission (CoMP) for at least one user equipment in a network, comprising:

receiving channel state information for CoMP from the user equipment, wherein the channel state information includes inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the inter-cell correlation property is represented by a cross-correlation channel matrix which is obtained by correlation between a first transmit channel matrix from the serving cell to the user equipment and a second transmit channel matrix from the cooperating cell to the user equipment, and

wherein a precoding matrix index (PMI) for the serving cell and the cooperating cell is selected by the user equipment with a joint channel matrix and a joint correlation matrix, wherein the joint channel matrix is constructed by the first transmit channel matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation matrix is constructed by the cross-correlation channel matrix, the first auto-correlation channel of the serving cell and the second auto-correlation channel matrix of the cooperating cell; and

deciding the precoding vector of CoMP based on the channel state information.

19. A computer-readable program stored in a recording medium, for functioning a program-controlled processor as a user equipment for transmitting channel state information for CoMP to a network, comprising:

generating the channel state information including inter-cell correlation property between a serving cell serving the user equipment and a cooperating cell for CoMP,

wherein the channel state information further includes second auto-correlation channel property between the cooperating cell and the user equipment, and

wherein a precoding matrix index (PMD) for the serving cell and the cooperating cell is selected by using a joint channel matrix and a joint, correlation matrix, wherein the joint channel matrix is constructed by the first transmit channel matrix from the serving cell to the user equipment and the second transmit channel matrix from the cooperating cell to the user equipment; and the joint correlation a is constructed by the cross-correlation channel matrix, the first auto-correlation channel of the serving cell and the second auto-co elation channel matrix of the cooperating cell; and

transmitting the channel state information to the serving cell.