Method and apparatus for reciprocity based CSI-RS transmission and reception

1. A user equipment (UE) comprising:

a transceiver configured to:

receive configuration information for at least one channel state information reference signal (CSI-RS) resource that comprises a number (P CSIRS ) of CSI-RS ports (P CSIRS CSI-RS ports); and

receive configuration information for channel state information (CSI) feedback that is based on a number (Q) of precoding dimensions (Q precoding dimensions),

wherein:

there is a mapping between the P CSIRS CSI-RS ports and the Q precoding dimensions, and

P CSIRS ≠Q; and

a processor operably coupled to the transceiver, the processor configured to:

measure the P CSIRS CSI-RS ports;

determine a measurement for the Q precoding dimensions based on the mapping and the measurement for the P CSIRS CSI-RS ports; and

determine a CSI feedback based on the measurement for the Q precoding dimensions;

wherein the transceiver is further configured to transmit, over an uplink (UL) channel, the determined CSI feedback.

2. The UE of claim 1 , wherein each precoding dimension is associated with a CSI-RS port via a beamforming vector that precodes the CSI-RS resource transmitted from the CSI-RS port.

3. The UE of claim 1 , wherein P CSIRS ×O f =Q, wherein O f =a number of precoding dimensions per CSI-RS port.

4. The UE of claim 3 , wherein the mapping corresponds to a frequency division multiplexing (FDM) of the O f precoding dimensions via each CSI-RS port.

5. The UE of claim 4 , wherein O f =2, and the FDM is such that a first precoding dimension is associated with even numbered physical resource blocks (PRBs) and a second precoding dimension is associated with odd numbered PRBs.

6. The UE of claim 1 , wherein the mapping is based on multiple CSI-RS resources such that:

a number of CSI-RS resources

O

f

=

Q

P

CSIRS

;

Q=a total number of precoding dimensions across O f CSI-RS resources; and

P CSIRS =a number of CSI-RS ports per CSI-RS resource.

7. The UE of claim 1 , wherein the mapping is based on a value of CSI-RS density, where the value of the CSI-RS density is configured such that the Q precoding dimensions are conveyed based on the P CSIRS CSI-RS ports.

8. A base station (BS) comprising:

a processor configured to:

generate configuration information for at least one channel state information reference signal (CSI-RS) resource that comprises a number (P CSIRS ) of ports CSI-RS (P CSIRS CSI-RS ports); and

generate configuration information for channel state information (CSI) feedback that is based on a number (Q) of precoding dimensions (Q precoding dimensions),

wherein:

there is a mapping between the P CSIRS CSI-RS ports and the Q precoding dimensions, and

P CSIRS ≠Q; and

a transceiver operably coupled to the processor, the transceiver configured to:

transmit the configuration information for the at least one CSI-RS resource;

transmit the configuration information for the CSI feedback;

transmit the at least one CSI-RS resource from the P CSIRS CSI-RS ports; and

receive, over an uplink (UL) channel, the CSI feedback;

wherein:

the CSI feedback is based on the Q precoding dimensions, and

the Q precoding dimensions are based on the mapping and the P CSIRS CSI-RS ports.

9. The BS of claim 8 , wherein each precoding dimension is associated with a CSI-RS port via a beamforming vector that precodes the CSI-RS resource transmitted from the CSI-RS port.

10. The BS of claim 8 , wherein P CSIRS ×O f =Q, wherein O f =a number of precoding dimensions per CSI-RS port.

11. The BS of claim 10 , wherein the mapping corresponds to a frequency division multiplexing (FDM) of the O f precoding dimensions via each CSI-RS port.

12. The BS of claim 11 , wherein O f =2, and the FDM is such that a first precoding dimension is associated with even numbered PRBs and a second precoding dimension is associated with odd numbered PRBs.

13. The BS of claim 8 , wherein the mapping is based on multiple CSI-RS resources such that:

a number of CSI-RS resources

O

f

=

Q

P

CSIRS

;

Q=a total number of precoding dimensions across O f CSI-RS resources; and

P CSIRS =a number of CSI-RS ports per CSI-RS resource.

14. The BS of claim 8 , wherein the mapping is based on a value of CSI-RS density, where the value of the CSI-RS density is configured such that the Q precoding dimensions are conveyed based on the P CSIRS CSI-RS ports.

15. A method for operating a user equipment (UE), the method comprising:

receiving configuration information for at least one channel state information reference signal (CSI-RS) resource that comprises a number (P CSIRS ) of CSI-RS ports (P CSIRS CSI-RS ports); and

receiving configuration information for channel state information (CSI) feedback that is based on a number (Q) of precoding dimensions (Q precoding dimensions),

wherein:

there is a mapping between the P CSIRS CSI-RS ports and the Q precoding dimensions, and

P CSIRS ≠Q;

measuring the P CSIRS CSI-RS ports;

determining a measurement for the Q precoding dimensions based on the mapping and the measurement for the P CSIRS CSI-RS ports;

determining a CSI feedback based on the measurement for the Q precoding dimensions; and

transmitting, over an uplink (UL) channel, the determined CSI feedback.

16. The method of claim 15 , wherein each precoding dimension is associated with a CSI-RS port via a beamforming vector that precodes the CSI-RS resource transmitted from the CSI-RS port.

17. The method of claim 15 , wherein P CSIRS ×O f =Q, wherein O f =a number of precoding dimensions per CSI-RS port.

18. The method of claim 17 , wherein the mapping corresponds to a frequency division multiplexing (FDM) of the O f precoding dimensions via each CSI-RS port.

19. The method of claim 18 , wherein O f =2, and the FDM is such that a first precoding dimension is associated with even numbered PRBs and a second precoding dimension is associated with odd numbered PRBs.

20. The method of claim 15 , wherein the mapping is based on multiple CSI-RS resources such that:

a number of CSI-RS resources

O

f

=

Q

P

CSIRS

;

Q=a total number of precoding dimensions across O f CSI-RS resources; and

P CSIRS =a number of CSI-RS ports per CSI-RS resource.