CSI feedback for MIMO wireless communication systems with polarized active antenna array

1. A base station capable of communicating with a user equipment (UE), the base station comprising:

a controller; and

a transceiver configured to:

transmit a signal comprising a Channel State Information-Reference Signal (CSI) process configuration, wherein the CSI process configuration comprises a plurality of CSI-reference signal (RS) resource configurations to identify CSI-RS resources; and

receive, from the UE, a first CSI feedback comprising channel direction information less frequently than a second CSI feedback comprising a channel quality indicator (CQI), a Precoding Matrix Index (PMI) and a rank indicator (RI), wherein the channel direction information is derived utilizing a first type of CSI-RS on a first CSI-RS resource, and the CQI, the PMI and the RI are derived by utilizing a second type of CSI-RS on a second CSI-RS resource.

2. The base station of claim 1 , wherein two CSI-RS on antenna ports 15 and 19 among an 8-port CSI-RS are respectively mapped onto a first and a second groups of a same number of antenna elements with substantially similar beamforming weight vectors being applied,

wherein an antenna element on the first group is polarized according to a first angle, an antenna element on the second group is polarized according to a second angle, and two antenna elements on the first and the second groups are on a same physical location comprising a dual-polarized pair, and

wherein a difference between the first and the second angles is substantially equal to 90 degrees.

3. The base station of claim 1 , wherein the channel direction information corresponds to DFT vectors.

4. The base station of claim 1 ,

wherein the CSI-RS is beamformed with a beamforming weight vector, and

wherein the controller is configured to derive the beamforming weight vector by processing a precoding vector reported by the UE.

5. The base station of claim 4 , wherein the transceiver is further configured to:

transmit

downlink signals containing a second CSI-RS configuration on PDSCH, and

N-port CSI-RS according to the second CSI-RS configuration, the N being a positive integer; and

receive, from the UE, uplink signals containing a second PMI comprising a nonnegative integer derived using the N-port CSI-RS; and

wherein the controller is further configured to determine the precoding vector as an oversampled DFT vector according to the second PMI.

6. The base station of claim 5 , wherein the transceiver is further configured to:

transmit

downlink signals containing a second CSI-RS configuration on PDSCH,

N-port CSI-RS according to the second CSI-RS configuration; and

receive uplink signals from the UE containing the second PMI comprising two nonnegative integers derived using the N-port CSI-RS, and

wherein the controller is further configured to determine the precoding vector as a Kronecker product of two oversampled DFT vectors corresponding to the second PMI.

7. The base station of claim 6 , wherein the NCSI-RS are mapped to a 2-dimensional array of N 2 transceiver units respectively mapped to N antenna subarrays placed on a 2-dimensional antenna panel.

8. A method for communicating with a user equipment (UE), the method comprising:

transmitting, by a transmitter in a base station (BS), a signal comprising a Channel State Information-Reference Signal (CSI) process configuration, wherein the CSI process configuration comprises a plurality of CSI-reference signal (RS) resource configurations to identify CSI-RS resources; and

receiving, from the UE, a first CSI feedback comprising channel direction information less frequently than a second CSI feedback comprising a channel quality indicator (CQI), a Precoding Matrix Index (PMI) and a rank indicator (RI), wherein the channel direction information is derived utilizing a first type of CSI-RS on a first CSI-RS resource, and the CQI, the PMI and the RI are derived by utilizing a second type of CSI-RS on a second CSI-RS resource.

9. The method of claim 8 , wherein two CSI-RS on antenna ports 15 and 19 among an 8-port CSI-RS are respectively mapped onto a first and a second groups of a same number of antenna elements with substantially similar beamforming weight vectors being applied,

wherein an antenna element on the first group is polarized according to a first angle, an antenna element on the second group is polarized according to a second angle, and two antenna elements on the first and the second groups are on a same physical location comprising a dual-polarized pair, and

wherein an difference between the first and the second angles is substantially equal to 180 degrees.

10. The method of claim 8 , wherein the channel direction information corresponds to DFT vectors.

11. The method of claim 8 , wherein the CSI-RS is beamformed with a beamforming weight vector, and wherein the method further comprises deriving the beamforming weight vector by processing a precoding vector reported by the UE.

12. The method of claim 11 , further comprising

transmitting downlink signals containing a second CSI-RS configuration on PDSCH, and N-port CSI-RS according to the second CSI-RS configuration; and

receiving, from the UE, uplink signals containing a second PMI comprising a nonnegative integer derived using the N-port CSI-RS; and

determining the precoding vector as an oversampled DFT vector according to the second PMI.

13. The method of claim 12 , further comprising:

transmitting

downlink signals containing a second CSI-RS configuration on PDSCH,

the N-port CSI-RS according to the second CSI-RS configuration;

receiving uplink signals from the UE containing the second PMI comprising two nonnegative integers derived using the N-port CSI-RS; and

determining the precoding vector as a Kronecker product of two oversampled DFT vectors corresponding to the second PMI.

14. The method of claim 13 , wherein the N-port CSI-RS are mapped to a 2-dimensional array of N transceiver units respectively mapped to N antenna subarrays placed on a 2-dimensional antenna panel.

15. A user equipment (UE) capable of communicating with a base station, the UE comprising:

a transceiver configured to:

receive a signal comprising a CSI process configuration, wherein the CSI process configuration comprises a plurality of CSI-RS resource configurations to identify CSI-RS resources; and

a controller configured to:

derive channel direction information utilizing a first type of CSI-RS on a first CSI-RS resource;

derive a channel quality indicator (CQI), a Precoding Matrix Index (PMI) and a rank indicator (RI) utilizing a second type of CSI-RS on a second CSI-RS resource; and

cause the transceiver to transmit a first CSI feedback comprising the channel direction information less frequently than a second CSI feedback comprising the CQI, the PMI and the RI.

16. The UE of claim 15 , the transceiver is further configured to:

receive

N-port CSI-RS according to a second CSI-RS configuration; and

downlink signals containing the second CSI-RS configuration on PDSCH; and

transmit uplink signals containing a second PMI; and

wherein the controller is further configured to derive the second PMI by utilizing channel estimates using the received N-port CSI-RS, and

wherein the second PMI comprises one nonnegative integer indicating an oversampled DFT vector.

17. The UE of claim 15 , wherein the transceiver is further configured to:

receive

N-port CSI-RS according to a second CSI-RS configuration; and

downlink signals containing the second CSI-RS configuration on PDSCH; and

transmit uplink signals containing a second PMI; and

wherein the controller is further configured to derive the second PMI by utilizing channel estimates using the received N-port CSI-RS, and

wherein the second PMI comprises two nonnegative integers indicating each of two oversampled DFT vectors and indicates a Kronecker product of two oversampled DFT vectors.

18. The UE of claim 15 , wherein the channel direction information corresponds to DFT vectors.

19. The UE of claim 15 , wherein the transceiver is further configured to receive downlink signals containing information on a trigger of a time window change for channel estimation, and

wherein the controller is further configured to:

determine a trigger timing to start a new channel estimation window from the downlink signals;

derive the PMI using an 8-port CSI-RS transmitted within a time window; and

discard the channel estimates for the 8-port CSI-RS according to the trigger timing.