CSI feedback for data transmission over multiple transmission points

1. A method performed by a wireless device for Channel State Information, CSI, feedback, the method comprising:

receiving a configuration comprising:

N Non-Zero Power, NZP, CSI Reference Signal, CSI-RS, resources or N sets of NZP CSI-RS resources; and

a size M of a to-be-selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources;

receiving a request for CSI feedback based on the configuration;

selecting the preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources; and

reporting, to a base station, CSI based on the selected preferred subset of the NZP CSI-RS resources.

2. The method of claim 1 wherein M<N.

3. The method of claim 2 wherein N≥2.

4. The method of claim 2 wherein N≥3, and M≥1.

5. The method of claim 2 wherein N≥3, and M≥2.

6. The method of claim 1 , wherein the CSI comprises an identity of each NZP CSI-RS resource in the selected preferred subset.

7. The method of claim 6 wherein, for each NZP CSI-RS resource in the selected preferred subset, the identity of the NZP CSI-RS resource is an index of the NZP CSI-RS resource within a set of NZP CSI-RS resources configured for the wireless device.

8. The method of claim 1 , further comprising receiving an indication of a restriction from the base station.

9. The method of claim 1 , wherein the selected preferred subset corresponds to a preferred subset of the N TRPs for a downlink transmission to the wireless device, wherein the downlink transmission is one of Non-Coherent Joint Transmission, NC-JT, a Dynamic Point Selection, DPS, transmission, or a diversity combining transmission.

10. The method of claim 1 , wherein the selected preferred subset is for any one or any combination of NC-JT, DPS, and diversity combining.

11. The method of claim 1 , wherein reporting the CSI comprises sending a CSI report comprising a first part and a second part, wherein a size of the selected preferred subset is encoded in the first part.

12. The method of claim 11 , wherein the first part has a predefined payload size, is encoded before encoding the second part at the wireless device, or both has a predefined payload size and is encoded before encoding the second part at the wireless device.

13. The method of claim 12 , wherein some part of the CSI is dropped from the second part of the CSI report.

14. The method of claim 11 , wherein the first part is decoded first at the base station.

15. The method of claim 1 wherein:

receiving the configuration comprises receiving two or more CSI reporting configurations, each for one transmission mode with Non-Coherent Joint Transmission, NC-JT, a Dynamic Point Selection, DPS, or diversity combining; and

receiving the request for CSI feedback comprises receiving a request for CSI feedback of two or more CSI reports.

16. The method of claim 1 , wherein reporting the CSI comprises reporting:

a common CSI component comprising a rank associated with each of the NZP CSI-RS resources in the selected preferred subset;

a common CSI component comprising precoding matrix indicators for each of the NZP CSI-RS resources in the selected preferred subset; and

two or more Channel Quality Indicators, CQIs, each for a different transmission mode.

17. A method performed by a base station for Channel State Information, CSI, feedback for Physical Downlink Shared Channel, PDSCH, transmission in a wireless network, the method comprising:

providing, to a wireless device, a configuration comprising:

N Non-Zero Power, NZP, CSI Reference Signal, CSI-RS, resources or N sets of NZP CSI-RS resources; and

a size M of a to-be-selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources;

requesting a CSI feedback from the wireless device based on the configuration; and

receiving, from the wireless device, CSI based on the selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources.

18. A wireless device for Channel State Information, CSI, feedback, the wireless device comprising:

one or more transmitters;

one or more receivers; and

processing circuitry associated with the one or more transmitters and the one or more receivers, the processing circuitry configured to cause the wireless device to:

receive a configuration comprising:

N Non-Zero Power, NZP, CSI Reference Signal, CSI-RS, resources or N sets of NZP CSI-RS resources; and

a size M of a to-be-selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources;

receive a request for CSI feedback based on the configuration;

select the preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources; and

report, to a base station, CSI based on the selected preferred subset of the NZP CSI-RS resources.

19. A base station for Channel State Information, CSI, feedback, the base station comprising:

processing circuitry configured to cause the base station to:

provide, to a wireless device, a configuration comprising:

N Non-Zero Power, NZP, CSI Reference Signal, CSI-RS, resources or N sets of NZP CSI-RS resources; and

a size M of a to-be-selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources;

request a CSI feedback from the wireless device based on the configuration; and

receive, from the wireless device, CSI based on a selected preferred subset of the NZP CSI-RS resources comprised in the N NZP CSI-RS resources or the N sets of NZP CSI-RS resources.