Primary cell (PCell) selection in mobility active set management

1. A method for wireless communications by a user equipment (UE), comprising:

receiving signaling indicating a set of cells supported by one or more distributed units (DUs) under a common central unit (CU);

identifying a subset of the set of cells activated to serve the UE, wherein a first cell of the activated cells comprises a primary cell (PCell) selected from cells included in a candidate set of PCells; and

identifying another one of the activated cells to serve as the PCell when the first cell is re-designated as a secondary cell (SCell), wherein the other one of the activated cells comprises a cell selected from the candidate set of PCells.

2. The method of claim 1 , further comprising: receiving physical (PHY) layer or medium access control (MAC) layer mobility signaling indicating that the first cell is to be de-activated, wherein the mobility signaling includes an identification of a new PCell in the set of activated cells.

3. The method of claim 1 , further comprising:

designating the other one of the activated cells as the PCell;

designating the first cell as a secondary cell; and

deactivating the first cell.

4. The method of claim 1 , further comprising:

receiving configuration information, from a network entity, identifying the candidate set of PCells in the set of cells, each cell in the candidate set of PCells being able to be used as the PCell when the first cell is re-designated as an SCell, and a subset of the candidate set of PCells that the UE can autonomously select as the PCell when the first cell is re-designated as an SCell.

5. The method of claim 4 , further comprising:

receiving, from the network entity, an indication of a cell in the subset of the candidate set of PCells to designate as the PCell;

designating the first cell as an SCell; and

designating the indicated cell as the PCell.

6. The method of claim 4 , wherein the configuration information is received via one of radio resource control (RRC) signaling, physical (PHY) layer signaling, or medium access control (MAC) layer signaling.

7. The method of claim 4 , further comprising:

identifying, in the subset of activated cells, a cell included in the candidate set of PCells;

designating the identified cell as the PCell;

designating the first cell as a secondary cell; and

deactivating the first cell.

8. The method of claim 7 , wherein identifying the other one of the activated cells to serve as the PCell when the first cell is de-activated comprises:

measuring channel quality for each cell in the candidate set of PCells; and

selecting a cell in the candidate set of PCells having a highest measured channel quality as the PCell; and

the method further comprises: signaling, to the network entity, information indicating that the selected cell is designated as the PCell.

9. The method of claim 1 , wherein a cell of the activated cells carries control for other activated cells and maintains a control mapping for communications between the UE and the set of cells, and the control mapping is used for communications with the identified other one of the activated cells.

10. The method of claim 9 , wherein:

the cell of the activated cells carrying control for the other activated cells comprises the first cell,

the control mapping comprises preconfigured physical uplink control channel (PUCCH) resources for each cell in the set of cells, and

the first cell is used for cross-cell scheduling.

11. The method of claim 9 , further comprising:

transferring the control mapping to the other one of the activated cells via physical (PHY) layer or medium access control (MAC) layer signaling based on preconfigured parameters provided to the UE via radio resource control (RRC) signaling.

12. The method of claim 9 , wherein:

each one of the activated cells manages at least some resources independently, and

the first cell manages a physical uplink control channel (PUCCH) for a plurality of the activated cells.

13. The method of claim 9 , wherein:

communications between the first cell and the UE are protected using a security key associated with the first cell; and

the method further comprises:

receiving configuration information including cell-specific security keys for each cell in the set of cells including the security key associated with the first cell and a security key associated with the other cell; and

activating communications with the other cell using the security key associated with the other cell.

14. The method of claim 13 , wherein the security key associated with the first cell is used to encrypt physical (PHY) layer or medium access control (MAC) layer signaling between the UE and the first cell.

15. A method for wireless communications by a network entity, comprising:

transmitting, to a user equipment (UE), signaling indicating a set of cells supported by one or more distributed units (DUs) under a common central unit (CU);

communicating with the UE via a subset of the cells that are activated for serving the UE, wherein a first cell of the activated cells is designated as a primary cell (PCell); and

identifying another one of the activated cells to serve as a PCell when the first cell is re-designated as a secondary cell (SCell).

16. The method of claim 15 , further comprising: transmitting physical (PHY) layer or medium access control (MAC) layer mobility signaling indicating that the first cell is to be de-activated, wherein the mobility signaling includes an identification of a new PCell in the activated cells.

17. The method of claim 15 , wherein identifying the other one of the activated cells to serve as the PCell comprises:

receiving, from the UE, signaling identifying the other one of the activated cells designated as the PCell; and

communicating with the UE using the other one of the activated cells as the PCell.

18. The method of claim 15 , further comprising:

transmitting, to the UE, configuration information identifying a candidate set of PCells in the set of cells, each cell in the candidate set of PCells being able to be used as the PCell when the first cell is re-designated as a secondary cell (SCell).

19. An apparatus, comprising:

a computer-readable medium having executable instructions stored thereon; and

a processor configured to execute the executable instructions to cause the apparatus to:

receive signaling indicating a set of cells supported by one or more distributed units (DUs) under a common central unit (CU);

identify a subset of the set of cells activated to serve the UE, wherein a first cell of the activated cells comprises a primary cell (PCell) selected from cells included in a candidate set of PCells); and

identify another one of the activated cells to serve as the PCell when the first cell is re-designated as a secondary cell (SCell), wherein the other one of the activated cells comprises a cell selected from the candidate set of PCells.

20. The apparatus of claim 19 , wherein the processor is further configured to cause the apparatus to:

receive physical (PHY) layer or medium access control (MAC) layer mobility signaling indicating that the first cell is to be de-activated, wherein the mobility signaling includes an identification of a new PCell in the set of activated cells.

21. The apparatus of claim 19 , wherein the processor is further configured to cause the apparatus to:

designate the other one of the activated cells as the PCell;

designate the first cell as a secondary cell; and

deactivate the first cell.

22. The apparatus of claim 19 , wherein the processor is further configured to cause the apparatus to:

receive configuration information, from a network entity, identifying the candidate set of PCells in the set of cells, each cell in the candidate set of PCells being able to be used as the PCell when the first cell is re-designated as an SCell, and a subset of the candidate set of PCells that the UE can autonomously select as the PCell when the first cell is re-designated as an SCell.

23. The apparatus of claim 22 , wherein the processor is further configured to cause the apparatus to:

identify, in the subset of activated cells, a cell included in the candidate set of PCells;

designate the identified cell as the PCell;

designate the first cell as a secondary cell; and

deactivate the first cell.

24. The apparatus of claim 23 , wherein:

in order to identify, in the subset of activated cells, the cell included in the candidate set of PCells, the processor is configured to cause the apparatus to:

measure channel quality for each cell in the candidate set of PCells; and

select a cell in the candidate set of PCells having a highest measured channel quality as the PCell; and

the processor is further configured to cause the apparatus to: signal, to the network entity, information indicating that the selected cell is designated as the PCell.

25. The apparatus of claim 19 , wherein a cell of the activated cells carries control for other activated cells and maintains a control mapping for communications between the UE and the set of cells, and the control mapping is used for communications with the identified other one of the activated cells.

26. The apparatus of claim 25 , wherein the processor is further configured to cause the apparatus to:

transfer the control mapping to the other one of the activated cells via physical (PHY) layer or medium access control (MAC) layer signaling based on preconfigured parameters provided to the UE via radio resource control (RRC) signaling.

27. The apparatus of claim 25 , wherein:

communications between the first cell and the UE are protected using a security key associated with the first cell; and

the processor is further configured to cause the apparatus to:

receive configuration information including cell-specific security keys for each cell in the set of cells including the security key associated with the first cell and a security key associated with the other cell; and

activate communications with the other cell using the security key associated with the other cell.

28. The apparatus of claim 27 , wherein the security key associated with the first cell is used to encrypt physical (PHY) layer or medium access control (MAC) layer signaling between the UE and the first cell.

29. An apparatus, comprising:

a computer-readable medium having executable instructions stored thereon; and

a processor configured to execute the executable instructions to cause the apparatus to:

transmit, to a user equipment (UE), signaling indicating a set of cells supported by one or more distributed units (DUs) under a common central unit (CU);

communicate with the UE via a subset of the cells that are activated for serving the UE, wherein a first cell of the activated cells is designated as a primary cell (PCell); and

identify another one of the activated cells to serve as a PCell when the first cell is re-designated as a secondary cell (SCell).

30. The apparatus of claim 29 , wherein in order to identify another one of the activated cells to serve as a PCell when the first cell is re-designated as an SCell, the processor is configured to cause the apparatus to:

receive, from the UE, signaling identifying the other one of the activated cells designated as the PCell; and

communicate with the UE using the other one of the activated cells as the PCell.