Beam failure detection

1 . A method performed by a user equipment (UE), the method comprising:

receiving one or more messages for activating at least i) a first set of configured TCI states and ii) a second set of configured TCI states, wherein the first set of activated TCI states is associated with a first physical cell identifier (PCI) and indicates a first set of reference signals, and the second set of activated TCI states is associated with a second PCI and indicates a second set of reference signals; and

performing beam failure detection (BFD) monitoring, wherein performing the BFD monitoring comprises:

determining whether a beam failure with respect to the first PCI has occurred based on the first set of reference signals; and

determining whether a beam failure with respect to the second PCI has occurred based on the second set of reference signals.

2 . The method of claim 1 , wherein the UE is not explicitly configured with any reference signals for BFD monitoring.

3 . The method of claim 1 , wherein

the first set of activated TCI states includes a first TCI state that indicates a first reference signal,

the second set of activated TCI states includes a second TCI state that indicates a second reference signal,

the first set of reference signals includes the first reference signal, but does not include the second reference signal, and

the second set of reference signals includes the second reference signal, but does not include the first reference signal.

4 . The method of claim 3 , wherein

the first reference signal is indicated as a QCL-type D source in the first TCI state, and

the second reference signal is indicated as a QCL-type D source in the second TCI state.

5 . The method of claim 3 , wherein

the first set of activated TCI states further includes a third TCI state that indicates a third reference signal,

the second set of activated TCI states includes a fourth TCI state that indicates a fourth reference signal,

the first TCI state is for a first control resource set, CORSET, belonging to a first CORESET group,

the second TCI state is for a second CORSET belonging to a second CORESET group,

the third TCI state is for a third CORSET belonging to the first CORESET group, and

the fourth TCI state is for a fourth CORSET belonging to the second CORESET group.

6 . The method of claim 5 , wherein

the first set of reference signals includes the first and third reference signals, but does not include the second and fourth reference signal, and

the second set of reference signals includes the second and fourth reference signals, but does not include the first and third reference signals.

7 . The method of claim 1 , wherein receiving one or more messages for activating the first and second sets of TCI states comprises:

receiving first a Medium Access Control (MAC) control element (CE) for activating the first set of TCI states and receiving a second MAC CE for activating the second set of TCI states, or

receiving a single MAC CE for activating both the first and second set of TCI states.

8 . The method of claim 1 , wherein

determining whether a beam failure with respect to the first PCI has occurred based on the first set of reference signals comprises maintaining a first out-of-sync (OOS) counter for the first PCI; and

determining whether a beam failure with respect to the second PCI has occurred based on the second set of reference signals comprises maintaining a second OOS counter for the second PCI.

9 . The method of claim 8 , wherein

the first OOS counter is a counter maintained by a) a physical layer of the UE or b) a MAC layer of the UE, and

the second OOS counter is a counter maintained by a) the physical layer of the UE or b) the MAC layer of the UE.

10 . The method of claim 9 , wherein

the first OOS counter is maintained by the MAC layer of the UE, and

maintaining the first OOS counter comprises:

the physical layer providing to the MAC layer an OOS indication indicating an occurrence of an OOS event for the first PCI; and

the MAC layer increasing a counting value of the first OOS counter in response to receiving the indication.

11 . The method of claim 9 , wherein:

the first OOS counter is maintained by the physical layer of the UE, and

maintaining the first OOS counter comprises the physical layer increasing a counting value of the first OOS counter as a result of detecting an occurrence of an OOS event for the first PCI.

12 . The method of claim 11 , wherein determining whether a beam failure with respect to the first PCI has occurred comprises:

determining that the value of the first OOS counter is greater than or equal to a predetermined threshold value; and

as a result of determining that the value of the first OOS counter is greater than or equal to the predetermined threshold value, the physical layer providing to the MAC layer an indication that a beam failure has occurred for the first PCI.

13 . The method of claim 12 , further comprising, prior to receiving said one or messages, receiving a configuration message indicating that the first set of configured TCI states is configured for the first PCI and the second set of configured TCI states is configured for the second PCI.

14 . The method of claim 1 , wherein the UE is in an L1/L2 mobility associated with a plurality of PCIs including the first and second PCIs or the UE is being served by multiple Transmission and Reception Points (TRPs) associated with a plurality of PCIs, including the first and second PCIs.

15 . A non-transitory computer readable storage medium storing a computer program comprising instructions which when executed by processing circuitry of a UE causes the UE to perform the method of claim 1 .

16 . A user equipment (UE), comprising:

a receiver for receiving one or more messages for activating at least i) a first set of configured TCI states and ii) a second set of configured TCI states, wherein the first set of activated TCI states is associated with a first physical cell identifier (PCI) configured for the UE and indicates a first set of reference signals, and the second set of activated TCI states is associated with a second PCI configured for the UE and indicates a second set of reference signals;

processing circuitry; and

a memory containing instructions executable by the processing circuitry, wherein the UE is configured to perform beam failure detection (BFD) monitoring, wherein performing the BFD monitoring comprises:

determining whether a beam failure with respect to the first PCI has occurred based on the first set of reference signals; and

determining whether a beam failure with respect to the second PCI has occurred based on the second set of reference signals.

17 . The UE of claim 16 , wherein

the first set of activated TCI states includes a first TCI state that indicates a first reference signal,

the second set of activated TCI states includes a second TCI state that indicates a second reference signal,

the first set of reference signals includes the first reference signal, but does not include the second reference signal, and

the second set of reference signals includes the second reference signal, but does not include the first reference signal.

18 . The UE of claim 17 , wherein the first reference signal is indicated as a QCL-type D source in the first TCI state, and the second reference signal is indicated as a QCL-type D source in the second TCI state.

19 . The UE of claim 16 , wherein

determining whether a beam failure with respect to the first PCI has occurred based on the first set of reference signals comprises maintaining a first out-of-sync (OOS) counter for the first PCI; and

determining whether a beam failure with respect to the second PCI has occurred based on the second set of reference signals comprises maintaining a second OOS counter for the second PCI.

20 . The UE of claim 19 , wherein

the first OOS counter is a counter maintained by a) a physical layer of the UE or b) a MAC layer of the UE, and

the second OOS counter is a counter maintained by a) the physical layer of the UE or b) the MAC layer of the UE.