Robust radio link monitoring framework for unlicensed spectrum

1. A method of wireless communication, comprising:

receiving, at a user equipment (UE), radio link monitoring (RLM) configuration information including a set of default RLM resources associated with a connected state of the UE and a set of additional RLM resources associated with one or more pre-defined criteria;

monitoring, by the UE, the set of default RLM resources for a default RLM reference signal (RLM-RS) from a serving base station during the connected state;

observing, by the UE, a pre-defined criteria of the one or more pre-defined criteria; and

monitoring, by the UE in response to the pre-defined criteria, the set of additional RLM resources for an additional RLM-RS.

2. The method of claim 1 , wherein the RLM configuration includes a first downlink bandwidth part (BWP) identifier (ID) identifying allocation of the set of default RLM resources to an active bandwidth part (BWP) of a channel bandwidth, and a second downlink BWP ID identifying allocation of the set of additional RLM resources to a non-active BWP of the channel bandwidth.

3. The method of claim 2 , wherein the monitoring the set of additional RLM resources includes:

tuning to the non-active BWP during a measurement gap from the active BWP; and

measuring one or more signals within the set of additional RLM-RS resources for detection of the additional RLM-RS.

4. The method of claim 3 , further including one of:

autonomously selecting, by the UE, the measurement gap; or

receiving, by the UE, identification of the measurement gap from the serving base station, wherein the measurement gap is designated for RLM measurements.

5. The method of claim 1 , wherein the additional RLM-RS includes a set of synchronization signal blocks (SSBs).

6. The method of claim 5 , further including one or more of:

receiving, by the UE, discovery reference signal (DRS) measurement timing configuration (DMTC) configuration including at least a time-frequency resource of the set of SSBs and one or more transmission parameters of the SSBs;

receiving, by the UE, a physical cell ID (PCI) associated with the additional RLM-RS; and

receiving, by the UE, a power offset for each SSB of the set of SSBs, wherein the power offset is relative to a cell-defining SSB of the serving base station.

7. The method of claim 5 , wherein the set of SSBs for the additional RLM-RS and a set of default SSBs for the default RLM-RS are indexed according to one of:

a same set of SSB indices, or

a set of default SSB indices and a set of additional SSB indices independent of the set of default SSB indices.

8. The method of claim 7 , wherein a quasi-co-location relation between the set of default SSB indices and the set of additional SSB indices is one of:

identified in a configuration message received by the UE from the serving base station, or

deemed by the UE as quasi-co-located for a same SSB index value between the set of default SSB indices and the set of additional SSB indices when not identified in the configuration message.

9. The method of claim 1 , wherein the set of additional RLM-RS resources includes a set of channel state information reference signals (CSI-RS) resources, wherein the set of CSI-RS resources include one of: static CSI-RS resources, semi-static CSI-RS resources, or dynamic CSI-RS resources.

10. The method of claim 9 , further including:

receiving, by the UE, a control activation signal from the serving base station triggering one of: the semi-static CSI-RS resources, or the dynamic CSI-RS resources, wherein the monitoring the set of additional RLM resources is in response to the control activation signal.

11. The method of claim 1 , wherein the observing the pre-defined criteria includes one of:

identifying, by the UE, activation of a radio link failure (RLF) timer at the UE;

determining, by the UE, a number of absence of RLM-RS indications received by the UE within a predetermined period of time exceeds a failure threshold; or

determining, by the UE, a number of consecutive out of synchronization (OOS) indications received by the UE exceed the failure threshold.

12. The method of claim 11 , further including:

monitoring, by the UE, for one or more pre-defined recovery criteria after initiating the monitoring the additional RLM resources; and

ceasing, by the UE, the monitoring the additional RLM resources in response to detection of the one or more pre-defined recovery criteria.

13. The method of claim 12 , wherein the detection of the one or more pre-defined recovery criteria includes one of:

identifying, by the UE, deactivation of a radio link failure (RLF) timer at the UE;

determining, by the UE, a number of successful transmission reception indications received by the UE within a predetermined period of time exceeds a success threshold; or

determining, by the UE, a number of consecutive in synchronization (IS) indications received by the UE exceeds the success threshold.

14. The method of claim 1 , wherein the observing the pre-defined criteria includes:

detecting, by the UE, a link issue criteria associated with a link quality between the UE and the serving base station; and

receiving, by the UE, a network indication in response to the link issue criteria, wherein the network indication represents the pre-defined criteria observed by the UE.

15. The method of claim 14 , wherein the network indication is received from one of:

the serving base station; or

a neighboring base station from a cell different that the serving base station.

16. The method of claim 14 , wherein the detecting the link issue criteria include one or more of:

identifying, by the UE, activation of a radio link failure (RLF) timer at the UE;

determining, by the UE, a number of absence of RLM-RS indications received by the UE within a predetermined period of time exceeds a failure threshold; or

determining, by the UE, a number of consecutive out of synchronization (OOS) indications received by the UE exceed the failure threshold.

17. The method of claim 14 , wherein the network indication includes one or more of:

identification of activated and deactivated RLM-RS resources within the set of additional RLM-RS resources;

identification of one or more RLM-RS resources within the set of additional RLM-RS resources to be monitored by the UE; and

a time duration for the activated RLM-RS resources.

18. A method of wireless communication, comprising:

transmitting, by a base station, radio link monitoring (RLM) configuration information to one or more served UEs, wherein the RLM configuration information includes a set of default RLM resources associated with a connected state of the one or more served UEs and a set of additional RLM resources associated with one or more pre-defined criteria;

monitoring, by the base station, for the one or more pre-defined criteria over a first predetermined time;

scheduling, by the base station, transmission of additional RLM reference signals (RLM-RS) using the set of additional RLM resources in response to detection of a pre-defined criteria of the one or more pre-defined criteria within the first predetermined time;

monitoring, by the base station after the scheduling, for one or more pre-defined recovery criteria over a second predetermined time; and

ceasing, by the base station, the scheduling in response to detection of one or more pre-defined recovery criteria within the second predetermined time.

19. The method of claim 18 , wherein the one or more pre-defined criteria include detected failure of listen before talk (LBT) procedures performed for each default RLM-RS attempted for transmission using the set of default RLM resources, and the one or more pre-defined recovery criteria include successful transmission of the each default RLM-RS and the additional RLM-RS.

20. The method of claim 19 ,

wherein the detection of the pre-defined criteria includes:

determining a number of failures of the LBT procedures within the first predetermined time exceeds a failure threshold, and

wherein the detection of the one or more pre-defined recovery criteria includes:

determining a number of successful transmissions of the each default RLM-RS and the additional RLM-RS within the second predetermined time exceeds a success threshold.

21. The method of claim 18 , wherein the one or more pre-defined criteria include detected failure of channel acquisition during a discovery reference signal (DRS) measurement timing configuration (DMTC), and the one or more pre-defined recovery criteria include successful channel acquisition for DRS transmission within the DMTC.

22. The method of claim 21 ,

wherein the detection of the pre-defined criteria includes:

determining a number of failures of the channel acquisition during the DMTC within the first predetermined time exceeds a failure threshold, and

wherein the detection of the one or more pre-defined recovery criteria includes:

determining a number of successful channel acquisitions for DRS transmission within the DMTC within the second predetermined time exceeds a success threshold.

23. A method of wireless communication, comprising:

receiving, at a user equipment (UE), radio link monitoring (RLM) configuration information including a set of default RLM resources associated with a connected state of the UE;

monitoring, by the UE, the set of default RLM resources for a default RLM reference signal (RLM-RS) from a serving base station during the connected state;

transmitting, by the UE, a failure report to the serving base station in response to detection of one or more pre-defined failure criteria associated with a failure of the UE to receive the default RLM-RS;

monitoring, by the UE, for one or more pre-defined recovery criteria associated with acceptable link quality between the UE and the serving base station; and

transmitting, by the UE, a recovery report to the serving base station in response to detection of the one or more pre-defined recovery criteria.

24. The method of claim 23 , wherein the detection of the one or more pre-defined failure criteria include one or more of:

identifying a triggered radio link failure (RLF) timer at the UE;

determining a number of absence of RLM-RS indications received by the UE within a predetermined period of time exceeds a failure threshold; and

determining a number of consecutive out of synchronization (OOS) indications received by the UE within the predetermined period of time exceeds the failure threshold.

25. The method of claim 23 , wherein the detection of the one or more pre-defined recovery criteria include one or more of:

identifying stoppage of a running radio link failure (RLF) timer at the UE;

determining a number successful transmission indications received by the UE within a predetermined period of time exceeds a success threshold; and

determining a number of consecutive in-synchronization (IS) indications received by the UE exceeds the success threshold.

26. The method of claim 23 , wherein the RLM configuration information further includes identification of a set of additional RLM resources associated with the one or more pre-defined failure criteria.

27. The method of claim 26 , further including:

monitoring, by the UE, the set of additional RLM resources for an additional RLM-RS in response to transmission of the failure report; and

ceasing, by the UE, the monitoring of the set of additional RLM resources in response to transmission of the recovery report.

28. A method of wireless communication, comprising:

transmitting, by a base station, radio link monitoring (RLM) configuration information to one or more served user equipments (UEs), wherein the RLM configuration information includes a set of default RLM resources associated with a connected state of the one or more served UEs;

receiving, by the base station, a failure report from the one or more served UEs, wherein the failure report is associated with a failure of the one or more served UEs to receive a default RLM reference signal (RLM-RS) transmitted by the base station; and

receiving, by the base station, a recovery report from the one or more served UEs, wherein the recovery report is associated with an acceptable link quality between the one or more served UEs and the serving base station.

29. The method of claim 28 , further including:

transmitting, by the base station, an additional RLM-RS in response to the failure report, wherein the additional RLM-RS are transmitted within a set of additional RLM resources included within the RLM configuration information transmitted to the one or more served UEs; and

ceasing transmission, by the base station, of the additional RLM-RS in response to the recovery report.

30. The method of claim 28 , further including:

adjusting, by the base station, connection parameters with the one or more served UEs based on one or both of the failure report and the recovery report.