Methods for relaxation of radio link monitoring requirements in wireless systems

A wireless transmit/receive unit (WTRU) may comprise a processor and memory. The processor and memory may be configured to receive configuration information indicating measurement relaxation criteria for radio link monitoring (RLM) or beam failure detection (BFD) and a prohibit time period for reporting a measurement relaxation state. The WTRU may determine that the measurement relaxation state of the WTRU has changed based on the measurement relaxation criteria. The WTRU may determine that the prohibit time period has ended. The WTRU may send a report based on the determination that the measurement relaxation state has changed and the determination that the prohibit time period has ended. The report may include an indication of a measurement relaxation state.

BACKGROUND

In 5G New Radio, a wireless transmit/receive unit (WTRU) monitors the downlink radio link quality based on the reference signal configured as RLM-RS resource(s) to detect the downlink radio link quality of the primary cell (PCell) and primary and secondary cell (PSCell). The configured radio link monitoring radio signal (RLM-RS) resources can be all synchronization signal blocks (SSBs), or all CSI-RSs, or a mix of SSBs and channel state information resource signals (CSI-RSs). The WTRU is not required to perform RLM outside the active downlink bandwidth part (DL BWP). Similarly, the WTRU assess the downlink radio link quality of a serving cell to detect beam failure.

SUMMARY

In one or more methods, systems, and/or apparatus, there may be the relaxation of radio link monitoring in wireless systems. In some cases, there may be the use of MAC CE or L1 signaling to report in an uplink and/or enable/disable in a downlink dynamically giving the network control. In some cases, abbreviated uplink reports indicating simple binary conditions may be used, concerning whether the report or relaxation criteria is met. For example, the report may be a single bit. For example, the report may include a limited number of multiple bits to provide more information, such as whether individual criteria are met. In some cases, dynamic downlink control may be used with simple on/off and/or up/down commands from the network indicating one or more measurement requirements.

A wireless transmit/receive unit (WTRU) may comprise a processor and memory. The processor and memory may be configured to receive configuration information indicating measurement relaxation criteria for radio link monitoring (RLM) or beam failure detection (BFD) and a prohibit time period for reporting a measurement relaxation state. The WTRU may determine that the measurement relaxation state of the WTRU has changed based on the measurement relaxation criteria. The WTRU may determine that the prohibit time period has ended. The WTRU may send a report based on the determination that the measurement relaxation state has changed and the determination that the prohibit time period has ended. The report may include an indication of a measurement relaxation state.

The WTRU may start the prohibit time period when the WTRU sends the report. The WTRU may be prohibited from changing the measurement relaxation state while the prohibit timer is running.

The report may indicate whether the WTRU is in the measurement relaxation state or that the WTRU is not in the measurement relaxation state. The indication of the measurement relaxation state may be specific to a first cell. The report may further include an indication of the measurement relaxation state specific to a second cell. The WTRU may receive signalling that enables the WTRU to send the report. In some examples, the signalling that enables the WTRU to send the report may be the same signalling as that which provides the prohibit time period.

The configuration information may indicate a prohibit time period out of a plurality of prohibit time periods.

The WTRU may perform RLM and/or BFD measurements using a first periodicity when the WTRU is not in the measurement relaxation state. The WTRU may perform RLM and/or BFD measurements using a second periodicity when the WTRU is in the measurement relaxation state.

The WTRU may determine to enter the measurement relaxation state based on a power measurement value being above a power threshold. The power threshold may include one or more of an SINR threshold, an RSRP threshold, an RSSI threshold, or a RSRQ threshold. The WTRU may determine to enter the measurement relaxation state based on a variation of power measurement values being below a variation/mobility threshold. The mobility threshold may include a change of RSRP within a specific time limit and/or a cell change count. The WTRU may determine to exit the measurement relaxation state based on a power measurement value being below a power threshold.

A method implemented the WTRU may include receiving configuration information indicating measurement relaxation criteria for radio link monitoring (RLM) or beam failure detection (BFD) and a prohibit time period for reporting a measurement relaxation state. The method may include determining that the measurement relaxation state of the WTRU has changed based on the measurement relaxation criteria. The method may include determining that the prohibit time period has ended. The method may include sending a report based on the determination that the measurement relaxation state has changed and the determination that the prohibit time period has ended. The report may be including an indication of a measurement relaxation state.

The method may be further including starting the prohibit time period when the WTRU sends the report. The method may be further including prohibiting changing the measurement relaxation state while the prohibit timer, which may track the prohibit time period, is running.

The report may indicate whether the WTRU is in the measurement relaxation state or that the WTRU is not in the measurement relaxation state.

The method may include indicating that the measurement relaxation state is specific to a first cell. The method may include indicating that the measurement relaxation state is specific to a second cell.

The method may include receiving signalling that enables the WTRU to send the report. The configuration information may indicate a prohibit time period out of a plurality of prohibit time periods.

The method may include performing RLM or BFD measurements using a first periodicity when the WTRU is not in the measurement relaxation state. The method may include performing RLM or BFD measurements using a second periodicity when the WTRU is in the measurement relaxation state. The method may include determining to enter the measurement relaxation state based on a power measurement value being above a power threshold. The method may include determining to exit the measurement relaxation state based on a power measurement value being below a power threshold.

DETAILED DESCRIPTION

In an embodiment, the base station114aand the WTRUs102a,102b,102cmay implement a radio technology such as NR Radio Access, which may establish the air interface116using NR.

The RAN104may be in communication with the CN106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs102a,102b,102c,102d. The data may have varying quality of service (QOS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN106may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown inFIG.1A, it will be appreciated that the RAN104and/or the CN106may be in direct or indirect communication with other RANs that employ the same RAT as the RAN104or a different RAT. For example, in addition to being connected to the RAN104, which may be utilizing a NR radio technology, the CN106may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN106shown inFIG.1Cmay include a mobility management entity (MME)162, a serving gateway (SGW)164, and a packet data network (PDN) gateway (PGW)166. While the foregoing elements are depicted as part of the CN106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator.

The CN106may facilitate communications with other networks. For example, the CN106may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN106and the PSTN108. In addition, the CN106may provide the WTRUs102a,102b,102cwith access to the other networks112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs102a,102b,102cmay be connected to a local DN185a,185bthrough the UPF184a,184bvia the N3 interface to the UPF184a,184band an N6 interface between the UPF184a,184band the DN185a,185b.

In wireless systems (e.g., 5G New Radio (NR)), the WTRU may monitor the downlink radio link quality based on the reference signal configured as radio link monitoring reference signal (RLM-RS) resource(s) to detect the downlink radio link quality of the primary cell (PCell) and primary and secondary cell (PSCell). The configured RLM-RS resources may be all synchronization signal blocks (SSBs), all channel state information reference signals (CSI-RSs), or a mix of SSBs and CSI-RSs. The WTRU may not be required to perform RLM outside the active downlink bandwidth part (DL BWP). Similarly, the WTRU may assess the downlink radio link quality of a serving cell to detect beam failure.

One method to save power may include the WTRU relaxing the RLM/BFD requirements. There may be one or more criteria for RLM/BFD relaxation, that may address one or more cases. In examples, there may be SSB based RLM/BFD measurement relaxation in frequency range 1 (FR1). In examples, there may be CSI-RS based RLM/BFD measurement relaxation in FR1. In examples, there may be CSI-RS based RLM/BFD measurement relaxation in frequency range 2 (FR2). In examples, there may be SSB based RLM/BFD measurement relaxation in FR2.

Relaxed BFD/RLM requirements may be supported for all deployment scenarios, such as new radio standalone (NR SA), E-UTRA-NR dual connectivity (EN-DC), NR-E-UTRA dual connectivity (NE-DC), NR intra-band carrier aggregation (CA), NR inter-band CA and new radio dual connectivity (NR-DC).

For the relaxation criteria, one or more of the following factors may apply and/or may be considered. For example, relaxation criteria may consider the network to enable and disable measurement relaxation. In examples, whether relaxed RLM/BFD requirements can be applied may depend on both the serving cell quality and WTRU mobility state. In examples, the measurement relaxation criteria may be based on channel quality and/or mobility. In examples, the relaxation criteria may also consider that if the WTRU fulfills any of the serving cell quality exit condition(s), low mobility exit condition(s), and/or the DRX cycle length is not allowed for relaxation, then the WTRU may exit relaxation mode. The WTRU may perform measurements for a certain time period when not I the relaxation state and then may perform additional measurements after entering the relaxation state. In examples, if the WTRU applies a DRX cycle longer than 80 ms, the WTRU may be assumed to not perform relaxed RLM/BFD measurements and the existing RLM/BFD requirements may apply. In examples, when neither serving cell quality criteria nor low mobility criteria is configured, the existing RLM/BFD requirements may apply. In examples, one or more of the prior list(s) may be revised if dedicated or broadcast signaling to indicate the WTRU that the WTRU may relax the RLM/BFD measurements. In some examples, one or more of the prior list(s) may be revised if good serving cell criteria is predefined.

The WTRU may determine to enter the measurement relaxation state based on a power measurement value (e.g., RSRP) being above a power threshold (e.g., being above the power threshold indicates high channel quality). The power threshold may include one or more of an SINR threshold, an RSRP threshold, an RSSI threshold, or a RSRQ threshold. Additionally and alternatively, the WTRU may determine to enter the measurement relaxation state based on a variation of power measurement values (e.g., RSRP variation) being below a variation/mobility threshold (e.g., being below the variation threshold indicates low mobility of the WTRU). The variation/mobility threshold may include a change of RSRP within a specific time limit and/or a cell change count. The WTRU may determine to exit the measurement relaxation state based on a power measurement value (e.g., RSRP) being below the power threshold and/or based on a variation of power measurement values being above the variation/mobility threshold. For a low mobility criterion, one or more of the following may apply and/or may be considered, (e.g. L3 reference signal receive power (RSRP) measurement variation and/or the related RS measurements for the L3 RSRP measurement).

For the cell quality criterion, one or more of the following may apply and/or may be considered: good serving cell quality criteria of RLM/BFD relaxation may be defined when the radio link quality is better than a threshold (e.g., the radio link quality in a good serving cell quality criteria for RLM/BFD relaxation may be based on signal to interference noise ratio (SINR)). In examples, the WTRU may reuse the SINR for RLM/BFD evaluation when determining whether the serving cell quality criteria is fulfilled or not. the WTRU may use a predefined or a configured threshold. The SINR definition for good serving cell quality may have one or more criteria of its own.

RLM/BFD relaxation criteria may be configured by dedicated signaling (e.g., RadioLinkMonitoringConfig) as a baseline if parameters are used instead of predefined and/or implementation specific scenarios. Access stratum (AS) capability procedure may be used to report WTRU capability of supporting RLM/BFD relaxation. The presence and/or absence of configuration for RLM/BFD relaxation criteria in signaling may indicate to the WTRU whether the WTRU can and/or should evaluate the criteria.

In examples, issues may arise regarding whether the network (NW) needs to control when the WTRU enters a relaxed state. In one example, radio resource control (RRC) signaling may be used to report and enable the relaxed state. However, this approach may create unwanted overhead for doing enable/disable in a dynamic manner whenever criteria is met.

In an example, medium access control-control element (MAC CE) and/or L1 signaling may be used (e.g., by the NW) to enable/disable RLM/BFD relaxation dynamically. The WTRU may be configured to receive signaling that enable the WTRU to send a report. For example, a MAC CE and/or L1 signaling may be used by the WTRU to send a report associated to RLM/BFD relaxation to the NW, such as, e.g., a report that contains an indication of whether relaxation criteria have been met.

FIG.2shows an example signaling message sequence200. The WTRU202send RRC radio access capability to the gNB204at206. At208, the gNB204may configure reporting criteria using RRC signaling. At210, when the criteria are met, the WTRU202may send an indication to the gNB204. At212, upon receiving an indication that the criteria are met, the gNB204may enable RLM/BFD relaxation.

Regarding the relaxation/reporting criteria, in examples, out-of-sync and in-sync block error rate (BLER) used for physical downlink control channel (PDCCH) mapping may be as shown in Table 1.

TABLE 1Out-of-Sync and In-Sync block error ratesConfigurationBLERoutBLERin010%2%

In this example, the ratio between PDCCH resource elements (RE) energy to average secondary synchronization signal (SSS) RE energy is 4 dB and 0 dB for out-of-sync (OOS) and in-sync (IS), respectively. Thus, a 5 dB difference may be defined.

The radio link monitoring may have specific evaluation periods for non-DRX and DRX cases TEvaluate_out_SSBand TEvaluate_in_SSBspecific for FR1 and FR2, respectively. In examples, the evaluation period based on SSB may be defined on CSI-RS as well. Thus, in the following examples the SSB reference may be used without reducing generality.

In examples, evaluation periods for OOS and IS may be valued as seen in Table 2. The example seen in Table 2 further considers FR1, where similar requirements may be applicable for CSI-RS.

As seen in Table 2, P is a factor that accounts for gaps overlapping and/or non-overlapping with the SSB related symbols and may take different values.

In examples, to perform RLM relaxation, the WTRU may use a first DRX cycle value to determine the requirements (e.g., the evaluation period) where the used DRX cycle value may be different than the value of the actual DRX cycle. For example, a scaling method may be used in which the first DRX cycle value may be determined by scaling the actual DRX cycle value (e.g., with an integer). The scaling factor, K, may be signaled by the network during RRC configuration. In examples, the scaling factor, K, may be signaled within the activation message. When the WTRU does not have a configured DRX cycle, the relaxation method and the first relaxation virtual DRX cycle for relaxed measurements may be configured semi-statically by the network into a RRC configuration. Further, the first relaxation virtual DRX cycle may be activated separately dynamically by MAC or DCI using PDCCH via an activation message.

In examples, the requirements may be scaled directly. For example, the evaluation period and/or the indication interval may be scaled with a scaling factor. Different requirements may be scaled with different scaling factors. The scaling factor(s) may be signaled by the network during RRC configuration. The scaling factor(s) may be signaled within the activation message.

In examples, the WTRU may use the value of a virtual DRX cycle while computing the RLM/BFD requirements, for example the evaluation period and/or the indication interval. The value of the virtual DRX cycle may be different than the actual DRX cycle (e.g., it may be larger). The virtual DRX cycle may be used when actual DRX is not configured. The possible set of values of the virtual DRX cycle may be configured by the base station (e.g., gNB). The specific value to use may be indicated by the base station within the activation message and/or it may be selected by the WTRU autonomously. For example, when indicated to enter the relaxed state, the WTRU may select one of the configured virtual DRX cycle values. This selection may be a first evaluation period that may be the lowest in a set of values signaled. Then, the WTRU may progressively increase the value (e.g., by choosing larger configured values).

Additionally and/or alternatively, the WTRU may follow base station instructions, for example UP or DOWN, while changing the virtual DRX cycle for RLM evaluation. The base station may send an UP or DOWN order according to reported cell/beam measurements, while the WTRU may be within the relaxation criteria condition. For example, if the WTRU is configured to be at the smallest configurable virtual DRX cycle and receives a DOWN command, then the WTRU may exit the RLM relaxation mode of operation. If the WTRU receives an UP command, following an even better cell/beam report (e.g. a report that indicates a higher beam RSRP than the previous report), the WTRU may move to a subsequent virtual DRX cycle in the configured list with a more relaxed measurement sampling for RLM.

Relaxation criteria for the RLM case may be a threshold defined as an offset to the OOS and/or IS SINR mappings. This may be, for example, a Y=2 dB offset against IS related SINR mapping for the serving cell good quality. This offset may be predefined, and/or a network configurable parameter. This offset may be uniquely defined relative to OOS or IS SINR mappings, and/or individually set or configured differently for each OOS and/or IS value. The RLM relaxation mode trigger may be based on measurements reaching and staying above this threshold for a certain amount of time. This time may be defined, e.g., configured semi-statically by network. This time may also be predefined.

Once the WTRU meets the conditions for low mobility based on the RSRP cell measurement variation over a certain time interval and the good cell quality in terms of RLM, the WTRU may report this favorable state of RLM/BFD relaxation to the network.

In examples, in addition to serving cell and low mobility criteria, relaxation criteria may include, e.g., a beam switch and/or a time to trigger (TTT). The beam change count may be detected in the WTRU or in the NW; e.g., in WTRU, beam(s) used for RSRP need to stay within a predefined time interval, t. The WTRU may report TTT criteria to be met for a time duration before triggering a report.

The relaxation criteria and reporting criteria may be separate. For example, the reporting criteria may use a lower threshold than the relaxation criteria. In examples, the WTRU may report an indication that reporting criteria is met. Upon reception of the report the NW may enable relaxation. The WTRU then may apply the actual relaxation when the relaxation criteria is met. DL control information may be received where the control information may have an activation indication.

The L1 (physical layer) indications interval for OOS and IS for non-DRX case may be configured as TIndication_intervalis max(10 ms, TRLM-RS,M), where TRLM,Mis the shortest periodicity of all configured RLM-RS resources for the monitored cell.

The L1 (physical layer) indications interval for OOS and IS for the DRX case may be configured as TIndication_intervalis Max(10 ms, 1.5×DRX_cycle_length, 1.5×TRLM-RS,M) if the DRX cycle_length is less than or equal to 320 ms, and TIndication_intervalis the DRX_cycle_length if the DRX cycle_length exceeds 320 ms.

When the network activates the relaxation state, the WTRU may scale the TIndication_intervalaccording to the measurement sampling rate after applying the relaxation factor K. The relaxation factor K may be configured semi-statically by network or alternatively indicated by network at the relaxation state activation.

For example, one way of scaling the TIndication_intervalmay be to use a virtual DRX relaxation cycle length. A virtual DRX relaxation cycle length may be defined as the sample measurements periodicity in the relaxation state. In this case the TIndication_intervalmay be defined as: TIndication_interval: max(10 ms, virtual DRX relaxation cycle length, TRLM-RS,M).

In examples, the TIndication_intervalmay be defined as: TIndication_interval: max(10 ms, R*TRLM-RS,M), where R is a scaling factor. If the scaling factor R is not an integer value, then the scaling factor R may be rounded up, e.g., by performing the ceiling operation such as ceil(R). The scaling factor R may not be an integer value when used to scale other measurements or thresholds for RLM Qin, Qout. The scaling factor R may be also related to the virtual DRX relaxation cycle length that may link the measurement opportunities for Tevaluateperiods. For example, virtual DRX relaxation cycle length may be defined as R*TRLM-RS,M.

A WTRU capable of RLM/BFD the relaxation feature may be configured with one or more parameters. For example, the WTRU may be configured with the one or more parameters for relaxation via RRC signaling. The WTRU may receive a MAC CE that may configure the parameters for, for instance, by indicating a value from a set of predefined values. These predefined values may include, e.g., a relative threshold Y against the IS mapped threshold for serving cell good quality, TTT for signaling RLM/BFD relaxation ready state to the network, a counter for the IS over good quality offset threshold that may reset each time the WTRU samples a measurement below offset level, and/or TTT for signaling out of RLM/BFD relaxation state to the network that is signaled when the WTRU samples a measurement where an OOS is detected.

Additionally and/or alternatively, a sampled measurement and/or a defined number of samples falling below the IS normal operation threshold mapping may signal the relaxation state. Additionally and/or alternatively, a prohibit timer may prevent the WTRU from signaling RLM/BFD relaxation ready state after signaling an out of RLM/BFD relaxation state. The prohibit timer, which may track a prohibit time period, may be included with the configuration information. The configuration information may also indicate one or more prohibit time period(s).

The relaxation state feature may involve an uplink report, which may be approached in one or more ways. For example, the UL report may be reported in a MAC CE and/or in uplink control information (e.g., in PUCCH and/or PUSCH), in a scheduling request, and/or in a buffer status report. The UL report may contain a single bit to indicate that the criteria are met (e.g., SINR threshold and/or low mobility criteria). The base station may configure the reporting criteria. The UL report may contain multiple bits (e.g., 2 bits to separately indicate criteria). For example, 1 bit may indicate that the SINR threshold are met, and/or 1 bit may indicate that the low mobility criteria are met. The UL report may contain 2 or more bits to request to increase or decrease the level of relaxation. For example, the bits may indicate an increasing and/or decreasing of the virtual DRX cycle value used for RLM/BFD requirements in relaxed state. For example, the bits may indicate an indication of the value of the virtual DRX cycle used for RLM/BFD requirements in relaxed state.

In examples, the bits may be used to increase and/or decrease the threshold values and/or choose a threshold from a set of thresholds. What data the report indicates (e.g., the meaning of the codepoint contained in the report) may depend on whether NW has enabled and/or disabled relaxation. For example, if the NW has disabled relaxation, then the report may indicate whether threshold and low mobility criteria are met. If the NW has enabled relaxation, then the report may indicate whether threshold and low mobility criteria are no longer met. Moreover, if the NW has enabled relaxation, then the bits may be set according to a different threshold, or indicate to increase/decrease the threshold).

Concerning dual connectivity carrier aggregation (DCCA), reporting and/or enabling separately may be performed per serving cell and/or per serving beam. Additionally and/or alternatively, concerning DCCA, the WTRU may report results either to the master cell group (MCG) and/or the secondary cell group (SCG). This may also imply multiple bits to enable/disable. Moreover, reporting separately per carrier may imply multiple bits for the report.

In examples, a prohibit timer may be applied to the reporting trigger, e.g. the WTRU may be configured to start the prohibit time period when the WTRU sends the report (e.g., the report to either to the MCG and/or the SCG). After the WTRU exits relaxation, a timer may start and the WTRU may be prohibited to request relaxation via the UL report and/or enter relaxation while the timer is running. Additionally and alternatively, the WTRU may be prohibited from changing the relaxation state while the timer is running. The UL report may include whether the WTRU is or is not in the relaxed state. The UL report may include an indication of whether any OOS indication has been detected during the relaxed state. The UL report may include an indication of whether fallback and/or exiting relaxed state has occurred (e.g., whether WTRU is currently relaxed and whether criteria are met). A new RRC re-establishment cause value may be introduced to explicitly indicate radio link failure (RLF) during relaxation (e.g., serving and/or neighbor cell measurements, location information, and other information related to supporting a self-organizing network and/or minimization of drive testing).

For DL control, upon reporting RLM/BFD relaxation ready state to the network, the WTRU may receive an activation order. The activation order may simply activate the relaxation configuration already received by WTRU through a RRC configuration. Activation may mean, e.g., that the WTRU may start performing RLM/BFD in a relaxed state. Additionally and alternatively, the network may indicate in the activation order the value of the relaxation factor K and/or the value of the virtual DRX cycle that the WTRU may use. The relaxation factor K and/or the virtual DRX cycle value may be applied to the current evaluation period rules that, in turn, may affect the TEvaluate_outand TEvaluate_nvalues.

The DL control information may use a single bit to allow and/or disallow relaxation based on NW knowledge of deployment. For example, the DL may be configured to indicate “enable” only. In that example, the WTRU may autonomously indicate “disable” when the criteria are no longer met, and/or “exit” criteria are met (e.g., where the “exit” criteria specifies when the WTRU is expected to exit the relaxed state.)

The DL control information may indicate multiple relaxation requirements. For example, different requirements are needed to meet a SINR threshold and/or low mobility criteria. Usage of multiple bits may indicate these different requirements. In examples, a stepwise relaxation may be performed (e.g. the DL control information may indicate how much the may relax). The DL control information may indicate what requirements are applied (e.g. used with up and/or down request from WTRU, and/or incrementing and/or decrementing the relaxation factor K value).

For DL control, the WTRU may relax if both the NW indicates “allowed” and the criteria are met. In this case, different threshold(s) may exist for reporting and/or applying relaxation. These different thresholds may be achieved by applying an offset to the configured and/or predefined criteria, and/or by signaling separate thresholds. Additionally and/or alternatively, the use of separate thresholds may allow reporting to occur ahead of the criteria which allow the WTRU to relax. In this case, the use of separate thresholds can advantageously compensate for processing delay at the gNB, and/or for propagation delay in case of non-terrestrial networks (NTN)).

The DL control may have an additional state that NW indicates “allowed” even if criteria are not met and/or reported. The NW may base this additional state on, e.g., low mobility detected at the network. The indication, if based on beam switching, may be more accurate than cell quality measurement by WTRU.

For RLF, the WTRU (e.g., NR WTRU) may use a counter and/or timer, such as the counters N310, N311and the timer T310to determine when to declare RLF. For example, upon detecting N310consecutive OOS indications from the physical layer, the WTRU may start a timer (e.g., T310). While T310is running, the WTRU may attempt to re-synchronize to the current cell. For example, if the physical layer sends N311consecutive IS indications, then the WTRU may stop T310and consider itself back IS. If T310expires before the physical layer sends N311IS indications, then WTRU may considers RLF to have occurred. Further, the T310may trigger an RRC re-establishment procedure.

While performing RLM using relaxed requirements, the WTRU may have its OOS and IS indication periods scaled accordingly, and thus the RLF detection may take longer. To address this situation and avoid network and/or WTRU performance issues, the T310may be scaled. For example, the T310may be scaled following the same scaling factor for DRX and/or indication to accommodate the same number (e.g., the T311timer) of IS indications within the timer period T310. Additionally and alternatively, the T310timer may be maintained with the same value and/or scale down the N310counter to fit the OOS indications within the same amount of time, and may use regular or relaxed requirements. RLF conditions may scale the N311counter such that the number of IS indications required to fulfil the “RLF recovery” conditions would be during the same T310regardless of whether relaxed or regular monitoring requirements are used.

Additionally and alternatively, a WTRU that meets the RLF condition while using relaxed requirements may avoid declaring RLF at this time. Instead, such a WTRU may fallback autonomously to the normal operation mode for RLM and/or restart the RLM timers and counters, then only when the normal operation conditions for RLF are met may the WTRU declare RLF.

While references are made to specific counters and/or timers herein, these references are intended only for illustrative purposes, and the related methods and/or approaches may apply generally to any counter and/or timer.

For fallback related to the relaxation feature, beside signaling RLM/BFD relaxation ready state and/or out of RLM/BFD relaxation state, the WTRU may fallback automatically to the normal RLM/BFD procedures based on one or more conditions. These conditions include, e.g., the network configures a new measurement, the network configures a new measurement with gaps, a cell activation and/or deactivation in the same cell group, and/or bandwidth part activation or change, the WTRU receives a new RLM/BFD relaxation configuration, where upon receiving a new RLM/BFD configuration, the WTRU may have to restart the procedures for entering the relaxation ready state, the WTRU detects one or more OOS indications, and/or the WTRU detects that the condition for RLM/BFD relaxation state is no longer met and/or detects the exit condition and falls back to normal RLM/BFD operation. Additionally and alternatively, separate criteria may be used for entering and exiting the relaxed state, e.g., the relaxed state is enabled if the threshold and hysteresis are met, and the relaxed state is exited if below the threshold and/or with no hysteresis. Additionally and alternatively, separate criteria such as TTT may be applied to enter relaxation or to report the criteria, while exiting and/or fallback happens instantly.

FIG.3illustrates an example flowchart300showing a method for relaxation operation. At302, the WTRU may be configured by RRC signaling to enable reporting of RLM/BFD relaxation. The configuration may include an indication of an SINR threshold for determining serving cell quality, and/or a relative RSRP threshold and time period for determining low mobility. At304, the reporting criteria may be initialized and/or updated to include serving cell quality and/or low mobility based on the configuration and predetermined rule(s). At306, the WTRU may continuously and/or periodically evaluate the reporting criteria until one or more of the reporting criteria are met. At308, the WTRU may transmit an uplink indication (e.g., in MAC CE) of whether the one or more criteria are met. At310, the WTRU may receive a downlink indication (e.g., in MAC CE) as to whether and/or how the WTRU may relax its RLM/BFD requirements. At312, the WTRU may determine whether the relaxation criteria are met. This may comprise of the value of the DL indication, and/or may include an indication of whether other criteria are met (e.g., serving cell quality and/or low mobility). At314, the WTRU may update the measurement requirements in use. Then, at314, the WTRU may proceed to update the reporting criteria based on the configuration and/or measurement requirements in use.

As described herein, a higher layer may refer to one or more layers in a protocol stack and/or a specific sublayer within the protocol stack. The protocol stack may comprise of one or more layers in a WTRU and/or a network node (e.g., eNB, gNB, other functional entity, etc.), where each layer may have one or more sublayers. Each layer and/or sublayer may be responsible for one or more functions. Each layer and/or sublayer may communicate with one or more of the other layers and/or sublayers, either directly and/or indirectly. In examples, these layers and/or sublayers may be numbered, such as, e.g., Layer 1, Layer 2, and Layer 3. For example, Layer 3 may comprise of one or more of the following, e.g., NAS, IP, and/or RRC. For example, Layer 2 may comprise of one or more of the following, e.g., packet data convergence control (PDCP), RLC, and/or MAC. For example, Layer 3 may comprise of physical (PHY) layer type operations. The greater the number of the layer, the higher it is relative to other layers (e.g., Layer 3 is higher than Layer 1).

In examples, the aforementioned examples may be called layers and/or sublayers themselves irrespective of layer number, and may be referred to as a higher layer as described herein. For example, from highest to lowest, a higher layer may refer to one or more of the following layers/sublayers, e.g. a NAS layer, a RRC layer, a PDCP layer, a RLC layer, a MAC layer, and/or a PHY layer. Any reference herein to a higher layer in conjunction with a process, device, or system may refer to a layer that is higher than the layer of the process, device, or system. In examples, reference to a higher layer herein may refer to a function or an operation performed by one or more layers described herein. In examples, reference to a higher layer herein may refer to information sent and/or received by one or more layers described herein. In examples, reference to a higher layer herein may refer to a configuration sent and/or received by one or more layers described herein.

FIG.4illustrates an example flowchart showing a procedure400that may be performed by a WTRU to determine measurements based on relaxation criteria, when to enter (or exit) the relaxation state, and how to report to the network and/or cell when it has entered (or exited) the relaxation state. At402, the WTRU may receive configuration information. The configuration information may include any combination of measurement relaxation criteria (e.g., a first set of relaxation criteria) for RLM or BDF, an indication that reporting to the cell is enabled, and/or a prohibit time period. After receiving the configuration information, the WTRU, at404, may perform measurements based on (e.g., using) the first set of relaxation criteria (e.g., a first evaluation period and/or a first periodicity). The measurements may include L3 RSRP measurement variation and/or the related RS measurements for the L3 RSRP measurement.

At406, the WTRU may compare the measurements to one or more thresholds. The thresholds may include one or more of a power threshold and/or a mobility threshold (e.g., such as an SINR threshold, RSRP threshold, RSSI threshold, RSRQ threshold and/or low mobility criteria, such as change of RSRP within a specific time limit, and/or a cell change count).

At408, the WTRU may select a set of relaxation criteria (e.g., the first set of relaxation criteria or a second set of relaxation criteria) based on the comparison between the measurements taken using the first set of relaxation criteria and the one or more thresholds. For example, if the measurements are above the one or more thresholds, the WTRU may select the first set of relaxation criteria, and if the measurements are below the one or more thresholds, the WTRU may select the second set of relaxation criteria. The second relaxation criteria may include a second evaluation period and/or a second periodicity (e.g., which may be different from the first evaluation period and/or the first periodicity). In some examples, the WTRU may use the first relaxation criteria when the WTRU is not in a measurement relaxation state and may use the second relaxation criteria when the WTRU is in the measurement relaxation state, or vice versa.

At410, the WTRU may perform measurement based on the set of relaxation criteria that was selected at408. At412, the WTRU may compare the measurements performed at410to the one or more threshold, for example, to determine whether a relaxation state change has occurred (e.g., so that the WTRU may determine whether to change into or out of the measurement relaxation state). The WTRU may use different relaxation criteria when in the measurement relaxation state as compared to when the WTRU is not in the measurement relaxation state. At414, the WTRU may determine whether the WTRU has changed relaxation states, for example, based on the comparison performed at412. If the WTRU determines the relaxation state has not changed, the WTRU may return to410and compare measurements taken using the set of relaxation criteria selected to the one or more thresholds.

If the WTRU determines the relaxation state has changed, the WTRU may determine whether a prohibit time period has expired (e.g., whether a prohibit timer is running) at416. As described in more detail herein, the WTRU may be configured to start a prohibit timer based on the prohibit time period that is received in the configuration information at402. For instance, the WTRU may be configured to start the prohibit timer in response to sending a report (e.g., the UL report) to the network that indicates the measurement relaxation state of the WTRU (e.g., whether the WTRU has entered or exited the measurement relaxation state), which for instance may occur at418. If the WTRU determines that the prohibit time period has not expired at416, the WTRU may return to410and compare measurements taken using the set of relaxation criteria selected to the one or more thresholds.

If the WTRU determines that the prohibit time period has expired, the WTRU may send a report to the network that it has entered (or exited) the relaxation state at418. For instance, if the WTRU determines that the prohibit time period has expired, the WTRU may change its measurement relaxation state. In some examples, the WTRU may report a measurement relaxation state indication when the relaxation state has changed, status reporting is enabled, and/or a prohibit timer is not running. By informing the network and/or cell when the WTRU has entered and/or exited the relaxation state, the network and/or cell may know when conditions are best and/or when the WTRU may react quickly or slowly.

At420, after the WTRU sends the report, the WTRU may restart the prohibit timer. In examples, the WTRU may start the prohibit time period when the WTRU sends the report (e.g., the UL report). In some examples, the WTRU may select a set of relaxation criteria for performing measurements (e.g., the first set of relaxation criteria when the WTRU is not in the relaxation state, or the second set of relaxation criteria when the WTRU is in the relaxation state), and then return to410. The use of the prohibit time period may, for example, prevent the WTRU from entering and exiting the relaxation state too often and/or in turn, reduce the number of reports (e.g., UL reports) the WTRU sends to the network.