Patent Description:
In 3GPP, a dual-connectivity (DC) solution has been specified, both for Long Term Evolution (LTE) and between LTE and New Radio (NR). In DC, two nodes may be involved, a master node (also referred to herein as a MN or MeNB) and a Secondary Node (also referred to herein as a SN or SeNB). Multi-connectivity (MC) is a case when there are more than two nodes involved. It has been proposed in 3GPP that DC is also used in the Ultra Reliable Low Latency Communications (URLLC) cases in order to enhance robustness and avoid or reduce connection interruptions. <NPL>] and <NPL>]form part of the related prior art.

The term "user equipment" is used in a non-limiting manner and, as explained below, can refer to any type of radio communication terminal/device. The term "UE" herein may be interchangeably replaced with the term "radio terminal," "radio communication terminal," "radio device," "mobile device", "wireless device", "device", or "user equipment". The term "network node" is used in a non-limiting manner and as explained below, can refer to any type of network node in, or in communication with, a radio communication network. The term "network node" herein may be interchangeably replaced with the term master node, secondary node, gNodeB, eNodeB, ng-eNB, NR node, LTE node, a base station, or a node deployed in a cloud environment.

For 3GPP DC, there may be different ways to deploy a <NUM> network with or without interworking with LTE (also referred to as E-UTRA) and evolved packet core (EPC). <FIG> illustrates some approaches for LTE and NR interworking options. In principle, NR and LTE may be deployed without any interworking, denoted by NR stand-alone (SA) operation. Options <NUM> and <NUM> illustrated in <FIG> illustrate NR SA options that may include a gNodeB (gNB) in NR connected to a <NUM> core network (5GC) and an eNodeB (eNB) connected to EPC with no interconnection between the two. On the other hand, a first supported version of NR may be referred to as E-UTRAN-NR Dual Connectivity (EN-DC) as illustrated by Option <NUM> in <FIG>. In such a deployment, dual connectivity between NR and LTE may be applied with LTE as a master and NR as a secondary node. The RAN node (gNB) supporting NR may not have a control plane connection to core network (EPC), instead it may rely on the LTE as a master node (MeNB). This option may be referred to as "Non-standalone NR". In the case of non-standalone NR, the functionality of a NR cell may be limited and may be be used for connected mode user equipment (also referred to herein as UE or UEs) as a booster and/or diversity leg, but an RRC_IDLE UE may not camp on these NR cells.

With introduction of 5GC, other options may be also valid. As mentioned above, option <NUM> may support stand-alone NR deployment where a gNB is connected to 5GC. Similarly, LTE may also be connected to 5GC using option <NUM> illustrated in <FIG> (which also may be referred to as eLTE, E-UTRA/SGC, or LTE/5GC and the node may be referred to as an ng-eNB). In these cases, both NR and LTE are seen as part of the NG-RAN (and both the ng-eNB and the gNB may be referred to as NG-RAN nodes). Options <NUM> and <NUM> of <FIG> may be other variants of dual connectivity between LTE and NR which may be standardized as part of NG-RAN connected to 5GC, denoted by Multi-Radio Dual Connectivity (MR-DC). The MR-DC umbrella may include:.

As migration for these options may differ for different operators, it may be possible to have deployments with multiple options in parallel in the same network e.g. there could be an eNB base station supporting option <NUM>, <NUM> and <NUM> illustrated in <FIG> in the same network as a NR base station supporting options <NUM> and <NUM> illustrated in <FIG>. In combination with dual connectivity solutions between LTE and NR it is also may be possible to support CA (Carrier Aggregation) in each cell group (e.g., master cell group (MCG) and secondary cell group (SCG)) and dual connectivity between nodes on same radio access terminal (RAT) (e.g. NR-NR DC). For the LTE cells, a possible consequence of these different deployments may be the co-existence of LTE cells associated to eNBs connected to EPC, 5GC or both EPC/5GC.

As described above, DC has been standardized for both LTE and E-UTRA - NR DC (EN-DC).

LTE DC and EN-DC are designed differently when it comes to which nodes control what. Generally, there may be two options:.

<FIG> illustrates a schematic control plane architecture for LTE DC and EN-DC. A difference here may include that in EN-DC, the SN may have a separate RRC entity (NR RRC). This may mean that the SN may control the UE also; sometimes without the knowledge of the MN. The SN may need to coordinate with the MN. In LTE-DC, the RRC decisions may always come from the MN (MN to UE). However, the SN may still decide the configuration of the SN, since it may be only the SN itself that has knowledge of what kind of resources, capabilities etc. the SN has.

For EN-DC, some changes compared to LTE DC may include:.

<FIG> and <FIG> illustrate exemplary user plane (UP) and control plane (CP) architectures for EN-DC.

<FIG> illustrates some network side protocol termination options for MCG, SCG and split bearers in MR-DC with EPC (EN-DC).

<FIG> illustrates an exemplary network architecture for a control plane in EN-DC.

A SN may sometimes be referred to as a SgNB (where a gNB is a NR base station), and a MN may sometimes be referred to as a MeNB in case the LTE is a master node and NR is a secondary node. In a case where a NR is a master node and a LTE is a secondary node, the corresponding terms may be SeNB and MgNB.

Split RRC messages may mainly be used for creating diversity. The sender may decide to either choose one of the links for scheduling the RRC messages, or it may duplicate the message over both links. In the downlink (DL), the path switching between the MCG or SCG legs or duplication on both may be left to network implementation. On the other hand, for the uplink (UL), the network may configure the UE to use the MCG, SCG or both legs. As used herein, the terms "leg", "path" and "RLC bearer" are used interchangeably.

When carrier aggregation (CA) is configured, a UE may only have one radio resource control (RRC) connection with the network. Further, at a RRC connection establishment/re-establishment/handover, one serving cell may provide the non-access stratum (NAS) mobility information; and at RRC connection re-establishment/handover, one serving cell may provide a security input. This cell may be referred to as a Primary Cell (PCell). In addition, depending on UE capabilities, a secondary cell(s) (SCell(s)) may be configured to form together with the PCell a set of serving cells. The configured set of serving cells for a UE therefore may include one PCell and one or more SCells. Further, when dual connectivity is configured, it may be the case that one carrier under the SCG may be used as the Primary SCell (PSCell). Hence, in this case, there may be one PCell and one or more SCell(s) over the MCG and one PSCell and one or more SCell(s) over the SCG.

The reconfiguration, addition and removal of SCells can be performed by RRC. At intra-RAT handover, RRC may also add, remove, or reconfigure SCells for usage with a target PCell. When adding a new SCell, dedicated RRC signalling may be used for sending required system information of the SCell, e.g. while in connected mode, UEs may not need to acquire broadcasted system information directly from the SCells.

The following explanation of potential problems is a present realization as part of the present disclosure and is not to be construed as previously known by others. While MCG/PCell fast recovery may be supported in Rel-<NUM> and a UE, depending on the network deployment and other factors, MCG/PCell fast recovery may provide inefficiencies. Additionally, a network may not have implemented the Rel-<NUM> feature of MCG/PCell fast recovery.

Radio link failures (RLF) may occur due to physical layer problems.

A UE may lose coverage to the cell that a UE is currently connected to. This may occur in a situation when a UE enters a fading dip, or that a handover was needed as described above, but the handover failed for one or another reason, particularly if a handover region is very short, as will be further described below.

The quality of a radio link may be monitored in the UE, e.g. on the physical layer, as described in 3GPP TS <NUM>, TS <NUM> and TS <NUM>, and which is summarized below.

Upon detection that the physical layer experiences problems according to criteria defined in TS <NUM>, the physical layer may send an indication to the RRC protocol of the detected problems (out-of-sync indication). After a configurable number (N310) of such consecutive indications, a timer (T310) may be started. If the link quality is not improved (recovered) while T310 is running (i.e. there are no N311 consecutive "in-sync" indications from the physical layer), a radio link failure may be declared in the UE, as illustrated in <FIG>.

<FIG> illustrates a radio link failure due to physical layer problems.

Relevant timers and counters described above, and with reference to <FIG>, are exemplary. A UE may read the timer-values from system information broadcasted in the cell. Alternatively, it is possible to configure the UE with UE-specific values of the timers and constants using dedicated signaling, e.g. where specific values are given to specific UEs with messages directed only to each specific UE.

<FIG> illustrates a table of timers, timer starts, timer stops, expiry events, constants and usages.

Referring to <FIG>, if T310 expires for MCG, the UE may initiate a connection re-establishment to recover the ongoing RRC connection. This procedure may include cell selection by the UE. That is, a RRC_CONNECTED UE may try to autonomously find a better cell to connect to, since the connection to the previous cell failed according to the described measurements (it could occur that the UE returns to the first cell anyway, but the same procedure may then be executed). Once a suitable cell is selected (as further described e.g. in TS <NUM>), the UE may request to re-establish the connection in the selected cell. It may be important to note the difference in mobility behaviour as an RLF results in UE based cell selection, in contrast to a normally applied network-controlled mobility.

If the re-establishment is successful (which may depend, among other things, if the selected cell and the gNB controlling that cell was prepared to maintain the connection to the UE), then the connection between the UE and the gNB may resume.

A failure of a re-establishment may mean that the UE goes to RRC_IDLE and the connection is released. To continue communication, a brand new RRC connection may then have to be requested and established.

A possible reason for introducing the timers T31x and counters N31x described with reference to <FIG> may be to add some freedom and hysteresis for configuring criteria for when a radio link should be considered as failed (and recovered). This may be desirable, since it may hurt the end-user performance if a connection is abandoned prematurely if it turned out that the loss of link quality was temporary, and the UE succeeded in recovering the connection without any further actions or procedures (e.g. before T310 expires, or before the counting reaches value N310).

Procedures for NR radio link failure detection related actions from 3GPP TS <NUM> are described in <NUM>.

In radio access network group <NUM> (RAN2) meetings, inclusion of a MCG fast recovery procedure in 3GPP was discussed with details still under discussion. The following description is based on the discussions and is not presently included in 3GPP specifications.

The discussions may have included:
SCG/MCG failure handling (<NUM> → R2-<NUM>).

If radio link failure is detected for MCG, and fast MCG link recovery can be used, the UE can report the failure via SCG, if configured. Otherwise, the UE may initiate the RRC connection re-establishment procedure.

The following MCG failure case may trigger fast MCG link recovery:.

During fast MCG link recovery, the UE may suspend MCG transmissions for all radio bearers and may report the MCG Failure Information to the MN via the SCG, using the SCG leg of split SRB1 (if configured), instead of triggering re-establishment.

If MCG failure information can be sent via SRB3 it may be for further study (FFS).

The UE may include in a MCG Failure Information message the measurement results available according to current measurement configuration of both the MN and the SN. Once the MCG failure indication is triggered, UE may maintain the current measurement configurations from both the MN and the SN, and may continue measurements based on configuration from the MN and the SN, if possible.

It may be FFS whether MCG failure can be reported via SCells.

FFS whether a guand timer is needed for MCG Failure Indication.

FFS whether UE needs to switch the primaryPath to SCG.

Upon reception of the MCG Failure Indication, MN can send RRC Rconfiguration with sync message or RRC Release message to UE, using the SCG leg of split SRB1. At reception of RRC Rconfiguration with sync message, UE can resume MCG transmissions for all radio bearers, if suspended.

The following SCG failure cases may be supported:.

Upon SCG failure, if MCG transmissions of radio bearers are not suspended, the UE may suspend SCG transmissions for all radio bearers and may report the SCG Failure Information to the MN, instead of triggering re-establishment. If SCG failure is detected while MCG transmissions of radio bearers are suspended, then UE may initiate RRC re-establishment procedure.

In all SCG failure cases, the UE may maintain the current measurement configurations from both the MN and the SN and the UE may continue measurements based on configuration from the MN and the SN if possible. The SN measurements configured to be routed via the MN may continue to be reported after the SCG failure.

It may be noted that a UE may not continue measurements based on configuration from the SN after SCG failure in certain cases (e.g. UE cannot maintain the timing of PSCell).

The UE may include in a SCG Failure Information message the measurement results available according to current measurement configuration of both the MN and the SN. The MN may handles the SCG Failure Information message and may decide to keep, change, or release the SN/SCG. In all the cases, the measurement results according to the SN configuration and the SCG failure type may be forwarded to the old SN and/or to the new SN.

<FIG> illustrates a message sequence for a MCG failure information exchanged between a UE and a radio access node (RAN, also referred to herein as a network node).

A purpose of MCG failure information procedure may be to inform NR MN about an MCG failure the UE has experienced, e.g. MCG radio link failure.

A UE configured with split signal radio bearer <NUM> (SRB1) may initiate the procedure to report MCG failures when SCG transmission is not suspended and when the following condition is met:
<NUM>> upon detecting radio link failure of the MCG, in accordance with <NUM>.

Upon initiating the procedure, the UE shall:.

The UE may set the MCG failure type as follows:.

The UE shall set the contents of the MeasResultMCG-Failure as follows:
FFS how to capture inclusion of MCG, SCG and non-serving cell measurement results <NUM>. <NUM> Actions related to transmission of MCGFailurelnformation message.

The UE may set the contents of the MCGFailurelnformation message as follows:.

The UE shall submit the MCGFailurelnformation message to lower layers for transmission.

While it may have been agreed or discussed in 3GPP RAN2 meetings that a MCG fast recovery procedure may be provided, in MR-DC a MCG fast recovery may be supported in Rel-<NUM> and the UE, in case of RLF detected on the MCG, the network should send an indication via the SCG leg of the split SRB to the MCG. However, depending on the deployment and on which frequencies the MCG and SCG are configured, it may be more efficient to perform the legacy RRC re-establishment rather than try to recovery the RRC connection. For example, if both the MCG and SCG are deployed on frequency range <NUM> (FR2), or if there is a strong correlation between RLF on MCG and SCG, recovery via RRC re-establishment could be preferred. Otherwise, e.g. if MCG failure recovery is applied, the UE may be disconnected for twice the RLF detection time. The first RLF detection time to detect the MCG RLF, then MCG failure report sent over the SCG, and the RLF detection time to detect the SCG RLF, followed by re-establishment. If re-establishment was triggered upon the MCG RLF, then the UE interruption time may be reduced by half.

There may also be the possibility that a network has not implemented the Rel-<NUM> feature of MCG fast recovery (also referred to as MCG failure information).

It may be noted that some of the same problems may be applied also in case the failure happens on a PCell and the UE trys to avoid the RRC Re-establishment procedure by applying some recovery mechanisms, e.g., sending an indication of the detected PCell-RLF over the SCell.

As used herein, the use of the terms "master cell group fast recovery procedure" and "master cell group/PCell fast recovery procedure" (MCG/PCell fast recovery procedure) include, and are not limited to, a master cell group fast recovery procedure and/or a PCell fast recovery procedure.

In various embodiments, a method may be provided for a radio communication network node to indicate to a UE whether a MCG/PCell fast recovery procedure should be used or not.

In some embodiments, if a UE timer (e.g. timeout timer) is used for the MCG/PCell fast recovery procedure (e.g. a timer that is started upon the detection of a MCG failure and a start of MCG failure recovery, and if it expires before the UE gets a reconfiguration that changes the PCell, re-establishment is triggered), then not configuring that timer can be used as an indication that the MCG/PCell fast recovery mechanism should not be used by the UE. Alternatively, the value <NUM> may be used to implicitly indicate to the UE that the MCG/PCell fast recovery mechanism should not be used.

In some embodiments, an indication of whether the MCG/PCell fast recovery mechanism should be used by a UE may be sent by the network by an explicit indication in RRC messages e.g., in the RRCReconfiguration message (e.g. included in existing Information Element RLF-TimersAndConstants or ServingCellConfig). This may be an explicit indication that the UE needs (or not) to use the MCG fast recovery. Similarly, there may be explicit indication in X2/Xn messages (e.g. SN addition) to coordinate between MN and SN whether MCG/PCell fast recovery is to be configured, or not, depending on the network support for the feature.

In some embodiments, an indication of whether the network supports (or not) the MCG/PCell fast recovery mechanism is added in one of the system information block(s) (SIB(s)) messages (e.g., SIB1) and the UE may trigger the MCG fast recovery only if the current serving cell supports it. In one embodiment, the SIB indication may be read from the PCell. In another embodiment, the SIB indication may be read from the PSCell. The UE also may trigger the MCG fast recovery only if both the PCell and PSCell indicate in their SIB that they support this feature.

In some embodiments, the network may activate or deactivate the MCG fast recovery using a medium access control (MAC) control element (CE). The UE may trigger MCG failure recovery only when it was activated. In one embodiment, the feature may be deactivated by default and a MAC CE may be required to activate it. In another embodiment, the feature may be active by default. In another embodiment, the activation/deactivation state can be configured initially via RRC (e.g. RRCReconfiguration that sets up the SCG), and can be changed via MAC CE after that.

In some embodiments, a UE capability may be introduced and only UEs supporting MCG failure recovery may initiate the MCG failure recovery procedure.

In some embodiments, in MR-DC, the MN may signal whether or not it supports the MCG fast recovery to the SN (e.g., during SN addition) and the SN may take different action based on this (e.g., reconfigure or re-establish the UE autonomously via signal radio bearer <NUM> (SRB3) or forward the RLF indication to the MN that then takes actions).

Various embodiments may be applied in combination.

While some embodiments are described for a NR case (e.g. the modification for the NR such as changes to NR SIB and NR RRCReconfiguration messages are equally applicable to LTE SIB and LTE RRCConnectionReconfiguration), the embodiments are not so limited. For example, various embodiments may be applicable to cases where a MN is an LTE or a NR base station.

Various embodiments may include cases where a RLF is detected on a MCG/PCell. As used herein, the terms "master cell group" and MCG include a master cell group (MCG) and/or a PCell (MCG/PCell). When such a RLF is detected, the network may have the flexibility to indicate whether the UE should use the MCG/PCell fast recovery or not in order to avoid RRC Re-establishment.

In some embodiments, the network may provide an indication to a UE in RRC_CONNECTED that a MCG/PCell fast recovery procedure is supported (or not supported). In one embodiment, this indication may be sent to the UE via dedicated RRC signaling (e.g., RRCReconfiguration). In another embodiment, the indication provided by the network may be sent by using another existing RRC message. In another embodiment, the indication provided by the network may be sent by using a new RRC message.

In some embodiments, the network, upon configuring a UE with MR-DC (e.g., adding an SCG configuration via RRCReconfiguration), the network may indicate to the UE whether it should apply the MCG fast recovery or not depending on several factors such the frequency bands used by the MCG and SCG serving cells.

In some embodiments, if there are UE-specific timers related the MCG/PCell fast recovery that may need to be configured on the UE-side by the network, the presence (or absence) or these timers indicates whether the MCG/PCell fast recovery procedure is supported or not. In another embodiment, if there are UE-specific timers related the MCG/PCell fast recovery that may need to be configured on the UE-side by the network, the network may set these timers to a specific value (e.g., <NUM> or infinity) to signal the UE that the MCG/PCell fast recovery procedure is supported or not.

In some embodiments, the network may provide an indication to a UE in RRC_IDLE/RRC_INACTIVE that the MCG/PCell fast recovery mechanism is supported (or not supported) via SIB. In one embodiment, the network may add an indication to signal to the UE whether the MCG/PCell fast recovery mechanism is supported in an existing SIB e.g., SIB1. In another embodiment, the network may add an indication to signal to the UE whether the MCG/PCell fast recovery mechanism is supported in a new SIB.

The SIB indication may be a simple on/off indicator, or it may be a detailed indicator that includes for which DC band combinations the MCG fast recovery should be used and for which the UE should trigger re-establishment directly. The UE, then may apply appropriate behavior depending on the frequency bands used by the MCG and SCG and comparing them with the broadcast information in the SIB.

In some embodiments, in MR-DC in case of MCG fast recovery, a UE may send an indication that an RLF has been detected on the MCG via the SRB3 to the SN. In such a case, in one embodiment upon adding an SN, the MN may send an indication to the SN that the MCG fast recovery mechanism is supported. In another embodiment, such indication may be added in one of the inter-node RRC messages e.g., CG-ConfigInfo. Alternatively, in another embodiment, such indication may be added in one of the X2/Xn messages used upon configuring MR-DC e.g., S-NODE ADDITION/MODIFICATION REQUEST, or S-NODE CHANGE REQUIRED.

In some embodiments, upon receiving an indication from a MN that the MN does not support a MCG fast recovery mechanism, the SN can configure the UE via SRB3 to perform PCell/MCG fast recovery by reporting via SRB3, given that the SN configures the UE with SRB3. Then, when receiving the MCGFailurelnformation from the UE via SRB3, the SN can autonomously decide the actions to perform, e.g. (re)configure or re-establish the UE via the SRB3 (e.g., if the SN supports the MCG fast recovery mechanism). In another embodiment, upon receiving an indication from the MN that the MN does support the MCG fast recovery mechanism, the SN can configure the UE with SRB3. Then, when receiving the MCGFailurelnformation from the UE via SRB3, the SN forwards the MCGFailurelnformation to the MN that takes the necessary actions.

In some embodiments, a MN may send an indication to the UE that a MCG fast recovery mechanism is supported (or not) via the SRB1. In another embodiment, the MN may send the indication to the UE that the MCG fast recovery mechanism is supported (or not) via the split SRB1. In another embodiment, the SN may send the indication to the UE that the MCG fast recovery mechanism is supported (or not) via SRB3.

In some embodiments, a UE, upon re-establishment due to a failed MCG fast recovery, may include a report (e.g. in the RLF report) that was the case (e.g., MCG fast recovery had failed), and possibly with additional information such as its configuration (e.g. frequencies used by the PCell and SCell), measurement results, etc. The network can collect such RLF reports and use them to decide whether to activate/deactivate MCG fast recovery. For example, if the number of times the MCG fast recovery fails (as indicated from these reports) is significantly more than the that it succeeds (as can be gathered by collecting the information on how many MCG fast recovery reports were successfully received by the network and PCell changed), the network can disable the feature (either for all UEs or DC band combinations, of for a particular band combination, if this failures seem to occur mainly for certain band combinations).

In some embodiments, the UE can be also be configured with signal level thresholds on a SCG side in order to trigger a MCG failure recovery or not. For example, the UE can be configured to trigger the MCG failure recovery only when the PSCell and/or one of the SCG SCells have a signal level greater than a threshold value.

In some embodiments, for a fast MCG recovery, different L2 parameters can be applied in a SCG as compared to sending other split SRB1 messages. For example, the maximum retransmissions on a RLC can be set to a value of <NUM> upon sending the MCG failure report. This way, the SCG may have only one chance to transmit the packet, and thus may trigger the re-establishment faster than if the maximum retransmission value was set to <NUM>, for example, thereby possibly saving considerable time that could have been lost doing unsuccessful retransmissions.

Presently disclosed embodiments may provide potential advantages including, but not limited to, allowing a network to have flexibility regarding whether the MCG/PCell fast recovery should be used or not by the UE when an RLF on the MCG/PCell is detected. Thus, the network may be able to apply the MCG failure recovery only when it is beneficial and can reduce UE interruption time, depending on the network deployment, current bands used for DC by the UE, current signal level towards the SCG, etc..

These and other related operations will now be described in the context of the operational flowcharts of <FIG>. <FIG> are flowcharts of operations that may be performed by a network node. <FIG> are flowcharts of operations that may be performed by a UE.

Referring initially to <FIG>, operations are performed in the claimed invention by a network node (e.g., <NUM> in <FIG>) in a radio communication network. The operations include detecting <NUM> a radio link failure on a master cell group. The operations further include indicating <NUM> to a user equipment <NUM> whether to use a master cell group fast recovery procedure to avoid a radio resource control re-establishment.

In some embodiments, the indicating <NUM> may include at least one indicator including: an indication that the master cell group fast recovery procedure is supported; an indication that the user equipment use the master cell group fast recovery procedure when defined criteria are met. In the claimed invention, the indicating <NUM> includes at least one indication that the user equipment use the master cell group fast recovery procedure when a timer for the master cell group fast recovery procedure is present at the user equipment.

In some embodiments, the indicating <NUM> to the user equipment may include at least one of:.

In at least some embodiments, the system information block indicator may include at least one or more of: an on/off indicator; a defined indicator including at least one dual connectivity band combination indicating to the user equipment to use the master cell group fast recovery procedure for the at least one dual connectivity band combination; and the defined indicator including at least one dual connectivity band combination triggering the user equipment to use the radio resource control re-establishment.

In at least some embodiments, the system information block indicator is read from at least one of: a primary cell and a primary secondary cell.

Referring to <FIG>, in at least some embodiments, the system information block indicator may include configuring <NUM> the user equipment with multi-radio dual connectivity. The indicating to the user equipment may include an indication included in the configuring <NUM> indicating whether the user equipment should apply the master cell group fast recovery procedure when the defined criteria are met.

In at least some embodiments, the defined criteria may include a specified frequency band used by a master cell group and/or a secondary cell group.

Referring to <FIG>, further operations that may be performed by the network node may include configuring <NUM> the timer to a value, wherein the value indicates to the user equipment whether the master cell group fast recovery procedure is supported.

In some embodiments, the operations may further include wherein the user equipment is in a multi-radio dual connectivity. The detecting <NUM> may include receiving from the user equipment a first indication that a radio link failure has been detected on the master cell group via a signal radio bearer to a secondary node.

Referring to <FIG>, in some embodiments, further operations that may performed by the network node may include sending <NUM> a second indication to the secondary node that the master cell group fast recovery procedure is supported. Some embodiments provide that sending the second indication includes at least one of including the second indication in an inter-network node message and including the second indication in a message when configuring the multi-radio dual connectivity.

In at least some embodiments, the network node may be a secondary node; and the indicating <NUM> may include receiving a first indication from a master node that the master node does not support the master cell group fast recovery procedure; and configuring the user equipment via a signal radio bearer to perform the master cell group fast recovery procedure using the signal radio bearer.

In at least some embodiments, the indicating <NUM> may include applying one or more parameters of a layer of a protocol stack in a secondary cell group. The one or more parameters may include a defined number of maximum retransmissions on a radio link control set upon sending a report. The report may include a master cell group failure.

Referring to <FIG>, in some embodiments, further operations that may be performed by the network node may include receiving <NUM> a report from the user equipment. The operations may further include deciding <NUM>, based on the report, whether to activate or deactivate the master cell group fast recovery procedure.

In some at least some embodiments, the indicating <NUM> may include activating or deactivating the master cell group fast recovery procedure using a medium access control (MAC) control element including at least one of: deactivating the master cell group fast recovery procedure by default and requiring the control element to activate the master cell group fast recovery procedure; activating the master cell group fast recovery procedure by default; and changing the activating or the deactivating via the control element.

<FIG> are flowcharts of operations that may be performed by a UE in a radio communications network (e.g., <NUM> in <FIG>) in accordance with some embodiments.

Referring to <FIG>, the operations include in the claimed invention receiving <NUM> an indicator indicating when to use a master cell group fast recovery procedure to avoid a radio resource control re-establishment. The operations further include using <NUM> the master cell group fast recovery procedure based on the indicator.

In some embodiments, the indicator may include at least one of:.

In some embodiments, the receiving <NUM> the indicator may include at least one of:.

In some embodiments, the system information clock indicator may include at least one or more of an on/off indicator; a defined indicator including at least one dual connectivity band combination indicating to the user equipment to use the master cell group fast recovery procedure for the at least one dual connectivity band combination; and the defined indicator including at least one dual connectivity band combination triggering the user equipment to use the radio resource control re-establishment.

In some embodiments, the system information clock indicator may be read from at least one of a primary cell and a primary secondary cell.

In some embodiments, the user equipment may be configured with multi-radio dual connectivity. The operations performed by the UE may further include wherein the receiving the indicator includes receiving the indicator in the configuration of the user equipment for multi-radio dual connectivity, wherein the indicator comprises an indication for whether the user equipment should use the master cell group fast recovery procedure when the defined criteria are met.

Referring to <FIG>, the UE may be in a multi-radio dual connectivity. Further operations that may be performed by the UE can include sending <NUM> a first indication that a radio link failure has been detected on the master cell group via a signal radio bearer to a secondary node. Further operations that may be performed by the UE may include sending <NUM> a second indication to the secondary node that the master cell group fast recovery procedure is supported. The sending the second indication may include at least one of including the second indication in an inter-network node message and including the second indication in a message when configuring the multi-radio dual connectivity.

The indicator may include receiving a configuration via a signal radio bearer to perform the master cell group fast recovery procedure using the signal radio bearer.

Referring to <FIG>, further the operations that may be performed by the UE can include triggering <NUM> a master cell group failure recovery only when a master cell group fast recovery procedure is activated.

Referring to <FIG>, further the operations that may be performed by the UE can include sending <NUM> a report. The report may include information including one or more of: a failure of the master cell group fast recovery procedure; a configuration of the user equipment; and measurement results of the user equipment.

<FIG> is a block diagram illustrating an exemplary UE <NUM> that is configured according to some embodiments. The UE <NUM> can include, without limitation, a wireless terminal, a wireless communication device, a wireless communication terminal, a terminal node/UE/device, etc. The UE <NUM> includes a RF front-end <NUM> comprising one or more power amplifiers the transmit and receive through antennas of an antenna array <NUM> to provide uplink and downlink radio communications with a radio network node (e.g., a base station, eNB, gNB, etc.) of a radio communications network. UE <NUM> further includes at least one processor circuit <NUM> (also referred to as at least one processor) coupled to the RF front end <NUM> and a memory circuit <NUM> (also referred to as memory). The memory <NUM> stores computer readable program code that when executed by the at least one processor <NUM> causes the at least one processor <NUM> to perform operations according to embodiments disclosed herein.

<FIG> is a block diagram illustrating an exemplary network node <NUM> (e.g., a base station, gNB, etc.) of a radio communications network. The network node <NUM> includes at least one processor circuit <NUM> (also referred to as at least one processor), a memory circuit <NUM> (also referred to as memory), and a network interface <NUM> (e.g., wired network interface and/or wireless network interface) configured to communicate with other network nodes. The network node <NUM> may be configured as a radio network node containing a RF front end with one or more power amplifiers <NUM> that transmit and receive through antennas of an antenna array <NUM>. The memory <NUM> stores computer readable program code that when executed by the at least one processor <NUM> causes the at least one processor <NUM> to perform operations according to embodiments disclosed herein.

Explanations are provided below for various abbreviations/acronyms used in the present disclosure.

Reference is now made to <FIG>, which is a schematic block diagram of a wireless network in accordance with some embodiments.

Although the subject matter described herein may be implemented in any appropriate type of system using any suitable components, the embodiments disclosed herein are described in relation to a wireless network, such as the example wireless network illustrated in <FIG>. For simplicity, the wireless network of <FIG> only depicts network <NUM>, network nodes <NUM> and 4160b, and WDs <NUM>, 4110b, and 4110c (also referred to as mobile terminals). In practice, a wireless network may further include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device, such as a landline telephone, a service provider, or any other network node or end device. Of the illustrated components, network node <NUM> and wireless device (WD) <NUM> are depicted with additional detail. The wireless network may provide communication and other types of services to one or more wireless devices to facilitate the wireless devices' access to and/or use of the services provided by, or via, the wireless network.

As used herein, wireless device (WD) refers to a device capable, configured, arranged and/or operable to communicate wirelessly with network nodes and/or other wireless devices. Unless otherwise noted, the term WD may be used interchangeably herein with user equipment (UE). Communicating wirelessly may involve transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information through air. In some embodiments, a WD may be configured to transmit and/or receive information without direct human interaction. For instance, a WD may be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the network. Examples of a WD include, but are not limited to, a smart phone, a mobile phone, a cell phone, a voice over IP (VoIP) phone, a wireless local loop phone, a desktop computer, a personal digital assistant (PDA), a wireless cameras, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, a laptop-embedded equipment (LEE), a laptop-mounted equipment (LME), a smart device, a wireless customer-premise equipment (CPE). a vehicle-mounted wireless terminal device, etc. A WD may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-everything (V2X) and may in this case be referred to as a D2D communication device. As yet another specific example, in an Internet of Things (IoT) scenario, a WD may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another WD and/or a network node. The WD may in this case be a machine-to-machine (M2M) device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the WD may be a UE implementing the 3GPP narrow band internet of things (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances (e.g. refrigerators, televisions, etc.) personal wearables (e.g., watches, fitness trackers, etc.). In other scenarios, a WD may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. A WD as described above may represent the endpoint of a wireless connection, in which case the device may be referred to as a wireless terminal. Furthermore, a WD as described above may be mobile, in which case it may also be referred to as a mobile device or a mobile terminal.

Claim 1:
A method performed by a network node (<NUM>) in a radio communication network, the method comprising:
detecting (<NUM>) a radio link failure on a master cell group; and
indicating (<NUM>) to a user equipment (<NUM>) when to use a master cell group fast recovery procedure to avoid a radio resource control re-establishment, wherein the indicating (<NUM>) includes at least one indicator comprising an indication that the user equipment uses the master cell group fast recovery procedure when a timer for the master cell group fast recovery procedure is present at the user equipment and wherein the timer for the user equipment for the master cell group fast recovery procedure is configured with a value, wherein the value indicates to the user equipment whether the master cell group fast recovery procedure is supported.