TECHNICAL FIELD

[0001] Disclosed are embodiments related to MCG failure reporting and RLF failure reporting.

BACKGROUND

[0002] 1.1 - 5G architecture

[0003] The current 5G Radio Access Network (RAN) (Next-Generation RAN) architecture is depicted and described in Technical Specification (TS) 38.401vl 5.7.0 (www.3gpp.org/ftp//Specs/archive/38_series/38.401/38401-f70. zip) as shown in FIG. 1.

[0004] The NG architecture can be further described as follows. The NG-RAN consists of a set of next generation nodeBs (gNBs) connected to the 5G core (5GC) through the next- generation (NG) interface. A gNB can support frequency division duplex (FDD) mode, time division duplex (TDD) mode or dual mode operation. gNBs can be interconnected through the Xn interface. A gNB may consist of a gNB central unit (gNB-CU) and one or more gNB distributed units (gNB-DU). A gNB-CU and a gNB-DU are connected via FI logical interface. One gNB-DU is connected to only one gNB-CU. For resiliency, a gNB-DU may be connected to multiple gNB-CU by appropriate implementation. NG, Xn and FI are logical interfaces. The NG-RAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The NG-RAN architecture, i.e., the NG-RAN logical nodes and interfaces between them, is defined as part of the RNL. For each NG-RAN interface (NG, Xn, FI) the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport and signalling transport.

[0005] Another architectural option is that where an Long Term Evolution (LTE) evolved NodeB (eNB) connected to the Evolved Packet Core network is connected over the X2 interface with a so called NR-gNB. The latter is a gNB not connected directly to a core network (CN) and connected via X2 to an eNB for the sole purpose of performing dual connectivity. [0006] The architecture in FIG. 1 can be expanded by spitting the gNB-CU into two entities. One gNB-CU-User Plane (gNB-CU-UP), which serves the user plane and hosts the packet data convergence protocol (PDCP) protocol and one gNB-CU-CP, which serves the control plane and hosts the PDCP and radio resource control (RRC) protocol. For completeness it should be said that a gNB-DU hosts the radio link control (RLC)/ medium access control (MAC)/ physical layer (PHY) protocols.

[0007] 1.2 - Mobility Robustness organization (MRO) and Radio Link Failure (RLF) in

LTE/NR

[0008] Seamless handovers are a key feature of 3rd Generation Partnership Project

(3GPP) technologies. Successful handovers ensure that a user equipment (UE) (i.e., any device capable of wireless communication with an access point (e.g. gNB, eNB, etc.) moves around in the coverage area of different cells without causing too much interruptions in the data transmission. However, there will be scenarios when the network fails to handover the UE to the ‘correct’ neighbor cell in time and in such scenarios the UE will declare the radio link failure (RLF) or Handover Failure (HOF).

[0009] Upon HOF and RLF, the UE may take autonomous actions i.e. trying to select a cell and initiate reestablishment procedure so that we make sure the UE is trying to get back as soon as it can, so that it can be reachable again. The RLF will cause a poor user experience as the RLF is declared by the UE only when it realizes that there is no reliable communication channel (radio link) available between itself and the network. Also, reestablishing the connection requires signaling with the newly selected cell (random access procedure, RRC Reestablishment Request, RRC Reestablishment RRC Reestablishment Complete, RRC Reconfiguration and RRC Reconfiguration Complete) and adds some latency, until the UE can exchange data with the network again.

[0010] According to the LTE/NR specifications (TS 36.331, TS 38.331), the possible causes for the radio link failure could be one of the following:

[0011] 1) expiry of the radio link monitoring related timer T310; [0012] 2) expiry of the measurement reporting associated timer T312 (not receiving the handover command from the network within this timer’s duration despite sending the measurement report when T310 was running);

[0013] 3) upon reaching the maximum number of RLC retransmissions for the MCG; and

[0014] 4) upon receiving random access problem indication from the MCG MAC entity.

[0015] As RLF leads to reestablishment which degrades performance and user experience, it is in the interest of the network to understand the reasons for RLF and try to optimize mobility related parameters (e.g. trigger conditions of measurement reports) to avoid later RLFs. Before the standardization of MRO related report handling in the network, only the UE was aware of some information associated to how did the radio quality looked like at the time of RLF, what is the actual reason for declaring RLF etc. For the network to identify the reason for the RLF, the network needs more information, both from the LIE and also from the neighboring base stations.

[0016] As part of the MRO solution in LTE, the RLF reporting procedure was introduced in the RRC specification in Rel-9 RAN2 work. That has impacted the RRC specifications (TS 36.331) in the sense that it was standardized that the UE would log relevant information at the moment of an RLF and later report to a target cell the UE succeeds to connect (e.g. after reestablishment). That has also impacted the inter-gNodeB interface, i.e., X2AP specifications (TS 36.423), as an eNodeB receiving an RLF report could forward to the eNodeB where the failure has been originated.

[0017] In LTE/NR , lower layers provide to upper layer Out-of-Sync (OOS) and In-

Sync (IS), internally by the UE’s physical layer, which in turn may apply RRC / layer 3 (i.e. higher layer) filtering for the evaluation of Radio Link Failure (RLF). The procedure is illustrated in FIG. 2. FIG. 2 shows higher layer RLF related procedures in LTE.

[0018] For the RLF report generated by the UE, its contents have been enhanced with more details in the subsequent releases. The measurements included in the measurement report based on the latest LTE RRC specification (3GPP TS 36.331 V12.8.0) are:

1) Measurement quantities (e.g., Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ)) of the last serving cell (PCell). 2) Measurement quantities of the neighbor cells in different frequencies of different RATs (Universal Terrestrial Radio Access (UTRA), Evolved-UTRA (E-UTRA), Global System for Mobile Communications (GSM) Edge RAN (GERAN), Code-Division Multiple Access (CDMA) 2000).

3) Measurement quantity (Received Signal Strength Indicator (RSSI)) associated to Wireless Local Area Network (WLAN) Aps.

4) Measurement quantity (RSSI) associated to Bluetooth beacons.

5) Location information, if available (including location coordinates and velocity)

6) Globally unique identity of the last serving cell, if available, otherwise the physical cell ID (PCI) and the carrier frequency of the last serving cell.

7) Tracking area code of the PCell.

8) Time elapsed since the last reception of the ‘Handover command’ message.

9) Cell Radio Network Temporary Identifier (C-RNTI) used in the previous serving cell.

10) Whether or not the UE was configured with a data radio bearer (DRB) having Quality of Service (QoS) Class Identifier (QCI) value of 1.

[0019] The detection and logging of the RLF related parameters is captured in section

5.3.11.3 of LTE RRC specification, which is reproduced in the table below.

[0020] After the RLF is declared, the RLF report is logged and, once the UE selects a cell and succeeds with a reestablishment, it includes an indication that it has an RLF report available in the RRC Reestablishment Complete message, to make the target cell aware of that availability. Then, upon receiving an UEInformationRequest message with a flag “rlf-ReportReq-r9” the UE shall include the RLF report (stored in a UE variable VarRLF-Report, as described above) in an UEInformationResponse message and send to the network.

[0021] The UEInformationRe quest and UEInformationResponse messages are described below.

[0022] UEInformationRequest - The UEInformationRequest is the command used by E-

UTRAN to retrieve information from the UE. The signalling radio bearer for the message is SRB1; the RLC-SAP is AM; the Logical channel is DCCH, and the direction is E-UTRAN to UE.

[0023] The below table illustrates various UEInformationRequest messages:

[0024] UEInformationRequest field descriptions - rach-ReportReq: This field is used to indicate whether the UE shall report information about the random access procedure.

[0025] UEInformationResponse

[0026] The UEInformationResponse message is used by the UE to transfer the information requested by the E-UTRAN. The signalling radio bearer for the UEInformationResponse is SRB1 or SRB2 (when logged measurement information is included); the RLC-SAP is AM; the Logical channel is DCCH; and the direction is UE to E-UTRAN.

[0027] The table below illustrates various UEInformationResponse messages. _ _

[0028] Based on the contents of the RLF report (e.g. the Globally unique identity of the last serving cell, where the failure was originated), the cell in which the UE reestablishes can forward the RLF report to the last serving cell. This forwarding of the RLF report is done to aid the original serving cell with tuning of the handover related parameters (e.g. measurement report triggering thresholds) as the original serving cell was the one who had configured the parameters associated to the UE that led to the RLF.

[0029] Two different types of inter-node messages have been standardized in LTE for that purpose, the Radio link failure indication and the handover report (in 36.423 REFERENCE).

[0030] The Radio link failure indication procedure is used to transfer information regarding RRC re-establishment attempts or received RLF reports between eNBs. This message is sent from the eNB in which the EE performs reestablishment to the eNB which was the previous serving cell of the EE.

[0031] 1.3 MCG fast recovery procedure

[0032] In LTE/NR rel-16, the fast MCG link recovery procedure was agreed. Fast MCG link recovery is an RRC procedure where the UE sends an MCG Failure Information message to the Master Node (MN) via the Secondary Cell Group (SCG) upon the detection of a radio link failure on the MCG, instead of triggering RRC re-establishment.

[0033] If radio link failure is detected for MCG, and fast MCG link recovery is configured, the UE triggers fast MCG link recovery. Otherwise, the UE initiates the RRC connection re-establishment procedure. During fast MCG link recovery, the UE suspends MCG transmissions for all radio bearers and reports the failure with MCG Failure Information message to the MN via the SCG, using the SCG leg of split Signaling Radio Bearer (SRB)l or SRB3.

[0034] The UE includes in the MCG Failure Information message the measurement results available according to current measurement configuration of both the MN and the Secondary Node (SN). Once the fast MCG link recovery is triggered, the EE maintains the current measurement configurations from both the MN and the SN, and continues measurements based on configuration from the MN and the SN, if possible. The EE initiates the RRC connection re-establishment procedure if it does not receive an RRC reconfiguration message or RRC release message within a certain time (determined by a timer called T316) after fast MCG link recovery was initiated. [0035] Upon reception of the MCG Failure Information, the MN can send RRC reconfiguration message or RRC release message to the UE, using the SCG leg of split SRB1 or SRB3. Upon receiving an RRC reconfiguration message (that contains the reconfigurationWithSync in case the MCG was NR or a mobilityControlInfo in case the MCG was LTE), the UE resumes MCG transmissions for all radio bearers. Upon receiving an RRC release message, the UE releases all the radio bearers and configurations.

[0036] It has also been agreed that the network can send an inter-RAT handover (HO) command to the UE in response to the MCG Failure Information. That is, in case the MCG was NR (NR-DC, NE-DC), the UE may receive a MobilityFromNR command containing an RRCConnectionReconfiguration message embedded within it that will be used to hand the UE over to LTE. If the MCG was LTE ((NG)EN-DC), the UE may receive a MobilityFromEUTRA command containing an RRCReconfiguration message embedded within it that will be used to hand the UE over to NR.

[0037] The structure of the MCGFailurelnformation message is shown below (see also

3GPP TS 38.331, V16.0.0 (hereafter “TS38.331”)). As can be seen, the message contains several measurement results the UE has (NR and LTE measurements, both based on the MN/SN measurement configuration).

[0038] The MCGFailurelnformation message is used to provide information regarding

NR MCG failures detected by the UE and has the following characteristics Signalling radio bearer: SRB1; RLC-SAP: AM; Logical channel: DCCH; Direction: UE to Network. The table below provides a description for the elements of the message.

[0039] Detection Of Radio Link Failure

[0040] As specified in section 5.3.10.3 of TS 38.331:

SUMMARY

[0041] As discussed above, in LTE/NR rel-16, the MCG fast recovery procedure is being specified such that a UE, instead of initiating a re-establishment procedure when the UE detects an RLF with respect to an MCG, the UE sends an MCG failure information report to the MN using the SCG leg of split SRB1 or SRB3. According to current procedure specified in TS 38.331 subclause 5.3.10.3 (reproduced above), the UE generates an RLF report when a radio link failure on the MCG is detected.

[0042] Thus, even if the network has received and responded to the MCG failure (e.g.

RRCConfiguration including reconfigurationWithSync is received), the UE may still indicate (e.g. in the RRCReconfigurationComplete message in response to the received reconfiguration that recovered the MCG) about the availability of RLF report at the UE. The network then sends a UE information Request to request the RLF report, which the UE sends in a UE information response message. This means that the UE reports the measurements related to the problem that led to the MCG failure recovery twice (first in the MCG failure Information, and next in the RLF report to the network). Apart from the double sending of the same measurement report to the network, the RLF report is usually gathered for SON/MDT purposes, which is aggregated and analysed for HO/mobility parameter tuning. Thus, sending the RLF report for an MCG failure that has already been recovered could cause some complications (e.g. network changing values of parameters unnecessarily/incorrectly, possibly increasing the chances of RLFs or handover failures in the future).

[0043] Accordingly, in one aspect there is provided a method for reporting radio link failure (RLF) information. The method includes a user equipment (UE) detecting an RLF with respect to a master cell group (MCG). The method also includes, in response to detecting the RLF with respect to the MCG, the UE storing RLF information. The method also includes the UE activating a timer and sending a first message comprising MCG failure information (e.g., the RLF information). The method also includes the UE receiving a second message after sending the first message and activating the timer. The method also includes the UE, in response to receiving the second message, determining that a condition is satisfied, wherein determining that the condition is satisfied comprises at least determining that the timer is still running. The method also includes, as a result of determining that the condition is satisfied, the UE deleting the RLF information

[0044] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a UE causes the UE to perform the any of the methods disclosed herein. In one embodiment, there is provided a carrier containing the computer program wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium. In another aspect there is provided a UE that is configured to perform the methods disclosed herein. The UE may include memory and processing circuitry coupled to the memory.

[0045] The advantages of the above described method include: 1) The UE will not report redundant measurement report related to a failure that has already been recovered by the network and 2) Future complications/errors are prevented by not sending reports (to nodes/functions handling MDT/SON) regarding problems that are already recovered by network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments. [0047] FIG. 1 shows an exemplary 5GRAN (NG-RAN) architecture.

[0048] FIG. 2 shows higher layer RLF related procedures in LTE.

[0049] FIG. 3 is a message flow diagram according to an embodiment.

[0050] FIG. 4 is a process according to some embodiments.

[0051] FIG. 5 shows a UE according to some embodiments.

DETAILED DESCRIPTION

[0052] 1. Example Realizations related to deleting the RLF report

[0053] 1.1 Deleting the RLF Report on receiving an RRCReconfiguration containing reconfigurationWithSync.

[0054] 1.1.1 The Deletion is Done in the reconfiguration with Sync Procedure

[0055] In one embodiment, the UE shall perform the actions specified in the table below to execute a reconfiguration with sync.

[0056] 1.1.2 The Deletion is done in the reconfiguration procedure

[0057] In some rare cases, reconfigurationWithSync procedure may be performed successfully, but there could be a failure (e.g. reconfiguration failure) while handling/compiling the other information contained in the RRCReconfiguration message. Thus, one alternative is to wait until the preparation of the sending of the complete message before deleting the RLF report. Accordingly, in one embodiment the UE performs the following actions upon reception of the RRCReconfiguration, or upon execution of the conditional configuration (CHO or CPC):

[0058] 1.2 Deleting the RLF report on receiving an RRCRelease

[0059] In one embodiment, when the UE receives RRCRelease message the UE performs a process that includes: 1) stop timer T380, if running; 2) stop timer T320, if running; 3) determine if timer T316 is running; and 4) if it is determined that the time is running, step the timer and clear the information included in VarRLF-Report, if any.

[0060] 1.3 Deleting the RLF report on receiving of MobilityFromNR

[0061] In on embodiment, the UE performs the following steps when the UE receives the

MobilityF romNRCommand:

[0062] As the current RRC specification already captures the storage of the RLF report in the UE internal memory (e.g., in the UE variable named varRLF -Report, which is defined in section 7.4 of TS 38.331 as containing an “RLF-report-rl6” (also defined in TS 38.311) and a PLMN-IdentitiyList) when the EE declares MCG failure (EE stores RLF report, suspends MCG and then the UE sends the MCGFailurelndication message), this disclosure proposes a set of methods wherein the EE can clear the information included in the RLF report (e.g., delete the RLF report) based on the result of the MCG failure recovery.

[0063] For example, in one embodiment the EE clears the contents of varRLF -Report if the EE receives a reconfigurationWithSync (within an RRCReconfiguration message) in response to a MCGFailurelnformation message and while the MCG is suspended. When this happens, the EE follows legacy operations such as stopping the timer T316 and performs the actions related to reconfigurationWithSync procedure and resumes MCG in the new PCell. We note that the RLF report needs to be cleared only after the reconfiguration with sync procedure (i.e., handover command) was successfully performed.

[0064] In another embodiment, the EE clears the contents of varRLF -Report if the EE receives an RRCRelease message in response to a MCGFailurelnformation message and while the MCG is suspended. When this happens, the EE stops T316 and performs the state transition to IDLE/INACTIVE as configured in the RRCRelease message and performs the actions upon going to IDLE/INACTIVE.

[0065] In another embodiment, the EE clears the contents of varRLF -Report if the EE receives a MobilityFromNR/MobilityFromEUTRA message in response to a MCGFailurelnformation and while the MCG is suspended. When this happens, the UE stops T316 and performs the actions related to handover procedure as configured in mobilityControlInfo/reconfigurationWithSync and resumes MCG in the new PCell in LTE/NR. We note that the RLF report needs to be cleared only after the reconfiguration with sync procedure (i.e., handover command) was successfully performed. [0066] FIG. 4 is a flowchart illustrating a process 400, according to an embodiment, for reporting RLF information. Process 400 may begin in step s402.

[0067] Step s402 comprises a UE 302 (see FIG. 3) detecting an RLF with respect to a master cell group (MCG).

[0068] Step s404 comprises the UE, after detecting the RLF, generating and storing RLF information. For example, storing the RLF information comprises storing the RLF information in the variable VarRLF -Report.

[0069] Step s406 comprises the UE activating a timer (e.g., the T316 timer) (i.e., the timer starts running and will expire (stop running) after a certain amount of time has elapsed) and sending to a master node (MN) 304 of the MCG, via a secondary node (SN), a first message 310 (see FIG. 3) comprising MCG failure information (e.g., the RLF information).

[0070] Step s408 comprises the UE receiving a second message 312 (e.g., second message 312 is sent in response to message 310).

[0071] Step s410 comprises the UE, in response to receiving second message 312, determining whether a condition is satisfied, which determining comprises determining whether the timer is still running.

[0072] Step s412 comprises the UE deleting the RLF information as a result of determining that the condition is satisfied (e.g., as a result of determining that the timer is still running or as a result of determining that the time is still running and determining that the second message 312 is a particular message). In one embodiment deleting the RLF information comprises clearing the RLF related information from the VarRLF-Report.

[0073] Step s414 (optional) comprises the UE deactivating (stopping) the timer.

[0074] In some embodiments, second message 312 is one of: i) an RRCReconfiguration message with a reconfigurationWithSync, ii) an RRCRelease message, iii) a MobilityFromNR message, iv) an RRCConnectionReconfigurationMessage with mobilityControlInfo, v) an RRCConnectionRelease message, or vi) a MobilityFromEUTRA message.

[0075] FIG. 5 is a block diagram of UE 302, according to some embodiments. As shown in FIG. 5, UE 302 may comprise: processing circuitry (PC) 502, which may include one or more processors (P) 555 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); communication circuitry 548, which is coupled to an antenna arrangement 549 comprising one or more antennas and which comprises a transmitter (Tx) 545 and a receiver (Rx) 547 for enabling UE 302 to transmit data and receive data (e.g., wirelessly transmit/receive data); and a local storage unit (a.k.a., “data storage system”) 508, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 502 includes a programmable processor, a computer program product (CPP) 541 may be provided. CPP 541 includes a computer readable medium (CRM) 542 storing a computer program (CP) 543 comprising computer readable instructions (CRI) 544. CRM 542 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 544 of computer program 543 is configured such that when executed by PC 502, the CRI causes UE 302 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, UE 302 may be configured to perform steps described herein without the need for code. That is, for example, PC 502 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0076] Summary of Various Embodiments

[0077] Al. A method 400 (see FIG. 4) for reporting RLF information. The method includes: a user equipment, UE 302 detecting s402 an RLF with respect to an MCG; in response to detecting the RLF with respect to the MCG, the UE storing s404 RLF information; the UE activating a timer and sending s406 a first message 310 comprising MCG failure information (e.g., the RLF information); after sending the first message and activating the timer, the UE receiving s408 a second message 312 (e.g., the second message 312 is sent in response to the first message 310 (e.g., in response to the MCG failure information contained in the first message)); the UE, in response to receiving the second message 312, determining s410 that a condition is satisfied, wherein determining that the condition is satisfied comprises at least determining (s410) that the timer is still running; and as a result of determining that the condition is satisfied, the UE deleting s412 the RLF information. [0078] A2. The method of embodiment Al, further comprising the UE deactivating s414 the timer in response to receiving the second message 312.

[0079] A3. The method of embodiment Al or A2, wherein the second message 312 is one of: i) an RRCReconfiguration message with a reconfigurationWithSync, ii) an RRCRelease message, iii) a MobilityFromNR message, iv) an RRCConnectionReconfigurationMessage with mobilityControlInfo, v) an RRCConnectionRelease message, or vi) a MobilityFromEUTRA message.

[0080] A4. The method of any one of the above embodiments, wherein determining that the condition is satisfied further comprises the UE determining that the second message is an RRC message containing a reconfiguration with synchronization indicator (e.g., an RRCReconfiguration message containing a ReconfigurationWithSync information element (IE)), wherein the UE performs the deleting step as a result of determining that the timer is still running and determining that the second message is an RRC message containing a reconfiguration with synchronization indicator.

[0081] A5. The method of any one of embodiments A1-A3, wherein determining that the condition is satisfied further comprises the UE determining that the second message is a release message (e.g., an RRCRelease message), wherein the UE performs the deleting step as a result of determining that the timer is still running and determining that the second message is a release message.

[0082] A6. The method of any one of embodiments A1-A3, wherein determining that the condition is satisfied further comprises the UE determining that the second message is one of: i) a MobilityFromNR message, ii) an RRCConnectionReconfigurationMessage with mobilityControlInfo, iii) an RRCConnectionRelease message, or iv) a MobilityFromEUTRA message, wherein the UE performs the deleting step as a result of determining that the timer is still running and determining that the second message is one of: i) a MobilityFromNR message, ii) an RRCConnectionReconfigurationMessage with mobilityControlInfo, iii) an RRCConnectionRelease message, or iv) a MobilityFromEUTRA message.

[0083] Bl. A computer program 543 comprising instructions 544 which when executed by processing circuitry 502 of a user equipment, UE 302 causes the UE 302 to perform the method of any one of the above embodiments. [0084] B2. A carrier containing the computer program of embodiment Bl, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium 542.

[0085] Cl . A user equipment, UE 302, the UE being adapted to perform the method of any one of the above embodiments.

[0086] Dl. A user equipment, EE 302, the EE comprising: processing circuitry 502; and a memory 542, said memory containing instructions 544 executable by said processing circuitry, whereby said UE is operative to perform the method of any one of the above embodiments.

[0087] El . A method executed by a EE for reporting radio link failure (RLF) related information. The UE is operating in dual connectivity between a master node (MN) and a secondary node (SN), where the MN is providing a set of serving cells, a master cell group (MCG), and the SN is providing a set of serving cells, a secondary cell group (SCG). The method includes: 1) the EE detecting an RLF on the MCG; 2) the EE generating an RLF report and storing it; and 3) the UE initiating the MCG failure recovery procedure.

[0088] E2. The method of embodiment El, wherein initiating the MCG failure recovery procedure comprises: the UE starting a timer T316; the EE preparing an MCG Failure Information, including information about the failure cause as well as measurements (in serving cells as well as neighbor cells) at the time of failure; and the UE sending the MCG failure information to the MN, via the SN (using either the secondary leg of split SRBl or SRB3, if configured). After determining that the network has responded to the MCG failure information before T316 has expired, the UE may delete the RLF report. In some embodiments, determining that the network has responded to the MCG failure information before T316 has expired comprise the EE receiving one of the following: A) in the case the MN is an NR node: i) an RRCReconfiguration message with a reconfigurationWithSync, ii) an RRCRelease message, or iii) a MobilityFromNR message or B) in the case the MN is an LTE node: i) an RRCConnectionReconfigurationMessage with mobilityControlInfo, ii) an RRCConnectionRelease message, or iii) a MobilityFromEUTRA message. In one alternative, the RLF report is deleted in all the above cases (i.e. on receiving of the reconfiguration, release or mobilityFromNR/mobilityFromEUTRA messages). In another alternative, the RLF report is not deleted in the reception of the release message. In another alternative, the RLF report is not deleted in the reception of the mobilityFromNR/mobilityFromLTE message.

[0089] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0090] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[0091] Abbreviations

[0092] ACK Acknowledgement

[0093] AP Application Protocol

[0094] BSR Buffer Status Report

[0095] BWP Bandwidth Part

[0096] C-RNTI Cell Radio Network Temporary Identifier

[0097] CA Carrier Aggregation

[0098] CE Control Element

[0099] CP Control Plane

[0100] CQI Channel Quality Indicator

[0101] DC Dual Connectivity

[0102] DCI Downlink Control Information

[0103] DL Downlink

[0104] DRB Data Radio Bearer [0105] eNB (EUTRAN) base station

[0106] E-RAB EUTRAN Radio Access Bearer

[0107] FDD Frequency Division Duplex

[0108] gNB NR base station

[0109] GTP-U GPRS Tunneling Protocol - User Plane

[0110] IP Internet Protocol

[0111] LTE Long Term Evolution

[0112] MCG Master Cell Group

[0113] MAC Medium Access Control

[0114] MeNB Master eNB

[0115] MgNB Master gNB

[0116] MN Master Node

[0117] NACK Negative Acknowledgement

[0118] NR New Radio

[0119] PDCP Packet Data Convergence Protocol

[0120] PCell Primary Cell

[0121] PCI Physical Cell Identity

[0122] PSCell Primary SCell

[0123] PUSCH Phyical Uplink Shared Channel

[0124] RLC Radio Link Control

[0125] RLF Radio Link Failure

[0126] RRC Radio Resource Control

[0127] SCell Secondary Cell

[0128] SCG Secondary Cell Group [0129] SCTP Stream Control Transmission Protocol

[0130] SeNB Secondary eNB

[0131] SINR Signal to Interference plus Noise Ratio

[0132] SN Secondary Node

[0133] SR Scheduling Request

[0134] SRB Signaling Radio Bearer

[0135] SUL Supplementary uplink

[0136] TDD Time Division Duplex

[0137] TEID Tunnel Endpoint IDentifier

[0138] TNL Transport Network Layer

[0139] UCI Uplink Control Information

[0140] UDP User Datagram Protocol

[0141] UE User Equipment

[0142] UL Uplink

[0143] UP User Plane

[0144] URLLC Ultra Reliable Low Latency Communication

[0145] X2 Interface between base stations