Layer 1 / layer 2 triggered mobility cell transitions

Abstract

A method performed by a user equipment (UE), the method comprising: receiving (201, 701) a layer 1 / layer 2 triggered mobility (LTM) configuration of one or more LTM candidate target cells, where the one or more LTM candidate target cells comprise a first target cell; receiving (202, 702) a first command for performing an LTM cell transition to a first target cell; obtaining (203, 703) a first Layer 2 (L2) reset indication, the first L2 reset indication comprising an indication as to whether an L2 reset should be performed during the LTM cell transition to the first target cell; and performing (204, 704) the LTM cell transition to the first target cell according to the first command.

Description

Technical Field

[0001] The present disclosure relates to the field of telecommunication networks, and in particular, to methods and apparatuses for layer 1 / layer 2 triggered mobility (LTM) cell handover. Background Art

[0002] L1 / L2 Triggered Mobility

[0003] In the 3rd Generation Partnership Project (3GPP) Release 18, a work item called "Further New Radio (NR) Mobility Enhancements" has been agreed upon. This work item includes a technical area called "Layer 1 (L1) / Layer 2 (L2)-Based Inter-Cell Mobility". According to the Work Item Description (WID): RP-222332, 3GPP Work Item Description: Further NR Mobility Enhancements (submitted by MediaTek, 3GPP TSG RAN Meeting #97-e, e-Meeting, September 12 - 16, 2022), when a User Equipment (UE) moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently, the serving cell change is triggered by layer 3 (L3) measurements and is completed through a synchronous reconfiguration triggered by Radio Resource Control (RRC) signaling for changing the Primary Cell (PCell) and the PSCell (which are the primary and secondary cells in Long Term Evolution (LTE) and the primary and secondary cell group (SCG) cells in NR), and the addition of the Secondary Cell (SCell) is released when applicable. All cases involve a complete L2 (and L1) reset, resulting in longer latency, greater overhead, and longer interruption times compared to beam switching mobility. The goal of L1 / L2-based inter-cell mobility is to achieve serving cell change via L1 / L2 signaling in order to reduce latency, overhead, and interruption time.

[0004] In this work item, according to WID RP-222332, the following is included as one of the goals of this work:

[0005]

[0006] In 3GPP, discussions have started on solutions for L1 / L2-based inter-cell mobility (which is also referred to as L1 / L2 triggered mobility (LTM) or lower layer triggered mobility).

[0007] The basic principle of L1 / L2-triggered mobility is as follows: The network pre-configures for the UE the RRC configuration for each LTM candidate target cell, which is also referred to as the LTM candidate target cell configuration. Such an LTM candidate target cell configuration can be an RRC reconfiguration (RRCReconfiguration) message or one or more information elements (IEs) / fields / parameters such as CellGroupConfig (including at least the special cell (SpCell) configuration and the configuration of one or more SCell associated with a cell group (e.g., the master cell group (MCG) or SCG)). The UE performs low-layer measurements (e.g., synchronization signal (SS) reference signal received power (RSRP) and / or L1 RSRP measurements) on these candidate LTM candidate target cells and sends the corresponding measurement reports to the network. Then, the network triggers the execution of an LTM cell transition, so the UE receives low-layer signals (such as media access control (MAC) control element (CE) or downlink control information (DCI)), and the UE connects to the target cell based on this low-layer signal and switches to the configuration of the LTM candidate target cell.

[0008] At the 3GPP RAN2#119-e and RAN2#119bis-e meetings, a number of agreements were reached on L1 / L2-triggered mobility, and the following items are among these agreements:

[0009] · Receive the L1 / L2 inter-cell mobility candidate (target) configuration within the RRC message before triggering the L1 / L2 dynamic transition.

[0010] · RAN2 uses "LTM" as the term for L1 / L2-triggered mobility.

[0011] · Use the term "cell switch" to represent the process of triggering a cell change via the LTM feature

[0012] · Use the term "subsequent" LTM for the case where the cell transition between L1 / L2 mobility candidates is done without an RRC reconfiguration in between.

[0013] · RAN2 assumes that sequential L1 / L2 cell changes between candidates can be supported without an RRC reconfiguration.

[0014] · RAN2 assumes that the L1 / L2 mobility trigger information is transmitted in the MAC CE, and it is for further study (FFS) if the MAC CE or DCI is used for the actual trigger.

[0015] · RAN2 assumes that the MAC CE used for L1 / L2 mobility trigger contains at least the candidate configuration index.

[0016] · For R2, it is assumed that when the UE performs cell handover between L1 and L2 cells, whether the UE performs a partial MAC reset or a full MAC reset (it remains to be further studied what a partial reset is, for example, to avoid data loss), reconstructs the radio link control (RLC), and performs data recovery using the packet data convergence protocol (PDCP) is explicitly controlled by the network. R2 assumes that this can be configured by RRC. Whether MAC CE indication is required remains to be further studied.

[0017] At the RAN3#117-e and RAN3#117bis-e meetings, several agreements were reached on L1 / L2-based inter-cell mobility, and the following items are among these agreements:

[0018]

[0019] Additional background information can be found in 3GPP Technical Specification 38.473, version 17.2.0, F1 Application Protocol (F1AP). SUMMARY OF THE INVENTION

[0020] There are currently some challenges. In L3 mobility, in both LTE and NR, an L2 reset (at least a MAC reset) is always performed as part of the synchronization reconfiguration process, as shown in the following excerpt from 3GPP TS 38.331:

[0021] ******************************************************************** [38.331]

[0023] 5.3.5.5.2 Synchronization Reconfiguration

[0024] The UE shall perform the following actions to perform synchronization reconfiguration.

[0025] 1> If AS security is not activated, perform the actions specified in 5.3.11 when entering the RRC_IDLE state, and end the process with the release cause "other";

[0026] […]

[0027] 1> Reset the MAC entity of this cell group;

[0028] […]

[0029] ********************************************************************

[0030] Since the main objective of L1 / L2-triggered mobility is to reduce latency and interruption time, 3GPP RAN2 assumes that L2 continues as much as possible (e.g., within the distributed unit (DU)), without reset, with the goal of avoiding data loss and additional latency for data recovery. However, since this may not be avoidable in all scenarios (e.g., performing an inter-DU LTM cell transition), one challenge is how to avoid performing MAC reset, RLC reconstruction, and PDCP recovery when they are not needed (e.g., for the in-DU case), but still perform these operations when they are required (e.g., for the inter-DU case). In other words, how does the UE determine whether to perform an L2 reset during an LTM cell transition from the first cell to a candidate cell?

[0031] An additional challenge is to avoid RRC reconfiguration during subsequent LTM cell transitions: i.e., when the UE is configured with LTM candidate target cell configurations (e.g., cell A, cell B, and cell C), while connected to the first cell (e.g., SpCell X), e.g., where these cells are associated with different distributed units (DUs). Figure 1 This scenario is illustrated. Then, the UE performs an LTM cell transition to a candidate cell (e.g., to cell A, in the same DU as SpCell X), but still considers the previous LTM candidate target cells (e.g., cell B and cell C) as possible candidates. Assuming that cell X and cell A are in the same DU, this cell transition will not require an L2 reset.

[0032] Now, assume that the UE in cell A moves to cell B and an L2 reset will be required (although an L2 reset would also be required if the UE moved from cell X to cell B, so the UE can still apply the LTM candidate target cell configuration it received in cell X). However, if the UE receives an LTM cell transition command (e.g., MACCE) indicating a change to cell C from cell B, then in principle an L2 reset will not be required (since cell B and cell C are served by the same DU), although an L2 reset would be required when configuring cell C (since the UE was in cell X when cell C was configured as a candidate). This causes the UE to perform an unnecessary MAC reset, which increases the LTM cell transition latency. Similarly, if the UE subsequently receives an LTM transition command indicating a transition back to cell A while in cell C, the stored target cell configuration will not include a MAC reset (since no MAC reset was required for the LTM transition from cell X to cell A), but a MAC reset will be required in this case since cell C and cell A are served by different DUs. This means that the LTM cell transition will fail.

[0033] In summary, the challenge is that the circumstances related to whether these L2 resets are performed may have changed because a given candidate cell that was previously controlled by a DU different from the serving DU is controlled by the serving DU after an LTM cell transition, and vice versa. In other words, for subsequent LTM cell transitions, it is not feasible to configure an indication for L2 reset within the LTM candidate target cell configuration because the need for L2 reset may change when the UE performs a subsequent LTM cell transition implementation.

[0034] Certain aspects of the present disclosure and their embodiments may provide solutions to these challenges or other challenges.

[0035] According to a first aspect, a method performed by a UE is provided. The method includes receiving an LTM configuration of one or more LTM candidate target cells. The one or more LTM candidate target cells include a first target cell. The method further includes: receiving a first command for performing an LTM cell transition to the first target cell; obtaining a first layer 2 (L2) reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during the LTM cell transition to the first target cell; and performing an LTM cell transition to the first target cell according to the first command.

[0036] According to a second aspect, a method performed by a network node serving a UE is provided. The method includes sending an LTM configuration of one or more LTM candidate target cells to the UE. The one or more LTM candidate target cells include a first target cell.

[0037] According to a third aspect, a UE including a processor and a memory is provided, the memory containing instructions executable by the processor, whereby the UE is operable to receive an LTM configuration of one or more LTM candidate target cells, wherein the one or more LTM candidate target cells include a first target cell. The UE is further operable to: receive a first command for performing an LTM cell transition to the first target cell; obtain a first L2 reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during the LTM cell transition to the first target cell; and perform an LTM cell transition to the first target cell according to the first command.

[0038] According to a fourth aspect, a UE adapted to perform the method according to any embodiment of the first aspect is provided.

[0039] According to a fifth aspect, a network node including a processor and a memory is provided, the memory containing instructions executable by the processor, whereby the network node is operable to send an LTM configuration of one or more LTM candidate target cells to the UE. The one or more LTM candidate target cells include a first target cell.

[0040] According to a sixth aspect, there is provided a network node adapted to perform the method according to any embodiment of the second aspect.

[0041] According to a seventh aspect, there is provided a computer program product comprising a computer-readable medium having computer-readable code embodied therein, the computer-readable code being configured to, when executed by a suitable computer or processor, cause the computer or processor to perform the method according to any embodiment of the first aspect, the second aspect, or the third aspect.

[0042] Thus, the present disclosure presents methods for User Equipment (UE) In these methods, the UE is configured with a serving cell (e.g., a SpCell, where there may be one or more SCell). The UE receives an LTM configuration of an L1 / L2-triggered mobility (LTM) candidate target cell, and also receives a lower layer command for performing an LTM cell transition to the target cell, and also obtains an indication of whether to perform an L2 reset during the execution of the LTM cell transition. In response, the UE performs the LTM cell transition, and based on the obtained indication, the UE determines whether to perform an L2 reset during the LTM cell transition.

[0043] In some methods, the UE receives an LTM configuration of an L1 / L2-triggered mobility (LTM) candidate target cell of a first target cell and an LTM configuration of an LTM candidate target cell of a second target cell, and also receives a first lower layer command for performing an LTM cell transition to the first target cell, and also obtains an indication of whether to perform an L2 reset during the execution of the LTM cell transition. In response, the UE performs the LTM cell transition to the first target cell, and based on the obtained indication, the UE determines whether to perform an L2 reset during the LTM cell transition. Then, when in the first target cell, the UE receives a second lower layer command for performing an LTM cell transition to the second target cell, and also obtains an indication of whether to perform an L2 reset during the execution of the LTM cell transition. In response, the UE performs the LTM cell transition to the second target cell, and determines whether to perform an L2 reset during the LTM cell transition based on the obtained indication.

[0044] The present disclosure also proposes methods for Source Network Node (such as a source gNB, a source distributed unit, or a serving network node such as a serving DU). In these methods, the source network node processes an indication of whether to perform an L2 reset during the execution of an LTM cell transition for a UE configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0045] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is sent to the UE. In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is included in a MAC CE (e.g., the same MAC CE as the MAC CE with LTM cell transition information), or in a separate MAC CE.

[0046] The present disclosure also provides methods for Third Network Node (or a serving network node) (such as a (serving) Central Unit (CU), a (serving) gNB-CU). In these methods, a third network node processes an indication of whether to perform an L2 reset during the execution of an LTM cell transition for a UE that is configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0047] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is included in the configuration of an LTM candidate target cell.

[0048] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is sent to the UE.

[0049] The present disclosure also provides methods for First Target Network Node (such as a first target gNB, a first target DU, or a first target gNB-DU). In these methods, a first target network node will process an indication of whether to perform an L2 reset during the execution of an LTM cell transition for a UE that is configured with a serving cell (e.g., cell X) and an LTM configuration including one or more candidate cells for LTM.

[0050] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is sent to the UE. In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is included in a MAC CE (e.g., the same MAC CE as the MAC CE with LTM cell transition information), or in a separate MAC CE.

[0051] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is included in the configuration of an LTM candidate target cell.

[0052] In some methods, an indication of whether to perform an L2 reset during the execution of an LTM cell transition is sent to a third network node.

[0053] The present disclosure also provides methods for Second Target Network NodeA method for (such as a second target gNB, a second target DU, or a second target gNB-DU). In these methods, the second target network node will process an indication on whether to perform an L2 reset during the execution of LTM cell transition for a UE configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0054] In some methods, an indication on whether to perform an L2 reset during the execution of LTM cell transition is included in the configuration of the LTM candidate target cell.

[0055] In some methods, an indication on whether to perform an L2 reset during the execution of LTM cell transition is sent to a third network node.

[0056] Certain embodiments may provide one or more of the following technical advantages. The proposed solution enables the network to control UE L2 reset during LTM cell transition when the UE moves along pre-configured candidate cells, thus avoiding the need to reconfigure the LTM candidate configuration to avoid unnecessary L2 resets and LTM failures in cases where an L2 reset will be required. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Some embodiments contemplated herein will now be described more fully with reference to the accompanying drawings, in which:

[0058] Figure 1 is a schematic illustration of the configuration of a cell;

[0059] Figure 2 is a flowchart showing a method performed by a UE according to some embodiments;

[0060] Figure 3 is a flowchart showing a method performed by a first network node according to some embodiments;

[0061] Figure 4 is a flowchart showing a method performed by a third network node according to some embodiments;

[0062] Figure 5 is a schematic illustration of a system architecture according to some embodiments;

[0063] Figure 6 is a signaling diagram showing a technique according to some embodiments;

[0064] Figure 7 is a flowchart showing another method performed by a UE according to some embodiments;

[0065] Figure 8 is a flowchart showing a method performed by a UE according to some embodiments;

[0066] Figure 9 is a schematic diagram of a communication system according to some embodiments;

[0067] Figure 10 is a block diagram showing a user equipment according to some embodiments;

[0068] Figure 11 is a block diagram showing a network node according to some embodiments; and

[0069] Figure 12 is a block diagram showing a virtualized environment. Detailed Description

[0070] Some embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. The embodiments are provided by way of example only to convey the scope of the subject matter to those skilled in the art.

[0071] This disclosure refers to the term "L1 / L2-based inter-cell mobility" as used in the work item descriptions in 3GPP, although this disclosure may also interchangeably use the terms L1 / L2 mobility, low layer mobility (LLM), L1 / L2-triggered mobility (LTM), low layer-triggered mobility (LTM), L1 mobility, L1-based mobility, L1 / L2-centric inter-cell mobility, or L1 / L2 inter-cell mobility.

[0072] The basic principle of L1 / L2-based inter-cell mobility is that the UE receives low layer signaling from the network, which indicates to the UE a change in its serving cell (e.g., a PCell change from a source PCell to a target PCell) and a possible change in the beam(s) to monitor for the control channel, e.g., a change in the transmission configuration indicator (TCI) state. Here, "low layer signaling" refers to messages or signaling of the low layer protocol.

[0073] The low layer protocol refers to the low layer protocol relative to the RRC protocol in the air interface protocol stack. For example, the media access control (MAC) is considered a low layer protocol because it is "below" the RRC in the air interface protocol stack, and in this case, the low layer signaling / message can correspond to a MAC control element (MAC CE). Another example of a low layer protocol is layer 1 (L1 or the physical layer), and in this case, the low layer signaling / message can correspond to downlink control information (DCI). Another related aspect is that in a multi-beam scenario, a cell can be associated with multiple synchronization signal blocks (SSBs), and during a half-frame, different SSBs can be sent in different spatial directions (i.e., using different beams, across the coverage area of the cell). Similar reasoning can apply to channel state information reference signal (CSI-RS) resources, which can also be sent in different spatial directions.

[0074] The phrase "LTM cell transition procedure" refers to the procedure by which a UE changes its cell from a source cell to a target cell using L1 / L2-triggered mobility. In the context of L1 / L2-based inter-cell mobility or L1 / L2-triggered mobility (LTM), the LTM cell transition procedure is sometimes also referred to as dynamic transition, LTM transition, (LTM) cell transition, (LTM) serving cell change, or (LTM) cell change. Even when using the term "cell change", it can include changes to the entire cell group configuration, which includes changes to the SpCell of the cell group (e.g., PCell change, or PSCell change) and SCell changes (e.g., addition, modification, and / or release of one or more SCell).

[0075] The phrase "lower layer signaling indicating the LTM cell transition procedure to the UE" used in this document refers to the message / signal / indication sent by the source network node to the UE for providing the information required for the LTM cell transition procedure to the UE. The fact that this signaling is "lower layer" means that this signaling is at a layer below the RRC layer in the protocol stack, such as signaling in L1 and / or L2, such as MAC CE. When the UE receives the lower layer signaling indicating the LTM cell transition procedure to the UE, it starts to execute the LTM cell transition procedure. However, this does not exclude the UE from starting to execute the LTM cell transition procedure based on other triggers or events.

[0076] The present disclosure relates to at least one configuration of an LTM candidate target cell and the UE is configured with at least one LTM candidate target cell. The configuration may be an RRC configuration such as encapsulated in an RRC reconfiguration message, which the UE receives when configured with inter-cell mobility between DU L1 / L2. The configuration of the LTM candidate target cell includes the configuration that the UE needs to start operating accordingly when performing an LTM cell transition procedure to the LTM candidate target cell (e.g., when receiving lower layer signaling indicating the LTM cell transition procedure to the LTM candidate target cell), and the LTM candidate target cell becomes the target cell and the current (new) SpCell, or an SCell on the serving frequency. The configuration of the LTM candidate target cell includes parameters of the serving cell (or serving cells, such as a cell group), including one or more sets of parameters, such as an RRC reconfiguration message, an IECellGroupConfig, or an IE SCellConfig (or an IE SCellConfig in the case of a secondary cell). In one example, the configuration of the LTM candidate target cell may include one or more of the following items: (i) the PCell configuration of the primary cell group (MCG) and one or more SCell configurations; and (ii) the PSCell configuration of the secondary cell group (SCG) and one or more SCell configurations. When referring to the configuration of the LTM candidate target cell, the terms (LTM) candidate configuration, LTM configuration, (LTM) candidate target cell configuration, (LTM) target candidate (cell) configuration may be used interchangeably herein.

[0077] The present disclosure relates to a serving cell. A serving cell is a cell configured for the UE, such as an SpCell, a PCell, a PSCell, or an SCell.

[0078] The present disclosure relates to a source cell and a target cell. A source cell is a cell that is configured as the serving cell of the UE before performing an LTM cell transition procedure. A target cell is a cell that is configured as the serving cell of the UE (e.g., an SpCell, a PCell, a PSCell, or an SCell) after performing an LTM cell transition procedure or due to performing an LTM cell transition procedure. The target cell may include the cell indicated in the lower layer signaling indicating the LTM cell transition procedure to the UE, or the cell configured due to the RRC configuration of the UE transitioning to the LTM candidate target cell, which is provided by the configuration index in the lower layer signaling indicating the LTM cell transition procedure to the UE. In the context of the LTM cell transition procedure performed by the UE, a given cell may be a source cell, a target cell, both a source cell and a target cell, or neither a source cell nor a target cell.

[0079] The present disclosure relates to an "L2 reset", which may be a MAC reset, a partial MAC reset, an RLC re-establishment, a PDCP data recovery, a PDCP re-establishment, or any combination thereof. Both an "L2 reset flag" and an "indication of L2 reset / no L2 reset / partial L2 reset" indicate whether to perform a MAC reset, a partial MAC reset, an RLC re-establishment, a PDCP data recovery, a PDCP re-establishment, or any combination thereof.

[0080] The present disclosure also relates to an "L2 reset indication" or a "reset indication", which is an indication of whether the UE will perform an L2 reset during an LTM cell transition.

[0081] Figure 2 is a flowchart showing a method 200 performed by a UE according to some embodiments. The UE may operate in a dual connection having an MCG including a PCell and at least one SCG including a PSCell.

[0082] Method 200 includes: at step 201, receiving an LTM configuration of one or more LTM candidate target cells, where the one or more LTM candidate target cells include a first target cell. The LTM configuration may be received from a third network node (e.g., a central unit (CU) serving the UE). The LTM configuration may be received from the CU serving the UE or a distributed unit (DU) serving the UE. The LTM configuration may be included in an RRC reconfiguration message.

[0083] Method 200 further includes: at step 202, receiving a first command for performing an LTM cell transition to the first target cell. The first command may be included in a lower layer signal. The first command may be included in a MAC CE or DCI. The first command for performing an LTM cell transition to the first target cell may be received from a first network node.

[0084] Method 200 further includes: at step 203, obtaining a first L2 reset indication, which includes an indication of whether an L2 reset should be performed during the LTM cell transition to the first target cell. The L2 reset may include a reset of one or more of a plurality of L2 protocols. The L2 reset may include a reset of only one or more of a plurality of L2 protocols.

[0085] The L2 reset may include one or more of the following: a full L2 reset of one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a MAC reset; a partial MAC reset; a re-establishment; an RLC re-establishment; a PDCP re-establishment; a data recovery; and a PDCP data recovery.

[0086] The step 203 of obtaining the first L2 reset indication may include: receiving the first L2 reset indication in the same L2 signaling as the LTM configuration of the first target cell; or receiving the first L2 reset indication in a different L2 signaling from the LTM configuration of the first target cell. Therefore, the first L2 reset indication may be included in (contained in) the LTM configuration received in step 201. In these embodiments, the step 203 of obtaining the first L2 reset indication is implemented by the step 201 of receiving the LTM configuration.

[0087] The step 203 of obtaining the first L2 reset indication may include receiving the first L2 reset indication from a first network node. The first network node may be a DU that provides services to the UE. The first L2 reset indication may be received in a MAC CE.

[0088] The first L2 reset indication may relate to one or more of the following items: a MAC entity, a cell group, an L2 protocol entity, a radio bearer, a data radio bearer, a signaling radio bearer, or an RLC bearer. The first L2 reset indication may include a list of one or more cells, where if the UE is in one of the listed cells when the UE performs an LTM cell transition, the L2 reset should not be performed.

[0089] The method 200 further includes: at step 204, performing an LTM cell transition to the first target cell according to the first command. Performing the LTM cell transition to the first target cell may include: determining whether an L2 reset should be performed during the LTM cell transition to the first target cell based on the first L2 reset indication. Performing the LTM cell transition may further include: in response to determining that the L2 reset should be performed, performing the L2 reset during the LTM cell transition to the first target cell; and in response to determining that the L2 reset should not be performed, performing the LTM cell transition to the first target cell without performing the L2 reset.

[0090] The one or more LTM candidate target cells may further include a second target cell. The method 200 may further include: after performing the cell transition to the first target cell in 204, receiving a second command for performing an LTM cell transition to the second target cell. The method 200 may include: obtaining a second L2 reset indication, where the second L2 reset indication includes an indication of whether an L2 reset should be performed during the LTM cell transition to the second target cell; and performing the LTM cell transition to the second target cell according to the second command.

[0091] The LTM cell transition to the second target cell may include: determining, based on a second L2 reset indication, whether an L2 reset should be performed during the LTM cell transition to the second target cell. The method may further include: in response to determining that an L2 reset should be performed, performing an L2 reset during the LTM cell transition to the second target cell; and in response to determining that an L2 reset should not be performed, performing the LTM cell transition to the second target cell without performing an L2 reset.

[0092] Figure 3 FIG. 4 is a flowchart showing a method 300 performed by a first network node according to some embodiments. The first network node may be, for example, a source network node (e.g., S-DU), a first target network node, or a second target network node. The first network node may be a DU.

[0093] Method 300 includes: at step 301, sending a first L2 reset indication that includes an indication as to whether an L2 reset should be performed during the LTM cell transition of the UE to the first target cell. The first L2 reset indication may be sent to the UE. The first L2 reset indication may be sent to a third network node, such as a central unit.

[0094] The first L2 reset indication may be sent in a MAC CE. The MAC CE may further include an LTM configuration of one or more LTM candidate target cells, where the one or more LTM candidate target cells include the first target cell. The first L2 reset indication may be included in the LTM configuration of one or more LTM candidate target cells, where the one or more LTM candidate target cells include the first target cell. The first L2 reset indication may be sent in the same L2 signaling as the LTM configuration of one or more LTM candidate target cells, or the first L2 reset indication may be sent in different L2 signaling from the LTM configuration of one or more LTM candidate target cells.

[0095] The L2 reset may include resetting one or more of a plurality of L2 protocols. The L2 reset may include resetting only one or more of a plurality of L2 protocols. The L2 reset may include one or more of the following: a full L2 reset of one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control (MAC) reset; a partial MAC reset; a reconstruction; a radio link control (RLC) reconstruction; a packet data convergence protocol (PDCP) reconstruction; a data recovery; and a PDCP data recovery.

[0096] The UE can operate in a cell group controlled by a first network node. The UE can operate under dual connectivity with an MCG including a PCell and at least one SCG including a PSCell, where the serving cell includes the PCell and the PSCell.

[0097] Figure 4 It is a flowchart showing a method 400 performed by a third network node according to some embodiments. The third network node is serving the UE. The third network node can be a CU or a DU.

[0098] Method 400 includes: at step 401, sending an LTM configuration of one or more LTM candidate target cells to the UE, where the one or more LTM candidate target cells include a first target cell. The LTM configuration can be included in an RRC reconfiguration message.

[0099] Method 400 can include sending a first L2 reset indication to the UE, the first L2 reset indication including an indication of whether an L2 reset should be performed during an LTM cell transition to the first target cell. The first L2 indication can be sent together with the LTM configuration of one or more LTM candidate target cells. The first L2 reset indication can be sent in the same L2 signaling as the LTM configuration of one or more candidate target cells. The first L2 reset indication can be included in the LTM configuration. Alternatively, the first L2 reset indication can be sent in different L2 signaling from the LTM configuration of one or more candidate target cells.

[0100] The L2 reset can include resetting one or more of a plurality of L2 protocols. The L2 reset can include resetting only one or more of a plurality of L2 protocols. The L2 reset can include one or more of the following: a full L2 reset for one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a MAC reset; a partial MAC reset; a reconstruction; an RLC reconstruction; a PDCP reconstruction; a data recovery; and a PDCP data recovery.

[0101] The first L2 reset indication can include a list of one or more cells, where if the UE is in one of the listed cells when the UE performs an LTM cell transition, the L2 reset should not be performed.

[0102] The first L2 indication can be received from a first network node (e.g., Figure 3 the first network node of method 300). The first network node can be a DU.

[0103] The first L2 indication can be received from a first target network node. The first target network node can be a candidate DU.

[0104] Figure 5 The system architecture including entities involved in the technologies described herein is shown. The user equipment (UE) 501 is a wireless terminal (such as a cellular smart phone), which is sometimes connected to the source network node 502 through the wireless interface 504 and sometimes connected to the first target network node 503, and the UE 501 is connected to the first target network node 503 through the wireless interface 505. In some cases, the UE 501 is connected to the second target network node 513, and the UE 501 is connected to the second target network node 513 through the wireless interface 514.

[0105] In the context of the mobility process of the UE (such as the LTM cell transition process), the source network node 502 (sometimes also referred to as the serving network node) controls the serving cell 509 (which can be referred to as the source cell in the context of the UE's mobility process), and the first target network node 503 controls the first target cell 510. In the context of the UE's mobility process, the second target cell 516 can alternatively be controlled by the first target network node 503, the second target network node 513, or the source network node 502. Each of the source network node 502 and the first target network node 503 can be a base station (such as a gNB), or for example, in the case of a distributed CU / DU radio access network (RAN) architecture, it can be a distributed unit, sometimes referred to as a gNB-DU or DU. Thus, the source network node 502 corresponds to the source DU, which is sometimes also referred to as the serving DU (S-DU), and the first target network node 503 corresponds to the target DU (T-DU). Both the source network node 502 and the target network node 503 are connected to the third network node 506, which can be referred to as the serving network node.

[0106] In addition, in the case of a distributed CU / DU RAN architecture, the third network node 506 can be a central unit (CU) (sometimes also referred to as the serving CU), which is called a gNB-CU, CU, gNB-CU control plane (gNB-CU-CP) or gNB-CU user plane (gNB-CU-UP), or a core network node such as a user plane function (UPF) or an access and mobility management function (AMF).

[0107] The second target network node 513 can be a base station (such as, for example, a gNB), or a distributed unit in the case of a distributed CU / DU RAN architecture, which is sometimes referred to as a gNB-DU or DU, (second) target DU, (second) T-DU.

[0108] In certain embodiments, methods for operating a UE are presented. In these methods, the UE is configured with a serving cell, and the UE receives an LTM configuration including one or more LTM candidate target cells. The UE also obtains an L2 reset indication (i.e., an indication as to whether to perform an L2 reset during an LTM cell transition), and determines whether to perform an L2 reset during the LTM cell transition based on the L2 reset indication.

[0109] In some embodiments, the UE receives an LTM configuration of an LTM candidate target cell and also receives a lower layer command for performing an LTM cell transition to the target cell. The UE also obtains an L2 reset indication and, in response, performs an LTM cell transition to the target cell. Based on the obtained L2 reset indication, the UE determines whether to perform an L2 reset during the LTM cell transition.

[0110] In some embodiments, the UE receives an LTM configuration of an LTM candidate target cell for a first target cell and an LTM configuration of an LTM candidate target cell for a second target cell. The UE also receives a first lower layer command for performing an LTM cell transition to the first target cell, and the UE also obtains an L2 reset indication. In response, the UE performs an LTM cell transition to the first target cell, and based on the obtained L2 reset indication, the UE determines whether to perform an L2 reset during the LTM cell transition. Then, when in the first target cell, the UE receives a second lower layer command for performing an LTM cell transition to the second target cell and also obtains an L2 reset indication. Then, in response, the UE performs an LTM cell transition to the second target cell, and based on the obtained L2 reset indication, the UE determines whether to perform an L2 reset during the LTM cell transition.

[0111] The L2 reset indication (i.e., an indication as to whether to perform an L2 reset during an LTM cell transition) can be an indication as to whether to perform a reset, a partial (L2) reset, a reconstruction, or a data recovery of at least one of the L2 protocol sublayers or L2 protocol entities configured for the UE.

[0112] The L2 reset indication can be one or a combination of an indication as to whether to perform a partial L2 reset, a MAC reset, a partial MAC reset, an RLC reconstruction, a PDCP data recovery, a PDCP reconstruction. That is, the L2 reset indication can individually indicate whether to perform a reset / recovery / reconstruction for each layer 2 protocol layer.

[0113] In some examples, the L2 reset indication can be encoded as a list with corresponding fields for MAC, RLC, and PDCP, as follows:

[0114]

[0115] The benefit of each protocol layer (MAC, RLC, PDCP) having a separate reset indication is that it allows the network to flexibly control whether to perform a reset / re-establishment for each protocol layer. For example, the network deployment can be such that: for a specific LTM cell handover process, only the MAC entity needs to be relocated from one network node, hardware, or software entity to another network node, hardware, or software entity, while for example, if the current node, hardware, or software entity of the RLC and PDCP protocol entities can serve both the source cell and the target cell, it may not be necessary to move the RLC and PDCP protocol entities. In this case, the network only indicates a MAC reset to the UE, and since no RLC re-establishment is performed afterwards, the amount of data lost or needing retransmission on the PDCP can be reduced compared to an RLC re-establishment (where the RLC buffer is flushed).

[0116] On the other hand, if the RLC entity also needs to be moved from the source to the target node, hardware, or software entity on the network side, the network will indicate a MAC reset, an RLC re-establishment, and a PDCP recovery in order to also trigger the RLC re-establishment and the PDCP data recovery to ensure that data is correctly carried to the UE during the transition from the source to the target node, hardware, or software entity.

[0117] In some embodiments, the L2 reset indication is indicated for a MAC entity, a cell group, an L2 protocol entity, a radio bearer, a data radio bearer, a signaling radio bearer, or an RLC bearer.

[0118] In one example, assuming the LTM candidate target cell configuration is CellGroupConfig, an L2-ResetIndicator is added for each RLC-BearerConfig in the CellGroupConfig. This means that the L2 reset action can be controlled for each data radio bearer (DRB). Here, with the L2-ResetIndicator, the network cannot signal an L2 reset separately for different entities, but when this indication is included, it means that at least the MAC and RLC should be reset for that RLC bearer.

[0119]

[0120] In another example, assuming the LTM candidate target cell configuration is CellGroupConfig, an L2-ResetIndicator can be added for each CellGroupConfig. This means that the L2 reset operation can be controlled for each MAC entity.

[0121] The advantage of placing the L2-ResetIndicator in the RLC-BearerConfig is that it can more precisely indicate whether an L2 reset is to be performed and to what extent. For example, the MAC, RLC, and PDCP entities of different DRBs can be terminated in different network nodes. Therefore, during an LTM cell transition, it may be necessary to reconstruct the RLC of some DRBs but not others.

[0122] The advantage of placing the L2-ResetIndicator in the CellGroupConfig is less signaling overhead, but the disadvantage is that this means that all DRBs will be treated the same during an LTM cell transition.

[0123] In some embodiments, the L2 reset indication can be indicated for a group of MAC entities, cell groups, L2 protocol entities, radio bearers, data radio bearers, signaling radio bearers, or RLC bearers.

[0124] In some embodiments, the L2 reset indication can indicate whether to perform an LTM cell transition to a target cell controlled by a network node different from the source network node. Alternatively, the L2 reset indication can indicate an inter-network node or an intra-network node, such as an LTM cell transition within a DU or an LTM cell transition between DUs.

[0125] In some embodiments, the L2 reset indication is obtained in the configuration of the LTM candidate target cell.

[0126] In some embodiments, the L2 reset indication is obtained in low-layer signaling (such as MAC CE). In one implementation, the L2 reset indication is included in the same low-layer signaling as the low-layer signaling including LTM cell transition information, such as in the LTM cell transition MAC CE. In one example, when receiving the low-layer signaling including LTM cell transition information, the UE performs an L2 reset during the LTM cell transition. In another implementation, the L2 reset indication is included in a separate low-layer signaling (such as a separate MAC CE).

[0127] One advantage of the low-layer signaling-based method is that each S-DU knows that its own cell is configured as an LTM candidate for a given UE. In other words, when an S-DU determines that an LTM cell transition to one of its own cells is triggered for a UE, it does not include the L2 reset indication. However, when an S-DU determines that an LTM cell transition to a cell that is not one of its own cells is triggered for a UE, it includes the L2 reset indication (in this case, each candidate DU may want to know in advance that an L2 reset is to be triggered, but it also knows that the UE is from another DU).

[0128] In some embodiments, an L2 reset indication received in a lower layer signaling (e.g., in a MAC CE) takes precedence over an indication received within an LTM candidate target cell.

[0129] In an alternative embodiment, an L2 reset indication received within an LTM candidate target cell takes precedence over an indication received in a lower layer signaling (e.g., in a MAC CE).

[0130] In some embodiments, when performing an LTM cell transition, an L2 reset indication is defined for each "incoming cell" (or source cell). An "incoming cell" may correspond to a cell in which the UE receives a lower layer command for an LTM cell transition. In one example, the UE receives a list of one or more possible incoming cells (source cells) from which the UE does not require an L2 reset if it transitions from these incoming cells. Thus, when the UE is in one of these cells and performs an LTM cell transition, the UE determines not to perform an L2 reset. In one example, for instance, an LTM candidate target cell configuration associated with a candidate cell C indicates one or more cells (e.g., cell B) from which the UE may transition to cell C during LTM execution without performing an L2 reset or only performing a partial L2 reset (e.g., by indicating one or more cell identities or LTM configuration identities associated with the source cell).

[0131] For example, when the UE is in cell B and receives a lower layer command (e.g., a MAC CE) for an LTM cell transition to cell C, the UE performs an LTM cell transition process from cell B to cell C without performing an L2 reset. In one option, a candidate DU (for the UE that configures cell C as a candidate cell for LTM based on a request from the CU and / or the source DU) knows that other cells in its cell may also be considered candidate cells for LTM of the same UE (e.g., candidate cell B) and may set these cells as source cells from which the UE may transition to cell C without performing an L2 reset. As another example, when the UE is in cell B and receives a lower layer command (e.g., a MAC CE) for an LTM to cell A, the UE performs a process with an L2 reset (since cell A is not listed as a cell from which the UE comes without an L2 reset).

[0132] In embodiments related to embodiments where the L2 reset indication is obtained in the configuration of the LTM candidate target cell, obtained in lower layer signaling, and / or defined for each incoming cell, when the UE in the source cell receives a lower layer command (e.g., MAC CE) for performing an LTM cell handover to the target cell; when the source cell is not associated as a cell that will not perform an L2 reset in the LTM target cell configuration, the UE performs an L2 reset. In terms of signaling, the UE may receive an indication to perform the above actions, and there may be different options.

[0133] In option (a), the UE receives an RRC reconfiguration message that includes the configuration of the LTM candidate target cell (hereinafter referred to as LTM-CandidateToAddMod), which includes an indication of one or more source cells. Thus, the UE receives an indication of one or more source cells for each LTM candidate cell, and the UE can perform an LTM cell handover from the one or more source cells to the LTM candidate target cell without performing an L2 reset. Therefore, when the UE is in one of the indicated source cells, when the UE receives lower layer signaling (e.g., MAC CE) for an LTM cell handover to the LTM candidate target cell, the UE performs the cell handover without performing an L2 reset. When the UE is in a cell that is not one of the indicated source cells, when the UE receives lower layer signaling (e.g., MAC CE) for an LTM cell handover to the LTM candidate target cell, the UE performs a cell handover with an L2 reset.

[0134] In an embodiment of option (a), the indication of one or more source cells (hereinafter referred to as sourceCellNoL2reset-List in the signaling) is included as a field / parameter / IE in the configuration of the LTM candidate target cell (hereinafter referred to as LTM-CandidateToAddMod). This indication is not necessarily nested in the actual target cell configuration that the UE applies or uses / converts to when performing an LTM cell handover, which is represented by candConfig-r18 of OCTET STRING (CONTAINING CellGroupConfig) hereinafter.

[0135]

[0136] In another embodiment of option (a), the indication of one or more source cells (denoted as sourceCellNoL2reset in the following signaling) is included as a field / parameter / IE in the configuration of the LTM candidate target cell (denoted as LTM-CandidateToAddMod below) and is included within the actual target cell configuration that the UE applies / uses / switches to when performing LTM cell transition. For example, the sourceCellNoL2reset-List is included within the IE of candConfig-r18, for example, within OCTET STRING (CONTAINING CellGroupConfig) or OCTET STRING (CONTAINING RRCReconfiguration).

[0137] In an embodiment of option (a), the indication of one or more source cells is provided to the UE as a list of cell identifiers. For example, the indication can correspond to one or more LTM configuration identifiers (one or more instances of the IE indicating the configuration ID of LTM, such as the IE Cand-LTM-Id-r18 shown above), and each LTM configuration identifier points to an LTM candidate target configuration. This is possible because these one or more source cells can be candidate cells for LTM, such that they are configured for LTM in the UE and have their own LTM configuration ID. For example, the UE has candidate cells A, B, and C for LTM configuration, and each candidate cell has a configuration ID, for example: cell A Cand-LTM-Id-r18=x1, cell B Cand-LTM-Id-r18=x2, and cell C Cand-LTM-Id-r18=x3. Then, for each candidate cell of the UE, the source cell from which the UE can come but without performing L2 reset is indicated as follows:

[0138] o Cell A:

[0139] · Cand-LTM-Id-r18=x1

[0140] o Cell B:

[0141] · Cand-LTM-Id-r18=x2

[0142] · sourceCellNoL2reset-List=x3

[0143] o Cell C:

[0144] · Cand-LTM-Id-r18 = x3

[0145] · sourceCellNoL2reset-List = x2

[0146] As another example, the indication of one or more source cells provided to the UE as a list of cell identifiers may correspond to one or more physical cell identities (PCIs). By assuming that the SSB frequency of the indicated PCI (e.g., the SSB absolute radio frequency channel number (ARFCN)) is the same SSB frequency as that of the associated target candidate, the UE can determine the SSB frequency. For example, this may correspond to one or more instances of the CellIdentity IE as defined in TS 38.331, or any other cell identifier used to uniquely identify a cell within a public land mobile network (PLMN).

[0147] In option (b), the UE receives an RRC reconfiguration message that includes the configuration of one or more LTM candidate target cells (hereinafter referred to as LTM-CandidateToAddMod), and an indication of at least one cell set (or group), where the group includes the LTM candidate cells configured for the UE. The indication of the at least one cell set is received by the UE as, for example, cell set 1 [cell A, cell X, cell Y], cell set 2 [cell B, cell C], to indicate that when the UE performs an LTM cell transition within the set, the UE does not perform an L2 reset. Or in other words, if the UE is in a serving cell and receives a lower layer command for an LTM cell transition to a cell not within the same set, the UE performs an L2 reset when the UE performs the LTM cell transition.

[0148] For example, if the UE is in cell A and receives a lower layer command for an LTM cell transition to cell X or cell Y, the UE does not perform an L2 reset. However, if the UE is in cell A and receives a lower layer command for an LTM cell transition to cell C, the UE performs an L2 reset.

[0149] As in option (a), the set (or group) can be indicated as one or more PCIs, cell identifiers, or LTM configuration identifiers (since these are also candidate cells). In the following examples, these sets are shown as LTM candidate identifiers.

[0150]

[0151] One benefit of option (b) is that it reduces signaling compared to option (a), because most likely, if an L2 reset from cell A to cell B does not need to be performed, then an L2 reset from cell B to cell A does not need to be performed either. Therefore, with this signaling, it is not necessary to indicate "no L2 reset from cell B" in the configuration of cell A or using the configuration of cell A, and it is not necessary to indicate "no L2 reset from cell A" in the configuration of cell B or using the configuration of cell B. An alternative for reducing signaling in option (a) is to have the UE receive an indication that no L2 reset is needed in an LTM cell transition from A to B (e.g., an indication in the configuration of LTM candidate target cell B), and furthermore, even if there is no indication in the configuration of LTM candidate target cell A, the UE interprets that no L2 reset is needed in an LTM cell transition from B to A to save signaling.

[0152] An overall advantage of the RRC signaling-based approach is that it can be transparent to the serving / source DU that triggers the LTM cell transition because the RRC signaling goes directly to the UE. In options where the source cell or set is indicated within the candidate configuration to be applied (e.g., CellGroupconfig), it can even be transparent to the CU. In options where the source cell or set is indicated outside the candidate CellGroupConfig, the CU may need to be involved because the CU generates the final message that the UE needs to apply or transition to. Additionally, in principle, it does not need to be visible because this is more of a deployment nature. However, it could be argued that to some extent, this deployment is exposed to the UE because the UE may figure out which candidate cells are grouped in the same DU. An alternative is to rely on more dynamic signaling via lower layer signaling (e.g., MAC CE), as shown below.

[0153] Therefore, in some embodiments, the L2 reset indication is obtained as a combination of: the LTM candidate target cell, and in lower layer signaling (e.g., MAC CE). In one method, when one of these indications indicates to perform an L2 reset and the other indicates "do not perform an L2 reset", the UE performs an L2 reset. In another method, when one of these indications indicates to perform an L2 reset and the other indicates "do not perform an L2 reset", the UE does not perform an L2 reset. In another method, the UE always performs an L2 reset unless both of these indications indicate "do not perform an L2 reset". In yet another method, the UE follows the indication of the lower layer signaling regardless of whether the indication in the LTM candidate target cell indicates an L2 reset or indicates no L2 reset.

[0154] In some embodiments, the first target cell is controlled by a first target network node. In some embodiments, the second target cell is controlled by a source target network node. In some embodiments, the second target cell is controlled by the first target network node. In some embodiments, the second target cell is controlled by a second target network node.

[0155] In some embodiments, the L2 reset indication is received from a source network node. In alternative embodiments, the L2 reset indication is received from a third network node. In alternative embodiments, the L2 reset indication is received from the first target network node.

[0156] The present disclosure also proposes a method performed by Source Network Node (e.g., a source DU) (such as a source gNB, a source DU, a serving DU, or a source CU). The source network node will process the L2 reset indication of a UE that is configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0157] In these methods, the L2 reset indication can be sent to the UE.

[0158] In these methods, the L2 reset indication can be included in lower layer signaling (e.g., MAC CE). In one method, the L2 reset indication can be included in the same lower layer signaling (e.g., MAC CE) as the lower layer signaling used to indicate the execution of the LTM cell transition process. In another method, the L2 reset indication can be included in a separate lower layer signal (e.g., MAC CE) that is different from the lower layer signal used to indicate the execution of the LTM cell transition.

[0159] In some embodiments, if the L2 reset indication is included in a lower layer signaling different from the lower layer signaling used to indicate the execution of the LTM cell transition, the source network node sends the lower layer signaling for L2 reset and the lower layer signal for LTM cell transition in the same protocol data unit (PDU) message. In one method, the lower layer signaling for the L2 reset indication is added to the PDU message before the lower layer signaling for the LTM cell transition. In another method, the lower layer signaling for the L2 reset indication is added to the PDU message after the lower layer signaling for the LTM cell transition. In yet another method, the UE always first executes / applies the lower layer signaling for the L2 reset indication and then executes / applies the lower layer signaling for the LTM cell transition. In another method, the UE always first executes / applies the lower layer signaling for the LTM cell transition and then executes / applies the lower layer signaling for the L2 reset indication.

[0160] In some embodiments, the source network node determines the value of the L2 reset indication. In one method, based on which network node controls the target cell during the LTM cell transition of the UE to the target cell, the source network node determines the value of the L2 reset indication.

[0161] The present disclosure also proposes a method performed by Third Network Node a (CU) (or serving network node) (such as a (serving) Central Unit (CU), a (serving) gNB-CU). The third network node will process the L2 reset indication for the UE that is configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0162] In some embodiments, the L2 reset indication is included in the configuration of the LTM candidate target cell.

[0163] In some embodiments, the L2 reset indication is sent to the UE. In some embodiments, the L2 reset indication is sent to the first target network node. In some embodiments, the L2 reset indication is sent to the source network node.

[0164] In some embodiments, the CU sends a request to any one or more of the source network node, the first target network node, and the second target network node to provide the L2 reset indication for the LTM candidate target cell configured by one of these network nodes. In one method, the request is explicit, which means the CU uses a specific field / structure / IE to request the information from the source network node, the first target network node, and / or the second target network node. In another method, the request is implicit, which means that each time a request to configure a new LTM candidate target cell is received, the source network node, the first target network node, and / or the second target network node provides the information to the CU.

[0165] In some embodiments, the third network node determines the value of the L2 reset indication. In one method, based on which network node controls the target cell during the LTM cell transition of the UE to the target cell, the third network node determines the value of the L2 reset indication.

[0166] The present disclosure also proposes a method performed by First Target Network Node (Target DU) (such as the first target gNB, the first target DU, or the first target CU). The first target network node will process the L2 reset indication for the UE that is configured with a serving cell and an LTM configuration including one or more LTM candidate target cells.

[0167] In some embodiments, the L2 reset indication is sent to the UE.

[0168] In some embodiments, the L2 reset indication is included in lower layer signaling (e.g., MAC CE). In one method, the L2 reset indication is included in the same lower layer signaling (e.g., MAC CE) as the lower layer signaling for performing an LTM cell transition to a second target network node. In one example, the L2 reset indication is sent only after the UE has received a lower layer command (e.g., MAC CE) for an LTM cell transition to a first target network node performed by the source network node and the LTM cell transition process has been successfully completed. In an alternative method, the L2 reset indication may be included in a separate lower layer signal (e.g., MAC CE) that is different from the lower layer signal for indicating the performance of an LTM cell transition.

[0169] In embodiments where the L2 reset indication is included in lower layer signaling, if the L2 reset indication is included in a lower layer signaling different from the lower layer signaling for indicating the performance of an LTM cell transition, the first target network node may send the lower layer signaling for the L2 reset indication and the lower layer signal for the LTM cell transition in the same PDU message. In one method, the lower layer signaling for the L2 reset indication may be added to the PDU message before the lower layer signaling for the LTM cell transition. In an alternative method, the lower layer signaling for the L2 reset indication may be added to the PDU message after the lower layer signaling for the LTM cell transition. In yet another method, the UE may always first execute / apply the lower layer signaling for the L2 reset indication and then execute / apply the lower layer signaling for the LTM cell transition. In yet another method, the UE may always first execute / apply the lower layer signaling for the LTM cell transition and then execute / apply the lower layer signaling for the L2 reset indication.

[0170] In some embodiments, the L2 reset indication may be included in the configuration of the LTM candidate target cell. In some embodiments, the L2 reset indication may be sent to a third network node. In some embodiments, the L2 reset indication may be sent to the source network node.

[0171] In some embodiments, the first network node determines the value of the L2 reset indication. In one method, based on which network node controls the target cell during an LTM cell transition to the target cell for the UE, the first network node may determine the value of the L2 reset indication.

[0172] The following Figure 6 illustrates an exemplary implementation of the techniques described herein. Figure 6 is an example of a message sequence diagram in an example. Figure 6It is a signaling diagram showing the signaling carried out by the UE, the source network node (S-DU), the third network node (e.g., CU), and the first target network node (e.g., candidate DU). In this example, the CU includes the L2 reset indication in the configuration of the LTM candidate target cell.

[0173] Reference Figure 6 , the main steps in this example are as follows.

[0174] Step 601. The CU initiates the configuration of the candidate target cell for L1 / L2 mobility and sends a UE context setup request (UE CONTEXT SETUP REQUEST) message to the candidate DU (the first target network node) to create a UE context and request the configuration of at least one LTM candidate target cell.

[0175] Step 602. The candidate DU responds to the gNB-CU with a UE context setup response (UE CONTEXT SETUP RESPONSE) message. This message includes the configuration of at least one LTM candidate target cell and at least one L2 reset indication. In this example, the L2 reset indication includes one or more source cells or a set of source cells for which no L2 reset needs to be performed if the UE comes from one of these source cells during an LTM cell transition to a specific candidate target cell.

[0176] Step 603. The CU sends a DL RRC message transfer (DL RRC MESSAGE TRANSFER) including an RRC reconfiguration message to the serving DU (source network node). The RRC reconfiguration message includes the configuration of at least one LTM candidate target cell and the at least one L2 reset indication. The S-DU forwards the RRC reconfiguration message to the UE.

[0177] Step 604. The UE stores the configuration of at least one LTM candidate target cell and the at least one L2 reset indication, and sends an RRCReconfigurationComplete message to the serving DU. The serving DU sends a DL RRC message transfer (DLRRC MESSAGET RANSFER) message to the CU to convey the received RRCReconfigurationComplete message.

[0178] Step 605. The UE performs L1 measurements on at least one LTM candidate target cell and sends a lower layer (e.g., L1 or MAC) report to the serving DU based on these measurements.

[0179] Step 606. The serving DU determines to trigger an LTM cell transition for the UE to the candidate cell.

[0180] Step 607. The serving DU sends a low-layer command to the UE for requesting to perform an LTM cell transition. This message indicates the candidate cell.

[0181] Step 608. The UE performs an LTM cell transition to the indicated cell and determines whether to perform an L2 reset during the transition based on an obtained L2 reset indication. In this example, the UE determines whether to perform an L2 reset depending on the candidate cell and the source cell.

[0182] Step 609. The UE completes the LTM cell transition and, as a result, may send an uplink signal to the candidate DU in the target cell to confirm successful execution of the LTM cell transition.

[0183] Figure 7 is a flowchart of the main operations performed by the UE.

[0184] Figure 7 illustrates the main operations performed by the UE in an example described herein. In this example, the UE performs an LTM cell transition to a first target cell and determines whether to perform an L2 reset based on the obtained L2 reset indication.

[0185] Reference Figure 7 , in this embodiment, the main steps performed by the UE are as follows:

[0186] Step 701. The UE receives the configuration of the LTM candidate target cell of the first target cell.

[0187] Step 702. The UE receives a low-layer command for performing an LTM cell transition to the first target cell.

[0188] Step 703. The UE obtains an L2 reset indication. In one example, the L2 reset indication is part of the configuration of the LTM candidate target cell of the first target cell. In another example, the L2 reset indication is part of the low-layer command.

[0189] Step 704. The UE performs an LTM cell transition to the first target cell and determines whether to perform an L2 reset during the transition based on the obtained L2 reset indication.

[0190] Figure 8 is a flowchart of the main steps performed by the UE in another example.

[0191] Figure 8 illustrates the main operations performed by the UE in another example described herein. In this example, the UE performs an LTM cell transition to a first target cell and then performs an LTM cell transition to a second target cell. During each LTM cell transition, it is determined whether to perform an L2 reset based on the obtained L2 reset indication.

[0192] Reference Figure 8 , the main steps performed by the UE in this example are as follows.

[0193] Step 801. The UE receives the configuration of the LTM candidate target cells of the first target cell and the second target cell.

[0194] Step 802. The UE receives the lower layer command for performing the LTM cell transition to the first target cell.

[0195] Step 803. The UE obtains an L2 reset indication. In one example, the L2 reset indication is part of the configuration of the LTM candidate target cell of the first target cell. In another example, the L2 reset indication is part of the lower layer command.

[0196] Step 804. The UE performs the LTM cell transition to the first target cell and determines whether to perform an L2 reset during the transition according to the obtained L2 reset indication.

[0197] Step 805. When the UE operates in the first target cell, it receives the lower layer command for performing the LTM cell transition to the second target cell.

[0198] Step 806. The UE obtains an L2 reset indication. In one example, the L2 reset indication is part of the configuration of the LTM candidate target cell of the first target cell. In another example, the L2 reset indication is part of the lower layer command.

[0199] Step 807. The UE performs the LTM cell transition to the second target cell and determines whether to perform an L2 reset during the transition according to the obtained L2 reset indication.

[0200] Figure 9 An example of a communication system 900 according to some embodiments is shown.

[0201] In this example, the communication system 900 includes: a telecommunication network 902, including an access network 904 such as a radio access network (RAN); and a core network 906, including one or more core network nodes 908. The access network 904 includes one or more access network nodes, such as access network nodes 910a and 910b (one or more of which may generally be referred to as access network node 910), or any other similar 3rd Generation Partnership Project (3GPP) access node or non-3GPP access point. The access network node 910 connects UEs 912a, 912b, 912c, and 912d (one or more of which may generally be referred to as UE 912) to the core network 906, for example, via one or more wireless connections, to facilitate the direct or indirect connection of wireless devices (also interchangeably referred to herein as user equipment (UE)). The access network node 910 may be, for example, an access point (AP) (e.g., a radio access point), a base station (BS) (e.g., a radio base station, NodeB, evolved NodeB (eNB), and NR NodeB (gNB)).

[0202] Example wireless communications via a wireless connection include sending and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for transmitting information without using wiring, cables, or other material conductors. Additionally, in different embodiments, the communication system 900 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that can facilitate or participate in the communication of data and / or signals, whether via a wired connection or a wireless connection. The communication system 900 may include any type of communication, telecommunication, data, cellular, radio network, and / or other similar types of systems, and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar types of systems.

[0203] The wireless device / UE 912 can be any of a variety of communication devices, including a wireless device arranged, configured, and / or operable to communicate wirelessly with network node 910 and other communication devices. Similarly, the access network node 910 is arranged, capable, configured, and / or operable to communicate directly or indirectly with UE 912 and / or with other network nodes or devices in the telecommunication network 902 to enable and / or provide network access (e.g., wireless network access) and / or to perform other functions in the telecommunication network 902 (e.g., management).

[0204] The core network 906 includes one or more core network nodes (e.g., core network node 908) that together with hardware and software components. The characteristics of these components can be substantially similar to the characteristics described with respect to the wireless device / UE and the access network node, such that their description generally applies to the corresponding components of the core network node 908. Example core network nodes include the functionality of one or more of the following: Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealment Function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or User Plane Function (UPF).

[0205] The host 916 can be owned or under the control of a service provider other than the operator or provider of the access network 904 and / or the telecommunications network 902, and can be operated by or on behalf of the service provider. The host 916 can host a variety of applications to provide one or more services. Examples of such applications include providing live and / or pre-recorded audio / video content, data collection services (e.g., retrieving and compiling data on various environmental conditions detected by multiple UEs), analytics functions, social media, functions for controlling or otherwise interacting with remote devices, functions for alarm and monitoring centers, or any other such functions performed by a server.

[0206] As a whole, Figure 9 the communication system 900 enables connections between the wireless device / UE, network nodes, and the host. In this sense, the communication system can be configured to operate according to predefined rules or procedures such as specific standards, including but not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE) and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standards (e.g., 6G); Wireless Local Area Network (WLAN) standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standards such as Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC), ZigBee, LiFi, and / or any Low Power Wide Area Network (LPWAN) standards such as LoRa and Sigfox.

[0207] In some examples, the telecommunications network 902 is a cellular network implementing 3GPP standardized features. Accordingly, the telecommunications network 902 can support network slicing to provide different logical networks to different devices connected to the telecommunications network 902. For example, the telecommunications network 902 can provide ultra-reliable low-latency communication (URLLC) services to some UEs, while providing enhanced mobile broadband (eMBB) services to other UEs, and / or providing massive machine type communication (mMTC) / massive IoT services to additional UEs.

[0208] In some examples, the UE 912 is configured to send and / or receive information without direct human interaction. For example, the UE can be designed to send information to the access network 904 according to a predetermined schedule when triggered by an internal or external event or in response to a request from the access network 904. Additionally, the UE can be configured to operate in a single RAT mode, a multi-RAT mode, or a multi-standard mode. For example, the UE can operate using any one or combination of Wi-Fi, NR (New Radio), and LTE, i.e., be configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0209] In Figure 9 In the example shown, the hub 914 communicates with the access network 904 to facilitate indirect communication between one or more UEs (e.g., UEs 912c and / or 912d) and an access network node (e.g., access network node 910b). In some examples, the hub 914 can be a controller, a router, a content source and analysis node, or any other communication device described herein with respect to the UE. For example, the hub 914 can be a broadband router that enables the UE to access the core network 906. As another example, the hub 914 can be a controller that sends commands or instructions to one or more actuators of the UE. The commands or instructions can be received from the UE, the network node 910, or through executable code, scripts, procedures, or other instructions in the hub 914. As another example, the hub 914 can be a data collector that acts as a temporary storage device for UE data and, in some embodiments, can perform analysis or other processing of the data. As another example, the hub 914 can be a content source. For example, for a UE that is a VR headset, a display, a speaker, or other media delivery device, the hub 914 can retrieve VR assets, videos, audio, or other media or data related to sensory information via the network node, and then the hub 914 can directly provide it to the UE after performing local processing and / or after adding additional local content. In yet another example, the hub 914 acts as a proxy server or orchestrator for the UE, especially if one or more of the UEs are low-energy IoT devices.

[0210] The central unit 914 may have a continuous / persistent or intermittent connection to the network node 910b. The central unit 914 may also allow for different communication schemes and / or scheduling between the central unit 914 and the UEs (e.g., UEs 912c and / or 912d) and between the central unit 914 and the core network 906. In other examples, the central unit 914 is connected to the core network 906 and / or one or more UEs via a wired connection. Additionally, the central unit 914 may be configured to connect to an M2M service provider via the access network 904 and / or to connect to another UE via a direct connection. In some scenarios, a UE may establish a wireless connection to the network node 910 while still being connected via the central unit 914 via a wired or wireless connection. In some embodiments, the central unit 914 may be a dedicated central unit, i.e., a central unit whose main function is to route communications from the network node 910b to the UEs / to route communications from the UEs to the network node 910b. In other embodiments, the central unit 914 may be a non-dedicated central unit, i.e., a device that is capable of operating to route communications between the UEs and the network node 910b but is additionally capable of operating as a communication origin and / or endpoint for certain data channels.

[0211] Figure 10 A wireless device or UE 1000 according to some embodiments is shown.

[0212] As used herein, a UE refers to a device that is capable of, configured to, arranged to, and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of wireless devices / UEs include, but are not limited to, smart phones, mobile phones, cellular phones, IP voice (VoIP) phones, wireless local loop phones, desktop computers, personal digital assistants (PDAs), wireless cameras, gaming consoles or devices, music storage devices, playback devices, wearable terminal devices, wireless endpoints, mobile stations, tablet computers, laptop computers, laptop embedded devices (LEEs), laptop mounted devices (LMEs), smart devices, wireless client devices (CPEs), vehicle-mounted or vehicle-embedded / integrated wireless devices, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including narrowband Internet of Things (NB-IoT) UEs, machine type communication (MTC) UEs, and / or enhanced MTC (eMTC) UEs.

[0213] A wireless device / UE can support device-to-device (D2D) communication, for example, by implementing 3GPP standards for sidelink communication, dedicated short range communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not have a user in the sense of a human user who owns and / or operates the associated device. Instead, a UE may represent a device that is intended to be sold to or operated by a human user but may not or initially may not be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended to be sold to or operated by an end user but may be associated with or operate in the interest of a user (e.g., a smart power meter).

[0214] UE 1000 includes processing circuitry 1002 that is operably coupled via a bus 1004 to an input / output interface 1006, a power supply 1008, a memory 1010, a communication interface 1012, and / or any other components or any combination thereof. Some UEs may utilize Figure 10 all or a subset of the components shown. The level of integration between components may vary with the UE. Additionally, some UEs may include multiple instances of components, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0215] The processing circuitry 1002 is configured to process instructions and data and may be configured to implement any sequential state machine operable to execute instructions stored as a machine-readable computer program in the memory 1010. The processing circuitry 1002 may be implemented as: one or more hardware-implemented state machines (e.g., implemented in discrete logic, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc.); programmable logic along with appropriate firmware; one or more stored computer programs, a general-purpose processor (such as a microprocessor or a digital signal processor (DSP)) along with appropriate software; or any combination of the foregoing. For example, the processing circuitry 1002 may include multiple central processing units (CPUs). The processing circuitry 1002 may be operable to provide the UE 1000 functionality either alone or in combination with other UE 1000 components (e.g., the memory 1010). For example, the processing circuitry 1002 may be configured to cause the UE 1002 to perform the methods described above with reference to Figure 4 and Figure 5 as described.

[0216] In an example, the input / output interface 1006 can be configured to provide one or more interfaces to an input device, an output device, or one or more input and / or output devices. Examples of output devices include speakers, sound cards, video cards, displays, monitors, printers, actuators, transmitters, smart cards, another output device, or any combination thereof. Input devices can allow a user to capture information into the UE 1000. Examples of input devices include touch-sensitive or presence-sensitive displays, cameras (e.g., digital cameras, digital video cameras, webcams, etc.), microphones, sensors, mice, trackballs, directional keyboards, touchpads, rollers, smart cards, etc. A presence-sensitive display can include a capacitive or resistive touch sensor to sense input from a user. Sensors can be, for example, accelerometers, gyroscopes, tilt sensors, force sensors, magnetometers, optical sensors, proximity sensors, biometric sensors, etc., or any combination thereof. Output devices can use the same type of interface port as input devices. For example, a Universal Serial Bus (USB) port can be used to provide input and output devices.

[0217] In some embodiments, the power supply 1008 is configured as a battery or a battery pack. Other types of power supplies can be used, such as an external power supply (e.g., a power outlet), a photovoltaic device, or a battery. The power supply 1008 can also include a power circuit for delivering power from the power supply 1008 itself and / or an external power supply to various parts of the UE 1000 via an input circuit or an interface such as a power cable. Delivering power can be used, for example, for charging the power supply 1008. The power circuit can perform any formatting, conversion, or other modification on the power from the power supply 1008 to make the power suitable for the corresponding components of the UE 1000 to which the power is supplied.

[0218] The memory 1010 can be or be configured to include a memory, such as a random access memory (RAM), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a magnetic disk, an optical disk, a hard disk, a removable magnetic tape, a flash drive, etc. In one example, the memory 1010 includes one or more applications 1014, such as an operating system, a web browser application, widgets, a gadget engine, or other applications, and corresponding data 1016. The memory 1010 can store any one or a combination of various operating systems used by the UE 1000.

[0219] The memory 1010 may be configured to include multiple physical drive units, such as Redundant Array of Independent Disks (RAID), flash memory, USB flash drives, external hard disk drives, thumb drives, pen drives, key drives, High-Definition Digital Versatile Disc (HD-DVD) disc drives, built-in hard disk drives, Blu-ray disc drives, Holographic Digital Data Storage (HDDS) disc drives, external mini Dual In-line Memory Modules (DIMMs), Synchronous Dynamic Random Access Memory (SDRAM), external micro DIMM SDRAM, smart card memories (e.g., tamper-resistant modules in the form of Universal Integrated Circuit Cards (UICCs) including one or more Subscriber Identity Modules (SIMs), such as USIMs and / or ISIMs), other memories, or any combination thereof. The UICC may be, for example, an Embedded UICC (eUICC), an Integrated UICC (iUICC), or a removable UICC commonly referred to as a "SIM card". The memory 1010 may allow the UE 1000 to access instructions, applications, etc. stored on a temporary or non-temporary storage medium to offload data or upload data. An article of manufacture, such as an article of manufacture using a communication system, may be tangibly embodied as or in the memory 1010, which may be or include a device-readable storage medium.

[0220] The processing circuitry 1002 may be configured to communicate with an access network or other network using the communication interface 1012. The communication interface 1012 may include one or more communication subsystems and may include an antenna 1022 or be communicatively coupled to an antenna 1022. The communication interface 1012 may include one or more transceivers for communicating (e.g., by communicating with one or more remote transceivers of another device capable of wireless communication, such as another UE or a network node in an access network). Each transceiver may include a transmitter 1018 and / or a receiver 1020 suitable for providing network communication (e.g., optical, electrical, frequency allocation, etc.). Additionally, the transmitter 1018 and the receiver 1020 may be coupled to one or more antennas (e.g., antenna 1022) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0221] In some embodiments, the communication functions of the communication interface 1012 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communication such as Bluetooth, near-field communication, location-based communication (e.g., using the Global Positioning System (GPS) to determine location), another type of communication function, or any combination thereof. The communication may be implemented according to one or more communication protocols and / or standards (e.g., IEEE 802.11, Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, Transmission Control Protocol / Internet Protocol (TCP / IP), Synchronous Optical Network (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), etc.).

[0222] Regardless of the type of sensor, the UE can provide an output of the data captured by its sensors via its communication interface 1012 over a wireless connection to a network node. The data captured by the sensors of the UE can be transmitted via another UE over a wireless connection to a network node. The output can be periodic (e.g., every 15 minutes if it reports the sensed temperature), random (e.g., to balance the load of reports from several sensors), in response to a triggering event (e.g., sending an alert when humidity is detected), in response to a request (e.g., a user-initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0223] As another example, the UE includes an actuator, a motor, or a switch associated with a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input, the state of the actuator, the motor, or the switch can change. For example, the UE may include a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input, or controls a robotic arm performing a medical procedure according to the received input.

[0224] When the UE is in the form of an Internet of Things (IoT) device, the UE can be a device used in one or more application areas, including but not limited to urban wearable technologies, extended industrial applications, and healthcare. Non-limiting examples of such IoT devices are devices that are or are embedded in the following devices: connected refrigerators or freezers, televisions, connected lighting devices, electricity meters, robotic vacuum cleaners, voice-controlled smart speakers, home security cameras, motion detectors, thermostats, smoke detectors, door / window sensors, flood / humidity sensors, electronic door locks, connected doorbells, air conditioning systems such as heat pumps, autonomous vehicles, surveillance systems, weather monitoring devices, vehicle parking monitoring devices, electric vehicle charging stations, smartwatches, fitness trackers, head-mounted displays for augmented reality (AR) or virtual reality (VR), wearable devices for tactile or sensory enhancement, sprinklers, animal or item tracking devices, sensors for monitoring plants or animals, industrial robots, drones (UAVs), and any type of medical device, such as a heart rate monitor or a remote surgery robot. In addition to the other components described for the UE 1000 as shown in Figure 12 the UE in the form of an IoT device also includes circuitry and / or software depending on the intended application of the IoT device.

[0225] As yet another specific example, in an IoT scenario, the UE can represent a machine or other device that performs monitoring and / or measurement and sends the results of such monitoring and / or measurement to another UE and / or a network node. In this case, the UE can be an M2M device, which can be referred to as an MTC device in the 3GPP context. As a specific example, the UE can implement the 3GPP NB-IoT standard. In other scenarios, the UE can represent a vehicle (e.g., a car, bus, truck, ship, and airplane) or other device that is capable of monitoring and / or reporting its operating state or other functions associated with its operation.

[0226] In fact, for a single use case, any number of UEs can be used together. For example, a first UE can be a drone or integrated in a drone and provide speed information of the drone (obtained through a speed sensor) to a second UE, which is a remote controller for operating the drone. When the user makes a change from the remote controller, the first UE can adjust the throttle on the drone (e.g., by controlling an actuator) to increase or decrease the speed of the drone. The first UE and / or the second UE can also include more than one of the above functions. For example, the UE can include sensors and actuators and process data communication for both the speed sensor and the actuator.

[0227] Figure 11 FIG. 1100 shows a network node according to some embodiments.

[0228] As used herein, a network node refers to a device that is capable of, configured to, arranged to, and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or devices in a telecommunication network. Examples of network nodes include, but are not limited to, access network nodes such as access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, NodeBs, evolved NodeBs (eNBs), and NR NodeBs (gNBs)). Figure 11 The network node 1100 in may represent any network node described herein, such as a source network node, S-DU, serving network node, first target network node, second target network node, DU, T-DU, third network node, CU, gNB-CU, gNB-CU-CP, gNB-CU-UP, or a core network node such as a UPF or AMF.

[0229] Base stations / DUs can be classified based on the amount of coverage they provide (or in other words, their transmit power levels), and thus, depending on the coverage provided, a base station can be referred to as a femto base station, pico base station, micro base station, or macro base station. A base station can be a relay node or a relay donor node that controls a relay. A network node can also include one or more (or all) parts of a distributed radio base station, such as a centralized digital unit and / or a remote radio unit (RRU), sometimes referred to as a remote radio head (RRH). These remote radio units can be integrated with antennas into radios with integrated antennas, or they can be not integrated with antennas into radios with integrated antennas. The parts of a distributed radio base station can also be referred to as nodes in a distributed antenna system (DAS).

[0230] Other examples of network nodes include multi-transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) devices (such as MSR BSs), network controllers (such as radio network controllers (RNCs) or base station controllers (BSCs)), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), operation and maintenance (O&M) nodes, operation support system (OSS) nodes, self-organizing network (SON) nodes, positioning nodes (e.g., evolved serving mobile location center (E-SMLC)), and / or drive test minimization (MDT).

[0231] The network node 1100 includes a processing circuit 1102, a memory 1104, a communication interface 1106, and a power supply 1108, and / or any other components or any combination thereof. The network node 1100 may consist of multiple physically separated components (e.g., Node B components and RNC components, BTS components and BSC components, etc.), and these components may have their own corresponding components. In certain scenarios where the network node 1100 includes multiple separate components (e.g., BTS and BSC components), one or more separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such scenarios, each unique "NodeB and RNC pair" may in some cases be considered a single separate network node. In some embodiments, the network node 1100 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be replicated (e.g., there may be separate memories 1104 for different RATs), and some components may be reused (e.g., the same antenna 1110 may be shared by different RATs). The network node 1100 may also include multiple sets of various components shown for different wireless technologies (e.g., GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, radio frequency identification (RFID), or Bluetooth wireless technologies) integrated into the network node 1100. These wireless technologies may be integrated into the same or different chips or chip sets and other components within the network node 1100.

[0232] The processing circuit 1102 may include a combination of one or more of the following: a microprocessor, a controller, a microcontroller, a central processing unit, a digital signal processor, an application-specific integrated circuit, a field-programmable gate array, or any other suitable computing device, resource, or a combination of hardware, software, and / or coded logic, which is operable to provide the network node 1100 functions either alone or in combination with other network node 1100 components (e.g., the memory 1104).

[0233] In some embodiments, the processing circuit 1102 includes a system-on-chip (SOC). In some embodiments, the processing circuit 1102 includes one or more of a radio frequency (RF) transceiver circuit 1112 and a baseband processing circuit 1114. In some embodiments, the radio frequency (RF) transceiver circuit 1112 and the baseband processing circuit 1114 may be on separate chips (or chip sets), boards, or units (e.g., radio units and digital units). In alternative embodiments, some or all of the RF transceiver circuit 1112 and the baseband processing circuit 1114 may be on the same chip or chip set, board, or group of units.

[0234] The memory 1104 may include any form of volatile or non-volatile computer-readable memory, including but not limited to permanent storage devices, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (e.g., hard disks), removable storage media (e.g., flash drives, compact discs (CDs) or digital video discs (DVDs)), and / or any other volatile memory or non-volatile, non-transitory device-readable and / or computer-executable memory device that stores information, data, and / or instructions that can be used by the processing circuitry 1102. The memory 1104 may store any suitable instructions, data, or information, including computer programs, software, applications including one or more of logic, rules, code, tables, and / or other instructions that can be executed by the processing circuitry 1102 and used by the network node 1100. The memory 1104 may be used to store any calculations performed by the processing circuitry 1102 and / or any data received via the communication interface 1106. In some embodiments, the processing circuitry 1102 and the memory 1104 are integrated together.

[0235] The communication interface 1106 is used for wired or wireless communication of signaling and / or data between the network node, access network, core network, and / or UE. As shown, the communication interface 1106 includes ports / terminals 1116 for sending data to and receiving data from the network, for example, via a wired connection.

[0236] In an embodiment, the communication interface 1106 further includes a radio front-end circuit 1118, which may be coupled to the antenna 1110 or, in certain embodiments, to a portion of the antenna 1110. The radio front-end circuit 1118 includes a filter 1120 and an amplifier 1122. The radio front-end circuit 1118 may be connected to the antenna 1110 and the processing circuitry 1102. The radio front-end circuit may be configured to condition the signals transmitted between the antenna 1110 and the processing circuitry 1102. The radio front-end circuit 1118 may receive digital data to be transmitted to other network nodes or UEs via a wireless connection. The radio front-end circuit 1118 may use a combination of the filter 1120 and / or the amplifier 1122 to convert the digital data into a radio signal with appropriate channel and bandwidth parameters. The radio signal may then be transmitted via the antenna 1110. Similarly, when data is received, the antenna 1110 may collect the radio signal, and then the radio front-end circuit 1118 converts it into digital data. The digital data may be passed to the processing circuitry 1102. In other embodiments, the communication interface may include different components and / or different combinations of components.

[0237] In some alternative embodiments, the access network node 1100 does not include a separate radio front-end circuit 1118. Instead, the processing circuit 1102 includes the radio front-end circuit and is connected to the antenna 1110. Similarly, in some embodiments, all or some of the RF transceiver circuits 1112 are part of the communication interface 1106. In yet another embodiment, the communication interface 1106 includes one or more ports or terminals 1116, a radio front-end circuit 1118, and RF transceiver circuits 1112 as part of a radio unit (not shown), and the communication interface 1106 communicates with a baseband processing circuit 1114, which is part of a digital unit (not shown).

[0238] The antenna 1110 may include one or more antennas or antenna arrays configured to transmit and / or receive wireless signals. The antenna 1110 may be coupled to the radio front-end circuit 1118 and may be any type of antenna capable of wirelessly transmitting and receiving data and / or signals. In certain embodiments, the antenna 1110 is separate from the network node 1100 and may be connected to the network node 1100 via an interface or port.

[0239] The antenna 1110, the communication interface 1106, and / or the processing circuit 1102 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by a network node. Any information, data, and / or signals may be received from a UE, another network node, and / or any other network device. Similarly, the antenna 1110, the communication interface 1106, and / or the processing circuit 1102 may be configured to perform any sending operations described herein as being performed by a network node. Any information, data, and / or signals may be sent to a UE, another network node, and / or any other network device.

[0240] The power supply 1108 supplies power to the various components of the network node 1100 in a form suitable for each component (e.g., at the voltage and current levels required for each respective component). The power supply 1108 may also include a power management circuit or be coupled to a power management circuit to supply power to the components of the network node 1100 for performing the functions described herein. For example, the network node 1100 may be connected to an external power supply (e.g., a power grid, a power outlet) via an input circuit or interface (e.g., a cable), and the external power supply supplies power to the power circuit of the power supply 1108. As another example, the power supply 1108 may include a power supply in the form of a battery or a battery pack, which is connected to or integrated in the power circuit. If the external power supply fails, the battery may provide backup power.

[0241] Embodiments of the network node 1100 may include beyond Figure 11An add-on to the component shown, for providing certain aspects of the functionality of a network node (including any functionality described herein and / or any functionality required to support the subject matter described herein). For example, network node 1100 may include a user interface device to allow information to be input into network node 1100 and to allow information to be output from network node 1100. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions on network node 1100.

[0242] Figure 12 is a block diagram showing a virtualization environment 1200 in which functions implemented by some embodiments may be virtualized.

[0243] In this context, virtualization means creating a virtual version of a device or apparatus that may include virtualized hardware platforms, storage devices, and network resources. As used herein, virtualization may be applied to any device or its components described herein and relates to embodiments in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functionality described herein may be implemented as virtual components executed by one or more virtual machines (VMs) that are implemented in one or more virtualization environments 1200 hosted by one or more of the hardware nodes (e.g., hardware computing devices operating as access network nodes, wireless devices / UEs, or core network nodes). Additionally, in embodiments where the virtual node does not require a radio connection (e.g., a core network node), the node may be fully virtualized.

[0244] Application 1202 (which may alternatively be referred to as a software instance, virtual application, network function, virtual node, virtual network function, etc.) runs in virtualization environment 1200 to implement some of the features, functions, and / or benefits of some embodiments disclosed herein.

[0245] Hardware 1204 includes processing circuitry, a memory storing software and / or instructions executable by the hardware processing circuitry, and / or other hardware devices described herein (such as network interfaces, input / output interfaces, etc.). The software may be executed by the processing circuitry to instantiate one or more virtualization layers 1206 (also referred to as a hypervisor or virtual machine monitor (VMM)), provide VMs 1208a and 1208b (one or more of which may generally be referred to as VMs 1208), and / or perform any functions, features, and / or benefits described in connection with some embodiments herein. The virtualization layer 1206 may present a virtual operating platform to the VMs 1208 that appears like network hardware.

[0246] VM 1208 includes virtual processing, virtual memory, virtual network or interface, and virtual storage, and can be operated by the corresponding virtualization layer 1206. Different embodiments of instances of virtual device 1202 can be implemented on one or more VMs 1208, and these implementations can be made in different ways. In some contexts, the virtualization of hardware is referred to as network function virtualization (NFV). NFV can be used to unify numerous network device types onto industrial standard high-volume server hardware, physical switches, and physical storage that can be located in data centers and customer premise equipment (CPE).

[0247] In the context of NFV, VM 1208 can be a software implementation of a physical machine that operates programs as if they were executed on a physical, non-virtualized machine. Each VM 1208, along with the hardware part of the hardware 1204 that executes that VM (whether it is hardware dedicated to that VM and / or hardware shared by that VM with other VMs), forms a separate virtual network element. Still in the context of NFV, the virtual network function is responsible for handling specific network functions that operate in one or more VMs 1208 above the hardware 1204 and correspond to the application 1202.

[0248] Hardware 1204 can be implemented in an independent network node with general or specific components. Hardware 1204 can implement some functions via virtualization. Alternatively, hardware 1204 can be part of a larger hardware cluster (e.g., in a data center or CPE), where many hardware nodes work together and are managed through management and coordination 1210, which in particular supervises the lifecycle management of the application 1202. In some embodiments, hardware 1204 is coupled to one or more radio units, each radio unit including one or more transmitters and one or more receivers that can be coupled to one or more antennas. The radio units can communicate directly with other hardware nodes via one or more appropriate network interfaces and can be used in combination with virtual components to provide radio capabilities to virtual nodes (e.g., radio access nodes or base stations). In some embodiments, some signaling can be provided by using the control system 1212, which can alternatively be used for communication between the hardware node and the radio unit.

[0249] Although the computing devices (e.g., UEs, network nodes) described herein may include a combination of the hardware components shown, other embodiments may include computing devices having different combinations of components. It should be understood that these computing devices may include any suitable combination of hardware and / or software required to perform the tasks, features, functions, and methods disclosed herein. The determinations, calculations, acquisitions, or similar operations described herein may be performed by a processing circuit, which may process information, for example, by converting the acquired information into other information, comparing the acquired information or the converted information with information stored in the network node, and / or performing one or more operations based on the acquired information or the converted information, and making a determination based on the result of the processing. Additionally, although a component is depicted as a single box located within a larger box or nested within multiple boxes, in reality, a computing device may include multiple different physical components that make up a single shown component, and the functionality may be divided among separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of a component may be divided between a processing circuit and a communication interface. In another example, the non-computation-intensive functionality of any such component may be implemented in software or firmware, and the computation-intensive functionality may be implemented in hardware.

[0250] In some embodiments, some or all of the functions described herein may be provided by a processing circuit that executes instructions stored in a memory, which in some embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functions may be provided, for example, in a hardwired manner by the processing circuit without executing instructions stored on a separate or discrete device-readable storage medium. In any of these particular embodiments, whether or not instructions stored on a non-transitory computer-readable storage medium are executed, the processing circuit may be configured to perform the described functions. The benefits provided by such functionality are not limited to the separate processing circuit or to other components of the computing device, but are enjoyed by the computing device as a whole and / or generally by the end user and the wireless network.

[0251] The foregoing merely illustrates the principles of the present disclosure. In light of the teachings herein, various modifications and alterations to the described embodiments will be apparent to those skilled in the art. Accordingly, it should be understood that those skilled in the art will be able to design many systems, arrangements, and programs that, although not explicitly shown or described herein, embody the principles of the present disclosure and are thus within the scope of the present disclosure. As will be understood by those of ordinary skill in the art, the various exemplary embodiments may be used together or may be interchangeable.

[0252] Embodiments

[0253] Group A Embodiments (UE)

[0254] 1. A method performed by a user equipment UE, the method comprising:

[0255] Receiving (701) an LTM configuration of one or more layer 1 / layer 2 triggered mobility LTM candidate target cells, wherein the one or more LTM candidate target cells include a first target cell;

[0256] Receiving (702) a first command for performing an LTM cell transition to the first target cell;

[0257] Obtaining (703) a first layer 2 (L2) reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during the LTM cell transition to the first target cell; and

[0258] Performing (704) an LTM cell transition to the first target cell according to the first command.

[0259] 2. The method according to embodiment 1, wherein the LTM configuration is received from a third network node.

[0260] 3. The method according to embodiment 2, wherein the third network node is a centralized unit (CU) providing service for the UE.

[0261] 4. The method according to any one of embodiments 1 to 3, wherein the LTM configuration is included in an RRC reconfiguration message.

[0262] 5. The method according to any one of embodiments 1 to 4, wherein the L2 reset includes a reset of (only) one or more of a plurality of L2 protocols.

[0263] 6. The method according to any one of embodiments 1 to 5, wherein the L2 reset includes one or more of the following: a full L2 reset of one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control (MAC) reset; a partial MAC reset; a reconstruction; a radio link control (RLC) reconstruction; a packet data convergence protocol (PDCP) reconstruction; a data recovery; and a PDCP data recovery.

[0264] 7. The method according to any one of embodiments 1 to 6, wherein the first command is included in a low layer signal.

[0265] 8. The method according to any one of embodiments 1 to 7, wherein the first command is included in a media access control (MAC) control element (CE) or downlink control information (DCI).

[0266] 9. The method according to any one of embodiments 1 to 8, wherein a first command for performing an LTM cell transition to the first target cell is received from a first network node.

[0267] 10. The method according to any one of embodiments 1 to 9, wherein obtaining (703) the first L2 reset indication includes:

[0268] Receiving the first L2 reset indication from the first network node.

[0269] 11. The method according to any one of embodiments 9 to 10, wherein the first network node is a distributed unit (DU) that provides service to the UE.

[0270] 12. The method according to any one of embodiments 1 to 11, wherein the first L2 reset indication is received in a media access control (MAC) control element (CE).

[0271] 13. The method according to any one of embodiments 1 to 12, wherein obtaining (703) the first L2 reset indication includes:

[0272] Receiving the first L2 reset indication in the same or a different L2 signaling as the LTM configuration of the first target cell.

[0273] 14. The method according to any one of embodiments 1 to 13, wherein the first L2 reset indication relates to one or more of the following: a media access control (MAC) entity, a cell group, an L2 protocol entity, a radio bearer, a data radio bearer, a signaling radio bearer, or a radio link control (RLC) bearer.

[0274] 15. The method according to any one of embodiments 1 to 14, wherein the first L2 reset indication includes a list of one or more cells, wherein if the UE is in one of the listed cells when the UE performs an LTM cell transition, the L2 reset should not be performed.

[0275] 16. The method according to any one of embodiments 1 to 15, wherein performing (704) an LTM cell transition to the first target cell includes:

[0276] Determining, based on the first L2 reset indication, whether an L2 reset should be performed during the LTM cell transition to the first target cell;

[0277] In response to determining that the L2 reset should be performed, performing the L2 reset during the LTM cell transition to the first target cell; and

[0278] In response to determining that the L2 reset should not be performed, perform (704) an LTM cell transition to the first target cell without performing the L2 reset.

[0279] 17. The method according to any one of embodiments 1 to 16, wherein the one or more LTM candidate target cells further include a second target cell.

[0280] 18. The method according to embodiment 17, wherein the method further includes:

[0281] After performing (704) a cell transition to the first target cell, receive a second command for performing an LTM cell transition to the second target cell;

[0282] Obtain a second L2 reset indication, the second L2 reset indication including an indication as to whether the L2 reset should be performed during the LTM cell transition to the second target cell; and

[0283] Perform an LTM cell transition to the second target cell according to the second command.

[0284] 19. The method according to embodiment 18, wherein performing an LTM cell transition to the second target cell includes:

[0285] Based on the second L2 reset indication, determine whether the L2 reset should be performed during the LTM cell transition to the second target cell;

[0286] In response to determining that the L2 reset should be performed, perform the L2 reset during the LTM cell transition to the second target cell; and

[0287] In response to determining that the L2 reset should not be performed, perform an LTM cell transition to the second target cell without performing the L2 reset.

[0288] 20. The method according to any one of embodiments 1 to 19, wherein the UE is operating in a dual connection having a master cell group (MCG) including a primary cell (PCell) and at least one secondary cell group (SCG) including a primary cell (PSCell).

[0289] Group B Embodiments (1) (First Network Node = Serving DU / S-DU and First Target NN / Second Target NN)

[0290] 21. A method performed by a first network node (e.g., a source network node, S-DU, first target network node, second target network node), the method including:

[0291] Send a first layer 2 (L2) reset indication, the first L2 reset indication including an indication as to whether the user equipment (UE) should perform an L2 reset during a layer 1 / layer 2 triggered mobility LTM cell transition to a first target cell.

[0292] 22. The method according to embodiment 21, wherein the first L2 reset indication is sent to the UE.

[0293] 23. The method according to any one of embodiments 21 to 22, wherein the first L2 reset indication is sent in a media access control (MAC) control element (CE).

[0294] 24. The method according to embodiment 23, wherein the MAC CE further includes an LTM configuration of one or more LTM candidate target cells, wherein the one or more LTM candidate target cells include the first target cell.

[0295] 25. The method according to any one of embodiments 21 to 24, wherein the first L2 reset indication is included in an LTM configuration of one or more LTM candidate target cells, wherein the one or more LTM candidate target cells include the first target cell.

[0296] 26. The method according to any one of embodiments 21 to 25, wherein the first L2 reset indication is sent in the same or different L2 signaling as an LTM configuration of one or more LTM candidate target cells.

[0297] 27. The method according to any one of embodiments 21 to 26, wherein the first L2 reset indication is sent to a third network node.

[0298] 28. The method according to embodiment 27, wherein the third network node is a central unit (CU).

[0299] 29. The method according to any one of embodiments 21 to 28, wherein the first network node is a distributed unit (DU).

[0300] 30. The method according to any one of embodiments 21 to 29, wherein the L2 reset includes a reset of (only) one or more of a plurality of L2 protocols.

[0301] 31. The method according to any one of embodiments 21 to 30, wherein the UE is operating in a cell group controlled by the first network node.

[0302] 32. A method according to any one of embodiments 21 to 31, wherein the UE is operating in a dual connection having a master cell group (MCG) including a primary cell (PCell) and at least one secondary cell group (SCG) including a primary secondary cell (PSCell), wherein the serving cell includes the PCell and the PSCell.

[0303] 33. A method according to any one of embodiments 21 to 32, wherein the L2 reset includes one or more of the following: a complete L2 reset of one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control (MAC) reset; a partial MAC reset; a reconstruction; a radio link control (RLC) reconstruction; a packet data convergence protocol (PDCP) reconstruction; a data recovery; and a PDCP data recovery.

[0304] Group B Embodiments (2) (Third Network Node = Serving CU)

[0305] 34. A method performed by a third network node serving a user equipment (UE), the method comprising:

[0306] sending, to the UE, an LTM configuration for one or more layer 1 / layer 2 triggered mobility (LTM) candidate target cells, wherein the one or more LTM candidate target cells include a first target cell.

[0307] 35. A method according to embodiment 34, wherein the LTM configuration is included in an RRC reconfiguration message.

[0308] 36. A method according to any one of embodiments 34 to 35, wherein the method further comprises:

[0309] sending, to the UE, a first L2 reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during an LTM cell transition to the first target cell.

[0310] 37. A method according to embodiment 36, wherein the first L2 indication is sent together with the LTM configuration of the one or more LTM candidate target cells.

[0311] 38. A method according to any one of embodiments 36 to 37, wherein the first L2 reset indication is sent in the same or different L2 signaling as the LTM configuration of one or more candidate target cells.

[0312] 39. A method according to any one of embodiments 36 to 38, wherein the first L2 indication is received from a first network node.

[0313] 40. The method according to embodiment 39, wherein the first network node is a distributed unit (DU).

[0314] 41. The method according to any one of embodiments 36 to 40, wherein the first L2 indication is received from a first target network node.

[0315] 42. The method according to embodiment 41, wherein the first target network node is a candidate distributed unit (DU).

[0316] 43. The method according to any one of embodiments 36 to 42, wherein the L2 reset includes a reset of one or more (only) of a plurality of L2 protocols.

[0317] 44. The method according to any one of embodiments 36 to 43, wherein the L2 reset includes one or more of the following: a full L2 reset of one or more L2 protocol sub-layers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control (MAC) reset; a partial MAC reset; a reconstruction; a radio link control (RLC) reconstruction; a packet data convergence protocol (PDCP) reconstruction; a data recovery; and a PDCP data recovery.

[0318] 45. The method according to any one of embodiments 34 to 44, wherein the third network node is a centralized unit (CU).

[0319] Group C Embodiments

[0320] 46. A computer program product comprising a computer-readable medium having computer-readable code configured to, when executed by a suitable computer or processor, cause the computer or processor to perform the method according to any one of Group A embodiments or Group B embodiments.

[0321] 47. A user equipment (UE) configured to perform the method according to any one of Group A embodiments.

[0322] 48. A user equipment (UE) comprising a processor and a memory, the memory containing instructions executable by the processor, whereby the UE is operable to perform the method according to any one of Group A embodiments.

[0323] 49. A network node configured to perform the method according to any one of Group B embodiments.

[0324] 50. A network node includes a processor and a memory, the memory containing instructions executable by the processor, whereby the first RAN node is operable to perform the method according to any one of the embodiments in Group B.

[0325] 51. A user equipment includes:

[0326] Processing circuitry configured to cause the user equipment to perform any step according to any one of the embodiments in Group A; and

[0327] Power circuitry configured to supply power to the processing circuitry.

[0328] 52. A network node includes:

[0329] Processing circuitry configured to cause the network node to perform any step according to any one of the embodiments in Group B;

[0330] Power circuitry configured to supply power to the processing circuitry.

[0331] 53. A user equipment (UE), the UE includes:

[0332] An antenna configured to transmit and receive wireless signals;

[0333] Radio front-end circuitry connected to the antenna and the processing circuitry and configured to condition signals transmitted between the antenna and the processing circuitry;

[0334] Processing circuitry configured to perform any step according to any one of the embodiments in Group A;

[0335] An input interface connected to the processing circuitry and configured to allow information to be input into the UE for processing by the processing circuitry;

[0336] An output interface connected to the processing circuitry and configured to output from the UE information that has been processed by the processing circuitry; and

[0337] A battery connected to the processing circuitry and configured to supply power to the UE.

Claims

1. A method performed by a user equipment UE, the method comprising: receiving (201, 701) an LTM configuration of one or more layer 1 / layer 2 triggered mobility LTM candidate target cells, wherein the one or more LTM candidate target cells include a first target cell; receiving (202, 702) a first command for performing an LTM cell transition to the first target cell; obtaining (203, 703) a first layer 2 "L2" reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during the LTM cell transition to the first target cell; and performing (204, 704) an LTM cell transition to the first target cell according to the first command.

2. The method according to claim 1, wherein, the LTM configuration is included in a radio resource control RRC reconfiguration message.

3. The method according to claim 1 or 2, wherein, L2 reset includes: resetting one or more of a plurality of L2 protocols.

4. The method according to any one of claims 1 to 3, wherein, L2 reset includes one or more of the following: a complete L2 reset for one or more L2 protocol sub-layers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control MAC reset; a partial MAC reset; a reconstruction; a radio link control RLC reconstruction; a packet data convergence protocol PDCP reconstruction; a data recovery; and a PDCP data recovery.

5. The method according to any of the preceding claims, wherein, the first command is included in a media access control MAC control element CE.

6. The method according to any of the preceding claims, wherein, obtaining (203, 703) the first L2 reset indication includes: receiving the first L2 reset indication in the same L2 signaling as the LTM configuration of the first target cell.

7. The method according to any of the preceding claims, wherein, the first L2 reset indication is included in the LTM configuration.

8. The method according to any of the preceding claims, wherein, the first L2 reset indication includes a list of one or more cells, wherein if the UE is in one of the listed cells when the UE performs an LTM cell transition, the L2 reset should not be performed.

9. The method according to any of the preceding claims, wherein, performing (204, 704) an LTM cell transition to the first target cell includes: determining, based on the first L2 reset indication, whether an L2 reset should be performed during the LTM cell transition to the first target cell; in response to determining that the L2 reset should be performed, performing the L2 reset during the LTM cell transition to the first target cell; and in response to determining that the L2 reset should not be performed, performing (204, 704) the LTM cell transition to the first target cell without performing the L2 reset.

10. The method according to any of the preceding claims, wherein, The LTM configuration is received from a central unit CU serving the UE or a distributed unit DU serving the UE.

11. A method performed by a network node serving a user equipment UE, the method comprising: sending (401) to the UE an LTM configuration of one or more layer 1 / layer 2 triggered mobility LTM candidate target cells, wherein the one or more LTM candidate target cells include a first target cell.

12. The method according to claim 11, wherein, the LTM configuration is included in a radio resource control RRC reconfiguration message.

13. The method according to claim 11 or 12, wherein, the method further comprises: sending to the UE a first L2 reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during an LTM cell transition to a first target cell.

14. The method according to claim 13, wherein, the first L2 indication is sent together with the LTM configuration of the one or more LTM candidate target cells.

15. The method according to any one of claims 13 to 14, wherein, the first L2 reset indication is included in the LTM configuration.

16. The method according to any one of claims 13 to 15, wherein, L2 reset includes resetting one or more of a plurality of L2 protocols.

17. The method according to any one of claims 13 to 16, wherein, L2 reset includes one or more of the following: a full L2 reset of one or more L2 protocol sublayers and / or one or more L2 protocol entities configured for the UE; a partial L2 reset; a media access control MAC reset; a partial MAC reset; a reconstruction; a radio link control RLC reconstruction; a packet data convergence protocol PDCP reconstruction; a data recovery; and a PDCP data recovery.

18. The method according to any one of claims 13 to 17, wherein, the first L2 reset indication includes a list of one or more cells, wherein if the UE is in one of the listed cells when the UE performs an LTM cell transition, the L2 reset should not be performed.

19. The method according to any one of claims 11 to 18, wherein, the network node is a central unit CU or a distributed unit DU.

20. A user equipment UE (501, 1000, 912A, 912B) adapted to perform the method according to any one of claims 1 to 10.

21. A user equipment UE, comprising a processor and a memory, the memory containing instructions executable by the processor, whereby the UE is operable to: receive an LTM configuration of one or more layer 1 / layer 2 triggered mobility LTM candidate target cells, wherein, the one or more LTM candidate target cells include a first target cell; receive a first command for performing an LTM cell transition to the first target cell; Obtain a first layer 2 "L2" reset indication, the first L2 reset indication including an indication as to whether an L2 reset should be performed during an LTM cell transition to the first target cell; and Perform an LTM cell transition to the first target cell according to the first command.

22. The UE according to claim 21, wherein, The UE is further operable to perform the method according to any one of claims 2 to 10.

23. A network node (506, 1100, 910A, 910B) adapted to perform the method according to any one of claims 11 to 19.

24. A network node comprising a processor and a memory, the memory containing instructions executable by the processor, whereby the network node is operable to send to a UE served by the network node one or more layer 1 / layer 2 trigger mobility LTM configuration of LTM candidate target cells, wherein, The one or more LTM candidate target cells include a first target cell.

25. The network node according to claim 24, wherein, The network node is further operable to perform the method according to any one of claims 12 to 19.

26. A computer program product comprising a computer-readable medium having computer-readable code embodied therein, the computer-readable code being configured to: when executed by a suitable computer or processor, cause the computer or processor to perform the method according to any one of claims 1 to 19.

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