Communication regarding SCG information for LTM cell change for ue

Abstract

A method includes receiving, by a user device (UE) from a serving node (e.g., source MN), an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

Description

COMMUNICATION REGARDING SCG INFORMATION FOR LTM CELL CHANGEFOR UETECHNICAL FIELD

[0001] This description relates to wireless communications.BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3rd Generation Partnership Project (3 GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. EUTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations or access points (APs), which are referred to as enhanced Node AP (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments. Aspects of LTE are also continuing to improve.

[0004] 5G New Radio (NR) development is part of a continued mobile broadband evolution process to meet the requirements of 5G, similar to earlier evolution of 3G and 4G wireless networks. In addition, 5G is also targeted at the new emerging use cases in addition to mobile broadband. A goal of 5G is to provide significant improvement in wireless performance, which may include new levels of data rate, latency, reliability, and security. 5G NR may also scale to efficiently connect the massive Internet of Things (loT) and may offer new types of mission- critical services. For example, ultra-reliable and low-latency communications (URLLC) devices may require high reliability and very low latency. 6G and other networks are also being developed.SUMMARY

[0005] In some aspects, the techniques described herein relate to a method including: receiving, by a user device from a serving node, an indication that instructs the user device not touse a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

[0006] In some aspects, the techniques described herein relate to an apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a user device from a serving node, an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

[0007] In some aspects, the techniques described herein relate to a method including: sending, by a source master node (MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device; and receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

[0008] In some aspects, the techniques described herein relate to an apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: sending, by a source master node(MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device; and receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

[0009] In some aspects, the techniques described herein relate to a method including: receiving, by a target master node (MN) from a source MN that is serving a user device, a handover request message for layer 1 / 2 triggered mobility (LTM) cell switch or handover of the user device, wherein the handover request message includes an indication that indicates a preference or requirement for the target MN to retain or prepare a secondary cell group (SCG) configuration or provide dual connectivity (DC) for the LTM cell switch or handover of the user device; and transmitting, by the target MN to the source MN, a handover request acknowledgement including an indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a SCG configuration or 2) a MCG configuration only, for the LTM cell switch or handover of the user device to a cell of the target MN.

[0010] In some aspects, the techniques described herein relate to an apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a target master node (MN) from a source MN that is serving a user device, a handover request message for layer 1 / 2 triggered mobility (LTM) cell switch or handover of the user device, wherein the handover request message includes an indication that indicates a preference or requirement for the target MN to retain or prepare a secondary cell group (SCG) configuration or provide dual connectivity (DC) for the LTM cell switch or handover of the user device; and transmitting, by the target MN to the source MN, a handover request acknowledgement including an indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a SCG configuration or 2) a MCG configuration only, for the LTM cell switch or handover of the user device to a cell of the target MN.

[0011] Other example embodiments are provided or described for each of the example methods, including: means for performing any of the example methods; a non-transitorycomputer-readable storage medium comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a computing system to perform any of the example methods; and an apparatus including at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform any of the example methods.

[0012] The details of one or more examples of embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a block diagram of a wireless network 130.

[0014] FIG. 2 is a diagram illustrating an example procedure for LTM according to an example embodiment.

[0015] FIG. 3 is a signaling diagram of a system according to an example embodiment.

[0016] FIG. 4 is a signaling diagram of a system according to another example embodiment.

[0017] FIG. 5 is a signaling diagram of a system according to another example embodiment.

[0018] FIG. 6 is a flow chart illustrating operation of a user device (UE) according to example embodiment.

[0019] FIG. 7 is a flow chart illustrating operation of a source master node according to example embodiment.

[0020] FIG. 8 is a flow chart illustrating operation of a target master node according to example embodiment.

[0021] FIG. 9 is a block diagram of a wireless station or node (e.g., UE, user device, AP, BS, eNB, gNB, RAN node, network node, TRP, or other node) 1300 according to an example embodiment.DETAILED DESCRIPTION

[0022] It shall be understood that although the terms “first,” “second,”... , etc., in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a secondelement, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0023] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0024] FIG. 1 is a block diagram of a wireless network 130. In the wireless network 130 of FIG. 1, user devices 131, 132, 133 and 135, which may also be referred to as mobile stations (MSs) or user equipment (UEs), may be connected (and in communication) with a base station (BS) 134, which may also be referred to as an access point (AP), an enhanced Node B (eNB), a gNB or a network node. The terms user device and user equipment (UE) may be used interchangeably. A BS may also include or may be referred to as a RAN (radio access network) node, and may include a portion of a BS or a portion of a RAN node, such as e.g., a centralized unit (CU) and / or a distributed unit (DU) in the case of a split BS or split gNB. At least part of the functionalities of a BS (e.g., access point (AP), base station (BS) or (e)Node B (eNB), gNB, RAN node) may also be carried out by any node, server or host which may be operably coupled to a transceiver, such as a remote radio head. BS (or AP) 134 provides wireless coverage within a cell 136, including to user devices (or UEs) 131, 132, 133 and 135. Although only four user devices (or UEs) are shown as being connected or attached to BS 134, any number of user devices may be provided. BS 134 is also connected to a core network 150 via a NG interface 151. This is merely one simple example of a wireless network, and others may be used.

[0025] A base station (e.g., such as BS 134) is an example of a radio access network (RAN) node within a wireless network. A BS (or a RAN node) may be or may include (or may alternatively be referred to as), e.g., an access point (AP), a gNB, an eNB, or portion thereof (such as a centralized unit (CU) and / or a distributed unit (DU) in the case of a split BS or split gNB), or other network node.

[0026] Some functionalities of the communication network may be carried out, at least partly, in a central / centralized unit, CU, (e.g., server, host or node) operationally coupled to distributed unit, DU, (e.g., a radio head / node). Thus, 5G networks architecture may be based on a so-called CU-DU split. The gNB-CU (central node) may control a plurality of spatially separated gNB-DUs, acting at least as transmit / receive (Tx / Rx) nodes. In someembodiments, however, the gNB-DUs (also called DU) may comprise e.g., a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the gNB-CU (also called a CU) may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layer. Other functional splits are possible too.

[0027] According to an illustrative example, a BS node (e.g., BS, eNB, gNB, CU / DU, ...) or a radio access network (RAN) may be part of a mobile telecommunication system. A RAN (radio access network) may include one or more BSs or RAN nodes that implement a radio access technology, e.g., to allow one or more UEs to have access to a network or core network (CN). Thus, for example, the RAN (RAN nodes, such as BSs or gNBs) may reside between one or more user devices or UEs and a core network. According to an example embodiment, each RAN node (e.g., BS, eNB, gNB, CU / DU, ... ) or BS may provide one or more wireless communication services for one or more UEs or user devices, e.g., to allow the UEs to have wireless access to a network, via the RAN node. Each RAN node or BS may perform or provide wireless communication services, e.g., such as allowing UEs or user devices to establish a wireless connection to the RAN node, and sending data to and / or receiving data from one or more of the UEs. For example, after establishing a connection to a UE, a RAN node or network node (e.g., BS, eNB, gNB, CU / DU, ... ) may forward data to the UE that is received from a network or the core network, and / or forward data received from the UE to the network or core network. RAN nodes or network nodes (e.g., BS, eNB, gNB, CU / DU, ... ) may perform a wide variety of other wireless functions or services, e.g., such as broadcasting control information (e.g., such as system information or on-demand system information) to UEs, paging UEs when there is data to be delivered to the UE, assisting in handover of a UE between cells, scheduling of resources for uplink data transmission from the UE(s) and downlink data transmission to UE(s), sending control information to configure one or more UEs, and the like. These are a few examples of one or more functions that a RAN node or BS may perform.

[0028] A user device or user node (user terminal, user equipment (UE), mobile terminal, handheld wireless device, etc.) may refer to a portable computing device that includes wireless mobile communication devices operating either with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (MS), a mobile phone, a cell phone, a smartphone, a personal digital assistant (PDA), a handset, adevice using a wireless modem (alarm or measurement device, etc.), a laptop and / or touch screen computer, a tablet, a phablet, a game console, a notebook, a vehicle, a sensor, and a multimedia device, as examples, or any other wireless device. It should be appreciated that a user device may also be (or may include) a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. Also, a user node may include a user equipment (UE), a user device, a user terminal, a mobile terminal, a mobile station, a mobile node, a subscriber device, a subscriber node, a subscriber terminal, or other user node. For example, a user node may be used for wireless communications with one or more network nodes (e.g., gNB, eNB, BS, AP, CU, DU, CU / DU) and / or with one or more other user nodes, regardless of the technology or radio access technology (RAT). In LTE (as an illustrative example), core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility / handover of user devices between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the Internet, and other control functions or blocks. Other types of wireless networks, such as 5G (which may be referred to as New Radio (NR)) may also include a core network.

[0029] In addition, the techniques described herein may be applied to various types of user devices or data service types, or may apply to user devices that may have multiple applications running thereon that may be of different data service types. New Radio (5G) development may support a number of different applications or a number of different data service types, such as for example: machine type communications (MTC), enhanced machine type communication (eMTC), Internet of Things (loT), and / or narrowband loT user devices, enhanced mobile broadband (eMBB), and ultra-reliable and low-latency communications (URLLC). Many of these new 5G (NR) - related applications may require generally higher performance than previous wireless networks.

[0030] loT may refer to an ever-growing group of objects that may have Internet or network connectivity, so that these objects may send information to and receive information from other network devices. For example, many sensor type applications or devices may monitor a physical condition or a status and may send a report to a server or other network device, e.g., when an event occurs. Machine Type Communications (MTC, or Machine to Machine communications) may, for example, be characterized by fully automatic data generation, exchange, processing andactuation among intelligent machines, with or without intervention of humans. Enhanced mobile broadband (eMBB) may support much higher data rates than currently available in LTE.

[0031] Ultra-reliable and low-latency communications (URLLC) is a new data service type, or new usage scenario, which may be supported for New Radio (5G) systems. This enables emerging new applications and services, such as industrial automations, autonomous driving, vehicular safety, e-health services, and so on. 3 GPP targets in providing connectivity with reliability corresponding to block error rate (BLER) of 10-5 and up to 1 ms U-Plane (user / data plane) latency, by way of illustrative example. Thus, for example, URLLC user devices / UEs may require a significantly lower block error rate than other types of user devices / UEs as well as low latency (with or without requirement for simultaneous high reliability). Thus, for example, a URLLC UE (or URLLC application on a UE) may require much shorter latency, as compared to an eMBB UE (or an eMBB application running on a UE).

[0032] The techniques described herein may be applied to a wide variety of wireless technologies or wireless networks, such as 5G (New Radio (NR)), cmWave, and / or mmWave band networks, loT, MTC, eMTC, eMBB, URLLC, 6G, etc., or any other wireless network or wireless technology. These example networks, technologies or data service types are provided only as illustrative examples.

[0033] A user device (or UE) may measure various signals and may transmit one or more measurement reports to the network. For example, a UE may measure reference signals received from one or more network nodes (e.g., gNBs or DUs), including channel state information-reference signals (CSI-RSs) and / or synchronization signal block (SSB) reference signals, demodulation references signals, and / or other reference signals. Based on received reference signals, the UE may measure various signal parameters, e.g., such as reference signal received power (RSRP), reference signal received quality (RSRQ), signal to interference plus noise ratio (SINR), received signal strength indicator (RSSI), or other signal parameter.

[0034] The PHY (physical) layer may refer to layer 1 (LI) and MAC (media access control) may refer to layer 2 (L2). RSRP, RSRQ, SINR and RSSI are signal quantities measured at layer 1 (LI). The UE may send LI measurement reports (e.g., CSI-RS reports, which include measurements of one or more signal parameters for one or more cells) to a gNB, source DU or serving cell. These LI measurement reports may be sent periodically, for example, or aperiodically. L1 / L2 measurement reports may include no averaging or filtering of measurementvalues or may include less averaging or filtering than what is performed for L3 measurement reports. LI (or L1 / L2) measurement reports may be transmitted by a UE to a serving network node or source DU and may cause the network node to trigger or initiate a L1 / L2 triggered mobility (LTM) handover of the UE to another cell. LI measurements (e.g., RSRP RSRQ, RSSI) may be provided or reported periodically to the DU (MAC / PHY).

[0035] Layer 3 (L3) measurement reports may be event-based measurement reports, e.g., which may be triggered when a cell (e.g., a neighbour cell) has a RSRP or RSSI (or other signal parameter) that meets some handover (HO) event criteria. For example, a L3 measurement report may be transmitted by a UE to a serving cell or network node if, e.g., a serving cell measured signal becomes / is worse than a threshold, a neighbour cell signal measurement is or becomes better than a first threshold and / or serving cell signal measurement becomes an offset threshold worse than a neighbouring cell’s signal measurement, etc. Thus, L3 measurement reports may be event-triggered measurement reports.

[0036] The L3 measurement report may include or may be based on averaging and / or filtering of multiple signal samples, or averaging over a longer period of time, as compared to the LI measurement report. Also, L3 measurement reports may be transmitted to a CU, and may be event-triggered measurement reports and may trigger a network node to initiate or trigger a handover (e.g., L3 handover, which may be basic handover or conditional handover) of the UE to another cell. A L3 handover (L3 HO) may be, for example, based on a L3 measurement report. In response to receiving a L3 measurement report from a UE, a source network node (e.g., gNB, or source CU) may send a handover request to a target network node (e.g., target CU). The source network node may transmit to the UE a RRC reconfiguration message including a HO command to cause the UE to perform handover to the target cell, or a CHO configuration (to configure the conditional handover conditions that will trigger or cause the UE to initiate CHO to the target cell).

[0037] Because the L3 HO (either HO or conditional handover (CHO)) is based on a L3 measurement report, e.g., which may require more time to obtain or measure (e.g., based on more signal measurement samples and / or filtering and / or averaging of the measurement samples) as compared to a LI measurement report, the L3 measurement report may be transmitted by a UE well after radio conditions with a serving cell / serving network node have already degraded. If a handover configuration is not already prepared for a HO or CHO to the target cell, then thesource network node may need to send a message to the target node to request and prepare the HO configuration for the UE, which may cause significant delay, e.g., of 100ms or more, before the UE can perform a L3 HO or CHO to the target cell. This significant delay may increase the likelihood the UE will suffer a radio link failure (RLF) or loss in connectivity.

[0038] In 3GPP Release 18, additional mobility enhancements, for example layer 1 / layer 2 or Ll / L2-triggered mobility (LTM) is introduced to facilitate faster inter-cell mobility than traditional mobility mechanisms based on RRC signalling. LTM is a procedure in which a gNB may receive LI measurement report(s) from a UE, and on this basis the gNB may change a serving cell of the UE by a cell switch command that may be transmitted or signalled via a media access control (MAC) control element (CE) (e.g., MAC CE). The cell switch command may indicate an LTM candidate cell configuration that the gNB previously prepared and provided to the UE through RRC signalling. In an example, the LTM candidate cell configuration may be within a configuration message such as RRC Reconfiguration, and may be part of an information element such as an LTM-Config IE. In an example, based on receiving the cell switch command, the UE may switch to a target cell (or a target cell configuration) according to the cell switch command, where the target cell is one of the candidate cells in the LTM candidate cell configuration. The LTM procedure may be employed to reduce latency of a mobility procedure.

[0039] In dual connectivity (DC), a UE may be simultaneously connected to two different RAN nodes, e.g., two different gNBs or two different DUs. The UE may be able to send and receive data with each of the two nodes, e.g., to improve performance for the UE. There may be different node types. For example, in the case of multi-radio dual connectivity (MR-DC), a master node (MN) may provide the control plane for the UE to the core network. A secondary node (SN) does not have a control plane connection to the core network, but provides additional resources for the UE. There may be two different types of cell groups. A master cell group (MCG) is a group of one or more serving cells associated with the primary RAN node (the MN), including at least a primary cell (PCell), and may include one or more secondary cells (SCells). The PCell may be used for initiating initial access. A secondary cell group (SCG) is a group of serving cells associated with the secondary RAN node (the SN), including at least a primary secondary cell (PSCell).

[0040] Also, in terms of a LTM handover or LTM procedure, the node (e.g., RAN node or network node, such as gNB, DU) that the UE is connected to before the LTM cell switch orhandover is referred to as the source MN (which is also the serving MN before LTM). The node that the UE is connected to after the LTM cell switch or handover of the UE is referred to as the target MN (which is the serving MN for the UE after the LTM cell switch). The target MN is the node associated with the candidate cell to which LTM cell switch of the UE is performed. The LTM procedure may include multiple phases, including LTM preparation, LI measurements and DL / UL (downlink / uplink) pre-synchronization, and LTM execution and completion. Briefly, in a LTM preparation phase, the UE is in RRC connected mode with a serving node or source node (source MN), and the UE is pre-configured with LTM candidate cells including RRC configuration for each cell (e.g., where a RRC configuration may include a MCG configuration and a SCG configuration). In a second phase, the UE transmits LI measurement reports for the current serving cell (associated with the source MN) and one or more LTM candidate cells, and the UE may perform DL and / or UL pre-synchronization with one or more of the candidate cells. Each of the candidate cells is associated with a candidate MN or target MN. At a third phase of LTM procedure, the source MN transmits a LTM cell switch command MAC CE (MAC control element) to the UE (instructing the UE to perform LTM cell switch to an indicated LTM candidate cell or target cell (associated with a target MN), and the UE performs the cell switch by: applying the stored RRC configuration for the indicated LTM candidate cell (to the target MN) and may perform a random access procedure to the target cell if the UL presynchronization was not performed.

[0041] FIG. 2 is a diagram illustrating an example procedure for LTM. At step 1, the UE 210 may send a measurement report message to the gNB 220. In an example, the UE may be in RRC connected state or mode. The gNB 220 may determine or decide to configure LTM and may initiate LTM preparation. At step 2, the gNB 220 may transmit an RRC reconfiguration message to the UE 210 that may include the LTM candidate configurations. At step 3, the UE 210 may store the LTM candidate configurations and transmit an RRC reconfiguration complete message to the gNB 220. At step 4a, the UE 210 may perform DL synchronization with the candidate cell(s) before receiving the cell switch command. At step 4b, when UE-based TA measurement is configured, the UE 210 may acquire the TA value(s) of the candidate cell(s) by measurement. The UE 210 may perform early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command. This may be done, e.g., via contention free random access (CFRA) triggered by a PDCCH order from the source cell, following which theUE sends preamble towards the indicated candidate cell(s). In order to minimize the data interruption due to CFRA during a switch from the source cell to the candidate cell(s), the UE 210 may not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell may be indicated in the cell switch command. In an example, the UE 210 may not maintain the TA timer for the candidate cell and may rely on network implementation to guarantee the TA validity. At step 5, the UE 210 may perform LI (layer 1) measurements on the configured candidate cell(s) and transmit LI measurement reports to the gNB 220. At step 6, the gNB 220 may determine or decide to execute cell switch to a target cell and may transmit a MAC CE. The MAC CE may trigger a cell switch by including (or indicating) the candidate (or candidate cell) configuration index of the target cell. Based on receiving the MAC CE (or cell switch command), the UE 210 may typically then perform cell switch (or RRC) processing for the target candidate cell configuration in which the UE decodes and performs validity confirmation of the target candidate cell configuration identified by the MAC CE (where the target candidate cell configuration was one of N (e.g., 8) candidate cell configurations previously received by the UE via message 2 above), and then the UE may perform a cell switch to the target cell and may apply the target candidate cell configuration indicated by candidate configuration index. At step 7, the UE 210 may perform the random access procedure towards the target cell, if UE 210 does not have a valid TA of the target cell. At step 8, the UE 210 may complete the LTM cell switch procedure by sending an RRC reconfiguration complete message to the target cell. If the UE 210 has performed a random access (RA) procedure in step 7, the UE 210 may consider or determine that the LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE 210 may determine or consider that the LTM cell switch execution is successfully completed when the UE 210 determines that the network has successfully received its first UL data. The steps 4-8 can be performed multiple times for subsequent LTM using the LTM candidate configuration(s) provided in step 2. The procedure described in FIG. 2 is applicable to both intra-gNB-DU LTM and inter-gNB-DU LTM.

[0042] Presently, a source MN may include a master cell group (MCG) configuration and a secondary cell group (SCG) configuration in a handover request message sent by the source MN to a target MN. However, presently, it is up to the target MN whether to use or prepare the SCG configuration (provide dual connectivity). Currently, the target MN may use (prepare) or not use(not prepare) the SCG configuration. In some cases, this can result in a dual connectivity for a UE changing to a single connectivity, if the target MN has not prepared a SCG configuration for UE LTM handover.

[0043] In some cases, it may be desirable (or preferred), or may even be required, to maintain dual connectivity for a UE, e.g., in order to maintain a specific level of performance for the UE. For example, the UE may have specific data rate or throughput requirements, latency requirements, and / or other QoS or performance related requirements, which may be only met or best met via use of dual connectivity (DC). The source MN may configure cells of one or more target MNs for a LTM handover or cell change of the UE from the source MN to the cell of the target MN (e.g., target gNB). However, in some cases, the target MN may be unable to prepare both a MCG configuration and a SCG configuration for dual connectivity for the LTM cell switch or handover. Existing specifications or techniques do not have any means for a source MN to indicate a preference to retain dual connectivity for a UE, nor techniques that allow for the target (or candidate) MNs to inform the source MN of whether dual connectivity can be retained (provided) (including MCG and SCG configurations prepared at the target MN) at the target MN for the UE. In such a case, the source MN triggering LTM handover to a target MN (e.g., which does not support dual connectivity for the UE, e.g., due to lack of preparation of a SCG configuration for the UE), may result in changing of dual connectivity to a single connectivity for the UE, and thereby result in a decrease in performance for the UE after LTM cell switch or handover to the cell of the target MN.

[0044] In some cases, the source MN may receive a UE context kept notification that may indicate whether the target MN has prepared the SCG configuration at the source secondary node context (SN context for the currently serving secondary node, that is currently serving the UE) for the UE. However, for example, in a case where the target MN has prepared a SCG configuration for a secondary node (SN) that is different than the currently serving SN, the UE context kept notification will not be useful to understand if the target MN has prepared SCG configuration in a different target SN. Furthermore, the MCG and the SCG configuration that the target MN prepares is included in the handover (HO) Command and is transparently forwarded to the UE, and the source MN is unaware if the target MN has prepared MCG configuration only or MCG + SCG configurations; such information may be useful to decide on which candidatenode to consider for LTM subsequent cell change preparation. Subsequent cell change may mean or include avoiding RRC configuration of the UE between cell switches.

[0045] Therefore, it may be desirable to include additional information about the prepared LTM configuration (i.e., MCG configuration only has been prepared, or both MCG and SCG configurations have been prepared) at the target MN, to allow the source node (source MN) to know whether the target node (target MN) has prepared MCG + SCG configuration or MCG only configuration, so that dual connectivity may be retained or continued for the UE even after a LTM cell switch or handover. Such awareness of Cell Group Configuration prepared by the target node (target MN), may enable the source node (source MN) to reconfigure the UE appropriately to avoid unspecified and ambiguous UE and Network behavior.

[0046] According to example embodiments, a “Need SCG Configuration” indication in a LTM handover request message may indicate a request, preference or requirement for the target MN to retain (or prepare) SCG (i.e., prepare both MCG and SCG configurations) for the LTM cell switch or handover of the UE (e.g., in order to support dual connectivity or dual connectivity with LTM subsequent cell change). The target MN may prepare MCG and SCG configurations (e.g., if the target MN retains the source SN), or MCG only configuration (e.g., if target MN cannot retain the source SN), and may respond to the LTM handover request message by sending a LTM handover request acknowledgement to the source MN. The LTM handover request acknowledgement may include a “MCG SCG configuration” indication that indicates whether the target MN has prepared: 1) both a MCG configuration and a SCG configuration that supports dual connectivity, or 2) a MCG configuration only, for the LTM cell switch or handover of the UE to a cell of the target MN.

[0047] For example, based on this “MCG SCG Configuration” indication received from one or more target MNs, the source MN may then avoid selecting one or more prepared candidate nodes (candidate or target MNs) that have not prepared dual connectivity configuration from LTM subsequent cell change preparation; instead the source MN may select only the candidate nodes (candidate or target MNs) that have prepared both MCG and SCG configurations (e.g., to enable dual connectivity support after LTM subsequent cell change). Thus, the network may control the source MN to send a LTM cell switch command only to the candidate cells (or target MNs) that are prepared with dual connectivity configuration (including both MCG and SCG configurations prepared at the target MN associated with the candidate cell). For example, flags,bits or bit mask values may be used for indications, such as for “Need SCG Configuration” indication and the “MCG SCG configuration” indication.

[0048] In example embodiments, the source MN after the preparation of candidate nodes (candidate or target MNs) with the LTM dual connectivity HO preparation, source MN may receive the “MCG_SCG_configuration” indication (indicating whether the target MN has prepared MCG configuration only, or MCG and SCG configurations) for each of a plurality of target candidate cells or target MNs for LTM handover of the UE. After a LTM handover or cell change of the UE to a target cell (associated with a target MN), the new serving node (new serving MN, which was the target MN that was selected for LTM cell change or switch) may need to decide on the target cell for next LTM cell change based on which candidate cell has prepared MCG and SCG configuration; for that “MCG SCG configuration” indication (e.g., indicating whether the target MN has prepared MCG and SCG configurations or only a MCG configuration), may be needed in order to trigger LTM cell change or handover of the UE only to those target MNs that have prepared both MCG and SCG configurations, in order to maintain dual connectivity for the UE (e.g., since dual connectivity (DC) for the UE is either required / needed or preferred).

[0049] However, according to example embodiments, source node (source MN) may forward to each of the prepared candidate nodes or cells the information about the configuration(s) each candidate node (each candidate or target MN) has prepared (i.e., MCG and SCG configurations, or MCG configuration only), and this may be done simply by forwarding the “MCG SCG Configuration” indication to each of the prepared candidate nodes (candidate or target MNs) to use this information to decide the control of LTM cell switch only, e.g., to the target cells that are prepared with both MCG and SCG configurations in order to retain the dual connectivity after LTM cell switch or cell change. In an alternate example embodiment, the source node may forward both the HO LTM configuration (including any prepared MCG and / or SCG configurations) that was prepared by the target node together with “MCG SCG Configuration” indication from the node, for each of the prepared candidate cells or nodes.

[0050] Thus, for example, the source MN may send to a plurality of target MNs a handover request message (which may or may not include the “Need SCG configuration” indication) for LTM handover of the UE. The handover request messages sent to the plurality of target MNsmay include a MCG configuration and a SCG configuration, e.g., to prepare the plurality of target MNs for LTM handover of the UE. The source MN may receive, from each of the target MNs, a handover request acknowledgement including an indication (e.g., “MCG_SCG_configuration” indication) for the respective target MN that indicates whether the target MN has prepared: 1) both a MCG configuration and a SCG configuration that supports dual connectivity, or 2) a MCG configuration only that does not support dual connectivity, for the LTM cell switch or handover of the UE to a cell of the target MN. The source MN may also receive the MCG and / or SCG configurations prepared by each of the target MNs.

[0051] The source MN may forward during LTM preparation phase (before LTM cell switch execution), to all the prepared candidate nodes or target MNs, the “MCG SCG configuration” indication alone or along with the prepared LTM HO configuration of the candidate nodes received in the HO Request Acknowledgement message to all the plurality of prepared candidate nodes. In this manner, the target MNs will obtain the “MCG SCG configuration” indication and the prepared configurations for each of the other prepared candidate target MNs, so that the other candidate target MNs will have this information before the initial LTM cell change, which may result in one of the candidate nodes becoming the new serving node. Thus, a more efficient technique is provided (or may be used) in which this information (the MCG and / or SCG configurations prepared by each of the target MNs and the “MCG_SCG_configuration” indication for each of the target MNs), acquired by a source MN, may be shared with target MNs during a LTM preparation phase (before the LTM cell switch execution of the UE to another node), so that they (the target MNs) can use this information to similarly make decisions as to which target MNs to select for LTM handover or cell change for the UE (e.g., to maintain dual connectivity for the UE), if they become a serving master node for the UE.

[0052] In example embodiments, the LTM handover request acknowledgement from the target MN may include a “MCG_SCG_configuration” indication that indicates whether the target MN has prepared: 1) both a MCG configuration and a SCG configuration that supports dual connectivity, or 2) a MCG configuration only, for the LTM cell switch or handover of the UE to a cell (target PCell) of the target MN. This information (“MCG SCG configuration” indication from a target MN) may be used by the source MN, for example, to initiate the release of SCG configuration of serving PSCell at the UE before (or after, or at the time of, or based on) LTM PCell switch to a target PCell that is not prepared with SCG configuration, e.g., based onan indication or information provided in a RRC message or LTM cell switch command sent to the UE.

[0053] The UE may receive from a source MN, a message including an indication (e.g., “Do_Not_Use_SCG_configuration” indication, or a “SCG Release” indication) that instructs the UE not to use a SCG configuration of the last serving PSCell after execution of LTM handover or cell switch to a cell of the target MN. This is because the target MN has only prepared a MCG configuration, and has not prepared a SCG configuration for LTM handover of the UE. The UE may receive information indicating the UE to release a SCG configuration of the last serving PSCell after performing a LTM cell switch or handover to a cell of a target MN. The SCG configuration of the last serving PSCell (SCG configuration prepared by a SN associated with the last serving PSCell before LTM cell swich) is not needed (and may be released) after LTM cell switch or handover of the UE, e.g., since the target MN has not prepared a SCG configuration, but has only prepared a MCG configuration for LTM cell switch or handover of the UE. For example, the UE may release or clear, based on the information, the SCG configuration of the last or latest serving PSCell at the time of LTM cell switch to a target PCell with no prepared SCG configuration. The information may include at least one of the following: an indication (e.g., “SCG Release" indication) included within the LTM cell switch command that instructs the UE to release the SCG configuration of the last serving PSCell; an indication (e.g., “SCG Release” indication) within a LTM candidate configuration that is provided within a radio resource control (RRC) message that instructs the user device to release the SCG configuration of the last serving PSCell; or an indication in MAC CE cell switch command.

[0054] In an example embodiment, the releasing or clearing by the UE may include: releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores a SCG configuration of the last serving PSCell. Or, releasing or clearing by the UE may include releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores the SCG configuration of the latest serving PSCell, while retaining or keeping, the SCG configuration stored in memory.

[0055] For example, the UE may establish a first connection to a PCell of source MN, and a second connection to a PSCell of a source SN, as part of dual connectivity for the UE. The UE may receive from the serving MN an indication via MAC CE cell switch command at the time of PCell switch indicating the UE to release a SCG configuration of the last serving PSCell at thetime of LTM PCell switch or handover to a target PCell of a target MN. Alternatively, the UE may receive via RRC Reconfiguration message during initial preparation, an indication in the LTM candidate target cell configuration indicating the UE to release the SCG configuration of the last serving PSCell at the time of LTM PCell switch. For example, the information (sent to the UE from the source MN to cause the UE to release the SCG configuration) may be based on the target MN preparing only a MCG configuration and not a SCG configuration, for a LTM handover that does not support dual connectivity (e.g., may be based on the “MCG_SCG_configuration” indication for the target MN indicating target MN’s preparation of only a MCG configuration for LTM cell switch or handover of the UE).

[0056] A UE may be reconfigured (via RRCReconfigurationRequest message) by the network (source MN) with the prepared LTM DC (dual connectivity) configuration list of prepared candidate nodes. The UE stores the received RRC configuration in its memory. The UE may maintain separate UE variables to store the serving cell configurations (both MCG and SCG serving cell configurations). For example, the UE may store the serving PCell (primary cell) MCG configuration (associated with serving MNs) in one UE variable (e.g., a LTM MCG configuration storage variable), and the UE stores the serving PSCell SCG configuration (associated with the serving SN) in another UE variable (e.g., a LTM SCG configuration storage variable). The LTM SCG configuration storage variable may be released or cleared by the UE based on the information (e.g., “SCG Release” indication), e.g., provided via LTM cell switch command or RRC message to the UE, since the target MN has not prepared any SCG configuration for LTM cell switch or handover of the UE, and thus, the SCG configuration of last PSCell may be released or cleared from the LTM SCG configuration storage variable as this SCG configuration will not be used for the connection between UE and the target MN (which is only single connectivity based on MCG only configuration).

[0057] In addition, after the LTM PCell change involving SCG release, the new serving master node may inform all the prepared candidate nodes (e.g., all or one or more prepared candidate target MNs) about the SCG release to avoid misalignment.

[0058] FIG. 3 is a signaling diagram of a system according to an example embodiment. Some of the steps of FIG. 3 will be briefly described. In FIGs. 3-5, a UE, source MN (S-MN), a source secondary node (S-SN), a first target MN (T-MN1), a second target MN (T-MN2), and UPF and AMF (core network entities) are shown.

[0059] Step 8: A handover (HO) request message includes a “Need SCG Configuration” indication, to enable the inter Master node candidate to identify the scenario as inter-CU MCG LTM with DC (dual connectivity) at the source MN and that the preparation is to configure subsequent LTM PCell (primary cell) change while retaining DC.

[0060] Step 8: T-MN1 receives a handover request including the“Need SCG configuration” indication, MCG configuration, and a SCG configuration.

[0061] Step 10: even with the “Need SCG configuration” indication received at step 8, the candidate MN (T-MN1) many decide to release the SCG configuration, or may be unable to prepare the SCG configuration.

[0062] Step 11 : candidate MN updates the new “MCG SCG configuration” indication in HO Request Acknowledgement that is sent to the source MN, with the information of whether it has prepared MCG only configuration or MCG + SCG configurations. The HO request acknowledgement may also include the configurations prepared by the T-MN1 (only the MCG configuration in this example). In this example, it is assumed that the T-MN1 has prepared a MCG configuration only (and not prepared SCG configuration) for LTM handover or cell change of the UE.

[0063] Step 12: the new “MCG SCG configuration” indication, received by the source MN (S-MN) at step 11, may be used by the source MN (S-MN) to prevent the configuration of subsequent cell change for a target MN that has prepared MCG only configuration, in case dual connectivity (DC) should or must be retained or continued after subsequent LTM PCell change (per the indication of “Need SCG configuation” indication).

[0064] Step 25: a LI measurement report is sent by the UE to the source MN, which may be a trigger for first LTM PCell switch.

[0065] Step 26: source MN (S-MN) with the awareness (based on step 11) that the target inter-MN PCell under target T-MN1 is prepared with MCG only configuration, prevents LTM PCell switch to T-MN1, since the T-MN1 will not be able to continue dual connectivity, since T- MN1 has only prepared MCG configuration.

[0066] Step 27. The X at the end of the arrow indicates that the MAC CE cell switch command, which should have been sent to UE to select T-MN1 for handover, was blocked, avoided or omitted, based on the “MCG-SCG_configuration” indication for T-MN1, which indicated that T-MN1 only prepared a MCG configuration, and thus a LTM cell switch or LTMHO to T-MN1 would not support DC. A LTM cell change or LTM HO may be performed by the S-MN to another T-MN (e.g., T-MN2) that has prepared both MCG configuration and SCG configuration.

[0067] FIG. 4 is a signaling diagram of a system according to another example embodiment.

[0068] In step 11 : candidate MN (T-MN1) updates the “MCG SCG configuration” indication indicator suitably based on the configuration(s) it has prepared, i.e., MCG configuration only or MCG + SCG configurations, and transmits a HO (handover) request acknowledgement to the S-MN with the “MCG SCG configuration” indication. In this example, it is assumed that the T-MN1 only prepares a MCG configuration for LTM HO of the UE, and therefore does not support DC for the UE.

[0069] Step 12: the “MCG SCG configuration” indication may be used by the source MN (S-MN) to prevent the configuration of subsequent cell change for a target MN that has prepared MCG configuration only, in case DC has to be (or should be) retained after subsequent LTM PCell change.

[0070] Step 13: S-MN transmits to UE a RRCReconfiguration message, and includes a “Do_Not_Use_SCG_configuration” indication or a “SCG Release” indication to indicate that the UE should not use the SCG configuration of the last serving PS Cell / last serving secondary node after LTM HO execution. This may be an alternative to step 38.

[0071] Step 14: At the time of LTM cell switch, the UE reads the indication (“Do_Not_Use_SCG_configuration” indication or “SCG Release” indication) in the LTM Candidate Config field. There may be two example options: Opt 1 : UE may clear or release the UE variable (LTM SCG configuration storage variable) associated with SCG configuration (storing the SCG configuration of the last serving PSCell) but retain (in memory) the SCG configuration that is part of RRCConfiguration. Opt2: UE may retain both the UE variable (LTM SCG configuration storage variable) and SCG configuration that is part of RRCConfiguration for SCG (in second option, the LTM SCG configuration storage variable is not cleared or released). For example, option 1 may be performed if the “Do_Not_Use_SCG_configuration” indication or “SCG Release” indication instructs the UE not to use the SCG configuration, and otherwise option 2 may be performed.

[0072] Steps 25, 29: UE report LI measurements enables the source MN to initiate LTM PCell change.

[0073] Step 37: the source MN knows (based on step 12) that the cell switch is to a target cell (or T-MN) that was prepared with MCG only configuration.

[0074] Step 39: source MN includes a new indication (“SCG Release” indication) in MAC CE cell switch command to instruct the UE to release the SCG configuration.

[0075] Step 40: UE applies the MCG configuration of the target PCell in LTM MCG configuration, and releases or clears the SCG configuration in the LTM SCG configuration storage variable (because there is no SCG configuration prepared, and the previously stored SCG configuration will not be used for LTM cell switch).

[0076] Step 41 : UE performs RACH (random access procedure) to the target PCell (of T- MN1) and completes the remaining steps related to inter-MN PCell HO.

[0077] Step 65: Current serving MN (S-MN) initiates MAC CE PCell switch command based on received LI measurements from UE in step 60.

[0078] Step 66: Current serving MN forwards the UE’s serving cell configuration before cell switch to the target MN.

[0079] Step 67: target MN uses the received UE’s serving cell configuration in step 65 to update its initial prepared inter-Master node HO configuration.

[0080] Steps 66 and 67 are to ensure the unwanted resources are released at the target MN.

[0081] FIG. 5 is a signaling diagram of a system according to another example embodiment.

[0082] In step 11 : candidate MN (T-MN1) updates the “MCG SCG configuration” indication indicator suitably based on the configuration it has prepared, e.g., MCG configuration only, or MCG + SCG configurations. This indication is sent to S-MN via HO request acknowledgement at step 11.

[0083] Step 12: the “MCG SCG configuration” indication for T-MN1 may be used by the source MN (S-MN) to prevent the configuration of subsequent cell change for a node that has prepared MCG only configuration, in case DC has to be retained after subsequent LTM PCell change.

[0084] Steps 24, 25: the source MN (S-MN) signals or sends the LTM radio configuration(s) (e.g., MCG and / or SCG configurations that have been prepared by the LTM candidate nodes or target MNs) and / or “MCG_SCG_configuration” indication of all the prepared inter-CU MCG LTM candidate nodes (or all target MNs) to each prepared inter-CU MCG LTM candidate node (to each of the target MNs, or candidate cells or nodes).

[0085] Steps 25, 27: the inter-CU MCG LTM candidate nodes (target MNs) store the received LTM configuration of other prepared candidate nodes, for use when they become serving node, to prevent PCell switch to a target cell or target MN that is prepared with MCG only configuration, if DC must or should be maintained after subsequent cell change.

[0086] Steps 31, 32: based on LI measurements reported by the UE in step 29, with the awareness from step 12 (of the “MCG SCG configuration” indication for T-MN1), the source MN prevents the LTM PCell change to T-MN1.

[0087] Step 42: serving node may use the LI measurements reported by UE in step 29 to identify the next best suitable PCell (which has prepared both MCG and SCG configurations) to trigger LTM cell change. Alternatively, the serving node may use fresh LI measurements reported by the UE in step 34 to trigger MAC CE LTM PCell switch to the target cell.

[0088] Step 40: Current serving MN forwards the UE’s serving cell configuration before cell switch to the target MN.

[0089] Step 41 : target MN uses the received UE’s serving cell configuration in step 65 to update its initial prepared inter-Master node HO configuration.

[0090] Note: Steps 40 and 41 are to ensure the unwanted resources are released at the target MN.

[0091] Step 43: UE performs RACH to the target PCell.

[0092] Clause 1. FIG. 6 is a flow chart illustrating operation of a user device (UE) according to example embodiment. At step 610, the method includes receiving, by a user device from a serving node, an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration. At step 620, the method includes receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN. And, at step 630, the method includes releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch]

[0093] Clause 2. The method of clause 1 wherein receiving the message comprises: receiving a radio resource control (RRC) reconfiguration message including an indication that instructs theuser device not to use a SCG configuration of the last serving PSCell at a time of LTM cell switch to the target PCell of the target MN that do not have SCG configuration.

[0094] Clause 3. The method of clause 1, further comprising: receiving, by the user device, a LTM cell switch command to perform a cell switch to the target PCell of the target MN; performing or executing of a LTM handover or cell switch to the PCell of the target MN.

[0095] Clause 4. The method of clause 1, wherein the information is based on the candidate node having prepared only a MCG configuration and not SCG configuration for a candidate target cell.

[0096] Clause 5. The method of clause 1, wherein the target MN only prepared a MCG configuration for LTM candidate target cell.

[0097] Clause 6. The method of any of clauses 1-5, wherein the information comprises at least one of the following: an indication included within the LTM cell switch command that instructs the user device to release the SCG configuration of the last serving PSCell; an indication within a LTM candidate configuration that is provided within a radio resource control (RRC) message that instructs the user device to release the SCG configuration of the last serving PSCell; or a radio resource control (RRC) reconfiguration message including a MCG configuration of a cell of the target MN for LTM cell switch of the user device, wherein the RRC reconfiguration message does not include a SCG configuration, thereby indicating that the SCG configuration of the last serving PSCell should be released or cleared.

[0098] Clause 7. The method of clause 6, wherein the indication comprises a SCG Release indication.

[0099] Clause 8. The method of any of clauses 1-7, wherein the releasing or clearing comprises: releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores a SCG configuration of the last serving PSCell.

[0100] Clause 9. The method of any of clauses 1-8, wherein the releasing or clearing comprises: releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores a SCG configuration of the last serving PSCell; and retaining or keeping, the SCG configuration stored in memory.

[0101] Clause 10. The method of any of clauses 1-9, comprising: receiving, by the user device from the serving node, a radio resource control (RRC) reconfiguration message including the MCG configuration of the target MN for the LTM cell switch, and a LTM candidateconfiguration, the LTM candidate configuration including an indication that instructs the user device to release the SCG configuration after execution of LTM handover or cell switch to a cell of the target MN.

[0102] Clause 11. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a user device from a serving node, an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

[0103] Clause 12. FIG. 7 is a flow chart illustrating operation of a source master node according to example embodiment. At step 710, the method includes sending, by a source master node (MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device. And, at step 720, the method includes receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

[0104] Clause 13. The method of clause 12, wherein the first indication indicates whether or not the target MN has prepared a SCG configuration to support dual connectivity for the LTM handover of the user device to a cell of the target MN.

[0105] Clause 14. The method of any of clauses 11-12 , wherein the handover request message comprises at least: a second indication that indicates a preference by the source MN for the target MN to retain SCG for the LTM handover of the user device.

[0106] Clause 15. The method of any of clauses 12-14, wherein the handover request message comprises at least: a MCG configuration; a SCG configuration; and second indicationthat indicates a preference by the source MN for the target MN to retain SCG for the LTM cell switch or handover of the user device.

[0107] Clause 16. The method of any of clauses 12-15, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only for the LTM handover of the user device to a cell of the target MN; current serving MN omitting to select the cell of the target MN for LTM subsequent cell change based on the target MN preparing a MCG configuration only that does not support dual connectivity when LTM subsequent cell change is configured and serving MN prefers to retain dual connectivity.

[0108] Clause 17. The method of any of clauses 12-15, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared both the MCG configuration and the SCG configuration for LTM cell switch or handover of the user device to the target MN; receiving, by the source MN from the user device, a layer 1 (LI) measurement report; sending, by the source MN to the user device, a LTM cell switch command, based on the LI measurement report and the target MN preparing both the MCG configuration and the SCG configuration.

[0109] Clause 18. The method of any of clauses 12-17, wherein the first indication is received within the handover request acknowledgement at least in a case where the target MN has prepared a SCG configuration for a PScell at a target SN and not the source SN.

[0110] Clause 19. The method of any of clauses 12-18, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only, indicating dual connectivity cannot be supported at the prepared target cell of the target MN; sending, by the source MN to the user device, a RRC reconfiguration message including a third indication that instructs the user device not to use a SCG configuration of a last serving primary secondary cell (PSCell) after execution of LTM handover or cell switch to a primary cell (PCell) of the target MN.

[0111] Clause 20. The method of clause 12 further comprising: determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration onlyfor the LTM cell switch or handover of the user device to a primary cell (PCell) of the target MN; based on determining that the target MN has prepared the MCG configuration only for handover to the PCell of the target MN, sending, by the source MN to the user device, a message including a fourth indication that instructs the user device to release a SCG configuration of a last primary secondary cell (PSCell) at the time of LTM handover or cell switch execution to the PCell of the target MN.

[0112] Clause 21. The method of clause 20, wherein the message including the fourth indication comprises at least one of: a LTM cell switch command including the fourth indication; or a radio resource control message including the fourth indication.

[0113] Clause 22. The method of any of clauses 20-21, wherein the fourth indication instructs the user device to release or clear a LTM SCG configuration storage variable, at the user device, that stores a SCG configuration of the last serving PSCell.

[0114] Clause 23. The method of clause 12, further comprising: determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only for the LTM handover of the user device to a cell of the target MN; and sending, by the source MN to the user device, a LTM cell switch command including a fourth indication that instructs the user device to release a SCG configuration of a last serving PSCell after execution of LTM handover or cell switch to the primary cell (PCell) of the target MN.

[0115] Clause 24. The method of clause 12, wherein: the sending comprises sending, by the source MN to each of a plurality of target MNs, a handover request message for LTM handover of the user device, the handover request message including a MCG configuration and a SCG configuration, to prepare the plurality of target MNs for LTM handover of the user device; wherein the receiving comprises receiving, by the source MN from each of the target MNs, a handover request acknowledgement including a first indication for the respective target MN that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration that supports dual connectivity, or 2) a MCG configuration only, indicative of dual connectivity not supported at prepared target PCell of the target MN; the method further comprising: forwarding, by the source MN to one or more of the target MNs, the fourth indication received for one or more of the plurality of target MNs, to notify the one or more target nodes of prepared configurations at each of the plurality of targetMNs, and one or both of a MCG configuration and a SCG configuration prepared by one or more of the plurality of target MNs.

[0116] Clause 25. The method of any of clauses 12-24, wherein: the first indication comprises a "MCG SCG configuration" indication; the second indication comprises a "Need SCG configuration" indication; the third indication comprises a "Do_Not_Use_SCG_configuration" indication; or the fourth indication comprises a "SCG Release" indication.

[0117] Clause 26. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: sending, by a source master node (MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device; and receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

[0118] Clause 27. FIG. 8 is a flow chart illustrating operation of a target master node according to an example embodiment. At step 810, the method includes receiving, by a target master node (MN) from a source MN that is serving a user device, a handover request message for layer 1 / 2 triggered mobility (LTM) cell switch or handover of the user device, wherein the handover request message comprises an indication that indicates a preference or requirement for the target MN to retain or prepare a secondary cell group (SCG) configuration or provide dual connectivity (DC) for the LTM cell switch or handover of the user device. And, at step 820, the method includes transmitting, by the target MN to the source MN, a handover request acknowledgement including an indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a SCG configuration or 2) a MCG configuration only, for the LTM cell switch or handover of the user device to a cell of the target MN.

[0119] Clause 28. The method of clause 27, wherein the handover request acknowledgement includes an indication indicating that the target MN has prepared a MCG configuration only for LTM cell change or cell switch of the user device.

[0120] Clause 29. The method of any of clauses 27-28, further comprising: after a LTM cell switch of the user device to a PCell of the target MN involving a release of a SCG configuration based on the target MN preparing only the MCG configuration, notifying one or more prepared candidate MNs or target MNs about the release of the SCG configuration for the user device.

[0121] Clause 30. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a target master node (MN) from a source MN that is serving a user device, a handover request message for layer 1 / 2 triggered mobility (LTM) cell switch or handover of the user device, wherein the handover request message comprises an indication that indicates a preference or requirement for the target MN to retain or prepare a secondary cell group (SCG) configuration or provide dual connectivity (DC) for the LTM cell switch or handover of the user device; and transmitting, by the target MN to the source MN, a handover request acknowledgement including an indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a SCG configuration or 2) a MCG configuration only, for the LTM cell switch or handover of the user device to a cell of the target MN.

[0122] FIG. 9 is a block diagram of a wireless station or node (e.g., UE, user device, AP, BS, eNB, gNB, RAN node, network node, TRP, or other node) 1300 according to an example embodiment. The wireless station 1300 may include, for example, one or more (e.g., two as shown in FIG. 9) RF (radio frequency) or wireless transceivers 1302A, 1302B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The wireless station also includes a processor or control unit / entity (controller) 1304 to execute instructions or software and control transmission and receptions of signals, and a memory 1306 to store data and / or instructions.

[0123] Processor 1304 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 1304, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 1302 (1302A or 1302B). Processor 1304 may control transmission of signals or messages over a wireless network, and may control the reception of signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver1302, for example). Processor 1304 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 1304 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and / or any combination of these. Using other terminology, processor 1304 and transceiver 1302 together may be considered as a wireless transmitter / receiver system, for example.

[0124] In addition, referring to FIG. 9, a controller (or processor) 1308 may execute software and instructions, and may provide overall control for the station 1300, and may provide control for other systems not shown in FIG. 9, such as controlling input / output devices (e.g., display, keypad), and / or may execute software for one or more applications that may be provided on wireless station 1300, such as, for example, an email program, audio / video applications, a word processor, a Voice over IP application, or other application or software.

[0125] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 1304, or other controller or processor, performing one or more of the functions or tasks described above.

[0126] According to another example embodiment, RF or wireless transceiver(s) 1302A / 1302B may receive signals or data and / or transmit or send signals or data. Processor 1304 (and possibly transceivers 1302A / 1302B) may control the RF or wireless transceiver 1302A or 1302B to receive, send, broadcast or transmit signals or data.

[0127] Example embodiments are provided or described for each of the example methods, including: An apparatus (e.g., 1300, FIG. 9) including means (e.g., processor 1304, RF transceivers 1302A and / or 1302B, and / or memory 1306, in FIG. 9) for carrying out any of the methods; a non-transitory computer-readable storage medium (e.g., memory 1306, FIG. 9) comprising instructions stored thereon that, when executed by at least one processor (processor 1304, FIG. 9), are configured to cause a computing system (e.g., 1300, FIG. 9) to perform any of the example methods; and an apparatus (e.g., 1300, FIG. 9) including at least one processor (e.g., processor 1304, FIG. 9), and at least one memory (e.g., memory 1306, FIG. 9) including computer program code, the at least one memory (1306) and the computer program code configured to, with the at least one processor (1304), cause the apparatus (e.g., 1300) at least to perform any of the example methods.

[0128] Embodiments of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments may be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. Embodiments may also be provided on a computer readable medium or computer readable storage medium, which may be a non-transitory medium. Embodiments of the various techniques may also include embodiments provided via transitory signals or media, and / or programs and / or software embodiments that are downloadable via the Internet or other network(s), either wired networks and / or wireless networks. In addition, embodiments may be provided via machine type communications (MTC), and also via an Internet of Things (IOT).

[0129] As used in this application, the term ‘circuitry’ or “circuit” refers to all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of circuits and soft-ware (and / or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s) / software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of ‘circuitry’ applies to all uses of this term in this application. As a further example, as used in this application, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and / or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in a server, a cellular network device, or another network device.

[0130] The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, photoelectrical and / or electrical carrier signal, telecommunications signal, and softwaredistribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer, or it may be distributed amongst a number of computers.

[0131] Furthermore, embodiments of the various techniques described herein may use a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the embodiment and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, ...) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals. The rise in popularity of smartphones has increased interest in the area of mobile cyberphysical systems. Therefore, various embodiments of techniques described herein may be provided via one or more of these technologies.

[0132] A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit or part of it suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0133] Method steps may be performed by one or more programmable processors executing a computer program or computer program portions to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0134] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer, chip or chipset. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storingdata, e.g., magnetic, magnetooptical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[0135] To provide for interaction with a user, embodiments may be implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a user interface, such as a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0136] Embodiments may be implemented in a computing system that includes a backend component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a frontend component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an embodiment, or any combination of such backend, middleware, or frontend components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[0137] While certain features of the described embodiments have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: receiving, by a user device from a serving node, an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

2. The method of claim 1 wherein receiving the message comprises: receiving a radio resource control (RRC) reconfiguration message including an indication that instructs the user device not to use a SCG configuration of the last serving PSCell at a time of LTM cell switch to the target PCell of the target MN that do not have SCG configuration.

3. The method of claim 1, further comprising: receiving, by the user device, a LTM cell switch command to perform a cell switch to the target PCell of the target MN; performing or executing of a LTM handover or cell switch to the PCell of the target MN.

4. The method of claim 1, wherein the information is based on the candidate node having prepared only a MCG configuration and not SCG configuration for a candidate target cell.

5. The method of claim 1, wherein the target MN only prepared a MCG configuration for LTM candidate target cell.

336. The method of any of claims 1-5, wherein the information comprises at least one of the following: an indication included within the LTM cell switch command that instructs the user device to release the SCG configuration of the last serving PSCell; an indication within a LTM candidate configuration that is provided within a radio resource control (RRC) message that instructs the user device to release the SCG configuration of the last serving PSCell; or a radio resource control (RRC) reconfiguration message including a MCG configuration of a cell of the target MN for LTM cell switch of the user device, wherein the RRC reconfiguration message does not include a SCG configuration, thereby indicating that the SCG configuration of the last serving PSCell should be released or cleared.

7. The method of claim 6, wherein the indication comprises a SCG Release indication.

8. The method of any of claims 1-7, wherein the releasing or clearing comprises: releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores a SCG configuration of the last serving PSCell.

9. The method of any of claims 1-8, wherein the releasing or clearing comprises: releasing or clearing, based on the information, a LTM SCG configuration storage variable that stores a SCG configuration of the last serving PSCell; and retaining or keeping, the SCG configuration stored in memory.

10. The method of any of claims 1-9, comprising: receiving, by the user device from the serving node, a radio resource control (RRC) reconfiguration message including the MCG configuration of the target MN for the LTM cell switch, and a LTM candidate configuration, the LTM candidate configuration including an indication that instructs the user device to release the SCG configuration after execution of LTM handover or cell switch to a cell of the target MN.

11. An apparatus comprising:at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a user device from a serving node, an indication that instructs the user device not to use a secondary cell group (SCG) configuration of the last serving PSCell after execution of layer 1 / 2 triggered mobility (LTM) handover or cell switch to a target primary cell (PCell) or a target cell of master cell group (MCG) of a target master node (MN) that do not have a secondary cell group (SCG) configuration; receiving by the user device, information indicating the user device to release a SCG configuration of the last serving primary secondary cell (PSCell) after performing a LTM cell switch or handover to the target PCell of the target MN; and releasing or clearing, by the user device based on the information, the SCG configuration of the last serving PSCell at a time of LTM cell switch.

12. A method comprising: sending, by a source master node (MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device; and receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

13. The method of claim 12, wherein the first indication indicates whether or not the target MN has prepared a SCG configuration to support dual connectivity for the LTM handover of the user device to a cell of the target MN.

14. The method of any of claims 11-12 , wherein the handover request message comprises at least: a second indication that indicates a preference by the source MN for the target MN to retain SCG for the LTM handover of the user device.

15. The method of any of claims 12-14, wherein the handover request message comprises at least: a MCG configuration; a SCG configuration; and second indication that indicates a preference by the source MN for the target MN to retain SCG for the LTM cell switch or handover of the user device.

16. The method of any of claims 12-15, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only for the LTM handover of the user device to a cell of the target MN; current serving MN omitting to select the cell of the target MN for LTM subsequent cell change based on the target MN preparing a MCG configuration only that does not support dual connectivity when LTM subsequent cell change is configured and serving MN prefers to retain dual connectivity.

17. The method of any of claims 12-15, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared both the MCG configuration and the SCG configuration for LTM cell switch or handover of the user device to the target MN; receiving, by the source MN from the user device, a layer 1 (LI) measurement report; sending, by the source MN to the user device, a LTM cell switch command, based on the LI measurement report and the target MN preparing both the MCG configuration and the SCG configuration.

18. The method of any of claims 12-17, wherein the first indication is received within the handover request acknowledgement at least in a case where the target MN has prepared a SCG configuration for a PScell at a target SN and not the source SN.

19. The method of any of claims 12-18, further comprising: determining, by the source MN, that there is a need to maintain dual connectivity for the user device; determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only, indicating dual connectivity cannot be supported at the prepared target cell of the target MN; sending, by the source MN to the user device, a RRC reconfiguration message including a third indication that instructs the user device not to use a SCG configuration of a last serving primary secondary cell (PSCell) after execution of LTM handover or cell switch to a primary cell (PCell) of the target MN.

20. The method of claim 12 further comprising: determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only for the LTM cell switch or handover of the user device to a primary cell (PCell) of the target MN; based on determining that the target MN has prepared the MCG configuration only for handover to the PCell of the target MN, sending, by the source MN to the user device, a message including a fourth indication that instructs the user device to release a SCG configuration of a last primary secondary cell (PSCell) at the time of LTM handover or cell switch execution to the PCell of the target MN.

21. The method of claim 20, wherein the message including the fourth indication comprises at least one of: a LTM cell switch command including the fourth indication; or a radio resource control message including the fourth indication.

22. The method of any of claims 20-21, wherein the fourth indication instructs the user device to release or clear a LTM SCG configuration storage variable, at the user device, that stores a SCG configuration of the last serving PSCell.

23. The method of claim 12, further comprising: determining, by the source MN, that the first indication indicates that the target MN has prepared a MCG configuration only for the LTM handover of the user device to a cell of the target MN; and sending, by the source MN to the user device, a LTM cell switch command including a fourth indication that instructs the user device to release a SCG configuration of a last serving PSCell after execution of LTM handover or cell switch to the primary cell (PCell) of the target MN.

24. The method of claim 12, wherein: the sending comprises sending, by the source MN to each of a plurality of target MNs, a handover request message for LTM handover of the user device, the handover request message including a MCG configuration and a SCG configuration, to prepare the plurality of target MNs for LTM handover of the user device; wherein the receiving comprises receiving, by the source MN from each of the target MNs, a handover request acknowledgement including a first indication for the respective target MN that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration that supports dual connectivity, or 2) a MCG configuration only, indicative of dual connectivity not supported at prepared target PCell of the target MN; the method further comprising: forwarding, by the source MN to one or more of the target MNs, the fourth indication received for one or more of the plurality of target MNs, to notify the one or more target nodes of prepared configurations at each of the plurality of target MNs, and one or both of a MCG configuration and a SCG configuration prepared by one or more of the plurality of target MNs.

25. The method of any of claims 12-24, wherein: the first indication comprises a “MCG SCG configuration” indication; the second indication comprises a “Need SCG configuration” indication; the third indication comprises a “Do_Not_Use_SCG_configuration” indication; or the fourth indication comprises a “SCG Release” indication.

26. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:. sending, by a source master node (MN) that is serving a user device to a target master node (MN), a handover request message for layer 1 / 2 triggered mobility (LTM) handover of the user device; and receiving, by the source MN from the target MN, a handover request acknowledgement including a first indication that indicates whether the target MN has prepared: 1) both a master cell group (MCG) configuration and a secondary cell group (SCG) configuration or 2) a MCG configuration only, for the LTM handover of the user device to a cell of the target MN.

27. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, by a target master node (MN) from a source MN that is serving a user device, a handover request message for layer 1 / 2 triggered mobility (LTM) cell switch or handover of the user device, wherein the handover request message comprises an indication that indicates a preference or requirement for the target MN to retain or prepare a secondary cell group (SCG) configuration or provide dual connectivity (DC) for the LTM cell switch or handover of the user device; and transmitting, by the target MN to the source MN, a handover request acknowledgement including an indication that indicates whether the target MN has prepared: 1) both a master cellgroup (MCG) configuration and a SCG configuration or 2) a MCG configuration only, for the LTM cell switch or handover of the user device to a cell of the target MN.40

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