Signaling for secondary node-initiated inter-secondary node l1 / l2 triggered mobility

Abstract

A method and apparatus for a signaling support for Source Secondary Node (SN)-initiated inter-SN L1 / L2 Triggered Mobility (LTM) preparation and configuration is provided. The source SN decides inter-SN LTM for a wireless device, transmits a modification required message to a Master Node (MN), receives a modification required response message from the MN in response to the modification required message, transmits a change required message to the MN, and receives a change confirm message from the MN in response to the change required message.

Description

SIGNALING FOR SECONDARY NODE-INITIATED INTER-SECONDARY NODE L1 / L2 TRIGGERED MOBILITY

[0001] The present disclosure relates to a signaling support for Secondary Node (SN)-initiated inter-SN L1 / L2 Triggered Mobility (LTM) preparation and configuration.

[0002] 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

[0003] 3GPP New Radio (NR) targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced Mobile BroadBand (eMBB), massive Machine Type Communications (mMTC), Ultra-Reliable and Low Latency Communications (URLLC), etc. The NR shall be inherently forward compatible. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future.

[0004] 6G is the successor to 5G cellular technology. 6G networks will be able to use higher frequencies than 5G networks and provide substantially higher capacity and much lower latency. The 6G technology market is expected to facilitate large improvements in the areas of imaging, presence technology and location awareness. Working in conjunction with Artificial Intelligence (AI), the 6G computational infrastructure will be able to identify the best place for computing to occur. This includes decisions about data storage, processing and sharing.

[0005] Layer 3 based mobility has evolved over several releases. Conditional Handover (CHO) and other conditional mobility procedures (Conditional PSCell Addition and Change (CPAC), Subsequent CPAC (SCPAC)) were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signaling exchange with source cell beforehand. L1 / L2 Triggered Mobility (LTM) as introduced in Rel-18 offers short interruption time but not with the same level of robustness as the conditional L3 mobility procedures. In Rel-19, enhancements should be specified so that the system can benefit from both the high robustness and short interruption.

[0006] In an aspect, a method is provided. The method comprises deciding, by a source secondary node (SN), inter-SN L1 / L2 triggered mobility (LTM) for a wireless device, transmitting, by the source SN, a modification required message to a master node (MN), receiving, by the source SN, a modification required response message from the MN in response to the modification required message, transmitting, by the source SN, a change required message to the MN, and receiving, by the source SN, a change confirm message from the MN in response to the change required message.

[0007] In another aspect, an apparatus for implementing the above method is provided.

[0008] FIG. 1 shows an example of a communication system to which implementations of the present disclosure are applied.

[0009] FIG. 2 shows an example of wireless devices to which implementations of the present disclosure are applied.

[0010] FIG. 3 shows an example of NG-RAN architecture to which implementations of the present disclosure are applied.

[0011] FIG. 4 shows another example of NG-RAN architecture to which implementations of the present disclosure are applied.

[0012] FIG. 5 shows an example of inter-gNB handover procedures to which implementations of the present disclosure are applied.

[0013] FIG. 6 shows an example of signaling procedure for LTM to which implementations of the present disclosure are applied.

[0014] FIG. 7 shows an example of a method to which implementations of the present disclosure are applied.

[0015] FIGS. 8 to 10 show an example of a procedure for SN-initiated inter-SN LTM preparation and configuration to which implementations of the present disclosure are applied.

[0016] The following techniques, apparatuses, and systems may be applied to a variety of wireless multiple access systems. Examples of the multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, a Single Carrier Frequency Division Multiple Access (SC-FDMA) system, and a Multi Carrier Frequency Division Multiple Access (MC-FDMA) system. CDMA may be embodied through radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be embodied through radio technology such as Global System for Mobile communications (GSM), General Packet Radio Service (GPRS), or Enhanced Data rates for GSM Evolution (EDGE). OFDMA may be embodied through radio technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is a part of a Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA in Downlink (DL) and SC-FDMA in Uplink (UL). Evolution of 3GPP LTE includes LTE-Advanced (LTE-A), LTE-A Pro, 5G New Radio (NR) and / or 6G.

[0017] For convenience of description, implementations of the present disclosure are mainly described in regards to a 3GPP based wireless communication system. However, the technical features of the present disclosure are not limited thereto. For example, although the following detailed description is given based on a mobile communication system corresponding to a 3GPP based wireless communication system, aspects of the present disclosure that are not limited to 3GPP based wireless communication system are applicable to other mobile communication systems.

[0018] For terms and technologies which are not specifically described among the terms of and technologies employed in the present disclosure, the wireless communication standard documents published before the present disclosure may be referenced.

[0019] In the present disclosure, "A or B" may mean "only A", "only B", or "both A and B". In other words, "A or B" in the present disclosure may be interpreted as "A and / or B". For example, "A, B or C" in the present disclosure may mean "only A", "only B", "only C", or "any combination of A, B and C".

[0020] In the present disclosure, slash ( / ) or comma (,) may mean "and / or". For example, "A / B" may mean "A and / or B". Accordingly, "A / B" may mean "only A", "only B", or "both A and B". For example, "A, B, C" may mean "A, B or C".

[0021] In the present disclosure, "at least one of A and B" may mean "only A", "only B" or "both A and B". In addition, the expression "at least one of A or B" or "at least one of A and / or B" in the present disclosure may be interpreted as same as "at least one of A and B".

[0022] In addition, in the present disclosure, "at least one of A, B and C" may mean "only A", "only B", "only C", or "any combination of A, B and C". In addition, "at least one of A, B or C" or "at least one of A, B and / or C" may mean "at least one of A, B and C".

[0023] Also, parentheses used in the present disclosure may mean "for example". In detail, when it is shown as "control information (PDCCH)", "PDCCH" may be proposed as an example of "control information". In other words, "control information" in the present disclosure is not limited to "PDCCH", and "PDCCH" may be proposed as an example of "control information". In addition, even when shown as "control information (i.e., PDCCH)", "PDCCH" may be proposed as an example of "control information".

[0024] Technical features that are separately described in one drawing in the present disclosure may be implemented separately or simultaneously.

[0025] Although not limited thereto, various descriptions, functions, procedures, suggestions, methods and / or operational flowcharts of the present disclosure disclosed herein can be applied to various fields requiring wireless communication and / or connection (e.g., 5G) between devices.

[0026] Hereinafter, the present disclosure will be described in more detail with reference to drawings. The same reference numerals in the following drawings and / or descriptions may refer to the same and / or corresponding hardware blocks, software blocks, and / or functional blocks unless otherwise indicated.

[0027] FIG. 1 shows an example of a communication system to which implementations of the present disclosure are applied.

[0028] The 5G usage scenarios shown in FIG. 1 are only exemplary, and the technical features of the present disclosure can be applied to other 5G usage scenarios which are not shown in FIG. 1.

[0029] Three main requirement categories for 5G include (1) a category of enhanced Mobile BroadBand (eMBB), (2) a category of massive Machine Type Communication (mMTC), and (3) a category of Ultra-Reliable and Low Latency Communications (URLLC).

[0030] Referring to FIG. 1, the communication system 1 includes wireless devices 100a to 100f, Base Stations (BSs) 200, and a network 300. Although FIG. 1 illustrates a 5G network as an example of the network of the communication system 1, the implementations of the present disclosure are not limited to the 5G system, and can be applied to the future communication system beyond the 5G system.

[0031] The BSs 200 and the network 300 may be implemented as wireless devices and a specific wireless device may operate as a BS / network node with respect to other wireless devices.

[0032] The wireless devices 100a to 100f represent devices performing communication using Radio Access Technology (RAT) (e.g., 5G NR or LTE) and may be referred to as communication / radio / 5G devices. The wireless devices 100a to 100f may include, without being limited to, a robot 100a, vehicles 100b-1 and 100b-2, an eXtended Reality (XR) device 100c, a hand-held device 100d, a home appliance 100e, an Internet-of-Things (IoT) device 100f, and an Artificial Intelligence (AI) device / server 400. For example, the vehicles may include a vehicle having a wireless communication function, an autonomous driving vehicle, and a vehicle capable of performing communication between vehicles. The vehicles may include an Unmanned Aerial Vehicle (UAV) (e.g., a drone). The XR device may include an Augmented Reality (AR) / Virtual Reality (VR) / Mixed Reality (MR) device and may be implemented in the form of a Head-Mounted Device (HMD), a Head-Up Display (HUD) mounted in a vehicle, a television, a smartphone, a computer, a wearable device, a home appliance device, a digital signage, a vehicle, a robot, etc. The hand-held device may include a smartphone, a smartpad, a wearable device (e.g., a smartwatch or a smartglasses), and a computer (e.g., a notebook). The home appliance may include a TV, a refrigerator, and a washing machine. The IoT device may include a sensor and a smartmeter.

[0033] In the present disclosure, the wireless devices 100a to 100f may be called User Equipments (UEs). A UE may include, for example, a cellular phone, a smartphone, a laptop computer, a digital broadcast terminal, a Personal Digital Assistant (PDA), a Portable Multimedia Player (PMP), a navigation system, a slate Personal Computer (PC), a tablet PC, an ultrabook, a vehicle, a vehicle having an autonomous traveling function, a connected car, an UAV, an AI module, a robot, an AR device, a VR device, an MR device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a FinTech device (or a financial device), a security device, a weather / environment device, a device related to a 5G service, or a device related to a fourth industrial revolution field.

[0034] The wireless devices 100a to 100f may be connected to the network 300 via the BSs 200. An AI technology may be applied to the wireless devices 100a to 100f and the wireless devices 100a to 100f may be connected to the AI server 400 via the network 300. The network 300 may be configured using a 3G network, a 4G (e.g., LTE) network, a 5G (e.g., NR) network, and a beyond-5G network. Although the wireless devices 100a to 100f may communicate with each other through the BSs 200 / network 300, the wireless devices 100a to 100f may perform direct communication (e.g., sidelink communication) with each other without passing through the BSs 200 / network 300. For example, the vehicles 100b-1 and 100b-2 may perform direct communication (e.g., Vehicle-to-Vehicle (V2V) / Vehicle-to-everything (V2X) communication). The IoT device (e.g., a sensor) may perform direct communication with other IoT devices (e.g., sensors) or other wireless devices 100a to 100f.

[0035] Wireless communication / connections 150a, 150b and 150c may be established between the wireless devices 100a to 100f and / or between wireless device 100a to 100f and BS 200 and / or between BSs 200. Herein, the wireless communication / connections may be established through various RATs (e.g., 5G NR) such as uplink / downlink communication 150a, sidelink communication (or Device-to-Device (D2D) communication) 150b, inter-base station communication 150c (e.g., relay, Integrated Access and Backhaul (IAB)), etc. The wireless devices 100a to 100f and the BSs 200 / the wireless devices 100a to 100f may transmit / receive radio signals to / from each other through the wireless communication / connections 150a, 150b and 150c. For example, the wireless communication / connections 150a, 150b and 150c may transmit / receive signals through various physical channels. To this end, at least a part of various configuration information configuring processes, various signal processing processes (e.g., channel encoding / decoding, modulation / demodulation, and resource mapping / de-mapping), and resource allocating processes, for transmitting / receiving radio signals, may be performed based on the various proposals of the present disclosure.

[0036] NR supports multiples numerologies (and / or multiple Sub-Carrier Spacings (SCS)) to support various 5G services. For example, if SCS is 15 kHz, wide area can be supported in traditional cellular bands, and if SCS is 30 kHz / 60 kHz, dense-urban, lower latency, and wider carrier bandwidth can be supported. If SCS is 60 kHz or higher, bandwidths greater than 24.25 GHz can be supported to overcome phase noise.

[0037] The NR frequency band may be defined as two types of frequency range, i.e., Frequency Range 1 (FR1) and Frequency Range 2 (FR2). The numerical value of the frequency range may be changed. For example, the frequency ranges of the two types (FR1 and FR2) may be as shown in Table 1 below. For ease of explanation, in the frequency ranges used in the NR system, FR1 may mean "sub 6 GHz range", FR2 may mean "above 6 GHz range," and may be referred to as millimeter Wave (mmW).

[0038] Frequency Range designationCorresponding frequency rangeSubcarrier SpacingFR1450MHz - 6000MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0039] As mentioned above, the numerical value of the frequency range of the NR system may be changed. For example, FR1 may include a frequency band of 410MHz to 7125MHz as shown in Table 2 below. That is, FR1 may include a frequency band of 6GHz (or 5850, 5900, 5925 MHz, etc.) or more. For example, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more included in FR1 may include an unlicensed band. Unlicensed bands may be used for a variety of purposes, for example for communication for vehicles (e.g., autonomous driving).

[0040] Frequency Range designationCorresponding frequency rangeSubcarrier SpacingFR1410MHz - 7125MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0041] Here, the radio communication technologies implemented in the wireless devices in the present disclosure may include NarrowBand IoT (NB-IoT) technology for low-power communication as well as LTE, NR and 6G. For example, NB-IoT technology may be an example of Low Power Wide Area Network (LPWAN) technology, may be implemented in specifications such as LTE Cat NB1 and / or LTE Cat NB2, and may not be limited to the above-mentioned names. Additionally and / or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may communicate based on LTE-M technology. For example, LTE-M technology may be an example of LPWAN technology and be called by various names such as enhanced MTC (eMTC). For example, LTE-M technology may be implemented in at least one of the various specifications, such as 1) LTE Cat 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-bandwidth limited (non-BL), 5) LTE-MTC, 6) LTE Machine Type Communication, and / or 7) LTE M, and may not be limited to the above-mentioned names. Additionally and / or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may include at least one of ZigBee, Bluetooth, and / or LPWAN which take into account low-power communication, and may not be limited to the above-mentioned names. For example, ZigBee technology may generate Personal Area Networks (PANs) associated with small / low-power digital communication based on various specifications such as IEEE 802.15.4 and may be called various names.

[0042] FIG. 2 shows an example of wireless devices to which implementations of the present disclosure are applied.

[0043] In FIG. 2, The first wireless device 100 and / or the second wireless device 200 may be implemented in various forms according to use cases / services. For example, {the first wireless device 100 and the second wireless device 200} may correspond to at least one of {the wireless device 100a to 100f and the BS 200}, {the wireless device 100a to 100f and the wireless device 100a to 100f} and / or {the BS 200 and the BS 200} of FIG. 1. The first wireless device 100 and / or the second wireless device 200 may be configured by various elements, devices / parts, and / or modules.

[0044] The first wireless device 100 may include at least one transceiver, such as a transceiver 106, at least one processing chip, such as a processing chip 101, and / or one or more antennas 108.

[0045] The processing chip 101 may include at least one processor, such a processor 102, and at least one memory, such as a memory 104. Additional and / or alternatively, the memory 104 may be placed outside of the processing chip 101.

[0046] The processor 102 may control the memory 104 and / or the transceiver 106 and may be adapted to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts described in the present disclosure. For example, the processor 102 may process information within the memory 104 to generate first information / signals and then transmit radio signals including the first information / signals through the transceiver 106. The processor 102 may receive radio signals including second information / signals through the transceiver 106 and then store information obtained by processing the second information / signals in the memory 104.

[0047] The memory 104 may be operably connectable to the processor 102. The memory 104 may store various types of information and / or instructions. The memory 104 may store a firmware and / or a software code 105 which implements codes, commands, and / or a set of commands that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 105 may implement instructions that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 105 may control the processor 102 to perform one or more protocols. For example, the firmware and / or the software code 105 may control the processor 102 to perform one or more layers of the radio interface protocol.

[0048] Herein, the processor 102 and the memory 104 may be a part of a communication modem / circuit / chip designed to implement RAT (e.g., LTE or NR). The transceiver 106 may be connected to the processor 102 and transmit and / or receive radio signals through one or more antennas 108. Each of the transceiver 106 may include a transmitter and / or a receiver. The transceiver 106 may be interchangeably used with Radio Frequency (RF) unit(s). In the present disclosure, the first wireless device 100 may represent a communication modem / circuit / chip.

[0049] The second wireless device 200 may include at least one transceiver, such as a transceiver 206, at least one processing chip, such as a processing chip 201, and / or one or more antennas 208.

[0050] The processing chip 201 may include at least one processor, such a processor 202, and at least one memory, such as a memory 204. Additional and / or alternatively, the memory 204 may be placed outside of the processing chip 201.

[0051] The processor 202 may control the memory 204 and / or the transceiver 206 and may be adapted to implement the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts described in the present disclosure. For example, the processor 202 may process information within the memory 204 to generate third information / signals and then transmit radio signals including the third information / signals through the transceiver 206. The processor 202 may receive radio signals including fourth information / signals through the transceiver 106 and then store information obtained by processing the fourth information / signals in the memory 204.

[0052] The memory 204 may be operably connectable to the processor 202. The memory 204 may store various types of information and / or instructions. The memory 204 may store a firmware and / or a software code 205 which implements codes, commands, and / or a set of commands that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 205 may implement instructions that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. For example, the firmware and / or the software code 205 may control the processor 202 to perform one or more protocols. For example, the firmware and / or the software code 205 may control the processor 202 to perform one or more layers of the radio interface protocol.

[0053] Herein, the processor 202 and the memory 204 may be a part of a communication modem / circuit / chip designed to implement RAT (e.g., LTE or NR). The transceiver 206 may be connected to the processor 202 and transmit and / or receive radio signals through one or more antennas 208. Each of the transceiver 206 may include a transmitter and / or a receiver. The transceiver 206 may be interchangeably used with RF unit. In the present disclosure, the second wireless device 200 may represent a communication modem / circuit / chip.

[0054] Hereinafter, hardware elements of the wireless devices 100 and 200 will be described more specifically. One or more protocol layers may be implemented by, without being limited to, one or more processors 102 and 202. For example, the one or more processors 102 and 202 may implement one or more layers (e.g., functional layers such as Physical (PHY) layer, Media Access Control (MAC) layer, Radio Link Control (RLC) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Resource Control (RRC) layer, and Service Data Adaptation Protocol (SDAP) layer). The one or more processors 102 and 202 may generate one or more Protocol Data Units (PDUs), one or more Service Data Unit (SDUs), messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure. The one or more processors 102 and 202 may generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure and provide the generated signals to the one or more transceivers 106 and 206. The one or more processors 102 and 202 may receive the signals (e.g., baseband signals) from the one or more transceivers 106 and 206 and acquire the PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure.

[0055] The one or more processors 102 and 202 may be referred to as controllers, microcontrollers, microprocessors, or microcomputers. The one or more processors 102 and 202 may be implemented by hardware, firmware, software, or a combination thereof. As an example, one or more Application Specific Integrated Circuits (ASICs), one or more Digital Signal Processors (DSPs), one or more Digital Signal Processing Devices (DSPDs), one or more Programmable Logic Devices (PLDs), or one or more Field Programmable Gate Arrays (FPGAs) may be included in the one or more processors 102 and 202. For example, the one or more processors 102 and 202 may be configured by a set of a communication control processor, an Application Processor (AP), an Electronic Control Unit (ECU), a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), and a memory control processor.

[0056] The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 and store various types of data, signals, messages, information, programs, code, instructions, and / or commands. The one or more memories 104 and 204 may be configured by Random Access Memory (RAM), Dynamic RAM (DRAM), Read-Only Memory (ROM), electrically Erasable Programmable Read-Only Memory (EPROM), flash memory, volatile memory, non-volatile memory, hard drive, register, cash memory, computer-readable storage medium, and / or combinations thereof. The one or more memories 104 and 204 may be located at the interior and / or exterior of the one or more processors 102 and 202. The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 through various technologies such as wired or wireless connection.

[0057] The one or more transceivers 106 and 206 may transmit user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, to one or more other devices. The one or more transceivers 106 and 206 may receive user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, from one or more other devices. For example, the one or more transceivers 106 and 206 may be connected to the one or more processors 102 and 202 and transmit and receive radio signals. For example, the one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may transmit user data, control information, or radio signals to one or more other devices. The one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may receive user data, control information, or radio signals from one or more other devices.

[0058] The one or more transceivers 106 and 206 may be connected to the one or more antennas 108 and 208. Additionally and / or alternatively, the one or more transceivers 106 and 206 may include one or more antennas 108 and 208. The one or more transceivers 106 and 206 may be adapted to transmit and receive user data, control information, and / or radio signals / channels, mentioned in the descriptions, functions, procedures, suggestions, methods and / or operational flowcharts disclosed in the present disclosure, through the one or more antennas 108 and 208. In the present disclosure, the one or more antennas 108 and 208 may be a plurality of physical antennas or a plurality of logical antennas (e.g., antenna ports).

[0059] The one or more transceivers 106 and 206 may convert received user data, control information, radio signals / channels, etc., from RF band signals into baseband signals in order to process received user data, control information, radio signals / channels, etc., using the one or more processors 102 and 202. The one or more transceivers 106 and 206 may convert the user data, control information, radio signals / channels, etc., processed using the one or more processors 102 and 202 from the base band signals into the RF band signals. To this end, the one or more transceivers 106 and 206 may include (analog) oscillators and / or filters. For example, the one or more transceivers 106 and 206 can up-convert OFDM baseband signals to OFDM signals by their (analog) oscillators and / or filters under the control of the one or more processors 102 and 202 and transmit the up-converted OFDM signals at the carrier frequency. The one or more transceivers 106 and 206 may receive OFDM signals at a carrier frequency and down-convert the OFDM signals into OFDM baseband signals by their (analog) oscillators and / or filters under the control of the one or more processors 102 and 202.

[0060] Although not shown in FIG. 2, the wireless devices 100 and 200 may further include additional components. The additional components 140 may be variously configured according to types of the wireless devices 100 and 200. For example, the additional components 140 may include at least one of a power unit / battery, an Input / Output (I / O) device (e.g., audio I / O port, video I / O port), a driving device, and a computing device. The additional components 140 may be coupled to the one or more processors 102 and 202 via various technologies, such as a wired or wireless connection.

[0061] In the present disclosure, a BS is also referred to as a node B (NB), an eNode B (eNB), or a gNB.

[0062] FIG. 3 shows an example of NG-RAN architecture to which implementations of the present disclosure are applied.

[0063] An Next Generation Radio Access Network (NG-RAN) node is either:

[0064] - a gNB, providing NR user plane and control plane protocol terminations towards the UE; or

[0065] - an ng-eNB, providing E-UTRA user plane and control plane protocol terminations towards the UE.

[0066] The gNBs and ng-eNBs are interconnected with each other by means of the Xn interface. The gNBs and ng-eNBs are also connected by means of the NG interfaces to the 5GC, more specifically to the Access and Mobility Management Function (AMF) by means of the NG-C interface and to the User Plane Function (UPF) by means of the NG-U interface.

[0067] FIG. 4 shows another example of NG-RAN architecture to which implementations of the present disclosure are applied.

[0068] A gNB may consist of a gNB-Centralized Unit (CU) and one or more gNB-Distributed Unit(s) (DU(s)). A gNB-CU and a gNB-DU is connected via F1 interface.

[0069] A gNB-CU is a logical node hosting Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP) and Packet Data Convergence Protocol (PDCP) protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected with the gNB-DU.

[0070] A gNB-DU is a logical node hosting Radio Link Control (RLC), Media Access Control (MAC) and Physical (PHY) layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU. For Dual Connectivity (DC) operation, the Master gNB (MgNB)-DU designates the gNB-DU of an en-gNB or a gNB acting as master node, and the Secondary gNB (SgNB)-DU designates the gNB-DU of an en-gNB or a gNB acting as secondary node.

[0071] One gNB-DU is connected to only one gNB-CU.

[0072] In case of network sharing with multiple cell Identity (ID) broadcast, each cell ID associated with a subset of Public land Mobile Networks (PLMNs) corresponds to a gNB-DU and the gNB-CU it is connected to, i.e., the corresponding gNB-DUs share the same physical layer cell resources.

[0073] For resiliency, a gNB-DU may be connected to multiple gNB-CUs by appropriate implementation.

[0074] NG, Xn and F1 are logical interfaces.

[0075] Network controlled mobility applies to UEs in RRC_CONNECTED and is categorized into two types of mobility: cell level mobility and beam level mobility. Beam level mobility includes intra-cell beam level mobility and inter-cell beam level mobility.

[0076] Cell level mobility requires explicit RRC signaling to be triggered, i.e., handover (HO).

[0077] FIG. 5 shows an example of inter-gNB handover procedures to which implementations of the present disclosure are applied.

[0078] For inter-gNB handover, the signaling procedures consist of at least the following elemental components described in FIG. 5.

[0079] 1. Step 1: The source gNB initiates handover and issues a HANDOVER REQUEST over the Xn interface.

[0080] 2. Step 2: The target gNB performs admission control and provides the new RRC configuration as part of the HANDOVER REQUEST ACKNOWLEDGE.

[0081] 3. Step 3: The source gNB provides the RRC configuration to the UE by forwarding theRRCReconfigurationmessage received in the HANDOVER REQUEST ACKNOWLEDGE. TheRRCReconfigurationmessage includes at least cell ID and all information required to access the target cell so that the UE can access the target cell without reading system information. For some cases, the information required for contention-based and contention-free random access can be included in theRRCReconfigurationmessage. The access information to the target cell may include beam specific information, if any.

[0082] 4. Step 4: The UE moves the RRC connection to the target gNB and replies with theRRCReconfigurationComplete.

[0083] User data may also be sent in step 4 if the grant allows.

[0084] Beam level mobility does not require explicit RRC signaling to be triggered. Beam level mobility can be within a cell, or between cells, the latter is referred to as Inter-Cell Beam Management (ICBM). For ICBM, a UE can receive or transmit UE dedicated channels / signals via a Transmission / Reception Point (TRP) associated with a Physical Cell ID (PCI) different from the PCI of a serving cell, while non-UE-dedicated channels / signals can only be received via a TRP associated with a PCI of the serving cell. The gNB provides via RRC signaling the UE with measurement configuration containing configurations of Synchronization Signal Block (SSB) / Channel State Information (CSI) resources and resource sets, reports and trigger states for triggering channel and interference measurements and reports. In case of ICBM, a measurement configuration includes SSB resources associated with PCIs different from the PCI of a serving cell. Beam level mobility is then dealt with at lower layers by means of physical layer and MAC layer control signaling, and RRC is not required to know which beam is being used at a given point in time.

[0085] SSB-based beam level mobility is based on　the SSB associated to the initial DL Bandwidth Part (BWP) and can only be　configured for　the initial DL BWPs and for　DL BWPs　containing the SSB associated to the initial DL BWP. For　other DL BWPs, beam level mobility can only be performed based on CSI-Reference Signal (RS).

[0086] A Conditional Handover (CHO) is defined as a handover that is executed by the UE when one or more handover execution conditions are met. The UE starts evaluating the execution condition(s) upon receiving the CHO configuration, and stops evaluating the execution condition(s) once a handover is executed.

[0087] The following principles apply to CHO:

[0088] - The CHO configuration contains the configuration of CHO candidate cell(s) generated by the candidate gNB(s) and execution condition(s) generated by the source gNB.

[0089] - An execution condition may consist of one or two trigger condition(s) (CHO events A3 / A5). Only single RS type is supported and at most two different trigger quantities (e.g., Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ), RSRP and Signal-to-Interference plus Noise Ratio (SINR), etc.) can be configured simultaneously for the evaluation of CHO execution condition of a single candidate cell.

[0090] - Before any CHO execution condition is satisfied, upon reception of HO command (without CHO configuration), the UE executes the HO procedure, regardless of any previously received CHO configuration.

[0091] - While executing CHO, i.e., from the time when the UE starts synchronization with target cell, the UE does not monitor source cell.

[0092] L1 / L2 Triggered Mobility (LTM) is a procedure in which a gNB receives L1 measurement report(s) from a UE, and on their basis the gNB changes UE's serving cell by a cell switch command signaled via a MAC Control Element (CE). The cell switch command indicates an LTM candidate cell configuration that the gNB previously prepared and provided to the UE through RRC signaling. Then the UE switches to the target cell according to the cell switch command. The LTM procedure can be used to reduce the mobility latency.

[0093] When configured by the network, it is possible to activate Transmission Configuration Index (TCI) states of one or multiple cells that are different from the current serving cell. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell. This allows the UE to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered.

[0094] When configured by the network, it is possible to initiate UL Timing Advance (TA) acquisition procedure to one or multiple cells that are different from the current serving cell. For instance, the network may request the UE to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition is triggered by Physical Downlink Control Channel (PDCCH) order or realized through UE-based TA measurement. In the former case, the gNB to which the candidate cell belongs calculates the TA value and sends it to the gNB to which the serving cell belongs. The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering LTM cell switch. In the latter case, the UE applies the TA value measured by itself and performs Random Access Channel (RACH)-less LTM upon receiving the cell switch command.

[0095] If UE-based TA measurement is configured, the UE performs RACH-less LTM upon receiving the cell switch command. Otherwise, the UE determines whether to access the target cell with the RA procedure depending on whether a TA value is provided in the cell switch command. For RACH-less LTM, the UE accesses the target cell via a configured grant provided in the LTM candidate cell configuration and selects the configured grant occasion associated with the beam indicated in the cell switch command. If the LTM candidate cell configuration does not include a configured grant, the UE may monitor PDCCH for dynamic scheduling from the target cell upon LTM cell switch. Before RACH-less LTM procedure completion, the UE may not trigger random access procedure if it does not have a valid Physical Uplink Control Channel (PUCCH) resource for triggered Scheduling Requests (SRs).

[0096] The following principles apply to LTM:

[0097] - The UE does not update its security key after an intra-gNB LTM cell switch.

[0098] - Subsequent LTM is supported.

[0099] LTM supports both intra-gNB-DU and intra-gNB-CU inter-gNB-DU mobility. LTM supports both intra-frequency and inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell. The following scenarios are supported:

[0100] - Primary Cell (PCell) change in non-Carrier Aggregation (CA) scenario and non-DC scenario,

[0101] - PCell change in CA scenario,

[0102] - DC scenario, Master Cell Group (MCG) PCell change and Secondary Cell Group (SCG) Primary Secondary Cell (PSCell) change without Master Node (MN) involvement case (i.e., intra-Secondary Node (SN) PSCell change).

[0103] While the UE has stored LTM candidate cell configurations, the UE can also execute any L3 handover command sent by the network.

[0104] FIG. 6 shows an example of signaling procedure for LTM to which implementations of the present disclosure are applied.

[0105] Cell switch command is conveyed in a MAC CE, which contains the necessary information to perform the LTM cell switch.

[0106] Subsequent LTM is done by repeating the early synchronization, LTM cell switch execution, and LTM cell switch completion steps without releasing other LTM candidate cell configurations after each LTM cell switch completion.

[0107] The signaling procedure for LTM is as follows.

[0108] 1. Step 1: The UE sends aMeasurementReportmessage to the gNB. The gNB decides to configure LTM and initiates candidate cell(s) preparation.

[0109] 2. Step 2: The gNB transmits anRRCReconfigurationmessage to the UE including the LTM candidate cell configurations of one or multiple candidate cells.

[0110] 3. Step 3: The UE stores the LTM candidate cell configurations and transmits anRRCReconfigurationCompletemessage to the gNB.

[0111] 4a. Step 4a: The UE may perform DL synchronization with the candidate cell(s) before receiving the cell switch command.

[0112] 4b. Step 4b: When UE-based TA measurement is configured, the UE may acquire the TA value(s) of the candidate cell(s) by measurement. Otherwise, the UE 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 via Contention-Free Random Access (CFRA) triggered by a PDCCH order from the source cell, following which the UE may send preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE may not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE may not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0113] 5. Step 5: The UE performs L1 measurements on the configured candidate cell(s) and transmits L1 measurement reports to the gNB. L1 measurement should be performed as long as RRC reconfiguration (step 2) is applicable.

[0114] 6. Step 6: The gNB decides to execute cell switch to a target cell and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell. The UE switches to the target cell and applies the configuration indicated by candidate configuration index.

[0115] 7. Step 7: The UE may perform the random access procedure towards the target cell, if the UE does not have valid TA of the target cell. The UE may perform CFRA if the LTM cell switch command MAC CE contains information for CFRA.

[0116] 8. Step 8: The UE completes the LTM cell switch procedure by sendingRRCReconfigurationCompletemessage to target cell. If the UE has performed a random access procedure in step 7, the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data. The UE determines successful reception of its first UL data by receiving a PDCCH addressing the UE's Cell Radio Network Temporary Identity (C-RNTI) in the target cell, which schedules a new transmission following the first UL data. The PDCCH carries either a DL assignment or an UL grant addressing the same HARQ process as the first UL data.

[0117] The steps 4-8 can be performed multiple times for subsequent LTM using the LTM candidate cell configuration(s) provided in step 2.

[0118] Scenarios considered in LTM have been limited to intra-CU case only, i.e., serving cell change within cells under a single CU. For NR mobility enhancement, support for inter-CU LTM has been studied.

[0119] Specifically, it has been studied to specify inter-CU LTM across different SNs while MCG is unchanged. That is, a case where NR-DC is configured and CU is acting as SN and MCG is unchanged may be supported by the present disclosure.

[0120] The present disclosure proposes some mechanisms to support inter-SN-CU LTM preparation and configuration initiated by the SN (while MCG is unchanged). The present disclosure introduces necessary signaling procedures to enable the SN-initiated inter-SN LTM preparation and configuration while keeping MCG unchanged.

[0121] The following definition of terms may be used for the description below.

[0122] - Master Node (MN): The radio access node currently serving the MCG of the UE

[0123] - Source Secondary Node (S-SN): The radio access node currently serving the SCG of the UE and connected with the MN of the UE by X2 or Xn interface

[0124] - S-SN Centralized Unit (S-SN-CU): CU of the S-SN

[0125] - S-SN Distributed Unit (S-SN-DU): DU currently serving the SCG of the UE and connected with the S-SN-CU by F1 or W1 interface

[0126] - Candidate SN-CU (C-SN-CU): CU of another radio access node and connected with the MN by X2 or Xn interface

[0127] - C-SN-DU: DU of another radio access node and connected with the C-SN-CU by F1 or W1 interface.

[0128] The following drawings are created to explain specific embodiments of the present disclosure. The names of the specific devices or the names of the specific signals / messages / fields shown in the drawings are provided by way of example, and thus the technical features of the present disclosure are not limited to the specific names used in the following drawings.

[0129] FIG. 7 shows an example of a method to which implementations of the present disclosure are applied.

[0130] In step S700, the method comprises deciding, by a source SN, inter-SN LTM for a wireless device.

[0131] In some implementations, the inter-SN LTM may be decided based on L3 measurement results for the inter-SN LTM. The L3 measurement results may be received from the wireless via a signaling radio bearer (SRB)-1 or an SRB-3.

[0132] In step S710, the method comprises transmitting, by the source SN, a modification required message to a MN.

[0133] In some implementations, the modification required message may include an inter-SN LTM indication. The modification required message may further include SN measurement results.

[0134] In step S720, the method comprises receiving, by the source SN, a modification required response message from the MN in response to the modification required message.

[0135] In some implementations, the modification required response message may include MN measurement results. The modification required response message may further include a list of proposed PSCell candidates and SN IDs of the proposed PSCell candidates for the inter-SN LTM.

[0136] Alternatively, the modification required response message may include a reason for rejection of the modification required message (e.g., intra-SN LTM is currently on-going for the wireless device).

[0137] In some implementations, the method may further comprise receiving at least one of an LTM suggestion or PSCell candidate suggestions from a DU of the source SN.

[0138] In step S730, the method comprises transmitting, by the source SN, a change required message to the MN.

[0139] In some implementations, the change required message may include at least one of i) an inter-SN LTM indication, ii) a reference configuration for the inter-SN LTM, iii) a configuration ID mapping list for proposed PSCell candidates, iv) a maximum number of PSCell candidates that can be prepared for each candidate SN, or v) a configuration ID range for a candidate SN to use to assign for PSCell candidates of the candidate SN to be prepared. The change required message may further include at least one of i) SN measurement results, ii) a list of proposed PSCell candidates and SN IDs of the proposed PSCell candidates for the inter-SN LTM, iii) proposed PSCell candidates in the source SN and configurations prepared with one or more SN DUs of the source SN for the inter-SN LTM, iv) a data forwarding proposal, or v) an ID of a DU that is currently serving the wireless device.

[0140] In some implementations, the method may further comprise configuring a DU of the source SN for execution of the inter-SN LTM and updating a current SCG configuration. The method may further comprise transmitting an updated SCG configuration to the MN.

[0141] In step S740, the method comprises receiving, by the source SN, a change confirm message from the MN in response to the change required message.

[0142] In some implementations, the change confirm message may inform that the inter-SN LTM is successfully configured to the wireless device. The change confirm message may include at least one of i) MN measurement results, or ii) data forwarding transport network layers (TNLs) assigned by each candidate SN.

[0143] In some implementations, the source SN may correspond to a CU of the source SN.

[0144] Furthermore, the method described above in FIG. 7 may be performed by a MN. The MN may be implemented by the second wireless device 200 shown in FIG. 2.

[0145] The source SN comprises at least one transceiver, at least one processor, and at least one memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform the method described in FIG. 7.

[0146] More specifically, the source SN decides inter-SN LTM for a wireless device.

[0147] In some implementations, the inter-SN LTM may be decided based on L3 measurement results for the inter-SN LTM. The L3 measurement results may be received from the wireless via an SRB-1 or an SRB-3.

[0148] The source SN transmits a modification required message to a MN.

[0149] In some implementations, the modification required message may include an inter-SN LTM indication. The modification required message may further include SN measurement results.

[0150] The source SN receives a modification required response message from the MN in response to the modification required message.

[0151] In some implementations, the modification required response message may include MN measurement results. The modification required response message may further include a list of proposed PSCell candidates and SN IDs of the proposed PSCell candidates for the inter-SN LTM.

[0152] Alternatively, the modification required response message may include a reason for rejection of the modification required message (e.g., intra-SN LTM is currently on-going for the wireless device).

[0153] In some implementations, the source SN may receive at least one of an LTM suggestion or PSCell candidate suggestions from a DU of the source SN.

[0154] The source SN transmits a change required message to the MN.

[0155] In some implementations, the change required message may include at least one of i) an inter-SN LTM indication, ii) a reference configuration for the inter-SN LTM, iii) a configuration ID mapping list for proposed PSCell candidates, iv) a maximum number of PSCell candidates that can be prepared for each candidate SN, or v) a configuration ID range for a candidate SN to use to assign for PSCell candidates of the candidate SN to be prepared. The change required message may further include at least one of i) SN measurement results, ii) a list of proposed PSCell candidates and SN IDs of the proposed PSCell candidates for the inter-SN LTM, iii) proposed PSCell candidates in the source SN and configurations prepared with one or more SN DUs of the source SN for the inter-SN LTM, iv) a data forwarding proposal, or v) an ID of a DU that is currently serving the wireless device.

[0156] In some implementations, the source SN may configure a DU of the source SN for execution of the inter-SN LTM and update a current SCG configuration. The source SN may transmit an updated SCG configuration to the MN.

[0157] The source SN receives a change confirm message from the MN in response to the change required message.

[0158] In some implementations, the change confirm message may inform that the inter-SN LTM is successfully configured to the wireless device. The change confirm message may include at least one of i) MN measurement results, or ii) data forwarding transport network layers (TNLs) assigned by each candidate SN.

[0159] In some implementations, the source SN may correspond to a CU of the source SN.

[0160] FIGS. 8 to 10 show an example of a procedure for SN-initiated inter-SN LTM preparation and configuration to which implementations of the present disclosure are applied.

[0161] First, FIG. 8 is described.

[0162] In step S800, the source SN (e.g., S-SN-CU) may configure the UE to report L3 measurement results via e.g., RRC reconfiguration procedure.

[0163] In step S802, the S-SN-CU may receive L3 measurement results for inter-SN LTM from the UE via SRB3 (if established) via the S-SN-DU. Additionally and / or alternatively, in step S804, the S-SN-CU may receive L3 measurement results for inter-SN LTM from the UE via SRB1 via the MN.

[0164] In step S810, the S-SN-CU may decide to configure inter-SN LTM for the UE. The inter-SN LTM for the UE may be decided based on the L3 measurement results received from the UE in step S802 and / or step S804.

[0165] In step S812, the S-SN-CU may initiate a SN modification procedure to the MN. For example, S-SN-CU may transmit a SN Modification Required message to the MN.

[0166] For example, the SN Modification Required message may include at least one of the following information.

[0167] - Inter-SN LTM indication;

[0168] - SN measurement results (received from the UE).

[0169] In step S814, the MN may reply to the S-SN-CU in response to the request by the S-SN-CU. For example, the MN may transmit a SN Modification Required Response message to the S-SN-CU.

[0170] For example, the SN Modification Required Response message may include at least one of the following information.

[0171] - MN measurement results (if received from the UE and available);

[0172] - A list of PSCell candidate(s) proposed for inter-SN LTM and the corresponding list of C-SN-CU IDs.

[0173] Alternatively, the MN may reject the request by the S-Sn-CU. The MN may also indicate to the S-SN-CU that the inter-SN LTM is not allowed. For example, the MN may provide the reason for rejection (e.g., L3 handover is on-going). Upon rejection of the MN, the SN-initiated inter-SN LTM procedure may stop in the S-SN-CU.

[0174] In step S816, the S-SN-CU may receive L1 measurement results from the UE via the S-SN-DU.

[0175] Next, FIG. 9, whose operation follows the operation of FIG. 8, is described.

[0176] In step S900, the S-SN-CU may decide the PSCell candidate(s) to prepare for inter-SN LTM. The PSCell candidate(s) for the inter-LTM may be decided based on the information received from the MN in step S814.

[0177] Additionally and / or alternatively, the S-SN-CU may also consider information provided from the S-SN-DU for the decision of the S-SN-CU. The S-SN-DU may provide at least one of the following information to the S-SN-CU.

[0178] - LTM (intra-SN or inter-SN) suggestion;

[0179] - PSCell candidate suggestions.

[0180] The S-SN-DU may provide the information above to the S-SN-CU based on the L1 measurement report of neighboring PSCell(s) received from the UE in step S816.

[0181] In step S902, upon determining PSCell candidate(s) for inter-SN LTM, the S-SN-CU may request SN change to the MN. For example, the S-SN-CU may transmit a SN Change Required message to the MN.

[0182] For example, the SN Change Required message may include at least one of the following information.

[0183] - Inter-SN LTM indication;

[0184] - Inter-SN LTM reference configuration;

[0185] - SN measurement results (received from the UE);

[0186] - A list of PSCell candidate(s) proposed for inter-SN LTM and the corresponding list of C-SN-CU IDs;

[0187] - Proposed PSCell candidate(s) in the source SN (if any) and their configurations prepared with its one or more SN-DU(s) for inter-SN LTM (i.e., if there are PSCell candidate(s) determined for inter-SN LTM under the S-SN-CU, the S-SN-CU may prepare inter-SN LTM with its S-SN-DU(s) and provide the corresponding configuration to the MN);

[0188] - Configuration ID mapping list (for those PSCells candidates);

[0189] - Maximum number of PSCell candidate(s) that can be prepared for each C-SN-CU;

[0190] - Configuration ID range for each C-SN-CU to use to assign for its candidate(s) to be prepared, if C-SN-CU assigns the Configuration IDs for its prepared PSCell candidate;

[0191] - A data forwarding proposal to be used for inter-SN LTM;

[0192] - S-SN-DU ID that is currently serving the UE for RACH resource preparation for early TA acquisition.

[0193] In step S910, the MN may request SN addition to one or more C-SN-CU(s) to be added for the UE for inter-SN LTM. For example, the MN may transmit a SN Addition Request message to the one or more C-SN-CU(s). The C-SN-CU(s) to be added for inter-SN LTM may be decided by the MN based on the list of C-SN-CU IDs and their PSCell candidates that the S-SN-CU proposed for inter-SN LTM.

[0194] For example, the SN Addition Request message may include at least one of the following information.

[0195] - Inter-SN LTM indication;

[0196] - Inter-SN LTM reference configuration (if already received from the S-SN-CU);

[0197] - Request for inter-SN LTM reference configuration;

[0198] - MN measurement results (if received from the UE and available);

[0199] - SN measurement results (if received from the S-SN-CU);

[0200] - S-SN-DU ID that is currently serving the UE (if received from the S-SN-CU);

[0201] - A list of proposed PSCell candidate(s) and their corresponding configuration ID mapping list;

[0202] - A maximum number of PSCell candidates;

[0203] - Configuration ID range for the C-SN-CU to use to assign for its PSCell candidates to be prepared, if the C-SN-CU assigns the configuration IDs for its prepared PSCell candidates;

[0204] - A data forwarding proposal (considering the data forwarding proposal from the S-SN-CU if received).

[0205] In step S912, the C-SN-CU may perform admission control and prepare inter-SN LTM with its underlying C-SN-DU(s) for the admitted PSCell candidates for the UE.

[0206] In step S914, once prepared, in response to the request from the MN by step S910, the C-SN-CU(s) may transmit a SN Addition Response message to the MN.

[0207] For example, the SN Addition Response message may include at least one of the following information.

[0208] - Inter-SN LTM reference configuration generated by the C-SN-CU (if requested);

[0209] - A list of PSCell candidates prepared for inter-SN LTM with their corresponding inter-SN LTM configurations: Each of the PSCell candidates may include, e.g., CSI report configuration, TCI state configuration, RACH configuration for early TA acquisition, etc.

[0210] - CSI resource configuration for the prepared PSCell candidates;

[0211] - Data forwarding proposal to be used for inter-SN LTM;

[0212] - A list of C-SN-DU ID(s) that will be involved during inter-SN LTM (for RACH resource preparation for early TA acquisition);

[0213] - Data forwarding TNLs assigned.

[0214] If the S-SN is configured as a C-SN for inter-SN LTM and the S-SN-CU have not provided or prepared the PSCell candidate(s) and their corresponding configurations for inter-SN LTM under the S-SN-CU, in step S920, the MN may initiate SN modification procedure with S-SN-CU to prepare inter-SN LTM with the S-SN-CU. That is, steps S910 / S912 / S914 describe above may be performed with S-SN-CU and underlying DU(s).

[0215] Next, FIG. 10, whose operation follows the operation of FIG. 9, is described.

[0216] In step S1000, once PSCell candidates are prepared with one or more C-SN-CU(s) for inter-SN LTM for the UE, the MN may further initiate SN modification procedure to each C-SN-CU for configuring the C-SN. For example, the MN may transmit a SN Modification Request message to each C-SN-CU.

[0217] For example, the SN Modification Request message may include at least one of the following information.

[0218] - Updated inter-SN LTM reference configuration (if already provided);

[0219] - A list of all the SN-DU ID(s) to be involved during inter-SN LTM;

[0220] - A list of all the accepted / prepared PSCell candidates with their configuration IDs;

[0221] - Collected configurations of all the accepted / prepared PSCell candidates for inter-SN LTM: Each configuration may include e.g., CSI resource configuration, TCI state configuration, RACH configuration, etc.

[0222] - Data forwarding proposal (considering the data forwarding proposal from the S-SN-CU if received).

[0223] In step S1002, each C-SN-CU may configure the involved C-SN-DU(s) with the received information from the MN for inter-SN LTM executions. Each C-SN-CU may further update the inter-SN LTM configurations for its PSCell candidates with the involved C-SN-DU(s).

[0224] In step S1004, once updated, in response to the request from the MN by step S1000, each C-SN-CU may transmit a SN Modification Response message to the MN. For example, the SN Modification Response message may include at least one of the updated inter-SN LTM configurations (including e.g., CSI report configuration, TCI state configuration, RACH configuration for early TA acquisition) for its PSCell candidates or data forwarding TNLs assigned.

[0225] If the S-SN is configured as a C-SN for inter-SN LTM, in step S1010, the MN may initiate SN modification procedure with S-SN-CU. That is, steps S1000 / S1002 / S1004 describe above may be performed with S-SN-CU and underlying DU(s), except exchange of information related to data forwarding.

[0226] If the S-SN is not configured as a C-SN for inter-SN LTM, in step S1020, the MN may initiate SN modification procedure with the S-SN-CU for configuring the S-SN. For example, the MN may transmit a SN Modification Request message to the S-SN-CU.

[0227] For example, the SN Modification Request message may include at least one of the following information.

[0228] - Information necessary to update the current SCG configuration of the UE for the initial inter-SN LTM execution and early TA acquisition from the current serving PSCell: For example, the information may include e.g., a list of all the accepted / prepared PSCell candidates with their configuration IDs, or collected configurations of all the accepted / prepared PSCell candidates (which may include CSI resource configuration, TCI state configuration, RACH configuration, etc.);

[0229] - Data forwarding TNLs assigned by the other C-SN-CU(s) (so that early data forwarding may be executed from the S-SN if applicable).

[0230] In step S1022, the S-SN-CU may configure S-SN-DU with the received information from the MN for initial inter-SN LTM execution. The S-SN-CU may further update the current SCG configuration with the S-SN-DU.

[0231] In step S1024, once updated, in response to the request from the MN by step S1020, the S-SN-CU may transmit a SN Modification Response message to the MN. The SN Modification Response message may include the updated SCG configuration.

[0232] In step S1030, the MN may compile the final inter-SN LTM configuration including the RRC reconfigurations generated for all the accepted / prepared PSCell candidate(s). The final inter-SN LTM configuration may be configured to the UE. Each RRC reconfiguration may include e.g., CSI resource configuration, CSI report configuration, TCI state configuration, RACH configuration, etc.

[0233] In step S1040, the MN may inform the S-SN-CU that inter-SN LTM is successfully configured to the UE. The MN may also provide the MN measurement results (to be considered for subsequent inter-SN LTM executions if available) and / or data forwarding TNLs of other C-SN-CU(s) (so that early data forwarding may be executed from if applicable).

[0234] The present disclosure may have various advantageous effects.

[0235] For example, the RAN nodes can prepare and configure the SN-initiated inter-SN LTM for a UE.

[0236] Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and / or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure.

[0237] Claims in the present disclosure can be combined in a various way. For instance, technical features in method claims of the present disclosure can be combined to be implemented or performed in an apparatus, and technical features in apparatus claims can be combined to be implemented or performed in a method. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in an apparatus. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in a method. Other implementations are within the scope of the following claims.

Claims

1.A method comprising:deciding, by a source secondary node (SN), inter-SN L1 / L2 triggered mobility (LTM) for a wireless device;transmitting, by the source SN, a modification required message to a master node (MN);receiving, by the source SN, a modification required response message from the MN in response to the modification required message;transmitting, by the source SN, a change required message to the MN; andreceiving, by the source SN, a change confirm message from the MN in response to the change required message.2.The method of claim 1, wherein the inter-SN LTM is decided based on L3 measurement results for the inter-SN LTM.3.The method of claim 2, wherein the L3 measurement results are received from the wireless via a signaling radio bearer (SRB)-1 or an SRB-3.4.The method of any claims 1 to 3, wherein the modification required message includes an inter-SN LTM indication.5.The method of any claims 1 to 4, wherein the modification required message includes SN measurement results.6.The method of any claims 1 to 5, wherein the modification required response message includes MN measurement results.7.The method of any claims 1 to 6, wherein the modification required response message includes a list of proposed primary secondary cell (PSCell) candidates and SN identifiers (IDs) of the proposed PSCell candidates for the inter-SN LTM.8.The method of any claims 1 to 7, wherein the change required message includes at least one of i) an inter-SN LTM indication, ii) a reference configuration for the inter-SN LTM, iii) a configuration ID mapping list for proposed PSCell candidates, iv) a maximum number of PSCell candidates that can be prepared for each candidate SN, or v) a configuration ID range for a candidate SN to use to assign for PSCell candidates of the candidate SN to be prepared.9.The method of any claims 1 to 8, wherein the change required message includes at least one of i) SN measurement results, ii) a list of proposed PSCell candidates and SN IDs of the proposed PSCell candidates for the inter-SN LTM, iii) proposed PSCell candidates in the source SN and configurations prepared with one or more SN distributed units (DUs) of the source SN for the inter-SN LTM, iv) a data forwarding proposal, or v) an ID of a DU that is currently serving the wireless device.10.The method of any claims 1 to 9, wherein the change confirm message informs that the inter-SN LTM is successfully configured to the wireless device.11.The method of any claims 1 to 10, wherein the change confirm message includes at least one of i) MN measurement results, or ii) data forwarding transport network layers (TNLs) assigned by a candidate SN.12.The method of any claims 1 to 11, wherein the method further comprises receiving at least one of an LTM suggestion or PSCell candidate suggestions from a DU of the source SN.13.The method of any claims 1 to 12, wherein the method further comprises configuring a DU of the source SN for execution of the inter-SN LTM and updating a current secondary cell group (SCG) configuration.14.The method of claim 13, wherein the method further comprises transmitting an updated SCG configuration to the MN.15.The method of any claims 1 to 14, wherein the modification required response message includes a reason for rejection of the modification required message.16.The method of any claims 1 to 15, wherein the source SN corresponds to a centralized unit (CU) of the source SN.17.A source secondary node (SN) comprising:at least one transceiver;at least one processor; andat least one memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform the method of any claims 1 to 16.

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