WO2025178313A1

WO2025178313A1 - Signaling for inter-secondary node-centralized unit l1/l2 triggered mobility

Info

Publication number: WO2025178313A1
Application number: PCT/KR2025/002094
Authority: WO
Inventors: Jaemin HAN; Daewook BYUN; Seokjung KIM
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2024-02-25
Filing date: 2025-02-13
Publication date: 2025-08-28
Anticipated expiration: 2026-08-25

Abstract

A method and apparatus for a signaling support for inter-Secondary Node (SN)-Centralized Unit (CU) L1/L2 Triggered Mobility (LTM) is provided. For example, a Master Node (MN) receives a Timing advance (TA) value for a candidate Primary Secondary cell (PSCell) from a candidate SN of inter-SN LTM, and transmits the TA value to a source SN. For another example, the MN receives a notification of a PSCell change for LTM from a source SN, transmits the notification to a candidate SN, receives an access success message from the candidate SN, and transmits the access success message to the source SN.

Description

SIGNALING FOR INTER-SECONDARY NODE-CENTRALIZED UNIT L1/L2 TRIGGERED MOBILITY

The present disclosure relates to a signaling support for inter-Secondary Node (SN)-Centralized Unit (CU) L1/L2 Triggered Mobility (LTM), specifically for early Uplink (UL) Primary Secondary cell (PSCell) synchronization and PSCell switch execution.

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.

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.

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.

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.

In an aspect, a first method is provided. The first method comprises, receiving, by a master node (MN), a timing advance (TA) value for a candidate primary secondary cell (PSCell) from a candidate SN of an inter-SN L1/L2 triggered mobility (LTM), and transmitting, by the MN, the TA value to a source SN.

In another aspect, a second method is provided. The second method comprises, receiving, by a master node (MN), a notification of a Primary Secondary cell (PSCell) change for L1/L2 triggered mobility (LTM) from a source secondary node (SN), transmitting, by the MN, the notification to a candidate SN, receiving, by the MN, an access success message from the candidate SN, and transmitting, by the MN the access success message to the source SN.

In another aspect, an apparatus for implementing the above methods is provided.

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

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

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

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

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

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

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

FIGS. 8 and 9 show an example of a procedure for inter-SN-CU LTM early UL PSCell synchronization to which implementations of the present disclosure are applied.

FIG. 10 shows an example of another method to which implementations of the present disclosure are applied.

FIGS. 11 to 14 show an example of a procedure for PSCell switch LTM execution across different SNs to which implementations of the present disclosure are applied.

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.

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.

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.

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".

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".

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".

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".

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".

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

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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).

Frequency Range designation	Corresponding frequency range	Subcarrier Spacing
FR1	450MHz - 6000MHz	15, 30, 60kHz
FR2	24250MHz - 52600MHz	60, 120, 240kHz

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).

Frequency Range designation	Corresponding frequency range	Subcarrier Spacing
FR1	410MHz - 7125MHz	15, 30, 60kHz
FR2	24250MHz - 52600MHz	60, 120, 240kHz

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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

A Next Generation Radio Access Network (NG-RAN) node is either:

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

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

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.

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.

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.

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.

One gNB-DU is connected to only one gNB-CU.

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.

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

NG, Xn and F1 are logical interfaces.

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.

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

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

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

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

3. Step 3: The source gNB provides the RRC configuration to the UE by forwarding the RRCReconfiguration message received in the HANDOVER REQUEST ACKNOWLEDGE. The RRCReconfiguration message 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 the RRCReconfiguration message. The access information to the target cell may include beam specific information, if any.

4. Step 4: The UE moves the RRC connection to the target gNB and replies with the RRCReconfigurationComplete.

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

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.

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).

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.

The following principles apply to CHO:

- 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.

- 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.

- 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.

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

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.

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.

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.

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).

The following principles apply to LTM:

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

- Subsequent LTM is supported.

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:

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

- PCell change in CA scenario,

- 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).

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

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

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.

The signaling procedure for LTM is as follows.

1. Step 1: The UE sends a MeasurementReport message to the gNB. The gNB decides to configure LTM and initiates candidate cell(s) preparation.

2. Step 2: The gNB transmits an RRCReconfiguration message to the UE including the LTM candidate cell configurations of one or multiple candidate cells.

3. Step 3: The UE stores the LTM candidate cell configurations and transmits an RRCReconfigurationComplete message to the gNB.

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

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.

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.

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.

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.

8. Step 8: The UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message 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.

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

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.

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 application.

The present disclosure proposes some mechanisms to support early UL PSCell synchronization (also known as early TA acquisition) and PSCell switch execution for inter-CU LTM across different SNs while keeping the MCG unchanged. The present disclosure necessary signaling procedures to enable early UL PSCell synchronization and PSCell switch execution, both of which are critical for inter-SN LTM operations.

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

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

- 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

- S-SN Centralized Unit (S-SN-CU): CU of the S-SN

- 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

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

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

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.

1. Embodiment 1: Inter-SN-CU LTM early UL PSCell synchronization

In step S700, the method comprises receiving, by a MN, a TA value for a candidate PSCell from a candidate SN of inter-SN LTM.

In some implementations, the TA value may be received from a DU of the candidate SN via a CU of the candidate SN.

In some implementations, the TA value may be transmitted to a DU of the source SN via a CU of the source SN.

In some implementations, the method may further comprise forwarding information informing that early UL PSCell synchronization was requested to a wireless device for the candidate PSCell from the source SN to the candidate SN. Forwarding of the information may comprises receiving the information from a DU of the source SN via a CU of the source SN, and transmitting the information to a DU of the candidate SN via a CU of the candidate SN. The early UL PSCell synchronization may be requested by a DU of the source SN to the wireless device.

In step S710, the method comprises transmitting, by the MN, the TA value to a source SN.

In some implementations, the TA value may be calculated by a DU of the candidate SN with a wireless device.

In some implementations, the method may further comprise sharing the TA value with other nodes for subsequent mobility.

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.

The MN 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.

More specifically, the MN receives a TA value for a candidate PSCell from a candidate SN of inter-SN LTM.

In some implementations, the MN may forward information informing that early UL PSCell synchronization was requested to a wireless device for the candidate PSCell from the source SN to the candidate SN. Forwarding of the information may comprises receiving the information from a DU of the source SN via a CU of the source SN, and transmitting the information to a DU of the candidate SN via a CU of the candidate SN. The early UL PSCell synchronization may be requested by a DU of the source SN to the wireless device.

The MN transmits the TA value to a source SN.

In some implementations, the MN may share the TA value with other nodes for subsequent mobility.

Hereinafter, early UL PSCell synchronization may be used interchangeably with early TA acquisition.

FIG. 8 is described first.

In step S800, after inter-SN LTM is configured to the UE, the current serving SN-CU (e.g., S-SN-CU) may decide early TA acquisition for some candidate PSCell(s).

In step S802, the S-SN-CU may request its serving DU (e.g., S-SN-DU) to perform/execute early TA acquisition for the UE for a specific candidate PSCell.

Or, in step S804, the S-SN-CU may inform the S-SN-DU that early TA acquisition is not required/needed for some candidate PSCell(s).

Or, in step S806, the S-SN-CU may provide TA values for some candidate PSCell(s) to the S-SN-DU (e.g., in case of known TA values). That is, the S-SN-CU may perform TA value information sharing with the S-SN-DU. The TA value may be later included in a PSCell switch command towards those candidate PSCell(s).

In step S810, the S-SN-DU may decide early TA acquisition towards a candidate PSCell in other DU.

In step S820, the S-SN-DU may command the UE to perform early TA acquisition for a candidate PSCell in other DU (e.g., candidate PSCell in C-SN-DU1).

Upon ordering the UE to execute early TA acquisition for a candidate PSCell in other DU, the S-SN-DU may inform the SN-DU of the candidate PSCell that early TA acquisition was requested to the UE for that candidate PSCell. The S-SN-CU, MN, and/or the SN-CU of the candidate PSCell (e.g., C-SN-CU1) may forward the information from the S-SN-DU to the SN-DU of the candidate PSCell. The SN-DU of the candidate PSCell may be e.g., C-SN-DU1. Or, the SN-DU of the candidate PSCell may be the same entity as the S-SN-DU.

For example, in step S822, the S-SN-DU may inform the S-SN-CU that early TA acquisition was requested to the UE for the candidate PSCell. In step S824, the S-SN-CU may inform the C-SN-CU1 that early TA acquisition was requested to the UE for the candidate PSCell, via the MN. In step S826, the C-SN-CU1 may inform the C-SN-DU1 that early TA acquisition was requested to the UE for the candidate PSCell.

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

In step S900, the UE may perform RACH procedure to the indicated candidate PSCell.

The SN-DU of the candidate PSCell that was requested for early TA acquisition (e.g., C-SN-DU1 or S-SN-DU) may calculate the TA value with the UE, and transfer the calculated TA value back to the S-SN-DU. The SN-CU of the candidate PSCell (e.g., C-SN-CU1), MN, and/or the S-SN-CU may forward the calculated TA value from the SN-DU of the candidate PSCell to the S-SN-DU.

For example, in step S910, the C-SN-DU1 may transmit the calculated TA value of the candidate PSCell to the C-SN-CU1. In step S912, the C-SN-CU1 may transmit the calculated TA value of the candidate PSCell to the S-SN-CU via the MN. In step S914, the S-SN-CU may transmit the calculated TA value of the candidate PSCell to the S-SN-DU.

The S-SN-CU and/or the SN-CU of the candidate PSCell (e.g., C-SN-CU1) that was requested for early TA acquisition may share the calculated TA value of the candidate PSCell with other SN-DU(s) (possibly through MN) for subsequent inter-SN LTM operations.

For example, in step S920, the C-SN-CU1 may share the calculated TA value of the candidate PSCell with the C-SN-DU2. In step S922, the S-SN-CU may share the calculated TA value of the candidate PSCell with another SN-DU in the S-SN-CU. In step S924, the S-SN-CU may share the calculated TA value of the candidate PSCell with the C-SN-CU2 via the MN.

In step S930, the S-SN-DU may decide early TA acquisition for a candidate PSCell within the S-SN-DU.

In step S940, the S-SN-DU may command the UE to perform early TA acquisition for a candidate PSCell belonging to the S-SN-DU.

In step S950, the UE may perform RACH procedure to the indicated candidate PSCell.

In step S960, the calculated TA value may be transferred to the S-SN-CU, for which S-SN-CU may share with other DU(s) (through the MN and/or other C-SN-CU(s)) for subsequent inter-SN LTM operations.

The early TA acquisition procedure described above may be initiated by the C-SN-CU or DU (other than the S-SN-DU) as serving PSCell change over the course of inter-SN LTM.

2. Embodiment 2: PSCell switch LTM execution across different SNs

In step S1000, the method comprises receiving, by a MN, a notification of a PSCell change for LTM from a source SN.

In some implementations, the notification may include at least one of an ID of a target PSCell, selected beam information and/or an ID related to the source SN.

In some implementations, the notification may be received from a DU of the source SN via a CU of the source SN.

In step S1010, the method comprises transmitting, by the MN, the notification to a candidate SN.

In some implementations, the notification may be transmitted to a DU of the candidate SN via a CU of the candidate SN.

In step S1020, the method comprises receiving, by the MN, an access success message from the candidate SN.

In some implementations, the access success message may include at least one of an ID of a target PSCell to which a wireless device accessed, an ID related to the source SN, a TA value, or a data forwarding proposal from the candidate SN.

In some implementations, the access success message may be received from a DU of the candidate SN via a CU of the candidate SN.

In step S1030, the method comprises transmitting, by the MN, the access success message to the source SN.

In some implementations, the access success message may be transmitted to a DU of the source SN via a CU of the source SN.

In some implementations, the method may further comprise performing a late data forwarding with the source SN.

In some implementations, the method may further comprise performing a sequence number (SN) status transfer for data radio bearers (DRBs) for which PDCP preservation is required with the source SN.

In some implementations, the method may further comprise sharing a TA value with other nodes for subsequent mobility.

In some implementations, the method may further comprise requesting data forwarding towards one or more candidates SNs other than the candidate SN (which may include the source SN, if the source SN remains as a candidate SN for inter-SN LTM).

In some implementations, the method may further comprise retrieving or assigning new forwarding transport network layers (TNLs) based on a data forwarding proposal from the candidate SN.

In some implementations, the method may further comprise delivering data forwarding TNLs assigned by one or more candidates SNs other than the candidate SN (which may include the source SN, if the source SN remains as a candidate SN for inter-SN LTM) to the candidate SN.

Furthermore, the method described above in FIG. 10 may be performed by a MN. The MN may be implemented by the second wireless device 200 shown in FIG. 2.

The MN 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. 10.

More specifically, the MN receives a notification of a PSCell change for LTM from a source SN.

The MN transmits the notification to a candidate SN.

The MN receives an access success message from the candidate SN.

The MN transmits the access success message to the source SN.

In some implementations, the MN may perform a late data forwarding with the source SN.

In some implementations, the MN may perform a SN status transfer for DRBs for which PDCP preservation is required with the source SN.

In some implementations, the MN may share a TA value with other nodes for subsequent mobility.

In some implementations, the MN may request data forwarding towards one or more candidates SNs other than the candidate SN (which may include the source SN, if the source SN remains as a candidate SN for inter-SN LTM).

In some implementations, the MN may retrieve or assign new forwarding TNLs based on a data forwarding proposal from the candidate SN.

In some implementations, the MN may deliver data forwarding TNLs assigned by one or more candidates SNs other than the candidate SN (which may include the source SN, if the source SN remains as a candidate SN for inter-SN LTM) to the candidate SN.

FIG. 11 is described first.

In step S1100, the UE is served under the current serving S-SN-DU.

In step S1102, the UE sends L1 measurement reporting as configured to the S-SN-DU.

Upon deciding PSCell switch, in step S1110, the S-SN-DU may command the UE to handover to a target PSCell (which is one of the prepared PSCell candidate(s)) in another SN-CU. For example, the S-SN-DU may transmit LTM command to a target PSCell A in the C-SN-DU1.

The S-SN-DU may inform the LTM PSCell change notification to the SN-DU of the target PSCell.

The LTM PSCell change notification may include at least one of the following information.

- Target PSCell ID

- Selected beam information (for proper UL scheduling)

- Source PSCell ID or S-SN-DU/CU ID (for proper routing of access success message)

The S-SN-CU, MN, and/or the SN-CU of the candidate PSCell (e.g., C-SN-CU1) may forward the LTM PSCell change notification from the S-SN-DU to the SN-DU of the candidate PSCell (e.g., C-SN-DU1).

For example, in step S1112, the S-SN-DU may transmit the LTM PSCell change notification to the S-SN-CU. In step S1114, the S-SN-CU may transmit the LTM PSCell change notification to the C-SN-CU1 via the MN. In step S1116, the C-SN-CU1 may transmit the LTM PSCell change notification to the C-SN-DU1.

In step S1120, the UE may perform RACH procedure and access the indicated target PSCell.

Once the UE successfully accessed, the SN-DU of the target PSCell (e.g., C-SN-DU1) becomes the new serving SN-DU. In step S1130, the C-SN-DU1 may inform the successful access of the UE to its respective SN-CU (new serving SN-CU, e.g., C-SN-CU1). For example, the C-SN-DU1 may transmit an access success message to the C-SN-CU1.

The access success message may include the target PSCell ID, and/or the TA value of the target PSCell calculated during the access of the UE. The TA value of the target PSCell may be shared with other SN-DU(s) for subsequent inter-SN LTM operations later.

In step S1140, the SN-CU of the target PSCell (i.e., new serving SN-CU) may inform the MN and the previous serving SN-CU of the successful PSCell switch of the UE. That is, the SN-CU of the target PSCell may inform the successful access of the UE and which PSCell the UE accessed to the MN and the previous serving SN-CU. For example, the C-SN-CU1 may transmit an access success message to the S-SN-CU via the MN.

The access success message may include at least one of the following information.

- Target PSCell ID to which the UE accessed

- The source PSCell ID or the previous serving SN-DU or SN-CU ID for proper routing of the message via the MN

- TA value of the target PSCell (received from its SN-DU (e.g., C-SN-DU1) of the target PSCell)

- Data forwarding proposals from the SN-CU of the target PSCell (e.g., C-SN-CU1).

Next, FIG. 12 whose operation follows the operation of FIG. 11 is described.

In step S1200, the previous serving SN-CU (e.g., S-SN-CU) may inform the its previous serving SN-DU (e.g., S-SN-DU) of the successful PSCell switch of the UE. That is, the S-SN-CU may inform the successful access of the UE and which PSCell the UE accessed to the S-SN-DU.

In step S1202, the S-SN-CU may also trigger SN status transfer procedure for DRBs for which PDCP preservation is required. This step may be omitted if the new serving SN-CU is the same entity as the current serving SN-CU.

In step S1204, the S-SN-CU may also perform late data forwarding toward the MN and the new serving SN-CU. This step may be omitted if the new serving SN-CU is the same entity as the current serving SN-CU.

In step S1206, the UE is served under C-SN-DU1.

In step S1210, the previous serving SN-CU (e.g., S-SN-CU) may share the TA value of the target PSCell with its SN-DU(s) for subsequent inter-SN LTM operations, if received from the new serving SN-CU (e.g., C-SN-CU1) through the MN.

In step S1212, the SN-CU of the target PSCell (i.e., new serving SN-CU) may share the TA value of the target PSCell with its other SN-DU(s) for subsequent inter-SN LTM operations, if received from its SN-DU of the target PSCell.

In step S1214, the previous serving SN-CU (e.g., S-SN-CU) may share the TA value of the target PSCell with other CU(s) for subsequent inter-SN LTM operations via the MN.

In step S1220, upon being informed of the successful access of the UE, the MN may request data forwarding towards SN-CU(s) other than the new serving SN-CU (e.g., C-SN-CU1). For example, the MN may transmit a data forwarding request message to the S-SN-CU and/or C-SN-CU2. The data forwarding request message may include the data forwarding proposal received from the C-SN-CU1.

In step S1222, the MN may retrieve/assign new data forwarding TNLs based on the data forwarding proposal from the new serving SN-CU (e.g., C-SN-CU1). For example, the MN may receive a data forwarding response message including new data forwarding TNLs from the S-SN-CU and/or C-SN-CU2.

In step S1224, the MN may deliver the data forwarding TNLs assigned by the SN-CU(s) other than the new serving SN-CU, if any, to the new serving SN-CU, for which, in step S1226, the new serving SN-CU may decide to perform early data forwarding. For example, the MN may transmit a data forwarding response message including data forwarding TNLs assigned by the SN-CU(s) other than the C-SN-CU1 to the C-SN-CU1, and the C-SN-CU1 may decide early data forwarding based on TNLs assigned by the SN-CU(s) other than the C-SN-CU1.

In step S1230, early TA acquisition may happen from the new serving SN-DU, based on the embodiment 1 of the present disclosure described above.

Steps described in FIGS. 13 and 14 may be repeated whenever an inter-SN LTM is executed from the current serving SN-DU to the new serving SN-DU under another SN-CU.

Path switch may be performed after each inter-SN LTM execution, which is omitted for brevity.

The present disclosure may have various advantageous effects.

For example, the RAN nodes can be enabled to facilitate early UL PSCell synchronization and execute PSCell switching for inter-SN LTM for a UE.

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.

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

A method comprising:

receiving, by a master node (MN), a timing advance (TA) value for a candidate primary secondary cell (PSCell) from a candidate SN of an inter-SN L1/L2 triggered mobility (LTM); and

transmitting, by the MN, the TA value to a source SN.
The method of claim 1, wherein the TA value is received from a distributed unit (DU) of the candidate SN via a centralized unit (CU) of the candidate SN.
The method of claim 1 or 2, wherein the TA value is transmitted to a DU of the source SN via a CU of the source SN.
The method of any claims 1 to 3, wherein the method further comprises forwarding information informing that early uplink (UL) PSCell synchronization was requested to a wireless device for the candidate PSCell from the source SN to the candidate SN.
The method of claim 4, wherein forwarding of the information comprises:

receiving the information from a DU of the source SN via a CU of the source SN; and

transmitting the information to a DU of the candidate SN via a CU of the candidate SN.
The method of claim 4 or 5, wherein the early UL PSCell synchronization was requested by a distribute unit (DU) of the source SN to the wireless device.
The method of any claims 1 to 6, wherein the TA value is calculated by a DU of the candidate SN with a wireless device.
The method of any claims 1 to 7, wherein the method further comprises sharing the TA value with other nodes for subsequent mobility.
A master node (MN) comprising:

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 of any claims 1 to 8.
A method comprising:

receiving, by a master node (MN), a notification of a primary secondary cell (PSCell) change for L1/L2 triggered mobility (LTM) from a source secondary node (SN);

transmitting, by the MN, the notification to a candidate SN;

receiving, by the MN, an access success message from the candidate SN; and

transmitting, by the MN, the access success message to the source SN.
The method of claim 10, wherein the notification includes at least one of an identifier (ID) of a target PSCell, selected beam information and/or an ID related to the source SN.
The method of claim 10 or 11, wherein the notification is received from a distributed unit (DU) of the source SN via a centralized unit (CU) of the source SN.
The method of any claims 10 to 12, wherein the notification is transmitted to a DU of the candidate SN via a CU of the candidate SN.
The method of any claims 10 to 13, wherein the access success message includes at least one of an ID of a target PSCell to which a wireless device accessed, an ID related to the source SN, a timing advance (TA) value, or a data forwarding proposal from the candidate SN.
The method of any claims 10 to 14, wherein the access success message is received from a DU of the candidate SN via a CU of the candidate SN.
The method of any claims 10 to 15, wherein the access success message is transmitted to a DU of the source SN via a CU of the source SN.
The method of any claims 10 to 16, wherein the method further comprises performing a late data forwarding with the source SN.
The method of any claims 10 to 17, wherein the method further comprises performing a sequence number (SN) status transfer for data radio bearers (DRBs) for which packet data convergence protocol (PDCP) preservation is required with the source SN.
The method of any claims 1 to 18, wherein the method further comprises sharing a TA value with other nodes for subsequent mobility.
The method of any claims 1 to 19, wherein the method further comprises requesting data forwarding towards one or more candidates SNs other than the candidate SN.
The method of any claims 1 to 20, wherein the method further comprises retrieving or assigning new forwarding transport network layers (TNLs) based on a data forwarding proposal from the candidate SN.
The method of any claims 1 to 21, wherein the method further comprises delivering data forwarding TNLs assigned by one or more candidates SNs other than the candidate SN to the candidate SN.
A master node (MN) comprising:

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 of any claims 10 to 22.