Timing advance management during layer (L1 / L2) triggered mobility (LTM)

Abstract

This disclosure describes techniques for timing advance management during layer (L1 / L2) triggered mobility (LTM). In one aspect, a method includes obtaining a timing advance (TA) for one or more LTM candidate cells based on an indication from a serving gNB-DU and storing the obtained TA, and receiving an LTM serving cell handover command for a current serving cell to a target cell. The method further includes sending a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs to a target gNB-DU serving the target cell in response to successful completion of the LTM cell handover.

Description

Technical Field

[0001] This disclosure relates in general to methods and apparatus for advance timing management during mobility (LTM) triggered at layer (L1 / L2). Background Technology

[0002] 5G New Radio (NR) is a wireless communication standard that defines the physical layer and protocol stack for fifth-generation mobile networks (5G). 5G NR operates on multiple frequency bands, allowing for wider coverage and higher data rates. Open Radio Access Network (ORAN) is a cloud-native, centralized cellular network architecture that offers significant benefits in terms of network scalability and performance. Open RAN decomposes the traditional monolithic, single-vendor radio access network (RAN) into Distributed Units (DUs), Centralized Units (CUs), and Radio Units (RUs) and connects these elements using open standard interfaces. This decomposition allows operators to virtualize CU and DU components and run them on Commercial Off-the-shelf (COTS) servers.

[0003] L1 / L2 triggered mobility (LTM) differs fundamentally from traditional or legacy Layer 3 mobility in its execution. Layer 3 mobility, or baseline mobility, or legacy mobility concepts revolve around a network that configures a user equipment (UE) using RRC measurements or Layer 3 measurements, then uses those measurements to prepare a target cell and subsequently sends a handover command to the UE. Target cell configuration and handover commands are provided to instruct the gNB's DU to hand over the UE to the target cell. With LTM, the UE can be configured for lower-layer mobility such as Layer 1 (L1) / Layer 2 (L2) mobility, where the UE can perform lower-layer handover procedures, allowing the UE to dynamically perform cell transfer handover procedures to cells of the same or neighboring base stations (i.e., gNBs).

[0004] In traditional cell handover or handover, the UE waits for the Physical Random Access Channel (PRACH) opportunity and performs RACH to synchronize with the uplink (UL) of the target cell. This is necessary because the timing advance of the target cell (configured for HO) may differ from that of the serving cell. During the RACH process, the UE acquires its timing advance (TA) at the target cell.

[0005] For LTM, to reduce user plane outage time during cell handover, a Physical Downlink Control Channel (PDCCH) command can be used (before the LTM serving cell change) to instruct the UE from the serving gNB-DU. The PDCCH command instructs the UE to perform UL synchronization with the indicated target gNB-DU cell. During this UL synchronization, the UE sends a Contention-Free Random Access (CFRA) preamble to the target gNB-DU and obtains the UE's TA in the target cell. The target gNB-DU's Random Access Response (RAR) can be configured to include the UE's target cell timing in advance. The benefit of this process is that the UE can avoid performing RACH during the actual LTM serving cell change because the target cell's TA is already available, thus reducing HO latency and consequently reducing user plane outages.

[0006] If the UE receives an LTM cell handover command from the serving DU to perform an LTM cell handover to the target cell of the target DU, the UE hands over to the target DU. The target DU can serve as the new serving DU. Even if the UE has successfully acquired the TA of one or more candidate cells before the handover, the new serving DU is unaware of the TA acquired by the UE and the TA stored in the UE.

[0007] This could lead to the expiration of the TA alignment timer defined for the corresponding timing advance and the loss of TA awareness at the UE. Furthermore, the new serving DU can instruct the UE to clear the TA stored at the UE and can instruct the UE to re-perform UL synchronization with the candidate cell, which affects the UE's data transmission at the new serving gNB-DU and may also incur overhead for the new serving gNB-DU. Additionally, when issuing an LTM cell handover command, the new serving DU may instruct the UE to perform a RACH-based HO, thereby removing all the expected benefits of a RACH-free HO and increasing HO latency.

[0008] Therefore, there is a need in the art to provide a technology / mechanism that overcomes the above problems by providing timed advance management during inter-cell changes centered on L1 / L2. Summary of the Invention

[0009] In a decomposed gNB architecture, a key objective during inter-cell changes (i.e., changes in serving cell) centered on L1 / L2 is to achieve RACH-free cell handover from the source cell to the target cell. The expiration of the timing advance (TA) alignment timer results in a loss of TA awareness at the user equipment (UE). Due to the TA alignment timer expiration, the UE needs to perform a cell handover based on the random access channel (RACH) procedure when a mobility (LTM) serving cell handover command is triggered at layer (L1 / L2), thus increasing cell handover latency. In the absence of TA awareness at the serving gNB-DU, if RACH-free LTM cell handover is desired, the serving gNB-DU can instruct the UE to re-execute the UL synchronization procedure with the target gNB-DU cell and obtain an updated TA. This process interrupts data transmission by the UE at the serving gNB-DU and also becomes an overhead for the target gNB-DU.

[0010] In one non-limiting aspect of this disclosure, a timing advance management method is disclosed during a Layer 1 (L1 / L2) triggered Mobility Transaction (LTM) event. The method discloses that a UE obtains a timing advance (TA) for one or more LTM candidate cells based on an indication from a serving gNB-DU, and stores the obtained TA. The method also discloses receiving an LTM serving cell handover command to hand over from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by a target gNB-DU. Finally, the method discloses that in response to a successful LTM cell handover, a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

[0011] In another non-limiting aspect of this disclosure, a timing advance management apparatus is disclosed during a layer (L1 / L2) triggered mobility (LTM) event. The apparatus includes at least one processor and a memory communicatively coupled to the at least one processor. The memory is configured to store processor-executable instructions that, upon execution, cause the at least one processor to obtain timing advances (TAs) for one or more LTM candidate cells based on indications from a serving gNB-DU, and to store the obtained TAs. Upon execution, the stored processor-executable instructions also cause the at least one processor to receive a layer LTM serving cell handover command to hand over from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by a target gNB-DU. Upon execution, the stored processor-executable instructions also cause the at least one processor, in response to a successful LTM cell handover, to send a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs to the target gNB-DU serving the target cell.

[0012] In another non-limiting aspect of this disclosure, a non-transitory computer-readable medium is disclosed for timing advance management during a mobility (LTM) event triggered at layer (L1 / L2). The non-transitory computer-readable medium has computer-readable instructions that, when executed by a processor, cause the processor to perform operations based on instructions from a serving gNB-DU to obtain timing advances (TAs) for one or more LTM candidate cells and store the obtained TAs. The computer-readable instructions, when executed by the processor, also cause the processor to perform operations to obtain an LTM serving cell handover command to hand over from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by a target gNB-DU. Finally, when executed by the processor, the computer-readable instructions also cause the processor, in response to a successful LTM cell handover, to send a list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs to the target gNB-DU serving the target cell.

[0013] In another non-limiting aspect of this disclosure, a method for timing advance management during a Layer (L1 / L2) triggered Mobility Transaction (LTM) event is disclosed. This method discloses receiving a list of candidate cell IDs and corresponding timing advances (TAs) from a User Equipment (UE). The method also discloses performing a Layer (L1 / L2) triggered LTM cell handover of the UE to switch from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by a target gNB-DU. Finally, the method discloses sending the list of candidate cell IDs and corresponding TAs to the target gNB-DU serving the target cell in response to the execution of the LTM cell handover.

[0014] In another non-limiting aspect of this disclosure, an apparatus for timing advance management during a layer (L1 / L2) triggered mobility (LTM) event is disclosed. The apparatus includes at least one processor and a memory communicatively coupled to the at least one processor. The memory stores processor-executable instructions that, when executed, cause the at least one processor to receive a list of candidate cell IDs and corresponding timing advances (TAs) from a user equipment (UE). The stored processor-executable instructions, when executed, also cause the at least one processor to perform a layer (L1 / L2) triggered mobility (LTM) cell handover of the UE from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB distributed unit (gNB-DU), and the target cell is served by a target gNB-DU. Finally, when executed, the stored processor-executable instructions cause the at least one processor, in response to the execution of the LTM cell handover, to send the list of candidate cell IDs and corresponding TAs to the target gNB-DU serving the target cell.

[0015] In another non-limiting aspect of this disclosure, a non-transitory computer-readable medium is disclosed for timing advance management during a layer (L1 / L2) triggered mobility (LTM) event. The non-transitory computer-readable medium has computer-readable instructions that, when executed by a processor, cause the processor to perform the following operations: obtain a list of candidate cell IDs and corresponding timing advances (TAs) from a user equipment (UE). When executed by the processor, the computer-readable instructions also cause the processor to perform the following operations: perform a layer (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell. The current serving cell is served by a serving gNodeB distributed unit (gNB-DU), and the target cell is served by a target gNB-DU. Finally, when executed by the processor, the computer-readable instructions cause the processor to perform the following operations: send the list of candidate cell IDs and corresponding TAs to the target gNB-DU serving the target cell in response to the execution of the LTM cell handover.

[0016] The foregoing description of the invention is merely illustrative and is not intended to be limiting in any way. In addition to the illustrative aspects, features, and characteristics described above, other aspects and features will become apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0017] Other aspects and advantages of this disclosure will be readily understood from the detailed embodiments described below with reference to the accompanying drawings. Reference numerals have been used to denote elements that are identical or functionally similar. These drawings, together with the detailed embodiments described below, are incorporated into and form part of this specification, and serve to further illustrate these aspects and explain the various principles and advantages, as shown in the drawings:

[0018] Figure 1 Exemplary aspects of a radio access network (RAN) communication system 100 having a decomposed gNB architecture, according to some aspects of this disclosure, are shown.

[0019] Figure 2A A high-level block diagram 200a illustrating mobility within the gNB-DU is shown, representing some aspects of this disclosure.

[0020] Figure 2B A high-level block diagram 200b illustrating mobility between gNB-DUs is shown, representing some aspects of this disclosure.

[0021] Figure 3A Signaling diagram 300a shows the timing advance management during inter-cell changes centered on L1 / L2 according to some aspects of this disclosure.

[0022] Figure 3BSignaling diagram 300b shows the timing advance management during inter-cell changes centered on L1 / L2 according to some aspects of this disclosure.

[0023] Figure 4 A high-level block diagram of an apparatus 400 for timing advance management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown.

[0024] Figure 5 A high-level block diagram of an apparatus 500 for timing advance management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown.

[0025] Figure 6 A flowchart of an exemplary method 600 for advance management of timing during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown.

[0026] Figure 6A A sub-flowchart of an exemplary method 602 for obtaining timing advances by a user equipment (UE) according to some aspects of this disclosure is shown.

[0027] Figure 7 A flowchart of another exemplary method 700 for advance management of timing during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown.

[0028] Those skilled in the art will understand that any block diagram herein represents a conceptual diagram of an illustrative system embodying the principles of this disclosure. Similarly, it should be understood that any flowchart, flow diagram, state transition diagram, pseudocode, etc., represents various processes that can be substantially represented in a computer-readable medium and executed by a computer or processor, regardless of whether such computer or processor is explicitly shown. Detailed Implementation

[0029] In this document, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any aspect or implementation of this disclosure described herein as “exemplary” should not be construed as being more preferred or advantageous than other aspects.

[0030] While this disclosure allows for various modifications and alternatives, certain aspects have been shown by way of example in the accompanying drawings and will be described in detail below. However, it should be understood that this is not intended to limit this disclosure to the specific forms disclosed; rather, this disclosure will cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

[0031] The term "comprise(s)" or any other variation thereof is intended to cover non-exclusive inclusion, such that an arrangement, device, apparatus, system, or method that includes a list of components or steps includes not only those components or steps, but may also include other components or steps not expressly listed or inherent to such arrangement, device, apparatus, system, or method. In other words, without further constraints, the presence of one or more elements in an apparatus, system, or device preceded by "comprise..." does not exclude the presence of other elements or additional elements in the system.

[0032] Throughout this specification, terms such as "at least one" and "one or more" may be used interchangeably. Terms such as "a plurality of / multiple" may be used interchangeably. Terms such as "distributed unit," "distributed unit entity," "DU," and "vDU" may be used interchangeably. Terms such as "central unit control plane," "CU-CP," "CU-CP entity," and "vCU-CP" may be used interchangeably. Terms such as "central unit user plane," "CU-UP," "CU-UP entity," and "vCU-UP" may be used interchangeably.

[0033] Throughout this specification, terms such as “COTS” and “commercial off-the-shelf server” may be used interchangeably. Terms such as “network operator,” “carrier,” and “service provider” may be used interchangeably. Terms such as “L1 / L2 triggered mobility” and “LTM” may be used interchangeably. Terms such as “timing advance” and “TA” may be used interchangeably. Terms such as “timing advance alignment timer,” “Time_Alignment_Timer,” and “TA alignment timer” may be used interchangeably. Terms such as “cell handover” and “handover” may be used interchangeably. Terms such as “MAC control element” and “MACCE” may be used interchangeably. It should be understood that the interchangeable terms disclosed in the foregoing paragraphs may be used repeatedly throughout this disclosure. However, these terms should not be construed in any way as limiting the scope of this disclosure.

[0034] In the following detailed description of various aspects of this disclosure, reference is made to the accompanying drawings, which form part of the detailed description, and are illustrated in the drawings by way of explaining specific aspects in which the disclosure may be practiced. These aspects are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it should be understood that other aspects may be utilized and changes may be made without departing from the scope of the disclosure. Therefore, the following description is not restrictive. Well-known functions or structures are not described in detail in the following description because they would be obscured by unnecessary detail.

[0035] The decomposition architecture of the gNB defined in 3GPP breaks down the gNB into multiple logical entities, such as one or more CUs and one or more DUs. Similarly, a single DU can host multiple cells (up to 512 in the current specification). CUs can be further divided into control plane entities (CU-CP) and one or more user plane entities (CU-UP). The gNB-CU-CP hosts the Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the gNB-DU hosts the Radio Link Control (RLC) / Media Access Control (MAC) and Physical (PHY) layers. Scheduling operations occur at the gNB-DU.

[0036] When a UE moves from the coverage area of ​​one cell to another, a serving cell change needs to be performed at some points. The current serving cell change is triggered by L3 measurements and a reconfiguration triggered by RRC signaling, which, when applicable, includes synchronization for the cell change. In this scenario, the full L2 and L1 are reset. A full L2 / L1 reset means a complete change to the L1 and L2 configurations of the cell at the UE's location. This results in longer latency, greater overhead, and longer downtime compared to beam-switching mobility.

[0037] In this regard, the 3rd Generation Partnership Project (3GPP) continues to add features in Release 18 to enhance 5G performance by working on areas such as network power saving, coverage, mobility support, MIMO evolution, multicast and broadcast services (MBS), and positioning. The purpose of the Mobility Enhancement Release 18 work item is to specify mechanisms and procedures for L1 / L2-based inter-cell mobility to reduce mobility latency. L1 / L2 mobility enhancement has been proposed to implement serving cell changes via L1 / L2 signaling to reduce latency, overhead, and downtime. Those skilled in the art will understand that L1 / L2 triggered mobility (LTM) is the process by which the gNB receives an L1 measurement report from the UE and, based on this, changes the UE's (multiple) serving cells via MAC CE. L1 measurements involve inter-cell beamforming (ICBM), which does not require a full L2 / L1 reset. The gNB prepares one or more candidate cells and provides the candidate cell configuration to the UE via an RRC message. The LTM cell handover is then triggered by the gNB selecting one of the candidate configurations as the target configuration for LTM. Candidate cell configurations can only be added, modified, and released by the network via RRC signaling.

[0038] In traditional cell handover or switching, the UE waits for the Physical Random Access Channel (PRACH) opportunity and performs RACH to synchronize with the uplink (UL) of the target cell. This is necessary because the timing advance of the target cell (configured for the HO) may differ from that of the serving cell. During the RACH process, the UE acquires its timing advance (TA) in the target cell. The TA is UE-specific and may differ for different UEs within a cell, depending on the distance from the base station. Timing advance is defined as the negative offset at the UE between the start of a received downlink subframe and the start of a transmitted uplink subframe. This offset at the UE is necessary to ensure that downlink and uplink subframes are synchronized at the gNB. The gNB controls the timing advance that each UE must apply. The gNB provides the UE with a configurable timer called Time_Alignment_Timer. Time_Alignment_Timer controls the length of time for which the UE is considered to be uplink time-aligned. The UE starts / restarts Time_Alignment_Timer based on the conditions at which it receives the timing advance command. When Time_Alignment_Timer is not running, the UE must not perform any uplink transmissions except for random access preamble transmissions.

[0039] For LTM, to reduce user plane outage time during HO (House Opening) phases, a consensus has been reached in RAN1 that the UE can be commanded by the serving gNB-DU (before the LTM serving cell change) using Physical Downlink Control Channel (PDCCH) commands. The PDCCH command instructs the UE to perform a UL (Upper Limit) synchronization operation with the indicated target gNB-DU cell. During this UL synchronization operation, the UE sends a Contention-Free Random Access (CFRA) preamble (reserved during LTM target cell preparation or provided later) to the target gNB-DU and obtains the UE's timing advance in the target cell. The target gNB-DU's Random Access Response (RAR) can be configured to include the UE's target cell TA. The benefit of this process is that the UE can avoid performing RACH during the actual LTM serving cell change because the target cell TA is already available, thus reducing HO latency and consequently reducing user plane outages.

[0040] Therefore, in order to support inter-cell changes (i.e., changes in serving cells) centered on L1 / L2 in the decomposed gNB architecture, a new mechanism is needed where HO preparation (i.e., preparation of target cell configuration) is performed at gNB-CU-CP, but is executed autonomously by gNB-DU without further interaction with the upper layers, in order to further improve HO latency.

[0041] In one non-limiting aspect of this disclosure, a method for timing advance management during inter-cell handover centered on L1 / L2 is disclosed. The method includes obtaining and storing the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2) based on an instruction from a serving gNB-DU, and receiving a layer (L1 / L2) triggered mobility (LTM) serving cell handover command to switch from the current serving cell to a target cell. The current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by a target gNB-DU. The method also includes sending a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs to the target gNB-DU serving the target cell in response to a successful LTM cell handover. Sending the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs to the target gNB-DU serving the target cell facilitates the target gNB-DU reusing the TA timer where needed. The list of candidate cell IDs and the TA also helps the target gNB-DU initiate UL synchronization in the correct cell without repeating the RACH process or negotiating UE data transmission at the target gNB-DU. Furthermore, the above solution also ensures RACH-free HO during subsequent inter-cell changes.

[0042] To understand the above scheme in detail, it is first necessary to understand the following reference. Figure 1 A detailed discussion of the decomposed gNB architecture. Figure 1 Exemplary aspects of a radio access network (RAN) communication system 100, including a 5G new radio (NR) base station system (also referred to as "gNodeB" or "gNB") 101, are shown according to some aspects of this disclosure. Although Figure 1 This description is made within the context of a 5G architecture where base stations are divided into multiple logical entities; however, it should be understood that the technologies described herein can be used with other radio interfaces, such as 4G LTE. In an exemplary aspect, gNB 101 can be configured to provide radio services to at least one user equipment (UE) 120 present in cells 116a, 116b, 118a, or 118a served by gNB 101. However, the number of cells is not limited to the examples above, and gNB 101 may include more cells than discussed in the examples above.

[0043] The at least one UE can be any mobile or non-mobile computing device, including but not limited to telephones (e.g., cellular phones or smartphones), pagers, laptops, desktop computers, wireless handheld devices, portable communication devices, portable computing devices (e.g., personal data assistants), entertainment devices (e.g., music or video devices, or satellite radios), GPS devices, or any other suitable computing device including wired or wireless communication interfaces. In some aspects of this disclosure, the at least one UE can be an Internet of Things (IoT) enabled device, including but not limited to vehicles configured to communicate with gNB101 or the core network.

[0044] As shown in the figure, gNB 101 can be divided into a central unit (CU) 106 and one or more distributed units (DUs) 112 and 114. In this configuration, CU 106 is configured to serve DUs 112 and DUs 114, and DUs 112 and DUs 114 are configured to serve one or more UEs 120. Figure 1 In this respect, CU 106 can be further divided into a control plane entity (CU-CP) 108 and one or more user plane entities (CU-UP) 110, which can handle the control plane and user plane processing of CU 106 respectively. CU-CP 108 is communicatively coupled to each of CU-UP 110 via an E1 interface. CU-CP 108 is communicatively coupled to each of DU 112 and 114 via an F1-C interface. Each of DU 112 and 114 can be communicatively coupled to each of CU-UP 110 via an F1-U interface.

[0045] In one non-limiting aspect, the CU and DU functions can run as virtual software functions on a standard Commercial Off-the-shelf (COTS) server. In this case, CU-CP entity 108 can also be referred to as "vCU-CP" 108 and each such user plane CU entity 110 can also be "vCU-UP" 110. The vCU-CP 108 and vCU-UP 110 entities can interconnect via an interface specified by the relevant 3GPP 5G NR technical specifications. The vCU-CP 108 and vCU-UP entities 110 can be communicatively coupled to virtual DUs (vDUs) such as vDU 112 and vDU 114 via an interface known to those skilled in the art. In one non-limiting aspect, each of the virtual DUs 112 and 114 can be hosted on a COTS server.

[0046] In this example, CU-CP 108 and vCU-UP entity 110 can be configured to communicate with the core network 102 of the associated wireless operator using a suitable backhaul network 104 (typically a public wide area network such as the Internet). In a non-limiting aspect of this disclosure, the core network 102 can be a 5G core network in a standalone deployment mode. The 5G core network can utilize a cloud-aligned, service-based architecture across all 5G functions and interactions including authentication, security, session management, etc. The 5G core network can also emphasize Network Functions Virtualization (NFV) as a holistic design concept with virtualized software capabilities.

[0047] In another non-limiting aspect, the core network 102 may be a Long Term Evolution Packet Core (LTE EPC) network in a non-standalone deployment mode, where previous-generation infrastructure (e.g., using an existing LTE Evolution Packet Core (EPC)) is used to provide services. In a non-standalone deployment, interface S1 may exist between gNB 101 and the LTE EPC. This disclosure may also be applicable to standalone and / or non-standalone deployment modes or other deployment modes that may be developed in the future.

[0048] In an implementation (such as) Figure 1 As shown), DU 112 can serve UE 120 located in cells 116a and 116b, and DU 114 can serve UE 120 located in cells 118a and 118b. Each UE 120 can be communicatively coupled to the respective DU 112 and 114, which are served by a fronthaul network that may include, but is not limited to, a private network and / or the Internet (but not limited to).

[0049] like Figure 1As shown, the decomposed architecture of gNB 101 illustrates that DU 112 and DU 114 have corresponding cell coverage defined by cells 116a, 116b and 118a, 118b, respectively. Intra-gNB-DU mobility can be defined as the cell handover of UE 120 from one cell to another within the same DU. Inter-gNB-DU mobility can be defined as the cell handover of UE 120 between cells of different gNB DUs. Intra-gNB-DU mobility and inter-gNB-DU mobility are discussed in detail below.

[0050] Now for reference Figure 2A , Figure 2A A high-level block diagram 200a illustrates intra-gNB-DU mobility according to some aspects of this disclosure. gNB-CU 106 may have DU 112, DU 113, and DU 114 connected to it. Consider UE 120 currently served by serving cell 116a serving DU 112. Cells 116b, 117a, 117b, 118a, and 118b can serve as candidate cells, their configurations defined using RRC configuration messages received by UE 120. Candidate cells 116b, 117a, 117b, 118a, and 118b can be served by candidate DUs 113 and 114.

[0051] Serving DU 112 can instruct UE 120 to perform UL synchronization with candidate cell 117a of candidate DU 113 and candidate cell 118b of candidate DU 114 using a PDCCH command. This UL synchronization is performed by executing a RACH procedure and sending RACH preambles to candidate DUs 113 and 114. UE 120 can then receive a Random Access Response (RAR) including the timing advance (TA) for the corresponding candidate cells 117a and 118b from candidate DU 113 and candidate DU 114, respectively. This RAR message can be received directly from the target gNB-DU or via gNB-CU and serving gNB-DU. UE 120 can store the corresponding TAs for the respective candidate cells 117a and 118b based on a timing advance alignment timer defined for the corresponding timing advance. The maximum number of TA values ​​stored by the UE depends on the UE's capabilities.

[0052] If Serving DU 112 instructs UE 120 to perform UL synchronization with candidate cell 117b using a PDCCH command, and UE 120 receives an LTM cell handover command from Serving DU 112 to perform an LTM cell handover to target cell 118b of target DU 114. Due to the higher priority of the LTM cell handover command, the LTM cell handover is performed first, and UE 120 is handed over to target DU 114. Target DU 114 can serve as the new Serving DU. Even if the UE successfully acquires the TA of candidate cell 117b, the new Serving DU 114 is unaware of the TA acquired by UE 120 and the TA stored in UE 120.

[0053] This could lead to the expiration of the TA alignment timer predefined for the corresponding timing and the loss of TA awareness at UE 120. Furthermore, the new service DU 114 can instruct UE 120 to clear the TA stored at UE 120 and can instruct the UE to re-perform UL synchronization with the candidate cell, which affects the UE's data transmission under the new service gNB-DU 114 and may also become an overhead of the new service gNB-DU 114. Additionally, the new service DU 114 may instruct UE 120 to perform RACH-based HO when issuing an LTM cell handover command, thereby losing all the expected benefits of RACH-free HO and increasing HO latency.

[0054] In one aspect, this disclosure addresses the aforementioned problem by sending, in advance whenever an LTM serving cell handover command is detected / executed, a list of all candidate cell IDs for which UE 120 has previously performed UL synchronization (maintaining TA), along with their corresponding time intervals, to the new serving gNB-DU 114. The list of candidate cell IDs and the corresponding TAs can be transmitted from UE 120 to the new serving DU114 via a UL MAC control element (CE) or a similar Layer 1 / 2 command.

[0055] On the other hand, this disclosure addresses the aforementioned problem by sending a list of all candidate cell IDs for which UE 120 has performed UL synchronization, along with their corresponding timers, from the old service gNB-DU 112 to the new service gNB-DU 114 after an LTM cell handover. The list of candidate cell IDs and the corresponding TAs can be received from UE 120 by the old service gNB-DU 112 when the candidate cells are acquired. The list of candidate cell IDs and the corresponding TAs can be transmitted directly or via gNB-CU 106 through the F1 interface to the new service DU 114.

[0056] Therefore, the two solutions described above in this disclosure help the new serving gNB-DU 114 reuse the TA timer received from the old serving gNB-DU 112 when needed. The list of candidate cell IDs and the TA help the new serving gNB-DU 114 initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU 114. Furthermore, the solutions discussed above ensure RACH-free HO during LTM inter-cell changes.

[0057] Now for reference Figure 2B , Figure 2B A high-level block diagram 200b illustrating inter-gNB-DU mobility according to some aspects of this disclosure is provided. gNB-CU 106 of gNB 101 may have connected DUs 112, 113, and 114. Similarly, gNB-CU 107 of gNB 103 may have connected DUs 122, 123, and 124. Considering that UE 120 is currently served by serving cell 117b serving DU 113, for intra-gNB-DU mobility, cells 116a, 116b, 117a, 118a, and 118b can serve as candidate cells, which can be defined using RRC configuration messages received by UE 120. Candidate cells 116a, 116b, 117a, 118a, and 118b can be served by candidate DUs 112, 113, and 114. Similarly, for inter-gNB-DU mobility, cells 126a, 126b, 127a, 127b, 128a, and 128b can be used as candidate cells, which can be defined using the RRC configuration message received by UE 120. Candidate cells 126a, 126b, 127a, 127b, 128a, and 128b can be served by candidate DUs 122, 123, and 124, respectively.

[0058] Serving DU 113 can instruct UE 120 to perform UL synchronization with candidate cell 126a of candidate DU 122 and candidate cell 128b of candidate DU 124 using PDCCH commands by sending a RACH preamble to candidate DUs 122 and 124. UE 120 can then receive random access responses (RARs) from candidate DUs 122 and 124, respectively, including the timing advance (TA) values ​​for the corresponding candidate cells 126a and 128b. UE 120 can store the corresponding TA values ​​for the respective candidate cells 126a and 128b based on the timing advance alignment timer defined for the corresponding timing advance. Similarly, it should be understood that the maximum number of TA values ​​stored by the UE depends on the UE's capabilities.

[0059] If Serving DU 113 instructs UE 120 to perform UL synchronization with candidate cell 127b using a PDCCH command, and while performing UL synchronization with candidate DU 123, UE 120 receives an LTM cell handover command from Serving DU 113 to perform an LTM cell handover to target cell 126a of target DU 122. Due to the higher priority of the LTM cell handover command, the LTM cell handover is performed first, and UE 120 is handed over to target DU 122. Target DU 122 can serve as the new Serving DU. Even if the UE successfully acquires the TA of candidate cell 127b, the new Serving DU 122 is unaware of the TA acquired by UE 120 and the TA stored in UE 120.

[0060] This leads to the expiration of the TA alignment timer predefined for the corresponding timing and the loss of TA awareness at UE 120. Furthermore, the new service DU 122 can instruct UE 120 to clear the TA stored at UE 120 and can instruct the UE to re-perform UL synchronization with candidate cells 128b and 127b, which affects the UE's data transmission under the new service gNB-DU 122 and may also become an overhead of the new service gNB-DU 122. In addition, the new service DU 122 can instruct UE 120 to perform RACH-based HO when issuing an LTM cell handover command, thereby losing all the expected benefits of RACH-free HO and increasing HO latency.

[0061] In one aspect, this disclosure addresses the aforementioned problem by sending, in advance whenever an LTM serving cell handover command is detected / executed, a list of all candidate cell IDs for which UE 120 has previously performed UL synchronization (maintaining TA) and their corresponding timeouts to the new serving gNB-DU 122. The list of candidate cell IDs and the corresponding TAs can be transmitted from UE 120 to the new serving DU 122 via a UL MAC control element (CE) or similar L1 / L2 commands.

[0062] On the other hand, this disclosure addresses the aforementioned problem by forwarding a list of all candidate cell IDs for which UE 120 has performed UL synchronization, along with their corresponding timings, from the old service gNB-DU 113 to the new service gNB-DU 122 after an LTM cell handover. The list of candidate cell IDs and the corresponding TAs can be received from UE 120 by the old service gNB-DU 113 when the corresponding candidate cells are acquired. The list of candidate cell IDs and the corresponding TAs can be transmitted to the new service DU 122 via gNB-CU 106 and gNB-CU 107. Alternatively, the old service gNB 113 and the new service gNB 122 can be served by the same gNB-CU 106.

[0063] Therefore, the solutions discussed above in this disclosure help the new serving gNB-DU 122 reuse the TA timer received from the old serving gNB-DU 113 when needed. The list of candidate cell IDs and the TA help the new serving gNB-DU 122 initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU 122. Furthermore, both solutions described above ensure RACH-free HO during inter-cell changes. For a more detailed understanding of the solutions discussed in the preceding paragraphs, please refer to the detailed discussions in the following paragraphs. Figure 3A and Figure 3B .

[0064] In another exemplary aspect of this disclosure, service DU 113 may instruct UE 120 to execute an LTM cell handover command from service DU 113 to perform an LTM cell handover to target cell 118a of target DU 114 within the same gNB 101. UE 120 is handed over to target DU 114. Target DU 114 may serve as the new service DU.

[0065] According to the above solution, UE 120 can send a list of all candidate cell IDs for which UL synchronization (maintaining TA) has been previously performed by UE 120, along with their corresponding time intervals, to the new serving gNB-DU 114 whenever the LTM serving cell handover is successfully completed. The list of candidate cell IDs and the corresponding TA can be transmitted from UE 120 to the new serving DU 114 via the UL MAC control element (CE) or similar L1 / L2 commands.

[0066] Alternatively, after performing an LTM cell handover, UE 120 can send a list of all candidate cell IDs that have undergone UL synchronization, along with their corresponding time advances, from the old service gNB-DU 113 to the new service gNB-DU 114. The list of candidate cell IDs and the corresponding TAs can be received from UE 120 by the old service gNB-DU 113 when the candidate cells are acquired. The list of candidate cell IDs and the corresponding TAs can be transmitted to the new service DU 114 via gNB-CU 106.

[0067] Therefore, the solutions discussed above in this disclosure help the new serving gNB-DU 114 reuse the TA timer received from the old serving gNB-DU 113 when needed. The list of candidate cell IDs and the TA help the new serving gNB-DU 114 initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU 114. Furthermore, both solutions described above ensure RACH-free HO during inter-cell changes. For a more detailed understanding of the solutions discussed in the preceding paragraphs, please refer to the detailed discussions in the following paragraphs. Figure 3A and Figure 3B .

[0068] refer to Figure 3A , Figure 3A Signaling diagram 300a for advance management of inter-cell change periods centered on L1 / L2, according to one aspect of this disclosure, is disclosed. Signaling diagram 300a includes user equipment (UE) 120, serving gNB-DU 112, serving gNB-CU 106, candidate gNB-DU 113, and another candidate gNB-DU 114.

[0069] Initially, UE 120 can perform Layer 3 (L3) RRC measurements and send the RRC measurement report to gNB-CU 106 (as shown in step S1). gNB-CU 106 can process the RRC measurement report and determine the use of Layer (L1 / L2) triggered mobility (LTM). gNB-CU 106 can prepare gNB-DU inter-LTM candidate cells based on the RRC measurement report received from UE 120.

[0070] In response, gNB-CU 106 can initiate LTM candidate cell preparation (as shown in step S2) by sending F1: Context Establishment Request to candidate gNB-DU 113 serving the candidate cell selected as the LTM candidate cell.

[0071] Upon receiving the F1: Context Establishment Request, candidate gNB-DU 113 may then send a context establishment response including CellGroupConfig to gNB-CU 106 (as shown in step S3). In one exemplary aspect, CellGroupConfig may at least include the target cell configuration prepared by candidate gNB-DU 113. However, the information in CellGroupConfig is not limited to the above example and may include any other information related to the cell of candidate gNB-DU 113. Furthermore, the features disclosed through step S3 are not limited to candidate gNB-DU 113 and may similarly be performed for other candidate gNB-DU 114.

[0072] It should be noted that the number of candidate gNB-DUs (i.e., candidate gNB-DU 113 and candidate gNB-DU 114) is exemplary and may vary based on the L3 RRC measurement performed by UE 120.

[0073] Continuing, gNB-CU 106 can perform an F1: Downlink (DL) RRC message transmission to the serving gNB-DU 112, which includes RRC reconfiguration (as shown in step S4). In one aspect, RRC reconfiguration may include LTM target cell configuration. Furthermore, it should be noted that the procedures disclosed in steps S2–S4 of the preceding paragraphs can be performed via an F1 interface that supports the exchange of signaling and information between the gNB-DU and gNB-CU.

[0074] As a next step, the serving gNB-DU 112 may forward an RRC reconfiguration message, including the LTM target cell configuration, to the UE 120 (as shown in step S5). Those skilled in the art will understand that the RRC reconfiguration message, including the LTM target cell configuration, can be used by the UE 120 during uplink synchronization with the candidate gNB-DU and after LTM serving cell handover.

[0075] Subsequently, serving gNB-DU 112 can send a Physical Downlink Control Channel (PDCCH) command to UE 120 (as shown in step S6). The PDCCH command can be used to instruct UE 120 to perform uplink synchronization with the candidate cells of candidate gNB-DU 113 and 114. The PDCCH command includes the PCI of the candidate cells served by candidate gNB-DU 113 and 114.

[0076] Then, UE 120 can perform UL synchronization with candidate gNB-DU 113 by sending a RACH preamble to candidate gNB-DU 113 in the RACH request (as shown in step S7). In one aspect, UE 120 can use the RACH preamble to obtain the timing advance (TA) associated with the candidate cell. In response, candidate gNB-DU 113 can configure a random access response (RAR) using the TA corresponding to the candidate cell and the cell ID of the candidate cell, and send a RAR including the TA of the candidate cell (as shown in step S8). This RAR can be sent directly from the target gNB-DU to the UE, or via gNB-CU and serving gNB-DU. The TA of the candidate cell is valid during the timing advance alignment timer, after which the TA expires at UE 120. In an important aspect, it should be noted that a process similar to that disclosed in steps S7 and S8 can also be performed in steps S9 and S10 to obtain the TA associated with the candidate cell of candidate gNB-DU 114, which will not be described further for the sake of brevity.

[0077] After receiving the TAs of multiple candidate cells, UE 120 can store the TAs of multiple candidate cells and their corresponding PCIs (as shown in step S11). Subsequently, UE 120 can perform intra-frequency layer 1 (L1) measurements on the configured LTM candidate target cells and send the L1 measurement report to serving gNB-DU 112 (as shown in step S12). Serving gNB-DU 112 can use the intra-frequency L1 measurement report to determine the best target cell for UE 120 from the target candidate cells. In one exemplary aspect, candidate cells of candidate gNB-DU 113 can be selected as target cells based on the intra-frequency L1 measurements performed by UE 120.

[0078] Then, the serving gNB-DU 112 can send the target cell PCI and the target cell beam information through the MAC control element (as shown in step S13). The MAC CE is sent by the serving gNB-DU 112 to the UE 120 to perform LTM cell handover to the target cell.

[0079] UE 120 can use the previously stored target cell TA to perform a RACH-free HO to gNB-DU 113 (as shown in step S14). Once the RACH-free HO is performed, UE 120 can release the resources of the previous service gNB-DU 112 and start uplink and downlink transmissions through the new service gNB-DU 113.

[0080] Finally, in response to the successful completion of the LTM serving cell handover, UE 120 can send a list of PCIs and their corresponding TAs to the new serving gNB-DU 113 (as shown in step S15). Sending the list of PCIs and their corresponding TAs may include sending a MAC CE or similar L1 / L2 command, which includes the list of PCIs and their corresponding TAs previously acquired by UE 120.

[0081] Therefore, sending the list of PCIs and their corresponding TAs to the new serving gNB-DU 113 helps the new serving gNB-DU 113 reuse the TA timer received from UE 120 when needed. The list of candidate cell IDs and TAs helps the new serving gNB-DU 113 initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU 113. Furthermore, sending the list of PCIs and their corresponding TAs to the new serving gNB-DU 113 ensures RACH-free HO during inter-cell changes.

[0082] refer to Figure 3B , Figure 3B Signaling diagram 300a for advance management of inter-cell change periods centered on L1 / L2, according to one aspect of this disclosure, is disclosed. Signaling diagram 300a includes user equipment (UE) 120, serving gNB-DU 112, gNB-CU 106, candidate gNB-DU 113, and another candidate gNB-DU 114.

[0083] Initially, UE 120 can perform Layer 3 (L3) RRC measurements and send the RRC measurement report to gNB-CU 106 (as shown in step S1). gNB-CU 106 can process the RRC measurement report and determine the use of Layer (L1 / L2) triggered mobility (LTM). gNB-CU 106 can prepare gNB-DU inter-LTM candidate cells based on the RRC measurement report received from UE 120.

[0084] In response, gNB-CU 106 can initiate LTM candidate cell preparation (as shown in step S2) by sending F1: Context Establishment Request to candidate gNB-DU 113 serving the candidate cell selected as the LTM candidate cell.

[0085] Upon receiving the context establishment request, candidate gNB-DU 113 may then send an F1: Context Establishment Response including CellGroupConfig to gNB-CU 106 (as shown in step S3). In one exemplary aspect, CellGroupConfig may include the target cell configuration prepared by candidate gNB-DU 113. However, the information in CellGroupConfig is not limited to the example above and may include any other information related to the cell of candidate gNB-DU 113. Furthermore, the features disclosed through step S3 are not limited to candidate gNB-DU 113 and may similarly be performed for other candidate gNB-DU 114.

[0086] It should be noted that the number of candidate gNB-DUs (i.e., candidate gNB-DU 113 and candidate gNB-DU 114) is exemplary and may vary based on the L3 RRC measurement performed by UE 120.

[0087] Continuing, gNB-CU 106 can send a downlink (DL) RRC message to the serving gNB-DU 112, which includes RRC reconfiguration (as shown in step S4). In one aspect, RRC reconfiguration may include LTM target cell configuration. Furthermore, it should be noted that the procedures disclosed in steps S2–S4 of the preceding paragraphs can be performed via the F1 interface, which supports the exchange of signaling and information between the gNB-DU and gNB-CU.

[0088] As a next step, serving gNB-DU 112 may forward an RRC reconfiguration message, including the LTM target cell configuration, to UE 120 (as shown in step S5). Those skilled in the art will understand that the RRC reconfiguration message, including the LTM target cell configuration, may be used by UE 120 during uplink synchronization with the candidate gNB-DU.

[0089] Subsequently, serving gNB-DU 112 can send a Physical Downlink Control Channel (PDCCH) command to UE 120 (as shown in step S6). The PDCCH command can be used to instruct UE 120 to perform uplink synchronization with the candidate cells of candidate gNB-DU 113 and 114. The PDCCH command includes the PCI of the candidate cells served by candidate gNB-DU 113 and 114.

[0090] Then, UE 120 can perform UL synchronization with candidate gNB-DU 113 by sending a RACH preamble to candidate gNB-DU 113 in a RACH request message (as shown in step S7). In one aspect, UE 120 can use the RACH preamble to obtain the timing advance (TA) associated with the candidate cell. In response, candidate gNB-DU 113 can configure a random access response (RAR) using the TA corresponding to the candidate cell and the cell ID of the candidate cell, and send a RAR including the TA of the candidate cell (as shown in step S8). The TA of the candidate cell is valid during the timing advance alignment timer, after which the TA expires at UE 120. In an important aspect, it should be noted that a process similar to that disclosed in steps S7 and S8 can be performed, i.e., steps S9 and S10, to obtain the TA associated with the candidate cell of candidate gNB-DU 114, which will not be described further for the sake of brevity.

[0091] After receiving the TAs of multiple candidate cells, UE 120 can send the TAs of multiple candidate cells and their corresponding PCIs to serving gNB-DU 112 (as shown in step S11). Subsequently, UE 120 can perform intra-frequency layer 1 (L1) measurements on the configured LTM candidate target cells and send the L1 measurement report to serving gNB-DU 112 (as shown in step S12). Serving gNB-DU 112 can use the intra-frequency L1 measurement report to determine the best target cell for UE 120 from the target candidate cells. In one exemplary aspect, based on the intra-frequency L1 measurements performed by UE 120, candidate cells of candidate gNB-DU 113 can be selected as target cells.

[0092] The serving gNB-DU 112 can send the target cell PCI and the target cell beam information through the MAC control element. The MAC CE is sent by the serving gNB-DU 112 to the UE 120 to perform LTM cell handover to the target cell (as shown in step S13).

[0093] UE 120 can use the previously stored target cell's TA to perform a RACH-free HO to gNB-DU 113 (as shown in step S14). Once the RACH-free HO is performed, UE 120 can release the resources of the previous service gNB-DU 112 and begin uplink and downlink transmissions through the new service gNB-DU 113.

[0094] The legacy service gNB-DU 112 may, in response to performing an LTM cell handover, send an F1: Context Modification request, including a list of PCIs and their corresponding TAs, to gNB-CU 106 (as shown in step S15). In response, gNB-CU 106 may send an F1: Context Modification ACK message back to the legacy service gNB-DU 112 (as shown in step S16).

[0095] gNB-CU 106 can send an F1: Context Modification Request to the new service gNB-DU 113 (as shown in step S17). The context modification request may include a list of PCIs previously acquired by UE120 and their corresponding TAs. In response, the new service gNB-DU 113 can send an F1: Context Establishment Response in response to receiving the list of PCIs and their corresponding TAs (as shown in step S18). Furthermore, it should be noted that the procedures disclosed in steps S15–S18 of the preceding paragraphs can be performed via an F1 interface that supports the exchange of signaling and information between the gNB-DU and gNB-CU.

[0096] Therefore, sending the list of PCIs and their corresponding TAs to the new serving gNB-DU 113 helps the new serving gNB-DU 113 reuse the TA timers received from the old gNB-DU 112 when needed. The list of candidate cell IDs and TAs helps the new serving gNB-DU 113 initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU 113. Furthermore, the above solution ensures RACH-free HO during inter-cell changes.

[0097] Now for reference Figure 4 , Figure 4 A block diagram of an apparatus 400 for timing advance management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown. Apparatus 400 may include at least one transmitter 402, at least one receiver 404, at least one processor 408, memory 410, at least one interface 412, and at least one antenna 414. At least one transmitter 402 may be configured to transmit data / information to one or more entities using antenna 414, and at least one receiver 404 may be configured to receive data / information from one or more nodes / devices using antenna 414. At least one transmitter and receiver may be collectively implemented as a single transceiver module 406. In a non-limiting aspect, at least one processor 408 may be communicatively coupled to transceiver 406, memory 410, interface 412, and antenna 414 for timing advance management during inter-cell changes centered on L1 / L2.

[0098] At least one processor 408 may include, but is not limited to, a microprocessor, microcomputer, microcontroller, central processing unit, state machine, logic circuit, and / or any device that manipulates signals based on operating instructions. The processor may also be implemented as a combination of computing devices, such as a combination of multiple microprocessors or any other such configuration. Memory 410 may be communicatively coupled to at least one processor 408 and may include various instructions for performing dynamic vDU scaling techniques. Memory 410 may include random access memory (RAM) cells and / or non-volatile memory cells, such as read-only memory (ROM), optical disc drives, disk drives, flash memory, electrically erasable read-only memory (EEPROM), memory space on servers or in the cloud, etc. At least one processor 408 may be configured to execute one or more instructions stored in memory 410.

[0099] Interface 412 may include various software and hardware interfaces, such as a web interface, a graphical user interface, an input / output (I / O) interface, a network interface, etc. The I / O interface allows device 400 to communicate directly with one or more nodes / devices or through other devices. The network interface allows device 400 to interact directly with one or more networks or via any other network.

[0100] In a non-limiting aspect, device 400 may be part of UE 120, but is not limited thereto.

[0101] At least one processor 408 may be configured to obtain a timing advance (TA) for mobility (LTM) candidate cells triggered at one or more layers (L1 / L2) based on an instruction from the serving gNB-DU, and store the obtained TA in memory 410. To determine one or more candidate cells, at least one processor 408 may be configured to perform L3 RRC measurements and send an L3 RRC measurement report to the gNB control unit (CU). The L3 RRC measurement report may be used by the gNB-CU to prepare inter-gNB-DU LTM candidate cells. At least one processor 408 may then be configured to receive an RRC reconfiguration message from the gNB-CU, including the configuration of at least one candidate cell, based on the L3 RRC measurement report.

[0102] Subsequently, at least one processor 408 can be configured to trigger a mobility (LTM) serving cell handover command at the receive layer (L1 / L2) to hand over from the current serving cell to the target cell. The current serving cell can be the current serving cell, and the target cell can be one of the candidate cells selected for the handover. Target cell selection can utilize the methods described above. Figure 3A and Figure 3B The process discussed in the description shall be carried out.

[0103] The current serving cell can be served by the serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by the target gNB-DU. At least one processor 408 can then be configured to send a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs to the target gNB-DU serving the target cell in response to a successful LTM cell handover.

[0104] To obtain a TA for one or more LTM candidate cells, at least one processor 408 can be configured to receive a Physical Downlink Control Channel (PDCCH) command from the serving gNB-DU to perform uplink synchronization with at least one candidate cell of the at least one candidate gNB-DU. The PDCCH command may include at least the Physical Cell ID (PCI) of the at least one candidate cell served by the at least one candidate gNB-DU. However, the PDCCH command is not limited to the PCI of the candidate cell and may also include other information related to the candidate cell.

[0105] At least one processor 408 can then be configured to send a Random Access Channel (RACH) preamble to at least one candidate gNB-DU, receive a random access response from at least one candidate gNB-DU including a TA of at least one candidate cell, and store the TA of at least one candidate cell based on a TA alignment timer. The TA alignment timer can indicate the duration of validity of the TA received from the candidate gNB-DU. The TA expires when the TA alignment timer expires. The transmission of the Random Access Channel (RACH) preamble can be performed for each candidate cell that receives the PDCCH command.

[0106] Furthermore, in order to receive LTM cell handover commands to switch from the current serving cell to the target cell, at least one processor 408 can be configured to periodically or after a predetermined duration perform in-frequency L1 measurements for at least one candidate cell. The at least one processor 408 can then be configured to send in-frequency L1 measurement reports of the at least one candidate cell to the serving gNB-DU. The in-frequency L1 measurement reports can be used by the serving gNB-DU to select the target cell from multiple candidate cells.

[0107] At least one processor 408 can then be configured to receive an LTM cell handover command from the serving gNB-DU based on an in-frequency L1 measurement report. The LTM cell handover command may include at least the physical cell ID (PCI) of the target cell and the beam information of the target cell. At least one processor 408 can then be configured to perform an LTM cell handover from the current serving cell to the target cell based on the LTM cell handover command.

[0108] In one non-limiting aspect, in order to send a list of candidate cell IDs and a stored TA corresponding to the list of candidate cell IDs, at least one processor 408 may be configured to send a MAC control element (CE) including the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs to the target gNB-DU.

[0109] In one aspect of this disclosure, at least one processor 408 may be configured to send a MAC control element (CE) to the serving gNB-DU, including a list of candidate cell IDs and stored TAs corresponding to the list of candidate cell IDs. The serving gNB-DU may store the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs.

[0110] In one non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to different gNBs to facilitate LTM between gNB-DUs. In another non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to the same gNB to facilitate LTM within the gNB-DU.

[0111] Furthermore, by sending the list of PCIs and their corresponding TAs to the new / target serving gNB-DU, system 400 enables the new serving gNB-DU to reuse the TA timer when needed. The list of candidate cell IDs and TAs allows the new serving gNB-DU to initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU. Additionally, sending the list of PCIs and their corresponding TAs to the new / target serving gNB-DU ensures RACH-free HO during inter-cell changes.

[0112] Now for reference Figure 5 , Figure 5 A block diagram of an apparatus 500 for timing advance management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure, is shown. Apparatus 500 may include at least one transmitter 502, at least one receiver 504, at least one processor 508, memory 510, at least one interface 512, and at least one antenna 514. At least one transmitter 502 may be configured to transmit data / information to one or more entities using antenna 514, and at least one receiver 504 may be configured to receive data / information from one or more nodes / devices using antenna 514. At least one transmitter and receiver may be collectively implemented as a single transceiver module 506. In a non-limiting aspect, at least one processor 508 may be communicatively coupled to transceiver 506, memory 510, interface 512, and antenna 514 for timing advance management during inter-cell changes centered on L1 / L2.

[0113] At least one processor 508 may include, but is not limited to, a microprocessor, microcomputer, microcontroller, central processing unit, state machine, logic circuit system, and / or any device that manipulates signals based on operating instructions. The processor may also be implemented as a combination of computing devices, such as a combination of multiple microprocessors or any other such configuration. Memory 510 may be communicatively coupled to at least one processor 508 and may include various instructions for performing dynamic vDU scaling techniques. Memory 510 may include random access memory (RAM) cells and / or non-volatile memory cells, such as read-only memory (ROM), optical disc drives, disk drives, flash memory, electrically erasable read-only memory (EEPROM), memory space on servers or in the cloud, etc. At least one processor 508 may be configured to execute one or more instructions stored in memory 510.

[0114] Interface 512 may include various software and hardware interfaces, such as a web interface, a graphical user interface, an input / output (I / O) interface, a network interface, etc. The I / O interface allows device 500 to communicate directly with one or more nodes / devices or through other devices. The network interface allows device 500 to interact directly with one or more networks or via any other network.

[0115] In a non-limiting aspect, device 500 may be part of the service gNB-DU, but is not limited thereto.

[0116] At least one processor 508 can be configured to receive a list of candidate cell IDs and corresponding timing advances (TAs) from a user equipment (UE). In a non-limiting aspect, at least one processor 508 can be configured to receive a MAC control element (CE) from the UE, including the list of candidate cell IDs and the corresponding TAs. The UE can use the above-described... Figure 3A and Figure 3B The process discussed in the description is used to obtain a list of candidate cell IDs and their corresponding timing advances (TAs).

[0117] At least one processor 508 can then be configured to perform a UE-triggered Layer 1 (L1 / L2) mobility (LTM) cell handover from the current serving cell to the target cell. The current serving cell can be the current serving cell, and the target cell can be one of the candidate cells selected for the handover. Target cell selection can utilize the methods described above. Figure 3A and Figure 3B The process discussed in the description shall be carried out.

[0118] The current serving cell can be served by the serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by the target gNB-DU. At least one processor 508 can then be configured to send a list of candidate cell IDs and their corresponding TAs to the target gNB-DU serving the target cell in response to the execution of an LTM cell handover.

[0119] To send a list of candidate cell IDs and their corresponding TAs, at least one processor 508 can be configured to send the list of candidate cell IDs and their corresponding TAs to a target gNB-DU via a gNB control unit (CU). In a non-limiting aspect, at least one processor 508 can be configured to send the list of candidate cell IDs and their corresponding TAs directly to the target gNB-DU.

[0120] In one non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to different gNBs to facilitate LTM between gNB-DUs. In another non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to the same gNB to facilitate LTM within the gNB-DU.

[0121] By sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU, system 500 enables the new serving gNB-DU to reuse the TA timer when needed. The list of candidate cell IDs and the TAs allow the new serving gNB-DU to initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU. Furthermore, sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU ensures RACH-free HO during inter-cell changes.

[0122] Now for reference Figure 6 A flowchart is described for an exemplary method 600 for advance timing management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure. Method 600 is provided for illustrative purposes only, and aspects are intended to include or cover the advance timing management process.

[0123] Method 600 may include, at block 602, obtaining, based on an indication from the serving gNB-DU, a timing advance (TA) for one or more L1 / L2-triggered mobility (LTM) candidate cells, and storing the obtained TA. For example, the TA for a candidate cell may be received from a candidate gNB-DU serving the corresponding candidate cell. The process of obtaining the TA for one or more candidate cells and storing the obtained TA will be described below. Figure 6A A more detailed discussion will follow in the description.

[0124] Method 600 may include, at block 604, a mobility (LTM) serving cell handover command triggered by the receiving layer (L1 / L2) to hand over from the current serving cell to the target cell. The current serving cell may be the current serving cell, and the target cell may be one of the candidate cells selected for the handover. The selection of the target cell will be discussed in more detail below. The current serving cell may be served by a serving gNodeB distributed unit (gNB-DU), and the target cell may be served by a target gNB-DU.

[0125] Furthermore, in order to receive LTM cell handover commands from the current serving cell to the target cell, method 600 may include periodically performing in-frequency L1 measurements on at least one candidate cell after each predetermined duration, and sending in-frequency L1 measurement reports of at least one candidate cell to the serving gNB-DU. The in-frequency L1 measurement reports can be used by the serving gNB-DU to select the target cell from the candidate cells.

[0126] Method 600 may further include receiving an LTM cell handover command from the serving gNB-DU based on an in-frequency L1 measurement report. The LTM cell handover command may include at least the physical cell ID (PCI) of the target cell and the beam information of the target cell. Method 600 may further include performing an LTM cell handover from the current serving cell to the target cell based on the LTM cell handover command.

[0127] Method 600 may include, at block 606, sending a list of candidate cell IDs and a stored TA corresponding to the list of candidate cell IDs to a target gNB-DU serving the target cell in response to a successful LTM cell handover. To send the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs, method 600 may include sending a MAC control element (CE) to the target gNB-DU that includes the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0128] In one non-limiting aspect of this disclosure, method 600 may further include sending a MAC control element (CE) to the serving gNB-DU, including a list of candidate cell IDs and a stored TA corresponding to the list of candidate cell IDs. The serving gNB-DU may store the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0129] In one aspect of this disclosure, method 600 may include performing an L3 RRC measurement and sending an L3 RRC measurement report to the gNB control unit (CU). The L3 RRC measurement report may be used by the gNB-CU to prepare inter-gNB-DU LTM candidate cells. The preparation process for LTM candidate cells has been described above. Figure 3A and Figure 3B The description provides a detailed discussion of this. Method 600 may also include receiving an RRC reconfiguration message from the gNB-CU that includes the configuration of at least one candidate cell.

[0130] In one non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to different gNBs to facilitate LTM between gNB-DUs. In another non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to the same gNB to facilitate LTM within the gNB-DU.

[0131] By sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU, method 600 enables the new serving gNB-DU to reuse the TA timer when needed. The list of candidate cell IDs and the TAs also enable the new serving gNB-DU to initiate UL synchronization in the correct cell without repeating the RACH procedure and without negotiating UE data transmission at the new serving gNB-DU. Furthermore, sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU ensures RACH-free HO during inter-cell changes.

[0132] Now for reference Figure 6A This document describes a sub-flowchart of an exemplary method 602 for obtaining timing advance from a user equipment (UE) according to some aspects of this disclosure. Method 602 is provided for illustrative purposes only, and aspects are intended to include or cover the timing advance obtaining method or process.

[0133] Method 602 may include, at block 602-1, receiving a Physical Downlink Control Channel (PDCCH) command to perform uplink synchronization with at least one candidate cell of at least one candidate gNB-DU. The PDCCH command can be received from the serving gNB-DU after receiving an RRC reconfiguration from the gNB-CU. The PDCCH command may include at least the Physical Cell ID (PCI) of at least one candidate cell served by at least one candidate gNB-DU. However, the PDCCH command is not limited to the PCI of the candidate cell and may also include other information related to the candidate cell. Furthermore, the PDCCH command may be received for any one of one or more candidate cells.

[0134] Method 602 may include, at block 602-2, sending a Random Access Channel (RACH) preamble to at least one candidate gNB-DU. Method 602 may also include, at block 602-3, receiving a random access response from at least one candidate gNB-DU, comprising a TA (Target Acquisition) of at least one candidate cell. The random access response may be configured by the candidate gNB-DU using the TA of the candidate cell from which the RACH preamble was received.

[0135] Method 602 may include: at block 602-4, storing the TA of at least one candidate cell based on a TA alignment timer. The TA alignment timer may indicate the duration of validity of the TA received from the candidate gNB-DU. The TA expires when the TA alignment timer expires. The transmission procedure of the random access channel (RACH) preamble may be performed for each candidate cell that receives the PDCCH command.

[0136] In one key aspect, method 602 facilitates the UE sharing the TA acquired by the UE with the target / new serving gNB-DU, which enables the new serving gNB-DU to initiate UL synchronization in the correct cell without repeating the RACH process and without negotiating UE data transmission at the new serving gNB-DU.

[0137] Now for reference Figure 7 This document describes a flowchart of another exemplary method 700 for advance timing management during inter-cell changes centered on L1 / L2, according to some aspects of this disclosure. Method 700 is provided for illustrative purposes only, and aspects are intended to include or otherwise cover any advance timing management method or process.

[0138] Method 700 may include, at block 702, receiving a list of candidate cell IDs and corresponding timing advances (TAs) from a user equipment (UE). The UE can use method 602 to obtain the TAs of the candidate cells, as described above. Figure 3A and Figure 3B As discussed in the description. In a non-limiting aspect, in order to receive a list of candidate cell IDs and corresponding timing advances (TAs), method 700 may include receiving from the UE a MAC control element (CE) including a list of candidate cell IDs and corresponding TAs.

[0139] Method 700 may include, at block 704, performing a Layer (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell. The current serving cell may be the current serving cell, and the target cell may be one of the candidate cells selected for the handover. The current serving cell may be served by a serving gNodeB distributed unit (gNB-DU), and the target cell may be served by a target gNB-DU. Target cell selection may utilize the methods described above. Figure 3A and Figure 3B The process discussed in the description shall be carried out.

[0140] Method 700 may include, at block 706, sending a list of candidate cell IDs and corresponding TAs to a target gNB-DU serving the target cell in response to the execution of an LTM cell handover. To send the list of candidate cell IDs and corresponding TAs, method 700 may include sending the list of candidate cell IDs and corresponding TAs to the target gNB-DU via a gNB control unit (CU). In a non-limiting aspect, method 700 may include sending the list of candidate cell IDs and corresponding TAs directly to the target gNB-DU.

[0141] In one non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to different gNBs to facilitate LTM between gNB-DUs. In another non-limiting aspect of this disclosure, the serving gNB-DU and the target gNB-DU may belong to the same gNB to facilitate LTM within the gNB-DU.

[0142] By sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU, method 700 enables the new serving gNB-DU to reuse the TA timer when needed. The list of candidate cell IDs and the TAs also enable the new serving gNB-DU to initiate UL synchronization in the correct cell without repeating the RACH procedure and without negotiating UE data transmission at the new serving gNB-DU. Furthermore, sending the list of PCIs and the corresponding TAs to the new / target serving gNB-DU ensures RACH-free HO during inter-cell changes.

[0143] The methods 600, 602, and 700 described above can be described within the general context of computer-executable instructions. Typically, computer-executable instructions can include routines, programs, objects, components, data structures, procedures, modules, and functions that perform specific functions or implement specific abstract data types.

[0144] For ease of explanation, Figure 6 and Figure 7 The blocks of methods 600, 602, and 700 shown are arranged in a generally sequential manner. However, it should be understood that this arrangement is merely exemplary, and it should be recognized that methods 600, 602, and 700 (and...) are not interchangeable. Figure 6 , Figure 6A and 7The processes associated with the blocks shown may occur in different orders (e.g., at least some of the processes associated with these blocks may be executed in parallel and / or in an event-driven manner). Additionally, individual blocks may be removed from the method without departing from the spirit and scope of the subject matter described herein. Furthermore, the method may be implemented in any suitable hardware, software, firmware, or a combination thereof.

[0145] The various operations of the methods described above can be performed by any suitable means capable of performing the corresponding functions. Means may include various hardware and / or software components and / or modules. Typically, in the presence of operations illustrated in the figures, those operations may have corresponding equivalent means plus functional components.

[0146] It can be noted here that, reference Figure 1 , Figure 2A , Figure 2B , Figure 3A and Figure 3B The topics described, some or all, may be relevant to these methods and will not be repeated for the sake of brevity.

[0147] In a non-limiting aspect of this disclosure, one or more non-transitory computer-readable media may be used to implement aspects consistent with this disclosure. A computer-readable medium refers to any type of physical memory (e.g., memories 410 and 510) on which processor-readable information or data can be stored. Thus, a computer-readable medium may store one or more instructions for execution by at least one processor 408 and 508, including instructions for causing at least one processor 408 and 508 to perform steps or phases consistent with the aspects described herein. The term "computer-readable medium" should be understood to include tangible items and exclude carrier waves and transient signals. By way of example and not limitation, such a computer-readable medium may include random access memory (RAM), read-only memory (ROM), volatile memory, non-volatile memory, hard disk drive, optical disc (CD) ROM, digital video disc (DVD), flash drive, disk, and any other known physical storage medium.

[0148] Therefore, certain non-limiting aspects may include a computer program product for performing the operations presented herein. For example, such a computer program product may include a computer-readable medium having instructions stored thereon (and / or encoded thereon) that are executable by one or more processors to perform the operations described herein. For certain non-limiting aspects, the computer program product may include packaging material.

[0149] As used herein, the phrase “at least one” or “one or more” in a list of items refers to any combination of those items, including a single member. For example, “at least one of the following: a, b, or c” is intended to cover: a, b, c, ab, ac, bc, and abc. The terms “a,” “an,” and “the” mean “one or more” unless otherwise explicitly stated.

[0150] The description of aspects involving several components that communicate with each other does not imply a requirement for all such components. Instead, various optional components are described to illustrate the diverse possible aspects of the disclosed methods and systems.

[0151] Finally, the language used in the specification has been chosen primarily for readability and indicative purposes and may not have been chosen to depict or limit the subject matter of the invention. Therefore, the scope of this disclosure is intended not to be limited by this specific embodiment, but rather by any claims made based on the application herein. Accordingly, aspects of this disclosure are intended to illustrate, and not limit, the scope of the disclosure as set forth in the appended claims.

[0152] This disclosure may also include the following aspects:

[0153] Aspect 1

[0154] An apparatus comprising:

[0155] At least one processor; and

[0156] A memory, communicatively coupled to at least one processor, wherein the memory stores processor-executable instructions, which, when executed, cause at least one processor to:

[0157] Based on the indication from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA;

[0158] Receive an LTM serving cell handover command to switch from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNB-DU, and the target cell is served by the target gNB-DU; and

[0159] In response to the successful completion of LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

[0160] Aspect 2

[0161] According to the apparatus of aspect 1, in order to obtain a TA for one or more LTM candidate cells, at least one processor is configured to:

[0162] Receive physical downlink control channel (PDCCH) commands from the serving gNB-DU to perform uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH commands include the physical cell ID (PCI) of at least one LTM candidate cell served by at least one candidate gNB-DU.

[0163] In the Random Access Channel (RACH) request message, a RACH preamble is sent to at least one candidate gNB-DU for at least one LTM candidate cell;

[0164] Receive a random access response including a TA from at least one LTM candidate cell, either directly from or via the serving gNB-DU; and

[0165] Based on the TA alignment timer, store the TA of at least one LTM candidate cell.

[0166] Aspect 3

[0167] According to the apparatus of aspect 1, in response to receiving an LTM cell handover command for switching from the current serving cell to the target cell, at least one processor is configured to:

[0168] Periodically perform intra-frequency L1 measurements for at least one LTM candidate cell;

[0169] Send at least one LTM candidate cell's frequency-in-frequency L1 measurement report to the serving gNB-DU;

[0170] Based on the intra-frequency L1 measurement report, an LTM cell handover command is received from the serving gNB-DU. The LTM cell handover command includes at least: the Physical Cell ID (PCI) of the target cell and the beam information of the target cell; and

[0171] Based on the LTM cell handover command, perform an LTM cell handover from the current serving cell to the target cell.

[0172] Aspect 4

[0173] According to the apparatus of aspect 1, in order to transmit a list of candidate cell IDs and a stored TA corresponding to the list of candidate cell IDs, at least one processor is configured to:

[0174] Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the target gNB-DU. The UL MAC CE or similar L1 / L2 command includes: a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0175] Aspect 5

[0176] According to the apparatus of aspect 1, at least one processor is configured to:

[0177] Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the serving gNB-DU. The UL MAC CE or similar L1 / L2 command includes: a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0178] Aspect 6

[0179] According to the apparatus of aspect 1, at least one processor is configured to:

[0180] Send an L3 RRC measurement report to the gNB control unit (CU); and

[0181] Receive an RRC reconfiguration message from gNB-CU, which includes the configuration of at least one candidate cell.

[0182] Aspect 7

[0183] According to the apparatus of aspect 1, the serving gNB-DU and the target gNB-DU belong to one of the following: different gNBs or the same gNB.

[0184] Aspect 8

[0185] An apparatus comprising:

[0186] At least one processor; and

[0187] A memory communicatively coupled to at least one processor, wherein the memory stores processor-executable instructions that, when executed, cause at least one processor to:

[0188] Receive a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE).

[0189] Perform a Layer 1 (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by the target gNB-DU; and

[0190] In response to the execution of LTM cell handover, a list of candidate cell IDs and their corresponding TAs are sent to the target gNB-DU serving the target cell.

[0191] Aspect 9

[0192] According to the apparatus of aspect 8, in order to receive a list of candidate cell IDs and corresponding TAs, at least one processor is configured to:

[0193] The UE receives an uplink (UL) MAC control element (CE) or similar L1 / L2 command, which includes a list of candidate cell IDs and their corresponding TAs.

[0194] Aspect 10

[0195] According to the apparatus of aspect 8, in order to send a list of candidate cell IDs and their corresponding TAs, at least one processor is configured to:

[0196] The list of candidate cell IDs and their corresponding TAs are sent directly to the target gNB-DU via the interface or via the gNB control unit (CU).

[0197] Aspect 11

[0198] According to the apparatus of aspect 8, the serving gNB-DU and the target gNB-DU belong to one of the following: different gNBs or the same gNB.

[0199] Aspect 12

[0200] One method includes:

[0201] Based on the indication from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA;

[0202] Receive an LTM serving cell handover command to switch from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNB-DU, and the target cell is served by the target gNB-DU; and

[0203] In response to the successful completion of LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

[0204] Aspect 13

[0205] According to the method of aspect 12, obtaining the TA for one or more LTM candidate cells includes:

[0206] Receive physical downlink control channel (PDCCH) commands from the serving gNB-DU for performing uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH commands include the physical cell ID (PCI) of at least one LTM candidate cell served by at least one candidate gNB-DU.

[0207] Send the random access channel (RACH) preamble to at least one candidate gNB-DU for at least one LTM candidate cell;

[0208] Receive a random access response including a TA from at least one LTM candidate cell, either directly from or via the serving gNB-DU; and

[0209] Based on the TA alignment timer, store the TA of at least one LTM candidate cell.

[0210] Aspect 14

[0211] According to aspect 12, the method, in response to receiving an LTM cell handover command for switching from the current serving cell to a target cell, includes:

[0212] Periodically perform intra-frequency L1 measurements for at least one LTM candidate cell;

[0213] Send at least one LTM candidate cell's frequency-in-frequency L1 measurement report to the serving gNB-DU;

[0214] Based on the intra-frequency L1 measurement report, an LTM cell handover command is received from the serving gNB-DU. This LTM cell handover command includes at least the Physical Cell ID (PCI) of the target cell and the beam information of the target cell; and

[0215] Based on the LTM cell handover command, perform an LTM cell handover from the current serving cell to the target cell.

[0216] Aspect 15

[0217] According to the method of aspect 12, the list of candidate cell IDs to be sent and the stored TA corresponding to the list of candidate cell IDs include:

[0218] Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the target gNB-DU. The UL MAC CE includes a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0219] Aspect 16

[0220] The method according to aspect 12 further includes:

[0221] Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the serving gNB-DU. The UL MAC CE or similar L1 / L2 command includes a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

[0222] Aspect 17

[0223] The method according to aspect 12 further includes:

[0224] Send an L3 RRC measurement report to the gNB control unit (CU); and

[0225] Receive an RRC reconfiguration message from gNB-CU, which includes the configuration of at least one candidate cell.

[0226] Aspect 18

[0227] One method includes:

[0228] Receive a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE).

[0229] Perform a Layer 1 (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by the target gNB-DU; and

[0230] In response to the execution of LTM cell handover, a list of candidate cell IDs and their corresponding TAs are sent to the target gNB-DU serving the target cell.

[0231] Aspect 19

[0232] According to the method described in aspect 18, receiving the list of candidate cell IDs and the corresponding TA includes:

[0233] The UE receives an uplink (UL) MAC control element (CE) or similar L1 / L2 command, which includes a list of candidate cell IDs and their corresponding TAs.

[0234] Aspect 20

[0235] According to the method described in aspect 18, wherein a list of candidate cell IDs and corresponding TAs are sent, at least one processor is configured to:

[0236] The list of candidate cell IDs and their corresponding advance timing (TA) are sent directly to the target gNB-DU via the interface or through the gNB control unit (CU).

[0237] Aspect 21

[0238] A non-transitory computer-readable medium having computer-readable instructions that, when executed by a processor, cause the processor to perform the following operations:

[0239] Based on the indication from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA;

[0240] Obtain an LTM serving cell handover command from the current serving cell to the target cell, where the current serving cell is served by the serving gNB-DU and the target cell is served by the target gNB-DU; and

[0241] In response to the successful completion of LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

[0243] A non-transitory computer-readable medium having computer-readable instructions that, when executed by a processor, cause the processor to perform the following operations:

[0244] Obtain a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE).

[0245] Perform a Layer 1 (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNodeB Distributed Unit (gNB-DU), and the target cell is served by the target gNB-DU; and

[0246] In response to the execution of LTM cell handover, a list of candidate cell IDs and their corresponding TAs are sent to the target gNB-DU serving the target cell.

Claims

1. An apparatus comprising: At least one processor; as well as A memory communicatively coupled to the at least one processor, wherein the memory stores processor-executable instructions that, when executed, cause the at least one processor to: Based on the instruction from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA; Receive an LTM cell handover command to switch from the current serving cell to a target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by the target gNB-DU; as well as In response to the successful completion of the LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

2. The apparatus of claim 1, wherein, in order to obtain a TA for the one or more LTM candidate cells, the at least one processor is configured to: The device receives a Physical Downlink Control Channel (PDCCH) command from the serving gNB-DU to perform uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH command includes the Physical Cell ID (PCI) of at least one LTM candidate cell served by the at least one candidate gNB-DU. In the Random Access Channel (RACH) request message, the RACH preamble is sent to the at least one candidate gNB-DU serving the at least one LTM candidate cell; Receive a random access response including the TA of the at least one LTM candidate cell directly from or via the at least one candidate gNB-DU; as well as Based on the TA alignment timer, the TA of the at least one LTM candidate cell is stored.

3. The apparatus of claim 1, wherein in response to receiving the LTM cell handover command for switching from the current serving cell to the target cell, the at least one processor is configured to: Periodically perform intra-frequency L1 measurements for at least one LTM candidate cell; Send the frequency-in-frequency L1 measurement report of the at least one LTM candidate cell to the serving gNB-DU; Based on the frequency-in-frequency L1 measurement report, an LTM cell handover command is received from the serving gNB-DU, wherein the LTM cell handover command includes at least: The physical cell ID (PCI) of the target cell and the beam information of the target cell; as well as Based on the LTM cell handover command, an LTM cell handover is performed from the current serving cell to the target cell.

4. The apparatus of claim 1, wherein, in order to transmit the list of candidate cell IDs and the stored TAs corresponding to the list of candidate cell IDs, the at least one processor is configured to: Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the target gNB-DU, wherein the ULMAC CE or similar L1 / L2 command includes: The list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

5. The apparatus of claim 1, wherein the at least one processor is configured to: Sending an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the serving gNB-DU, the ULMAC CE or similar L1 / L2 command including: The list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

6. The apparatus of claim 1, wherein the at least one processor is configured to: Send an L3 RRC measurement report to the gNB control unit (CU); and Receive an RRC reconfiguration message from the gNB-CU, which includes the configuration of at least one candidate cell.

7. The apparatus of claim 1, wherein the serving gNB-DU and the target gNB-DU are either different gNBs or the same gNB.

8. An apparatus comprising: At least one processor; as well as A memory communicatively coupled to the at least one processor, wherein the memory stores processor-executable instructions that, when executed, cause the at least one processor to: Receive a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE). Perform a Layer (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNodeB Distributed Unit (gNB-DU) and the target cell is served by the target gNB-DU; as well as In response to the execution of the LTM cell handover, the list of candidate cell IDs and the corresponding TA are sent to the target gNB-DU serving the target cell.

9. The apparatus of claim 8, wherein, in order to receive the list of candidate cell IDs and the corresponding TA, the at least one processor is configured to: The UE receives an uplink (UL) MAC control element (CE) or similar L1 / L2 command, the UL MAC CE or similar L1 / L2 command including the list of candidate cell IDs and the corresponding TA.

10. The apparatus of claim 8, wherein, in order to send the list of candidate cell IDs and the corresponding TA, the at least one processor is configured to: The list of candidate cell IDs and their corresponding TAs are sent directly to the target gNB-DU via an interface or via the gNB control unit (CU).

11. The apparatus of claim 8, wherein the serving gNB-DU and the target gNB-DU are either different gNBs or the same gNB.

12. A method comprising: Based on the instruction from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA; Receive an LTM serving cell change cell handover command to switch from the current serving cell to a target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by the target gNB-DU; as well as In response to the successful completion of the LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

13. The method of claim 12, wherein obtaining the TA for the one or more LTM candidate cells comprises: The physical downlink control channel (PDCCH) command is received from the serving gNB-DU to perform uplink synchronization with at least one LTM candidate cell of at least one candidate gNB-DU, wherein the PDCCH command includes the physical cell ID (PCI) of at least one LTM candidate cell served by the at least one candidate gNB-DU. Send the random access channel (RACH) preamble to the at least one candidate gNB-DU for the at least one LTM candidate cell; Receive a random access response including the TA of the at least one LTM candidate cell directly from or via the at least one candidate gNB-DU; as well as Based on the TA alignment timer, the TA of the at least one LTM candidate cell is stored.

14. The method of claim 12, wherein in response to receiving the LTM cell handover command for handing over from the current serving cell to the target cell, the method comprises: Periodically perform intra-frequency L1 measurements for at least one LTM candidate cell; Send the frequency-in-frequency L1 measurement report of the at least one LTM candidate cell to the serving gNB-DU; Based on the frequency-in-frequency L1 measurement report, an LTM cell handover command is received from the serving gNB-DU, wherein the LTM cell handover command includes at least the physical cell ID (PCI) of the target cell and the beam information of the target cell; as well as Based on the LTM cell handover command, an LTM cell handover is performed from the current serving cell to the target cell.

15. The method of claim 12, wherein the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs comprise: Send an uplink (UL) MAC control element (CE) to the target gNB-DU, the UL MAC CE including the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

16. The method of claim 12, further comprising: Send an uplink (UL) MAC control element (CE) or similar L1 / L2 command to the serving gNB-DU, the ULMAC CE or similar L1 / L2 command including the list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs.

17. The method of claim 12, further comprising: Send the L3 RRC measurement report to the gNB control unit (CU); as well as Receive an RRC reconfiguration message from the gNB-CU, which includes the configuration of at least one candidate cell.

18. A method comprising: Receive a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE). Perform a Layer (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNodeB Distributed Unit (gNB-DU) and the target cell is served by the target gNB-DU; as well as In response to the execution of the LTM cell handover, the list of candidate cell IDs and the corresponding TA are sent to the target gNB-DU serving the target cell.

19. The method of claim 18, wherein receiving the list of candidate cell IDs and the corresponding TA comprises: The UE receives an uplink (UL) MAC control element (CE) or similar L1 / L2 command, the UL MAC CE or similar L1 / L2 command including the list of candidate cell IDs and the corresponding TA.

20. The method of claim 18, wherein the at least one processor is configured to send the list of candidate cell IDs and the corresponding TAs. The list of candidate cell IDs and the corresponding advance timing (TA) are sent directly to the target gNB-DU via the interface or via the gNB control unit (CU).

21. A non-transitory computer-readable medium having computer-readable instructions that, when executed by a processor, cause the processor to perform the following operations: Based on the instruction from the serving gNodeB Distributed Unit (gNB-DU), obtain the timing advance (TA) for mobility (LTM) candidate cells triggered by one or more layers (L1 / L2), and store the obtained TA; Obtain an LTM serving cell handover command from the current serving cell to the target cell, wherein the current serving cell is served by the serving gNB-DU and the target cell is served by the target gNB-DU; as well as In response to the successful completion of the LTM cell handover, a list of candidate cell IDs and the stored TA corresponding to the list of candidate cell IDs are sent to the target gNB-DU serving the target cell.

22. A non-transitory computer-readable medium having computer-readable instructions that, when executed by a processor, cause the processor to perform the following operations: Obtain a list of candidate cell IDs and their corresponding timing advances (TAs) from the user equipment (UE). Perform a Layer 1 (L1 / L2) triggered mobility (LTM) cell handover for the UE from the current serving cell to the target cell, wherein the current serving cell is served by a serving gNodeB Distributed Unit (gNB-DU) and the target cell is served by a target gNB-DU; and In response to the execution of the LTM cell handover, the list of candidate cell IDs and the corresponding TA are sent to the target gNB-DU serving the target cell.

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