Timing advance resource management

Abstract

A user equipment device (UE) includes processor (s) and memory storing instructions. The instructions, when executed by the processor (s), cause the UE to at least: establish a connection with the control network node via a serving cell, where the serving cell is supported by the source network node; a timing advance (TA) cell configuration for a set of timing advance (TA) cells is received from a control network node and / or a source network node, where the TA cell configuration comprises a TA-associated random access (RA) configuration, where the set of TA cells comprises a first TA cell, the first TA cell comprising a candidate target cell, with which the UE may be connected and / or by other TA cells, where the UE may be connected to the candidate target cell. In the case where the UE is connected with one of the candidate target cells, other TA cells are requested by the candidate target cell and the UE may be connected with the other TA cells; and obtaining the TA for the TA cell based on the RA configuration associated with the TA.

Description

TECHNICAL FIELD

[0001] Various example embodiments relate generally to wireless networks, and in particular, to timing advance management in wireless networks. BACKGROUND

[0002] Wireless networks provide significant advantages for user mobility. The ability for users to remain connected while moving provides advantages not only to the users, but also to society as a whole with higher efficiency and productivity. As users' expectations for connection reliability, data speed, and device battery life become more demanding, technology for wireless networks must keep pace with such expectations. Thus, there is a continued interest in improving wireless network technology. SUMMARY

[0003] According to aspects of the disclosure, a user equipment apparatus includes at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the user equipment apparatus to at least: establish a connection with a control network node via a serving cell, wherein the control network node supports at least one of: a central unit control plane (CU-CP) function or layer 3 protocol of a radio access network; and wherein the serving cell is supported by a source network node that supports at least one of: a distributed unit (DU) function or layer 2 protocol of the radio access network; receive, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a TA cell set, wherein the plurality of TA cell configurations includes a TA-associated random access (RA) configuration for a TA acquisition for a particular TA cell of the plurality of TA cells, and wherein the TA cell set includes at least one of: a first TA cell including a candidate target cell to which the UE can connect, or other TA cells requested by at least one of the candidate target cells to which the UE is connected, and to which the UE can connect; and acquire a TA for the particular TA cell based on the TA-associated RA configuration and an associated TA acquisition request.

[0004] In one aspect of the user equipment apparatus, the TA-associated RA configuration can be specified in at least one of: a physical downlink control channel (PDCCH) order from the source network node, a medium access control element (MAC-CE), or a radio resource control (RRC) reconfiguration.

[0005] In one aspect of the user equipment apparatus, the TA-associated RA configuration can include a contention-free random access (CFRA) configuration.

[0006] In one aspect of the user equipment apparatus, the TA-associated RA configuration can comprise at least one of: a timer on validity of the CFRA resource corresponding to the CFRA configuration, wherein the timer comprises at least one of: a time length, a timer trigger, a timer start point, a timer stop point, a condition for timer reset, or a condition for timer restart; information indicating that the CFRA resource is valid before receiving a cell handover command, before cell handover, and after cell handover; or information indicating that the CFRA resource is valid for multiple RA transmissions within a time period.

[0007] In one aspect of the user equipment apparatus, the instructions, when executed by the at least one processor, can further cause the user equipment apparatus at least to generate at least one of: information on TA cell channel quality or information on handover probability by performing at least one of: selecting a specific CFRA resource of the CFRA configuration for acquiring the TA, or transmitting a random access preamble of the TA-associated RA configuration for acquiring the TA.

[0008] In one aspect of the user equipment apparatus, the instructions, when executed by the at least one processor, can further cause the user equipment apparatus at least to receive a random access response (RAR) from a TA network node supporting at least one of: a specific TA cell and a distributed unit (DU) function or layer 2 protocol of a radio access network.

[0009] In one aspect of the user equipment apparatus, the RAR can comprise at least one of: a validity indicator for a TA value, a time alignment timer (TAT), an uplink resource available after handover, a validity timer for the uplink resource, a TA command, a TAG associated with the TA command, TAG information comprising a cell or TCI state ID, a TAG timer, or a validity condition of the TA command.

[0010] In one aspect of the user equipment apparatus, the instructions, when executed by the at least one processor, can further cause the user equipment apparatus at least to perform at least one of: transmitting an ACK signal or a NACK signal of a subset of other TA cells requested by a target cell of the candidate target cells to a TA network node supporting the target cell, or transmitting an ACK signal or a NACK signal of a subset of other TA cells requested by the target cell to a source network node, or transmitting TA information to the source network node in at least one of: a L1 measurement report or a medium access control-control element (MAC-CE) after a cell handover to the target cell of the candidate target cells.

[0011] In one aspect of the user equipment apparatus, the RAR reception configuration for the RAR can be included in at least one of: a TA-associated RA configuration for the UE or a PDCCH order, the RAR reception configuration enabling the UE to determine where to decode the RAR.

[0012] In one aspect of the user equipment apparatus, the instructions, when executed by the at least one processor, further cause the user equipment apparatus at least to: receive a TA command in downlink control information (DCI).

[0013] In one aspect of the user equipment apparatus, the TA-associated RA configuration can include a gap for performing RF tuning and RA preamble transmission based on at least one of: a RA occasion of a particular TA cell being on a different frequency than an active frequency band of the UE with the serving cell, or the RAR reception configuration specifying a frequency for receiving the RAR that is a different frequency than the active frequency band of the UE with the serving cell.

[0014] According to aspects of the present disclosure, a processor-implemented method in a user equipment apparatus includes: establishing a connection with a control network node via a serving cell, wherein the control network node supports at least one of: a central unit control plane (CU-CP) function or a layer 3 protocol of a radio access network; and wherein the serving cell is supported by a source network node that supports at least one of: a distributed unit (DU) function or a layer 2 protocol of the radio access network; receiving, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a set of TA cells, wherein the plurality of TA cell configurations includes a TA-associated random access (RA) configuration for TA acquisition for a particular TA cell of the plurality of TA cells, and wherein the set of TA cells includes at least one of: a first TA cell comprising a candidate target cell to which the UE can connect, or other TA cells requested by at least one of the candidate target cells to which the UE can connect in a case that the UE connects with at least one of the candidate target cells; and acquiring a TA for the particular TA cell based on the TA-associated RA configuration and an associated TA acquisition request.

[0015] In one aspect of the processor-implemented method, the TA-associated RA configuration can be specified in at least one of: a physical downlink control channel (PDCCH) order from the source network node, a medium access control element (MAC-CE), or a radio resource control (RRC) reconfiguration.

[0016] In one aspect of the processor-implemented method, the TA-associated RA configuration can comprise a contention-free random access (CFRA) configuration.

[0017] In one aspect of the processor-implemented method, the TA-associated RA configuration can comprise at least one of: a timer on validity of a CFRA resource corresponding to the CFRA configuration, wherein the timer comprises at least one of: a time length, a timer trigger, a timer start point, a timer stop point, a condition for timer reset, or a condition for timer restart; information indicating that the CFRA resource is valid before receiving a cell handover command, before cell handover, and after cell handover; or information indicating that the CFRA resource is valid for multiple RA transmissions within a time period.

[0018] In one aspect of the processor-implemented method, the processor-implemented method can further comprise generating at least one of: information on TA cell channel quality or information on handover probability, by performing at least one of: selecting a specific CFRA resource of the CFRA configuration for acquiring the TA, or transmitting a random access preamble of the TA-associated RA configuration for acquiring the TA.

[0019] In one aspect of the processor-implemented method, the processor-implemented method can further comprise receiving a random access response (RAR) from a TA network node supporting at least one of: a specific TA cell and a distributed unit (DU) function or layer 2 protocol of a radio access network.

[0020] In one aspect of the processor-implemented method, the RAR can comprise at least one of: a validity indicator for a TA value, a time alignment timer (TAT), an uplink resource available after handover, a validity timer for the uplink resource, a TA command, a TAG associated with the TA command, TAG information including a cell or TCI state ID, a TAG timer, or a validity condition of the TA command.

[0021] In one aspect of the processor-implemented method, the processor-implemented method can further comprise, after a cell handover to a target cell of the candidate target cells, performing at least one of: transmitting, to a TA network node supporting the target cell, an ACK signal or a NACK signal of a subset of other TA cells requested by the target cell, or transmitting, to a source network node, the ACK signal or the NACK signal of the subset of other TA cells requested by the target cell, or transmitting, to the source network node, TA information in at least one of: a L1 measurement report or a medium access control-control element (MAC-CE).

[0022] In one aspect of the processor-implemented method, the RAR reception configuration for the RAR can be included in at least one of: the TA-associated RA configuration for the UE or the PDCCH order, the RAR reception configuration enabling the UE to determine where to decode the RAR.

[0023] In one aspect of the processor-implemented method, the processor-implemented method can further include receiving the TA command in downlink control information (DCI).

[0024] In one aspect of the processor-implemented method, the TA-associated RA configuration can include a gap for performing RF tuning and RA preamble transmission based on at least one of: the RA occasion of the particular TA cell is on a different frequency than an active frequency band of the UE with the serving cell, or the RAR reception configuration specifies a frequency for receiving the RAR that is a different frequency than an active frequency band of the UE with the serving cell.

[0025] According to some aspects, the subject matter of the independent claims is provided. Some further aspects are defined in the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0026] Some example embodiments will now be described with reference to the drawings.

[0027] Figure 1 is a diagram of an example embodiment of a wireless network between a network system and a user equipment device, UE, according to an illustrated aspect of the disclosure; Figure 2 is a diagram of an example embodiment of components of a device, according to an illustrated aspect of the disclosure; Figure 3 is a diagram of example embodiments of dual connectivity, DC, and carrier aggregation, CA, according to an illustrated aspect of the disclosure; Figure 4 is a diagram of example embodiments of a handover procedure, according to an illustrated aspect of the disclosure; Figure 5 is a diagram of example embodiments of a contention-based random access procedure, according to an illustrated aspect of the disclosure; Figure 6A and Figure 6B is a diagram of example embodiments of signals and operations between a UE, a central unit, CU, a source distributed unit, DU, and a target DU, according to an illustrated aspect of the disclosure; Figure 7A and Figure 7B is a diagram of example embodiments of signals and operations between a UE, a CU, a source DU, a target DU, and other cells, according to an illustrated aspect of the disclosure; and Figure 8A andFigure 8B is a diagram of another example embodiment of signals and operations between a UE, a CU, a source DU, a target DU, and other cells according to an illustrated aspect of the disclosure. DETAILED DESCRIPTION

[0028] In the following description, specific details are set forth to provide a thorough understanding of the disclosed aspects. However, one skilled in the relevant art will recognize that aspects can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with transmitters, receivers, or transceivers are not shown or described in detail to avoid obscuring aspects.

[0029] Reference throughout this specification to “one aspect” or “an aspect” means that a particular feature, structure, or characteristic described in connection with the aspect is included in at least one aspect. Thus, the appearances of the phrases “in one aspect” or “in an aspect” in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more aspects.

[0030] Aspects or embodiments described in this disclosure can be implemented in wireless network devices, such as, but not limited to, devices utilizing Worldwide Interoperability for Microwave Access (WiMAX), Global System for Mobile Communications (GSM, 2G), GSM EDGE Radio Access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on Basic Wideband Code Division Multiple Access (W-CDMA), High Speed Packet Access (HSPA), Long Term Evolution (LTE), LTE-Advanced, Enhanced LTE (eLTE), 5G New Radio (5G NR), and 802.11ax (Wi-Fi 6), among other wireless network systems. The term “eLTE” denotes LTE evolution connected to a 5G core here. LTE is also referred to as Evolved UMTS Terrestrial Radio Access (EUTRA) or Evolved UMTS Terrestrial Radio Access Network (EUTRAN).

[0031] Aspects of the disclosure relate to timing advance management in 5G NR. Aspects of the disclosure provide various advantages, including, for example, better efficiency during and after handover using L1 / L2 triggered mobility (LTM).

[0032] As used herein, the terms “transmitting to,” “receiving from,” “cooperating with,” and “coordinating with” (and variations of these terms) include communication that can or can not involve communication through one or more intermediary devices or nodes. The term “acquiring” (and variations of this term) includes acquiring at a first instance or reacquiring after the first instance. The term “connected” can mean either a physical or a logical connection.

[0033] Figure 1 FIG. 1 is a diagram depicting an example of a wireless network between a network system 100 and user equipment devices, UEs 150. The network system 100 may, for example, include one or more network nodes 120, one or more servers 110, and / or one or more network devices 130 (e.g., test devices). The network nodes 120 will be described in more detail below. As used herein, the term “network device” can refer to any component of the network system 100, such as a server 110, a network node 120, a network device 130, any component(s) of the foregoing, and / or any other component(s) of the network system 100. Examples of network devices include, but are not limited to, devices implementing 5G NR and devices implementing Wi-Fi 6, among others. The present disclosure describes embodiments related to 5G NR and embodiments involving aspects defined by the Third Generation Partnership Project (3GPP). However, it is contemplated that embodiments related to other wireless network technologies are encompassed within the scope of the present disclosure.

[0034] The following description provides further details of examples of network nodes. In a 5G NR network, a gNodeB (also referred to as gNB) can include, for example, a node that provides NR user plane and control plane protocol terminations towards the UE and that connects via an NG interface to a 5G core (5GC), e.g., in accordance with 3GPP TS 38.300 V16.6.0 (2021-06) section 3.2 (incorporated herein by reference).

[0035] The gNB supports various protocol layers, e.g., Layer 1 (LI) - physical layer, Layer 2 (L2), and Layer 3 (L3).

[0036] Layer 2 (L2) of NR is divided into the following sub-layers: Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Service Data Adaptation Protocol (SDAP), where, for example: The physical layer provides transport channels to the MAC sublayer; The MAC sublayer provides logical channels to the RLC sublayer; The RLC sublayer provides RLC channels to the PDCP sublayer; The PDCP sublayer provides radio bearers to the SDAP sublayer; The SDAP sublayer provides quality of service (QoS) flows to the 5GC; “Comp.” refers to head compression and “Segm.” refers to segment; The control channels include a broadcast control channel (BCCH) and a physical control channel (PCCH).

[0037] Layer 3 (L3) includes, for example, a radio resource control RRC, for example, according to 3GPP TS 38.300 V16.6.0 (2021-06) section 6, which is incorporated herein by reference.

[0038] The gNB central unit gNB-CU includes, for example, logical nodes hosting, for example, a radio resource control RRC, a service data adaptation protocol SDAP, and a packet data convergence protocol PDCP protocol of a gNB or an RRC and a PDCP protocol of an en-gNB, the gNB-CU controlling operation of one or more gNB distributed units (gNB-DUs). The gNB-CU terminates the F1 interface connected with the gNB-DU. The gNB-CU can also be referred to herein as a CU, central unit, centralized unit, or control unit.

[0039] The gNB distributed unit gNB-DU includes, for example, logical nodes hosting, for example, a radio link control RLC, a medium access control MAC, and a physical PHY layer of a gNB or an en-gNB, and operation of the gNB-DU is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU. The gNB-DU can also be referred to herein as a DU or distributed unit.

[0040] The gNB-CU-control-plane (gNB-CU-CP) includes, for example, logical nodes hosting, for example, an RRC and a control-plane part of a PDCP protocol of a gNB-CU for an en-gNB or a gNB. The gNB-CU-CP terminates the E1 interface connected with the gNB-CU-user-plane (gNB-CU-UP) and the F1-C interface connected with the gNB-DU.

[0041] A gNB-CU-User Plane (gNB-CU-UP) includes, for example, a logical node that hosts the user plane part of the PDCP protocol for gNB-CU of en-gNB, and the user plane part of the PDCP protocol and the SDAP protocol for gNB-CU of gNB, for example. The gNB-CU-UP terminates the El interface connected with the gNB-CU-CP and the Fl-U interface connected with the gNB-DU, for example, in accordance with 3GPP TS 38.401 V16.6.0 (2021-07) section 3.1, which is incorporated herein by reference.

[0042] Different functional splits between the central and distributed units are possible, for example, referred to as options: Option 1 (split similar to 1A): The functional split in this option is similar to the 1A architecture in Dual Connectivity (DC). RRC is in the central unit. PDCP, RLC, MAC, physical layer, and RF are in the distributed unit.

[0043] Option 2 (split similar to 3C): The functional split in this option is similar to the 3C architecture in DC. RRC and PDCP are in the central unit. RLC, MAC, physical layer, and RF are in the distributed unit.

[0044] Option 3 (RLC-in split): Low RLC (part of the functionality of RLC), MAC, physical layer, and RF are in the distributed unit. PDCP and high RLC (another part of the functionality of RLC) are in the central unit.

[0045] Option 4 (RLC-MAC split): MAC, physical layer, and RF are in the distributed unit. PDCP and RLC are in the central unit.

[0046] Alternatively, for example, in accordance with 3GPP TR 38.801 V14.0.0 (2017-03) section 11, which is incorporated herein by reference.

[0047] As used herein, the term “network node” can refer to any one or any combination of a gNB, a gNB-CU, a gNB-DU, a gNB-CU-CP, or a gNB-CU-UP, or any combination thereof.

[0048] A RAN (Radio Access Network) node or network node, such as e.g. a gNB, a base station, a gNB-CU, or a gNB-DU, or parts thereof, can be implemented using e.g. an apparatus having at least one processor and / or at least one memory having processor-readable instructions (“programs”) configured to support and / or provide and / or handle CU and / or DU related functions and / or features, and / or at least one protocol (sub)layer of a RAN (Radio Access Network) (e.g. Layer 2 and / or Layer 3). Examples of such apparatuses will be described below in connection with Figure 2 Examples of such apparatuses and components are described.

[0049] The gNB-CU and gNB-DU parts can e.g. be co-located or physically separated. The gNB-DU can even be further split into e.g. two parts, one part comprising processing devices and one part comprising antennas. The central unit (CU) can also be referred to as BBU / REC / RCC / C-RAN / V-RAN, O-RAN or parts thereof. The distributed unit (DU) can also be referred to as RRH / RRU / RE / RU or parts thereof. In the following, in various example embodiments of the present disclosure, a network node supporting at least one of central unit control plane functions or Layer 3 protocols of a Radio Access Network can be e.g. a gNB-CU-CP. Similarly, a network node supporting at least one of distributed unit functions or Layer 2 protocols of a Radio Access Network can be e.g. a gNB-DU.

[0050] The gNB-CU can support one or more gNB-DUs. The gNB-DU can support one or more cells and thus can support serving cells for user equipment apparatuses (UEs), or candidate cells for handover, dual connectivity and / or carrier aggregation and other procedures. Examples of such apparatuses will be described below in connection with Figure 3 and Figure 4 Examples of such procedures are described.

[0051] A user equipment apparatus (UE) 150 can be, or can include, a wireless or mobile device, an apparatus having a radio interface to interact with a RAN (Radio Access Network), a smartphone, a vehicular apparatus, an IoT device or M2M device, and other types of user equipment. Such a UE 150 can include at least one processor; and at least one memory including program code; wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform certain operations, such as e.g. RRC connection with a RAN. Examples of such apparatuses will be described below in connection with Figure 2Examples of components of a UE are described. In embodiments, the UE 150 can be configured to generate messages (e.g., including a cell ID) to be transmitted to the RAN via radio (e.g., to reach and communicate with a serving cell). In embodiments, the UE 150 can generate and transmit and receive RRC messages containing one or more RRC PDUs (Packet Data Units). Those skilled in the art will understand the RRC protocol and other procedures that can be performed by the UE.

[0052] With continued reference to Figure 1 In examples of a 5G NR network, the network system 100 provides a cell, which defines a coverage area of the network system 100. As described above, the network system 100 can include a gNB of a 5G NR network, or can include any other apparatus configured to control radio communications and manage radio resources within a cell. As used herein, the term“resource” can refer to a radio resource, such as a resource block (RB), a physical resource block (PRB), a radio frame, a subframe, a slot, a subband, a frequency region, a subcarrier, a beam, etc. In embodiments, the network node 120 can be referred to as a base station.

[0053] Figure 1 Examples are provided and only the network system 100 and the UE 150 are shown. Those skilled in the art will understand that the network system 100 includes Figure 1 components not shown in FIG. 1 and will understand that other user equipment apparatuses can communicate with the network system 100.

[0054] Referring now to Figure 2 a block diagram of example components of a UE or network apparatus is shown. The apparatus includes an electronic storage 210, a processor 220, a memory 250, and a network interface 240. The various components can be communicatively coupled to one another. The processor 220 can be and can include any type of processor such as a single core central processing unit (CPU), a multi-core CPU, a microprocessor, a digital signal processor (DSP), a system on a chip (SoC), or any other type of processor. The memory 250 can be a volatile type of memory, such as RAM, or a non-volatile type of memory, such as NAND flash. The memory 250 includes processor-readable instructions that are executable by the processor 220 to cause the apparatus to perform various operations, including those mentioned herein.

[0055] The electronic storage 210 can be and can include any type of electronic memory for storing data such as hard drives, solid state drives, and / or optical discs, among other types of electronic storage. The electronic storage 210 stores processor-readable instructions for causing the device to perform its operations, and stores data associated with such operations, such as storing data related to the 5G NR standard, among other data. The network interface 240 can implement wireless network technologies such as 5G NR, Wi-Fi 6, and / or other wireless network technologies.

[0056] Figure 2 The illustrated components are merely examples and those skilled in the art will appreciate that devices include other components not shown and that embodiments can include multiples of any of the illustrated components. Such and other embodiments are contemplated within the scope of this disclosure.

[0057] Figure 3 is a diagram depicting examples of dual connectivity (DC) and carrier aggregation (CA). Dual connectivity allows a UE 310 to connect to two network nodes at the same time, which can be referred to as a master node (MN) 320 and a secondary node (SN) 330. In embodiments, the MN 320 and / or SN 330 can be 5G New Radio (NR) nodes (e.g., gNBs) as well as other types of nodes. In embodiments, the MN 320 and / or SN 330 can be base stations.

[0058] In embodiments, the MN 320 connects to a core network, such as a 5G core (5GC), and provides a control plane connection between the UE 310 and the core network, while the SN 330 connects to the MN 320 (e.g., via an Xn interface) and provides additional resources for user plane traffic. In embodiments, the MN 320 handles signaling messages, such as radio resource control (RRC) signaling messages. In embodiments, the SN 330 can also handle signaling messages, such as RRC signaling messages, using a signaling radio bearer (SRB) for a 5G NR network (e.g., SRB3). Those skilled in the art will appreciate RRC and SRBs.

[0059] Figure 3 Carrier aggregation is shown in the middle. While Figure 3Carrier aggregation in conjunction with dual connectivity is shown, but carrier aggregation can also be used without dual connectivity. Carrier aggregation enables a UE 410 to connect with multiple cells simultaneously to operate at multiple frequencies simultaneously. In embodiments, multiple cells can be located at a single base station and / or common location (e.g., small cells or femto cells at a facility), among other examples. One or more cells that can be used by a UE under carrier aggregation can be referred to as a “cell group.” When carrier aggregation is used with dual connectivity, a master node and / or a secondary node can have a cell group. A cell group of a master node can be referred to as a master cell group (MCG), and a cell group of a secondary node can be referred to as a secondary cell group (SCG). As shown, the MCG includes a primary cell (Pcell) and can include one or more secondary cells (Scell). The SCG includes a primary cell of a secondary cell group (PSCell) and can include one or more secondary cells (Scell). A person of skill in the art will understand the characteristics and functionality of such cells and cell groups. Figure 3

[0060] Figure 3 Examples are shown for dual connectivity and carrier aggregation. The following description can refer to dual connectivity and / or carrier aggregation. For example, with respect to establishing dual connectivity, a candidate cell for a PSCell can be referred to as a target cell, a candidate cell, or a target candidate cell, which can be used interchangeably. As another example, with respect to carrier aggregation, a candidate cell for a Scell can also be referred to as a target cell, a candidate cell, or a target candidate cell. It should be understood that such references are not limited to the examples shown. Figure 3 Figure 3 Other arrangements different from those shown are contemplated within the scope of the present disclosure.

[0061] Figure 4 Examples of handover scenarios are depicted. Handover (HO) refers to a process of transitioning a service of a UE from a source node and / or cell to a target node and / or cell. Handover can be performed, for example, when a UE transitions between cells, among other scenarios. Figure 4 A UE 410, a source MN 420, a source SN 430, a target MN 440, and a target SN 450 are shown.

[0062] ​​5G 3GPP (3rd Generation Partnership Project) Release 15, 16 and 17 standards enhance handover operations in various ways. Further enhancements are being developed under the term Layer 1 / Layer 2 triggered mobility (LTM), which can also be referred to as L1 / L2 triggered mobility, L1 / 2 inter-cell mobility, L1 / 2 handover, or lower layer (L1 / 2) mobility. These terms can be used interchangeably. An L1 / L2 signal, message or command sent by a network node to trigger a cell handover at a UE is referred to as a “cell handover command.” In LTM, the decision about a cell handover is based on L1 measurements and made in the MAC layer in the distributed unit (DU). The cell handover command includes a MAC control element (MAC CE). A cell that is a target of a handover can be referred to herein as a target cell, a candidate cell, or a target candidate cell, which can be used interchangeably.

[0063] In the case of dual connectivity, the handover can involve a handover from the source MN 420 to the target MN 440, a handover from the source SN 430 to the target SN 450, a change of Pcell within the MN, and / or a change of PSCell within the SN. In the case of dual connectivity, the handover to the target MN 440 can also involve coordination with the target SN 450. Particular standards that can be relevant include, but are not limited to, 3GPP TS 37.340 and TS 38.423.

[0064] Figure 4 The examples of handovers depicted are merely illustrative. Variations are contemplated to be within the scope of the present disclosure.

[0065] Figure 3 and Figure 4 Examples are shown that involve operations and functions of multiple network nodes and / or cells. Other operations and functions can also involve multiple nodes and / or cells, such as multi-transmission and reception point (mTRP), fast handover and dynamic point switching, etc. Such operations can involve a UE communicating with a target DU that supports a candidate target cell. The process by which the UE establishes communication with the target DU is referred to as a random access procedure. Random access procedures can be used for initial access, inactive small data transmission, and transition from RRC_Inactive to RRC_Connected, as well as beam failure recovery, connection reestablishment, handover, and cell addition, among other procedures as will be recognized by those skilled in the art.

[0066] Two types of random access procedures include contention-based random access (CBRA) and contention-free random access (CFRA). Figure 5is a diagram of an example of a contention-based random access (CBRA) procedure. In the example shown, the signals include a random access preamble (MSG1) transmitted by the UE 550 to the network node 510, a random access response (MSG2) transmitted from the network node 510 to the UE 550, a scheduled transmission (MSG3) transmitted from the UE 550 to the network node 510, and a contention resolution (MSG4) transmitted from the network node 510 to the UE 550.

[0067] For MSG1, the UE 550 selects an available random access preamble based on information elements in a signal synchronization block (SSB) that will be understood by those skilled in the art. The UE 550 sends the random access preamble (MSG1) to the network node 510 using specific time and frequency resources called random access occasions (ROs). The UE 550 also provides an identification to the network called a random access radio network temporary identification (RA-RNTI) so that the network can address the identification in the next step.

[0068] For MSG2, the network node 110 detects the preamble, computes various quantities, and sends a physical uplink shared channel (PUSCH) uplink (UL) grant to the UE 550. This is called a random access response (RAR), which is sent as MSG2 addressed to the UE 550 with the associated RA-RNTI, and indicates to the UE 550 where in frequency and when in time it can transmit MSG3 on the PUSCH.

[0069] For MSG3, in response to receiving MSG2 from the network node 510, the UE 550 sends MSG3 using the UL grant provided in the RAR. Because the RAR provides a time resource allocation, the UE 550 sends MSG3 to the network node 510 at the time specified by the time resource allocation, and it is a scheduled transmission. This MSG3 can be referred to as a radio resource control (RRC) connection request message.

[0070] For MSG4, the network node 510 can send MSG4 to the UE 550 for contention resolution. Contention resolution can operate in the manner specified by 3GPP for 5G NR. After the random access procedure, assuming contention resolution is favorably resolved, the UE 550 is connected to the network node 510. After the connection is established, various procedures will be handled by the gNB-CU according to the CU-DU split, such as the example split described above. Other aspects of contention-based random access (CBRA) will be understood by those skilled in the art.

[0071] Another type of random access procedure is contention free random access (CFRA) (not shown). Generally, for CFRA, the network node 510 provides a configuration that specifies one or more assigned random access preamble indices and random access occasions for each signal synchronization block (SSB). The network node 510 transmits the CFRA configuration, such as the preamble indices and random access occasions, to the UE 550. The UE 550 receives the CFRA configuration and sends a random access preamble as MSG1 in a random access request to the network node 510. MSG2 and MSG3 are then similar to those described in connection with CBRA. Based on the use of the assigned random access preambles, collision resolution is not needed in CFRA. Those skilled in the art will appreciate other aspects of contention free random access (CFRA).

[0072] According to aspects of the present application, the present disclosure relates to timing advance (TA) management with respect to candidate target cells, which can be targets of handover, dual connectivity, carrier aggregation, mTRP, fast handover and / or dynamic point switching, among other procedures. Timing advance refers to information used by a UE to time its uplink transmissions toward a network node to arrive at the network node in alignment with a reception time window. This information can be referred to herein as a timing advance value or TA value, and the process of acquiring the timing advance value can be referred to herein as timing advance acquisition, TA acquisition, acquiring timing advance, or acquiring TA (or variations thereof). As noted above, the term “acquiring” (and variations thereof) includes acquiring in a first instance or re-acquiring after the first instance. A UE with a longer propagation delay to a network node can have a greater TA value than a UE with a shorter propagation delay to the network node.

[0073] In embodiments, the UE can acquire a separate TA value for each candidate target cell. The TA value for a candidate target cell can be determined based on information provided by the DU supporting the candidate target cell, e.g., in a MAC control element (MAC CE) or a random access response (RAR).

[0074] In embodiments, the UE can acquire a TA value for a timing advance group (TAG). A timing advance group (TAG) is a group of serving cells configured by RRC and for which the same timing reference cell and the same timing advance value are used for cells with UL configuration. The TAG containing the SpCell (which is the Pcell + PSCell) of the MAC entity is referred to as the primary timing advance group (PTAG), while the term secondary timing advance group (STAG) refers to a TAG that does not include the SpCell.

[0075] Each TAG can include a time alignment timer (TAT) that controls how long a MAC entity considers a serving cell belonging to the associated TAG to be uplink time aligned. The TAT can also be referred to as a timeAlignmentTimer. Procedures for maintaining uplink time alignment can involve 3GPP specification 38.331, which can provide procedures for, for example, when a timing advance command MAC CE is received, when a timing advance command is received in a random access response message for a serving cell belonging to a TAG or in a MSGB for a SpCell, when an absolute timing advance command is received in response to a MSGA transmission including a C-RNTI MAC CE, when a timeAlignmentTimer expires when it is associated with a PTAG, and / or when a timeAlignmentTimer expires when it is associated with an STAG, among other procedures.

[0076] In embodiments, TA can be acquired based on a random access (RA) procedure (CFRA or CBRA), such as but not limited to a physical downlink control channel (PDCCH)-ordered RA procedure, a UE-triggered RA procedure, and / or a high-layer triggered RA procedure from a network node (in addition to an L3 handover command), among others. In embodiments, TA can be acquired based on a non-RA procedure approach, such as but not limited to a sounding reference signal (SRS)-based TA acquisition, a receive timing difference-based mechanism (such as those in LTE), and / or a UE-based TA measurement (including a UE-based TA measurement with one TAC from a serving cell), among others. Such RA-based and non-RA-based approaches for TA acquisition are within the scope of the present disclosure.

[0077] Reference is now made to Figure 6A and Figure 6BThe example signals and operations for TA management are shown with respect to an inter-DU handover procedure. The handover procedure is merely illustrative, and it is contemplated that aspects of the disclosed technology can be applied to other procedures involving TA acquisition, such as but not limited to dual connectivity, carrier aggregation, mTRP, fast handover, and / or dynamic point switching, etc. Additionally, the inter-DU scenario is illustrative, and aspects of the present disclosure can also be applied to intra-DU and / or inter-CU scenarios. In cases where the source DU and target DU are supported by different CUs, the source DU can be supported by a source CU, and the target DU can be supported by a target CU, which can communicate via an Xn interface. As noted above, the terms “transmit to,” “receive from,” and “cooperate with” (and variations thereof) include communications that can or can not involve communication through one or more intermediary devices or nodes. It is intended that any description involving a DU is also a description involving a network node that supports at least one of the DU functions or Layer 2 protocols of a radio access network (RAN). Any description involving a CU is also to be considered a description involving a network node that supports at least one of the CU functions or Layer 3 protocols of a radio access network (RAN).

[0078] The following paragraphs describe various signals and operations. It should be understood that the described signals can have associated operations, and the described operations can have associated signals. Thus, the described signals can also be operations, and the described operations can also be signals.

[0079] Prior to signal 601, the UE has established a connection with a DU (i.e., a source DU) that supports a serving cell for the UE, and has established a (logical) connection with a CU that supports the DU.

[0080] For signal 601, the UE transmits an L3 measurement report to the source DU, and the source DU receives the L3 measurement report from the UE. Those skilled in the art will understand an L3 measurement report, which can include, for example, an average measurement sample for a reference signal of the serving cell. The L3 measurement report can indicate, for example, that the UE is approaching the edge of the cell, and thus a handover procedure should be initiated. For signal 602, the source DU forwards the L3 measurement report by transmitting the L3 measurement report to the CU, and the CU receives the L3 measurement report from the source DU. For operation 603, the CU performs a handover (HO) decision based on the L3 measurement report as to whether a handover should be prepared. For the illustrated embodiment, the CU decides that a handover should be prepared.

[0081] For signal 604, the CU transmits a UE context setup request to the target DUs to prepare the target DUs for the handover by setting up a UE context in the target DUs. The target DUs receive the UE context setup request from the CU and set up the UE context. For signal 605, the target DUs provide an acknowledgement by transmitting a UE context setup response to the CU, and the CU receives the UE context setup response from the target DUs. While one target DU is shown, there can be more than one target DU if there are multiple candidate target cells. The signals at 604 and 605 can be used for each target DU and multiple candidate target cells. The following description will refer to candidate target cell(s) to indicate that there can be one candidate target cell or multiple candidate target cells, and where appropriate, target DU(s) that support the candidate target cell(s) will be referred to. If the target DUs and the source DU are supported by different CUs, the CUs can communicate using an Xn interface. For convenience, only one CU (the CU that supports the source DU) is shown, but the disclosed techniques are also intended to be applicable to the multiple-CU case.

[0082] For signal 606, the CU transmits a UE context modification request to the source DU to modify the UE context in the source DU, if needed, and to provide target cell information (e.g., target cell RS configuration, TCI state, etc.). The source DU receives the UE context modification request from the CU, modifies the UE context if needed, and receives the target cell information. For signal 607, the source DU provides an acknowledgement by transmitting a UE context modification response to the CU, and the CU receives the UE context modification response from the source DU.

[0083] According to aspects of the present disclosure, for signals 604-607, the CU, target DU(s), and source DU can coordinate with each other regarding TA acquisition and configuration for the candidate target cell(s). For example, the source DU and target DU(s) can coordinate (via the CU) the method for the UE to acquire the TA, such as a particular RA-based method or a particular non-RA-based method for acquiring the TA. Further details of the coordination and TA configuration will be described in more detail later herein.

[0084] For operation 608, the CU creates an RRC reconfiguration message that includes measurement configuration for L1 cell change, configuration of the prepared cell, and TA acquisition configuration and triggering for candidate target cells. In embodiments, the RRC reconfiguration message can include TA configuration if the CU needs to be involved later (in the execution phase). The TA configuration can for example specify a method for the UE to acquire TA, which can be specified based on the cooperation between the source DU and the target DU(s) described above. In embodiments, the TA acquisition method can be configured / triggered by the CU-CP (in coordination with the source-DU) based on L3 measurements. The TA configuration can specify other TA management options, which will be described later in this document.

[0085] For signal 609, the CU transmits the RRC reconfiguration message to the source DU using a downlink (DL) RRC message transfer, and the source DU receives the RRC reconfiguration message from the CU. As described above, the RRC reconfiguration message can include the TA configuration described above. For signal 610, the source DU transmits the RRC reconfiguration message to the UE for forwarding to the UE, and the UE receives the RRC reconfiguration message from the source DU. The UE performs reconfiguration based on the RRC reconfiguration message. For signal 611, the UE responds by transmitting an RRC reconfiguration complete message to the source DU using an uplink (UL) RRC message transfer, and the source DU receives the RRC reconfiguration complete message from the UE. For signal 612, the source DU transmits the RRC reconfiguration complete message to the CU for forwarding to the CU, and the CU receives the RRC reconfiguration complete message from the source DU. In embodiments, signals 609-612 can be described as part of a logical connection between the UE and the CU, such that the CU transmits RRC messages to the UE, and the UE receives RRC messages from the CU.

[0086] In embodiments, the above-described signals and operations 601-612 can be referred to as a preparation phase. The preparation phase is followed by an execution phase.

[0087] In the execution phase, the UE provides periodic L1 measurement reports based on its configuration. Those skilled in the art will appreciate L1 measurements. For signal 613, the UE periodically transmits L1 measurement reports to the source DU, and the source DU receives the periodic L1 measurement reports from the UE.

[0088] For operation 614, the source DU decides whether to trigger the UE to acquire TA for the set of candidate cells (i.e., the candidate cells for handover configured by the CU for operation 608) based on the received L1 measurement reports. The source DU can decide to trigger TA acquisition if, for example, the L1 measurements move below or above a measurement threshold, or other criteria.

[0089] As mentioned above, in embodiments, the TA acquisition method can be configured / triggered by the CU-CP (in coordination with the source-DU) based on L3 measurements. Thus, in embodiments, signal 613 can be an L3 measurement report transmitted to the CU, and operation 614 can be an operation in the CU to decide on TA acquisition.

[0090] For operation 615, the UE acquires TA for the candidate target cell(s) using the TA acquisition method specified in the RRC reconfiguration message at operation 608. As mentioned above, the TA can be acquired based on a random access (RA) procedure (CFRA or CBRA), such as but not limited to a physical downlink control channel (PDCCH) ordered RA procedure, a UE triggered RA procedure, and / or a high layer triggered RA procedure from the network node (in addition to the L3 handover command), etc. In embodiments, the TA can be acquired based on a non-RA procedure method, such as but not limited to a sounding reference signal (SRS) based TA acquisition, a received timing difference based mechanism (such as those in LTE), and / or a UE based TA measurement (including UE based TA measurement with one TAC from the serving cell), etc. Such RA based methods and non-RA based methods for TA acquisition are within the scope of the present disclosure. After operation 615, the UE will have TA values for the candidate target cell(s) before triggering the cell handover.

[0091] For signal 616, the UE continues the L1 measurement reporting and periodically transmits the L1 measurement report to the source DU, and the source DU receives the periodic L1 measurement report from the UE. For operation 617, the source DU decides whether the UE should change the serving cell. In embodiments, for example, if the L1 measurements move below or above a threshold, the source DU can decide that the UE should change the serving cell. Once the source DU decides that the UE should handover to a cell (e.g., a target cell supported by a target DU), the source DU triggers the cell handover using a cell handover command (e.g., a MAC CE).

[0092] For signal 618, the cell handover command (e.g., a MAC CE) is transmitted by the source DU to the UE, and the UE receives the cell handover command (e.g., a MAC CE) from the source DU. In embodiments, the cell handover command can contain a TA value for the target cell. In embodiments, the cell handover command can contain a TA configuration for the UE to use during and / or after the cell handover. The source DU can have the TA configuration from receiving the RRC message for signal 609. Further details of the TA configuration will be described later herein.

[0093] In response to the cell handover command, the UE applies the RRC configuration for the target cell of the target DU indicated by the cell handover command to hand over to the target DU / target cell as a serving cell. In embodiments, the UE can be configured to perform a random access (RA) procedure to the target cell and the target DU, as shown by signal 619 and signal 620. However, in embodiments, if the UE has acquired the TA value of the target cell, the UE can be configured to not perform the RA procedure to the target cell / target DU.

[0094] For signal 621, to initiate communication with the target DU, the UE transmits an RRC reconfiguration complete message to the target DU using the already configured uplink (UL) resources, and the target DU receives the RRC reconfiguration complete message from the UE. (Signal 622 and signal 623 will be described below). For signal 624, the target DU forwards the RRC reconfiguration complete message using an UL RRC message, transmits the RRC reconfiguration complete message to the CU, and the CU receives the RRC reconfiguration complete message from the target DU. For signal 625, the CU transmits a UE context release command / request to the source DU to release the UE context from the source DU, and the source DU receives the UE context release command / request from the CU. The source DU releases the UE context in response to the UE context release command / request. For signal 626, the source DU transmits a UE context release complete message to the CU, and the CU receives the UE context release complete message from the source DU. For operation 627, the CU performs path switching to the target DU as a new DU supporting the serving cell.

[0095] More details will be provided below regarding various signals and operations of Figure 6A and Figure 6B .

[0096] According to aspects of the disclosure, and as described above, for signals and operations 604-609, the source DU, candidate target DU(s), and the CU can coordinate with each other regarding TA acquisition for the UE of the candidate target cell(s) and regarding TA configuration. For example, the source DU and the target DU(s) can coordinate (via the CU) the method for the UE to acquire the TA, such as a particular RA-based method or a particular non-RA-based method for acquiring the TA. As another example, the TA configuration can contain information regarding how the TA should be managed in the UE before the cell handover, after receiving the cell handover command, and during and / or after the cell handover.

[0097] In an embodiment, the target DU can inform the source DU whether the UE can maintain the timing advance values (acquired prior to the cell switch for a set of candidate target cells) during or after the cell switch. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0098] In an embodiment, the target DU can inform the source DU whether the UE can maintain a subset of the timing advance values (acquired prior to the cell switch) or a subset of the timing advance groups during or after the cell switch. The subset of the timing advance values can correspond to a subset of candidate target cells having at least one of: a measurement quality above a predefined value, a measurement quality above a threshold relative to the serving cell for a predefined duration, a measurement quality above a threshold relative to the serving cell for a predefined number of samples, a measurement quality above a threshold relative to a cell (in the set of candidate target cells) for a predefined duration, a measurement quality above a threshold relative to a cell (in the set of candidate target cells) for a predefined number of samples. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0099] In an embodiment, the target DU can inform the source DU whether the UE can expire any running time alignment timer at the cell switch. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0100] In an embodiment, the source DU can provide the UE with additional conditions and configurations on how to update the TAG at the time of TAT expiry, during the time after receiving the cell switch command, during the cell switch procedure (e.g., after receiving the cell switch command), and after switching to the new target cell.

[0101] In an embodiment, the source DU can inform the UE not to re-acquire / update the TA for the candidate target cell(s) if the candidate target cell(s) are not within the Q best cells (Q < N), or if the candidate target cell has at least one of: a measurement quality below a predefined value, a measurement quality below a threshold relative to the serving cell, or a measurement quality below a threshold relative to at least one other candidate target cell in the set of candidate target cells. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0102] In an embodiment, the source DU can inform the UE not to reacquire TA or TAG for the candidate target cell after receiving the cell switch command, during the cell switch procedure, and / or for a period of time after moving to the new target cell. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0103] In an embodiment, the source DU can inform the UE that it can use a different method / configuration (e.g., to reduce interruption and UE complexity) to acquire / update TA after TAT expiry, during the time after receiving the cell switch command, during the cell switch, and after moving to the new cell. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0104] In an embodiment, the source DU can configure the UE to reset / restart the TA timer or provide the UE with a new timer configuration (for a set of cells) upon receiving the cell switch command or after the cell switch. The CU can include the indication in the TA configuration for operation 608, the source DU can inform the UE of the indication in signal 618, and the UE can receive the indication.

[0105] As mentioned above, for signal and operations 613-615, the source DU makes the decision on TA acquisition based on the L1 measurement report, and for operation 615, the UE acquires TA for one or more candidate target DUs. According to aspects of the disclosure, the candidate target cells (and the candidate target DUs supporting them) can be selected based on L1 measurements, such as measurement quality above a pre-defined value, measurement quality above a threshold relative to the serving cell for a pre-defined time duration, or measurement quality above a threshold relative to the serving cell for a pre-defined number of samples.

[0106] According to aspects of the disclosure, after making the decision for cell switch for operation 617, the source DU informs the UE via signal 618 on how to maintain and update TA during the time after receiving the cell switch command, during the cell switch, and after the cell switch by considering target node feedback and UE capabilities.

[0107] In an embodiment, the cell handover command (also referred to as LTM trigger command) can include one or more of the following: an indication of whether the UE should expire the running TAT at cell handover; an indication of whether the UE should maintain the obtained TAs after / during the cell handover procedure; an indication of whether the UE should maintain and report the obtained TAs after / during the cell handover procedure; an indication of whether the UE should maintain and report the obtained cell IDs (e.g., PCI / TCI state or any similar ID) for which the TAs are obtained after / during the cell handover procedure; an indication of whether the UE should maintain and report the obtained cell IDs (e.g., PCI / TCI state or any similar ID) and TA values for which the TAs are obtained after / during the cell handover procedure; and / or an indication of whether the UE should maintain and report the obtained cell IDs (e.g., PCI / TCI state or any similar ID) and TA values for which the TAs are obtained if the TAT timer for the corresponding cell is running and will not expire within a predetermined duration after / during the cell handover procedure.

[0108] According to aspects of the present disclosure, after the UE transmits the RRC reconfiguration complete message for signal 621, the UE transmits a timing advance (TA) report for signal 622 to the target DU, and the target DU receives the TA report from the UE. The target DU determines whether a TA configuration update is needed based on the TA report. For signal 623, the target DU transmits a TA configuration update to the UE, and the UE receives the TA configuration update from the target DU.

[0109] In an embodiment, the UE receives configuration information from the source DU or CU for transmitting a timing advance report. In an embodiment, the configuration information indicates to include at least one of the following in the timing advance report: a physical cell ID (PCI) and / or a TCI state ID of a timing advance group (TAG), a transmission configuration index state of the TAG, a timing advance value associated with the TAG, a time alignment timer state associated with the TAG, a timing advance acquisition method and UE preference for timing advance acquisition, or a UE capability for timing advance acquisition. The UE capability includes at least one of the following: a number of TAGs, a number of cells, a method for acquiring timing advance, or a timing advance update limit. In an embodiment, the configuration information includes an uplink resource allocated by the target DU that enables the UE to transmit the TA report to the target DU after cell handover.

[0110] In an embodiment, for the signal 623, the UE receives, from the target DU after the cell is switched to the target cell, updated TA configuration information including at least one of: an indication of whether to maintain a timing advance value of at least one of the candidate target cell set, an indication to add the cell to a timing advance group, an indication to remove the cell from a timing advance group, an indication to configure a new timing advance group, a time alignment timer configuration, or a configuration of a method for acquiring a timing advance after a time alignment timer expires.

[0111] Embodiments of the signals 622 and 623 are merely illustrative, and variations are contemplated to be within the scope of the present disclosure. For example, in an embodiment, after the cell is switched, the UE can receive a request for a TA report from the target DU, and the UE can transmit the TA report to the target DU in response to the request. In an embodiment, before or during the cell is switched to the target cell, the UE can transmit a TA report to the source DU, which can relay the TA report to the target DU (e.g., through the CU). Such variations and other variations are contemplated to be within the scope of the present disclosure.

[0112] Embodiments of operations from the perspective of a UE, in accordance with aspects of the present disclosure, are as follows. In embodiments, a UE establishes a connection with a first network node (e.g., a source DU) via a serving cell, where the first network node supports the serving cell and at least one of a distributed unit (DU) function or layer 2 protocol of a radio access network; receives, from a second network node (e.g., a CU) supporting at least one of a central unit control plane (CU-CP) function or layer 3 protocol of a radio access network, a radio resource control (RRC) message including configuration information related to timing advance, the configuration information configured to prepare a user equipment device (UE) for at least one candidate target cell to which the UE can connect, where the RRC message is received before the UE connects with any of the at least one candidate target cell; and implements the configuration based on the configuration information.

[0113] Embodiments of operations from the perspective of a CU, in accordance with aspects of the present disclosure, are as follows. In an embodiment, a CU establishes a connection with a user equipment device (UE) via a serving cell; determines a radio resource control (RRC) message including configuration information related to timing advance, where the configuration information is configured to prepare the UE for at least one candidate target cell to which the UE can connect; and transmits the RRC message including the configuration information to the UE before the UE connects with any of the at least one candidate target cell.

[0114] According to aspects of the present disclosure, implementation of operations from the perspective of a source DU are as follows. In embodiments, a source DU establishes a connection with a user equipment device (UE) via a cell that is a serving cell; receives, from a control network node (e.g., a CU) that supports at least one of a central unit control plane (CU-CP) function or a layer 3 protocol of a radio access network, an L1 / L2 triggered mobility (LTM) configuration related to the UE; and transmits, to the UE, a message including timing advance related configuration information before the UE connects with any candidate target cell.

[0115] According to aspects of the present disclosure, implementation of operations from the perspective of a target DU are as follows. In embodiments, a target DU receives, from a control network node (e.g., a CU) that supports at least one of a central unit control plane (CU-CP) function or a layer 3 protocol of a radio access network, an L1 / L2 triggered mobility (LTM) configuration related to a user equipment device (UE), wherein the control network node connects to the UE via a serving cell; and coordinates, with a source network node (e.g., a source DU) that supports the serving cell and that supports at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access, regarding timing advance management before, during, or after a handover from the serving cell to the target cell, before a cell handover command is sent to the UE.

[0116] Figure 6A and Figure 6B The signals and operations of Figure 6A and Figure 6B are merely illustrative and variations are expected within the scope of the present disclosure. For example, the signals and operations can assume one TA value per physical cell ID (PCI). In embodiments, to cover multi-TRP (multi-transmission reception point) scenarios, a UE can be configured and required to acquire multiple Tas for a PCI, e.g., different TA values for different TCI state sets (transmission configuration indicator states). In embodiments, the signals and operations can include other signals and operations not shown in Figure 6A and Figure 6B . In embodiments, the signals and operations can not include each of the signals and operations shown in Figure 6A and Figure 6B . In embodiments, the signals and operations can be implemented in a different order than shown in

[0117] Reference is now made to Figure 7A and Figure 7B, showing example signals and operations for TA management in relation to an inter-DU handover procedure, in which the target DU requests the UE to acquire TAs for other candidate target cells with which the UE can connect after a cell handover. The handover procedure is merely illustrative, and it is contemplated that aspects of the disclosed technology can be applied to other procedures involving TA acquisition, such as but not limited to dual connectivity, carrier aggregation, mTRP, fast handover, and / or dynamic point switching, etc. Additionally, the inter-DU scenario is illustrative, and aspects of the present disclosure can also be applied to intra-DU and / or inter-CU scenarios. In a case where the source DU and the target DU are supported by different CUs, the source DU can be supported by a source CU, and the target DU can be supported by a target CU, which can communicate via an Xn interface. In this scenario, the target DU or the target CU can request the UE to acquire TAs for other candidate target cells with which the UE can connect after a cell handover. As noted above, the terms “transmit to,” “receive from,” and “cooperate with” (and variations thereof) include communications that can or can not involve communication through one or more intermediary devices or nodes. It is intended that any description involving a DU is also a description involving a network node that supports at least one of the DU functions or Layer 2 protocols of a radio access network (RAN). Any description involving a CU is also to be considered a description involving a network node that supports at least one of the CU functions or Layer 3 protocols of a radio access network (RAN).

[0118] Figure 7A and Figure 7B Aspects of the signals and operations of Figure 6A and Figure 6B are the same as or similar to various signals and operations of Figure 7A and Figure 7B will be described in detail. Figure 7A and Figure 7B Aspects of Figure 6A and Figure 6B are intended for use with aspects of

[0119] The following paragraphs describe various signals and operations. It should be understood that the described signals can have associated operations, and that the described operations can have associated signals. Consequently, the described signals can also be operations, and the described operations can also be signals.

[0120] Prior to signal 701, the UE has established a connection with a DU (i.e., a source DU) that supports a serving cell for the UE, and has established a (logical) connection with a CU that supports the DU.

[0121] For signal 701, the UE transmits an L3 measurement report to the source DU, and the source DU receives the L3 measurement report from the UE. Those skilled in the art will understand an L3 measurement report, which can include, for example, an average measurement sample for a reference signal of a serving cell. The L3 measurement report can indicate, for example, that the UE is approaching the edge of the cell and, therefore, a handover procedure should be initiated. For signal 702, the source DU forwards the L3 measurement report using an uplink (UL) RRC message transfer by transmitting the L3 measurement report to the CU, and the CU receives the L3 measurement report from the source DU. For operation 703, the CU performs a handover (HO) decision based on the L3 measurement report as to whether a handover should be prepared. For the illustrated embodiment, the CU decides that a handover should be prepared.

[0122] For signal 704, the CU transmits a UE context setup request to the target DU to prepare the target DU for the handover by establishing a UE context in the target DU. The target DU receives the UE context setup request from the CU and establishes the UE context. (Signals and operations 705-707 are described below.) For signal 708, the target DU provides an acknowledgement by transmitting a UE context setup response to the CU, and the CU receives the UE context setup response from the target DU. While one target DU is shown, there can be more than one target DU if there are multiple candidate target cells. The signals at 704 and 708 can be used for each target DU and multiple candidate target cells. The following description will refer to candidate target cell(s) to indicate that there can be one candidate target cell or multiple candidate target cells, and where appropriate, will refer to target DU(s) that support the candidate target cell(s). If the target DU and the source DU are supported by different CUs, the CUs can communicate using an Xn interface. For convenience, only one CU (the CU that supports the source DU) is shown, but the disclosed techniques are also intended to apply to the multiple CU case.

[0123] Signals and operations 705-707 relate to the target DU determining other cells with which the UE can connect after cell handover (e.g., for dual connectivity or carrier aggregation, etc.) and for which the target DU wants the UE to acquire TA. If the target DU and source DU are supported by different CUs, the target DU or the target CU can determine other cells with which the UE can connect after cell handover (e.g., for dual connectivity or carrier aggregation, etc.) and for which the target DU wants the UE to acquire TA. For signal 705, the CU informs the target DU(s) / target cell(s) that the UE acquired / maintained TA of other cells before cell handover and potentially reported their capabilities after cell handover. The CU transmits this information to the target DU(s), which receive this information from the CU. (In embodiments, the source DU or CU can provide UE measurements of other detected cells so that the target DU can estimate their signal strength and / or quality.) If the target DU and source DU are supported by different CUs, the source CU can transmit the above information to the target CU. For operation 706, the target DU or the target CU determines, based on the information about UE capabilities, a set of other cells / TRPs (or TCI states) for which the target DU wants the UE to acquire TA. For signal 707, the target DU coordinates with the DU(s) that support the set of other cells for methods, resources, and configurations related to TA acquisition and update and for reporting acquired TA information. For signal 709, the target DU informs the CU about TA configurations (which can include IDs) of other cells for which the UE should acquire TA, about methods / resources for acquiring and updating TA, about TAT configurations, and / or about configurations for reporting acquired TA, and other possible information related to other cells. The target DU transmits this information to the CU, which receives this information from the target DU. If the target DU and source DU are supported by different CUs, the target CU can transmit the above information to the source CU. The target cell that requests other cells can form a set of associated cells with the other cells so that subsequent handover or other actions can be prepared before / in case of handover to the target cell (thus, in case of handover, TA of associated other cells has already been requested).

[0124] In embodiments, instead of or in addition to performing coordination by the target DU with the other DU(s) (for signal 707), the CU can perform coordination with the DU(s) of the other cell(s) (for signal 710), and / or the source DU can perform coordination with the DU(s) of the other cell(s) (for signal 712). The coordination of signal 707, signal 710, and / or signal 712 can include exchanging RRC, UE context, and / or measurement configurations.

[0125] For signal 711, the CU coordinates the TA configuration with the source DU by transmitting a UE context modification request to the source DU, and the source DU receives the UE context modification request from the CU. The TA configuration includes the cells for which the UE shall acquire TA before cell handover (i.e., the target cell(s) supported by the target DU and other cells requested by the target DU), and includes TA reporting configuration and corresponding uplink (UL) resources for reporting acquired TA after cell handover.

[0126] The source DU receives the UE context modification request from the CU and modifies the UE context if needed. For signal 713, the source DU provides an acknowledgement by transmitting a UE context modification response to the CU, and the CU receives the UE context modification response from the source DU.

[0127] For operation 714, the CU creates an RRC reconfiguration message that includes the TA configuration for the target cell(s) and for other cell(s) requested by the target cell(s). The TA configuration includes one or more of the following: measurement configuration for L1 cell change, configuration of the prepared target cell(s), TA acquisition configuration and trigger for the target cell(s), and measurement, TA acquisition configuration and trigger, and reporting configuration for other cells requested by the target cell(s). The TA configuration may, for example, specify the method for the UE to acquire TA. In embodiments, the TA acquisition method can be configured / triggered by the CU-CP (in coordination with the source-DU) based on L3 measurements. The TA configuration can specify other TA management options such as those described above in connection with Figure 6A and Figure 6B those described above.

[0128] For signal 715, the CU transmits the RRC reconfiguration message to the source DU using a downlink (DL) RRC message transfer, and the source DU receives the RRC reconfiguration message from the CU. As described above, the RRC reconfiguration message can include the TA configuration described above. For signal 716, the source DU transmits the RRC reconfiguration message to the UE for forwarding to the UE, and the UE receives the RRC reconfiguration message from the source DU. The UE performs reconfiguration based on the RRC reconfiguration message. For signal 717, the UE responds by transmitting an RRC reconfiguration complete message to the source DU using an uplink (UL) RRC message transfer, and the source DU receives the RRC reconfiguration complete message from the UE. For signal 718, the source DU transmits the RRC reconfiguration complete message to the CU for forwarding to the CU, and the CU receives the RRC reconfiguration complete message from the source DU. In embodiments, signals 715-718 can be described as part of a logical connection between the UE and the CU, such that the CU transmits RRC messages to the UE, and the UE receives RRC messages from the CU.

[0129] In an embodiment, the above signals and operations 701-718 can be referred to as a preparation phase. The preparation phase is followed by an execution phase.

[0130] In the execution phase, the UE provides periodic L1 measurement reports based on its configuration. Those skilled in the art will understand L1 measurements. For signal 719, the UE periodically transmits L1 measurement reports to the source DU, and the source DU receives the periodic L1 measurement reports from the UE.

[0131] For operation 720, the source DU decides whether to trigger the UE to acquire TA for the set of candidate target cells (i.e., candidate target cells for handover configured by the CU for operation 714) based on the received L1 measurement reports. The source DU can decide to trigger TA acquisition if, for example, the L1 measurements move below or above a measurement threshold or other criteria.

[0132] In an embodiment, the TA acquisition method can be configured / triggered by the CU-CP (in coordination with the source-DU) based on L3 measurements. Thus, in an embodiment, signal 719 can be L3 measurement reports transmitted to the CU, and operation 720 can be operations in the CU for deciding TA acquisition.

[0133] For operation 721, the UE acquires TA for the candidate target cell(s) using the TA acquisition method specified in the RRC reconfiguration message of operation 714. As mentioned above, the TA can be acquired based on a random access (RA) procedure (CFRA or CBRA), such as but not limited to a physical downlink control channel (PDCCH) ordered RA procedure, a UE triggered RA procedure, and / or a high layer triggered RA procedure from a network node (in addition to the L3 handover command), and so on. In an embodiment, the TA can be acquired based on a non-RA procedure method, such as but not limited to a sounding reference signal (SRS) based TA acquisition, a mechanism based on reception timing difference (such as those in LTE), and / or a UE based TA measurement (including UE based TA measurement with one TAC from the serving cell), and so on. Such RA based methods and non-RA based methods for TA acquisition are within the scope of the present disclosure. After operation 721, the UE will have TA values for the candidate target cell(s) before triggering a cell handover.

[0134] For signal 722, the UE continues L1 measurement reporting and periodically transmits L1 measurement reports to the source DU, and the source DU receives the periodic L1 measurement reports from the UE.

[0135] Based on the L1 measurement report (and prior to the cell handover), the source DU can trigger TA acquisition of other cells requested by the target cell (if not already acquired). For signal 723, the source DU transmits a TA acquisition message to the UE, and the UE receives the TA acquisition message from the source DU. For operation 724, if the target DU and the source DU are supported by different CUs, the UE initiates TA acquisition for other cells requested by the target DU or the target CU. Operation 724 for acquiring TA of other cell(s) is similar to operation 721 for acquiring TA of target cell(s). Thus, the description related to operation 721 can apply to operation 724.

[0136] Signals and operations 725-727, 31, and 32 relate to TA reporting. Such signals and operations are similar to the TA reporting aspects of Figure 6A and Figure 6B and will be described later.

[0137] For operation 728, the source DU decides whether the UE should change the serving cell. In embodiments, the source DU can decide that the UE should change the serving cell, for example, if the L1 measurement moves below or above a threshold. Once the source DU decides that the UE should handover to a cell (e.g., a target cell supported by a target DU), the source DU triggers the cell handover using a cell handover command (e.g., a MAC CE).

[0138] For signal 729, the cell handover command (e.g., a MAC CE) is transmitted by the source DU to the UE, and the UE receives the cell handover command (e.g., a MAC CE) from the source DU. In embodiments, the cell handover command can contain a TA value for the target cell. In embodiments, the cell handover command can contain a TA configuration for the UE to use during and / or after the cell handover. The source DU can have the TA configuration from receiving the RRC message for signal 715. The TA configuration for the UE to use during and / or after the cell handover is similar to the TA configuration described in connection with Figure 6A and Figure 6B These aspects of the RRC message for signal 715 can be used for the cell handover command of signal 729. Figure 6A and Figure 6B

[0139] ​In response to the cell handover command, the UE applies the RRC configuration for the target cell of the target DU indicated by the cell handover command to hand over to the target DU / target cell as a serving cell. For signal 730, to initiate communication with the target DU, the UE transmits an RRC reconfiguration complete message to the target DU using the already configured uplink (UL) resources, and the target DU receives the RRC reconfiguration complete message from the UE. (Signals 731 and 732 will be described below). For signal 733, the target DU transmits the RRC reconfiguration complete message to the CU using the UL RRC message transfer, and the CU receives the RRC reconfiguration complete message from the target DU. For signal 734, the CU transmits a UE context release command / request to the source DU to release the UE context from the source DU, and the source DU receives the UE context release command / request from the CU. The source DU releases the UE context in response to the UE context release command / request. For signal 735, the source DU transmits a UE context release complete message to the CU, and the CU receives the UE context release complete message from the source DU. For operation 736, the CU performs path switching to the target DU as a new DU supporting the serving cell.

[0140] More details will be provided below regarding various signals and operations of Figure 7A and Figure 7B .

[0141] According to aspects of the disclosure, for signals and operations 704, 708, 711, and 713, the source DU, candidate target DU(s), and the CU can coordinate with each other regarding TA acquisition for the UE of the candidate target cell(s) and regarding TA configuration. Such coordination is similar to the coordination described in Figure 6A and Figure 6B , and such aspects of Figure 6A and Figure 6B may be used for Figure 7A and Figure 7B . The source DU can inform the UE of the result of the coordination.

[0142] According to aspects of the disclosure, for signals and operations 719-721, the DU makes a decision regarding TA acquisition based on the L1 measurement report, and for operation 721, the UE acquires the TA of the one or more candidate target cells. The candidate target cells (and the candidate target DUs supporting them) can be selected based on the L1 measurements in a manner similar to that described in Figure 6A and Figure 6B , and these aspects of Figure 6A and Figure 6B may be used for Figure 7A and Figure 7B .

[0143] According to aspects of the present disclosure, after a decision is made for cell handover for operation 728, the source DU informs the UE via signal 729 how to maintain and update the TA at times after receiving the cell handover command, during the cell handover, and after the cell handover. In embodiments, the cell handover command (also referred to as the LTM trigger command) can include one or more indications similar to the indications described in Figure 6A and Figure 6B , and Figure 6A and Figure 6B , can be used to Figure 7A and Figure 7B .

[0144] According to aspects of the present disclosure, after the UE transmits the RRC reconfiguration complete message for signal 730, the UE transmits a timing advance (TA) report for signal 731 to the target DU, and the target DU receives the TA report from the UE. The target DU determines whether a TA configuration update is needed according to the TA report. For signal 732, the target DU transmits a TA configuration update to the UE, and the UE receives the TA configuration update from the target DU. The TA report and the TA configuration update, and their transmission and reception, are similar to those described in Figure 6A and Figure 6B , and Figure 6A and Figure 6B , can be used to Figure 7A and Figure 7B .

[0145] According to aspects of the present disclosure, before the source DU decides to trigger the cell handover (for operation 728), the source DU can transmit a TA report configuration and request to the UE for signal 725. The UE can transmit a timing advance (TA) report to the source DU for signal 727, and the source DU receives the TA report from the UE. In cases where the UE can not automatically transmit the TA report to the source DU, signal 727 can include a request from the source DU to the UE to have the UE obtain the TA report and transmit the TA report to the source DU. After the source DU receives the TA report from the UE, the source DU can transmit the TA report to the target DU through the CU (option 1) or directly to the target DU (option 2). In embodiments, other cells can also provide the TA report to the target DU (option 3). The TA report is similar to the TA report described in Figure 6A and Figure 6B , and Figure 6A and Figure 6B , can be used to Figure 7A and Figure 7B .

[0146] According to aspects of the present disclosure, and as described above for signal 705, the CU informs the target DU about the UE capability to be configured to acquire, store, and maintain TAs for other set of cells and the possibility to report TA information to the target DU after a cell handover. In an embodiment, for signal 705, the CU can indicate the maximum number of other cells (and / or TA values) for which the target DU or target CU can request TA acquisition, and can indicate the method used by the UE for acquiring, maintaining, and updating TA values (e.g., PDCCH order, CFRA / CBRA, SRS, DL-RS based estimation, etc.). In an embodiment, for signal 705, the CU can indicate information about measurements of other cells so that the target DU can determine whether the other cells have sufficient signal quality for TA acquisition.

[0147] According to aspects of the present disclosure, and as described above for signal 709, the target DU can inform the CU about other cell IDs (or TCI states) for TA acquisition and corresponding configuration. The configuration can include one or more of the following: TAGs (PCI-IDs and potentially corresponding TCI states); TAT states (PCI / TCI states) associated with each TAG; TA acquisition / update method and preference for TA acquisition / update; TA reporting configuration and method; potential configuration and resources for other cell measurement and TA acquisition / update resources (e.g., CBRA, CFRA, SRS, measurement gaps, etc.) (the configuration can also be acquired by the source DU or CU); and / or signal related conditions that the other cell(s) must satisfy before the UE can acquire TA for them (e.g., threshold for RSRP of the other cell(s)).

[0148] According to aspects of the present disclosure, and as described above for signal 710 and signal 712, the CU and / or source DU can accept the target DU’s request to have the UE acquire TA values for other cells proposed by the target cell, and in case of acceptance, the CU and / or source DU can coordinate with the requested other cells on resources / configuration for measurement and TA acquisition (if the target cell did not obtain for signal 707).

[0149] According to aspects of the present disclosure, and as described above for operation 714, the CU configures the UE to acquire, maintain, and update the TA value(s) for the target cell and other cell(s) requested by the target cell using RRC reconfiguration. In an embodiment, the configuration can include different configurations on how to handle TA values acquired based on UE-based timing (i.e., before the cell handover command, after receiving the cell handover command, or after the cell handover). These configurations can be similar to the configurations described in Figure 6A and Figure 6B and Figure 6Aand Figure 6B These aspects of the application can be used Figure 7A and Figure 7B .

[0150] According to aspects of the disclosure, implementation of operations from the perspective of a UE are as follows. In an embodiment, a UE establishes a connection with a controlling network node (e.g., a CU) via a serving cell, wherein the controlling network node supports at least one of a control unit - control plane (CU-CP) function or a layer 3 protocol of a radio access network; receives, from the controlling network node, an RRC message including: configuration information configured to prepare a user equipment device (UE) for at least one candidate target cell to which the UE can connect, wherein the configuration information is received prior to the UE connecting with any of the at least one candidate target cell, and further configuration information configured to prepare the user equipment device (UE) for at least one of: obtaining a timing advance (TA) of at least one other cell to which the UE can connect, or performing cell detection or measurement of the at least one other cell, in the event that the UE connects with one of the at least one candidate target cell, wherein the further configuration information is received prior to the UE connecting with any of the at least one other cell; and implementing the configuration based on the configuration information and the further configuration information.

[0151] According to aspects of the disclosure, implementation of operations from the perspective of a CU are as follows. In an embodiment, a CU establishes a connection with a user equipment device (UE) via a serving cell; determines at least one candidate target cell to which the UE can connect; receives, from at least one target network node (e.g., a target DU) that supports the at least one candidate target cell and that supports at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network, a selection of at least one other cell to which the UE can connect in the event that the UE connects with one of the at least one candidate target cell; determines a radio resource control (RRC) message including: configuration information configured to prepare the UE for the at least one candidate target cell, and further configuration information configured to prepare the UE to obtain a timing advance (TA) for the at least one other cell; and transmits, to the UE prior to the UE connecting with any of the at least one candidate target cell, the RRC message including the configuration information and the further configuration information.

[0152] According to aspects of the present disclosure, implementation of operations from the perspective of a target DU is as follows. In an embodiment, a target DU receives, from a control network node (e.g., a CU) that supports at least one of a control unit - control plane (CU-CP) function or a layer 3 protocol, a context setup request for a user equipment device (UE) and information about a capability of the UE to be configured to acquire, store, and maintain timing advance (TA) for multiple cells; selects at least one other cell in the multiple cells that the UE can connect to in a case that the UE is connected with a target cell; and transmits, to the control network node, a request for the UE to acquire TA for the at least one other cell.

[0153] According to aspects of the present disclosure, implementation of operations from the perspective of a source DU is as follows. In an embodiment, a source DU establishes a connection with a user equipment device (UE) via a serving cell, where the UE is prepared for at least one candidate target cell that the UE can connect to, and the UE is configured to acquire timing advance (TA) for at least one other cell that the UE can connect to in a case that the UE is connected with one of the at least one candidate target cell; and triggers the UE to acquire TA for the at least one other cell before the UE is connected with the one of the at least one candidate target cell.

[0154] Figure 6A And Figure 6B The signals and operations of Figure 6A and Figure 6B are merely illustrative and variations are expected within the scope of the present disclosure. For example, the signals and operations can assume one TA value per physical cell ID (PCI). In an embodiment, to cover multi-TRP (multi-transmission reception point) scenarios, a UE can be configured and required to acquire multiple Tas for a PCI, e.g., different TA values for different TCI state sets (transmission configuration indicator states). In an embodiment, the signals and operations can include other signals and operations not shown in Figure 7A and Figure 7B . In an embodiment, the signals and operations can not include each of the signals and operations shown in Figure 6A and Figure 6B . In an embodiment, the signals and operations can be implemented in a different order than shown in

[0155] Reference is now made to Figure 6A and Figure 6Bsignals and operations for TA resource and reporting management with respect to an inter-DU handover procedure. The handover procedure is merely illustrative, and it is contemplated that aspects of the disclosed technology can be applied to other procedures involving TA acquisition, such as, but not limited to, dual connectivity, carrier aggregation, mTRP, fast handover, and / or dynamic point switching, etc. Additionally, the inter-DU scenario is illustrative, and aspects of the present disclosure can also be applied to intra-DU and / or inter-CU scenarios. In cases where the source DU and target DU are supported by different CUs, the source DU can be supported by a source CU, and the target DU can be supported by a target CU, which can communicate via an Xn interface. As noted above, the terms “transmit to,” “receive from,” and “cooperate with” (and variations thereof) include communications that can or can not involve communication through one or more intermediary devices or nodes. It is intended that any description involving a DU is also a description involving a network node that supports at least one of the DU functions or Layer 2 protocols of a radio access network (RAN). Any description involving a CU is also to be considered a description involving a network node that supports at least one of the CU functions or Layer 3 protocols of a radio access network (RAN).

[0156] Figure 8A and Figure 8B the aspects of the signals and operations of Figure 8A , Figure 8B , Figure 6A and Figure 6B are the same as or similar to various signals and operations of Figure 7A and Figure 7B the signals and operations of Figure 8A and Figure 8B are intended for use with aspects of Figure 8A , Figure 8B , Figure 6A and Figure 6B .

[0157] The following paragraphs describe various signals and operations. It should be understood that the described signals can have associated operations, and the described operations can have associated signals. Thus, the described signals can also be operations, and the described operations can also be signals.

[0158] A benefit of the disclosed technology is to enhance RACH-based timing advance (TA) acquisition resource allocation and provide methods for TA reporting during mobility. The disclosed technology supports LTM as well as other mobility scenarios where a user equipment device (UE) 150 needs to acquire TA before a cell handover / cell addition.

[0159] Figure 7A and Figure 7BAspects of radio resource allocation and indication (e.g., random access resources) for early TA acquisition, update (maintenance), and reporting during mobility are shown. As used herein, the term “TA cell” refers to a cell subject to TA acquisition, and can refer to either or both of: 1) a candidate target cell for which the source DU / CU wants the UE to perform TA acquisition; or 2) a set of other cells requested by the candidate target cell for TA acquisition by the UE (e.g., because the candidate target cell can establish CA, DC, or multi-TRP, etc.). For the latter, the candidate target cell can be referred to as a “parent target cell,” and the set of other cells requested by the parent target cell(s) can be referred to as “other TA cells.”

[0160] Prior to signal 801, the UE has established a connection with a DU (i.e., a source DU) that supports a serving cell for the UE, and has established a (logical) connection with a CU that supports the DU.

[0161] For signal 801, the UE transmits an L3 measurement report to the source DU, and the source DU receives the L3 measurement report from the UE. Those skilled in the art will appreciate an L3 measurement report, which can include, for example, an average measurement sample for a reference signal of the serving cell. The L3 measurement report can indicate, for example, that the UE is approaching the edge of the cell, and thus a handover procedure should be initiated. For signal 802, the source DU forwards the L3 measurement report using an uplink (UL) RRC message transfer by transmitting the L3 measurement report to the CU, and the CU receives the L3 measurement report from the source DU. For operation 803, the CU performs a handover (HO) decision regarding whether a handover should be prepared based on the L3 measurement report. For the illustrated embodiment, the CU decides that a handover should be prepared.

[0162] Signals 804, 805, and 808 will be described below.

[0163] For signal 804, the CU transmits a UE context setup request to the target DU to prepare the target DU for the handover by establishing a UE context in the target DU. The target DU receives the UE context setup request from the CU and establishes the UE context. For signal 805, the CU and the target DU collaborate regarding TA configuration and resource validity for the UE to acquire TA for a target cell supported by the target DU. Other aspects of the collaboration of signal 805 will be described below. For signal 808, the target DU provides an acknowledgement to the UE context setup request by transmitting a UE context setup response to the CU, and the CU receives the UE context setup response from the target DU.

[0164] While one target DU is shown, there can be more than one target DU if there are multiple candidate target cells. The signals at 804, 805, and 808 can be used for each target DU and multiple candidate target cells. The following description will refer to candidate target cell(s) to indicate that there can be one candidate target cell or multiple candidate target cells, and where appropriate, will refer to target DU(s) that support the candidate target cell(s). If the target DU and the source DU are supported by different CUs, the CUs can communicate using the Xn interface. For convenience, only one CU (the CU that supports the source DU) is shown, but the disclosed techniques are intended to be applicable to the multi-CU case as well.

[0165] The signals and operations 804, 806, 807, and 809 will be described below.

[0166] Referring again to signal 804, the CU also informs the target DU(s) / target cell(s) of the UE’s capability to acquire / maintain TAs of other cells prior to cell handover and potentially report them after cell handover. The CU transmits this information to the target DU, and the target DU receives this information from the CU. For operation 806, the target DU determines, based on the information about the UE’s capability, a set of other cells / TRPs (or TCI states) that the target DU wants the UE to acquire TAs for. As mentioned above, the set of other cells is referred to as other TA cells. For signal 807, the target DU and the DU(s) that support the TA cells coordinate on TA configuration and resource availability for the UE to acquire TAs for the other TA cells. Other aspects of the coordination for signal 807 will be described later in this document. For signal 809, the target DU informs the CU of the TA configuration and resources of the other TA cells for the UE to acquire TAs for the other TA cells. The target DU transmits this information to the CU, and the CU receives this information from the target DU.

[0167] In embodiments, instead of or in addition to the coordination by the target DU with the TA cells (for signal 807), the CU can coordinate with the DU(s) that support the TA cells (for signal 810), and / or the source CU can coordinate with the DU(s) that support the TA cells (for signal 812). Any one of signals 807, 810, and 812, or a combination thereof, can be used to coordinate the TA configuration and resource availability for the UE to acquire TAs for the other TA cells. These coordinations will be described in more detail later.

[0168] For signal 811, the CU coordinates the TA configuration with the source DU by transmitting a UE context modification request to the source DU, and the source DU receives the UE context modification request from the CU. The TA configuration includes the cells for which the UE should acquire TA before cell handover (i.e., TA cells). As described above, for signal 812, the source DU can perform coordination with the DU(s) supporting other TA cells regarding TA configuration and resource availability for the UE to acquire TA for the TA cells (for signal 812). The source DU receives the UE context modification request from the CU and modifies the UE context if needed. For signal 813, the source DU provides an acknowledgement by transmitting a UE context modification response to the CU, and the CU receives the UE context modification response from the source DU. Signal 813 can also include a TA report configuration response, which can include the TA configuration and resource availability from signal 812. The source DU can transmit the TA report configuration response to the CU, and the CU can receive the TA report configuration response from the source DU.

[0169] For operation 814, the CU creates an RRC reconfiguration message that includes TA configuration for the target cell(s) and for other cell(s) requested by the target cell(s). The TA configuration includes one or more of the following: measurement configuration for L1 cell change, configuration of the prepared target cell(s), measurement and TA acquisition resource configuration and triggering for the target cell(s). The TA configuration may, for example, specify a method for the UE to acquire TA. The TA configuration can specify other TA management options such as those described above in connection with Figure 8A and Figure 8B . Figure 6A and Figure 6B These aspects can be used in Figure 6A and Figure 6B aspects.

[0170] For signal 815, the CU transmits an RRC reconfiguration message to the source DU using a downlink (DL) RRC message transfer, and the source DU receives the RRC reconfiguration message from the CU. As described above, the RRC reconfiguration message can include TA configuration for the TA cells. For signal 816, the source DU transmits the RRC reconfiguration message to the UE for forwarding to the UE, and the UE receives the RRC reconfiguration message from the source DU. The UE performs reconfiguration based on the RRC reconfiguration message. For signal 817, the UE responds by transmitting an RRC reconfiguration complete message to the source DU using an uplink (UL) RRC message transfer, and the source DU receives the RRC reconfiguration complete message from the UE. For signal 818, the source DU transmits the RRC reconfiguration complete message to the CU for forwarding to the CU, and the CU receives the RRC reconfiguration complete message from the source DU. In an embodiment, signals 815-818 can be described as part of a logical connection between the UE and the CU, such that the CU transmits RRC messages to the UE, and the UE receives RRC messages from the CU.

[0171] In an embodiment, the above-described signals and operations 801-818 can be referred to as a preparation phase. The preparation phase is followed by an execution phase.

[0172] In the execution phase, the UE provides periodic L1 measurement reports based on its configuration. Those skilled in the art will understand L1 measurements. For signal 819, the UE periodically transmits L1 measurement reports to the source DU, and the source DU receives the periodic L1 measurement reports from the UE.

[0173] For operation 820, the source DU decides whether to trigger the UE to acquire TA for the TA cells (i.e., the candidate target cell(s) and other TA cells) based on the received L1 measurement reports. The source DU can decide to trigger TA acquisition if, for example, the L1 measurements move below or above a measurement threshold, or other criteria. In the illustration, the source DU decides to trigger TA acquisition for the TA cells.

[0174] For signal 821, the source DU activates TA acquisition resources for the TA cells (i.e., the target cell(s) and other TA cells) for the UE to acquire TA.

[0175] For operation 822, the UE acquires the TA for the TA cell using the TA acquisition method specified in the RRC reconfiguration message at operation 814. As will be described below, the TA can be acquired based on a random access (RA) procedure (CFRA or CBRA), such as but not limited to a physical downlink control channel (PDCCH) ordered RA procedure, a UE triggered RA procedure, and / or a high layer triggered RA procedure from the network node (in addition to the L3 handover command), etc. In embodiments, the TA can be acquired based on a non-RA procedure method, such as but not limited to a sounding reference signal (SRS) based TA acquisition, a received timing difference based mechanism (such as those in LTE), and / or a UE based TA measurement (including UE based TA measurement with one TAC from the serving cell), etc. Such RA based methods and non-RA based methods for TA acquisition are within the scope of the present disclosure. After operation 822, the UE will have the TA value for the TA cell before triggering the cell change.

[0176] For signal 823, the UE continues the L1 measurement reporting and periodically transmits the L1 measurement report to the source DU, and the source DU receives the periodic L1 measurement report from the UE.

[0177] For operation 824, the source DU decides whether the UE should change the serving cell. In embodiments, for example, if the L1 measurement moves below or above a threshold, the source DU can decide that the UE should change the serving cell. Once the source DU decides that the UE should switch to a cell (e.g., a target cell supported by a target DU), the source DU triggers the cell change using a cell change command (e.g., a MAC CE).

[0178] For signal 825, the cell change command (e.g., a MAC CE) is transmitted by the source DU to the UE, and the UE receives the cell change command (e.g., a MAC CE) from the source DU. In embodiments, the cell change command can contain the TA value for the target cell. In embodiments, the cell change command can contain the TA configuration for the UE to use during and / or after the cell change. The TA configuration for the UE to use during and / or after the cell change is similar to the TA configuration described in connection with Figure 8A and Figure 8B . Figure 6A and Figure 6B These aspects of the cell change command of signal 825.

[0179] In response to the cell handover command, the UE applies the RRC configuration for the target cell of the target DU indicated by the cell handover command to hand over to the target DU / target cell as a serving cell. For signal 826, to initiate communication with the target DU, the UE transmits an RRC reconfiguration complete message to the target DU using the already configured uplink (UL) resources, and the target DU receives the RRC reconfiguration complete message from the UE. (Signals 827 and 828 will be described below). For signal 829, the target DU transmits the RRC reconfiguration complete message to the CU using the UL RRC message transfer, and the CU receives the RRC reconfiguration complete message from the target DU. For signal 830, the CU transmits a UE context release command to the source DU to release the UE context from the source DU, and the source DU receives the UE context release command from the CU. The source DU releases the UE context in response to the UE context release command. For signal 831, the source DU transmits a UE context release complete message to the CU, and the CU receives the UE context release complete message from the source DU. For operation 832, the source DU releases and updates TA resource reservations from other TA cells. For operation 833, the CU performs path switching to the target DU as a new DU supporting the serving cell.

[0180] More details about various signals and operations for Figure 6A and Figure 6B will be provided below.

[0181] According to aspects of the disclosure, and as described above, for signals 805, 807, 809, and 812, the signals include TA resources that include validity indications. In embodiments, the CU can configure the UE with a number of trials / tries using early TAC F RA resources (within a sliding window). After reaching the number of trials / tries using the CFRA resources, the UE stops using these CFRA resources and can inform the CU.

[0182] According to aspects of the disclosure, for signal 821, the TA resource activation message can be sent from the source DU to the DU(s) supporting other TA cell(s). In embodiments, the source DU can send the activation message to the target DU. The target DU can then send the message to its own other TA cells. Similar approach can be applied to the TA resource release message.

[0183] How to provide TA configuration to the UE and how to trigger TA acquisition are described below.

[0184] In an embodiment, for RA-based TA acquisition, the TA-associated RA configuration of a TA cell (e.g., target cell) can be provided as part of the corresponding candidate cell configuration given to the UE during the handover preparation phase (signals 815, 816). In such an embodiment, the source DU can later indicate the candidate cell for TA acquisition to the UE, e.g., within a physical downlink control channel (PDCCH) command (operation 822). Such an embodiment can be applicable to both CFRA and CBRA.

[0185] In an embodiment, the UE can be initially configured to perform RA on the RA occasion(s) of the highest measured beam (L1 or L3), and thus the CU configures the UE with a target cell ID and a RA preamble ID with a PDCCH command. For example, the CU can transmit to the UE a list of contention-free random access (CFRA) resources for TA acquisition. The CFRA resource list can include a target cell ID, a RA preamble ID, and random access occasion and RA transmission power control parameters. The CU can then transmit a PDCCH command to the UE. The UE can select a valid CFRA resource for TA acquisition in the CFRA resource list in response to the transmission. Such an embodiment can be applicable to CFRA.

[0186] In an embodiment, the UE can be configured such that the selection of a particular CFRA resource or the triggering of sending a RA for TA acquisition can provide implicit information to the TA cell about the TA cell channel quality (or quality difference relative to the serving cell) and / or supplemental information about the HO procedure (e.g., indicating the HO probability to the target cell).

[0187] In an embodiment, triggering TA acquisition for a target cell can also implicitly trigger TA acquisition for other TA cell(s) requested by the target cell. Such an embodiment can be applicable to both CFRA and CBRA.

[0188] In an embodiment, the source DU can directly include part or full random access configuration (or configuration ID) within the PDCCH command. Such an embodiment can be applicable to both CFRA and CBRA.

[0189] In an embodiment, each TA cell can broadcast the TA-associated RA configuration (e.g., as part of a SIB). The CU and source DU then send the cell ID to the UE to trigger TA acquisition. Such an embodiment can be applicable to both CFRA and CBRA.

[0190] In an embodiment, the DU supporting a TA cell can reject the request for CFRA resources and can provide CBRA configuration.

[0191] The following describes for the scenario that specific random access resources (e.g. RA preambles, random access occasions (beams) in time and frequency) are provided for TA acquisition (e.g. CFRA) targeting the random access configuration of the TA cell for which the UE performs TA acquisition.

[0192] In an embodiment, the TA cell (coordinated with the source DU or the target DU supporting the parent target cell) can provide a timer on the validity of the early TA CFRA resources for early TA acquisition.

[0193] In an embodiment, the source cell (or the parent target cell) can inform the TA cell on the required validity time of the TA resources.

[0194] In an embodiment, the provision of the configuration means that the TA resources are valid for a certain number of RA transmissions during a pre-defined time duration.

[0195] In an embodiment, the provision of the configuration requires information on when the TA resources are valid: before the UE receives the cell change command, before switching to the target cell, or after moving to the target cell. In the case of moving to the target cell afterwards, the source cell sends the resource allocation information to the target cell.

[0196] In an embodiment, the CU and the source DU (or the DU supporting the parent target cell) can send an activation or release message to the TA cell to release the early TA CFRA resources, respectively.

[0197] In an embodiment, the parent target cell informs its own other TA cells on the activation and / or release of the CFRA resources.

[0198] In an embodiment, if the CFRA resources are configured, activated and / or used for TA acquisition, the target cell can implicitly know whether to provide a RAR response for the direct to UE CFRA transmission and / or whether to transmit the TA value to the UE's serving cell. This can also be configurable per resource. The RAR reception configuration can be included in the TA related RACH configuration or PDCCH command for the UE, enabling the UE to know where to decode the RAR response. The configuration can be provided to the UE, e.g. in the candidate cell configuration, containing e.g. the common CORESET and search space configuration for receiving the RAR message from the target cell.

[0199] In an embodiment, the validity of the CFRA resource of other TA cell requested by the parent target cell depends on the validity of the requested target cell's resource. In this case, the TA acquisition / maintenance / update of the TA cell depends on the TA status of the parent target cell (e.g., the UE can be configured to reset the TA timer and not acquire / require TA for the TA cell if it stops TA acquisition, update or resets TA for the parent target cell).

[0200] In an embodiment, the provided TA resource is valid until the target cell receives a UE context release message (signal 830).

[0201] The random access configuration of a TA cell for UE's TA acquisition is described below for scenarios involving gap configuration for inter-frequency preamble transmission and / or random access response (RAR) reception. Such embodiments can be applicable to both CFRA and CBRA.

[0202] In scenarios where the RA occasion of the candidate target cell is on a different frequency (inter-frequency scenario) compared to the UE's active frequency band (e.g., BWP) of the serving cell, the UE can also be configured with a gap (e.g., TAAcquisitionGap similar to measurement gap) to perform RF tuning and preamble transmission. Similarly, if the UE is configured to receive RAR (or similar message containing TA) from the candidate target cell on a different frequency, an additional gap can need to be configured to the UE. This can be configured by the source DU (if the source DU has information of the RA configuration of the candidate target cell) or the CU.

[0203] The random access response (RAR) including TA command is described below. Such embodiments can be applicable to both CFRA and CBRA.

[0204] In an embodiment, the TA cell can send the TA value directly to the UE. The UE can then be provided with a configuration different from the traditional RA response to search / decode the transmitted TA command. In an embodiment, the TA cell can send a modified (i.e., shorter) random access response (MSG2) to the UE including the TA value (and possibly the TAT or validity of acquired TA). This MSG2 can include additional resources (possibly including resource validity timer) for UE UL transmission after handover. In an embodiment, the TA value can be transmitted as part of DCI (from the source cell or the TA cell).

[0205] The UE behavior with respect to the received RAR (TA command) is described below. Such embodiments can be applicable to both CFRA and CBRA.

[0206] In an embodiment, the UE can be configured to send ACK or NACK for RAR directly to the TA cell or the parent target cell.

[0207] In an embodiment, the UE can be configured to send ACK or NACK for other TA cell requested by the target cell directly to the target cell after cell handover.

[0208] In an embodiment, the network can provide the UE with a specific configuration (i.e., specific UL resource or feedback ID) to send ACK or NACK to the source cell.

[0209] In an embodiment, the UE can be configured to send TA information that has been acquired (or acquisition confirmation) together with the L1 measurement report (signal 823) or additional field in the MAC-CE (signal 825).

[0210] In an embodiment, the source cell can inform the TA cell of the TA acquisition status (TA value has been acquired by the UE or TA value has not been acquired by the UE) and request retransmission of the TA command (in case of failure, the source cell can request retransmission of the TA value to the target cell).

[0211] Embodiments of operations from the perspective of a UE, in accordance with aspects of the present disclosure, are as follows. In an embodiment, the UE establishes a connection with a control network node (e.g., a CU) via a serving cell, where the control network node supports at least one of: a CU-CP function of a radio access network and / or a layer 3 protocol, where the serving cell is supported by a source network node (e.g., a source DU) that supports at least one of: a distributed unit (DU) function of a radio access network or a layer 2 protocol; receives, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a set of timing advance (TA) cells, where the plurality of TA cell configurations includes a TA-associated random access (RA) configuration for TA acquisition for a particular TA cell of the plurality of TA cells, where the set of TA cells includes at least one of: a first TA cell including a candidate target cell to which the UE can connect or other TA cells requested by at least one of the candidate target cells to which the UE can connect and to which the UE can connect; and acquires a TA for the particular TA cell based on the TA-associated RA configuration and an associated TA acquisition request.

[0212] According to aspects of the present disclosure, implementations of operations from the perspective of a CU are as follows. In embodiments, a CU establishes a connection with a user equipment device (UE) via a serving cell; determines a set of timing advance cells (TA cells) for timing advance (TA) acquisition by the UE, the set of TA cells comprising at least one of: a first TA cell comprising a candidate target cell to which the UE can connect, or a further TA cell requested by at least one of the candidate target cells to which the UE can connect in case of connection with at least one of the candidate target cells; coordinates with a TA network node (e.g., a target DU) supporting the set of TA cells and at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network on a TA-associated random access (RA) configuration for the TA cells; and transmits a TA configuration comprising the TA-associated RA configuration for the TA cells to the UE for timing advance (TA) acquisition.

[0213] According to aspects of the present disclosure, implementations of operations from the perspective of a source DU are as follows. In embodiments, a source DU establishes a connection with a user equipment device (UE) via a serving cell; receives, from a control network node (e.g., a CU) supporting at least one of a control unit - control plane (CU-CP) function or a layer 3 protocol of a radio access network, information on a set of timing advance cells (TA cells) subject to timing advance (TA) acquisition by the UE, the set of TA cells comprising at least one of: a first TA cell comprising a candidate target cell to which the UE can connect, or a further TA cell requested by at least one of the candidate target cells to which the UE can connect in case of connection with at least one of the candidate target cells; coordinates with at least one TA network node (e.g., a target DU) supporting the set of TA cells and at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network on a time period corresponding to a contention free random access (CFRA) resource for the UE to acquire a TA for the TA cells prior to handover, wherein the time period comprises a start point, an end point, and a duration.

[0214] According to aspects of the present disclosure, implementations of operations from the perspective of a target DU are as follows. In embodiments, a target DU determines a further TA cell to which the UE can connect in case of connection with a first TA cell; coordinates with at least one TA network node supporting the further TA cell and at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network on a time period corresponding to a contention free random access (CFRA) resource for the UE to acquire a TA for the further TA cell prior to handover, wherein the time period comprises a start point, an end point, and a duration.

[0215] Figure 8A and Figure 8B The signals and operations described herein are merely illustrative and variations are expected to exist within the scope of the present disclosure. For example, the signals and operations can assume one TA value per physical cell ID (PCI). In embodiments, to cover multi-TRP (multi-transmission reception point) scenarios, a UE can be configured and required to acquire multiple Tas for a PCI, e.g., different TA values for different TCI state (transmission configuration indicator state) sets. In embodiments, the signals and operations can include other signals and operations not shown in Figure 8A and Figure 8B . In embodiments, the signals and operations can not include each of the signals and operations shown in Figure 8A and Figure 8B . In embodiments, the signals and operations can be implemented in a different order than the order shown in Figure 8A and Figure 8B Figure 8A Figure 8B . Such and other embodiments are expected to be within the scope of the present disclosure.

[0216] Other embodiments of the present disclosure include the following embodiments.

[0217] Example 8.1.1. A network node supporting at least one of a CU-CP function of a radio access network and / or a layer 3 protocol, the network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to: establish a connection with a user equipment device (UE) via a serving cell; determine a set of timing advance cells (TA cells) for timing advance (TA) acquisition by the UE, the set of TA cells comprising at least one of: a first TA cell comprising a candidate target cell with which the UE can connect, or a further TA cell requested by at least one of the candidate target cells in a case that the UE is connected with at least one of the candidate target cells and with which the UE can connect; coordinate, on a TA-related random access (RA) configuration for the TA cells, with a TA network node supporting at least one of a distributed unit (DU) function of the radio access network or a layer 2 protocol of the TA cells; and transmit, to the UE for TA acquisition, a TA configuration comprising the TA-related RA configuration for the TA cells.

[0218] Example 8.1.2. The network node of Example 8.1.1, wherein the TA- associated RA configurations are contention-free random access (CFRA) configurations.

[0219] Example 8.1.3. The network node of Example 8.1.2, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: coordinate, with a plurality of TA network nodes that support at least one of a set of TA cells and a distributed unit (DU) function or layer 2 protocol of a radio access network, on a plurality of TA-associated RA configurations for the set of TA cells, wherein the plurality of TA-associated RA configurations includes contention-free random access (CFRA) resources for TA acquisition; transmit, to the UE, the plurality of TA-associated RA configurations including the CFRA resources, wherein the CFRA resources enable the UE to select a CFRA resource from the CFRA resources for TA acquisition.

[0220] Example 8.1.4. The network node of Example 8.1.3, wherein coordinating with the plurality of TA cell network nodes includes a request for the CFRA resources, and wherein the plurality of TA-associated RA configurations includes a contention- based random access (CBRA) configuration, the CBRA configuration being associated with at least one of the plurality of TA network nodes that denied the request for the CFRA resources.

[0221] Example 8.1.5. A processor-implemented method comprising: establishing a connection with a user equipment device (UE) via a serving cell; determining a set of timing advance cells (TA cells) for timing advance (TA) acquisition by the UE, the set of TA cells including at least one of: a first TA cell including a candidate target cell with which the UE can connect, or a further TA cell requested by at least one of the candidate target cells in the event the UE connects with at least one of the candidate target cells and with which the UE can connect; coordinating, on TA-associated random access (RA) configurations for the TA cells, with TA network nodes that support at least one of a TA cell in the set of TA cells and a distributed unit (DU) function or layer 2 protocol of a radio access network; and transmitting, to the UE, a TA cell configuration including the TA-associated RA configurations for the TA cells for timing advance (TA) acquisition.

[0222] Example 8.1.6. The processor-implemented method of Example 8.1.5, wherein the plurality of TA-associated RA configurations is contention-free random access (CFRA) configurations.

[0223] Example 8.1.7. The processor-implemented method of Example 8.1.6, further comprising: coordinating, with a plurality of TA network nodes that support at least one of a distributed unit (DU) function or layer 2 protocol of a radio access network and a set of TA cells, on a plurality of TA-associated RA configurations for the set of TA cells, wherein the plurality of TA-associated RA configurations includes contention-free random access (CFRA) resources for TA acquisition; and transmitting, to the UE, the plurality of TA-associated RA configurations including the CFRA resources, wherein the CFRA resources enable the UE to select a CFRA resource from the CFRA resources for TA acquisition.

[0224] Example 8.1.8. The processor-implemented method of Example 8.1.7, wherein coordinating with the plurality of TA cell network nodes includes a request for the CFRA resources, and wherein the plurality of TA-associated RA configurations includes a contention-based random access (CBRA) configuration, the CBRA configuration being associated with at least one of the plurality of TA network nodes that denied the request for the CFRA resources.

[0225] Example 8.2.1. A network node that supports at least one of a distributed unit (DU) function or layer 2 protocol of a radio access network and a serving cell, the network node comprising: at least one processor; and at least one memory having instructions stored therein that, when executed by the at least one processor, cause the network node to at least: establish a connection with a user equipment device (UE) via the serving cell; receive, from a control network node that supports at least one of a control unit - control plane (CU-CP) function or layer 3 protocol of the radio access network, information about a set of timing advance cells (TA cells) subject to timing advance (TA) acquisition by the UE, the set of TA cells including at least one of: a first TA cell including a candidate target cell with which the UE can connect, or other TA cells, the other TA cells being requested by at least one of the candidate target cells and to which the UE can connect in case the UE connects with at least one of the candidate target cells; coordinating with at least one TA network node supporting the set of TA cells and at least one of a distributed unit (DU) function or layer 2 protocol of a radio access network, a time period corresponding to valid contention-free random access (CFRA) resources for the UE to acquire TA for the TA cells before handover, the time period comprising a start point, an end point, and a duration.

[0226] Example 8.2.2. The network node of example 8.2.1, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: coordinate with the at least one TA network node on a RA configuration associated with TA for the set of TA cells.

[0227] Example 8.2.3. The network node of example 8.2.2, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: specify the RA configuration associated with TA in a physical downlink control channel (PDCCH) order; and transmit the PDCCH order to the UE.

[0228] Example 8.2.4. The network node of example 8.2.2, wherein the RA configuration associated with TA is a CFRA configuration.

[0229] Example 8.2.5. The network node of example 8.2.4, wherein the RA configuration associated with TA comprises at least one of: a timer on validity of the CFRA resources corresponding to the CFRA configuration; information indicating that the CFRA resources are valid before receiving a cell handover command, before cell handover, and after cell handover.

[0230] Example 8.2.6. The network node of example 8.2.1, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: transmit to the at least one TA network node one of: an activation message configured to activate the CFRA resources; or a release message configured to release the CFRA resources.

[0231] Example 8.2.7. The network node of Example 8.2.1, wherein the CFRA resource is valid until a UE context release command is received from the at least one TA network node.

[0232] Example 8.2.8. A processor-implemented method comprising: providing, for a serving cell, at least one of a distributed unit (DU) function of a radio access network and / or a layer 2 protocol; establishing a connection with a user equipment device (UE) via the serving cell; receiving, from a control network node supporting at least one of a control unit - control plane (CU-CP) function of the radio access network or a layer 3 protocol, information about a set of timing advance cells (TA cells) subject to timing advance (TA) acquisition by the UE, the set of TA cells comprising at least one of: a first TA cell comprising a candidate target cell with which the UE can connect, or other TA cells requested by at least one of the candidate target cells in a case where the UE is connected with at least one of the candidate target cells and the UE can connect with the other TA cells; coordinating, with at least one TA network node supporting the set of TA cells and supporting at least one of a distributed unit (DU) function of the radio access network or a layer 2 protocol, a time period corresponding to a valid contention-free random access (CFRA) resource for the UE to acquire a TA for the TA cells prior to a handover, wherein the time period comprises a start point, an end point, and a duration.

[0233] Example 8.2.9. The processor-implemented method of Example 8.2.8, further comprising: coordinating with the at least one TA network node on a TA-associated RA configuration for the set of TA cells.

[0234] Example 8.2.10. The processor-implemented method of Example 8.2.9, further comprising: specifying the TA-associated RA configuration in a physical downlink control channel (PDCCH) command; and transmitting the PDCCH command to the UE.

[0235] Example 8.2.11. The processor-implemented method of Example 8.2.9, wherein the TA-associated RA configuration is a CFRA configuration.

[0236] Example 8.2.12. The processor-implemented method of Example 8.2.11, wherein the TA-associated RA configuration comprises at least one of: a timer regarding validity of CFRA resources corresponding to a CFRA configuration; information indicating that a CFRA resource is valid before receiving a cell switch command, before a cell switch, and after a cell switch.

[0237] Example 8.2.13. The processor-implemented method of Example 8.2.8, further comprising: transmitting to at least one TA network node one of: an activation message configured to activate the CFRA resource; or a release message configured to release the CFRA resource.

[0238] Example 8.2.14. The processor-implemented method of Example 8.2.8, wherein the CFRA resource is valid until receiving a UE context release command from the at least one TA network node.

[0239] Example 8.3.1. A network node supporting at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network and a first timing advance (TA) cell to which a user equipment device (UE) can connect, the network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to: determine, in a case that the UE is connected with the first TA cell, other TA cells to which the UE can connect; coordinate, with at least one TA network node supporting the other TA cells and at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network, a time period corresponding to valid contention-free random access (CFRA) resources for the UE to acquire a TA for the other TA cells before a handover, wherein the time period comprises a start point, an end point, and a duration.

[0240] Example 8.3.2. The network node of Example 8.3.1, wherein the instructions, when executed by the at least one processor, further cause the network node at least to: coordinate, with the at least one TA network node, on a RA configuration associated with the TA for the UE to acquire the TA for the other TA cells; and transmit, to a control network node supporting at least one of a control unit - control plane (CU-CP) function or a layer 3 protocol of a radio access network and connected to the UE via a serving cell, the RA configuration associated with the TA for the other TA cells and the RA configuration associated with the TA for the first TA cell.

[0241] Example 8.3.3. The network node of Example 8.3.2, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: transmit to at least one TA network node one of: an activation message configured to activate CFRA resources of the other TA cell; or a release message configured to release the CFRA resources of the other TA cell.

[0242] Example 8.3.4. The network node of Example 8.3.1, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: receive a CFRA preamble for TA acquisition; and based on the received CFRA preamble, perform one of: provide a random access response or transmit a TA value to a serving cell serving the UE.

[0243] Example 8.3.5. The network node of Example 8.3.1, wherein the instructions, when executed by the at least one processor, further cause the network node to at least: cause the first TA cell to broadcast a TA-associated RA configuration of the first TA cell.

[0244] Example 8.3.6. The network node of Example 8.3.1, wherein a validity of the CFRA resources of the other TA cell depends on a validity of the CFRA resources of the first TA cell.

[0245] Example 8.3.7. A processor-implemented method comprising: providing, for a first timing advance (TA) cell to which a user equipment device (UE) can connect, at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network; determining, in a case that the UE is connected with the first TA cell, an other TA cell to which the UE can connect; coordinating, with at least one TA network node supporting the other TA cell and supporting at least one of a distributed unit (DU) function or a layer 2 protocol of a radio access network, a time period corresponding to valid contention-free random access (CFRA) resources for the UE to acquire a TA for the other TA cell prior to a handover, wherein the time period comprises a start point, an end point, and a duration.

[0246] Example 8.3.8. The processor-implemented method of Example 8.3.7, further comprising: coordinating, with the at least one TA network node, on a TA-associated RA configuration for the UE to acquire the TA for the other TA cell; and transmitting, to a control network node supporting a control unit - control plane (CU-CP) function and / or layer 3 protocol of a radio access network and connected with the UE via a serving cell, a RA configuration associated with a TA for a first TA cell and a RA configuration associated with a TA for other TA cells.

[0247] Example 8.3.9. The processor-implemented method of example 8.3.8, further comprising: transmitting, to at least one TA network node, one of: an activation message configured to activate CFRA resources for other TA cells; or a release message configured to release CFRA resources for other TA cells.

[0248] Example 8.3.10. The processor-implemented method of example 8.3.7, further comprising: receiving a CFRA preamble for TA acquisition; and based on the received CFRA preamble, performing one of: providing a random access response or transmitting a TA value to a serving cell serving the UE.

[0249] Example 8.3.11. The processor-implemented method of example 8.3.7, further comprising: causing the first TA cell to broadcast a RA configuration associated with a TA for the first TA cell.

[0250] Example 8.3.12. The processor-implemented method of example 8.3.7, wherein a validity of CFRA resources for other TA cells depends on a validity of CFRA resources for the first TA cell.

[0251] Example 8.4.1. A user equipment apparatus comprising: means for establishing a connection with a control network node via a serving cell, the control network node supporting at least one of: a central unit control plane (CU-CP) function or a layer 3 protocol of a radio access network, wherein the serving cell is supported by a source network node supporting at least one of: a distributed unit (DU) function or a layer 2 protocol of the radio access network; means for receiving, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a set of timing advance (TA) cells, wherein the plurality of TA cell configurations comprises a TA associated random access (RA) configuration for TA acquisition for a particular TA cell of the plurality of TA cells, wherein the set of TA cells comprises at least one of: a first TA cell comprising a candidate target cell with which the UE can connect, or other TA cells, the other TA cells being requested by at least one of the candidate target cells and to which the UE can connect in case the UE connects with at least one of the candidate target cells; and a means for acquiring the TA for the specific TA cell based on the TA-associated RA configuration and the associated TA acquisition request.

[0252] Example 8.4.2. The user equipment device of Example 8.4.1, wherein the TA-associated RA configuration is specified in at least one of: a physical downlink control channel (PDCCH) order from a source network node, a medium access control element (MAC-CE), or a radio resource control (RRC) reconfiguration.

[0253] Example 8.4.3. The user equipment device of Example 8.4.1 or 8.4.2, wherein the TA-associated RA configuration comprises a contention-free random access (CFRA) configuration.

[0254] Example 8.4.4. The user equipment device of Example 8.4.3, wherein the TA-associated RA configuration comprises at least one of: a timer regarding validity of a CFRA resource corresponding to the CFRA configuration, the timer comprising at least one of: a time length, a timer trigger, a timer start point, a timer stop point, a condition for timer reset, or a condition for timer restart; information indicating that the CFRA resource is valid before receiving a cell handover command, before a cell handover, and after the cell handover; or information indicating that the CFRA resource is valid for multiple RA transmissions within a time period.

[0255] Example 8.4.5. The user equipment device of Example 8.4.3 or 8.4.4, further comprising: a means for generating at least one of: information regarding channel quality of the TA cell or information regarding handover probability by performing at least one of: selecting a specific CFRA resource of the CFRA configuration for acquiring the TA or transmitting a random access preamble of the TA-associated RA configuration for acquiring the TA.

[0256] Example 8.4.6. The user equipment device of any one of Examples 8.4.1 to 8.4.5, further comprising: a means for receiving a random access response (RAR) from a TA network node supporting at least one of: a specific TA cell and a distributed unit (DU) function or layer 2 protocol of a radio access network.

[0257] Example 8.4.7. The user equipment device of example 8.4.6, wherein the RAR comprises at least one of: an indication of validity for a TA value, a time alignment timer (TAT), an uplink resource available after the handover, a validity timer for the uplink resource, a TA command, a timing advance group (TAG) associated with the TA command, TAG information comprising a cell or TCI state ID, a TAG timer, or a validity condition for the TA command.

[0258] Example 8.4.8. The user equipment device of example 8.4.6, further comprising: means for performing at least one of the following after a cell handover to a target cell in the candidate target cells: transmitting an ACK signal or a NACK signal for a subset of other TA cells requested by the target cell to a TA network node supporting the target cell; or transmitting an ACK signal or a NACK signal for a subset of other TA cells requested by the target cell to a source network node; transmitting TA information in at least one of the following to the source network node: a L1 measurement report or a medium access control-control element (MAC-CE).

[0259] Example 8.4.9. The user equipment device of example 8.4.6, wherein a RAR reception configuration for the RAR is comprised in at least one of: a TA associated RA configuration for the UE or a PDCCH order, the RAR reception configuration enabling the UE to determine where to decode the RAR.

[0260] Example 8.4.10. The user equipment device of any one of examples 8.4.1 to 8.4.9, further comprising: means for receiving a TA command in a downlink control information (DCI).

[0261] Example 8.4.11. The user equipment device of any one of examples 8.4.1 to 8.4.10, wherein the TA associated RA configuration comprises a gap for performing RF tuning and RA preamble transmission based on at least one of: a RA occasion for a specific TA cell is on a different frequency than an active frequency band of the UE with the serving cell, or The RAR reception configuration specifies a frequency for receiving the RAR, which is a different frequency from an active frequency band of the UE with the serving cell.

[0262] Embodiments and aspects disclosed herein are examples of the present disclosure and can be embodied in various forms. For example, although certain embodiments herein are described as separate embodiments, each embodiment herein can be combined with one or more other embodiments herein. The specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure. Throughout the drawings, like reference numerals can refer to similar or identical elements.

[0263] The phrases “in one aspect,” “in an aspect,” “in various aspects,” “in some aspects,” or “in other aspects” can each refer to one or more aspects according to the present disclosure. The phrase “plurality” can refer to two or more.

[0264] The phrases “in one embodiment,” “in an embodiment,” “in various embodiments,” “in some embodiments,” or “in other embodiments” can each refer to one or more embodiments according to the present disclosure. The phrase “A or B” means “(A), (B), or (A and B).” The phrase “at least one of A, B, or C” means “(A), (B), (C), (A and B), (A and C), (B and C), or (A and B and C).”

[0265] Any of the methods, programs, algorithms, or code described herein can be converted to or expressed as a programming language or computer program. The terms "programming language" and "computer program" as used herein each include any language used to specify instructions to a computer, and include (but are not limited to) the following languages and their derivatives: assembly, basic, batch files, BCPL, C, C+, C++, Delphi, Fortran, Java, JavaScript, machine code, operating system command languages, Pascal, Perl, PL1, Python, scripting languages, Visual Basic, meta-languages that specify programs per se, and all first, second, third, fourth, fifth, or future generations of computer languages. Database and other data schemas and any other meta-languages are also included. There is no distinction between languages that are interpreted, compiled, or use a combination of compilation and interpretation methods. There is no distinction between compiled and source versions of a program. Thus, a reference to a program in which a programming language can exist in more than one state (such as source, compiled, object, or linked) is a reference to any and all such states. A reference to a program can encompass the actual instructions and / or the intent of those instructions.

[0266] While aspects of the disclosure have been shown in the drawings, the disclosure is not intended to be limited to the aspects shown, as the disclosure is intended to encompass all variations that would be permitted under the scope of the disclosure, and the specification is to be interpreted accordingly. Thus, the above description should not be interpreted as limiting, but merely as exemplifications of particular aspects. Other modifications will be posited by those skilled in the art, within the scope and spirit of the claims that follow.

Claims

1. A user equipment device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment device at least to: establish a connection with a control network node via a serving cell, the control network node supporting at least one of: a central unit control plane (CU-CP) function or layer 3 protocol of a radio access network, wherein the serving cell is supported by a source network node supporting at least one of: a distributed unit (DU) function or layer 2 protocol of the radio access network; receive, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a TA cell set, wherein the plurality of TA cell configurations comprises a TA associated random access (RA) configuration for TA acquisition for a particular TA cell of the plurality of TA cells, wherein the TA cell set comprises at least one of: a first TA cell comprising a candidate target cell to which the UE can connect, or other TA cells requested by at least one of the candidate target cells to which the UE can connect in case the UE is connected to the at least one of the candidate target cells, and to which the UE can connect; and acquire a TA for the particular TA cell based on the TA associated RA configuration and an associated TA acquisition request. 2.The user equipment device of claim 1, wherein the TA associated RA configuration is specified in at least one of: a physical downlink control channel (PDCCH) order from the source network node, a medium access control element (MAC-CE), or a radio resource control (RRC) reconfiguration. 3.The user equipment device of claim 1, wherein the TA associated RA configuration comprises a contention free random access (CFRA) configuration. 4.The user equipment device of claim 3, wherein the TA associated RA configuration comprises at least one of: a timer on validity of a CFRA resource corresponding to the CFRA configuration, the timer comprising at least one of: a time length, a timer trigger, a timer start point, a timer stop point, a condition for timer reset, or a condition for timer restart; information indicating that the CFRA resource is valid before receiving a cell handover command, before cell handover, and after cell handover; or information indicating that the CFRA resource is valid for multiple RA transmissions within a time period. 5.The user equipment device of claim 3, wherein the instructions, when executed by the at least one processor, further cause the user equipment device at least to: generating at least one of information on channel quality of a TA cell or information on handover probability by performing at least one of the following: selecting a specific CFRA resource of the CFRA configuration used for acquiring a TA or transmitting a random access preamble of the TA-associated RA configuration used for acquiring a TA.

6. The user equipment device of claim 1, wherein the instructions, when executed by the at least one processor, further cause the user equipment device at least to: receive a random access response (RAR) from a TA network node that supports at least one of a radio access network’s distributed unit (DU) function or layer 2 protocol and the specific TA cell.

7. The user equipment device of claim 6, wherein the RAR includes at least one of: a validity indicator for a TA value, a time alignment timer (TAT), an uplink resource that can be used after handover, a validity timer for the uplink resource, a TA command, a timing advance group (TAG) associated with the TA command, TAG information including a cell or TCI state ID, a TAG timer, or a validity condition for a TA command.

8. The user equipment device of claim 6, wherein the instructions, when executed by the at least one processor, further cause the user equipment device at least to: after a cell handover to a target cell of the candidate target cells, perform at least one of: transmitting, to the TA network node supporting the target cell, ACK signals or NACK signals for a subset of the other TA cells requested by the target cell; or transmit an ACK signal or NACK signal for the subset of the other TA cells requested by the target cell to the source network node; transmit TA information to the source network node in at least one of: a L1 measurement report or a medium access control-control element (MAC-CE).

9. The user equipment device of claim 6, wherein a RAR reception configuration for the RAR is included in at least one of: the TA-associated RA configuration for the UE or a PDCCH order, the RAR reception configuration enabling the UE to determine where to decode the RAR.

10. The user equipment device of claim 1, wherein the instructions, when executed by the at least one processor, further cause the user equipment device at least to: receive a TA command in downlink control information (DCI).

11. The user equipment device of claim 1, wherein the TA-associated RA configuration includes a gap for performing RF tuning and RA preamble transmission based on at least one of: a RA occasion of the specific TA cell is on a different frequency than an active frequency band of the UE with the serving cell, or a RAR reception configuration specifies a frequency for receiving a RAR, the frequency being a different frequency than the active frequency band of the UE with the serving cell.

12. A processor-implemented method in a user equipment device, the processor- implemented method comprising: establishing a connection with a control network node via a serving cell, the control network node supporting at least one of: a central unit control plane (CU-CP) function or layer 3 protocol of a radio access network, wherein the serving cell is supported by a source network node supporting at least one of: a distributed unit (DU) function or layer 2 protocol of the radio access network; receiving, from at least one of the control network node or the source network node, a plurality of timing advance (TA) cell configurations for a TA cell set, wherein the plurality of TA cell configurations comprises a TA-associated random access (RA) configuration for TA acquisition for a particular TA cell of the plurality of TA cells, wherein the TA cell set comprises at least one of: a first TA cell comprising a candidate target cell to which the UE can connect, or other TA cells requested by at least one of the candidate target cells to which the UE can connect in case the UE connects with at least one of the candidate target cells, and to which the UE can connect; and acquiring a TA for the particular TA cell based on the TA-associated RA configuration and an associated TA acquisition request.

13. The processor-implemented method of claim 12, wherein the TA-associated RA configuration is specified in at least one of: a physical downlink control channel (PDCCH) order from the source network node, a medium access control element (MAC-CE), or a radio resource control (RRC) reconfiguration.

14. The processor-implemented method of claim 12, wherein the TA-associated RA configuration comprises a contention-free random access (CFRA) configuration.

15. The processor-implemented method of claim 14, wherein the TA-associated RA configuration comprises at least one of: a timer on validity of a CFRA resource corresponding to the CFRA configuration, the timer comprising at least one of: a time length, a timer trigger, a timer start point, a timer stop point, a condition for timer reset, or a condition for timer restart; information indicating that the CFRA resource is valid before receiving a cell handover command, before cell handover, and after cell handover; or information indicating that the CFRA resource is valid for multiple RA transmissions within a time period.

16. The processor-implemented method of claim 14, further comprising: generating at least one of information on TA cell channel quality or information on handover probability by performing at least one of: selecting a particular CFRA resource of the CFRA configuration for acquiring a TA or transmitting a random access preamble of the TA-associated RA configuration to acquire a TA.

17. The processor-implemented method of claim 12, further comprising: receiving a random access response (RAR) from a TA network node supporting at least one of a specific TA cell and a distributed unit (DU) function or layer 2 protocol of a radio access network.

18. The processor- implemented method of claim 17, wherein the RAR comprises at least one of: a validity indicator for a TA value, a time alignment timer (TAT), an uplink resource available after a handover, a validity timer for the uplink resource, a TA command, a timing advance group (TAG) associated with the TA command, TAG information including a cell or TCI state ID, a TAG timer, or a validity condition for a TA command.

19. The processor- implemented method of claim 17, further comprising: after a cell handover to a target cell of the candidate target cells, performing at least one of: transmitting, to the TA network node supporting the target cell, an ACK signal or a NACK signal for a subset of the other TA cells requested by the target cell; or transmitting, to the source network node, an ACK signal or a NACK signal for the subset of the other TA cells requested by the target cell; transmitting, to the source network node, TA information in at least one of: a Ll measurement report or a medium access control - control element (MAC-CE).

20. The processor- implemented method of claim 17, wherein a RAR reception configuration for the RAR is included in at least one of: a TA-associated RA configuration for the UE or a PDCCH order, the RAR reception configuration enabling the UE to determine where to decode the RAR.

21. The processor- implemented method of claim 12, further comprising: receiving a TA command in downlink control information (DCI).

22. The processor- implemented method of claim 12, wherein the TA-associated RA configuration includes a gap for performing RF tuning and RA preamble transmission based on at least one of: a RA occasion of the specific TA cell is on a different frequency from an active band of the UE with the serving cell, or a RAR reception configuration specifies a frequency for receiving a RAR, the frequency being a different frequency from the active band of the UE with the serving cell.

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