Switching

Abstract

Embodiments of the present disclosure relate to handover. An apparatus configurable for operation as a central unit (CU), the apparatus comprising: means for enabling mobility (LTM) random access triggered by a user equipment (UE) to a lower layer of a target distributed unit (DU) using contention-free random access (CFRA) resources for early timing advance acquisition, contention-free random access (CFRA) resources are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs. An apparatus configurable for operation as a distributed unit (DU), the apparatus comprising: means for enabling mobility (LTM) random access triggered by a user equipment (UE) to a lower layer of a target distributed unit (DU) using contention-free random access (CFRA) resources for early timing advance acquisition, contention-free random access (CFRA) resources are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

Description

Technical Field

[0001] Examples of the present disclosure relate to contention-free random access. Some examples relate to using contention-free random access for handover between cells controlled by different distributed units. Background Art

[0002] Handover transfers an ongoing communication session of a User Equipment (UE) from one cell to another cell in a connected state. Handover is used to provide continuity of service to the user, especially when the user is moving.

[0003] Historically, cell level mobility has been configured at layer 3 (e.g., radio resource control RRC). The network controls UE mobility based on UE measurement reports. The trigger for completing the handover can be the network, or the user equipment with conditional handover. Conditional handover is performed by the user equipment only when the execution conditions configured by the network are met. The handover decision is made on layer 3 measurements.

[0004] Dual Active Protocol Stack (DAPS) handover allows the user equipment to initiate a handover to a target cell while maintaining a connection with the source cell by activating two protocol stacks, one for the source cell and the other for the target cell.

[0005] Lower Layer Triggered Mobility (LTM) enables handover via L1 / L2 signaling while maintaining the configuration of upper layers and / or minimizing changes in the configuration of lower layers. The network triggers LTM cell transition by sending a MAC control element to the UE.

[0006] In contention-free random access (CFRA), each UE is configured with a dedicated CFRA resource, and this resource is unique, i.e. no other UE can use this resource. This has the following advantages: there is no possibility of collision when sending preambles over PRACH based on dedicated CFRA resources. CFRA resources need to be uniquely configured for each UE (i.e. multiple UEs cannot share resources), which may lead to resource scarcity, especially in dense urban deployments. Summary of the invention

[0007] Examples are provided as claimed in the following claims according to various but not necessarily all examples.

[0008] Although the above examples and optional features of the present disclosure are described separately, it should be understood that their provision in all possible combinations and arrangements is included in the present disclosure. It should be understood that various examples of the present disclosure may include any one or all of the features described with respect to other examples of the present disclosure, and vice versa. Moreover, it should be understood that any one or more or all of the features may be implemented / included in / executable by devices, methods, and / or computer program instructions in any combination, as desired and appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Some examples will now be described with reference to the accompanying drawings, in which:

[0010] Figures 1 to 13 An example of the subject matter described herein is shown.

[0011] The drawings are not necessarily drawn to scale. For clarity and conciseness, certain features and views of the drawings may be shown schematically or scaled up. For example, the dimensions of some elements in the drawings may be enlarged relative to other elements to aid illustration. Similar reference numerals are used in the drawings to refer to similar features. For clarity, all reference numerals may not necessarily be shown in all drawings.

[0012] In the following description, a category (or set) may be referenced using a reference numeral without a subscript index (e.g., 10), and a specific instance of a category (member of a set) may be referenced using a reference numeral with a numeric type subscript index (e.g., 10_1), and a non-specific instance of a category (member of a set) may be referenced using a reference numeral with a variable type subscript index (e.g., 10_i). DETAILED DESCRIPTION

[0013] The present description relates to an apparatus 202 configured to operate as a central unit (CU), the apparatus 202 comprising: Components for enabling lower layer triggered mobility (LTM) random access by a user equipment 110 (UE) to a target distributed unit 204_2 (tDU) using contention free random access (CFRA) resources 602 for early timing advance acquisition, the contention free random access (CFRA) resources being reserved for the UE 110 for early timing advance acquisition by the UE to prevent use by a UE 110 served by a different DU 204.

[0014] The description relates to an apparatus 204 configured to operate as a distributed unit (DU), the apparatus 204 comprising: components for enabling lower layer triggered mobility (LTM) random access by a user equipment 110 (UE) to a target distributed unit (DU) using contention free random access (CFRA) resources 602 for early timing advance acquisition, the contention free random access (CFRA) resources being reserved for the UE for early timing advance acquisition by the UE 110 to prevent use by a UE 110 served by a different DU 204.

[0015] Figure 1 An example of a network 100 is shown that includes a plurality of network nodes, including a terminal node 110, an access node 120, and one or more core nodes 129. The terminal node 110 and the access node 120 communicate with each other. The one or more core nodes 129 communicate with the access node 120.

[0016] In this example, the network 100 is a wireless telecommunication network in which at least some of the terminal nodes 110 and the access nodes 120 communicate with each other using transmission / reception of radio waves.

[0017] In some examples, one or more core nodes 129 can communicate with each other. In some examples, one or more access nodes 120 can communicate with each other.

[0018] The network 100 may be a cellular network comprising a plurality of cells 122, each cell 122 being served by an access node 120. The interface between the terminal node 110 and the access nodes 120 defining the cells 122 is a wireless interface 124 in this example.

[0019] The access node 120 is a cellular radio transceiver. The terminal node 110 is a cellular radio transceiver.

[0020] In the example shown, the cellular network 100 is a 3rd Generation Partnership Project (3GPP) network, where the terminal nodes 110 are user equipments (UEs) and the access nodes 120 are base stations.

[0021] In the example shown, the network 100 is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN consists of E-UTRAN Node Bs (eNBs) 120, which provide E-UTRA user plane and control plane (RRC) protocol terminations to the UE 110. The eNBs 120 are interconnected to each other via an X2 interface 126. The eNBs are also connected to a Mobility Management Entity (MME) 129 by means of an S1 interface 128.

[0022] In other examples, the network 100 is a next generation (or new radio, NR) radio access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs) 120, which provide user plane and control plane (RRC) protocol terminations to the UE 110. The gNBs 120 are interconnected to each other via an X2 / Xn interface 126. The gNBs are also connected to an access and mobility management function (AMF) via an N2 interface 128.

[0023] A user device comprises a mobile device. Where reference is made to a user device, the reference includes and encompasses (where possible) reference to a mobile device.

[0024] Figure 2 A network according to current 3GPP specifications is shown. The network is hierarchical. It comprises a core 129 and a radio access node 120. The core 129 is connected to the radio access node 120 via an interface 128 (NG interface). The radio access node 120 is connected to user equipment via an air interface 124 (Uu). The radio access node 120 is connected to other radio access nodes 120 via an interface 126 (Xn interface).

[0025] In this example, the one or more radio access nodes 120 are logically divided into a central unit (CU) 202 and one or more distributed units (DU) 204. The DU 204 uses one or more transmit receive points (TRP) 126.

[0026] The CU 202 controls the operation of one or more DUs 204. The CU 202 terminates the F1 interface connected with the DUs 204. The CU 202 hosts higher layer protocols, for example, at least a Radio Resource Control (RRC) protocol layer and a Packet Data Convergence Protocol (PDCP) protocol layer.

[0027] The DU 204 is partially controlled by the CU 202. One DU 204 supports one or more radio transmission points 126. One TRP 126 is supported by only one DU 204. The DU 204 terminates the F1 interface connected to the CU 202. The DU 204 hosts the lower layer protocols, such as the radio link control (RLC) protocol layer, the medium access control (MAC) protocol layer, and the physical (PHY) protocol layer. The DU 204 can communicate with the RRC layer hosted by the CU 302 via a dedicated interface (e.g., the F1 interface).

[0028] The interface 127 supports information exchange between the CUs 202 of two different radio access nodes 120. The interface 127 enables interconnection of radio access nodes 120 supplied by different manufacturers. In at least some examples, data exchange through the interface 127 is between two radio access nodes 120 belonging to the same operator or between operators with an agreement.

[0029] Although the foregoing examples use a split architecture utilizing a central unit CU 202 and distributed units 204 , other examples may use other architectures.

[0030] Although the foregoing examples use a split architecture utilizing a central unit CU 202 and distributed units 204, where there is no direct DU to DU communication, other examples may use other architectures where there is direct DU to DU communication. The identity of the serving DU may then be provided directly to the target DU (without passing through the CU). A subset of the CFRA resources may then be provided directly to the serving DU by the target DU (without passing through the CU).

[0031] Although the following examples use contention-free random access as part of a lower layer triggered mobility (LTM) handover (HO), CFRA resources may be used for any random access procedure.

[0032] Lower Layer Triggered Mobility (LTM) is a lower layer procedure, ie, below Layer 3, and is performed by the DU 204 .

[0033] The user equipment 110 may for example enable low latency triggered mobility (LTM) which enables serving cell change (handover) via low latency signaling, for example below layer 3. The latency in a handover once triggered may for example be less than 10 ms.

[0034] LTM is a process in which a network node (e.g., DU 202) receives measurement reports from UE 110, and based on them, the network node controls the change of (multiple) serving cells of the UE via MAC CE. The network node prepares one or more candidate cells and provides the UE with cell change configurations for the prepared candidate cells. Then, by selecting one of the cell change configurations as the target configuration for LTM, the LTM cell transition is triggered. The trigger for the selection can be at the network node (normal handover) or at the user equipment (conditional handover). The cell change configuration can, for example, define the information used in the random access procedure 910 for connecting to the new cell. The cell change configuration can be provided as an incremental configuration (which changes relative to a reference configuration) or as a fully explicit cell change configuration.

[0035] exist Figure 3AIn the example, a random access 910 using CFRA resources 602 precedes a cell switch, for example during a preparation phase 902 of the LTM 900 before an execution phase 904. The execution phase is triggered 904. This is an early synchronization for early timing advance acquisition.

[0036] exist Figure 3B In FIG. 1 , the random access 910 using the CFRA resources 602 is during the execution phase 906 of the LTM 900 after the preparation phase 902 of the LTM 900 following the cell switch command. The execution phase is triggered 904

[0037] Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 The process is shown occurring early, for example, before a cell change is performed by the UE 110 to a cell controlled by the target distributed unit 204_2 (tDU).

[0038] The central unit 202 enables lower layer triggered mobility (LTM) random access (RA) by a user equipment (UE) to a target distributed unit (tDU) for early timing advance acquisition. The UE's LTM RA uses contention-free random access (CFRA) resources, which are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0039] Distributed unit 204_1 (sDU1) enables lower layer triggered mobility (LTM) random access by user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources, which are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0040] For early timing advance acquisition by the UE, a contention-free random access (CFRA) resource 602 may be selected from a shared pool of CFRA resources for the target DU 204_2 (tDU). The shared pool of CFRA resources is for sharing by multiple UEs served by different DUs.

[0041] The selected contention-free random access (CFRA) resource 602 for early timing advance acquisition by the UE is temporarily reserved for the UE. The reservation may be centrally recorded at the central node ( Figure 6 , Figure 7 ) and / or one or more service DUs ( Figure 4 , Figure 5 , Figure 8 ), such as UE 110 ( Figure 4 , Figure 5 )'s service DU 204_1 (sDU1) and UE ( Figure 5 , Figure 8 )’s non-service DU204_3 (sDU2).

[0042] In the figure, a lower layer triggered mobility (LTM) random access 40 by a user equipment 110 (UE) to a target distributed unit 204_2 (tDU) obtains a timing advance 42. The lower layer triggered mobility (LTM) random access 40 uses a contention free random access (CFRA) resource 602 for early timing advance acquisition by the UE 110. The contention free random access (CFRA) resource 602 is reserved for the UE 110 to be used by the UE 110 served by a different DU 204.

[0043] refer to Figure 4 , in this example, DU 204_1 (sDU1) is a serving DU and controls the cell via which UE 110 is connected.

[0044] DU 204_1 (sDU1) obtains 10 contention-free random access resources 602 (CFRAR) for early timing advance acquisition 40 by UE 110.

[0045] The CFRAR is selected from a shared pool of available contention-free random access (CFRA) resources for the target DU 204_2 (tDU). The shared pool of contention-free random access (CFRA) resources is used to share multiple UEs served by different DUs.

[0046] The CFRAR is reserved for a UE when selected. The CFRAR is dedicated to the UE at a given point in time (ie, during a certain duration).

[0047] In this example, DU 204_1 (sDU1) records 20 the CFRAR as unavailable. This reserves the CFRAR for the UE. The CFRAR is dedicated to the UE until the CFRAR becomes available.

[0048] DU 204_1 (sDU1) provides the obtained CFRAR 602 to UE 110 so that UE 110 performs early timing advance acquisition 40.

[0049] UE 110 performs early timing advance acquisition via a low layer triggered mobility (LTM) random access from the UE to a target distributed unit (DU) using CFRAR. The random access uses CFRAR.

[0050] The DU 204_1 (sDU1) receives the early acquired timing advance 42 (TA) from the target DU 204_2 (tDU) via the CU 202.

[0051] In response to receiving the early acquired timing advance 42 (TA) from the target DU 204_2, the DU 204_1 (sDU1) records 22 the CFRAR as available.

[0052] DU 204_1 (sDU1) includes a delayed handover decision component for, in response to receiving the early acquired timing advance 42 (TA), commanding UE 110 to connect to target distributed unit 204_2 (tDU) using the received early acquired timing advance 42. The cell switch command 50 sent by DU 204_1 (sDU1) to UE 110 may, for example, include the timing advance 42. The UE responds by performing access 70 using the provided timing advance.

[0053] Optionally, the sending of the cell switch command 50 by DU204_1 (sDU1) is controlled by a switch timer triggered by obtaining the CFRAR. When the CFRAR is obtained, the switch timer is started 30, and when the switch timer expires 32, the cell switch command 50 is sent. The duration of the switch timer count can be configured by the central unit (CU).

[0054] In some examples, upon receiving the cell switch command 50, a UE timer is triggered 60, and only when the UE timer expires 62, the UE 110 performs random access by sending a PRACH. The UE timer may be pre-configured or configured by the CU / gNB.

[0055] Figure 5 and Figure 6 Shows something like Figure 4 In these examples, DU 204_1 (sDU1) obtains 10 CFRAR by selecting CFRAR from a shared pool of available contention-free random access (CFRA) resources for target DU 204_2 (tDU), which is used for early timing advance acquisition 40 by UE 110. The shared pool of contention-free random access (CFRA) resources is used to share multiple UEs served by different DUs.

[0056] Previously referenced Figure 4 The local reservation of CFRAR at DU 204_1 (sDU1) is explained. It reduces the available CFRA resource pool.

[0057] Figure 5 A remote reservation of CFRAR at a DU (eg, serving DU 204_3 (sDU2)) is shown. The DU serves a different UE. Figure 6 Remote reservation of CFRAR at CU 202 is shown.

[0058] Figure 5 DU 204_1 (sDU1) serving the UE is shown, and the DU 204_1 (sDU1) is configured to select a CFRAR for early timing advance acquisition by the UE from a set of available contention-free random access (CFRA) resources for early timing advance acquisition by the UE. DU 204_1 (sDU1) provides 81, 82 the selected CFRAR to DU 204_3 (sDU2) via CU 202. DU 204_3 does not serve UE 100, but serves a different UE (not shown).

[0059] DU 204_3 (sDU2) is configured to record 84 the CFRAR as unavailable to the UE after obtaining the CFRAR.

[0060] DU 204_3 (sDU2) is configured to record 86 the CFRAR as available after receiving an indication 85 from the CU 202 that the early acquired timing advance 42 associated with the CFRAR has been received at the CU 202.

[0061] The CU 202 is configured to receive 81 CFRAR resources from sDU1 204_1 and indicate 84 the received CFRAR to different DUs.

[0062] The CFRAR for early timing advance acquisition by the UE is selected from a shared pool of available contention-free random access (CFRA) resources for the target distributed unit. The shared pool of contention-free random access (CFRA) resources is shared by a plurality of UEs served by a first group of different DUs and by the sDU1 204_1 serving the UE 110. The CU 202 may indicate 82 the received CFRAR resources to all DUs of the first group or to a subset of the DUs of the first group.

[0063] Figure 6 A DU 204_1 (sDU1) is shown, which is configured to select a CFRAR for early timing advance acquisition by the UE from a set of available contention-free random access (CFRA) resources for early timing advance acquisition by the UE. The DU 204_1 (sDU1) provides the selected CFRAR to the central unit 202.

[0064] exist Figure 6 and Figure 7In the embodiment, CU 202 is configured to reserve CFRAR for early timing advance acquisition by UE to prevent use by UEs served by different DUs. The reservation of CFRA prevents use by UEs served by different DUs, preventing user equipment (UE) other than user equipment from using CFRA resources for early timing advance acquisition by UEs for random access to the target distributed unit (DU).

[0065] The CU 202 is configured to make the CFRAR record 94 unavailable to other UEs after obtaining the CFRAR.

[0066] CU 202 is configured to make the CFRAR record 86 available to other UEs after receiving the early acquired timing advance 42 associated with the CFRAR. This confirms that the UE's random access to the target DU is complete and enables the CFRAR to be released for use by other UEs served by different DUs.

[0067] Figure 7 CU 202 is shown, which is configured to select a CFRAR for early timing advance acquisition by the UE from a set of available contention-free random access (CFRA) resources for early timing advance acquisition by the UE. CU 202 provides the selected CFRAR to sDU1 204_1 serving UE 110.

[0068] In this example, sDU1 204_1 serving UE 110 sends a request 91 to CU 202 for CFRAR, which is used for early timing advance acquisition by the UE relative to target DU 204_2 (tDU).

[0069] The CU 202 is configured to select a CFRAR from a set of contention-free random access (CFRA) resources for the target DU 204_2 (tDU) for early timing advance acquisition by the UE. The CU 202 provides the selected CFRAR 602 to the sDU1 204_1 serving the UE 110.

[0070] The CU 202 is configured to make the CFRAR record 94 unavailable to other UEs after selecting the CFRAR.

[0071] The CU 202 is configured to record 86 the CFRAR as available to other UEs after receiving the early acquired timing advance 42 associated with the CFRAR. This confirms that the random access by the UE to the target DU is complete and enables the CFRAR to be released for use by other UEs served by different DUs.

[0072] Figure 8202 manages the reservation of the CFRAR selected by the DU ( Figure 6 ), an example of CFRAR reservation management by CU 202.

[0073] After selecting CFRAR, CU 202 makes CFRAR record 94 unavailable to other UEs.

[0074] In this example, the DU, sDU2 204_3, selects a CFRAR from a set of contention-free random access (CFRA) resources for the target DU 204_2 (tDU) for early timing advance acquisition by the UE. The DU 204_3 (sDU2) provides 95 the selected CFRAR to the central unit 202. The CU 202 determines that the received CFRAR is reserved because it is recorded 94 as unavailable. The CU 202 rejects 97 the CFRAR provided by the DU 204_3 (sDU2). The CU 202 may, for example, notify the DU 204_3 (sDU2) that the provided CFRAR, which was recorded 94 as unavailable at the CU 202, is unavailable.

[0075] In these examples, the rejection 97 by CU 202 may cause DU 204_3 (sDU2) to record 20 the CFRAR as unavailable and cause DU 204_3 (sDU2) to reselect 10 the CFRAR. sDU 204_3 reselects a new CFRAR from a set of contention-free random access (CFRA) resources for the target DU 204_2 (tDU) suitable for removing the rejected CFRAR for early timing advance acquisition by the UE. DU 204_3 (sDU2) provides the newly selected CFRAR to the central unit 202.

[0076] CU 202 can therefore determine that more than one DU has selected the same CFRA resource, and thus trigger a reselection of the CFRA resource.

[0077] In this example, DU 204_3 (sDU2) reserves the rejected CFRAR for a maximum time period determined by the availability timer 98. The availability timer 98 is started when the rejected CFRAR is recorded 20 as unavailable. When the availability timer expires, the rejected CFRAR is recorded 22 as available. The availability timer may be configured by the CU 202.

[0078] The duration of the availability timer can be compared with the reference Figure 4 The durations of the described transition timers are the same or similar.

[0079] As can be appreciated from the foregoing, in at least some examples, DU 204_3 (sDU2) is configured to, in response to a signal from central unit 202 (CU), record the CFRAR as unavailable to any UE in any cell, the CFRAR being used for early timing advance acquisition by the UE relative to the target DU. DU 204_3 (sDU2) is a non-serving DU and does not serve the subject UE. Figure 5 In the example of , the signal 82 is provided from CU 202 to DU 204_3 (sDU2) with the selected CFRAR. Figure 8 In the example, the signal is provided by CU 202 as reject 97 .

[0080] FIG9 (divided into three parts) is an example of using early synchronization, and like reference numerals are used for like features in previous figures. CFRA is selected at DU 240, and management of CFRAR contention is at DU 240. Thus, FIG9 is based on Figure 3A and Figure 5 .

[0081] UE1 110_1 is served by a cell under source DU1 204_1 (sDU1). UE2 110_3 is served by a cell under source DU2 204_3 (sDU2). The target cell is under target DU 204_2 (tDU).

[0082] The target DU and the source DU may be the same entity (i.e., both the serving cell and the target cell may be under the same DU). The target DU and the source DU may be different entities (i.e., the serving cell and the target cell may be under different DUs). In the latter inter-DU scenario, the target DU and the source DU may be under the control of the same CU, or the target DU and the source DU may be under the control of different CUs.

[0083] The illustrated LTM process 900 has a preparation phase 902 and an execution phase 906. The execution phase is initiated by a trigger 904.

[0084] The random access 910 using a CFRA resource 602 selected from a set of CFRA resources occurs before the cell switch command 50 is sent, in this example during the preparation phase 902 of the LTM 900 before the execution phase 904. It occurs before the cell switch command. This is early synchronization for early timing advance acquisition.

[0085] UE1 110_1 sends L3 measurement report messages 311_1, 313_1 to CU 202 via source DU 204_1 (sDU1) (sDU1 204_1 sends UL RRC messaging message 313_1 including L3 measurement report to CU 202). CU 202 decides to use LTM and initiates LTM candidate cell preparation 702_1.

[0086] CU 202 sends a UE context setup request 302_1 to the target DU 204_2 (tDU) to prepare the target cell. Then, the target DU 204_2 (tDU) sends a UE context setup request message 321_1. This includes a set of CFRA resources for the target DU 204_2 (tDU) shared between UEs 110 of different serving DUs (sDUs). CU 202 receives the message 321_1.

[0087] CU 202 prepares 704 RRC configuration and provides 323_1, 330_1 to UE 110_1 (UE1) via source DU 204_1 (sDU1). In this example, the message 323_1 from CU 202 to sDU1 204_1 is a DL RRC messaging message 323_1. The message 330_1 from sDU1 204_1 to UE1 110_1 is a RRC reconfiguration message 330_1.

[0088] UE 110_1 (UE1) stores the configuration of (multiple) LTM candidate target cells and sends RRC reconfiguration complete messages 706_1, 708_1 to CU 202 via source DU 204_1 (sDU1). Message 706_1 from UE1 110_1 to sDU1 204_1 is an RRC reconfiguration complete message. Message 708_1 from sDU1 204_1 to CU 202 is an UL RRC messaging message 708_1.

[0089] UE 110_1 (UE1) may perform DL early synchronization and early TA acquisition with the candidate target cell(s) before receiving the LTM cell switch command 724_1.

[0090] The early timing advance (TA) acquisition steps are:

[0091] Once the source DU 204_1 (sDU1) decides to trigger PRACH signal transmission from UE1 110_1 to the target DU 204_2 (tDU), it selects 712_1 a CFRA resource 602 from a set of CFRA resources 602 .

[0092] The source DU 204_1 (sDU1) sends a CFRA resource indication 741_1 to the CU 202. This indicates the selected CFRA resource (CFRAR).

[0093] The CU 202 sends an indication 743_1 that the CFRA resource is in use to the source DU 204_3 (sDU2). This indicates the selected CFRA resource.

[0094] Source DU 204_3 (sDU2) reserves 745_1 the CFRA resource selected. The reservation of the CFRA resource by DU 204 prevents the CFRA resource from being selected by that DU, sDU2.

[0095] The process shown with respect to sDU2 may occur at other DUs.

[0096] Therefore, when the source DU decides to trigger a PRACH signal transmission from the UE to the target DU 204_2 (tDU), it selects 712a a CFRA resource 602 from a set of CFRA resources 602 for tDU, excluding the CFRA resources already reserved by the source DU.

[0097] DU 204_1 (sDU1) then sends a PDCCH order 714_1 to UE1 110_1. The PDCCH order 714_1 contains relevant configuration information (eg, preamble id, SS / PBCH index, RACH timing, etc.), including the selected UE-specific CFRA resource 602.

[0098] The source DU 204_1 (sDU1) marks the UE-specific CFRA resources 602 as 'reserved' until the UE 110_1 (UE1) completes random access using the UE-specific CFRA resources 602 or there is a release of the UE-specific CFRA resources.

[0099] Based on the received information, the UE 110_1 (UE1) triggers a random access procedure 910_1 to the target DU 204_2 (tDU), ie, a preamble transmission through a PRACH (ie, physical random access channel) of the target DU 204_2 (tDU).

[0100] After acquiring the timing advance (TA) associated with the UE 110_1 (UE1), the target DU 204_2 (tDU) provides 718_1, 720_1 the TA value for LTM switching of the target cell and other relevant information (e.g., preamble id, SS / PBCH index, RACH timing, etc.) to the source DU 204_1 (sDU1) via the CU 202. The source DU 204_1 (sDU1) can now associate the received TA value with the specific UE 110_1 (UE1).

[0101] In this example, the message 720_1 is a UE context modification request 720_1 indicating the TA value acquired for the target cell. The sDU1 204_1 responds to the UE context modification response 722_1.

[0102] The source DU 204_1 (sDU1) releases 751_1 the CFRA resource selected and reserved. Thus, when the source DU 204_1 (sDU1) subsequently decides to trigger a PRACH signal transmission from the UE to the target DU 204_2 (tDU), it selects 712a a CFRA resource 602 from a set of CFRA resources 602 that include the CFRA resources that were previously reserved and are now unreserved.

[0103] In response to receiving the TA, CU 202 sends an indication 753_1 to other source DUs, such as DU 204_3 (sDU2), that CFRA resources should now be available. Source DU 204_3 (sDU2) records 755_1 the indicated CFRA resources as available.

[0104] The execution phase is triggered 904_1 by a lower layer measurement report 720_1 sent from UE1 110_1 to serving DU 204_1 (sDU1). UE 110_1 (UE1) performs L1 measurements on the configured LTM candidate target cell(s) and sends a lower layer measurement report 904_1 to source DU 204_1 (sDU1).

[0105] The source DU 204_1 (sDU1) decides 722_1 to perform an LTM cell switch to the target cell (tDU204_2) and sends an LTM command 724_1 (MACCE) to the UE 110_1 (UE1), thereby triggering the LTM cell switch at the UE 110_1 (UE1). The LTM command 724_1 includes the TA value of the target cell.

[0106] UE 110_1 (UE1) switches to the configuration of the LTM candidate target cell (tDU204_2) and accesses 726_1 the target cell. If necessary (i.e., if timing advance is not available / valid), it performs a random access (not shown). UE 110_1 (UE1) may use RRC Reconfiguration Complete to indicate the successful completion of the LTM cell to target cell transition.

[0107] UE2 110_3 sends L3 measurement report messages 311_3, 313_3 to CU 202 via source DU 204_3 (sDU2) (sDU2 204_3 sends UL RRC messaging message 313_3 including L3 measurement report to CU 202). CU 202 decides to use LTM and initiates LTM candidate cell preparation 702_3.

[0108] The CU 202 sends a UE context establishment request 302_3 to the target DU 204_2 (tDU) to prepare the target cell.

[0109] The target DU 204_2 (tDU) then sends a UE context setup response message 321_3. This includes a set of CFRA resources for the target DU 204_2 (tDU) shared between UEs 110 of different serving DUs (sDUs).

[0110] CU 202 receives message 321_3

[0111] CU 202 prepares 704 the RRC configuration and provides 323_3, 330_3 it to UE110_3 (UE2) via source DU 204_3 (sDU2). In this example, the message 323_3 from CU 202 to sDU2 204_3 is a DL RRC messaging message 323_3. The message 330_3 from sDU2 204_3 to UE2 110_3 is an RRC reconfiguration message 330_3.

[0112] UE 110_3 (UE2) stores the configuration of (multiple) LTM candidate target cells and sends RRC reconfiguration complete messages 706_3, 708_3 to CU202 via source DU 204_3 (sDU2). Message 706_3 from UE2 110_3 to sDU2 204_3 is an RRC reconfiguration complete message. Message 708_3 from sDU2 204_3 to CU 202 is an UL RRC messaging message 708_3.

[0113] UE 110_3 (UE2) may perform DL early synchronization and early TA acquisition with the candidate target cell(s) before receiving the LTM cell switch command 724_3.

[0114] The early timing advance (TA) acquisition steps are:

[0115] Once the source DU 204_3 (sDU2) decides to trigger PRACH signal transmission from UE1 110_3 to the target DU 204_2 (tDU), it selects 712_3 a CFRA resource 602 from a set of available CFRA resources 602 .

[0116] The source DU 204_3 (sDU2) sends a CFRA resource indication 741_3 to the CU 202. This indicates the selected CFRA resource.

[0117] The CU 202 sends an indication 743_3 that the CFRA resource is in use to the source DU 204_1 (sDU1). This indicates the selected CFRA resource.

[0118] Source DU 204_1 (sDU1) reserves 745_3 the selected CFRA resource. The reservation of the CFRA resource by DU 204 prevents the CFRA resource from being selected by the DU.

[0119] Therefore, when the source DU decides to trigger a PRACH signal transmission from the UE to the target DU 204_2 (tDU), it selects 712 a CFRA resource 602 from a set of CFRA resources 602 for tDU, excluding the CFRA resources already reserved by the source DU.

[0120] The source DU 204_3 (sDU2) then sends a PDCCH order 714_3 to the UE2 110_3. The PDCCH order 714_3 contains relevant configuration information (eg, preamble id, SS / PBCH index, RACH timing, etc.), including the selected UE-specific CFRA resource 602.

[0121] The source DU 204_3 (sDU2) marks the UE-specific CFRA resources as “reserved” until the UE 110_3 (UE2) completes random access using the UE-specific CFRA resources 602 or there is a release of the UE-specific CFRA resources 602.

[0122] Based on the received information, the UE 110_3 (UE2) triggers a random access procedure 910_3 to the target DU 204_2 (tDU), ie, a preamble transmission on a PRACH (ie, physical random access channel) of the target DU 204_2 (tDU).

[0123] After acquiring the timing advance (TA) related to UE 110_3 (UE2), the target DU 204_2 (tDU) provides 718_3, 720_3 the TA value for LTM switching of the target cell and other relevant information (e.g., preamble id, SS / PBCH index, RACH opportunity, etc.) to the source DU 204_3 (sDU2) via CU202. The source DU 204_3 (sDU2) can now associate the received TA value with the specific UE 110_3 (UE2). In this example, the message 720_3 is a UE context modification request 720_3 indicating the TA value acquired for the target cell. The sDU2 204_3 responds to the UE context modification 722_3.

[0124] The source DU 204_3 (sDU2) releases 751_3 the CFRA resources selected and reserved. Therefore, when the source DU 204_3 (sDU2) subsequently decides to trigger a PRACH signal transmission from the UE to the target DU 204_2 (tDU), it selects 712_3 a CFRA resource 602 from a set of CFRA resources 602 that includes the CFRA resources that were previously reserved and are now unreserved.

[0125] In response to receiving the TA, the CU 202 sends an indication 753_3 to other source DUs (eg, DU 204_1 (sDU1)) that CFRA resources should now be available. The source DU 204_1 (sDU1) records 755_3 the indicated CFRA resources as available.

[0126] The execution phase is triggered 904_3 by a lower layer measurement report 720_3 sent from UE2 110_3 to serving DU 204_3 (sDU2). UE 110_3 (UE2) performs L1 measurements on the configured LTM candidate target cell(s) and sends a lower layer measurement report 904_3 to source DU 204_3 (sDU2).

[0127] The source DU 204_3 (sDU2) decides 722_3 to perform an LTM cell switch to the target cell (tDU 204_2) and sends an LTM command 724_3 (MAC CE) to the UE 110_3 (UE2) triggering the LTM cell switch at the UE 110_3 (UE2).

[0128] UE 110_3 (UE2) switches to the configuration of the LTM candidate target cell (tDU 204_2) and accesses 726_3 the target cell. If required (ie, if timing advance is not available / valid), it performs a random access (not shown).

[0129] UE 110_3 (UE2) may use RRC Reconfiguration Complete to indicate successful completion of the LTM cell switch to the target cell.

[0130] The above process avoids PRACH collisions in the case where CFRA resources are shared between UEs connected to different DUs. This prevents different UEs from using the same source DU of CFRA resources, which may cause PRACH collisions.

[0131] CFRA resources are configured per DU per UE. This prevents CFRA resources from being shared by UEs belonging to different source DUs.

[0132] This process avoids the CFRA resource starvation problem in dense environments, enables low latency handover by avoiding RACH collisions (HO failures), and enables shared CFRA resources for early TA acquisition.

[0133] Fig.10 is an example of using early synchronization, and similar reference numerals are used for similar features in previous figures. CFRAR is selected at CU 202, and CFRAR contention is managed at CU 202. Therefore, Fig.10 based on Figure 3A and Figure 7 .

[0134] The preparation phase previously shown in FIG. 9 (1 / 3) is the same and is not reproduced. The execution phase shown and described in FIG. 9 (1 / 3) is the same.

[0135] The synchronization phases are different, as shown by the dashed boxes.

[0136] The early timing advance (TA) acquisition steps are:

[0137] Once the source DU 204_1 (sDU1) decides to trigger PRACH signal transmission from UE1 110_1 to the target DU 204_2 (tDU), it sends a CFRA resource request 761_1 to the CU 202.

[0138] The CU allocates 763_1 of CFRA resources 602 from a set of available CFRA resources 602 for tDU.

[0139] The CU sends a CFRA resource response 765_1 to the source DU 204_1 (sDU1), which indicates the CFRA resources 602 allocated to the UE from a set of CFRA resources 602 for the tDU.

[0140] The source DU 204_1 (sDU1) then sends a PDCCH order 714_1 to the UE1 110_1. The PDCCH order 714_1 contains relevant configuration information (eg, preamble id, SS / PBCH index, RACH timing, etc.), including the selected UE-specific CFRA resource 602.

[0141] Optionally, the source DU 204_1 (sDU1) marks the UE-specific CFRA resources 602 as “reserved” until the UE 110_1 (UE1) completes random access using the UE-specific CFRA resources 602 or there is a release of the UE-specific CFRA resources.

[0142] Based on the received information, the UE 110_1 (UE1) triggers a random access procedure 910_1 to the target DU 204_2 (tDU), ie, a preamble transmission through a PRACH (ie, physical random access channel) of the target DU 204_2 (tDU).

[0143] After acquiring the timing advance (TA) related to the UE 110_1 (UE1), the target DU 204_2 (tDU) provides 718_1, 720_1 the TA value for LTM switching of the target cell and other relevant information (e.g., preamble id, SS / PBCH index, RACH timing, etc.) to the source DU 204_1 (sDU1) via the CU 202. The source DU 204_1 (sDU1) can now associate the received TA value with the specific UE 110_1 (UE1).

[0144] In this example, the message 720_1 is a UE context modification request 720_1 indicating an acquired TA value for the target cell. sDU1 204_1 is responsive to the UE context modification.

[0145] The early timing advance (TA) acquisition steps are:

[0146] Once the source DU 204_3 (sDU2) decides to trigger PRACH signal transmission from UE1 110_3 to the target DU 204_2 (tDU), it sends a CFRA resource request 761_3 to the CU 202.

[0147] The CU 202 allocates 763_3 of CFRA resources 602 from a set of available CFRA resources 602 for tDU.

[0148] The CU 202 sends a CFRA resource response 765_3 to the source DU 204_3 (sDU2), which indicates the CFRA resources 602 allocated to the UE 110_3 from a set of CFRA resources 602 for the tDU.

[0149] The source DU 204_3 (sDU2) then sends a PDCCH order 714_3 to the UE1 110_3. The PDCCH order 714_3 contains relevant configuration information (eg, preamble id, SS / PBCH index, RACH timing, etc.), including the selected UE-specific CFRA resource 602.

[0150] Optionally, the source DU 204_3 (sDU2) marks the UE-specific CFRA resources 602 as “reserved” until the UE 110_3 (UE2) completes random access using the UE-specific CFRA resources 602 or there is a release of the UE-specific CFRA resources.

[0151] Based on the received information, UE 110_3 (UE2) triggers a random access procedure 910_3 to the target DU 204_2 (tDU), ie, preamble transmission through the PRACH (ie, physical random access channel) of the target DU 204_2 (tDU).

[0152] After acquiring the timing advance (TA) related to the UE 110_3 (UE2), the target DU 204_2 (tDU) provides 718_3, 720_3 the TA value for LTM switching of the target cell and other relevant information (e.g., preamble id, SS / PBCH index, RACH timing, etc.) to the source DU 204_3 (sDU2) via the CU 202. The source DU 204_3 (sDU2) can now associate the received TA value with the specific UE 110_3 (UE2).

[0153] In this example, the message 720_3 is a UE context request 720_3 indicating the acquired TA value for the target cell. sDU1 204_3 is responsive to the UE context modification 722_3.

[0154] Fig.11AAn example of a method 500 is shown. The method 500 may be performed, for example, by a distributed unit 204 (DU) operating as a target distributed unit (tDU). The method 500 includes, at block 502, enabling a lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) using contention free random access (CFRA) resources for early timing advance acquisition, the contention free random access (CFRA) resources being reserved for the UE for early timing advance acquisition to prevent use by UEs served by a different DU.

[0155] Fig. 11B An example of a method 510 is shown. The method 510 may be performed, for example, by a central unit 202 (CU) in communication with a target distributed unit (tDU). The method 510 includes, at block 512, enabling lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) using contention free random access (CFRA) resources for early timing advance acquisition, the contention free random access (CFRA) resources being reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0156] Fig.12 An example of a controller 400 suitable for use in an apparatus such as network apparatus 202, 204 is shown. Implementation of controller 400 may be as a controller circuit. Controller 400 may be implemented solely in hardware, with certain aspects of software including separate firmware, or may be a combination of hardware and software (including firmware).

[0157] like Fig.12 As shown, the controller 400 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 406 in a general or special purpose processor 402, which instructions may be stored on a computer-readable storage medium (disk, memory, etc.) for execution by such processor 402.

[0158] The processor 402 is configured to read from and write to the memory 404. The processor 402 may also include an output interface and an input interface, through which the processor 402 outputs data and / or commands, and through which data and / or commands are input to the processor 402.

[0159] The memory 404 stores a computer program 406, which includes computer program instructions (computer program code) that control the operation of the apparatus 202, 204 when loaded into the processor 402. The computer program instructions of the computer program 406 provide logic and routines that enable the apparatus to perform the methods shown in the drawings. The processor 402 can load and execute the computer program 406 by reading the memory 404.

[0160] The device 202 (central unit) comprises: at least one processor 402; and at least one memory 404 comprising computer program code, The at least one memory stores instructions that, when executed by the at least one processor 402, cause the apparatus 202 to at least: Enable lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources, which are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0161] The device 204 (distributed unit) comprises: at least one processor 402; and at least one memory 404 comprising computer program code, The at least one memory stores instructions that, when executed by the at least one processor 402, cause the apparatus 204 to at least: Enable lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) using contention free random access (CFRA) resources for early timing advance acquisition, and the contention free random access (CFRA) resources are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0162] like Fig.13 As shown, the computer program 406 may arrive at the apparatus 202, 204 via any suitable delivery mechanism 408. The delivery mechanism 408 may be, for example, a machine-readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a recording medium such as a compact disk read-only memory (CD-ROM) or a digital versatile disk (DVD) or a solid-state memory, an article of manufacture including or tangibly embodying the computer program 406. The delivery mechanism may be a signal configured to reliably transmit the computer program 406. The apparatus 202, 204 may propagate or transmit the computer program 406 as a computer data signal.

[0163] Computer program instructions for causing the device 202 as a central unit to at least perform the following or for at least performing the following: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition to prevent use by UEs served by different DUs.

[0164] Computer program instructions for causing the apparatus 204 to perform at least the following as a distributed unit or for performing at least the following: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0165] The computer program instructions may be included in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some, but not necessarily all, examples, the computer program instructions may be distributed over more than one computer program.

[0166] Although memory 404 is shown as a single component / circuit, it may be implemented as one or more separate components / circuit(s), some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cache storage.

[0167] Although processor 402 is shown as a single component / circuit, it may be implemented as one or more separate components / circuit, some or all of which may be integrated / removable.Processor 402 may be a single-core or multi-core processor.

[0168] According to some examples, a set of CFRA resources of a target cell belonging to a target DU is shared by UEs in different source cells belonging to a first source DU and a second source DU, however, one CFRA resource from the set of CFRA resources is used by a UE in a cell belonging to the first source DU or the second source DU at a given point in time.

[0169] The above solution can be implemented through the following two alternative solutions.

[0170] Alternative 1:

[0171] According to some examples, a first source DU selects a CFRA resource from a set of CFRA resources to be used by a UE in a cell belonging to the first source DU, and the first source DU provides the CFRA resource selected from the set of CFRA resources to a second source DU via a CU. Upon receiving the CFRA resource selected from the set of CFRA resources, the second source DU determines that the CFRA resource from the set of CFRA resources is not available for use by a UE in a cell belonging to the second source DU.

[0172] According to some examples, a CFRA resource selected from a set of CFRA resources is signaled by a first source DU to a CU and / or by a CU to a second source DU, thereby reusing a UE context modification procedure.

[0173] According to some examples, a CFRA resource selected from a set of CFRA resources is signaled by a first source DU to a CU using a new unidirectional signaling procedure and / or by a CU to a second source DU.

[0174] According to some examples, a timer "T" is defined on a per-UE basis for a first source DU, and a PDCCH command for the UE acquired by the TA is triggered when the timer "T" expires, and the timer "T" is triggered based on selecting a CFRA resource from a set of CFRA resources for the UE.

[0175] According to some examples, the CU indicates CFRA resources from a set of CFRA resources to a second source DU upon determining that a TA value of the UE based on the CFRA resources from the set of CFRA resources has been acquired by the target DU and provided to the first set of source DUs.

[0176] According to some examples, after receiving the indication from the CU, the second source DU determines that a CFRA resource from a set of CFRA resources is available for use by a UE in a cell belonging to the second source DU.

[0177] According to some examples, the first source DU, after receiving the TA value of the UE for which the CFRA resources are selected, determines that the CFRA resources in the set of CFRA resources are available for use by other UEs in the cell belonging to the first source DU.

[0178] According to some examples, a timer 'T' is defined for the second source DU on each CFRA resource in the CFRA resource set. Upon receiving an indication from the first source DU that the first CFRA resource has been selected, the timer 'T' of the first CFRA resource from the CFRA resource set is triggered, and upon expiration of the timer 'T', the second source DU determines that the first CFRA resource is available.

[0179] According to some examples, a timer "T" is defined for the UE, and the timer "T" is triggered when a PDCCH command is received, and only when the timer "T" expires, the UE performs random access by sending a PRACH. The timer "T" may be pre-configured or configured by the CU / gNB.

[0180] According to some examples, if the CU determines that more than one source DU has selected the same CFRA resource, the CU sends an indication to the corresponding source DUs to trigger reselection of the CFRA resource.

[0181] According to some examples, the target DU sends the detected preamble and the acquired TA value to the CU via a unidirectional signaling process. Based on the information available at the CU, the CU forwards the TA value to the relevant source DU.

[0182] In summary: Step 1: During the preparation process, the target DU decides to configure a shared CFRA resource pool between UEs of different source DUs. Step 2: When source DU1 selects a CFRA resource, the selected CFRA resource is indicated to other DUs via the CU. In one case, the CU indicates the selected CFRA resource to all DUs that share the selected CFRA resource. In other cases, the CU indicates the selected CFRA resource to a subset of DUs that share the selected CFRA resource. Step 3: All other DUs mark the selected CFRA resources as “reserved”. Step 4: Once the TA is acquired and indicated to the source DU, the CU indicates the selected CFRA resources to other DUs. Step 5: All other DUs mark the selected CFRA resources as “available”.

[0183] Alternative 2:

[0184] According to some examples, the first source DU sends a request to the CU to select and provide CFRA resources from a set of CFRA resources for use by a UE in a cell belonging to the first source DU, and the CU sends a response to the first source DU to provide the CFRA resources selected from the set of CFRA resources. When selecting the CFRA resources from the set of CFRA resources, the CU determines that the CFRA resources from the set of CFRA resources are not available for use by a UE in a cell belonging to the first source DU or the second source DU.

[0185] According to some examples, as part of the UE context modification procedure, the first source DU sends a request to the CU to select and provide a CFRA resource from a set of CFRA resources.

[0186] According to some examples, a new request and response process is defined such that a first source DU sends a request to a CU to select and provide a CFRA resource from a set of CFRA resources and receives a selected CFRA resource from the set of CFRA resources.

[0187] According to some examples, the CU rejects a request from the first source DU to select and provide CFRA resources from a set of CFRA resources for use by a UE in a cell belonging to the first source DU. In some cases, in the case of rejection, a cause value is also indicated as part of the response message. One possible cause value may be "unavailable CFRA resources from a set of CFRA resources".

[0188] In summary: Step 1: During the preparation process, the target DU decides to configure a shared CFRA resource pool between UEs of different source DUs. Step 2: When the source DU1 needs to initiate early TA acquisition, it sends a CFRA resource request to the CU. Step 3: The CU selects a CFRA resource from the CFRA resource pool. Step 4: CU indicates the selected CFRA resources to the source DU1.

[0189] Further embodiments of the present disclosure are provided by the following examples:

[0190] Example 1. An apparatus configurable to operate as a central unit (CU), the apparatus comprising: Components for enabling lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0191] Example 2. The apparatus of Example 1, comprising: means for causing the contention-free random access (CFRA) resources used for early timing advance acquisition by the UE to be reserved to prevent use by UEs served by different DUs.

[0192] Example 3. An apparatus according to Example 1 or 2, wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by UEs served by the different DUs, and The reservation of the contention-free random access (CFRA) resources for early timing advance acquisition by the UE and preventing use by the UE served by the different DU prevents user equipment (UE) other than the user equipment from randomly accessing the target distributed unit (DU) using the contention-free random access (CFRA) resources.

[0193] Example 4. The apparatus of example 1, 2 or 3, comprising: Before a cell is changed by the UE to a cell controlled by the target distributed unit (DU), means for: obtaining the CFRA resource for early timing advance acquisition for the UE, so that the CFRA resource is reserved to prevent use by other UEs served by the different DUs, receiving a confirmation of completion of random access by the UE to the target DU, The CFRA resources are released for use by other UEs served by the different DU.

[0194] Example 5. The apparatus according to any of the preceding examples, comprising: means for preparing the target DU to become a serving DU of the UE via a contention free random access (CFRA) connection using the contention free random access (CFRA) resource reserved for the UE.

[0195] Example 6. The apparatus according to any of the preceding examples, comprising: Means for enabling early LTM synchronization for early timing advance acquisition during a prepare phase of the LTM prior to an execute phase of the LTM.

[0196] Example 7. The apparatus according to any of the preceding examples, comprising: A component for recording a contention-free random access (CFRA) resource as unavailable; means for notifying the distributed units that a contention free random access (CFRA) resource recorded as unavailable is unavailable, and / or Means for rejecting a request for contention free random access (CFRA) resources from a distributed unit if the requested contention free random access (CFRA) resources are recorded as unavailable.

[0197] Example 8. The apparatus according to any of the preceding examples, comprising: means for selecting said CFRA resource; means for providing the selected CFRA resources to the UE via a DU serving the UE.

[0198] Example 9. The apparatus according to any of the preceding examples, comprising: means for receiving the CFRA resources from a DU serving the UE; Means for indicating the received CFRA resources to the different DUs.

[0199] Example 10. The apparatus of Example 9, comprising: wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources for the target distributed unit, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by the DU serving the UE and UEs served by a first group of different DUs, and the apparatus comprises: means for indicating the received CFRA resources to all the DUs of the first group.

[0200] Example 11. The apparatus of Example 9, comprising: wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources for the target distributed unit, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by the DU serving the UE and UEs served by a first group of different DUs, and the apparatus comprises: Means for indicating the received CFRA resources to a subset of the DUs of the first group.

[0201] Example 12. The apparatus of Example 9, 10 or 11, comprising: means for determining that more than one DU has selected the same said CFRA resource; Means for sending an indication to the DU to trigger reselection of CFRA resources.

[0202] Example 13. The apparatus of any one of Examples 9 to 12, comprising: means for reserving the CFRA resources for the UE for a maximum period of time; and Means for indicating said maximum time period to the DU.

[0203] Example 14. A method comprising: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition to prevent use by UEs served by different DUs.

[0204] Example 15. A computer program comprising instructions that, when executed by one or more processors of a device, enable the device to perform: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition to prevent use by UEs served by different DUs.

[0205] Example 16. An apparatus configurable to operate as a distributed unit (DU), the apparatus comprising: Components for enabling lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0206] Example 17. An apparatus according to Example 16, comprising: a component for providing the contention-free random access (CFRA) resource to the UE for early timing advance acquisition by the UE, the contention-free random access (CFRA) resource being reserved for the UE to prevent use by UEs served by different DUs.

[0207] Example 18. The apparatus according to Example 16 or 17 comprises: an early timing advance acquisition component for communicating with the UE to enable lower layer triggered mobility (LTM) random access of the target distributed unit (DU) by the UE using the contention-free random access (CFRA) resources for early timing advance acquisition.

[0208] Example 19. The apparatus of Example 16, 17 or 18, comprising: means for receiving, from the target distribution unit (DU) via a control unit, a timing advance for early acquisition of the UE and the target distribution unit (DU).

[0209] Example 20. The apparatus of any one of Examples 16 to 19, comprising a delayed handover decision component for commanding the UE to connect to the target distributed unit (DU) using the received early acquired timing advance.

[0210] Example 21. The apparatus of Example 20, wherein the medium access command for commanding the UE to connect to the target distributed unit (DU) using the received early acquired timing advance includes the received early acquired timing advance.

[0211] Example 22. The apparatus of any one of Examples 16 to 21, comprising: means for obtaining the contention-free random access (CFRA) resources for early timing advance acquisition by the UE; means for providing to the UE the obtained contention free random access (CFRA) resources for early timing advance acquisition by the UE; A component for recording a contention-free random access (CFRA) resource as unavailable; means for receiving an early acquired timing advance; means for recording the contention-free random access (CFRA) resource as available; A component for sending a cell switching command to the UE.

[0212] Example 23. The apparatus of Example 22, wherein the means for sending a cell switch command is controlled by a switch timer, the switch timer being triggered by obtaining the contention free random access (CFRA) resource.

[0213] Example 24. The apparatus of Example 23, wherein the conversion timer is configured by a central unit (CU).

[0214] Example 25. The apparatus of any one of Examples 16 to 24, comprising:

[0215] Means for recording, in response to a signal from a central unit (CU), a contention free random access (CFRA) resource used for early timing advance acquisition by the UE as unavailable to any UE in any cell.

[0216] Example 26. The apparatus of any one of Examples 16 to 25, comprising: Means for recording contention-free random access (CFRA) resources for early timing advance acquisition by the UE as available to any UE in any cell in response to a signal from a CU or expiration of an availability timer.

[0217] Example 27. The apparatus of Example 26, wherein the availability timer is configured by a central unit.

[0218] Example 28. The apparatus of any one of Examples 16 to 27, comprising: Means for selecting the contention free random access (CFRA) resource for early timing advance acquisition by the UE from a set of contention free random access (CFRA) resources for early timing advance acquisition by the UE. Means for providing said selected contention free random access (CFRA) resource to a central unit.

[0219] Example 29. The apparatus of any one of Examples 16 to 28, comprising: means for recording the contention free random access (CFRA) resource as unavailable to other UEs in the same cell after obtaining the contention free random access (CFRA) resource for early timing advance acquisition by the UE; Means for recording the contention-free random access (CFRA) resources used for early timing advance acquisition by the UE as available to other UEs in the same cell after receiving the early acquired timing advance.

[0220] Example 30. The apparatus of any one of Examples 16 to 29, comprising: Means for receiving said contention free random access (CFRA) resources for early timing advance from a central unit.

[0221] Example 31. A method at a distributed unit (DU), comprising: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0222] Example 32. A computer program comprising instructions that, when executed by one or more processors of a device, cause the device to perform as a distributed unit: A lower layer triggered mobility (LTM) random access is enabled by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

[0223] References to "computer-readable storage medium," "computer program product," "tangibly embodied computer program," etc. or "controller," "computer," "processor," etc. should be understood to include not only computers having different architectures (such as single / multi-processor architectures and sequential (von Neumann) / parallel architectures), but also special-purpose circuits (such as field-programmable gate arrays (FPGAs), application-specific circuits (ASICs), signal processing devices, and other processing circuits). References to computer programs, instructions, code, etc. should be understood to include software for a programmable processor or firmware, e.g., the programmable content of a hardware device, whether instructions for a processor or configuration settings for a fixed-function device, gate array, or programmable logic device, etc.

[0224] As used in this application, the term "circuitry" may refer to one or more or all of the following: (a) hardware circuit implementation only (e.g., implementation only in analog and / or digital circuits), and (b) a combination of hardware circuitry and software such as (where applicable): (i) a combination of analog and / or digital hardware circuits and software / firmware, and (ii) any portion of a hardware processor(s) or multiple memories having software (including digital signal processor(s)), software, and operating together to enable a device such as a mobile phone or server to perform various functions, and (c) Hardware circuit(s) and processor(s) that require software (e.g., firmware) for operation, such as microprocessor(s) or portions of microprocessor(s), but the software may not be present when not needed for operation.

[0225] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely hardware circuits or processors and their accompanying software and / or firmware. For example, and if applicable to the particular claim element, the term circuitry also covers a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, cellular network device, or other computing or network device.

[0226] The blocks shown in the accompanying drawings may represent steps in a method and / or code sections in a computer program 406. The description of a particular order of blocks does not necessarily imply that the blocks have a required or preferred order, and the order and arrangement of the blocks may vary. In addition, some blocks may be omitted.

[0227] Where a structural feature has been described, it may be replaced by a component for performing one or more of the functions of the structural feature, whether that function or functions are explicitly or implicitly described.

[0228] As used herein, a "module" refers to a unit or device excluding specific parts / components to be added by a terminal manufacturer or user. The devices 202, 204 may be modules.

[0229] The above example finds applications that are the following enabling components:

[0230] automotive systems; telecommunications systems; electronic systems, including consumer electronics; distributed computing systems; media systems for generating or reproducing media content, including audio, visual and audio-visual content and mixed, mediated, virtual and / or augmented reality; personal systems, including personal health systems or personal fitness systems; navigation systems; user interfaces, also known as human-machine interfaces; networks, including cellular, non-cellular and optical networks; ad-hoc networks; the Internet; the Internet of Things; virtualized networks; and related software and services.

[0231] According to the examples of the present disclosure, the device can be provided in an electronic device such as a mobile terminal. However, it should be understood that the mobile terminal is only an illustration of an electronic device that will benefit from the examples of the embodiments of the present disclosure, and therefore, it should not be considered to limit the scope of the present disclosure to this. Although in some implementation examples, the device can be provided in a mobile terminal, other types of electronic devices (such as but not limited to: mobile communication devices, handheld portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices, and other types of electronic systems) can easily use the examples of the present disclosure. In addition, the device can easily use the examples of the present disclosure, regardless of their intention to provide mobility.

[0232] The term "comprising" is used in this document in an inclusive, rather than exclusive, sense. That is, any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If "comprising" is intended to be used in an exclusive sense, this will become clear in the context by reference to "comprising only one..." or by use of "consisting of..."

[0233] In this specification, the terms "connected", "coupled" and "in communication" and their derivatives refer to being operatively connected / coupled / in communication. It should be understood that any number or combination of intermediate components (including no intermediate components) may be present, i.e., to provide direct or indirect connection / coupling / in communication. Any such intermediate components may include hardware and / or software components.

[0234] As used herein, the term "determine / determine" (and grammatical variations thereof) may include at least: calculate, compute, process, derive, measure, investigate, identify, look up (e.g., look up in a table, database or other data structure), ascertain, etc. Moreover, "determine" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), obtaining, etc. Moreover, "determine / determine" may include resolving, selecting, choosing, establishing, etc.

[0235] In this specification, reference has been made to various examples. The description of features or functions of an example indicates that those features or functions are present in the example. The use of the term "example" or "for example" or "may" or "can" herein indicates that, whether explicitly stated or not, such features or functions are present in at least the described example, whether described as an example or not, and they may (but not necessarily) be present in some or all other examples. Therefore, "example", "for example", "may" or "can" refers to a specific instance in a class of examples. The attributes of an instance may be attributes of only that instance or attributes of that class or attributes of a subclass of that class, which subclass includes some but not all examples in that class. It is therefore implicitly disclosed that the features described with reference to one example rather than with reference to another example may be used in that other example as part of a working combination where possible, but not necessarily in that other example.

[0236] Although the examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0237] Features described in the above description may be used in combinations other than the combinations explicitly described above.

[0238] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0239] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0240] The terms "a", "an" or "the" are used in this document with an inclusive, rather than an exclusive, meaning. That is, any reference to X that includes a / the Y indicates that X may include only one Y or may include more than one Y, unless the context clearly indicates otherwise. If the use of "a" or "the" is intended to have an exclusive meaning, it will become clear from the context. In some cases, the use of "at least one" or "one or more" may be used to emphasize the inclusive meaning, but the absence of these terms should not be taken to infer any exclusive meaning.

[0241] The presence of a feature (or combination of features) in a claim is a reference to the feature or (combination of features) itself, and also to features that achieve substantially the same technical effect (equivalent features). Equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. Equivalent features include, for example, features that perform substantially the same function in substantially the same way to achieve substantially the same result.

[0242] In this specification, reference has been made to various examples using adjectives or conjunctive phrases to describe features of the examples. Such descriptions of features of the examples indicate that the features exist in some examples exactly as described, and exist in other examples substantially as described.

[0243] The above description describes some examples of the present disclosure, however, those of ordinary skill in the art will be aware of possible alternative structures and method features that provide equivalent functionality to the specific examples of such structures and features described above, and have been omitted from the above description for the sake of brevity and clarity. Nevertheless, the above description should be understood to implicitly include reference to such alternative structures and method features that provide equivalent functionality, unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0244] While an effort has been made in the foregoing description to draw attention to those features regarded as being of importance, it will be understood that the applicant may seek protection by way of claims for any patentable feature or combination of features heretofore mentioned and / or shown in the drawings, whether or not emphasis has been placed thereon.

Claims

1. An apparatus configurable to operate as a central unit (CU), the apparatus comprising: Components for enabling lower layer triggered mobility (LTM) random access by a user equipment (UE) to a target distributed unit (DU) for early timing advance acquisition using contention free random access (CFRA) resources that are reserved for the UE for early timing advance acquisition by the UE to prevent use by UEs served by different DUs.

2. The device according to claim 1, comprising: Means for causing the contention-free random access (CFRA) resources used for early timing advance acquisition by the UE to be reserved to prevent use by UEs served by different DUs.

3. The apparatus of claim 1 or 2, wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by UEs served by the different DUs, and The reservation of the contention-free random access (CFRA) resources for early timing advance acquisition by the UE and preventing use by the UE served by the different DU prevents user equipment (UE) other than the user equipment from randomly accessing the target distributed unit (DU) using the contention-free random access (CFRA) resources.

4. The device according to claim 1 or 2, comprising: Before a cell is changed by the UE to a cell controlled by the target distributed unit (DU), means for: obtaining the CFRA resource for early timing advance acquisition for the UE, causing the CFRA resources to be reserved to prevent use by other UEs served by the different DUs, receiving a confirmation of completion of random access by the UE to the target DU, The CFRA resources are released for use by other UEs served by the different DU.

5. The device according to claim 1 or 2, comprising: means for preparing the target DU to become a serving DU of the UE via a contention free random access (CFRA) connection using the contention free random access (CFRA) resource reserved for the UE.

6. The device according to claim 1 or 2, comprising: Means for enabling early LTM synchronization for early timing advance acquisition during a prepare phase of the LTM prior to an execute phase of the LTM.

7. The device according to claim 1 or 2, comprising: A component for recording a contention-free random access (CFRA) resource as unavailable; means for notifying the distributed units that a contention free random access (CFRA) resource recorded as unavailable is unavailable, and / or Means for rejecting a request for contention free random access (CFRA) resources from a distributed unit if the requested contention free random access (CFRA) resources are recorded as unavailable.

8. The device according to claim 1 or 2, comprising: means for receiving the CFRA resources from a DU serving the UE; Means for indicating the received CFRA resources to the different DUs.

9. The device according to claim 8, comprising: wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources for the target distributed unit, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by the DU serving the UE and UEs served by a first group of different DUs, and the apparatus comprises: means for indicating the received CFRA resources to all the DUs of the first group.

10. The device according to claim 9, comprising: wherein the contention-free random access (CFRA) resource reserved for early timing advance acquisition by the UE is selected from a shared pool of contention-free random access (CFRA) resources for the target distributed unit, wherein the shared pool of contention-free random access (CFRA) resources is used to be shared by the DU serving the UE and UEs served by a first group of different DUs, and the apparatus comprises: Means for indicating the received CFRA resources to a subset of the DUs of the first group.

Images