Enhancement for timing advance acquisition in l1 / 2 triggered mobility

Abstract

In accordance with example embodiments of the present disclosure there is at least a method and apparatus configured to receive, from a source distributed unit, a configuration comprising a timing advance of a cell; receive, from the source distributed unit, an indication to perform a cell change; and apply the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

Description

Enhancement For Timing Advance Acquisition In Ll / 2 Triggered MobilityTECHNICAL FIELD

[0001] The examples and non-limiting example embodiments relate generally to communications and, more particularly, to enhancement for timing advance acquisition in Ll / 2 triggered mobility.BACKGROUND

[0002] It is known to perform a handover from a source cell to a target cell in a communication network.BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The foregoing aspects and other features are explained in the following description, taken in connection with the accompanying drawings.

[0004] FIG. 1 is a block diagram of one possible and non-limiting system in which the example embodiments may be practiced.

[0005] FIG. 2 is a signaling diagram for Ll / 2 triggered mobility (LTM).

[0006] FIG. 3 is a signaling diagram showing the implementation details of solution 1.

[0007] FIG. 4 is a signaling diagram showing the implementation details of solution 2.

[0008] FIG. 5 is an example apparatus configured to implement the examples described herein.

[0009] FIG. 6 shows a representation of an example of non-volatile memory media used to store instructions that implement the examples described herein.

[0010] FIG. 7 is an example method, based on the examples described herein.

[0011] FIG. 8 is an example method, based on the examples described herein.

[0012] FIG. 9 is an example method, based on the examples described herein.

[0013] FIG. 10 is an example method, based on the examples described herein.DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0014] Turning to FIG. 1, this figure shows a block diagram of one possible and nonlimiting example in which the examples may be practiced. A user equipment (UE) 110, radio access network (RAN) node 170, and network element(s) 190 are illustrated. In the example of FIG. 1 , the user equipment (UE) 110 is in wireless communication with a wireless network 100. A UE is a wireless device that can access the wireless network 100. The UE 110 includes one or more processors 120, one or more memories 125, and one or more transceivers 130 interconnected through one or more buses 127. Each of the one or more transceivers 130 includes a receiver, Rx, 132 and a transmitter, Tx, 133. The one or more buses 127 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The one or more transceivers 130 are connected to one or more antennas 128. The one or more memories 125 include computer program code 123. The UE 110 includes a module 140, comprising one of or both parts 140-1 and / or 140- 2, which may be implemented in a number of ways. The module 140 may be implemented in hardware as module 140-1 , such as being implemented as part of the one or more processors 120. The module 140-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the module 140 may be implemented as module 140-2, which is implemented as computer program code 123 and is executed by the one or more processors 120. For instance, the one or more memories 125 and the computer program code 123 may be configured to, with the one or more processors 120, cause the user equipment 110 to perform one or more of the operations as described herein. The UE 110 communicates with RAN node 170 via a wireless link 111.

[0015] The RAN node 170 in this example is a base station that provides access for wireless devices such as the UE 110 to the wireless network 100. The RAN node 170 may be, for example, a base station for 5G, also called New Radio (NR). In 5G, the RAN node 170 may be a NG-RAN node, which is defined as either a gNB or an ng-eNB. A gNB is a node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface (such as connection 131) to a 5GC (such as, for example, the network element(s) 190). The ng-eNB is a node providing E-UTRA user plane and controlplane protocol terminations towards the UE, and connected via the NG interface (such as connection 131) to the 5GC. The NG- RAN node may include multiple gNBs, which may also include a central unit (CU) (gNB-CU) 196 and distributed unit(s) (DUs) (gNB-DUs), of which DU 195 is shown. Note that the DU 195 may include or be coupled to and control a radio unit (RU). The gNB-CU 196 is a logical node hosting radio resource control (RRC), SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that control the operation of one or more gNB-DUs. The gNB-CU 196 terminates the Fl interface connected with the gNB-DU 195. The Fl interface is illustrated as reference 198, although reference 198 also illustrates a link between remote elements of the RAN node 170 and centralized elements of the RAN node 170, such as between the gNB-CU 196 and the gNB- DU 195. The gNB-DU 195 is a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU 196. One gNB-CU 196 supports one or multiple cells. One cell may be supported with one gNB-DU 195, or one cell may be supported / shared with multiple DUs under RAN sharing. The gNB-DU 195 terminates the Fl interface 198 connected with the gNB-CU 196. Note that the DU 195 is considered to include the transceiver 160, e.g., as part of a RU, but some examples of this may have the transceiver 160 as part of a separate RU, e.g., under control of and connected to the DU 195. The RAN node 170 may also be an eNB (evolved NodeB) base station, for LTE (long term evolution), or any other suitable base station or node.

[0016] The RAN node 170 includes one or more processors 152, one or more memories 155, one or more network interfaces (N / W FF(s)) 161, and one or more transceivers 160 interconnected through one or more buses 157. Each of the one or more transceivers 160 includes a receiver, Rx, 162 and a transmitter, Tx, 163. The one or more transceivers 160 are connected to one or more antennas 158. The one or more memories 155 include computer program code 153. The CU 196 may include the processor(s) 152, one or more memories 155, and network interfaces 161. Note that the DU 195 may also contain its own memory / memories and processor(s), and / or other hardware, but these are not shown.

[0017] The RAN node 170 includes a module 150, comprising one of or both parts 150-1 and / or 150-2, which may be implemented in a number of ways. The module 150 may be implemented in hardware as module 150-1, such as being implemented as part of the one or more processors 152. The module 150-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the module150 may be implemented as module 150-2, which is implemented as computer program code 153 and is executed by the one or more processors 152. For instance, the one or more memories 155 and the computer program code 153 are configured to, with the one or more processors 152, cause the RAN node 170 to perform one or more of the operations as described herein. Note that the functionality of the module 150 may be distributed, such as being distributed between the DU 195 and the CU 196, or be implemented solely in the DU 195.

[0018] The one or more network interfaces 161 communicate over a network such as via the links 176 and 131. Two or more gNBs 170 may communicate using, e.g., link 176. The link 176 may be wired or wireless or both and may implement, for example, an Xn interface for 5G, an X2 interface for LTE, or other suitable interface for other standards.

[0019] The one or more buses 157 may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers 160 may be implemented as a remote radio head (RRH) 195 for LTE or a distributed unit (DU) 195 for gNB implementation for 5G, with the other elements of the RAN node 170 possibly being physically in a different location from the RRH / DU 195, and the one or more buses 157 could be implemented in part as, for example, fiber optic cable or other suitable network connection to connect the other elements (e.g., a central unit (CU), gNB-CU 196) of the RAN node 170 to the RRH / DU 195. Reference 198 also indicates those suitable network link(s).

[0020] A RAN node / gNB can comprise one or more TRPs to which the methods described herein may be applied. FIG. 1 shows that the RAN node 170 comprises two TRPs, TRP 51 and TRP 52. The RAN node 170 may host or comprise other TRPs not shown in FIG. 1.

[0021] A relay node in NR is called an integrated access and backhaul node. A mobile termination part of the IAB node facilitates the backhaul (parent link) connection. In other words, the mobile termination part comprises the functionality which carries UE functionalities. The distributed unit part of the IAB node facilitates the so called access link (child link) connections (i.e. for access link UEs, and backhaul for other IAB nodes, in the case of multi-hop IAB). In other words, the distributed unit part is responsible for certain base station functionalities. The IAB scenario may follow the so called split architecture, wherethe central unit hosts the higher layer protocols to the UE and terminates the control plane and user plane interfaces to the 5G core network.

[0022] It is noted that the description herein indicates that “cells” perform functions, but it should be clear that equipment which forms the cell may perform the functions. The cell makes up part of a base station. That is, there can be multiple cells per base station. For example, there could be three cells for a single carrier frequency and associated bandwidth, each cell covering one-third of a 360 degree area so that the single base station’s coverage area covers an approximate oval or circle. Furthermore, each cell can correspond to a single carrier and a base station may use multiple carriers. So if there are three 120 degree cells per carrier and two carriers, then the base station has a total of 6 cells.

[0023] The wireless network 100 may include a network element or elements 190 that may include core network functionality, and which provides connectivity via a link or links 181 with a further network, such as a telephone network and / or a data communications network (e.g., the Internet). Such core network functionality for 5G may include location management functions (LMF(s)) and / or access and mobility management function(s) (AMF(S)) and / or user plane functions (UPF(s)) and / or session management function(s) (SMF(s)). Such core network functionality for LTE may include MME (mobility management entity) / SGW (serving gateway) functionality. Such core network functionality may include SON (self- organizing / optimizing network) functionality. These are merely example functions that may be supported by the network element(s) 190, and note that both 5G and LTE functions might be supported. The RAN node 170 is coupled via a link 131 to the network element 190. The link 131 may be implemented as, e.g., an NG interface for 5G, or an SI interface for LTE, or other suitable interface for other standards. The network element 190 includes one or more processors 175, one or more memories 171, and one or more network interfaces (N / W I / F(s)) 180, interconnected through one or more buses 185. The one or more memories 171 include computer program code 173. Computer program code 173 may include SON and / or MRO functionality 172.

[0024] The wireless network 100 may implement network virtualization, which is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, or a virtual network. Network virtualization involves platform virtualization, often combined with resource virtualization. Network virtualization is categorized as either external, combining many networks, or partsof networks, into a virtual unit, or internal, providing network-like functionality to software containers on a single system. Note that the virtualized entities that result from the network virtualization are still implemented, at some level, using hardware such as processors 152 or 175 and memories 155 and 171, and also such virtualized entities create technical effects.

[0025] The computer readable memories 125, 155, and 171 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, non-transitory memory, transitory memory, fixed memory and removable memory. The computer readable memories 125, 155, and 171 may be means for performing storage functions. The processors 120, 152, and 175 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as nonlimiting examples. The processors 120, 152, and 175 may be means for performing functions, such as controlling the UE 110, RAN node 170, network element(s) 190, and other functions as described herein.

[0026] In general, the various example embodiments of the user equipment 110 can include, but are not limited to, cellular telephones such as smart phones, tablets, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback devices having wireless communication capabilities, internet appliances including those permitting wireless internet access and browsing, tablets with wireless communication capabilities, head mounted displays such as those that implement virtual / augmented / mixed reality, as well as portable units or terminals that incorporate combinations of such functions. The UE 110 can also be a vehicle such as a car, or a UE mounted in a vehicle, a UAV such as e.g. a drone, or a UE mounted in a UAV. The user equipment 110 may be terminal device, such as mobile phone, mobile device, sensor device etc., the terminal device being a device used by the user or not used by the user.

[0027] UE 110, RAN node 170, and / or network element(s) 190, (and associated memories, computer program code and modules) may be configured to implement (e.g. in part) the methods described herein, including enhancement for timing advance acquisition in Ll / 2triggered mobility. Thus, computer program code 123, module 140-1, module 140-2, and other elements / features shown in FIG. 1 of UE 110 may implement user equipment related aspects of the examples described herein. Similarly, computer program code 153, module 150-1, module 150-2, and other elements / features shown in FIG. 1 of RAN node 170 may implement gNB / TRP related aspects of the examples described herein. Computer program code 173 and other elements / features shown in FIG. 1 of network element(s) 190 may be configured to implement network element related aspects of the examples described herein.

[0028] Having thus introduced a suitable but non- limiting technical context for the practice of the example embodiments, the example embodiments are now described with greater specificity.

[0029] The examples described herein are related to 5G New Radio and, in particular, a mobility enhancement concept targeted for 3 GPP Rel-18 and beyond which enables and improves mobility / cell-changes in RAN where the Central-Unit - Distributed-Unit (CU-DU) structure is deployed, i.e., enabling operations between different DU (inter-DU) of different providers via CU (involving the control Plane or / and user Plane aspects of the Central-Unit, CU-CP, CU-UP);

[0030] The Rel-18 work item on mobility enhancements (RP-223520, RP-221799, RP- 213565) includes one objective to support lower layer triggered mobility (LTM) to improve the interruption time and execution delay for switching between cells of the same or different DU but controlled by same CU. Unlike L3 based mobility where the handover decision is based on L3 cell quality measurement results, the handover in LTM is triggered by the DU based on LI beam measurement results. When UE switches cells via LTM, usually a TA acquisition procedure is executed by the UE towards the target cell of the target DU before actually accessing the target cell of the target DU. The Network node / gNB / DU does not need to request the TA acquisition procedure, if the UE already knows about the TA towards the target cell / DU.

[0031] Described herein is a method for the CU or the target DU to provide information to the serving DU allowing the serving DU to distinguish the prepared candidate target cells with unknown TA from the other prepared candidate target cells with known / predefined TA. Using this information, the serving DU can trigger the PDCCH order for TA acquisition only for the prepared candidate target cells with unknown TA. Candidate target cells arediscriminated by knowing or not knowing the TA and the value of the TA is attached or stored related to the candidate target cells and the UE.

[0032] New information is provided to distinguish the prepared candidate target cells with unknown TA from the other prepared candidate target cells with known or predefined TA. Using this information, the UE may access the target cell without the TA acquisition procedure, or skip the TA acquisition procedure, which therefore reduces signaling overhead and UE interruption.

[0033] A first solution of the examples described herein relates to where a new IE TA- known is implemented to indicate for the serving cell (controlled by a source DU) whether the TA of a candidate target cell is known and if so, a new IE TA-value carries the value of the TA related to the candidate target cell and the UE.

[0034] A serving DU triggers the TA acquisition procedure to the UE only for prepared candidate target cells which have an unknown TA. For the others, the UE accesses the cell without a TA acquisition procedure.

[0035] The target DU / CU provides information towards the source DU whether a prepared candidate target cell has a known / pre-defined TA or unknown TA related to the UE.

[0036] A second solution of the examples described herein relates to a source DU indicating in a MAC CE cell change trigger to use the TA provided in the LTM configuration earlier on. The CU configures the UE with a TA that can be possibly associated to an SSB index and / or LI measurements. The UE retrieves the TA from the LTM configuration and applies it when requested by a source DU in a MAC CE cell change trigger.

[0037] TA acquisition and a random access (RA) procedure are two procedures to perform when switching cells. To reduce the period of time to switch cells for a UE, skipping unnecessary steps may be implemented, but information on TA is required and a TA acquisition procedure ensures availability at UE.

[0038] Currently, the source DU does not know whether the UE has obtained already the known TA value (if available) of one or more candidate target cells and of which candidate target cells. Therefore, providing TA information to the source DU on each candidate target cell may be a straight forward solution.

[0039] Candidate cell, target cell, and candidate target cell are used interchangeably herein. Serving cell and serving DU are used interchangeably herein. Serving cell / DU and source cell / DU are used interchangeably herein. Layer 1 / 2 (Ll / 2) triggered mobility (LTM) is a 3GPP RAN2 agreed term for lower layer (Ll / 2) mobility. Cell Switch and handover are used interchangeably herein.

[0040] L1 / L2 triggered mobility (LTM)

[0041] LTM denoted also as Ll / 2 inter-cell mobility, is one of the objectives for mobility enhancement in the Rel. 18 work item. In LTM, the decision about the cell change is based on LI measurements and is made in the MAC layer in the Distributed Unit (DU).

[0042] FIG. 2 shows one example message exchange for the inter-DU LTM scenario, captured for disaggregated architecture, showing a message exchange between UE 110, a source DU 230, a target DU 240, and a CU 250. The signaling exchange is as follows:

[0043] The UE provides the L3 measurements to the source distributed unit (DU), which are forwarded to the centralized unit (CU) (steps 1-2). Based on these measurements, the CU decides about the cell preparation (HO Decision - step 3) and proceeds in setting up the UE context in the target DU (steps 4-5). The CU communicates with the source DU for the modification of the UE context if needed and the provision of the target cell information (i.e., target cell RS configuration, TCI states, etc.) (steps 6-7).

[0044] In step 8, the CU creates and forwards the RRC Reconfiguration message to the source DU using a DL RRC message transfer and the latter forwards it to the UE (steps 9- 10). The UE responds with an RRC Reconfiguration Complete message to the CU (steps 11- 12).

[0045] Based on its configuration, the UE provides the periodic LI reports to the source DU(step 13).

[0046] Based on the received LI measurement report, the source DU may trigger the UE, e.g., by sending a PDCCH order, to acquire TA for the set of candidate cells (i.e., candidate cells for the handover) (step 14-15). That is in step 15, the UE sends a PRACH preamble transmission to the candidate target cell which then estimates the TA value and forwards it to the serving DU via the CU. The serving DU stores the TA value and provides it to the UEwhen triggering the cell switch towards the same target cell using a MAC CE in step 18.

[0047] In addition to a PDCCH order-based mechanism, other RACH-less mechanisms are being considered. For instance, if the TA of the target cell is known or predefined (equal to 0, or equal to that of the source cell or any other value), the TA acquisition procedure of step 15 is not needed and the UE can apply directly the configured TA, the predefined TA, and / or the provided TA.

[0048] The source-DU / CU and candidate target-DUs / CUs coordinate on the TA acquisition method during the LTM preparation phase (e.g., steps 4-5).

[0049] The UE continues LI measurement reporting. Once the source DU decides that the UE should be handed over to a cell (i.e., target cell) of another DU (i.e., target DU) it triggers the cell switch, using a cell switch command (e.g., a MAC CE) (steps 16-18). The MAC CE may contain the TA of the target cell that has been acquired by the network prior to the cell switch by triggering a PDCCH order for TA acquisition.

[0050] Then the UE applies the RRC configuration for the target cell of the target DU indicated by the cell switch command (via MAC CE) and switches to the target DU. The UE may perform random access (RA) to the target cell as shown in steps 19-20. However, in other solutions, the UE may be configured to not perform the RA to the target cell as it has already acquired the TA of the target cell. To initiate the communication with the target DU, the UE transmits an RRC reconfiguration complete using already configured UL resources to the target cell of the target DU, which is forwarded to the CU-CP (steps 21-22).

[0051] The CU releases the UE context from the source DU with a UE context release request and performs a path switch to the new DU (steps 23-25).

[0052] Physical Downlink Control Channel (PDCCH) Order Details [Section 7.3.1.2.1, TS 38.212]

[0053] Layer 1 Downlink Control Indication (DCI) format l_0 is used to send a PDCCH order. The following information (1-7 as follows) is transmitted by means of the DCI format l_0 with CRC scrambled by a Cell- Radio Network Temporary Identifier (C-RNTI):

[0054] 1. Identifier for DCI formats - 1 bit. The value of this bit field is always set to 1, indicating a DL DCI format.

[0055] 2. Frequency domain resource assignment - l '1in0ger - ( Ml D!BL’Bwr( NR DBL’Bwr+ l 1 / ? bits whereDL.BWP |<[1is the size of CORESET 0 if CORESET 0 is configured for the cell; otherwise, it is the size of initial DL bandwidth part. The value of this field is set to all ones.

[0056] 3. Random Access Preamble index - 6 bits according to ra-Preamblelndex in Clause 5.1.2 of [8, TS38.321]. It indicates which random-access preamble to use in case of contention free random access (CFRA) or the value 000000 in the case of the contention based random access (CBRA) procedure. If the preamble index bit is set as ‘0’ then the UE will trigger a contention-based random-access procedure or else if the preamble index is > 0, then the UE will trigger a contention-free random-access procedure. Non-zero values are used to allocate the dedicated PRACH index (0 to 63) to the UE.

[0057] 4. UL / SUL indicator - 1 bit. If the value of the "Random Access Preamble index" is not all zeros and if the UE is configured with supplementary Uplink in ServingCellConfig in the cell, this field indicates which UL carrier in the cell to transmit the PRACH according to Table 7.3.1.1.1-1 in TS 38.212; otherwise, this field is reserved.

[0058] 5. SS / PBCH index - 6 bits. If the value of the "Random Access Preamble index" is not all zeros, this field indicates the SS / PBCH that shall be used to determine the RACH occasion for the PRACH transmission; otherwise, this field is reserved.

[0059] 6. PRACH Mask index - 4 bits. If the value of the "Random Access Preamble index" is not all zeros, this field indicates the RACH occasion associated with the SS / PBCH indicated by "SS / PBCH index" for the PRACH transmission, according to Clause 5.1.1 of [8, TS38.321]; otherwise, this field is reserved.

[0060] 7. Reserved bits - 12 bits for operation in a cell with shared spectrum channel access in frequency range 1 or when the DCI format is monitored in a common search space for operation in a cell in frequency range 2-2; otherwise, 10 bits.

[0061] To send the PDCCH order for TA acquisition, the serving DU is made aware by the CU about the RACH configurations that shall be used for TA acquisition with respect to a prepared cell. This is necessary for the serving DU to indicate the 1) PRACH preamble index and 2) SSB / PBCH index used for determining the RACH occasion for the PRACH transmission.

[0062] The TA acquisition procedure (triggered by the PDCCH order) is used for prepared target cells with unknown TA which shall be acquired by the UE using a PRACH transmission. However, there are cases where the TA of a prepared target cell is predefined and known by the network. For instance, the TA of a prepared target cell could be 0 (in case of small cells), or equal to that of source cell or to a different value that is determined by the network using e.g. 0AM, statistics, AI-ML techniques or measurements. As the source DU is not aware if the TAs of prepared target cells are unknown or predefined / known, the source DU may trigger the TA acquisition for target cells with known TA. This leads to unnecessary TA acquisitions towards the target cells causing higher signalling overhead and interruption for sending the PRACH transmissions.

[0063] The examples described herein serve to address the problem in which the serving DU triggers the PDCCH order for TA acquisition unnecessarily for prepared target cells with known TA.

[0064] Described herein is a method for the CU or the target DU to provide information to the serving DU allowing the serving DU to distinguish the prepared candidate target cells with unknown TA from the other prepared candidate target cells with known or predefined TA. Using this information, the serving DU can trigger the PDCCH order for TA acquisition only for the prepared candidate target cells with unknown TA.

[0065] The serving DU is informed by the CU or target DU (via CU) about the prepared candidate target cells with unknown or known TA or predefined TA. The indication can be made using a flag, for instance.

[0066] Solution 1: in one embodiment, the serving DU is informed as well with the predefined TAs of the prepared candidate target cells. Using this information, the serving DU skips the PDCCH order for a prepared candidate target cell with known TA and indicates the known TA in the MAC CE triggering the cell switch. Upon receiving the MAC CE containing the known TA, the UE uses the received TA to perform RACH-less LTM.

[0067] In another embodiment, a predefined TA is associated with a set of (e.g., one or more) reference signals, e.g., SSB or CSI-RS, indices for the same prepared candidate target cell. Multiple TAs, each TA associated with a different set of reference signal indices, may be provided. For instance, the serving DU may receive for the same candidate target cell that TAI applies for the SSB index: 1 to 3 and TA2 for SSB index 4 to 7 and unknown TA forSSB index 8. Based on the LI measurements received from the UE, the serving DU may identify the SSB to be used to determine the predefined TA value for the UE and may send the corresponding TA in the MAC CE cell switch command. In another option, the predefined TA values TAI and TA2 can be used by the serving DU for cell switch if the MAC CE triggering the cell switch indicates an SSB index that is associated with the predefined TA. In other words, if the SSB index e.g., 1 is indicated in the MAC CE, the serving DU can indicate TAI for the UE, TA2 if SSB index e.g. 4 and so on. If the UE reports strong LI beam measurements for SSB index 8, the serving DU can trigger the TA acquisition as the TA associated with SSB index 8 is unknown.

[0068] In another embodiment, a predefined TA is associated with receive LI measurements or a range of received LI measurements, e.g.: TAI is applicable for SSB 1 to 3 and Ll-RSRP range: (-X dB to -X+4 dB), TA2 is applicable for SSB 1 to 3 and Ll-RSRP range: (- X+5 dB to -X+10 dB), TA 3 is applicable for SSB 1 to 3 and Ll-RSRP range: (-X+10 dB to -X+15 dB), TA4 is applicable for SSB 4 to 8 and Ll-RSRP range: (-X dB to -X+4 dB), TA5 is applicable for SSB 4 to 8 and Ll-RSRP range: (-X+5 dB to -X+10 dB).

[0069] Alternatively, in Solution 2: in case the known TAs have been configured to the UE during the LTM preparation, i.e., known TA is indicated in the LTM configuration to the UE, the MAC CE triggering the cell switch to a prepared candidate target cell with known TA includes an indication instructing the UE to use the TA value (if any) that is provided in the LTM configuration. In this case, there is no need to signal the known TA in the MAC CE. If no TA is provided in the LTM configuration, the UE performs RACH-based LTM.

[0070] In another embodiment, the TA that is received by the UE during the LTM preparation can be associated with a set of (e.g., one or more) reference signals, e.g., SSB or CSLRS or with a range of LI measurements. In this case, the UE may receive more than one predefined TA value for the same prepared target cell. Upon receiving the MAC CE triggering the cell switch containing the SSB index, the UE will apply the TA that is associated with the SSB index that is indicated in the MAC CE. If the SSB index is not indicated in the MAC CE, the UE may select the right TA to be applied based on the measurements of the SSB indices. For instance, if the UE detects that SSB 1 has the strongest LI measurement, then the UE will select the TA that is associated with SSB 1.

[0071] In another embodiment, if the UE receives a MAC CE triggering the cell switch without an explicit TA value, the UE applies the TA (if any) that is provided in the LTMconfiguration. Otherwise (if TA is not in the LTM configuration), the UE performs RACH- based LTM.

[0072] In another embodiment (applicable for both solutions 1 and 2), the MAC CE triggering the cell switch may contain an indication instructing the UE to perform RACH- based LTM irrespective of whether the TA value for RACH-less LTM execution is included in the LTM configuration.

[0073] This can be useful for instance when the UL grants for sending Message 3: e.g., when RRC Reconfiguration Complete to the target cell in RACH-less LTM cannot be used anymore due to radio reasons.

[0074] The implementation details of solutions 1 and 2 are shown in FIG. 3 and FIG. 4.

[0075] Solution 1:

[0076] The steps of FIG. 3 implementing solution 1 are described as follows:

[0077] In step 1 , the UE sends an L3 measurement report identifying potential candidate cells to be prepared for LTM. The L3 measurement report is received by the CU in step 2 from the source DU controlling serving PCell 1.

[0078] In step 3, the CU makes the decision to prepare the LTM handover and in step 4 requests from the target DU to provide the LTM configurations for prepared cells 2 and 3.

[0079] In Option 1, the target DU informs the CU in step 5 that the prepared cell 2 has an unknown TA and cell 3 has a known TA. Moreover, target DU informs the CU about the TA value for cell 3 that can be associated with the SSB index or LI measurements. This information that is generated by the target DU is relayed to the serving DU via the CU in step 6.

[0080] In Option 2, the target DU informs the CU in step 5 about the IDs of the prepared cells 2 and 3 and the CU informs the serving DU in step 6 that the cell 2 has an unknown TA and cell 3 has a predefined known TA. Moreover, the CU informs the serving DU in step 6 about the TA value for cell 3 that can be associated with an SSB index or LI measurements.

[0081] In step 10, the UE receives the RRC reconfiguration message containing the LTM configurations of prepared cells 2 and 3.

[0082] In step 13, the UE reports the LI beam measurements of serving and prepared cells.

[0083] In step 14, the serving DU identifies using LI beam measurements that the prepared cell 3 is a good candidate cell for handover. Given that the TA of cell 3 is known, the serving DU does not have to trigger the TA acquisition for cell 3.

[0084] In step 16, the serving DU identifies using the LI beam measurements that a cell switch should be triggered to prepared target cell 3 with known TA.

[0085] In step 17, the serving DU sends a MAC CE triggering the cell change to prepared target cell 3 and includes the known TA that is received from the target DU or CU in step 5 and 6, respectively.

[0086] Solution 2:

[0087] The steps of FIG. 4 implementing solution 2 are described as follows:

[0088] In step 1 , the UE sends an L3 measurement report identifying potential candidate cells to be prepared for LTM. The L3 measurement report is received by the CU in step 2 from the source DU controlling serving PCell 1.

[0089] In step 3, the CU makes the decision to prepare the LTM handover and in step 4 requests from the target DU to provide the LTM configurations for prepared cells 2 and 3.

[0090] In Option 1, the target DU informs the CU in step 5 that the prepared cell 2 has an unknown TA and cell 3 has a known TA. The target DU provides the known TA value for PCell 3 that can be associated with an SSB index and LI measurements. Upon receiving this information, the CU forwards it to the UE in steps 8, 9 and 10.

[0091] In Option 2, the target DU informs the CU about the IDs of the prepared cells 2 and 3 and the CU informs the serving DU in step 6 that the cell 2 has an unknown TA and cell 3 has a predefined known TA. In this case, the CU decides on the known TA value and the possibly associated SSB index and LI measurements in step 8.

[0092] In step 10, the UE receives the RRC reconfiguration message containing the LTM configurations of prepared cells 2 and 3. The LTM configuration of prepared cell 3 may contain the predefined TA that is possibly associated with an SSB index and LI measurements.

[0093] In step 13, the UE reports the LI beam measurements of serving and prepared cells.

[0094] In step 14, the serving DU identifies using LI beam measurements that the prepared cell 3 is a good candidate cell for handover. Given that the TA of cell 3 is known, the serving DU does not have to trigger the TA acquisition for cell 3.

[0095] In step 16, the serving DU identifies using the LI beam measurement that a cell switch should be triggered to prepared target cell 3 with known TA.

[0096] In step 17, the serving DU sends a MAC CE triggering the cell change to prepared target cell 3 and includes an indication that the UE shall use the TA that is provided in the LTM configuration to perform RACH-less LTM.

[0097] In step 18, the UE applies TA (if any) that is provided in the LTM configuration. If no TA is found, the UE performs RACH-based LTM.

[0098] One benefit of solution 2 over solution 1 is that the UE receives the known TA of the prepared target cell. In case of a link failure between the UE and serving cell, the UE can still make use of the acquired TA to perform RACH-less recovery of the radio link by executing the LTM configuration of a prepared target cell.

[0099] Advantages and technical effects of the herein described solutions include that unnecessary triggering of TA acquisition is skipped with respect to prepared target cells with known TA. There is less radio and network signaling overhead, and less UE interruption.

[0100] FIG. 5 is an example apparatus 500, which may be implemented in hardware, configured to implement the examples described herein. The apparatus 500 comprises at least one processor 502 (e.g. an FPGA and / or CPU), one or more memories 504 including computer program code 505, the computer program code 505 having instructions to carry out the methods described herein, wherein the at least one memory 504 and the computer program code 505 are configured to, with the at least one processor 502, cause the apparatus 500 to implement circuitry, a process, component, module, or function (implemented with control module 506) to implement the examples described herein, including enhancement for timing advance acquisition in Ll / 2 triggered mobility. The memory 504 may be a non-transitory memory, a transitory memory, a volatile memory (e.g. RAM), or a non-volatile memory (e.g. ROM). L1 / L2 triggered mobility 530 of the control module implements the herein describedaspects related to enhancement for timing advance acquisition in Ll / 2 triggered mobility.

[0101] The apparatus 500 includes a display and / or I / O interface 508, which includes user interface (UI) circuitry and elements, that may be used to display aspects or a status of the methods described herein (e.g., as one of the methods is being performed or at a subsequent time), or to receive input from a user such as with using a keypad, camera, touchscreen, touch area, microphone, biometric recognition, one or more sensors, etc. The apparatus 500 includes one or more communication e.g. network (N / W) interfaces (I / F(s)) 510. The communication I / F(s) 510 may be wired and / or wireless and communicate over the Internet / other network(s) via any communication technique including via one or more links 524. The link(s) 524 may be the link(s) 131 and / or 176 from FIG. 1. The link(s) 131 and / or 176 from FIG. 1 may also be implemented using transceiver(s) 516 and corresponding wireless link(s) 526. The communication I / F(s) 510 may comprise one or more transmitters or one or more receivers.

[0102] The transceiver 516 comprises one or more transmitters 518 and one or more receivers 520. The transceiver 516 and / or communication FF(s) 510 may comprise standard well-known components such as an amplifier, filter, frequency-converter, (de)modulator, and encoder / decoder circuitries and one or more antennas, such as antennas 514 used for communication over wireless link 526.

[0103] The control module 506 of the apparatus 500 comprises one of or both parts 506-1 and / or 506-2, which may be implemented in a number of ways. The control module 506 may be implemented in hardware as control module 506-1, such as being implemented as part of the one or more processors 502. The control module 506-1 may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the control module 506 may be implemented as control module 506-2, which is implemented as computer program code (having corresponding instructions) 505 and is executed by the one or more processors 502. For instance, the one or more memories 504 store instructions that, when executed by the one or more processors 502, cause the apparatus 500 to perform one or more of the operations as described herein. Furthermore, the one or more processors 502, the one or more memories 504, and example algorithms (e.g., as flowcharts and / or signaling diagrams), encoded as instructions, programs, or code, are means for causing performance of the operations described herein.

[0104] The apparatus 500 to implement the functionality of control 506 may be UE 110, RAN node 170 (e.g. gNB), or network element(s) 190. Thus, processor 502 may correspond to processor(s) 120, processor(s) 152 and / or processor(s) 175, memory 504 may correspond to one or more memories 125, one or more memories 155 and / or one or more memories 171, computer program code 505 may correspond to computer program code 123, computer program code 153, and / or computer program code 173, control module 506 may correspond to module 140-1, module 140-2, module 150-1, and / or module 150-2, and communication I / F(s) 510 and / or transceiver 516 may correspond to transceiver 130, antenna(s) 128, transceiver 160, antenna(s) 158, N / W I / F(s) 161, and / or N / W I / F(s) 180. Alternatively, apparatus 500 and its elements may not correspond to either of UE 110, RAN node 170, or network element(s) 190 and their respective elements, as apparatus 500 may be part of a self- organizing / optimizing network (SON) node or other node, such as a node in a cloud. Apparatus 500 may also correspond to source DU 230, target DU 240, or CU 250.

[0105] The apparatus 500 may also be distributed throughout the network (e.g. 100) including within and between apparatus 500 and any network element (such as a network control element (NCE) 190 and / or the RAN node 170 and / or the UE 110).

[0106] Interface 512 enables data communication and signaling between the various items of apparatus 500, as shown in FIG. 5. For example, the interface 512 may be one or more buses such as address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. Computer program code (e.g. instructions) 505, including control 506 may comprise object-oriented software configured to pass data or messages between objects within computer program code 505. The apparatus 500 need not comprise each of the features mentioned, or may comprise other features as well. The various components of apparatus 500 may at least partially reside in a common housing 528, or a subset of the various components of apparatus 500 may at least partially be located in different housings, which different housings may include housing 528.

[0107] FIG. 6 shows a schematic representation of non-volatile memory media 600a (e.g. computer / compact disc (CD) or digital versatile disc (DVD)) and 600b (e.g. universal serial bus (USB) memory stick) and 600c (e.g. cloud storage for downloading instructions and / or parameters 602) storing instructions and / or parameters 602 which when executed by a processor allows the processor to perform one or more of the steps of the methods describedherein.

[0108] FIG. 7 is an example method 700, based on the example embodiments described herein. At 710, the method includes receiving, from a source distributed unit, a configuration comprising a timing advance of a cell. At 720, the method includes receiving, from the source distributed unit, an indication to perform a cell change. At 730, the method includes applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value. Method 700 may be performed with UE 110 or apparatus 500.

[0109] FIG. 8 is an example method 800, based on the example embodiments described herein. At 810, the method includes transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell. At 820, the method includes receiving, from the target distributed unit, a user context setup response to the user equipment context setup request. At 830, the method includes wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell. At 840, the method includes generating a configuration for the layer 1 or layer 2 triggered mobility handover. Method 800 may be performed with CU 196, CU 250, or apparatus 500.

[0110] FIG. 9 is an example method 900, based on the example embodiments described herein. At 910, the method includes receiving, from a central unit, a user equipment context setup request. At 920, the method includes wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell. At 930, the method includes transmitting, to the central unit, a user context setup response to the user equipment context setup request. At 940, the method includes wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell. Method 900 may be performed with DU 195, target DU 240, or apparatus 500.

[0111] FIG. 10 is an example method 1000, based on the example embodiments described herein. At 1010, the method includes receiving, from a central unit, a user equipment context modification request. At 1020, the method includes wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell. At 1030, the method includes wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement. At 1040, the method includes receiving, from the user equipment, the at least one layer 1 measurement. At 1050, the method includes determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance. Method 1000 may be performed with DU 240, source DU 230, or apparatus 500.

[0112] The following examples are provided and described herein.

[0113] Example 1. An apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a source distributed unit, a configuration comprising a timing advance of a cell; receive, from the source distributed unit, an indication to perform a cell change; and apply the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

[0114] Example 2. The apparatus of example 1 , wherein the configuration comprises a layer 1 or layer 2 triggered mobility configuration.

[0115] Example 3. The apparatus of any of examples 1 to 2, wherein the indication includes an instruction to perform random access channel-based layer 1 or layer 2 triggered mobility.

[0116] Example 4. The apparatus of any of examples 1 to 3, wherein the instructions, when executed by the at least one process, cause the apparatus at least to: receive an indication within the configuration that the timing advance is associated with a synchronization signal block index or at least one layer 1 measurement.

[0117] Example 5. The apparatus of any of examples 1 to 4, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: perform a handover to the cell having a timing advance of zero or that of a source cell.

[0118] Example 6. An apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: transmit, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; receive, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generate a configuration for the layer 1 or layer 2 triggered mobility handover.

[0119] Example 7. The apparatus of example 6, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit within the user equipment context setup request a request for the target distributed unit to provide a layer 1 or layer 1 triggered mobility configuration for the second cell and a layer 1 or layer 2 triggered mobility configuration for the third cell.

[0120] Example 8. The apparatus of any of examples 6 to 7, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to a source distributed unit serving the first cell, an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance.

[0121] Example 9. The apparatus of any of examples 6 to 8, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive, from the target distributed unit, a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

[0122] Example 10. The apparatus of example 9, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to a source distributed unit serving the first cell, the timing advance value of the third cell that can be associated with the synchronization signal block index or the at least one layer 1 measurement.

[0123] Example 11. The apparatus of any of examples 9 to 10, wherein the instructions, when executed by the at least one processor, cause the apparatus to: forward, to the user equipment, the timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

[0124] Example 12. The apparatus of any of examples 9 to 11, wherein the configuration for the layer 1 or layer 2 triggered mobility handover comprises the timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

[0125] Example 13. The apparatus of any of examples 6 to 12, wherein the instructions, when executed by the at least one processor, cause the apparatus to: determine to prepare a layer 1 or layer 2 triggered mobility handover to switch the user equipment from the first cell to either the second cell or the third cell.

[0126] Example 14. An apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmit, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

[0127] Example 15. The apparatus of example 14, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive within the user equipment context setup request a request for the apparatus to provide a layer 1 or layer 2 triggered mobility configuration for the second cell and a layer 1 or layer 2 triggered mobility configuration for the third cell.

[0128] Example 16. The apparatus of any of examples 14 to 15, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to the central unit, a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

[0129] Example 17. An apparatus including: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receive, from the user equipment, the at least one layer 1 measurement; and determine, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

[0130] Example 18. The apparatus of example 17, wherein the instructions, when executed by the at least one processor, cause the apparatus to: determine, based on the known timing advance of the third cell, to not trigger a timing advance acquisition for the third cell.

[0131] Example 19. The apparatus of any of examples 17 to 18, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit, to the user equipment, a configuration comprising the known timing advance of the third cell.

[0132] Example 20. The apparatus of example 19, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit, to the user equipment, an indication to use the known timing advance of the third cell within the configuration.

[0133] Example 21. The apparatus of any of examples 19 to 20, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit, to the user equipment, an indication that the known timing advance is associated with a synchronization signal block index or the at least one layer 1 measurement.

[0134] Example 22. A method including: receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; receiving, from the source distributed unit, an indication to perform a cell change; and applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

[0135] Example 23. A method including: transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generating a configuration for the layer 1 or layer 2 triggered mobility handover.

[0136] Example 24. A method including: receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

[0137] Example 25. A method including: receiving, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receiving, from the user equipment, the at least one layer 1 measurement; and determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

[0138] Example 26. An apparatus including: means for receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; means for receiving, from the source distributed unit, an indication to perform a cell change; and means for applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timingadvance value.

[0139] Example 27. An apparatus including: means for transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; means for receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and means for generating a configuration for the layer 1 or layer 2 triggered mobility handover.

[0140] Example 28. An apparatus including: means for receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and means for transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

[0141] Example 29. An apparatus including: means for receiving, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; means for receiving, from the user equipment, the at least one layer 1 measurement; and means for determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

[0142] Example 30. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performingoperations, the operations including: receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; receiving, from the source distributed unit, an indication to perform a cell change; and applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

[0143] Example 31. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations including: transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generate a configuration for the layer 1 or layer 2 triggered mobility handover.

[0144] Example 32. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations including: receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

[0145] Example 33. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations including: receiving, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modificationrequest comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receiving, from the user equipment, the at least one layer 1 measurement; and determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

[0146] References to a ‘computer’, ‘processor’, etc. should be understood to encompass not only computers having different architectures such as single / multi-processor architectures and sequential or parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGAs), application specific circuits (ASICs), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, 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.

[0147] The memories as described herein may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, non-transitory memory, transitory memory, fixed memory and removable memory. The memories may comprise a database for storing data.

[0148] As used herein, the term ‘circuitry’ may refer to the following: (a) hardware circuit implementations, such as implementations in analog and / or digital circuitry, and (b) combinations of circuits and software (and / or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s) / software including digital signal processor(s), software, and memories that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessors ) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. As a further example, as used herein, the term ‘circuitry’ would also cover an implementation of merely a processor (or multiple processors) or a portion of a processor and its (or their) accompanying software and / or firmware. The term ‘circuitry’ would also cover, for example and if applicable to the particular element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone ora similar integrated circuit in a server, a cellular network device, or another network device.

[0149] It should be understood that the foregoing description is only illustrative. Various alternatives and modifications may be devised by those skilled in the art. For example, features recited in the various dependent claims could be combined with each other in any suitable combination(s). In addition, features from different example embodiments described above could be selectively combined into a new example embodiment. Accordingly, this description is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

[0150] The following acronyms and abbreviations that may be found in the specification and / or the drawing figures are given as follows (the abbreviations and acronyms may be appended with each other or with other characters using e.g. a dash, hyphen, slash, or number, and may be case insensitive):3GPP third generation partnership project4G fourth generation5G fifth generation5GC 5G core networkAMF access and mobility management functionASIC application-specific integrated circuitBWP bandwidth partCBRA contention based random accessCD compact / computer discCE control elementCFRA contention free random accessCORESET control resource setCP control planeCPU central processing unitCRC cyclic redundancy checkC-RNTI cell radio network temporary identifierCSI channel state informationCU central unit or centralized unitDCI downlink control informationDL downlinkDSP digital signal processorDVD digital versatile disc eNB evolved Node B (e.g., an LTE base station)EN-DC E-UTRAN new radio - dual connectivity en-gNB node providing NR user plane and control plane protocol terminations towards the UE, and acting as a secondary node in EN- DCE-UTRA evolved universal terrestrial radio access, i.e., the LTE radio access technologyE-UTRAN E-UTRA networkFl interface between the CU and the DUFPGA field-programmable gate array gNB base station for 5G / NR, i.e., a node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GCHO handoverIAB integrated access and backhaulID identifierIE information elementPF interfaceI / O input / outputLI layer 1L2 layer 2L3 layer 3LMF location management functionLTE long term evolution (4G)LTM lower layer triggered mobility, or layer 1 or layer 2 triggered mobilityMAC medium access controlML machine learningMME mobility management entityMRM multi-RAT mobilityMRO mobility robustness optimizationNCE network control elementng or NG new generation ng-eNB new generation eNB NG-RAN new generation radio access networkNR new radioN / W network0AM operations, administration and maintenancePBCH physical broadcast channelPCell primary cellPDA personal digital assistantPDCCH physical downlink control channelPDCP packet data convergence protocolPHY physical layerPRACH physical random access channelRB resource blockRA random accessRACH random access channelRAM random access memoryRAN radio access networkRANI radio layer 1RAN2 radio layer 2Rel releaseRLC radio link controlROM read-only memoryRP RAN plenaryRRC radio resource controlRS reference signalRSRP reference signal received powerRU radio unitRx receiver or receptionSDAP service data adaptation protocolSGW serving gatewaySMF session management functionSON self-organizing / optimizing network ss synchronization sSSB synchronization signal blockSUL supplementary uplinkUL uplinkTA timing advanceTCI transmission configuration indicatorTRP transmission reception pointTS technical specificationTx transmitter or transmissionUAV unmanned aerial vehicleUE user equipment (e.g., a wireless, typically mobile device)UP user planeUPF user plane functionUSB universal serial busX2 network interface between RAN nodes and between RAN and the core networkXn network interface between NG-RAN nodes

Claims

CLAIMSWhat is claimed is:

1. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a source distributed unit, a configuration comprising a timing advance of a cell; receive, from the source distributed unit, an indication to perform a cell change; and apply the timing advance within the configuration for random access channelless layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

2. The apparatus of claim 1, wherein the configuration comprises a layer 1 or layer 2 triggered mobility configuration.

3. The apparatus of any of claims 1 to 2, wherein the indication includes an instruction to perform random access channel-based layer 1 or layer 2 triggered mobility.

4. The apparatus of any of claims 1 to 3, wherein the instructions, when executed by the at least one process, cause the apparatus at least to: receive an indication within the configuration that the timing advance is associated with a synchronization signal block index or at least one layer 1measurement.

5. The apparatus of any of claims 1 to 4, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: perform a handover to the cell having a timing advance of zero or that of a source cell.

6. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: transmit, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; receive, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generate a configuration for the layer 1 or layer 2 triggered mobility handover.

7. The apparatus of claim 6, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit within the user equipment context setup request a request for the target distributed unit to provide a layer 1 or layer 1 triggered mobility configuration for the second cell and a layer 1 or layer 2 triggered mobility configuration for the third cell.

8. The apparatus of any of claims 6 to 7, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to a source distributed unit serving the first cell, an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance.

9. The apparatus of any of claims 6 to 8, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive, from the target distributed unit, a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

10. The apparatus of claim 9, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to a source distributed unit serving the first cell, the timing advance value of the third cell that can be associated with the synchronization signal block index or the at least one layer 1 measurement.

11. The apparatus of any of claims 9 to 10, wherein the instructions, when executed by the at least one processor, cause the apparatus to: forward, to the user equipment, the timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

12. The apparatus of any of claims 9 to 11, wherein the configuration for the layer 1 or layer 2 triggered mobility handover comprises the timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement.

13. The apparatus of any of claims 6 to 12, wherein the instructions, when executed by the at least one processor, cause the apparatus to: determine to prepare a layer 1 or layer 2 triggered mobility handover to switchthe user equipment from the first cell to either the second cell or the third cell.

14. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmit, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

15. The apparatus of claim 14, wherein the instructions, when executed by the at least one processor, cause the apparatus to: receive within the user equipment context setup request a request for the apparatus to provide a layer 1 or layer 2 triggered mobility configuration for the second cell and a layer 1 or layer 2 triggered mobility configuration for the third cell.

16. The apparatus of any of claims 14 to 15, wherein the instructions, when executed by the at least one processor, cause the apparatus to: transmit, to the central unit, a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1measurement.

17. An apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receive, from the user equipment, the at least one layer 1 measurement; and determine, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

18. The apparatus of claim 17, wherein the instructions, when executed by the at least one processor, cause the apparatus to: determine, based on the known timing advance of the third cell, to not trigger a timing advance acquisition for the third cell.

19. The apparatus of any of claims 17 to 18, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to:transmit, to the user equipment, a configuration comprising the known timing advance of the third cell.

20. The apparatus of claim 19, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit, to the user equipment, an indication to use the known timing advance of the third cell within the configuration.

21. The apparatus of any of claims 19 to 20, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to: transmit, to the user equipment, an indication that the known timing advance is associated with a synchronization signal block index or the at least one layer 1 measurement.

22. A method comprising: receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; receiving, from the source distributed unit, an indication to perform a cell change; and applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

23. A method comprising: transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell;receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generating a configuration for the layer 1 or layer 2 triggered mobility handover.

24. A method comprising: receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

25. A method comprising: receiving, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a firstcell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receiving, from the user equipment, the at least one layer 1 measurement; and determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

26. An apparatus comprising: means for receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; means for receiving, from the source distributed unit, an indication to perform a cell change; and means for applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

27. An apparatus comprising: means for transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell;means for receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and means for generating a configuration for the layer 1 or layer 2 triggered mobility handover.

28. An apparatus comprising: means for receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and means for transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell.

29. An apparatus comprising: means for receiving, from a central unit, a user equipment context modification request;wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; means for receiving, from the user equipment, the at least one layer 1 measurement; and means for determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

30. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations comprising: receiving, from a source distributed unit, a configuration comprising a timing advance of a cell; receiving, from the source distributed unit, an indication to perform a cell change; and applying the timing advance within the configuration for random access channel-less layer 1 or layer 2 triggered mobility, when at least one of: the indication includes an instruction to use the timing advance provided within the configuration, or the indication does not contain a timing advance value.

31. A non-transitory program storage device readable by a machine, tangiblyembodying a program of instructions executable by the machine for performing operations, the operations comprising: transmitting, to a target distributed unit serving a second cell or a third cell, a user equipment context setup request related to a switch of a user equipment from a first cell; receiving, from the target distributed unit, a user context setup response to the user equipment context setup request; wherein the user context setup response received from the target distributed unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or an identifier of the second cell and an identifier of the third cell; and generate a configuration for the layer 1 or layer 2 triggered mobility handover.

32. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations comprising: receiving, from a central unit, a user equipment context setup request; wherein the user context setup request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; and transmitting, to the central unit, a user context setup response to the user equipment context setup request; wherein the user context setup response transmitted to the central unit comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, oran identifier of the second cell and an identifier of the third cell.

33. A non-transitory program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine for performing operations, the operations comprising: receiving, from a central unit, a user equipment context modification request; wherein the user equipment context modification request is associated with a layer 1 or layer 2 triggered mobility handover to switch a user equipment from a first cell to either a second cell or a third cell; wherein the user equipment context modification request comprises at least one of: an indication that the second cell has an unknown timing advance and that the third cell has a known timing advance, or a timing advance value of the third cell that can be associated with a synchronization signal block index or at least one layer 1 measurement; receiving, from the user equipment, the at least one layer 1 measurement; and determining, based on the layer 1 measurement, to switch the user equipment from the first cell to the third cell with the known timing advance.

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