Uplink synchronization groups in layer 1 / layer 2 triggered mobility

Abstract

A method performed by a user equipment (UE) is disclosed, for enabling Layer 1 / Layer 2 5 Triggered Mobility (LTM). The method comprises: obtaining a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtaining at least one UL synchronization parameter associated with the UL synchronization group; and utilizing the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM 0 candidate cells.

Description

UPLINK SYNCHRONIZATION GROUPS IN LAYER 1 / LAYER 2 TRIGGERED MOBILITYTechnical field

[0001] Embodiments of the disclosure relate to wireless networks, and particularly to methods and apparatuses for enabling mobility within wireless networks.BackgroundTiming Advance (TA) and Uplink (UL) Synchronization in New Radio (NR)

[0002] Transmissions from different User Equipments (UEs) experience different delays until they are received at the base station. The reception of these uplink (UL) transmissions at the base station within the corresponding receive window is ensured by an UL timing control procedure. This procedure helps to mitigate the intracell interference which occurs between the UEs transmitting in consecutive subframes and the UEs which are allocated adjacent subcarriers for transmission. Time alignment of the UL transmissions is performed by adjusting the UE transmitter’s timing relative to the received downlink timing, primarily to offset propagation delays among different UEs.

[0003] The time alignment for UL synchronization is obtained by calculation of a Timing Advance (TA) value at the base station, which is indicated to the UE. During the initial cell access, the UE performs a random-access (RA) procedure in which the received Physical Random Access Channel (PRACH) preamble, e.g. Msgl, is utilized by the base station to determine the UE’s initial TA values for UL transmissions within the cell. The UE then uses that TA value in sending UL transmissions to the base station. Throughout the connection, the base station continuously monitors whether any adjustments are required for the UE to advance or delay the UL transmissions, compensating for changes in propagation delay. The UE is informed if there is a need to modify the TA value (see for example, 3GPP TS 38.300, VI 8.0.0 (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18).).

[0004] When the UE does not perform any UL transmissions for some duration in a serving cell, the previously used TA value may become inaccurate, possibly due to the UE’s movement leading to changes in propagation delay. In that case, an UL transmission with the outdated TA value may result in reception outside the receiving window at the base station, leading to incorrect reception or even interference with other UL transmissions. To addressthis, a timer known as the Time alignment timer is configured. This timer indicates the duration during which the UE can consider itself synchronized with the uplink timing of serving cell(s) without receiving any updates in the TA value. Once the Time alignment timer expires and the TA value is not updated, the UE is no longer considered UL synchronized to the serving cell (s) (see for example, 3GPP TS 38.300, V18.0.0 (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18).).Layer 1 / Layer 2 (L1 / L2) Triggered Mobility (LTM)

[0005] LTM is specified as a lower layer mobility procedure in Rel- 18 in which a network node (e.g., gNB) receives measurement report(s), sent by a user equipment (UE), using LI signaling. The LI -measurement reports are utilized by the network to make different mobility- related decisions such as LTM cell switch execution to another target cell by sending an LTM cell switch MAC control element (MAC CE) command. The step-by-step process for LTM is summarized below, and illustrated in Figure 1:

[0006] 1. The UE sends Measurement report(s) for the measurements performed on one or more cells to the gNB. Based on the received measurement report(s), the gNB decides to configure one or more LTM candidate cell(s). This procedure is referred to as LTM preparation.

[0007] 2. The gNB transmits a Radio Resource Control (RRC) Reconfiguration message to the UE including the LTM candidate configuration(s).

[0008] 3. The UE stores the LTM candidate configuration(s) and responds to gNB with anRRC Reconfiguration Complete message.

[0009] 4a. The UE may perform an early Downlink (DL) synchronization with the LTM candidate cell(s) before LTM cell switch execution. The DL pre-synchronization is performed upon reception of a “Candidate Cell TCI States Activation / Deactivation MAC CE” by the UE for the TCI states in the configured LTM candidate cell(s). Since the DL synchronization is already acquired before the LTM cell switch, the UE is not required to wait for performing synchronization signal block (SSB) reference signal (RS) measurements after moving to the target cell which consequently reduces the mobility interruption.

[0010] 4b. The UE may also perform uplink (UL) pre-synchronization with the LTM candidate cell(s) if it receives the Physical Downlink Control Channel (PDCCH) order for early timing advance (TA) acquisition for those candidate cells. This means that the delay occurringin the random-access procedure after the baseline L3-moblity can be reduced from the overall mobility interruption in LTM.

[0011] 5. The UE performs LI measurements on the configured LTM candidate cell(s) and transmits LI measurement reports to the gNB. LI measurement should be performed for the LTM candidate cell(s) which were configured in step 2.

[0012] 6. The gNB decides to execute cell switch to a candidate target cell and transmits a MAC CE triggering cell switch by including the candidate configuration index of the LTM target cell. The UE switches to the target cell and applies the LTM candidate configuration indicated by candidate configuration index.

[0013] 7. The UE performs the random-access procedure towards the target cell if UE does not have valid TA of the target cell. Otherwise, if the UE receives a valid TA value in LTM cell switch command using early TA acquisition method in step 4b, the UE is not required to perform random-access. Moreover, if the target cell TCI state, which is included in the LTM Cell Switch MAC CE, is different from the TCI state activated in early DL synchronization, the UE may experience some delay in synchronization with the new TCI.

[0014] 8. The UE completes the LTM cell switch procedure by sending RRCReconfiguration Complete message to target cell. If the UE has performed a random-access procedure in step 7, the UE considers that LTM cell switch execution is successfully completed when the random-access procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data (see for example, 3GPP TS 38.300, V18.0.0 (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18)).

[0015] When configured by the network, it is possible to initiate an early TA acquisition procedure for one or multiple LTM candidate cells that are different from the current source cell, before the LTM cell switch. The early TA acquisition procedure is triggered by the UE receiving from the serving distributed unit (S-DU) (gNB-DU operating as serving DU) a PDCCH order, so the UE sends a Physical Random-Access Preamble (PRACH) preamble to the LTM candidate cell indicated in the PDCCH order; or TA acquisition is realized through UE-based TA measurement as configured at the UE by RRC. In the former case, the gNB / gNB- DU to which the candidate cell belongs, i.e., a candidate DU (C-DU), calculates the TA value and sends it to the gNB / gNB-DU to which the source cell belongs, i.e., a source DU (S-DU), via the serving central unit (e.g. gNB-CU). The source cell sends the TA value in the LTM cell switch command MAC CE to the UE when triggering LTM cell switch. Depending on theavailability of a valid TA value, the S-DU may include a valid TA value in the LTM cell switch command, so the UE performs a RACH-less LTM; otherwise, when a special value indicating non-valid TA is included, the UE performs a RACH-based LTM cell switch. If the valid TA value is provided in the cell switch command, the UE applies the TA value as instructed by the network and performs RACH-less LTM cell switch upon receiving the cell switch command. If no valid TA value is available, the UE performs RACH-based LTM cell switch (see for example, 3GPP TS 38.300, V18.0.0 (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR andNG-RAN Overall Description; Stage 2 (Release 18)).

[0016] The step-by-step procedure related to the inter-node signaling for early TA acquisition in inter-gNB DU LTM is shown in Figure 2 and explained below:

[0017] The network (e.g., source gNB-DU or S-DU) triggers the TA acquisition for an LTM candidate cell by sending the PDCCH order to the UE. The PDCCH order is a LI DCI format 1 0 message which provides information about random-access towards the LTM candidate cell, such as random-access preamble index, SSB index for the random-access channel (RACH) occasion in LTM candidate cell and physical random-access channel (PRACH) mask index (see for example, 3GPP TS 38.212, VI 8.1.0, (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Multiplexing and channel coding (Release 18)).

[0018] The UE uses the information indicated in the PDCCH order for sending PRACH preamble to the LTM candidate cell (i.e., a candidate gNB-DU or C-DU). The candidate g-NB DU calculates the TA value based on the reception timing of PRACH preamble.

[0019] The candidate gNB-DU sends the calculated TA value, the LTM candidate cell ID, the source gNB-DU ID, the preamble index used in PRACH transmission and other related parameters (e.g., Random Access Radio Network Temporary Identifier, RA-RNTI) to the gNB- CU via distributed unit - central unit (DU-CU) TA Information Transfer message.

[0020] The gNB-CU forwards this received information to source gNB-DU in CU-DU TA Information Transfer message (3GPP TS 38.401, V18.1.0, (2024-03); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NG-RAN; Architecture Description (Release 18).). Both the DU-CU TA Information Transfer and CU- DU TA Information Transfer messages provide the TA information as a list of individual TA Information item or TA information IE, exchanged between a given candidate cell and source gNB-DU pair (see for example, 3GPP TS 38.473, V18.0.0, (2024-03); 3rd GenerationPartnership Project; Technical Specification Group Radio Access Network; NR; NG-RAN; Fl Application Protocol (Release 18).).

[0021] Once the source gNB-DU decides to execute LTM cell switch to the LTM candidate cell (which is now the target cell) via LTM cell switch MAC CE transmission to the UE, the received TA value for that LTM candidate cell is included in the LTM cell switch MAC CE command. This allows the UE to perform RACH-less LTM cell switch to the candidate target cell. Figure 2 shows the inter-node signaling involved in early TA acquisition.Conditional LTM (CLTM)

[0022] Conditional handover (CHO) and the related conditional mobility procedures were introduced in NR for improving the mobility robustness by preparing the UE (and the CHO candidate cells) in advance before there are any radio link outages. The UE is provided the RRC configuration of the candidate CHO cells, alike LTM, and some CHO execution conditions, which once fulfilled lead the UE to directly perform the handover without sending measurement report to the network, unlike LTM. However, there are other differences between the legacy CHO and LTM, for example, the CHO does not include the procedure of early synchronization in Rel-18.

[0023] To facilitate the advantages of short handover interruption as in LTM and enhanced robustness as in CHO, Rel-19 aims to introduce Conditional LTM (CLTM) as part of the mobility-related enhancements. The following Conditional LTM-related objectives have been agreed upon in NR mobility enhancements phase 4 WI:• Specify support of Conditional LTM [RAN2, RAN3, RANI]• Specify UE evaluated conditions for triggering LTM.• Aim to support conditional LTM including subsequent LTM.• Prioritise intra-CU LTM

[0024] See for example, RP-241515, New WID: NR mobility enhancements Phase 4, 3GPP TSG RAN Meeting #104, Shanghai, China, June 17-20, 2024.Summary

[0025] There currently exist certain challenge(s). Rel-18 LTM supports both intrafrequency and inter-frequency mobility scenarios. The LTM candidate cells are configured at the UE during LTM preparation phase, and it is possible that the UE is configured with one or more LTM candidate cell(s) which share similar UL synchronization characteristics.

[0026] One example is when a C-DU has provided (upon request) multiple LTM candidate cell(s) to a given UE, wherein those LTM candidate cells share similar UL properties i.e., a single timing advance (TA) value could be applicable to more than one LTM candidate cell. An important property of all these cells or cell groups with identical UL characteristic is that they share similar TA value and possibly the corresponding Time alignment timer for a given UE. Therefore, it is reasonable to assume that once a UE is time-synchronized with one of these cells (i.e., obtains a valid TA value), the UE may be equally time-synchronized with the remaining cells in that group with similar UL synchronization characteristics.

[0027] Another example of this phenomenon is the configuration of two or more serving cells, e.g., secondary cell(s) (SCell), which belong to the same cell group (either master cell group (MCG) or secondary cell group (SCG), which may also be configured as LTM candidate cells.

[0028] In the existing solution, specified for the TA acquisition procedure in assistance to Rel-18 LTM, the UE acquires the TA value for an LTM candidate cell before cell switch by sending a PRACH preamble to the indicated (by the network) LTM candidate cell. The TA value is calculated at the candidate cell or candidate gNB-DU and then sent to the source cell or source gNB-DU via gNB-CU using the DU-CU TA information transfer procedure and CU- DU TA Information Transfer procedure. However according to 3GPP TS 38.401, V18.1.0, and 3GPP TS 38.473, V18.0.0, multiple LTM candidate cells may have identical UL synchronization characteristics of the other LTM candidate cells in the same C-DU, and the S- DU would be unaware of that, such that when the TA value is acquired for that LTM candidate cell, it is also re-usable for the other LTM candidate cells which share the same UL synchronization characteristics. Thus, the S-DU may unnecessarily trigger multiple PDCCH orders for triggering TA acquisition for multiple LTM candidate cells of the same C-DU which may possibly share the same TA properties, so the UE sends multiple PRACH preambles unnecessarily: that would be waste of UL signaling, waste of unnecessary UE energy consumption, waste of UL resources in the C-DU, and C-DU processing, as the calculated TA is very likely to be the same. That would also mean more signaling over Fl AP from the C-DU to the S-DU (via the CU), to include similar information.

[0029] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges.

[0030] According to a first aspect of the disclosure, there is provided a method performed by a user equipment (UE) is disclosed, for enabling Layer 1 / Layer 2 Triggered Mobility(LTM). The method comprises: obtaining a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtaining at least one UL synchronization parameter associated with the UL synchronization group; and utilizing the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM candidate cells.

[0031] According to a second aspect of the disclosure, there is provided a method performed by a first candidate network node for enabling LTM by a UE. The method comprises: transmitting, to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

[0032] According to a third aspect of the disclosure, there is provided a method performed by a second network node for enabling LTM by a UE served by the second network node. The method comprises: receiving from a first candidate network node, an indication of an UL synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

[0033] Apparatus adapted to perform the methods according to the first, second and third aspects is also provided.

[0034] For example, apparatus for performing the first aspect may comprise a user equipment for enabling LTM. The UE comprises: processing circuitry configured to cause the user equipment to: obtain a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtain at least one UL synchronization parameter associated with the UL synchronization group; and utilize the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM candidate cells.

[0035] In another example, apparatus for performing the second aspect may comprise a first network node for enabling LTM. The first network node comprises: processing circuitry configured to cause the first network node to: transmit to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

[0036] In a further example, apparatus for performing the third aspect may comprise a second network node for enabling LTM by a UE served by the second network node. The second network node comprises: processing circuitry configured to cause the second network node to: receive (502) from a first candidate network node, an indication of an ULsynchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

[0037] Certain embodiments may provide one or more of the following technical advantage(s). The embodiments described herein offer advantages in the case in which an early UL synchronization has been accomplished for one LTM candidate cell, and there are other LTM candidate cells for the UE with identical UL synchronization properties, e.g., the LTM candidate cells belong to the same UL sync group with similar UL synchronization characteristics. The primary advantages provided by the proposed embodiments are mentioned below:

[0038] There is no requirement for the repeated PDCCH-order transmission and randomaccess to the network for different LTM candidate cells with similar UL synchronization characteristics if early TA acquisition has already been performed for one of those candidate cells. This helps in reducing the energy consumption at the UE and network nodes, and better utilization of time-frequency resources in the UL due to reduced repeated signaling overhead.

[0039] In the scenario when early TA acquisition has been carried out for one LTM candidate cell in the group with similar UL synchronization characteristics, but the channel conditions for another LTM candidate cell are better, the UE can execute a RACH-less LTM cell switch to that cell. In other words, once the UE receives a LTM cell switch command for the LTM candidate cell or the Conditional LTM execution conditions are fulfilled for a CLTM cell, the UE does not send a PRACH preamble to the candidate target cell for acquiring the TA value exclusively, even if there was no PRACH transmission to that cell before cell switch execution. Instead, the UE can re-use the earlier acquired TA value for another LTM candidate cell with similar UL synchronization properties, if it is still valid, and can perform RACH-less access to the target cell.

[0040] The UE can also carry out RACH-less access to the LTM candidate cell during LTM fast failure recovery after radio link failure even if the UE has not particularly acquired the TA value for that LTM candidate cell. The UE can simply re-utilize the previously obtained TA value for another LTM candidate cell with identical UL synchronization characteristics during RACH-less cell access.

[0041] The teachings of certain embodiments may improve the power consumption of UEs and / or network nodes.Brief Description of the Drawings

[0042] For a beter understanding of the embodiments of the present disclosure, and to show how it may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0043] Fig. 1 illustrates an LTM Signaling Procedure;

[0044] Fig. 2 shows inter-node Signaling for Early TA Acquisition in LTM;

[0045] Fig. 3 is a flow chart illustrating a method in accordance with some embodiments;

[0046] Fig. 4 is a flow chart illustrating a method in accordance with some embodiments;

[0047] Fig. 5 is a flow chart illustrating a method in accordance with some embodiments;

[0048] Fig. 6 illustrates Inter-node Signaling for TA Acquisition in LTM. Figure 6 illustrates an example implementation of the methods of Figures 3 to 5;

[0049] Fig. 7 illustrates Inter-node Signaling for TA Acquisition in LTM. Figure 7 is an example implementation of the methods of Figures 3 to 5;

[0050] Fig. 8 illustrates Inter-node Signaling for TA Acquisition in LTM;

[0051] Fig. 9 illustrates Inter-node Signaling for TA Acquisition in Conditional LTM. Figure 9 is an example implementation of the methods of Figures 3 to 5;

[0052] Fig. 10 illustrates Inter-node Signaling for TA Acquisition in Conditional LTM. Figure 10 is an example implementation of the methods of Figures 3 to 5.

[0053] Fig. 11 shows an example of a communication system in accordance with some embodiments;

[0054] Fig. 12 shows a UE in accordance with some embodiments;

[0055] Fig. 13 shows a network node in accordance with some embodiments; and

[0056] Fig. 14 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.Detailed description

[0057] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject mater to those skilled in the art.

[0058] As noted above, multiple LTM candidate cells may be configured for a given UE, wherein those LTM candidate cells share similar UL properties e.g., a single timing advance (TA) value could be applicable to more than one LTM candidate cell. An important propertyof all these cells or cell groups with identical UL characteristics is that they share similar TA value and possibly the corresponding Time alignment timer for a given UE. Therefore, it is reasonable to assume that once a UE is time-synchronized with one of these cells (i. e. , obtains a valid TA value), the UE may be equally time-synchronized with the remaining cells in that group with similar UL synchronization characteristics. Another example of this phenomenon is the configuration of two or more serving cells, e.g., secondary cell(s) (SCell), which belong to the same cell group (either master cell group (MCG) or secondary cell group (SCG), which may also be configured as LTM candidate cells.

[0059] Consider the example where Cell A, Cell B and Cell C are the three cells in an LTM configuration which have similar UL synchronization properties known to their own C- DU for a given UE. These cells have the same TA value and possibly the same validity properties e.g., Time alignment timer value. The following problems in LTM and Conditional LTM execution may occur:

[0060] In case the signaling quality for an LTM candidate cell (e.g., Cell B or Cell C) gets even better than the LTM candidate cell with UL pre-synchronization (e.g., Cell A), the UE may be required (by the source node) to perform UL synchronization separately for that LTM candidate cell (e.g., Cell B or Cell C) even if the UE already would have an acquired TA value for another LTM candidate cell (e.g., Cell A) that could be re-used. This may potentially result in:• Delayed LTM cell switch execution, leading to potential radio link failures.• RACH-based cell switch execution to the other LTM candidate cell (e.g., Cell B or Cell C) which in turn results in higher mobility interruption.• Unnecessary waste of time-frequency resources in the repeated inter-node signaling for UL pre-synchronization.• Energy consumption overhead at the UE and network nodes due to transmission, reception and processing of the messages involved in UL presynchronization.

[0061] Embodiments described herein comprise UE-centric solutions and network-centric solutions for the problem described above. It will however be appreciated that for the UE- centric solutions, some of the network-centric embodiments may be utilized and vice versa.UE-centric solution

[0062] As mentioned above, these embodiments are referred to as a UE-centric solution because it contains methods performed by a UE for solving the aforementioned problems. However, what is called herein as the UE-centric solution also contains network-related embodiments.

[0063] Some embodiments described herein comprise a method at a UE configured with a plurality of LTM candidate cells for LTM (and / or Conditional LTM), wherein the UE is configured with an indication that the plurality of LTM candidate cells is associated to an UL synchronization (sync) group. This means that UL synchronization properties (or parameters) for use with LTM candidate cells in the UL synchronization group may be acquired in a single TA acquisition process for the given UE, e.g. that a received TA value can be used for any LTM candidate cell within the UL sync group and / or a received time alignment timer value can be used for any LTM candidate cell within the UL sync group.

[0064] The indication of the UL sync group may be received in an RRC Reconfiguration message e.g., the message in which the plurality of LTM candidate cells are configured. The RRC Reconfiguration message may further include other parameters for the UL sync group e.g., a Time alignment timer value. The UE may then further receive at least one UL synchronization parameter (e.g., a TA value, a Time alignment timer) associated with the UL sync group (i.e., with the multiple LTM candidate cells). For example, the UE may transmit a random-access preamble to one of the LTM candidate cells in the UL sync group (e.g. a first LTM candidate cell). And, upon performing an LTM cell switch to the same or another LTM candidate cell (e.g. a second LTM candidate cell) within the UL sync group, the UE applies the at least one UL synchronization parameter. In some examples, the UE may receive the at least one UL synchronization parameter (e.g. the TA value) in a message after the RRC Reconfiguration configuring the LTM candidate cell(s) e.g., in a Medium Access Control (MAC) Control Element (CE) including a TA value.

[0065] In one example, the UE receives a TA value (e.g. an example of an UL sync parameter), associated to the UL sync group, and starts a Time alignment timer, also associated to the UL sync group (e.g., possibly configured in the message in which the UE is informed of the UL sync group information). While the Time alignment timer is running the UE considers the TA value as valid and in case the UE executes an LTM cell switch procedure (e.g., upon fulfillment of CLTM execution condition) the UE may use the TA value for any LTM candidate cell in the UL sync group (e.g. when the cell the UE selects upon fulfillment of CLTM execution condition is a cell of the UL sync group). When the Time alignment timer associatedto the UL sync group expires, the UE may consider the TA value as invalid for the UL sync group, e.g., if the UE executes an LTM cell switch to any of those LTM candidate cells the UE triggers a random-access procedure. In this option, the Time alignment timer may be configured at the UE as part of the LTM configuration (or CLTM configuration), associated to one of the LTM candidate cells of the UL sync group, or configured for an UL sync group.

[0066] In one example, the UE receives a TA value, associated to the UL sync group, and starts a Time alignment timer, also associated to the UL sync group (e.g., possibly configured in the message in which the UE is informed of the UL sync group information). While the time alignment timer is running the UE may consider the TA value as valid and if the UE executes an LTM cell switch procedure (e.g. upon fulfillment of CLTM execution condition) the UE may restart the Time alignment timer and use the TA value for any LTM candidate cell in the UL sync group (e.g. when the cell has been indicated to the UE by the network or the UE selects a cell of the UL sync group upon fulfillment of CLTM execution condition).

[0067] In one option, when the UE is configured with a plurality of LTM candidate cells, each LTM candidate cell configuration may comprise an UL sync group identifier (e.g., UL sync group ID=3). In that option, this corresponds to the so called “indication that the plurality of LTM candidate cells are associated to an UL sync group”.

[0068] In other words, a plurality of LTM candidate cells that have in their configuration the same value for the UL sync group ID means that they are within the same UL sync group. Thus, for LTM candidate cells within the same UL sync group, the same UL sync group identifier is included e.g., LTM candidate cell A (e.g., UL sync group ID=3), LTM candidate cell B (e.g., UL sync group ID=3), LTM candidate cell C (e.g., UL sync group ID=3). When the UE receives a TA value associated to one of the LTM candidate cells within the group (e.g., TA value for cell A equals x), the UE assumes that the same value can be used for cells B and C, if needed.

[0069] Equivalently, a plurality of LTM candidate cells having associated to their configuration different values for the UL sync group ID means that they are not within the same UL sync group i.e., the UE may not assume the same UL properties among these cells.

[0070] In another option, applicable for LTM (i.e., non-conditional LTM, triggered by the Network (NW) signaling), the at least one UL sync parameter (e.g. TA value) may be received in the LTM Cell Switch command (e.g., a MAC CE), which may also comprise an identifier associated to a first LTM candidate cell (e.g. Cell A).

[0071] The received TA value is applicable for the first LTM candidate cell indicated in the LTM Cell Switch command, and, in case that LTM cell switch execution fails, the UE mayselect another LTM candidate cell for performing an LTM Cell Switch and, in case the UE selects cells B or C (i.e. a cell in the same UL sync group as the first LTM candidate cell indicated in the LTM Cell Switch command), the UE may use the previously acquired TA value for Cell A, since they are within the same UL sync group (in case RACH-less LTM cell switch is used in fast recovery i.e. when the first LTM cell switch attempt fails and the UE, upon initiating re-establishment, triggers another LTM cell switch to a selected cell).

[0072] In another option, applicable for LTM (i.e., non-conditional LTM, triggered by the NW signaling), the TA value is received in a new LTM Cell Switch command (e.g., a MAC CE), which includes also an identifier associated to the UL sync group (e.g., UL sync group ID=3). The received TA value may be applicable for any LTM candidate cell within the UL sync group, according to the previously provided RRC configuration for the UL sync group.

[0073] In another option, applicable for LTM (i.e., non-conditional LTM, triggered by the NW signaling), the TA value may be received in a lower layer message (e.g., a MAC CE) from the serving cell (e.g., from the PCell or PSCell), prior to performing an LTM cell switch, the lower layer message also including an indication of the UL sync group, e.g., an LTM candidate cell ID (e.g., for Cell A). Owing to the RRC configuration related to the UL sync group the UE knows the value is applicable for LTM candidate cells within the same group (e.g., Cell B and Cell C). Then when the UE further receives an LTM Cell Switch command indicating another LTM candidate cell within the same UL sync group for which the UE has previously received the TA value, the UE considers the TA value applicable. In one sub-option the UE starts a Time alignment timer when it receives the TA value and while the timer is running the UE considers the received TA value as valid.

[0074] In another option, applicable for LTM (i.e. non-conditional LTM, triggered by the NW signaling), the TA value may be received in a lower layer message (e.g. a MAC CE) from the serving cell (e.g. from the PCell or PSCell), prior to performing an LTM Cell Switch, including an indication of the UL sync group (e.g., an UL sync group ID for cells A, B, C). Owing to the RRC configuration for the UL sync group the UE knows the value is applicable for LTM candidate cells within the indicated group (e.g., Cell A, Cell B and Cell C). Then when the UE further receives an LTM Cell Switch command indicating any LTM candidate cell within the same UL sync group for which the UE has previously received the TA value, the UE considers the TA value applicable. In one sub-option the UE starts a Time alignment timer when it receives the TA value and while the timer is running the UE considers the received TA value as valid.

[0075] In the case of Conditional LTM, the at least one UL sync parameter (e.g. TA value) may be received in a lower layer message (e.g. a MAC CE) from the serving cell (e.g. from the PCell or PSCell), and when the execution conditions for conditional LTM is fulfilled for Cell A, and / or Cell B and / or Cell C, the same received TA value may be used for Cell A, or Cell B or Cell C, for the cell the UE selects to perform CLTM execution.

[0076] In one option, the at least one UL sync parameter (e.g. TA value) is received with an LTM candidate identifier (e.g., cell identifier, candidate configuration identifier) associated with the LTM candidate cell (e.g., TA value and identifier received in the same MAC CE from the source cell) to which the UE has transmitted the PRACH preamble for TA acquisition. For example, the S-DU may have been aware that cells A, B, C belong to an UL sync group, and triggered TA acquisition only for cell A, so the UE transmits a PRACH preamble to cell A; the C-DU calculates the TA value for Cell A, which is also applicable for cells B and C. The UE receives the TA value (e.g., from the S-DU or the C-DU) including the LTM candidate identifier associated with Cell A, and owing to the previously provided RRC configuration it knows that the same value is applicable for Cell B and Cell C. Thus, after the UE has received that TA value, when CLTM execution condition is fulfilled and the UE selects Cell B (or Cell C), the UE uses the TA value received for Cell A, during the RACH-less Conditional LTM.

[0077] In one sub-option, upon receiving the TA value the UE also starts the Time alignment timer associated to the UL sync group, wherein the Time alignment timer value has been provided in the UL sync group configuration.

[0078] In another option, the TA value is received with an LTM candidate identifier associated with any LTM candidate cell of an UL sync group including a cell for which the UE has transmitted the PRACH preamble for TA acquisition. For example, the S-DU may have been aware that cells A, B, C belong to the same UL sync group, and triggered TA acquisition only for cell A, so the UE transmits a PRACH preamble to Cell A; the C-DU calculates the TA value for cell A, which is also applicable for cells B and C. The UE receives the TA value (e.g., from the S-DU or the C-DU) including an LTM candidate identifier associated with Cell B or Cell C, and owing to the previously provided RRC configuration it knows that the same value is applicable for Cell A. Thus, after the UE has received that TA value, when CLTM execution condition is fulfilled and the UE selects Cell A (or Cell B or C), the UE uses the TA value received for cell B or C, during the RACH-less Conditional LTM.

[0079] In another option, the TA value is received with an identifier associated with the UL sync group, or any information enabling the UE to identify to which group the TA value is associated with. For example, the S-DU may have been aware that cells A, B, C belong to thesame UL sync group (e.g., UL sync group ID=3), and triggered TA acquisition only for Cell A, so the UE transmits a PRACH preamble to Cell A; the C-DU calculates the TA value for Cell A, which is also applicable for cells B and C. The UE receives the TA value (e.g., from the S-DU or the C-DU) including an identifier associated with the UL sync group (e.g. UL sync group ID=3, or UL sync group ID minus 1), and owing to the previously provided RRC configuration it knows that the same value is applicable for any cell within the group e.g. Cell A, Cell B and Cell C. Thus, after the UE has received that TA value, when CLTM execution condition is fulfilled and the UE selects any of the cells that belong to the UL sync group (i.e., Cell A, Cell B or Cell C), the UE uses the TA value received for the UL sync group during the RACH-less Conditional LTM.

[0080] In another sub-case of Conditional LTM, the TA value is received via some random-access response (RAR)-like message from an LTM candidate cell (i.e., C-DU) to which the random-access was performed for TA acquisition. The RAR-like message may include the LTM candidate identifier of the cell to which random-access was performed (e.g., Cell A), along with the TA value, and owing to the previously provided RRC configuration the UE knows that the same value is applicable for cells B and C.

[0081] In one option of Conditional LTM, the TA value is received via some randomaccess response (RAR)-like message from an LTM candidate cell (i.e., C-DU) to which the random-access was performed for TA acquisition. The UE determines that the TA value is applicable for the LTM candidate cell in which the UE has transmitted the preamble and received the TA value, and applicable for other LTM candidate cell(s) in the same UL sync group as the cell in which the UE has received the RAR-like message. In that case, the RAR- like message may not need to include the LTM candidate identifier of the cell to which randomaccess was performed (e.g., Cell A), since owing to the previously provided RRC configuration the UE knows that the same value is applicable for cells B and C.

[0082] In another option of Conditional LTM, the TA value is received via some randomaccess response (RAR)-like message from an LTM candidate cell (i.e., C-DU) to which the random-access was performed for TA acquisition. The RAR-like message may include the UL sync group (e.g., UL sync group ID=3) of the cell to which random-access was performed along with the TA value, and owing to the previously provided RRC configuration it knows that the same value is applicable for any cell within the group e.g., Cell A, Cell B and Cell C.

[0083] In one option, when the UE expects as RAR-like message from an LTM candidate cell in response to a preamble transmitted by the UE for TA acquisition (e.g. in response to a PDCCH order for TA acquisition), the UE uses, to decode the RAR-like message, a RandomAccess temporary identifier (e.g. an RA-RNTI) associated to the random access configuration of the LTM candidate cell for TA acquisition.

[0084] In one option, when the UE expects a RAR-like message from an LTM candidate cell in response to a preamble transmitted by the UE for TA acquisition (e.g., in response to a PDCCH order for TA acquisition), the UE uses, to decode the RAR-like message, the UE’s C- RNTI used in the serving cell.

[0085] In one option, applicable to both LTM and conditional LTM, the UE derives the UL Sync group for a TA indirectly by some existing configuration which is part of an LTM candidate cell.

[0086] In one option, the UE determines the UL sync group from the L2 reset group to which an LTM candidate cell belongs to. Two LTM candidate cells which belong to the same L2 reset group can be considered as being hosted in the same DU and thus in this case the L2 reset group can be considered the same as the UL sync group.

[0087] In one option, the UE determines the UL sync group from the UE-based TA group to which an LTM candidate cell belongs to. Two LTM candidate cells which belong to the same UE-based TA group can be considered as being tightly synchronized and thus in this case the UE-based TA group can be considered the same as the UL sync group.

[0088] At the network side, for the UE centric solution, a first candidate network node (e.g. operating as C-DU) may indicate to the UE in the LTM or CLTM configuration (provided in an RRC information element and / or field and / or message) that multiple LTM candidate cells are associated to an UL sync group, meaning that similar UL synchronization properties can be acquired in a single TA acquisition process for the given UE, e.g. that a received TA value can be used for any cell within the UL sync group. That may be indicated to the CU and forwarded to the UE and / or to a second network node (operating as S-DU), when the UE is configured with LTM or CLTM.

[0089] The second network node may also be informed (e.g., in F1AP signaling and / or within an RRC container) that multiple LTM candidate cells are associated to an UL sync group, meaning that similar UL synchronization properties can be acquired in a single TA acquisition process for the given UE, e.g., that a received TA value can be used for any cell within the UL sync groupMn this context, being indicated means that the second network node should be able to interpret the information. Owing to the UL sync group information the second network node (e.g., the S-DU) triggers TA acquisition for a single LTM candidate cell of an UL sync group, since a later obtained TA value is applicable for any cell within an UL sync group.

[0090] In the following a network centric solution is described. Some of the embodiments for the network centric solution are also applicable for the UE centric solution.Network centric solution

[0091] As mentioned above, some embodiments are described as network centric because the comprise methods performed by oe or more network nodes. However, the network centric embodiments may also be applicable to the network aspects of the UE centric solution.

[0092] Some embodiments described herein provide a method at one or more network nodes for performing inter-node signaling such that at least one UL sync parameter (e.g. a Timing Advance (TA) value) for multiple LTM candidate cells with similar UL synchronization properties can be acquired in a single TA acquisition process for the given UE and the obtained TA value can then be re-used at different instances when required, as long as the TA value is valid (e.g. Time alignment timer for that TA value is running).

[0093] According to the method, a first candidate network node (e.g. operating as a Candidate DU / C-DU) for a UE configured with LTM or CLTM, may transmit UL sync group information (of an UL sync group) to a second network node (e.g. a node operating as an S- DU), indicating one or more LTM candidate cells of that first candidate network node (e.g. C- DU) which have similar UL synchronization characteristics, such that the LTM candidate cells of the first candidate network node have the same applicable Timing advance (TA) and the same Time alignment timer for which the TA value is valid.

[0094] In one main option, the UL sync group information is transmitted from the C-DU to the S-DU via a CU (i.e., C-DU to CU, and CU to S-DU, over Fl AP; or, directly from the C- DU to the S-DU; or from a Candidate CU to a Source CU, via XnAP).

[0095] The first candidate network node may in some examples further receive from a UE a PRACH preamble, on a PRACH of an LTM candidate cell of an UL sync group and may transmit to the second candidate network node a calculated TA value, associated to the LTM candidate cell of the UL sync group, which is also applicable for other LTM candidate cells within that same UL sync group. The TA value may be calculated based on the reception of the PRACH preamble.

[0096] In such scenario, the TA acquisition and early UL synchronization for LTM cell switch execution, in more detail, may take place according one or more of the steps of the following procedure:

[0097] The second network node, operating as a S-DU (e.g., a source gNB-DU), which has received the UL sync group information, triggers TA acquisition (PDCCH order) for one LTM candidate cell within at least one UL sync group.

[0098] The S-DU sends to the UE a PDCCH order for triggering TA acquisition and in response the UE sends the PRACH preamble to the indicated LTM candidate cell (of the candidate gNB-DU), according to the information provided in the PDCCH order.

[0099] The first network node operating as a C-DU calculates the TA value and sends the calculated TA value as well as the LTM candidate cell ID of the cell to which random-access was performed. The gNB-CU transmits the TA value as well as the LTM candidate cell ID of the cell to which random-access was performed to the S-DU.

[0100] The S-DU, therefore, gets a TA value for the UL sync group (i.e. , the group with identical UL characteristics) and the LTM candidate cell ID of the cell to which random-access was performed. Since the S-DU is already configured with the UL sync group information and is informed about the other LTM candidate cell(s) (as well as their corresponding LTM cell identifiers) which form the same UL sync group, the S-DU can deduce that the TA value is applicable for those LTM candidate cells as well.

[0101] When the measurements for one of the LTM candidates in the UL sync, group are favorable for LTM cell switch execution, the source cell within S-DU sends the LTM cell switch MAC CE for that LTM candidate cell and includes the calculated TA value (even though the UE may not have sent a preamble to that cell).

[0102] The network centric solution for the UE may also involve the UE configuration with multiple LTM candidate cells which may share the same UL sync group, identified by an UL sync group identifier (e.g., UL sync group ID=3). Each LTM candidate cell configuration includes an UL sync group identifier., e.g., LTM candidate cell A (e.g., UL sync group ID=3), LTM candidate cell B (e.g., UL sync group ID=3), LTM candidate cell C (e.g., UL sync group ID=3). In that scenario, the S-DU sends the UE a TA value associated with one of the LTM candidate cells within the group (e.g., TA value for Cell A equals to x ms) in LTM cell switch. Using the configuration received earlier, the UE assumes that the same value could be used for cells B and C, if needed, e.g., by performing RACH-less cell switch to Cell B or Cell C during LTM fast failure recovery.

[0103] The network centric solution may be used for Conditional LTM. However, there would be differences in the ways the second network node (e.g., S-DU) uses the UL sync group information and the TA value provided from the first network node. For example, in the case of conditional LTM, a primary difference is in the ways in which LTM execution is carried out(step “v”) and the fact that the TA value (for one or more LTM candidate cells) is provided to the UE before an LTM Cell Switch occurs. In Conditional LTM, there is no LTM cell switch MAC CE transmission and the LTM execution is conditioned to the fulfillment of the execution conditions defined for the Conditional LTM. Therefore, the step “v” is modified for providing the LTM candidate cell(s) TA value:

[0104] The network may provide UE the LTM candidate cell TA value before an LTM cell switch, e.g., in a message sent by source gNB-DU (such as a MAC CE), which is not the same message as for LTM cell switch, but something received earlier.

[0105] The S-DU may send UE a message before the cell switch (e.g., MAC CE) with an UL sync group identifier (e.g., UL sync group ID=3) and the calculated TA value for the UL sync group which is obtained by executing random-access to one of the LTM candidate cells in the UL sync group. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of those LTM candidate cells.

[0106] In another option, the S-DU sends the message (e.g., MAC CE) to the UE which includes one of the LTM candidate cell identifiers in the UL sync group and the obtained TA value. The LTM candidate identifier can be associated to the cell to which the UE performed random-access to acquire TA value (e.g., Cell A) or another LTM candidate cell identifier in the same UL sync group (e.g., Cell B or Cell C). Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of those LTM candidate cells.

[0107] The network may provide UE the LTM candidate cell TA value before an LTM Cell Switch, e.g., in a RAR-like message sent by C-DU.

[0108] The C-DU may send UE a RAR-like message in response to the random-access which includes an UL sync group identifier (e.g., UL sync group ID=3) and the calculated TA value for the UL sync group which is obtained by performing random-access to the LTM candidate cell in the UL sync group. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of the LTM candidate cells in the UL sync group.

[0109] In another option, the C-DU sends the RAR-like message to the UE which includes an LTM candidate cell identifier for the cell to which random access was performed (e.g., Cell A) and the calculated TA value. Or alternatively there is possible no LTM candidate cell identifier in the RAR-like message because the UE can comprehend the LTM cell identity based on the received RAR response. Owing to the UL sync group configuration providedearlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to the other LTM candidate cells in the same UL sync group (e.g., Cell B or Cell C) in both the cases.

[0110] In the other options of the network-related solution, the S-DU is not aware in advance (e.g. in advance of the TA acquisition procedure) of the other LTM candidate cells which belong to the same UL sync group or share the similar UL sync characteristics but has the functionality that it may receive the TA value for an LTM candidate cell for which the PDCCH order was not triggered at all. In such case, one or more of the following inter-node signaling steps take place at the network side during the early TA acquisition:

[0111] The S-DU sends to the UE a PDCCH order for triggering TA acquisition to an LTM candidate cell (e.g., Cell A) and in response the UE sends the PRACH preamble to the indicated LTM candidate cell (i.e., Cell A), according to the information provided in the PDCCH order.

[0112] The first network node operating as a C-DU calculates the TA value for the LTM candidate cell (i.e., Cell A) but it also knows that the other LTM candidate cells (e.g., Cell B and Cell C) also belong to the same UL sync group within the C-DU.

[0113] The candidate gNB-DU or C-DU provides the TA value for the LTM candidate cell to which the UE performed random-access (i.e., Cell A), LTM candidate cell identifier which received the random-access request (i.e., Cell A), and other LTM candidate cells identifiers which belong to the same UL sync group as Cell A (i.e., Cell B and Cell C), since the S-DU was not earlier informed about the LTM candidate cell forming the same UL sync group.

[0114] The S-DU, therefore, receives the TA value along with the LTM candidate cell identifier for which the PDCCH order was triggered (i.e., Cell A), and the other LTM candidate cell identifiers which have the identical UL sync characteristics as Cell A (i.e., Cell B and Cell C) or form the same UL sync group.

[0115] In yet another option of the network-centric solution, the S-DU is informed about the LTM candidate cells which form the similar UL sync group (e.g. prior to the TA acquisition procedure) but receives the UL synchronization configuration for only one LTM candidate cell (e.g., Cell A) in that UL sync group. This way the S-DU does not repeatedly trigger the PDCCH order for the other cells in the UL sync group (e.g., cells B or C) but still receives the TA value for the other LTM candidate cells in the UL sync group. In that case, the procedure for early TA acquisition includes one or more of the following steps:

[0116] The S-DU sends to the UE a PDCCH order for triggering TA acquisition to the LTM candidate cell for which it received the early UL synchronization configuration (e.g., Cell A). In response, the UE sends the PRACH preamble to the indicated LTM candidate cell (i.e. , Cell A), according to the information provided in the PDCCH order.

[0117] The first candidate network node operating as a C-DU calculates the TA value for the LTM candidate cell (i.e., Cell A) and knows that the other LTM candidate cells (e.g., Cell B and Cell C) also belong to the same UL sync group within the C-DU.

[0118] The candidate gNB-DU or C-DU provides the TA value for the LTM candidate cell to which the UE performed random-access (i.e., Cell A), and the LTM candidate cell identifier which received the random-access request (i.e., Cell A). There is no requirement to provide information about the other LTM candidate cell identifiers which form the same UL sync group because the S-DU is already informed about the LTM candidate cells which belong to the same UL sync group.

[0119] The S-DU, therefore, receives the TA value along with the LTM candidate cell identifier for which it received the early UL synchronization configuration (i.e., Cell A).

[0120] In another option of the network-centric solution, the C-DU, after calculating the TA value for one LTM candidate cell, sends to the S-DU the calculated TA value for the LTM candidate cell and send also the exact same TA value for all the others LTM candidate cell which belongs to the same UL sync group. The C-DU may send to the S-DU a TA value for an LTM candidate cell in one network signaling or can alternatively send a list of TA values which refer to a list of LTM candidate cells in one network signaling. In both cases, if one or more LTM candidate cells have the same TA value, this is an implicit indication for the S-DU that the one or more LTM candidate cells belongs to the same UL sync group.

[0121] The methods disclosed are applicable for LTM, thus the text refers to the term “L1 / L2 based inter-cell mobility (LTM)” as defined in Release 18, though it interchangeably also uses the terms L1 / L2 mobility, LI -mobility, LI based mobility, Ll / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility Ll / L2-Triggered Mobility (LTM), Lower-layer triggered Mobility or simply LTM, as more widely used. The basic principle is that the UE receives a lower layer signaling from the network (e.g., a MAC Control Element - MAC CE) indicating to the UE a change (or switch or activation) of its PCell or PSCell, wherein a lower layer signaling is a message / signaling carried via a lower layer protocol, which may be referred as a L1 / L2 inter-cell mobility execution command or LTM cell switch command. The change of PCell or PSCell may also lead to a change in SCell(s) for the same cell group e.g., in case the command triggers the UE to change to another cell group configuration of the same type (e.g.,another MCG configuration). Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more LTM candidate cell configurations (e.g., reception of an RRC Reconfiguration message, with at least one LTM candidate cell configuration). An LTM candidate cell configuration may include parameters in the IE CellGroupConfig per candidate cell and / or an embedded RRC Reconfiguration per LTM candidate cell.

[0122] The term “LTM cell switch procedure” refers to the process of a UE switching (or changing) its cell from a source cell to a target cell (which may be called here an LTM candidate cell or a neighbor cell), using LTM. In the context of LTM, an LTM cell switch procedure may sometimes also be known as L1 / L2 based inter-cell mobility execution, LTM cell switch execution, LTM execution, dynamic switch, LTM switch, (LTM) cell switch, (LTM) serving cell change or (LTM) cell change. In the context of the disclosure, switching to the LTM candidate cell configuration comprises the UE considering that an LTM candidate cell becomes its new special cell (SpCell) e.g., PCell in case of LTM being configured for a Master Cell Group (MCG) and / or PS Cell in case of LTM being configured for a Secondary Cell Group (SCG); or, changing its SpCell from the current PCell to an LTM candidate cell. Even if the term “change of cell” is used, that may comprise a change of a whole cell group configuration, which includes a change in the SpCell (e.g., change of PCell, or change of PSCell) and a change in SCells of the cell group (e.g., addition, modification and / or release of one or more SCells).

[0123] An LTM cell switch procedure or LTM execution procedure may be triggered in the UE by reception of an LTM cell switch command (e.g., LTM Cell Switch MAC CE), or alternatively, triggered in response to the detection of a failure (in case of LTM fast failure recovery). The text refers to a LTM candidate cell, which is a cell the UE is configured with when configured with Ll / L2-triggered mobility. That is a cell the UE can move to in a LTM cell switch procedure, upon reception of a LTM cell switch command. These cells may also be termed as candidate cell(s), candidates, candidate target cell, implied target cell, mobility candidates, non-serving cells, additional cells, or deactivated cells etc. According to the method, an LTM candidate cell may potentially be a target PCell or PSCell, or an SCell of a cell group (e.g., MCG SCell or SCG SCell) or PSCell. In other words, a configured LTM candidate cell may be a currently configured serving cell, i.e., an SCell from MCG or an SCell from SCG or PSCell. An LTM candidate cell might also pertain to a candidate cell in a 5G Radio Access Technology like NR or a future 6G Radio Access Technology.

[0124] An LTM candidate cell is a cell the UE may be configured to perform measurements on (e.g., channel station information, CSI, measurements) so that the UE reportsthese measurements and network may take educated decision on which beam (e.g., TCI state) and / or cell the UE is to be switched to. In the case of an LTM fast failure recovery, when a failure is detected, the UE selects a cell and when the cell is an LTM candidate cell the UE does not have to perform re-establishment, but instead performs an LTM cell switch towards the selected LTM candidate cell e.g., by applying the LTM candidate cell configuration associated to the selected LTM candidate cell.

[0125] Furthermore, the method disclosed is also applicable for Conditional LTM (CLTM), which may be viewed as a form of conditional reconfiguration. In CLTM, the UE is configured with an LTM candidate cell (denoted as a CLTM candidate cell), by receiving an LTM candidate cell configuration, as in legacy LTM, and called herein a Conditional LTM candidate cell configuration, and an associated execution condition, denoted CLTM execution condition. The CLTM execution condition associated to a CLTM candidate cell is associated to the assessment of lower layer measurements, such as Layer 1 (LI) RSRP and / or SS-RSRP, derived from SSBs and / or CSI-reference signals (CSI-RSs) of either the source cell and / or an CLTM candidate cell. Lower layer measurements, in this context, are measurements reported to support lower layer procedures like beam management, TCI state activations / deactivations, early timing advance (TA) acquisition, and link adaptation, and they aren't filtered based on Layer 3 (L3) parameters, though there may be some filtering of these measurements based on lower layer parameters. The reception of CLTM execution condition may also involve receiving an indication of the condition and / or configuring it with parameters such as event identifier(s), offset(s), threshold(s), reference signal (RS) type, trigger quantity, time-to-trigger (TTT), and so forth.

[0126] When configured with CLTM, the UE evaluates the CLTM execution condition (referred to as Conditional LTM execution condition, LTM execution condition, or triggering condition) or a combination thereof. And, when the condition for a CLTM candidate cell is fulfilled, the UE performs a CLTM execution, which may be seen as a kind of LTM execution (but not triggered by the reception of an LTM cell switch command); this may also be considered as a kind of LTM cell switch, or Conditional LTM cell switch, or Conditional LTM execution. During the execution, the UE may apply a message, parts of a message, or at least one information element (IE), or perform a source cell switch or change. According to the methods outlined herein, upon satisfaction of the execution condition(s), the UE initiates an LTM cell switch.

[0127] The text also mentions an LTM candidate cell within the framework of Conditional LTM. The candidate cell may be referred to as a Conditional LTM candidate cell, CLTM cell,simply candidate cell, candidate target cell, simply target cell, LTM candidate cell, or L1 / L2 inter-cell mobility candidate cell, depending on the context or terminology used. Essentially, it denotes a cell to which the UE is directed or switches in the event of executing a conditional L1 / L2 inter-cell mobility procedure after meeting the associated execution condition(s). These cells may also be termed as candidate cells, mobility candidates, non-serving cells, additional cells, or deactivated cells. A Conditional LTM candidate cell may also be a currently configured as a serving cell, i.e., an SCell from MCG or an SCell from SCG or PSCell. A Conditional LTM candidate cell might also pertain to a candidate cell in a 5G Radio Access Technology like NR or a future 6G Radio Access Technology.

[0128] In the context of both LTM and CLTM, the term “beam” may correspond to a spatial direction in which a Reference signal (RS), such as Synchronization Signal Block-RS (SSB-RS), Mobility Reference Signal (MRS), a Channel State Information - RS (CSI-RS), or a RS defined for a 6G radio interface, is transmitted (e.g., by a network node) or received (e.g. by the UE), or a spatial filter applied to a signal which is transmitted or received. Thus, transmitting signals in different beams could correspond to transmitting signals in different spatial directions. The beam measurement may correspond to a measurement on an RS transmitted in that beam e.g., an SSB measurement and involves determining a measurement quantity value such as a Synchronization Signal based Reference Signal Received Power (SS- RSRP) and / or Synchronization Signal based Reference Signal Received Quality (SS-RSRQ) and / or Synchronization Signal based Signal to Noise and Interference Ratio (SS-SINR). In the text the beam is identified by beam index and / or a Reference Signal (RS) index or identifier, such as an SSB index, or a CSI-RS resource identifier.

[0129] For both LTM and CLTM, the text refers to a RACH-less LTM execution procedure in which the UE does not transmit a Physical Random-Access Channel (PRACH) preamble to the LTM candidate cell as its first UL message. Instead, the UE either i) transmits a Scheduling Request (SR) over the Physical Uplink Control Channel (PUCCH), or any other UL control channel which requires the UE to be UL synchronized (or UL time aligned); or ii) transmits UL payload (bits associated to a complete message, e.g., RRC Reconfiguration Complete), e.g., using at least a pre-configured grant, over a Physical Uplink Shared Channel (PUSCH). In a RACH-less access, the UE has a valid timing advance (TA) for the selected LTM or CLTM candidate cell.

[0130] In the method outlined for both LTM and CLTM, the LTM candidate cells may have similar UL synchronization properties and may be identified by some group identity (e.g., UL sync group ID). Such LTM candidate cells may have an identical TA value applicable tothe UE for the same Time alignment timer in case the UE executes cell switch to any of those candidate target cells. This phenomenon may also be modelled as Timing Advance Group (TAG) which is defined as a group of serving cells per UE that is configured by RRC and that, for the cells with an Uplink (UL) configured, using the same timing reference cell and the same TA value. TAG configuration is done per serving cell group, which means that serving cells can share the same TAG if they belong to the same cell group (MCG or SCG). In legacy operation, the UE keeps a time alignment timer associated to a TAG). While the timer alignment timer is running, the UE considers the UL sync and therefore, the TA value, as valid (see for example, 3GPP TS 38.300, V18.0.0 (2023-12); 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18).). However, it is also possible that multiple LTM candidate cells share similar UL synchronization characteristics irrespective of the fact that they may or may not belong to a serving cell group (e.g., MCG or SCG) or may not be one of the UE’s serving cell(s).

[0131] The overall architecture for both LTM and CLTM includes a Centralized Unit (CU) and a Distributed Unit (DU) in a Radio Access Network (RAN). The RAN is a Next-Generation RAN (NG-RAN), which may be referred to as the 5G RAN, however, the method is applicable to any RAN such as a 6G RAN architecture. The RAN (e.g., NG-RAN) consists of a set of RAN nodes (e.g., gNBs) connected to a Core Network (e.g., a 5GC) through a RAN / CN interface (e.g., NG interface). A gNB may consist of a gNB-CU and one or more gNB-DU(s). A gNB-CU and a gNB-DU is connected via Fl interface. Throughout the text, the source cell the UE is located in belongs to the source gNB-DU or S-DU whereas the candidate target cell is associated to the candidate gNB DU or C-DU. The method is presented as applicable to the NG-RAN as an example, however, the method is also applicable to any RAN architecture, such as a 6G RAN.

[0132] In some embodiments, a UE receives a Timing advanced (TA) value acquired during TA acquisition (also called early UL synchronization) of an LTM candidate cell, which may also be applicable for other LTM candidate cells. According to some embodiments, once the UE performs the TA acquisition (UL pre-synchronization) for a LTM candidate which is in an UL sync group, it is not required to perform early UL synchronization for the other LTM candidate cells in the same UL sync group when the UE executes the cell switch to one of those LTM candidate cells. An example for such UL sync group(s) is indicated in the table below:Table 1: LTM Candidate Cells with Identical UL Properties

[0133] As indicated in table 1, a UE is configured with multiple different LTM candidate cells such that the Cell A, Cell B and Cell C share the same UL synchronization characteristics while Cell D and Cell E belong to different UL sync group with similar UL synchronization properties. This means that, for example, each group shall have a similar TA value and Time alignment timer for the given UE (e.g., TA value 1 applicable for x ms in Group 7). However, in some of the options in which the UE is initially configured with the UL sync group information, or the S-DU initially receives UL sync group information, the UL sync group information comprises the LTM Candidate cells ID(s) and possibly a Time alignment timer value. Then, at a later moment, the S-DU and / or the UE further receives a TA value associated to the group e.g. after the UE has transmitted a preamble associated to at least an LTM candidate cell within the UL sync group and the C-DU has calculated such a TA value.

[0134] Figure 3 depicts a method in accordance with particular embodiments. The method may be performed by a UE or wireless device (e.g. the UE 1112 or UE 1200 as described later with reference to Figures 11 and 12 respectively). The method of Figure 3 may be performed by a UE for enabling LTM The method begins at step 302 with obtaining a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group.

[0135] In some examples, the UE may receive an indication that the plurality of LTM candidate cells is associated with the UL sync group. For example, the indication may comprise an UL synchronization group identifier associated with each of the plurality of LTM candidate cells. In other examples, the indication of the UL sync group may comprise identifications of the plurality of LTM candidate cells being associated with the at least one synchronization parameter (e.g. obtained in step 304). In other examples, the UL sync group may be derived bythe UE from other information, e.g., an L2 reset group or a UE-based timing advance group. The indication that the plurality of LTM candidate cells is associated with the UL sync group may be received in a RRC message (e.g. with the configuration of the plurality of LTM candidate cells).

[0136] In some embodiments, the S-DU may derive the information in Table 1 implicitly via the information received for LTM candidate cells by the other C-DUs. For instance, in an option applicable to both LTM and conditional LTM, the UE derive the UL sync group for a TA indirectly by some existing configuration which is part of an LTM candidate cell.

[0137] In one option, the UE determines the UL sync group from the L2 reset group to which an LTM candidate cell belongs. Two LTM candidate cells which belong to the same L2 reset group can be considered as being hosted in the same DU and thus in this case the L2 reset group can be considered the same as the UL sync group. In other words, when two LTM candidate cells have the same “L2 No reset identities”, the UE may assume that they have the same TA value. When the network receives this “L2 No reset group” information per LTM candidate cell the network (e.g., the S-DU) may also derive that two or more LTM candidate cells belong to the same UL sync group.

[0138] In one option, the UE determines the UL sync group from the UE-based TA estimation group to which an LTM candidate cell belongs. Two LTM candidate cell which belong to the same UE-based TA group (i.e., share the same UE-based TA estimation configuration) can be considered as being tightly synchronized and thus in this case the UE- based TA estimation group can be considered the same as the UL sync group.

[0139] In some embodiment, the UE itself can determine that one or more LTM candidate cells belong to the same UL sync group if the UE receives exactly the same TA value and the same Time alignment timer value for these LTM candidate cells.

[0140] In step 304 the method comprises obtaining at least one UL synchronization parameter associated with the UL synchronization group. The at least one UL synchronisation parameter may comprise a timing advance (TA) value and / or a time alignment timer. The at least one UL synchronisation parameter may be received from a first candidate network node (e.g. a C-DU) in a random access response like message (e.g. in response to a PRACH preamble transmitted on a LTM candidate cell. In other examples, the at least one UL synchronisation parameter may be received from a second network node (e.g. a S-DU).

[0141] For example, step 304 may comprise receiving the at least one UL synchronization parameter in a message that further comprises an indication of the first LTM candidate cell (e.g. an indication of the UL sync group or an identification of the first LTM candidate cells(potentially indicating other LTM candidate cells in the UL sync group)). The message may be transmitted using a MAC CE.

[0142] In other examples, step 304 may comprise receiving the at least one UL synchronization parameter responsive to transmitting a Physical Random Access Channel, PRACH, preamble for timing advance, TA, acquisition to one of the plurality of LTM candidate cells (e.g. the first LTM candidate cells or one of the other LTM candidate cells in the UL sync group).

[0143] In step 306 the method comprises utilizing the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell (e.g. Cell A) of the plurality of LTM candidate cells. It will be appreciated that the at least one UL synchronisation parameter may comprise a TA value that has been determined based on a PRACH preamble sent by the UE to one of the other LTM candidate cells (e.g. a second LTM candidate cell) in the UL sync group.

[0144] In some examples, the method of Figure 3 further comprises the UE receiving a PDCCH order for performing TA acquisition (by transmission of a PRACH preamble) towards a neighbor cell, e.g. an LTM candidate cell, which belongs to the UL sync group, and the UE selects to perform TA acquisition (i.e. transmit a PRACH preamble) towards any of the cells that belong to the same UL sync group as the cell indicated with the PDCCH order.

[0145] For example, if cells A, B and C belong to the same UL sync group and the UE receives a PDCCH order to perform a TA acquisition (e.g., through transmission of PRACH preamble) to Cell A, the UE can select to perform the TA acquisition towards any of the cells A, B and C. When the UE receives a TA value based on the TA acquisition (e.g., based on transmission of a PRACH preamble) in any of the cells, it is considered valid for all the cells that belong to the same UL sync group. As an example, the UE receives a PDCCH order for performing TA acquisition (e.g., by transmission of a PRACH preamble) towards Cell A (e.g. the first LTM candidate cell), but the UE selects to perform the TA acquisition (by transmission of a PRACH preamble) in Cell B. When the UE receives the corresponding TA value, e.g., via the source cell or from Cell B (where the PRACH preamble was transmitted), the TA value can be used for any of the cells A, B or C (so the TA value for cell B may be used in step 306 to perform the LTM cell switch to the cell A).

[0146] To be able to perform the TA acquisition (e.g., PRACH transmission) towards any of the cells in the same UL sync group has the benefit that the UE could select the cell where the TA acquisition procedure e.g., would have the least impact to the UE’s current connection (in serving cell(s)) and / or where the UE’s energy consumption would be the lowest.

[0147] In one option, the UE receives an indication (e.g., as part of the RRC configuration or in the PDCCH order) whether it can perform the TA acquisition (e.g., the transmission of the PRACH preamble) towards any of the cells that belong to the same UL sync group as the cell indicated in the PDCCH order. In one option, the UE receives an indication (e.g., as part of the RRC configuration or in the PDCCH order) about which other cells that the UE can perform the TA acquisition (e.g., the transmission of the PRACH preamble) instead of the one indicated in the PDCCH order.

[0148] In one alternative, the UE receives a PDCCH order for performing TA acquisition (by transmission of a PRACH preamble) wherein the PDCCH includes an indication of UL sync group e.g., an UL sync group ID. In response, the UE selects an LTM candidate cell of the indicated group (e.g., Cell A, Cell B or Cell C) to perform TA acquisition (i.e., transmit a PRACH preamble). For example, if cells A, B and C belong to the same UL sync group (e.g., with UL sync group ID=3) and the UE receives a PDCCH order to perform a TA acquisition to the UL sync group with ID=3 (e.g., through transmission of PRACH preamble), the UE can select to perform the TA acquisition towards any of the cells A, B and C. When the UE receives a TA value based on the TA acquisition (e.g., based on transmission of a PRACH preamble) in any of the cells, it is considered valid for all the cells that belong to the same UL sync group.

[0149] In one alternative, the UE receives a PDCCH order for performing TA acquisition (by transmission of a PRACH preamble) wherein the PDCCH includes an indication of multiple candidate cells where the UE can perform the TA acquisition (i.e. transmit a PRACH preamble). In response, the UE selects one of the included candidate cells for performing the TA acquisition procedure.

[0150] In one set of alternatives, the UE is also configured with criteria for performing the TA acquisition towards another cell than the main one that is indicated in the PDCCH order, e.g. that there is a threshold value for radio quality that needs to be fulfilled for the other candidate cell (possibly related also to the radio quality of a serving cell) in order to perform the TA acquisition towards any of the other candidate cells (that e.g. belong to the same UL sync group). There could e.g., be a threshold for the measured Reference Signal Received Power (RSRP) value for the other candidate cell, which needs to be fulfilled in order for the UE to perform the TA acquisition procedure towards that candidate cell. In one example, the UE receives from the network a request to perform the early TA acquisition (e.g., in the PDCCH order) towards any of a number of candidate cells, including a threshold that needs to be fulfilled. The UE then checks whether the threshold is fulfilled for any of the candidate cellsand, if that is the case, selects such a cell and performs the TA acquisition procedure towards that cell (or those cells).

[0151] In one option, which may be applicable to any of the previous option, the UE receives a TA acquisition configuration associated to one or more cells of a UL sync group or to one or more UL sync groups. In one alternative, the PDCCH order includes different TA acquisition configurations for the different cells where the UE can perform the corresponding TA acquisition procedure.

[0152] In one alternative, the indication to perform the TA acquisition procedure for a candidate cell is sent to the UE using a different type of message, e.g., as a MAC Control Element (MAC CE) or as an RRC message.

[0153] In some examples, where the UL synchronization parameter comprises a timing advance, TA, value, the method of Figure 3 further comprises starting a time alignment timer responsive to receiving the TA value (e.g. responsive to step VV014).

[0154] The method of Figure 3 may then further comprise responsive to the LTM cell switch being triggered whilst the time alignment timer in running, performing step 306. The method of Figure 3 may then further comprise restarting the time alignment timer responsive to performing the LTM cell switch.

[0155] In other examples, the method of Figure 3 may comprise responsive to the LTM cell switch being triggered after the time alignment timer has expired, performing a randomaccess procedure to perform the LTM cell switch to the first LTM candidate cell (e.g. the TA value obtained in step VV014 is no longer considered valid)

[0156] In some examples, step 306 is triggered by a LTM cell switch command (e.g. received from a second network node (e.g. S-DU) to perform LTM cell switch to the first LTM candidate cell. In some examples, the at least one UL synchronization parameter of step 304 is received in a message with the LTM cell switch command.

[0157] In some examples, the method of Figure 3 comprises responsive to the LTM cell switch to the first LTM candidate cell failing, selecting a second LTM candidate cell from the plurality of LTM candidate cells (e.g. from within the UL sync group) and performing an LTM cell switch to the second LTM candidate cell utilizing the UL synchronization parameter.

[0158] In some examples, step 304 comprises receiving the UL synchronization parameter in a lower layer message prior to receiving the LTM cell switch command.

[0159] In some examples, step 306 is triggered by fulfilment of a condition (e.g. in the case of CLTM). In these examples, step 304 may comprise receiving the at least one UL synchronization parameter via lower layer signaling (e.g. in a MAC CE MAC CE or randomaccess response (RAR) message.). In some examples, step 304 comprises receiving the at least one UL synchronization parameter in a random-access response from a LTM candidate cell (e.g. one of the UL sync group).

[0160] In step 304 the at least one UL synchronization parameter may be associated with the UL synchronization group by being received with an indication of a second LTM candidate cell of the plurality of LTM candidate cells (which may be the first LTM candidate cell) or with an indication of the UL synchronization group.

[0161] Figure 4 depicts a method in accordance with particular embodiments. The method may be performed by a network node (e.g. the network node 1110 or network node 1300 as described later with reference to Figures 11 and 13 respectively). The method may be performed by a first candidate network node, for enabling Layer 1 / Layer2 Triggered Mobility, LTM, by a user equipment, UE.

[0162] The method begins at step 402 with transmitting to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node. The second network node may comprise an S-DU.

[0163] The method of Figure 4 may further comprise transmitting to the second network node at least one UL synchronization parameter associated with the UL synchronization group. The at least one UL synchronization parameter may be associated with the UL synchronization group by being transmitted with an identification a first LTM candidate cell of the plurality of LTM candidate cells or a UL synchronization group identification. The at least one UL synchronization parameter may comprise a timing advance, TA, value and / or a time alignment timer associated with the TA value.

[0164] In some examples, the method of Figure 4 may further comprise transmitting to the user equipment at least one UL synchronization parameter. For example, the user equipment may transmit a PRACH preamble on a first LTM candidate cell served by the first candidate network node. The first candidate network node may therefore transmit a random access response like message containing, for example, a TA value for the first LTM candidate cell. For example, the method of Figure 4 may further comprise receiving a Physical Random- Access Channel, PRACH, preamble on a first LTM candidate cell of the plurality of LTM candidate cells; calculating a timing advance, TA, value based on the received PRACH preamble, wherein the at least one UL synchronization parameter comprises the TA value.

[0165] In some examples, the indication of the UL synchronization group of step 402 is transmitted concurrently with the at least one UL synchronization parameter. For example, theindication of the UL synchronization group may comprise identifications of the plurality of LTM candidate cells.

[0166] In other examples, the indication of the UL synchronization group is transmitted prior to the at least one UL synchronization parameter.

[0167] In some examples, the indication of the UL synchronization group comprises an implicit indication in that the plurality of LTM candidate cells are associated with the same at least one UL synchronization parameter.

[0168] In some examples, the second network node comprises a serving distributed unit, S-DU, and step 402 comprises transmitting the indication of UL synchronization group via a serving central unit, S-CU.

[0169] Figure 5 depicts a method in accordance with particular embodiments. The method of Figure 5 may be performed by a network node (e.g. the network node 1110 or network node 1300 as described later with reference to Figures 11 and 13 respectively). The method may be performed by a second network node for enabling Layer 1 / Layer Triggered Mobility, LTM, by a user equipment, UE, served by the second network node. The method begins at step 502 with receiving from a first candidate network node, an indication of an UL synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

[0170] The method of Figure 5 may further comprise transmitting the indication of the UL synchronization group to the user equipment.

[0171] The method of Figure 5 may further comprise receiving, from the first candidate network node, at least one UL synchronization parameter associated with the UL synchronization group.

[0172] The method of Figure 5 may further comprise transmitting the at least one UL synchronization parameter associated with the UL synchronization group to the user equipment. The at least one UL synchronization parameter may be transmitted to the UE in a MAC CE.

[0173] The at least one UL synchronization parameter may be associated with the UL synchronization group by being received with an identification of a first LTM candidate cell in the plurality of LTM candidate cells or an identification of the UL synchronization group.

[0174] In some examples, the method of Figure 5 comprises receiving the indication of the UL synchronization group (e.g. Step 502) prior to receiving the at least one UL synchronization parameter. The at least one UL synchronization parameter may be received associated with an identification of a first LTM candidate cell in the plurality of LTM candidate cells.

[0175] In some examples, the indication of the UL synchronization group is received concurrently with the at least one UL synchronization parameter. The indication of the UL synchronization group may comprise identifications of the plurality of LTM candidate cells.

[0176] The method of Figure 5 may comprise initiating the UE to utilize the at least one UL synchronization parameter to perform a LTM cell switch to any of the plurality of LTM candidate cells.

[0177] Figure 6 illustrates Inter-node Signaling for TA Acquisition in LTM. Figure 6 illustrates an example implementation of the methods of Figures 3 to 5.

[0178] In the example of Figure 6, both the S-DU (second network node performing the method of Figure 4) and UE (performing the method of Figure 3) are pre-configured with the LTM candidate cells which form an UL sync group.

[0179] In the first embodiment of the solution for LTM, the S-DU receives information that (e.g. from the C-DU either directly or by using F1AP signaling via gNB-CU) that one or more LTM candidate cells (e.g. Cell A, Cell B and Cell C) form an UL sync group which means that these LTM candidate cells share similar UL synchronization characteristics (e.g. have the same TA value and / or Time alignment timer value). The indication of the UL sync group may be received in the UE Context Setup Request as illustrated in Figure 6. In this example therefore the UE Context Setup Request comprises an example implementation of step 402 or step 502.

[0180] The indication of the UL sync group (e.g. Cell A, Cell B and Cell C) may also be in the form of an associated UL sync group identifier (e.g., UL sync group ID = 3) which is provided to S-DU for different LTM candidate cells during LTM configuration phase e.g. each LTM candidate cell configuration has an UL sync group ID and LTM candidate cells with the same UL sync group ID from the same group and LTM candidate cells with different IDs are from the different groups.

[0181] Because of this, the UE should be able to perform early UL synchronization (also denoted here as TA acquisition) with just one of the LTM candidate cells in the UL sync group and still be able to perform RACH-less LTM cell switch to the other LTM candidate cells in the group.

[0182] The proposed method is applied to the network configuration described in table 1 and is explained below:

[0183] Consider an example in which UE is currently in the source cell or PCell for the UE.

[0184] The source cell located in source gNB-DU triggers TA acquisition (PDCCH order) for one LTM candidate cell (e.g., Cell A).

[0185] In this example, UE transmits the PRACH preamble to Cell A located in candidate gNB-DU, according to the information provided in the PDCCH order. This information mostly includes Preamble index, SSB index and PRACH mask index for random-access.

[0186] Cell A, which is the LTM candidate cell in this context, calculates the TA value, then the TA value is transmitted to the gNB-CU along with the LTM candidate cell identifier (i.e. , Cell A ID), source gNB-DU identifier (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in random-access) via DU-CU TA information transfer. There is no requirement to provide information about the other LTM candidate cell identifiers which form the same UL sync group because the S-DU is already informed about the LTM candidate cells which belong to the same UL sync group.

[0187] The gNB-CU forwards the TA value to the source cell in S-DU, along with the LTM candidate cell identifier to which random-access was performed (i.e., Cell A ID), source gNB-DU ID (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in randomaccess). Since the S-DU is already configured with the UL sync group information and is informed about the other LTM candidate cell(s) (as well as their corresponding LTM cell identifiers) which form the same UL sync group, the S-DU can deduce that the TA value is applicable for those LTM candidate cells as well.

[0188] The source cell in S-DU, therefore, gets one valid TA value (e.g., TA value 1) for all the LTM candidate cells which form an UL sync group, i.e., cells A, B and C, even though the UE performed random-access with only one of those cells, i.e., Cell A.

[0189] However, after the early UL synchronization with Cell A, the measurements for Cell B become better than both Cell A and the source cell, i.e., the Cell B measurements are favorable for LTM cell switch execution while the Time alignment timer for the obtained TA value is still running.

[0190] Therefore, the source cell sends an LTM cell switch MAC CE which includes the previously acquired TA value and the LTM candidate cell identifier for Cell B. The LTM cell switch MAC CE comprises an example implementation of step 304 of Figure 3.

[0191] Using this method, the UE can perform RACH-less LTM cell switch to Cell B, even though the UE has not performed any random-access towards Cell B. This RAC -less TLM cell switch to cell B comprises an example implementation of step 306 of Figure 3.

[0192] In another sub-option for the proposed method, the UE is pre-configured with the LTM candidate cells which form an UL sync group via RRC signaling such that each LTM candidate cell configuration includes an UL sync group identifier (e.g., UL sync group ID=3). Thus, for LTM candidate cells within the same UL sync group, the same UL sync groupidentifier is included e.g., LTM candidate cell A (e.g., UL sync group ID=3), LTM candidate cell B (e.g., UL sync group ID=3), LTM candidate cell C (e.g. UL sync group ID=3).

[0193] In such a scenario, the LTM cell switch command may include TA value and LTM candidate cell identifier for any of the cells (i.e., Cell A ID, Cell B ID or Cell C ID) in the same UL sync group which is identified by UL sync group ID = 3.

[0194] Owing to the UL sync group configuration received earlier, the UE is informed that the received TA value in LTM cell switch is applicable to any of the LTM candidate cells in the same UL sync group.

[0195] If there is radio link failure during LTM cell switch execution, the UE can perform RACH-less access to another LTM candidate cell in the same UL sync group during LTM fast failure recovery.

[0196] Figure 7 illustrates Inter-node Signaling for TA Acquisition in LTM. Figure 7 is an example implementation of the methods of Figures 3 to 5. In this example of Figure 7 the UE is pre-configured with the LTM candidate cells which form an UL sync group, but S-DU does not receive any information about the other LTM candidate cells in the UL sync group).

[0197] In the example illustrated in Figure 7 the S-DU (e.g. the second network node) does not receive, in advance of receiving the at least one UL sync parameter, any information about the LTM candidate cells which may belong to the similar UL sync group or share the identical UL synchronization properties. In this example therefore the UE Context Setup Request does not contain the indication of the UL sync group.

[0198] However, the S-DU implementation can receive the TA value for the LTM candidate cell(s) even if the source cell did not send the PDCCH order for those LTM candidate cells to perform TA acquisition to those cells.

[0199] The only pre-requisite is that the other LTM candidate cell(s) should belong to the same UL sync group as the LTM cell for which the random-access was initiated.

[0200] Consider the example where the UE is currently in the source cell or PCell for the UE.

[0201] The source cell located in source gNB-DU (e.g. second network node) triggers TA acquisition (PDCCH order) for one LTM candidate cell (e.g., Cell A).

[0202] The UE transmits the PRACH preamble to Cell A located in candidate gNB-DU, according to the information provided in the PDCCH order. This information mostly includes Preamble index, SSB index and PRACH mask index for random-access.

[0203] Cell A, which is the LTM candidate cell in this context, calculates the TA value, Then the TA value is transmitted to the gNB-CU along with the LTM candidate cell identifier(i.e. , Cell A ID), source gNB-DU identifier (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in random-access) via DU-CU TA information transfer IE as shown in table 2. Since Cell B and Cell C also belong to the same UL sync group as Cell A and S-DU is not pre-configured with the UL sync group info, the C-DU also includes the LTM candidate cell identifiers for those cells in DU-CU TA information transfer.Table 2: DU-CU TA Information Transfer (the new IES compared to the current format of the message (given in 3GPP TS 38.473 V18.0.0) are shown in bold and underlined).

[0204] The gNB-CU forwards the TA value to the source cell in S-DU, along with the LTM candidate cell identifier to which random-access was performed (i.e. , Cell A ID), other LTM candidate cell ID(s) in the same UL sync group (i.e., Cell B ID and Cell C ID), source gNB-DU ID (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in randomaccess) via CU-DU TA information transfer IE as depicted in Table 3. In this example therefore, the TA information transfer (e.g. illustrated in Table 3 below) comprises an example implementation of steps 402 and 502.Table 3: CU-DU TA information Transfer (the new IES compared to the current format of the message (given in 3GPP TS 38.473 V18.0.0) are shown in bold and underlined).

[0205] The source cell in S-DU has the functionality to receive the TA value for LTM candidate cell(s) even if the source cell did not trigger PDCCH order to acquire TA value for those LTM cell(s). Therefore, S-DU receives one valid TA value (e.g., TA value 7) for all the LTM candidate cells which form an UL sync group, i.e., cells A, B and C, even though the UE performed random-access with only one of those cells, i.e., Cell A.

[0206] The remaining steps for LTM cell switch execution, after early TA acquisition and reception of the LTM candidate cell identifiers in the similar UL sync group, are the same as explained above in the first embodiment. The step-by-step description of the entire solution is depicted in Figure 7.

[0207] Figure 8 illustrates Inter-node Signaling for TA Acquisition in LTM. In this example, the second network node (S-DU) has an UL Sync Configuration only for one LTM Cell in an UL Sync Group.

[0208] In yet another embodiment of the described method for LTM, the S-DU is still informed by C-DU either directly or by using Fl AP signaling via gNB-CU that Cell A, Cell B and Cell C form an UL sync group which means that all these LTM candidate cells share similar UL synchronization characteristics.

[0209] However, the S-DU receives the UL synchronization configuration for only one LTM candidate cell (either Cell A or Cell B or Cell C) in that UL sync group during the LTM preparation phase, as shown in Figure 5. This way the S-DU does not repeatedly trigger the PDCCH order for the other cells in the UL sync group but still receives the TA value for the other LTM candidate cell(s) in the UL sync group. In other words, the same DU-CU and C- DU TA information transfer steps as mentioned in the embodiment for LTM shown in Figure 6, can be applied to this embodiment of Figure 8 as well. The remaining steps for early TA acquisition and UL synchronization are identical and the detailed explanation of the entire step- by-step procedure is provided in Figure 6.Embodiments for Conditional LTM

[0210] The difference between LTM and Conditional LTM is the absence of LTM cell switch MAC CE transmission from the source cell to the UE. And the cell switch execution depends upon the fulfilment of pre-configured Conditional LTM execution condition(s).

[0211] The proposed embodiments for Conditional LTM may therefore be modified for Conditional LTM such that the at least one UL sync parameter (e.g. TA value) and the indication of the UL sync group (e.g. respective LTM candidate cell identifiers in Group 1 (i.e., Cell A ID, Cell B ID and Cell C ID) or the UL sync group identifier) may be provided to the UE via some signaling before the Conditional LTM execution conditions are fulfilled.

[0212] Figure 9 illustrates Inter-node Signaling for TA Acquisition in Conditional LTM. Figure 9 is an example implementation of the methods of Figures 3 to 5.

[0213] In the example of Figure 9 for Conditional LTM, the S-DU is pre-configured (e.g. informed by C-DU either directly or by using F1AP signaling via gNB-CU) that Cell A, Cell B and Cell C form an UL sync group which means that all these LTM candidate cells share similar UL synchronization characteristics. The indication of the UL sync group may be provided in the US Context Setup Request, which in this example comprises an example implementation of step 402 or 502.

[0214] This information about Cell A, Cell B and Cell C forming a similar UL sync group may also be in the form of an associated UL sync group identifier (e.g., UL sync group ID = 3) which is provided to S-DU for different LTM candidate cells during the LTM configuration phase. Using the method explained below, the UE will perform early UL synchronization with only one of the LTM candidate cells in the UL sync group and still be able to perform RACH- less Conditional LTM execution to the other LTM candidate cells in the group. Moreover, thecells A, B and C in the UL sync group have their associated Conditional LTM execution conditions.

[0215] The example of Figure 9 is applied to the network configuration described in table 1 (in the embodiments for LTM) and is explained below:

[0216] Consider the example in which the UE is currently in the source cell or PCell for the UE.

[0217] The source cell located in source gNB-DU triggers TA acquisition (PDCCH order) for one LTM candidate cell (e.g., Cell A) in the UL sync group.

[0218] The UE transmits the PRACH preamble to Cell A located in candidate gNB-DU, according to the information provided in the PDCCH order. This information mostly includes Preamble index, SSB index and PRACH mask index for random-access.

[0219] Cell A, which is the LTM candidate cell in this context, calculates the TA value, then the TA value is transmitted to the gNB-CU along with the LTM candidate cell identifier (i.e. , Cell A ID), source gNB-DU identifier (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in random-access) via DU-CU TA information transfer. There is no requirement to provide information about the other LTM candidate cell identifiers which form the same UL sync group because the S-DU is already informed about the LTM candidate cells which belong to the same UL sync group.

[0220] The gNB-CU forwards the TA value to the source cell in S-DU, along with the LTM candidate cell identifier to which random-access was performed (i.e., Cell A ID), source gNB-DU ID (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in randomaccess). Since the S-DU is already configured with the UL sync group information and is informed about the other LTM candidate cell(s) (as well as their corresponding LTM cell identifiers) which form the same UL sync group, the S-DU can interpret that the TA value is applicable for those LTM candidate cells as well.

[0221] The source cell in S-DU, therefore, gets one valid TA value (e.g., TA value 7) for all the LTM candidate cells which form an UL sync group, i.e., cells A, B and C, even though the UE performed random-access with only one of those cells, i.e., Cell A.

[0222] In the case of Conditional LTM, the UE is always pre-configured with the LTM candidate cells which form an UL sync group via RRC signaling such that each LTM candidate cell configuration includes an UL sync group identifier (e.g., UL sync group ID=3). The reason for this is that there is no LTM cell switch MAC CE, and the UE can execute LTM handover to any of the cells in the UL sync group, as determined by the Conditional LTM execution conditions. Thus, for LTM candidate cells within the same UL sync group, the same UL syncgroup identifier is included in the LTM candidate cell configuration e.g., LTM candidate Cell A (e.g., UL sync group ID=3), LTM candidate Cell B (e.g., UL sync group ID=3), LTM candidate Cell C (e.g., UL sync group ID=3).

[0223] In the case of Conditional LTM, the TA value may be received in some message other than the LTM cell switch MAC CE, e.g., another MAC CE with TA information, transmitted by the source cell (e.g. S-DU / second network node), and when the execution conditions for conditional LTM is fulfilled for Cell A, and / or Cell B and / or Cell C, the same received TA value may be used for Cell A, or Cell B or Cell C.

[0224] The S-DU (which is aware of the LTM candidate cells in the same UL sync group) may send UE a message before the cell switch (e.g., MAC CE) with an UL sync group identifier (e.g. UL sync group ID=3) and the calculated TA value for the UL sync group which is obtained by executing random-access to Cell A in the UL sync group. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to any of the LTM candidate cells in the UL sync group (i.e., Cell B or Cell B) as well.

[0225] In another option, the S-DU sends the message (e.g., MAC CE) to the UE which includes one of the LTM candidate cell identifiers in the UL sync group and the obtained TA value. The LTM candidate identifier can be associated to the cell to which the UE performed random-access to acquire TA value (e.g., Cell A) or another LTM candidate cell identifier in the same UL sync group (e.g., Cell B or Cell C). Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of those LTM candidate cells.

[0226] In this example therefore, the TA MAC CE for Early Sync comprises an example implementation of step 304 of Figure 4.

[0227] As the UE receives the TA value for the UL sync group, it starts the Time alignment timer and can execute RACH-less Conditional LTM cell switch to any of the LTM candidate cells in the same UL sync group, given that the Time alignment timer is running, i.e., TA value is valid.

[0228] The network may provide the UE with the LTM candidate cell TA value before an LTM Cell Switch, e.g., in a RAR-like message sent by C-DU. Receiving the TA value in a RAR-like message sent by the C-DU would comprise an alternative implementation of step 304.

[0229] The C-DU may send the UE a RAR-like message in response to the random-access which includes an UL sync group identifier (e.g., UL sync group ID=3) and the calculated TAvalue for the UL sync group which is obtained by performing random-access to the LTM candidate cell in the UL sync group. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of the LTM candidate cells in the UL sync group.

[0230] In another option, the C-DU sends the RAR-like message to the UE which includes an LTM candidate cell identifier for the cell to which random access was performed (e.g., Cell A) and the calculated TA value. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to the other LTM candidate cells in the same UL sync group (e.g., Cell B or Cell C).

[0231] The UE receives the TA value and starts the Time alignment timer. The UE can perform RACH-less Conditional LTM cell switch to any of the LTM candidate cells in the same UL sync group, provided that the TA value is valid.

[0232] Figure 10 illustrates Inter-node Signaling for TA Acquisition in Conditional LTM. Figure 10 is an example implementation of the methods of Figures 3 to 5.

[0233] In the embodiment of Figure 10 for Conditional LTM, the S-DU does not receive information, in advance, about the LTM candidate cells which may belong to the similar UL sync group or share the identical UL synchronization properties. However, the S-DU implementation can receive the TA value for the LTM candidate cell(s) even if the source cell did not send the PDCCH order for those LTM candidate cells. The only pre-requisite is that the other LTM candidate cell(s) should belong to the same UL sync group as the LTM cell for which the random-access was initiated. The following inter-node signaling steps are performed at the network side during the early TA acquisition:

[0234] Consider the example in which the UE is currently in the source cell or PCell for the UE.

[0235] The source cell located in source gNB-DU triggers TA acquisition (PDCCH order) for one LTM candidate cell (e.g., Cell A).

[0236] The UE transmits the PRACH preamble to Cell A located in candidate gNB-DU, according to the information provided in the PDCCH order. This information mostly includes Preamble index, SSB index and PRACH mask index for random-access.

[0237] Cell A, which is the LTM candidate cell in this context, calculates the TA value, Then the TA value is transmitted to the gNB-CU along with the LTM candidate cell identifier (i.e., Cell A ID), source gNB-DU identifier (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in random-access) via DU-CU TA information transfer IE as shown in table 2 (see LTM embodiments section). Since Cell B and Cell C also belong to the same UL syncgroup as Cell A and S-DU is not pre-configured with the UL sync group info, the C-DU also includes the LTM candidate cell identifiers for those cells in DU-CU TA information transfer.

[0238] The gNB-CU forwards the TA value to the source cell in S-DU, along with the LTM candidate cell identifier to which random-access was performed (i.e. , Cell A ID), other LTM candidate cell ID(s) in the same UL sync group (i.e., Cell B ID and Cell C ID), source gNB-DU ID (i.e., S-DU ID), and preamble index (i.e., index of the preamble used in randomaccess) via CU-DU TA information transfer IE as depicted in table 3 (see LTM embodiments section). This TA information transfer may be considered an example implementation of steps 402 and 502.

[0239] The source cell in S-DU has the functionality to receive TA value for LTM candidate cell(s) even if the source cell did not trigger PDCCH order to acquire TA value for those LTM cell(s). Therefore, S-DU receives one valid TA value (e.g., TA value 7) for all the LTM candidate cells which form an UL sync group, i.e., cells A, B and C, even though the UE performed random-access with only one of those cells, i.e., Cell A.

[0240] In the case of Conditional LTM, the UE may always be pre-configured with the LTM candidate cells which form an UL sync group via RRC signaling because there is no LTM cell switch MAC CE in Conditional LTM and the UE can execute LTM handover to any of the cells in the UL sync group, as determined by the Conditional LTM execution conditions.

[0241] In the case of Conditional LTM, the TA value may be received in some message other than the LTM cell switch MAC CE, e.g., another MAC CE with TA information, transmitted by the source cell, and when the execution conditions for conditional LTM is fulfilled for Cell A, and / or Cell B and / or Cell C, the same received TA value may be used for RACH-less access to Cell A, or Cell B or Cell C. The TA MAC CE for Early Sync may therefore comprise an example implementation of step 304.

[0242] The S-DU may not be aware of the LTM candidate cells in the same UL sync group but can receive different LTM candidate cell identifiers in the UL sync group due to the added functionality. The S-DU sends the message (e.g., MAC CE) to the UE which includes one of the LTM candidate cell identifiers in the UL sync group and the obtained TA value. The LTM candidate identifier can be associated to the cell to which the UE performed random-access to acquire TA value (e.g., Cell A) or another LTM candidate cell identifier in the same UL sync group (e.g., Cell B or Cell C). Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to one of those LTM candidate cells.

[0243] The UE receives the TA value and starts the Time alignment timer. The UE can perform RACH-less Conditional LTM cell switch to any of the LTM candidate cells in the same UL sync group, provided that the TA value is valid. The RACH-less Conditional LTM cell switch would, in this example, comprise an example implementation of step 306 of Figure 3.

[0244] The network may provide UE the LTM candidate cell TA value before an LTM Cell Switch, e.g., in a RAR-like message sent by C-DU. Providing the TA value in a RAR-like message from the C-DU may comprise an alternative example implementation of step 306.

[0245] The C-DU sends the RAR-like message to the UE which includes an LTM candidate cell identifier for the cell to which random access was performed (e.g., Cell A) and the calculated TA value. Owing to the UL sync group configuration provided earlier by the network, the UE can re-use that TA value to perform RACH-less cell switch to the other LTM candidate cells in the same UL sync group (e.g., Cell B or Cell C).

[0246] As the UE receives the TA value for the UL sync group, it starts the Time alignment timer and can execute RACH-less Conditional LTM execution to any of the LTM candidate cells in the same UL sync group, given that the Time alignment timer is running, i.e., TA value is valid.

[0247] In yet another embodiment of the described method for Conditional LTM, the S- DU is still informed by C-DU either directly or by using Fl AP signaling via gNB-CU that Cell A, Cell B and Cell C form an UL sync group which means that all these LTM candidate cells share similar UL synchronization characteristics. However, the S-DU receives the UL synchronization configuration for only one LTM candidate cell (either Cell A or Cell B or Cell C) in that UL sync group during the LTM preparation phase, as shown in Figure 8 (see the section for LTM embodiments). This way the S-DU does not repeatedly trigger the PDCCH order for the other cells in the UL sync group but still receives the TA value for the other LTM candidate cell(s) in the UL sync group. In other words, the same DU-CU and C-DU TA information transfer steps, as mentioned in the first embodiment of Conditional LTM, are applicable to this embodiment as well. The remaining steps for early TA acquisition and UL synchronization are identical and the detailed explanation of the entire step-by-step procedure is provided in the first embodiment for Conditional LTM solution.

[0248] Figure 11 shows an example of a communication system 1100 in accordance with some embodiments.

[0249] In the example, the communication system 1100 includes a telecommunication network 1102 that includes an access network 1104, such as a radio access network (RAN),and a core network 1106, which includes one or more core network nodes 1108. The access network 1104 includes one or more access network nodes, such as network nodes 1110a and 1110b (one or more of which may be generally referred to as network nodes 1110), or any other similar 3rd Generation Partnership Project (3GPP) access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, the telecommunication network 1102 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 1102 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in the telecommunication network 1102, including one or more network nodes 1110 and / or core network nodes 1108.

[0250] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O- CU-CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. The network nodes 1110 facilitate direct or indirect connection of user equipment (UE), such as by connecting UEs 1112a, 1112b, 1112c, and 1112d (one or more of which may be generally referred to as UEs 1112) to the core network 1106 over one or more wireless connections.

[0251] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires,cables, or other material conductors. Moreover, in different embodiments, the communication system 1100 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. The communication system 1100 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0252] The UEs 1112 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with the network nodes 1110 and other communication devices. Similarly, the network nodes 1110 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 1112 and / or with other network nodes or equipment in the telecommunication network 1102 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in the telecommunication network 1102.

[0253] In the depicted example, the core network 1106 connects the network nodes 1110 to one or more host computing systems, such as host 1116. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 1106 includes one more core network nodes (e.g., core network node 1108) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 1108. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0254] The host 1116 may be under the ownership or control of a service provider other than an operator or provider of the access network 1104 and / or the telecommunication network 1102. The host 1116 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controllingor otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0255] As a whole, the communication system 1100 of Figure 11 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0256] In some examples, the telecommunication network 1102 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 1102 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 1102. For example, the telecommunications network 1102 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0257] In some examples, the UEs 1112 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 1104 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 1104. Additionally, a UE may be configured for operating in single- or multi-RAT or multi -standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi -radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN- DC).

[0258] In the example, the hub 1114 communicates with the access network 1104 to facilitate indirect communication between one or more UEs (e.g., UE 1112c and / or 1112d) and network nodes (e.g., network node 1110b). In some examples, the hub 1114 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 1114 may be a broadband routerenabling access to the core network 1106 for the UEs. As another example, the hub 1114 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1110, or by executable code, script, process, or other instructions in the hub 1114. As another example, the hub 1114 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 1114 may be a content source. For example, for a UE that is a VR device, display, loudspeaker, or other media delivery device, the hub 1114 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 1114 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 1114 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0259] The hub 1114 may have a constant / persistent or intermittent connection to the network node 1110b. The hub 1114 may also allow for a different communication scheme and / or schedule between the hub 1114 and UEs (e.g., UE 1112c and / or 1112d), and between the hub 1114 and the core network 1106. In other examples, the hub 1114 is connected to the core network 1106 and / or one or more UEs via a wired connection. Moreover, the hub 1114 may be configured to connect to an M2M service provider over the access network 1104 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 1110 while still connected via the hub 1114 via a wired or wireless connection. In some embodiments, the hub 1114 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to the network node 1110b. In other embodiments, the hub 1114 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1110b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0260] Figure 12 shows a UE 1200 in accordance with some embodiments. The UE 1200 presents additional details of some embodiments of the UE 1112 of Figure 11. As used herein, a UE refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage / playback device, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME),an Augmented Reality (AR) or Virtual Reality (VR) device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0261] A UE may support device-to-device (D2D) communication, for example by implementing a 3 GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle- to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0262] The UE 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input / output interface 1206, a power source 1208, a memory 1210, a communication interface 1212, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 12. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0263] The processing circuitry 1202 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 1210. The processing circuitry 1202 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general -purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1202 may include multiple central processing units (CPUs). The processing circuitry 1202 may be configured to cause the UE 1202 to perform the methods as described with reference to Figure 3.

[0264] In the example, the input / output interface 1206 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 1200. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0265] In some embodiments, the power source 1208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 1208 may further include power circuitry for delivering power from the power source 1208 itself, and / or an external power source, to the various parts of the UE 1200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1208. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1208 to make the power suitable for the respective components of the UE 1200 to which power is supplied.

[0266] The memory 1210 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 1210 includes one or more application programs 1214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1216. The memory 1210 may store, for use by the UE 1200, any of a variety of various operating systems or combinations of operating systems.

[0267] The memory 1210 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, externalhard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD- DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 1210 may allow the UE 1200 to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 1210, which may be or comprise a device-readable storage medium.

[0268] The processing circuitry 1202 may be configured to communicate with an access network or other network using the communication interface 1212. The communication interface 1212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1222. The communication interface 1212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1218 and / or a receiver 1220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1218 and receiver 1220 may be coupled to one or more antennas (e.g., antenna 1222) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0269] In the illustrated embodiment, communication functions of the communication interface 1212 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / intemet protocol (TCP / IP), synchronous optical networking(SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0270] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0271] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0272] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to the UE 1200 shown in Figure 12.

[0273] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results ofsuch monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0274] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0275] Figure 13 shows a network node 1300 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), O-RAN nodes or components of an O-RAN node (e g., O-RU, O-DU, O-CU).

[0276] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0277] Other examples of network nodes include multiple transmission point (multi-TRP)5G access nodes, multi -standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), basetransceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0278] The network node 1300 includes a processing circuitry 1302, a memory 1304, a communication interface 1306, and a power source 1308. The network node 1300 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1300 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 1300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1304 for different RATs) and some components may be reused (e.g., a same antenna 1310 may be shared by different RATs). The network node 1300 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1300, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1300.

[0279] The processing circuitry 1302 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1300 components, such as the memory 1304, to provide network node 1300 functionality. For example, the processing circuitry 1302 may be configured to cause the network node to perform the methods as described with reference to Figure 4 and / or Figure 5.

[0280] In some embodiments, the processing circuitry 1302 includes a system on a chip (SOC). In some embodiments, the processing circuitry 1302 includes one or more of radio frequency (RF) transceiver circuitry 1312 and baseband processing circuitry 1314. In some embodiments, the radio frequency (RF) transceiver circuitry 1312 and the baseband processingcircuitry 1314 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on the same chip or set of chips, boards, or units.

[0281] The memory 1304 may comprise any form of volatile or non-volatile computer- readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computerexecutable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1302. The memory 1304 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 1302 and utilized by the network node 1300. The memory 1304 may be used to store any calculations made by the processing circuitry 1302 and / or any data received via the communication interface 1306. In some embodiments, the processing circuitry 1302 and memory 1304 is integrated.

[0282] The communication interface 1306 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 1306 comprises port(s) / terminal(s) 1316 to send and receive data, for example to and from a network over a wired connection. The communication interface 1306 also includes radio front-end circuitry 1318 that may be coupled to, or in certain embodiments a part of, the antenna 1310. Radio front-end circuitry 1318 comprises filters 1320 and amplifiers 1322. The radio front-end circuitry 1318 may be connected to an antenna 1310 and processing circuitry 1302. The radio front-end circuitry may be configured to condition signals communicated between antenna 1310 and processing circuitry 1302. The radio front-end circuitry 1318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 1318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1320 and / or amplifiers 1322. The radio signal may then be transmitted via the antenna 1310. Similarly, when receiving data, the antenna 1310 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1318. The digital data may be passed to the processing circuitry 1302. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0283] In certain alternative embodiments, the network node 1300 does not include separate radio front-end circuitry 1318, instead, the processing circuitry 1302 includes radio front-end circuitry and is connected to the antenna 1310. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1312 is part of the communication interface 1306. In still other embodiments, the communication interface 1306 includes one or more ports or terminals 1316, the radio front-end circuitry 1318, and the RF transceiver circuitry 1312, as part of a radio unit (not shown), and the communication interface 1306 communicates with the baseband processing circuitry 1314, which is part of a digital unit (not shown).

[0284] The antenna 1310 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 1310 may be coupled to the radio frontend circuitry 1318 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 1310 is separate from the network node 1300 and connectable to the network node 1300 through an interface or port.

[0285] The antenna 1310, communication interface 1306, and / or the processing circuitry 1302 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, the antenna 1310, the communication interface 1306, and / or the processing circuitry 1302 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0286] The power source 1308 provides power to the various components of network node 1300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1308 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1300 with power for performing the functionality described herein. For example, the network node 1300 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1308. As a further example, the power source 1308 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0287] Embodiments of the network node 1300 may include additional components beyond those shown in Figure 13 for providing certain aspects of the network node’sfunctionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the network node 1300 may include user interface equipment to allow input of information into the network node 1300 and to allow output of information from the network node 1300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1300. In some embodiments providing a core network node, such as core network node 108 of FIG. 11, some components, such as the radio front-end circuitry 1318 and the RF transceiver circuitry 1312 may be omitted.

[0288] Figure 14 is a block diagram illustrating a virtualization environment 1400 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1400 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1400 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface. Virtualization may facilitate distributed implementations of a network node, UE, core network node, or host.

[0289] Applications 1402 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0290] Hardware 1404 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1406 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1408a and 1408b (one or more of which may be generally referred to as VMs 1408), and / orperform any of the functions, features and / or benefits described in relation with some embodiments described herein. The virtualization layer 1406 may present a virtual operating platform that appears like networking hardware to the VMs 1408.

[0291] The VMs 1408 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1406. Different embodiments of the instance of a virtual appliance 1402 may be implemented on one or more of VMs 1408, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0292] In the context of NFV, a VM 1408 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1408, and that part of hardware 1404 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1408 on top of the hardware 1404 and corresponds to the application 1402.

[0293] Hardware 1404 may be implemented in a standalone network node with generic or specific components. Hardware 1404 may implement some functions via virtualization. Alternatively, hardware 1404 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1410, which, among others, oversees lifecycle management of applications 1402. In some embodiments, hardware 1404 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1412 which may alternatively be used for communication between hardware nodes and radio units.

[0294] Although the computing devices described herein (e.g., UEs, network nodes) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or softwareneeded to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[0295] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer- readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer- readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.EMBODIMENTSGroup A Embodiments1. A method performed by a user equipment for enabling Layer 1 / Layer2 Triggered Mobility, LTM, the method comprising: obtaining a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtaining at least one UL synchronization parameter associated with the UL synchronization group; and utilizing the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM candidate cells.2. The method of embodiment 1 wherein the at least one UL synchronization parameter comprises a timing advance value and / or a time alignment timer.3. The method of any one of embodiments 1 to 2, further comprising receiving an indication that the plurality of LTM candidate cells is associated with the UL synchronization group.4. The method of embodiment 3, wherein the indication that the plurality of LTM candidate cells is associated with the UL synchronization group comprises an UL synchronization group identifier associated with each of the plurality of LTM candidate cells.5. The method of embodiment 4 wherein the indication that the plurality of LTM candidate cells is associated with the UL synchronization group and the configuration of the plurality of LTM candidate cells are received in a radio resource control, RRC, message.6. The method of any one of embodiments 1 to 5, wherein obtaining the at least one UL synchronization parameter comprises receiving the at least one UL synchronization parameter in a message that further comprises an indication of the first LTM candidate cell.7. The method of embodiments 6, wherein the message is transmitted using a MAC CE.8. The method of embodiment 1 to 5, wherein obtaining the at least UL synchronization parameter comprises receiving the at least one UL synchronization parameter responsiveto transmitting a Physical Random Access Channel, PRACH, preamble for timing advance, TA, acquisition to one of the plurality of LTM candidate cells. The method of any one of embodiments 1 to 8 wherein the UL synchronization parameter comprises a timing advance, TA, value, the method further comprising: starting a time alignment timer responsive to receiving the TA value. The method of embodiment 9, further comprising: responsive to the LTM cell switch being triggered whilst the time alignment timer in running, performing utilizing the least one UL synchronization parameter when performing the LTM cell switch to the first LTM candidate cell of the plurality of LTM candidate cells. The method of embodiment 10 further comprising restarting the time alignment timer responsive to performing the LTM cell switch. The method of embodiment 9 further comprising: responsive to the LTM cell switch being triggered after the time alignment timer has expired, performing a random-access procedure to perform the LTM cell switch to the first LTM candidate cell. The method of any preceding embodiments, wherein the LTM cell switch is triggered by a LTM cell switch command to perform LTM cell switch to the first LTM candidate cell. The method of embodiment 13 wherein the at least one UL synchronization parameter is received in a message with the LTM cell switch command. The method of embodiment 14 further comprising: responsive to the LTM cell switch to the first LTM candidate cell failing, selecting a second LTM candidate cell from the plurality of LTM candidate cells and performing an LTM cell switch to the second LTM candidate cell utilizing the UL synchronization parameter. The method of embodiment 13 further comprising receiving the UL synchronization parameter in a lower layer message prior to receiving the LTM cell switch command.17. The method as of any one of embodiments 1 to 12, wherein the LTM cell switch is triggered by fulfilment of a condition.18. The method of embodiment 17 wherein the UL synchronization parameter is received via lower layer signaling.19. The method of embodiment 17 wherein the UL synchronization parameter is received in a random-access response from a LTM candidate cell.20. The method of any previous embodiment, wherein the at least one UL synchronization parameter is associated with the UL synchronization group by being received with an indication of a second LTM candidate cell of the plurality of LTM candidate cells or with an indication of the UL synchronization group.21. The method of any previous embodiment wherein the UL synchronization group is derived from one of: an L2 reset group to which the first LTM candidate cell belongs, and a UE-based timing advance (TA) group to which the first LTM candidate cell belongs.AL A method at a User Equipment for TA acquisition comprising:Receiving at least one UL synchronization parameter associated with a plurality of LTM candidate cells;Upon performing an LTM cell switch to an LTM candidate cell within the plurality of LTM candidate cells, applying the at least one UL synchronization parameter.A2. A method of Al, wherein the at least one UL synchronization parameter comprises a TA value and / or a time alignment timer value associated to a TA value.A3. A method of Al, wherein the UE is configured with Conditional LTM (CLTM) or LTM.A4. A method of Al and all, wherein prior to receiving the UL synchronization parameter (e.g., TA value), receiving a configuration indicating that the plurality of LTM candidate have UL synchronization properties which can be acquired in a single TA acquisition process and / or that a further received TA value can be used for any cell in the plurality of LTM candidate cells.A5. A method of Al and all, wherein the at least one UL synchronization parameter associated with a plurality of LTM candidate cells is received in a message (e.g., MACCE) which also includes an indication of one of the LTM candidate cells within the plurality of LTM candidate cells.A6. A method of A5, wherein the indication of one of the LTM candidate cells within the plurality of LTM candidate cells comprises an indication of the LTM candidate cell for which the UE has transmitted a PRACH preamble for TA acquisition.A5b. A method of Al and all, wherein the at least one UL synchronization parameter associated with a plurality of LTM candidate cells is received in a message (e.g., MAC CE) which also includes an indication of the plurality of LTM candidate cells.A5c. A method of A5b, wherein the indication of the plurality of LTM candidate cells comprises a group identifier, associated to each LTM candidate cell within the plurality of LTM candidate cells.Group B Embodiments22. A method performed by a first candidate network node for enabling Layer 1 / Layer2 Triggered Mobility, LTM, by a user equipment, UE, the method comprising: transmitting to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.23. The method of embodiment 22 further comprising transmitting to the second network node at least one UL synchronization parameter associated with the UL synchronization group.24. The method of embodiment 23 further wherein the UL synchronization parameter is associated with the UL synchronization group by being transmitted with an identification a first LTM candidate cell of the plurality of LTM candidate cells or a UL synchronization group identification.25. The method of embodiment 22 further comprising transmitting to the user equipment at least one UL synchronization parameter.26. The method of any one of embodiments 23 to 27, wherein the at least one ULsynchronization parameter comprises a timing advance, TA, value and / or a time alignment timer associated with the TA value.27. The method of any one of embodiments 23 to 26 further comprising: receiving a Physical Random- Access Channel, PRACH, preamble on a first LTM candidate cell of the plurality of LTM candidate cells; calculating a timing advance, TA, value based on the received PRACH preamble, wherein the at least one UL synchronization parameter comprises the TA value.28. The method of any one of embodiments 23 to 27, wherein the indication of the UL synchronization group is transmitted concurrently with the at least one UL synchronization parameter.29. The method of embodiment 28 wherein the indication of the UL synchronization group comprises identifications of the plurality of LTM candidate cells.30. The method of any one of embodiments 23 to 27, wherein the indication of the UL synchronization group is transmitted prior to the at least one UL synchronization parameter.31. The method of embodiment 22, wherein the indication of the UL synchronization group comprises an implicit indication in that the plurality of LTM candidate cells are associated with the same at least one UL synchronization parameter.32. The method of any one of embodiments 22 to 31, wherein the second network node comprises a serving distributed unit, S-DU, and transmitting the indication of the UL synchronization group comprises transmitting the indication of UL synchronization group via a serving central unit, S-CU.33. A method performed by a second network node for enabling Layer 1 / Layer Triggered Mobility, LTM, by a user equipment, UE, served by the second network node, the method comprising: receiving from a first candidate network node, an indication of an ULsynchronization group associated with a plurality of LTM candidate cells served by the first candidate network node. The method of embodiment 33, further comprising transmitting the indication of the UL synchronization group to the user equipment. The method of embodiment 34, further comprising receiving, from the first candidate network node, at least one UL synchronization parameter associated with the UL synchronization group. The method of embodiment 35, further comprising transmitting the at least one UL synchronization parameter associated with the UL synchronization group to the user equipment. The method of embodiment 36, wherein the at least one UL synchronization parameter is transmitted to the UE in a MAC CE. The method of embodiment 35 to 37 wherein the at least one UL synchronization parameter is associated with the UL synchronization group by being received with an identification of a first LTM candidate cell in the plurality of LTM candidate cells or an identification of the UL synchronization group. The method of any one of embodiment 35 to 38, further comprising receiving the indication of the UL synchronization group prior to receiving the at least one UL synchronization parameter. The method of embodiment 39, wherein the at least one UL synchronization parameter is received associated with an identification of a first LTM candidate cell in the plurality of LTM candidate cells.41. The method of any one of embodiments 35 to 38, wherein the indication of the UL synchronization group is received concurrently with the at least one UL synchronization parameter.42. The method of embodiment 41 wherein the indication of the UL synchronization group comprises identifications of the plurality of LTM candidate cells.43. The method of any one of embodiments 35 to 42, further comprising initiating the UE to utilize the at least one UL synchronization parameter to perform a LTM cell switch to any of the plurality of LTM candidate cells.BL A method at a first candidate network node (e.g., C-DU, C-CU) for TA acquisition comprising:Transmitting to a second network node at least one UL synchronization parameter associated with a plurality of LTM candidate cells of the first candidate network node.Bib. A method of Bl, wherein the at least one UL synchronization parameter comprises a TA value and / or a time alignment timer value associated to a TA value.B2. A method of Bl, wherein the first candidate network node operates as a Candidate network node for LTM, wherein that is a Candidate DU or a Candidate CU.B3. A method of Bl and all, wherein the first candidate network node operates as a Candidate network node for Conditional LTM (CLTM), wherein that is a Candidate DU or a Candidate CU.B4. A method of Bl and all, wherein prior to transmitting the at least one UL synchronization parameter, transmitting to the second network node an indication of the plurality of LTM candidate cells of the first candidate network node.CL A method at a second network node (e.g., S-DU, S-CU) for TA acquisition comprising:Receiving from a first candidate network node at least one UL synchronization parameter associated with a plurality of LTM candidate cells of the first candidate network node.C2. A method of Cl and all, wherein the at least one UL synchronization parameter comprises a TA value and / or a time alignment timer value associated to a TA value.C3. A method of Cl and all, wherein the second network node operates as a Source / Serving network node for LTM, wherein that is a Serving DU or Serving CU.C4. A method of Cl and all, wherein prior to receiving the at least one UL synchronization parameter, receiving from the first candidate network node an indication of the plurality of LTM candidate cells of the first candidate network node.C5. A method of Cl and all, comprising transmitting to a UE at least one UL synchronization parameter associated with a plurality of LTM candidate cells of the first candidate network node.C6. A method of Cl and all, prior to transmitting to a UE at least one UL synchronization parameter associated with a plurality of LTM candidate cells of the first candidate network node, transmitting to the UE an indication of the plurality of LTM candidate cells of the first candidate network node.Group C Embodiments44. A user equipment for enabling Layerl / Layer2 Triggered Mobility, LTM, comprising: processing circuitry configured to cause the user equipment to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.45. A network node for enabling Layerl / Layer2 Triggered Mobility, LTM, the network node comprising: processing circuitry configured to cause the network node to perform any of the steps of any of the Group B embodiments; power supply circuitry configured to supply power to the processing circuitry.46. A user equipment (UE) for enabling Layerl / Layer2 Triggered Mobility, LTM, the UE comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to cause the user equipment to perform anyof the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

Claims

CLAIMS1. A method performed by a user equipment for enabling Layer 1 / Layer 2 Triggered Mobility, LTM, the method comprising: obtaining (302) a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtaining (304) at least one UL synchronization parameter associated with the UL synchronization group; and utilizing (306) the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM candidate cells.

2. The method of claim 1 wherein the at least one UL synchronization parameter comprises a timing advance value and / or a time alignment timer.

3. The method of any one of claims 1 to 2, further comprising receiving an indication that the plurality of LTM candidate cells is associated with the UL synchronization group.

4. The method of claim 3, wherein the indication that the plurality of LTM candidate cells is associated with the UL synchronization group comprises an UL synchronization group identifier associated with each of the plurality of LTM candidate cells.

5. The method of any one of claims 1 to 4, wherein obtaining the at least one UL synchronization parameter comprises: receiving the at least one UL synchronization parameter in a message that further comprises an indication of the first LTM candidate cell or a second LTM candidate cell of the plurality of LTM candidate cells; and / or receiving the at least one UL synchronization parameter responsive to transmitting a Physical Random Access Channel, PRACH, preamble for timing advance, TA, acquisition to a second LTM candidate cell of the plurality of LTM candidate cells.

6. The method of any preceding claims, wherein the LTM cell switch is triggered by a LTM cell switch command to perform LTM cell switch to the first LTM candidate cell.

7. The method of claim 6 wherein the at least one UL synchronization parameter is received in a message with the LTM cell switch command.

8. The method of claim 7 further comprising: responsive to the LTM cell switch to the first LTM candidate cell failing, selecting a second LTM candidate cell from the plurality of LTM candidate cells and performing an LTM cell switch to the second LTM candidate cell utilizing the UL synchronization parameter.

9. The method of claim 6 further comprising receiving the UL synchronization parameter in a lower layer message prior to receiving the LTM cell switch command.

10. The method as claimed in any one of claims 1 to 5, wherein the LTM cell switch is triggered by fulfilment of a condition.

11. The method of claim 10 wherein the UL synchronization parameter is received via lower layer signaling, or in a random-access response from a LTM candidate cell.

12. The method of any previous claim, wherein the at least one UL synchronization parameter is associated with the UL synchronization group by being received with an indication of a second LTM candidate cell of the plurality of LTM candidate cells or with an indication of the UL synchronization group.

13. The method of any previous claim wherein the UL synchronization group is derived from one of: an L2 reset group to which the first LTM candidate cell belongs, and a UE-based timing advance (TA) group to which the first LTM candidate cell belongs.

14. A method performed by a first candidate network node for enabling Layer 1 / Layer2 Triggered Mobility, LTM, by a user equipment, UE, the method comprising: transmitting (402) to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

15. The method of claim 14 further comprising transmitting to the second network node at least one UL synchronization parameter associated with the UL synchronization group.

16. The method of claim 15 further wherein the UL synchronization parameter is associated with the UL synchronization group by being transmitted with an identification a first LTM candidate cell of the plurality of LTM candidate cells or a UL synchronization group identification.

17. The method of claim 14 further comprising transmiting to the user equipment at least one UL synchronization parameter.

18. The method of any one of claims 15 to 17, wherein the at least one UL synchronization parameter comprises a timing advance, TA, value and / or a time alignment timer associated with the TA value.

19. The method as claimed in any one of claims 15 to 18 further comprising: receiving a Physical Random- Access Channel, PRACH, preamble on a first LTM candidate cell of the plurality of LTM candidate cells; calculating a timing advance, TA, value based on the received PRACH preamble, wherein the at least one UL synchronization parameter comprises the TA value.

20. The method of any one of claims 15 to 19, wherein the indication of the UL synchronization group is transmited concurrently with the at least one UL synchronization parameter.

21. The method of claim 20 wherein the indication of the UL synchronization group comprises identifications of the plurality of LTM candidate cells.

22. The method of any one of claims 15 to 21, wherein the indication of the UL synchronization group is transmited prior to the at least one UL synchronization parameter.

23. The method of claim 14, wherein the indication of the UL synchronization group comprises an implicit indication in that the plurality of LTM candidate cells are associated with the same at least one UL synchronization parameter.

24. The method of any one of claims 14 to 23, wherein the second network node comprises a serving distributed unit, S-DU, and transmiting the indication of the UL synchronization group comprises transmiting the indication of UL synchronization group via a serving central unit, S-CU.

25. A method performed by a second network node for enabling Layer 1 / Layer Triggered Mobility, LTM, by a user equipment, UE, served by the second network node, the method comprising:receiving (502) from a first candidate network node, an indication of an UL synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

26. The method of claim 25, further comprising transmitting the indication of the UL synchronization group to the user equipment.

27. The method of claim 25 or 26, further comprising receiving, from the first candidate network node, at least one UL synchronization parameter associated with the UL synchronization group.

28. The method of claim 27, further comprising transmitting the at least one UL synchronization parameter associated with the UL synchronization group to the user equipment.

29. The method of claim 28, wherein the at least one UL synchronization parameter is transmitted to the UE in a MAC CE.

30. The method of any one of claims 27 or 29 wherein the at least one UL synchronization parameter is associated with the UL synchronization group by being received with an identification of a first LTM candidate cell in the plurality of LTM candidate cells or an identification of the UL synchronization group.

31. The method of any one of claims 27 to 30, further comprising receiving the indication of the UL synchronization group prior to receiving the at least one UL synchronization parameter.

32. The method of claim 31, wherein the at least one UL synchronization parameter is received associated with an identification of a first LTM candidate cell in the plurality of LTM candidate cells.

33. The method of any one of claims 27 to 30, wherein the indication of the UL synchronization group is received concurrently with the at least one UL synchronization parameter.

34. The method of claim 33, wherein the indication of the UL synchronization group comprises identifications of the plurality of LTM candidate cells.

35. The method of any one of claims 25 to 34, further comprising initiating the UE to utilize the at least one UL synchronization parameter to perform a LTM cell switch to any of the plurality of LTM candidate cells.

36. A user equipment (1200) for enabling Layerl / Layer2 Triggered Mobility, LTM, comprising: processing circuitry (1202) configured to cause the user equipment to: obtain (302) a configuration of a plurality of LTM candidate cells, where the plurality of LTM candidate cells is associated with an uplink, UL, synchronization group; obtain (304) at least one UL synchronization parameter associated with the UL synchronization group; and utilize (306) the at least one UL synchronization parameter when performing an LTM cell switch to a first LTM candidate cell of the plurality of LTM candidate cells.

37. The user equipment of claim 36, wherein the processing circuitry (1202) is further configured to cause the user equipment to perform the method according to any one of claims 2 to 13.

38. A user equipment (1200) adapted to perform the method of any one of claims 1 to 13.

39. A first network node (1300) for enabling Layerl / Layer2 Triggered Mobility, LTM, the first network node comprising: processing circuitry (1302) configured to cause the first network node to: transmit (402) to a second network node serving the user equipment, an indication of an uplink, UL, synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

40. The first network node of claim 39, wherein the processing circuitry (1302) is further configured to cause the first network node to perform the method of any one of claims 15 to 24.

41. A first network node (1300) adapted to perform the method of any one of claims 14 to42. A second network node (1300) for enabling Layerl / Layer2 Triggered Mobility, LTM, by a user equipment, UE, served by the second network node, the second network node comprising: processing circuitry (1302) configured to cause the second network node to: receive (502) from a first candidate network node, an indication of an UL synchronization group associated with a plurality of LTM candidate cells served by the first candidate network node.

43. The second network node of claim 42, wherein the processing circuitry (1302) is further configured to cause the second network node to perform the method of any one of claims 26 to 35.

44. A second network node (1300) adapted to perform the method of any one of claims 25

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