Time-aligned fallback during mobility

Abstract

A method performed by a wireless device for Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM). The method comprises: obtaining an uplink configuration of an LTM candidate cell; receiving, from the serving cell, a first indication to perform uplink transmission in the candidate cell; transmitting the first uplink transmission in the candidate cell using the first transmit power and on the first uplink time / frequency resource; receiving, from the serving cell, a second indication to perform uplink transmission in the candidate cell; transmitting a second uplink transmission in the candidate cell, where the second uplink transmission is transmitted using one or more of the following: a second transmission power different from the first transmission power, and a second uplink time / frequency resource different from the first time / frequency resource; and receiving a timing advance value of the candidate cell from the serving cell based on the second uplink transmission.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to wireless communications, and more particularly, to time-aligned backoff during mobility. Background Art

[0002] Generally, unless clearly given and / or different meanings are suggested from the context, all terms used in this article will be interpreted according to their ordinary meaning in the relevant technical field. Unless otherwise clearly stated, all references to "one / an / element, equipment, component, device, step, etc." should be openly interpreted as referring to at least one instance in an element, equipment, component, device, step, etc. Unless a step must be clearly described as being after or before another step and / or a step must be after or before another step implicitly, the steps of any method disclosed herein need not be performed in the exact order disclosed. Where appropriate, any feature of any embodiment disclosed herein may be applied to any other embodiment. Similarly, any advantage of any embodiment may be applicable to any other embodiment, and vice versa. By the description below, other purposes, features and advantages of the attached embodiments will be apparent.

[0003] Fifth-generation (5G) New Radio (NR) wireless networks use timing advance (TA) for uplink synchronization. Different user equipment (UE) in the same cell are typically located at different locations within that cell and therefore at different distances from the base station (e.g., NR gNodeB). Consequently, transmissions from different UEs experience different delays before they reach the base station. To ensure that uplink (UL) transmissions from UEs arrive at the base station within its corresponding receive window, an uplink timing control procedure is used. This prevents intra-cell interference between UEs assigned to transmit in consecutive subframes and between UEs transmitting on adjacent subcarriers.

[0004] Time alignment of uplink transmissions is achieved by applying a timing advance at the UE transmitter relative to the received downlink timing. Its main purpose is to offset the different propagation delays between different UEs, as shown in the following example for an LTE eNodeB:

[0005] To achieve time alignment for uplink synchronization, a base station (e.g., gNodeB, eNodeB) derives the TA value that the UE needs to use for uplink transmissions to arrive at the base station within the receive window and indicates this TA value to the UE. When a UE first accesses a cell, it uses a random access procedure, in which the base station uses the received Msg1 (Physical Random Access Channel (PRACH) preamble) to determine the initial TA to be used by the UE for uplink transmissions in that cell. The base station then continuously monitors whether the UE needs to advance / delay uplink transmissions to compensate for variations in propagation delay and indicates to the UE whether the TA value needs to be changed. The timing advance value, which can be referred to as the TA value, can be the actual timing adjustment value to be applied and / or an index (e.g., TA) pointing to the timing adjustment value to be applied.

[0006] When a UE is connected to several different serving cells, the same TA value can sometimes be used for more than one cell, for example, if these cells are co-located and therefore always at the same distance from the UE. These cells can then be configured to belong to the same timing advance group (TAG). TAG configuration is done per cell group, i.e., only if the serving cells belong to the same cell group (Master Cell Group (MCG) or Secondary Cell Group (SCG)) can these cells be configured to belong to the same TAG. Further details are provided below.

[0007] When a UE has not performed an uplink transmission in a serving cell for a period of time, the TA value previously used by the UE may no longer be accurate, for example, because the UE has moved and therefore has different propagation delays. In this case, if the UE performs an uplink transmission using the most recently received TA value, the uplink transmission may arrive at the base station outside the reception window and thus not be correctly received by the base station. This transmission may even interfere with other uplink transmissions (from other UEs). Therefore, a timer, timeAlignmentTimer (also known as the time alignment timer or TA timer), is configured for each TAG to indicate the length of time the UE can consider itself uplink time-aligned with the serving cell belonging to the associated TAG, without receiving any updates to the TA value. Therefore, timeAlignmentTimer indicates the duration for which the UE can consider a received TA value valid. If the UE does not receive an updated value before the timeAlignmentTimer expires, the UE is no longer uplink synchronized with the serving cell belonging to the corresponding TAG.

[0008] In the random access (RA) procedure in NR, the UE first selects a beam (spatial direction) by selecting the synchronization signal block (SSB) or channel state information reference signal (CSI-RS) resources of the target cell in which the UE intends to perform the RA procedure. The selected SSB or CSI-RS resources are mapped to the RA resources (i.e., the preamble and / or time / frequency resources of the RA channel (RACH) of the target cell).

[0009] The UE sends the selected preamble in the selected RACH resource and expects to receive an RAR within the configured RA response (RAR) time window. If the UE sends a preamble but does not receive an RAR during the configured RAR time window, the UE performs a so-called RA fallback, which includes: the UE reselects the RA resource by selecting a new beam (i.e., new SSB and / or CSI-RS) mapped to the new RA resource and / or performing a preamble power ramp-up (i.e., increasing the transmit power used for the preamble transmission). This process can be performed up to a maximum number of times configured by the network, and when the maximum number of times is reached, the UE declares RA failure.

[0010] For the case of contention-based random access during reconfiguration with synchronization to the target cell, it can be summarized as follows:

[0011] ********************************************************************* [38.321]

[0013] 5.1.4 Random Access Response Reception

[0014] Once the random access preamble is sent, regardless of whether measurement gaps may occur, the MAC entity shall:

[0015] […]

[0016] 1> If the ra-ResponseWindow configured in RACH-ConfigCommon expires and a random access response containing a random access preamble identifier matching the sent PREAMBLE_INDEX has not been received:

[0017] 2> The random access response reception is considered unsuccessful;

[0018] 2>Increment PREAMBLE_TRANSMISSION_COUNTER by 1;

[0019] 2> If PREAMBLE_TRANSMISSION_COUNTER = preambleTransMax + 1, then:

[0020] 3> If a random access preamble is sent on the SpCell, then:

[0021] 4>Indicate random access problem to upper layer;

[0022] […]

[0023] 2> If the random access process is not completed, then:

[0024] 3> Select a random backoff time based on a uniform distribution between 0 and PREAMBLE_BACKOFF;

[0025] 3> If the criteria for selecting non-contention random access resources (defined in Section 5.1.2) are met during the backoff time, then:

[0026] 4> Perform random access resource selection process (see Section 5.1.2);

[0027] 3> Otherwise:

[0028] 4> Perform the random access resource selection process after the backoff time (see Section 5.1.2).

[0029] […] [38.321]

[0031] 5.1.2 Random Access Resource Selection

[0032] The MAC entity shall:

[0033] […]

[0034] 1> Otherwise (i.e., for contention-based random access preamble selection):

[0035] 2> If at least one of the SSBs with SS-RSRP higher than rsrp-ThresholdSSB is available, then:

[0036] 3> Select an SSB whose SS-RSRP is higher than rsrp-ThresholdSSB.

[0037] 2> Otherwise:

[0038] 3>Select any SSB.

[0039] […]

[0040] 2> Randomly select a random access preamble with equal probability from the random access preambles associated with the selected SSB and the selected random access preamble group.

[0041] 2> Set PREAMBLE_INDEX to the selected random access preamble.

[0042] […]

[0043] 1> Otherwise, if SSB is selected in the above process:

[0044] 2> If configured or indicated by PDCCH, determine the next available PRACH opportunity corresponding to the selected SSB allowed by the restriction given by ra-ssb-OccasionMaskIndex from the PRACH opportunities (the MAC entity shall randomly select the PRACH opportunity corresponding to the selected SSB with equal probability in consecutive PRACH opportunities according to section 8.1 of TS38.213; the MAC entity may take into account possible measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB).

[0045] 1> Otherwise, if CSI-RS is selected in the above process:

[0046] […]

[0047] 1> Perform the random access preamble transmission process (see Section 5.1.3).

[0048] NOTE: When the UE determines that there is an SSB with an SS-RSRP higher than rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement value.

[0049] 5.1.3 Random Access Preamble Transmission

[0050] For each random access preamble, the MAC entity shall:

[0051] 1> If PREAMBLE_TRANSMISSION_COUNTER is greater than 1; and

[0052] 1> If a notification to suspend the power ramp counter has not been received from the lower layer; and

[0053] 1> If the selected SSB or CSI-RS has not changed compared to the selection of the previous random access preamble code transmission, then:

[0054] 2>Increment PREAMBLE_POWER_RAMPING_COUNTER by 1.

[0055] 1>Select the value of DELTA_PREAMBLE according to Section 7.3;

[0056] 1>Set PREAMBLE_RECEIVED_TARGET_POWER to preambleReceivedTarget Power+ DELTA_PREAMBLE + (PREAMBLE_POWER_RAMPING_COUNTER – 1) × PREAMBLE_POWER_RAMPING_STEP;

[0057] 1> Calculate the RA-RNTI associated with the PRACH opportunity on which the random access preamble is sent, except for the non-contention random access preamble used for beam failure recovery request;

[0058] 1> Instructs the physical layer to send a random access preamble using the selected PRACH opportunity, the corresponding RA-RNTI (if available), PREAMBLE_INDEX and Preamble_RECEIVED_TARGET_POWER.

[0059] […]

[0060] *********************************************************************

[0061] The 3rd Generation Partnership Project (3GPP) includes work items to further enhance NR mobility, specifically a technical area called L1 / L2-based inter-cell mobility. For more details, see the work item description (WID) in RP-213565.

[0062] Depending on the WID, a UE sometimes needs to perform a serving cell change when it moves from one cell's coverage area to another. Currently, serving cell changes are triggered by Layer 3 (L3) measurements and accomplished through synchronized reconfiguration (for changes in PCell and PSCell) triggered by Radio Resource Control (RRC) signaling, along with the addition of released SCells when applicable. All cases involve a full Layer 2 (L2) (and Layer 1 (L1)) reset, which results in higher latency, greater overhead, and longer disruption than beam switching mobility. L1 / L2 mobility enhancements aim to reduce latency, overhead, and disruption by implementing serving cell changes via L1 / L2 signaling.

[0063] One goal is that L1-L2 inter-cell mobility should be similar to inter-cell beam management, that is, to support L1-L2 inter-cell mobility, the UE should be configured to perform measurements on cells that are not the serving cell (defined before Release 17). In Release 17, to support inter-PCI mTRP operation, a solution has been standardized where CSI resources can be associated with a primary cell identifier (PCI) that is different from the PCI of one of the serving cells. In this solution, the UE receives an explicit indication of which beams (SSBs) and PCIs to measure for a given reporting configuration.

[0064] The goal is to specify mechanisms and procedures for L1 / L2-based inter-cell mobility to reduce mobility latency. These mechanisms and procedures include: configuring and maintaining multiple candidate cells to enable rapid application of candidate cell configurations; dynamic switching between candidate serving cells (including SpCells and SCells) for potential use cases based on L1 / L2 signaling; L1 enhancements for inter-cell beam management, including L1 measurement and reporting, and beam indication; timing advance management; and CU-DU interface signaling to support L1 / L2 mobility when needed.

[0065] The L1 / L2-based inter-cell mobility procedures are applicable to the following scenarios: standalone, carrier aggregation (CA) and NR dual connectivity (DC) cases, where the serving cell changes within one CG; intra-DU cases and intra-CU inter-DU cases (applicable to standalone and CA); both intra-frequency and inter-frequency; both frequency range 1 (FR1) and frequency range 2 (FR2); and the source and target cells can be synchronized or unsynchronized.

[0066] There are certain challenges. For example, one of the issues to be addressed in L1 / L2 inter-cell mobility is timing advance management (which can include handling of time alignment timers). In traditional L3 handover, the timing advance is established between the UE and the target cell through a random access procedure, with the UE sending a preamble to the target cell and receiving a RAR from the target cell. The RAR includes the time alignment value to be applied.

[0067] To reduce handover interruption time, performance improvements for L1 / L2-based inter-cell mobility include solutions that reduce the time required for UE reconfiguration and downlink and uplink synchronization after a handover decision. In one proposed solution, the UE sends an RA preamble to a candidate cell, and unlike the traditional RA procedure, the UE does not expect a RAR including a TA value in response from the candidate cell. Instead, the UE sends the RA preamble to enable the candidate target network node (e.g., candidate distributed unit – DU) to calculate the timing advance value (i.e., the timing adjustment that the UE needs to apply for uplink synchronization) and provide this value (or an index / indication of this value) to the source DU (S-DU). The S-DU only provides this value or associated values to the UE when L1 / L2 triggered mobility (LTM) is required to perform on the candidate cell. Figure 1A and Figure 1B An example is shown.

[0068] Figure 1A and Figure 1B This is a flowchart illustrating an example in which the TA is established based on sending an RA preamble to a candidate and receiving a TA value only when LTM is executed (e.g., in a MAC CE for an LTM cell handover command). In this solution, the UE can send a preamble that enables the network to calculate the timing advance value of the candidate cell without requiring the UE to wait for the RAR in the candidate cell. This reduces transmission / reception interruptions in the source cell, as after the RA preamble in the candidate cell is transmitted, the UE must also monitor the control channels (such as the Physical Downlink Control Channel (PDCCH)) in the candidate cell to potentially receive the RAR.

[0069] 3GPP work items include the following agreements on LTM.

[0070] *********************************************************************

[0071] - In Release 18 LTM, regarding the mechanism for obtaining the TA of a candidate cell, at least RACH indicated by PDCCH is supported.

[0072] oPDCCH command is triggered only by the source cell

[0073] - In L1 / L2 based mobility, support obtaining the TA of candidate cells before receiving a cell handover command.

[0074] -For RACH indicated by PDCCH in LTM, at least the following enhancements are supported:

[0075] o Introducing candidate cell indication and / or candidate cell RO in DCI

[0076] o Provide the configuration of RACH resources of candidate cells before PDCCH command

[0077] - TA update (ie re-acquisition of TA) of a candidate cell may be triggered by the NW.

[0078] o In the candidate cell, the same triggering mechanism is reused for initial TA acquisition, i.e., RACH triggered by PDCCH command

[0079] *********************************************************************

[0080] The fact that the UE does not expect a RAR in the candidate cell after transmitting an RA preamble poses a problem, as receiving a RAR is a confirmation that the UE's preamble transmission was correctly received by the network. Therefore, without a RAR from the candidate cell, the UE cannot know whether the preamble was successfully received and / or whether the UE needs to resend the preamble. At the same time, having a RAR means that the UE needs to monitor the control channel of the candidate cell, which can increase interference with the source cell. Summary of the Invention

[0081] As mentioned above, there are currently certain challenges with fallback for time alignment during mobility. Certain aspects of the present disclosure and its embodiments may provide solutions to these and other challenges. For example, certain embodiments include network-based fallback for timing advance (TA) establishment / update.

[0082] Some embodiments include a method at a user equipment (UE) that supports Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) and is configured with at least one LTM candidate cell. The method includes handling a failed attempt to perform TA establishment and / or TA update (e.g., performing another preamble transmission by the UE).

[0083] The method includes: a UE receiving (1) a first downlink (DL) indication from a source network node (e.g., a source distributed unit (DU) (S-DU)); and (2) in response to the first downlink indication, the UE sending a first uplink (UL) message (e.g., a first random access (RA) preamble) to an LTM candidate cell, wherein the uplink message is sent using a first transmit power and on a first uplink resource (e.g., an RA resource in time and frequency), wherein the first uplink resource is associated with the LTM candidate cell.

[0084] In some embodiments, the UE selects a first beam, and based on the selected first beam, the UE selects a first uplink resource associated therewith to send a first uplink message.

[0085] In some embodiments, the UE also receives a second downlink indication from the source network node (e.g., an S-DU). In response to the second downlink indication, the UE also transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell, wherein the second uplink message (e.g., a second RA preamble) is transmitted to the LTM candidate cell according to: i) an increased transmit power compared to the first transmit power; or ii) on second uplink resources associated with the LTM candidate cell (e.g., RA resources in time and frequency). Typically, the source network node (e.g., an S-DU) transmits the second downlink indication to the UE when the first uplink message is unsuccessfully received (at the candidate DU (C-DU)), but the UE is not necessarily aware of the failure at the C-DU.

[0086] In some embodiments, the second downlink indication is associated with the first downlink indication. Based on the second indication associated with the first downlink indication, the UE transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell according to: i) an increased transmit power compared to the first transmit power, or ii) on second uplink resources associated with the LTM candidate cell (e.g., RA resources in time and frequency).

[0087] In some embodiments, in response to receiving the second downlink indication, the UE selects a second beam (e.g., a synchronization signal block (SSB) or a channel state information reference signal (CSI-RS) of the LTM candidate cell), and based on the selected second beam, the UE selects a second uplink resource associated with the LTM candidate cell (e.g., RA resources in time and frequency) to send a second uplink message.

[0088] Generally speaking, the UE also receives an (n+1)th downlink indication from the source network node (e.g., an S-DU). In response to the (n+1)th downlink indication, the UE also transmits an (n+1)th uplink message (e.g., an (n+1)th RA preamble) to the LTM candidate cell. The (n+1)th uplink message (e.g., an (n+1)th RA preamble) is transmitted to the LTM candidate cell using: i) an increased transmit power compared to the nth transmit power, or ii) on the (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell. On the network side, the S-DU continues to transmit downlink indications triggering preamble transmission until one or more criteria are met (e.g., a maximum number of attempts is reached) or until an uplink signal / message is successfully received. In other words, this process repeats until the candidate DU successfully receives the uplink signal / message and is able to calculate the TA value, or until the maximum number of attempts is reached (see the network description for more details).

[0089] In some embodiments, the (n+1)th downlink indication is associated with the nth downlink indication. Based on the (n+1)th indication associated with the nth downlink indication, the UE transmits an (n+1)th uplink message (e.g., an (n+1)th RA preamble) to the LTM candidate cell according to: i) an increased transmit power compared to the nth transmit power, or ii) on an (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell.

[0090] In a dependent step, (3) in response to receiving the (n+1)th downlink indication, the UE selects the kth beam (e.g., the SSB or CSI-RS of the LTM candidate cell), and based on the selected kth beam, the UE selects the (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell to send the (n+1)th uplink message.

[0091] In some embodiments, the UE also receives a TA value (calculated by the network based on a second uplink message received at the candidate DU). The various sets of embodiments described herein disclose different ways of providing a TA value, for example, during LTM execution / cell handover to an LTM candidate cell (based on the received second uplink signal, the candidate DU can calculate a TA value for the UE associated with the LTM candidate cell).

[0092] In some embodiments, upon LTM cell handover (performing LTM) to an LTM candidate cell, the UE sends an uplink message on a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) based on the received TA value.

[0093] Figure 2A and Figure 2B is a flow chart outlining UE actions in network-based TA establishment fallback.

[0094] Some embodiments include a method at a serving DU (S-DU), comprising: the S-DU transmitting a first downlink indication to a UE, the UE transmitting a first uplink message (e.g., a first RA preamble) to an LTM candidate cell based on the first downlink indication, wherein the UE is to transmit the uplink message using a first transmit power and on first uplink resources associated with the LTM candidate cell (e.g., RA resources in time and frequency). The S-DU then detects that the first uplink message was not successfully received at a C-DU responsible for the LTM candidate cell, and in response, transmitting a second downlink indication associated with the first downlink indication to the UE, the UE further transmitting a second uplink message (e.g., a second RA preamble) to the LTM candidate cell based on the second downlink indication, wherein the second uplink message is to be transmitted to the candidate cell according to: i) an increased transmit power compared to the first transmit power, or ii) on second uplink resources associated with the LTM candidate cell (e.g., RA resources in time and frequency).

[0095] In some embodiments, the S-DU receives a TA value from the candidate DU (calculated by the C-DU based on a second uplink signal received at the C-DU).

[0096] In some embodiments, the S-DU also sends the TA value (calculated by the C-DU based on the second uplink signal received at the C-DU) to the UE, for example, included in the LTM cell handover command instructing the UE to move to the LTM candidate cell.

[0097] In some embodiments, when a supervision timer expires, the S-DU determines that the first uplink message was not successfully received at the candidate DU. The S-DU starts the timer when it sends a first downlink indication to the UE. The timer is stopped when the S-DU receives a message from the C-DU (e.g., via the CU) that includes a TA value calculated based on the transmission of the first uplink message. This timer is referred to herein as a supervision timer, but its functionality can also be modeled as a time window within which a message from the C-DU is expected to be received. If the message is not received within this time window, the S-DU considers the attempt a failed attempt.

[0098] In some embodiments, the S-DU monitors a counter for uplink signal / message transmission attempts (e.g., the maximum number of RA preamble transmission attempts). Thus, after the first downlink indication, the counter increments each time the S-DU provides a downlink indication to the UE. This counter has a maximum value that can be reached, and upon reaching this value, the S-DU declares the TA establishment procedure failed. Before sending the second indication, the S-DU checks whether the maximum value has been reached. If so, the S-DU declares the TA establishment procedure failed.

[0099] In some embodiments, if the S-DU determines that the first uplink message was not successfully received at the candidate DU, then when sending the second downlink message to trigger the second RA preamble transmission at the UE, the S-DU may also indicate a new LTM candidate cell (e.g., by indicating an LTM configuration ID) and / or a beam or transmission configuration indicator (TCI) status (to which the second RA preamble needs to be sent) .

[0100] In some embodiments, the S-DU counts the increments in transmit power for uplink signals / messages. When the UE instructs an increase in transmit power, the S-DU increments this variable. There is a maximum transmit power value, and when this value is reached after retransmissions, the S-DU declares the TA establishment procedure failed.

[0101] Some embodiments include a method at a candidate DU (C-DU), comprising: the C-DU detecting whether a first uplink message is successfully received at the C-DU (responsible for the LTM candidate cell); and when the uplink message is successfully received, calculating a TA value based on the received first uplink message and sending the TA value to the S-DU in the message; or when the first uplink message is not successfully received, performing one or more of the following: i) sending a message not including a TA value to the S-DU (e.g., via the CU); ii) not sending a message to the S-DU (e.g., via the CU).

[0102] In summary, a method at a UE supporting LTM and configured with at least one LTM candidate cell includes: (1) receiving a first downlink indication from a serving cell (of a source network node, such as a source DU (S-DU)); and (2) in response to the first downlink indication, the UE sending a first uplink message (e.g., a first RA preamble) to a first LTM candidate cell, wherein the uplink message is sent using a first transmit power and on a first uplink resource (e.g., an RA resource in time and frequency). The method also includes: receiving a second downlink indication from the source network node (e.g., the S-DU). In response to receiving the second downlink indication, the method includes: sending a second uplink message (e.g., a second RA preamble) to a second LTM candidate cell, wherein the second uplink message (e.g., the second RA preamble) is sent to the LTM candidate cell according to: i) an increased transmit power compared to the first transmit power, or ii) on a second uplink resource (e.g., an RA resource in time and frequency) associated with the LTM candidate cell.

[0103] In some embodiments, the LTM candidate cell is the same as the second LTM candidate cell. In some embodiments, the first LTM candidate cell is different from the second LTM candidate cell.

[0104] In some embodiments, the method further includes: the UE selecting a first beam, and based on the selected first beam, the UE selecting a first uplink resource associated therewith to send the first uplink message.

[0105] According to some embodiments, a method for LTM performed by a wireless device includes: obtaining an uplink configuration for an LTM candidate cell; receiving a first indication from a serving cell to perform an uplink transmission in the LTM candidate cell; transmitting the first uplink transmission in the LTM candidate cell using a first transmit power and on a first uplink time / frequency resource; receiving a second indication from the serving cell to perform an uplink transmission in the LTM candidate cell; transmitting a second uplink transmission in the LTM candidate cell, wherein the second uplink transmission is transmitted using one or more of: a second transmit power different from the first transmit power and a second uplink time / frequency resource different from the first time / frequency resource; and receiving a timing advance value for the LTM candidate cell from the serving cell based on the second uplink transmission.

[0106] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmissions of random access preambles.

[0107] In a particular embodiment, the wireless device does not expect a RAR in response to the transmission of the random access preamble.

[0108] In a particular embodiment, the first uplink transmission uses a first beam and in response to receiving a second indication to perform an uplink transmission, the method further includes: selecting a second beam for a second uplink transmission, and when the second beam is the same as the first beam, sending the second transmission using a second transmit power different from the first transmit power, and when the second beam is different from the first beam, sending the second transmission using a second uplink time / frequency resource different from the first time / frequency resource.

[0109] In a particular embodiment, the second indication to perform uplink transmission includes an indication of a second transmit power for the second uplink transmission or an indication of a second uplink time / frequency resource for the second uplink transmission.

[0110] In a particular embodiment, the first indication and the second indication include a PDCCH order.

[0111] In certain embodiments, receiving the timing advance value from the serving cell includes receiving an LTM execution command.

[0112] In a specific embodiment, the uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

[0113] In a particular embodiment, at least one of the first indication and the second indication comprises an indication of an SSB associated with the first uplink transmission or the second uplink transmission, respectively.

[0114] In a particular embodiment, the uplink configuration of the uplink candidate cell includes more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication includes an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

[0115] According to some embodiments, a wireless device comprises processing circuitry operable to perform any of the wireless device methods described above.

[0116] Another computer program product includes a non-transitory computer-readable medium having computer-readable program code stored thereon, which, when executed by a processing circuit, is operative to perform any of the methods performed by the wireless device described above.

[0117] According to some embodiments, a method performed by a network node acting as an S-DU for TA management between a wireless device and at least one LTM candidate cell includes sending a first indication to the wireless device to perform an uplink transmission in the LTM candidate cell, and sending a second indication to the wireless device to perform an uplink transmission in the LTM candidate cell.

[0118] In certain embodiments, the method further includes, upon detecting that the uplink transmission in the LTM candidate cell is unsuccessful, sending a second indication to the wireless device to perform uplink transmission in the LTM candidate cell.

[0119] In certain embodiments, detecting that the uplink transmission in the LTM candidate cell is unsuccessful includes not receiving a response from the LTM candidate cell, or receiving an indication from the LTM candidate cell that the uplink transmission in the LTM candidate cell is unsuccessful.

[0120] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmissions of random access preambles.

[0121] In certain embodiments, the second indication to perform an uplink transmission includes an indication of a transmit power or uplink time / frequency resource to be used for the second uplink transmission.

[0122] In a particular embodiment, the first indication and the second indication include a PDCCH order.

[0123] In certain embodiments, the method further includes receiving a timing advance value from the candidate LTM cell and sending the timing advance value to the wireless device.

[0124] In certain embodiments, sending the timing advance value to the wireless device includes sending an LTM execute command to the wireless device.

[0125] In certain embodiments, sending the second indication to the wireless device to perform an uplink transmission includes determining that a threshold number of uplink transmissions by the wireless device with the LTM candidate cell has not been exceeded.

[0126] In certain embodiments, the method further includes transmitting an uplink configuration of the uplink candidate cell to the wireless device. The uplink configuration of the uplink candidate cell may include one or more random access parameters, and at least one of the first indication and the second indication includes an indication of which of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively. The uplink configuration of the uplink candidate cell may include multiple uplink configurations for multiple uplink candidate cells, and at least one of the first indication and the second indication includes an indication of which uplink candidate cell is used to transmit the first uplink transmission or the second uplink transmission, respectively.

[0127] In a particular embodiment, at least one of the first indication and the second indication comprises an indication of a synchronization signal block SSB associated with the first uplink transmission or the second uplink transmission, respectively.

[0128] According to some embodiments, a network node comprises processing circuitry operable to perform any of the network node methods described above.

[0129] Another computer program product includes a non-transitory computer-readable medium having computer-readable program code stored thereon, the computer-readable program code being operative, when executed by a processing circuit, to perform any of the methods performed by the network node described above.

[0130] Certain embodiments may provide one or more of the following technical advantages. For example, certain embodiments establish and update time alignment (timing advance adjustment) between a UE and an LTM candidate cell, which may be a cell that is not uplink synchronized with the UE's configured serving cell (and therefore, not uplink synchronized with the UE). Consequently, certain embodiments enable the UE to perform an LTM cell handover (e.g., upon receiving a MAC CE for LTM) and transmit uplink information to the candidate cell without first performing an RA procedure (e.g., on the PUSCH or PUCCH), thereby reducing the interruption time during LTM execution, thereby more efficiently utilizing network radio resources, and reducing UE energy consumption.

[0131] Furthermore, one advantage of certain embodiments is the ability to handle failed attempts to transmit uplink signals / messages (e.g., RA preambles) during TA establishment and / or update between a UE and an LTM candidate cell. Thus, when a candidate DU fails to detect a previous preamble transmission, retransmission of an uplink message to the candidate LTM can be triggered, making TA establishment and update more robust, efficient, and unambiguous in interoperable networks.

[0132] Certain embodiments include network-based TA establishment fallback. In one set of embodiments, the UE sends an RA preamble to the LTM candidate cell, but does not rely on receiving the RAR in the LTM candidate cell; therefore, the interruption time with the serving cell during the TA establishment and update process is minimized, which benefits the data rate provided by the serving cell because more data can be scheduled (due to fewer scheduling restrictions imposed by the serving cell). At the same time, due to the lack of RAR, the UE cannot determine whether the attempted transmission was successful. However, the advantage of network-based fallback is that the S-DU determines whether the attempt was successful, and if the attempt was unsuccessful, it instructs the UE to send another uplink signal / message, i.e., the S-DU indicates that the UE needs to fall back, such as power ramping and / or beam selection.

[0133] In other words, compared to the RA procedure, some differences are: i) the downlink indication received by the UE in response to the preamble transmission on the LTM candidate cell is received from the serving cell (from the S-DU); ii) receiving the downlink indication indicates a failed attempt, unlike RAR, which indicates a successful attempt. Another difference compared to the traditional RA procedure is that the monitoring of failed and successful attempts is performed on the network side rather than at the UE, which relieves the UE of some responsibilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0134] For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0135] Figure 1A and Figure 1B is a flow chart illustrating an example in which a timing advance (TA) is established based on sending a random access (RA) preamble to a candidate and receiving a TA value only when layer 1 (L1) / layer 2 (L2) triggered mobility (LTM) is performed;

[0136] Figure 2A and Figure 2B is a flow chart outlining UE actions in network-based TA establishment fallback;

[0137] Figure 3 A block diagram illustrating the architecture of a Central Unit (CU) and a Distributed Unit (DU) in a Radio Access Network (RAN);

[0138] Figure 4A and Figure 4B Abstract syntax notation (ASN) showing six examples of LTM candidate configurations;

[0139] Figure 5A 、 Figure 5B and Figure 5C is a flow chart illustrating an example of steps for LTM configuration and TA establishment / update according to certain embodiments;

[0140] Figure 6A 、 Figure 6B and Figure 6C is a flow chart illustrating a fallback process of a TA update process;

[0141] Figure 7A 、 Figure 7B and Figure 7C is a flow chart illustrating another fallback process of the TA update process;

[0142] Figure 8A and Figure 8B is a flowchart showing an example of actions at the S-DU when a TA establishment failure is detected;

[0143] Figure 9 An example communication system according to certain embodiments is shown;

[0144] Figure 10 shows an example user equipment (UE) according to certain embodiments;

[0145] Figure 11 shows an example network node according to certain embodiments;

[0146] Figure 12 A method performed by a user equipment according to some embodiments is shown; and

[0147] Figure 13 A method performed by a network node according to certain embodiments is shown. DETAILED DESCRIPTION

[0148] As mentioned above, there are currently certain challenges with fallback for time alignment during mobility. Certain aspects of the present disclosure and embodiments thereof may provide solutions to these and other challenges. For example, certain embodiments include network-based fallback for timing advance (TA) establishment / update.

[0149] Certain embodiments are described more fully with reference to the accompanying drawings. However, other embodiments are within the scope of the subject matter disclosed herein. The disclosed subject matter should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0150] Figure 3 The present invention is a block diagram illustrating the architecture of a central unit (CU) and distributed units (DU) in a radio access network (RAN). In the example shown, the RAN is a next-generation RAN (NG-RAN), which may be referred to as a fifth-generation (5G) RAN. However, certain embodiments are applicable to any RAN, such as a sixth-generation (6G) RAN architecture.

[0151] The illustrated architecture (with both NG-RAN and 5GC) shows a split NG-RAN between the CU and DU, connected via the F1 interface. The RAN (e.g., NG-RAN) consists of a set of RAN nodes (e.g., gNBs) connected to the core network (e.g., 5GC) via the RAN / CN interface (e.g., NG interface). The NG-RAN may include one or more ng-eNBs, where an ng-eNB may include an ng-eNB-CU and one or more ng-eNB-DUs. A gNB may include a gNB-CU and one or more gNB-DUs. The gNB-CU and gNB-DUs are connected via the F1 interface. A gNB-DU may be connected to multiple gNB-CUs through appropriate implementation.

[0152] NG, Xn, and F1 are logical interfaces. For NG-RAN, the gNB's NG and Xn-C interfaces terminate at the gNB-CU, which consists of both the gNB-CU and gNB-DU. For EN-DC, the gNB's S1-U and X2-C interfaces terminate at the gNB-CU, which consists of both the gNB-CU and gNB-DU. The gNB-CU and its connected gNB-DU are visible only to other gNBs and the 5GC acting as the gNB.

[0153] Some embodiments relate to a serving DU or source DU, whose acronyms may be used interchangeably as S-DU. The S-DU may correspond to a gNode-DU, which is responsible for one or more serving cells configured for a user equipment (UE).

[0154] In some embodiments, the CU refers to a CU connected to the UE, ie, a CU where a higher layer protocol (eg, radio resource control (RRC)) for communicating with the UE is terminated and a UE access stratum (AS) context is stored.

[0155] Some embodiments relate to a candidate DU (C-DU), which refers to a DU (which may correspond to a gNodeB-DU) responsible for Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) candidate cells configured for a UE. As part of LTM configuration, the CU sends a request to the C-DU to configure LTM candidate cells for the UE. In response, the CU receives at least the LTM candidate cell configuration, based on which the UE determines the configuration it should use when performing a handover to that LTM candidate cell during LTM execution (also known as LTM cell handover).

[0156] This document refers to the term "L1 / L2-based inter-cell mobility" as used in the 3GPP work item description, although the terms L1 / L2 mobility, L1 mobility, L1-based mobility, L1 / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility, or L1 / L2-triggered mobility may also be used interchangeably. The basic principle is that a UE receives low-layer signaling from the network instructing the UE to change (or switch or activate) its serving cell (e.g., change PCell from source PCell to target PCell). The low-layer signaling is a message / signaling from the lower layer protocol and may be referred to as an L1 / L2 inter-cell mobility execution command (or LTM cell handover command). A change in serving cell (e.g., PCell) may result in a change in Scells within the same cell group, for example, when the command triggers the UE to change to another cell group configuration of the same type (e.g., another master cell group (MCG) configuration). Before the UE receives the LTM cell handover command, the network configures one or more LTM candidate cells for the UE (e.g., receives an RRC reconfiguration message with at least one candidate cell configuration). The candidate cell configuration may include the information element (IE) CellGroupConfig for each candidate cell and / or parameters in the embedded RRC reconfiguration configuration for each candidate cell.

[0157] A low-layer protocol refers to a protocol that is lower in the air interface protocol stack than the RRC protocol. For example, medium access control (MAC) is considered a low-layer protocol because it is "below" RRC in the air interface protocol stack. In this case, low-layer signaling / messages may correspond to MAC control elements (MAC CEs). Another example of a low-layer protocol is Layer 1 (or physical layer, L1). In this case, low-layer signaling / messages may correspond to downlink control information (DCI). Signaling information in a protocol layer lower than RRC can reduce processing time, thereby reducing interruption time during mobility. It can also improve mobility robustness because the network can respond to rapid changes in channel conditions.

[0158] Another relevant aspect of L1 / L2 inter-cell mobility is that in a multi-beam scenario, a cell can be associated with multiple synchronization signal blocks (SSBs), and different SSBs can be transmitted in different spatial directions (i.e., using different beams, across the cell's coverage area) during a half-frame. A similar principle applies to channel state information reference signal (CSI-RS) resources, which can also be transmitted in different spatial directions. Therefore, in L1 / L2 inter-cell mobility (LTM), receiving low-layer signaling instructs the UE to change from one beam in the serving cell to another beam in a neighboring cell (configured candidate cell), and through it, change serving cells.

[0159] The term "LTM cell handover procedure" refers to the process by which a UE changes its cell from a source cell to a target cell (which may be referred to as a candidate cell) using L1 / L2-triggered mobility. In the context of L1 / L2-based inter-cell mobility or L1 / L2-triggered mobility, the LTM cell handover procedure may also be referred to as dynamic handover, LTM handover, LTM cell handover, LTM serving cell change, or LTM cell change. Even when the term "cell change" is used, it can encompass changes to the entire cell group configuration, including changes to the SpCell (e.g., a PCell or PSCell) and changes to the SCells of a cell group (e.g., adding, modifying, and / or releasing one or more SCells).

[0160] Some examples use the term target candidate configuration (or candidate cell configuration, or LTM candidate cell configuration, or LTM candidate cell configuration) to refer to the configuration of "L1 / L2 inter-cell mobility candidate cells." These are cells configured by a UE when L1 / L2 inter-cell mobility is configured. These are cells to which the UE can move during L1 / L2 inter-cell mobility upon receiving lower layer signaling (e.g., a MAC CE including an LTM candidate cell configuration identifier). These cells may also be referred to as candidate cells, candidates, mobility candidates, non-serving cells, additional cells, target candidate cells, target candidates, etc. These are cells on which the UE performs measurements (e.g., CSI measurements), allowing the UE to report these measurements and the network to make an informed decision about which beam (e.g., transmission configuration indicator (TCI) state) and / or cell to switch the UE to. L1 / L2 inter-cell mobility candidate cells can be candidates for becoming the target PCell or PSCell, or they can be SCells of a cell group (e.g., MCG SCells).

[0161] The term "beam" can correspond to a spatial direction in which a signal is transmitted (e.g., by a network node) or received (e.g., by a UE), or a spatial filter applied to a transmitted or received signal. Thus, transmitting signals on different beams can correspond to transmitting signals in different spatial directions. When the text refers to a "selected beam," it can refer to a beam index and / or a reference signal (RS) index or identifier, such as an SSB index or a CSI-RS resource identifier. Thus, selecting a beam can correspond to selecting an SSB associated with an SSB index. Alternatively, selecting a beam can correspond to selecting a CSI-RS associated with a CSI-RS resource identifier.

[0162] The actual LTM candidate configuration, its contents, and / or the structure of the IE and / or embedded message can be referred to as the RRC model of the candidate configuration, or simply the RRC model. The LTM candidate cell configuration includes the configuration necessary for the UE to operate accordingly when performing L1 / L2 inter-cell mobility to the target candidate cell (which becomes the target cell on the serving frequency and the current (new) PCell or SCell) upon receiving low-layer signaling indicating L1 / L2 inter-cell mobility to the target candidate cell. The UE can be configured with multiple target candidate cells, and the candidate DU generates multiple configurations and sends them to the CU. The target candidate configuration includes at least parameters for the serving cell (or cells), including one or more sets of parameters within the IE SpCellConfig (or IE SCellConfig for secondary cells). The actual LTM candidate cell configuration received by the UE during LTM configuration may be incremental signaling applied to the reference configuration, and the actual configuration to be used by the UE in the candidate cell during LTM cell handover is a combination of the LTM candidate cell configuration and the reference configuration (e.g., separately signaled to the UE by the network).

[0163] Some examples of how to implement signaling of LTM candidate configurations in RRC are described as an RRC model for L1 / L2-based inter-cell mobility and include the following. One example includes RRC reconfiguration for each candidate cell. In this case, the UE receives multiple RRC messages (a list of RRC messages) within a single RRCReconfiguration message (i.e., an RRCReconfiguration message). Each RRCReconfiguration message identifies a target candidate configuration that is stored by the UE and applied / used / activated upon receipt of low-layer signaling for L1 / L2 inter-cell mobility. This model allows for full flexibility, as in L3 reconfiguration, the target node can modify / release / retain any parameters / fields in the RRCReconfiguration message, such as measurement configuration, bearers, etc.

[0164] Another example includes a CellGroupConfig for each candidate cell. With this model, the UE receives a list of CellGroupConfig IEs within the RRCReconfiguration, and each CellGroupConfig IE in the list identifies the target candidate configuration. Each CellGroupConfig IE is stored at the UE and is applied / used / activated upon receipt of low-layer signaling for L1 / L2 inter-cell mobility. This model forces the target node to modify / release / retain any parameters / fields that were part of the CellGroupConfig IE, while the rest of the RRCReconfiguration message (from which the UE received the CellGroupConfig IE) remains unchanged. This means that, for example, measurement configuration, bearers, and security remain unchanged and are not changed by the target node.

[0165] Another example includes "K" SpCellConfigs per cell, "K" ServingCellConfigCommons per cell, or both. With this model, the UE receives "K" SpCellConfigs per cell, "K" ServingCellConfigCommons per cell, or "K" SpCellConfigs and "K" ServingCellConfigCommons per cell as target candidate configurations. This solution provides minimal flexibility for the target node, as only cell-specific parameters (e.g., bandwidth fraction, downlink, and uplink configurations) can be modified / released / retained.

[0166] Another example includes "K" PCIs in the same PCell. With this model, multiple PCIs are configured for the same TCI state configuration, where each PCI identifies a target candidate configuration. This approach offers less flexibility because all parameters / fields used to configure the target candidate configuration are fixed, and only the target node is allowed to change the PCI, scrambling ID, and C-RNTI. Figure 4A and Figure 4B An example is shown in .

[0167] Figure 4A and Figure 4BSix examples of LTM candidate configurations are shown in Abstract Syntax Notation (ASN). An L1 / L2 inter-cell mobility configuration may correspond to fields and / or information elements defined in the RRC protocol (e.g., in ASN.1 format), including one or more target candidate cell configurations. When a UE is configured with multiple target candidate cells for L1 / L2 inter-cell mobility, the L1 / L2 inter-cell mobility configuration may include multiple target candidate cell configurations. The L1 / L2 inter-cell mobility configuration may be included in an RRCReconfiguration message (as defined in TS 38.331) or an RRCResume message received by the UE, for example, during a state transition to RRC_CONNECTED.

[0168] The L1 / L2 inter-cell mobility configuration may be generated by a CU (e.g., a gNB-CU) and include information generated and sent from a candidate DU, such as a target candidate cell configuration and / or a measurement configuration instructing the UE to perform measurements on reference signaling (RS) (e.g., SSB and / or CSI-RS resources) of the target candidate cell, for reporting to the network to assist in L1 / L2 inter-cell mobility execution decisions.

[0169] The first downlink indication, the second downlink indication, the nth downlink indication or the (n+1)th downlink indication that triggers the UE to send an uplink message to the LTM candidate cell for establishing or updating the TA may correspond to: RRC signaling, such as an RRC message (RRC reconfiguration) and / or IE and / or field associated with the LTM candidate cell; MAC signaling, such as a MAC CE (e.g., message and / or IE and / or field) associated with the candidate cell; and / or L1 signaling, such as a physical downlink control channel (PDCCH) command, which may indicate an indication of a beam and / or a count value and / or a power level for sending the uplink message to the candidate cell.

[0170] The first uplink message, the nth uplink message, or the (n+1)th uplink message sent by the UE to the candidate cell for establishing or updating the TA may correspond to: a random access (RA) preamble, a sequence having at least one property similar to the RA preamble (e.g., orthogonal, semi-orthogonal, low correlation property, etc.), and / or a sequence that can be sent in the uplink channel of the LTM candidate cell and does not require the UE to be tightly synchronized with the specific uplink of the LTM candidate cell.

[0171] Some examples mention a TA value, which may specify a time advance value. Some examples mention a TA timer, which may correspond to a time alignment timer.

[0172] As used herein, a "TA value" may correspond to an actual TA value to be applied or an indication of a TA value, such as an integer value received by the UE that maps to an actual TA value or an offset to be used for uplink transmissions. An example of a TA value is a timing advance command, which includes a plurality of bits indicating an index value TA that is used to control the amount of timing adjustment that the MAC entity must apply to candidates for uplink transmissions on, for example, a sounding reference signal (SRS), a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), and the like.

[0173] A set of embodiments includes embodiments of network controlled TA establishment / update procedure fallback. In one set of embodiments, a UE supporting LTM and configured with at least one LTM candidate cell receives (1) a first downlink indication from a source network node (e.g., a source DU (S-DU)), the first downlink indication may correspond to a PDCCH order, the PDCCH order may follow a previous configuration of the LTM candidate cell. In response to the first downlink indication, the UE sends a first uplink message (e.g., a first RA preamble) to the LTM candidate cell, wherein the uplink message is sent using a first transmit power, and wherein the UE sends the uplink message to a first uplink resource (e.g., an RA resource in time and frequency) associated with the LTM candidate. In some embodiments, the UE selects a first beam, and based on the selected first beam, the UE selects a first uplink resource associated with the first beam to send the first uplink message.

[0174] The S-DU (also referred to as serving DU (abbreviated as S-DU)) detects that the first uplink message (eg, RA preamble) is not successfully received at the candidate DU, which is called preamble transmission failure of TA establishment / update.

[0175] In one option, the S-DU detects a failure in the preamble transmission for TA establishment / update by expiration of a timer. When the S-DU sends the first downlink indication to the UE, the S-DU starts the timer. While the timer is running, the S-DU expects to receive a message from the candidate DU (C-DU) directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or from the CU (from the C-DU to the S-DU via the F1AP interface). The message includes the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). If the timer expires and the S-DU does not receive the message including the TA value, the S-DU considers that the preamble transmission for TA establishment / update has failed.

[0176] In one option, the S-DU detects a failure in the transmission of the preamble for TA establishment / update by receiving a failure indication from a candidate DU (associated with the candidate cell to which the UE transmitted the uplink message) directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or from the CU (from the C-DU to the S-DU via the F1AP interface). The S-DU sends a first downlink indication to the UE, and the message is expected to include the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). When the S-DU receives the failure indication from the C-DU, the S-DU considers the transmission of the preamble for TA establishment / update to have failed.

[0177] In one option, the S-DU detects a failure in the preamble transmission for TA establishment / update by receiving a message from a candidate DU (associated with the candidate cell from which the UE transmitted the uplink message) directly via the interface between the S-DU and C-DU (e.g., the E5 interface) and / or the CU (from the C-DU to the S-DU via the F1AP interface), where the TA value is absent from the message. The S-DU sends a first downlink indication to the UE, anticipating a message including the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). When the S-DU receives a message from the C-DU lacking the TA value, the S-DU deems the preamble transmission for TA establishment / update to have failed.

[0178] When the S-DU detects that the first uplink message (e.g., RA preamble) was not successfully received at the C-DU (preamble transmission failure for TA establishment / update), the S-DU sends a second downlink indication to the UE. This can be called a fallback for TA establishment triggered by the S-DU.

[0179] The UE also receives a second downlink indication from the S-DU, and based on the second downlink indication, the UE sends a second uplink message (e.g., a second RA preamble) to the candidate cell, wherein the second uplink message (e.g., the second RA preamble) to the candidate cell is sent according to the following manner: i) with an increased transmit power compared to the first transmit power; or ii) on second uplink resources associated with the LTM candidate cell (e.g., RA resources in time and frequency).

[0180] In some embodiments, the second downlink indication is associated with the first downlink indication. Based on the second downlink indication associated with the first downlink indication, the UE transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell: i) at an increased transmit power compared to the first transmit power; or ii) on second uplink resources (e.g., RA resources in time and frequency) associated with the LTM candidate cell.

[0181] In some embodiments, in response to receiving the second downlink indication, the UE selects a second beam (e.g., the SSB or CSI-RS of the LTM candidate cell), and based on the selected second beam, the UE selects a second uplink resource associated with the LTM candidate cell (e.g., RA resources in time and frequency) to send a second uplink message.

[0182] In some embodiments, the UE also receives a TA value (calculated based on the second uplink signal received at the candidate DU). Different sets of embodiments include different ways of providing the TA value, for example, during LTM execution / cell handover to an LTM candidate cell (based on the received second uplink signal, the candidate DU can calculate the TA value for the UE associated with the LTM candidate cell).

[0183] In some embodiments, upon LTM cell handover to a candidate cell (LTM execution), the UE sends an uplink message on the PUCCH or PUSCH based on the received TA value.

[0184] In some embodiments, the UE sends a second uplink message to the candidate cell, and the S-DU detects that another preamble transmission for TA establishment / update fails. In response to the failure detection, the S-DU sends a third downlink indication to the UE (i.e., a fallback for TA establishment triggered by the S-DU).

[0185] The UE also receives a third downlink indication from the S-DU, and based on the third downlink indication, the UE sends a third uplink message (e.g., a third RA preamble) to the candidate cell, wherein the third uplink message (e.g., a third RA preamble) is sent to the candidate cell according to the following manner: i) an increased transmit power compared to the second transmit power; or ii) on a third uplink resource associated with a third beam selected by the UE (e.g., RA resources in time and frequency).

[0186] In some embodiments, attempts to establish a TA (backoff) are repeated until one or more conditions are met. The backoff for TA establishment includes: after the S-DU has provided an nth downlink indication that caused the preamble transmission to fail for TA establishment / update, the S-DU transmits an (n+1)th downlink indication to the UE, wherein the (n+1)th downlink indication instructs the UE to transmit an (n+1)th uplink message according to the following manner: with an increased or increased transmit power compared to the transmit power of the nth uplink message transmission, or indicates that the transmission of the (n+1)th uplink message will be towards an (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the (n+1)th beam selected by the UE.

[0187] The one or more conditions may correspond to: the S-DU detecting a preamble transmission failure for TA establishment / update; and / or the S-DU detecting a preamble transmission failure for TA establishment / update reaching a maximum number for a given LTM candidate cell and / or UE.

[0188] In one option, the maximum value may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0189] In one option, the S-DU increments a counter each time it detects a preamble transmission failure for TA establishment / update (e.g., based on one or more of the solutions proposed above). The S-DU checks whether the counter has reached a maximum value before sending a downlink indication to the UE. If the S-DU determines that the counter has reached the maximum value, it does not send a downlink indication and considers TA establishment to have failed: this is referred to as a TA establishment failure.

[0190] In other words, when the number of preamble transmission failures for TA establishment reaches its maximum value, the S-DU declares that TA establishment has failed.

[0191] In one option, the maximum number of preamble transmission failures for TA establishment may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0192] In some embodiments, the S-DU detects that the maximum transmit power for the UE to transmit uplink messages to the LTM candidate cell has been reached. The maximum value may be reached after multiple transmit power increases after a preamble transmission failure during TA establishment.

[0193] In one option, the maximum transmit power for TA establishment may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0194] Figure 5A 、 Figure 5B and Figure 5C 4b is a flowchart illustrating an example of LTM configuration and TA establishment / update steps according to certain embodiments. This example illustrates a failed RA preamble transmission attempt for TA establishment for LTM. Steps 1 to 4b include configuring LTM candidate cells for the UE and configuring TA establishment and / or update.

[0195] In one set of embodiments, the UE sends an RRC measurement report message to the network (e.g., a CU), which includes measurements of one or more neighboring cells at a certain frequency (e.g., based on the cell's reference signal received power (RSRP), reference signal received quality (RSRQ), and / or signal to interference and noise ratio (SINR)), where the neighboring cells may include beam measurement information (to be used later to configure the TA establishment procedure). The report is sent in response to network configuration: the UE is configured by the network (e.g., by the CU) to send RRC measurement reports (e.g., based on meeting conditions associated with A3 and / or A5 measurement events, as defined in TS 38.331), which include neighboring cells and serving cells.

[0196] The UE (based on the measurement configuration) includes beam measurement information of one or more neighboring cells in the RRC measurement report, such as RSRP and / or RSRQ and / or SINR of one or more beams (e.g., one or more SSBs and / or CSI-RS resources) of the neighboring cell and the associated beam identifier (e.g., SSB index and / or CSI-RS resource identifier) or only the beam identifier, depending on the reporting configuration.

[0197] The network (e.g., CU, gNB-CU) determines to configure L1 / L2 inter-cell mobility for the UE. It may determine the configuration of one or more neighboring cells included in the requested RRC measurement report as target candidate cells for L1 / L2 inter-cell mobility.

[0198] In one set of embodiments, a CU (e.g., gNB-CU, gNB) sends a request message to a candidate DU (e.g., candidate gNB-DU, via the CU) to configure L1 / L2 inter-cell mobility for at least one LTM candidate cell. In one option, the same request is used for multiple LTM candidate cells of the same candidate DU. In one option, there is a request for each target candidate cell, even if the request is for cells of the same candidate DU. In one option, the CU sends a request for multiple candidate DUs, i.e., one request for each target candidate cell and / or one request for multiple target candidate cells in the same candidate DU. The requested target candidate cell can be one of the neighboring cells included in the RRC measurement report that the CU may have received.

[0199] In one set of embodiments, the CU also requests the candidate DU to establish a TA between the UE and at least one of its target candidate cells, for example, by including an indication thereof in the request message. When the CU determines to configure L1 / L2 inter-cell mobility for at least one target candidate cell in the candidate DU, the CU determines that the UE is not synchronized with the at least one target candidate cell on the uplink and decides to request TA establishment from the candidate DU (responsible for the target candidate cell). This may be referred to as CU-initiated TA establishment for L1 / L2 inter-cell mobility.

[0200] In one embodiment, the CU includes a TA establishment request for each target candidate cell with which it wants to establish a TA, for example, if they are in different candidate DUs, or in the same candidate DU but different TRPs.

[0201] In one embodiment, the CU sends a request to establish a TA to multiple candidate DUs, one request for each target candidate cell. In one embodiment, the CU sends a request to establish a TA for a group of target candidate cells in the same candidate DU.

[0202] In one embodiment, the CU also includes beam measurement information associated with the requested target candidate cell in the request for the candidate DU (e.g., beam measurement of one or more SSBs of the requested target candidate cell for the candidate DU). This enables the candidate DU to generate an uplink configuration based on the beam measurement information, such as a physical random access channel (PRACH) preamble mapped to one or more SSBs that are reported to be sufficiently good / suitable in terms of RSRP and / or RSRQ and / or SINR.

[0203] In one embodiment, the request message from the CU to the candidate DU may correspond to a UE context establishment request (F1AP message).

[0204] In one embodiment, the request to establish a TA between the UE and at least one of its target candidate cells is an indication (encoded as an IE) in a UE Context Setup Request (F1AP message).

[0205] In one embodiment, for example, if the candidate DU is the same as the serving DU, the request message from the CU to the candidate DU may correspond to a UE Context Modification Request (F1AP message).

[0206] In one embodiment, the request to establish a TA between the UE and at least one of its target candidate cells is an indication (encoded as an IE) in a UE Context Modification Request (F1AP message), for example, if the candidate DU is identical to the serving DU.

[0207] In one embodiment, the request to establish a TA between the UE and at least one of its candidate cells includes a request to perform TA establishment fallback by the S-DU upon detecting a preamble transmission failure for TA establishment.

[0208] In one set of embodiments, when the CU determines to configure LTM for at least one target candidate cell in the candidate DU, this indicates an implicit request to the candidate DU for TA establishment. The candidate DU then decides whether to provide a single TA that is valid for all L1 / L2 inter-cell mobility target candidate cells being configured, or to provide a TA for each L1 / L2 inter-cell mobility target candidate cell.

[0209] In one set of embodiments, when a CU determines to configure TA establishment for an LTM candidate cell in a candidate DU, this indicates to the candidate DU an implicit request that TA establishment fallback may be required. In response, the candidate DU may provide one or more parameters to the S-DU and / or CU to control the TA establishment fallback process and / or enable the S-DU to detect a preamble transmission failure for TA establishment. For example, the maximum number of uplink signal (e.g., RA preamble) transmission attempts by the UE for TA establishment is configured by the C-DU responsible for the LTM candidate cell, which is the C-DU that has configured uplink resources for TA establishment and / or TA update. In one option, this is configured per LTM candidate unit. In one option, this is configured per C-DU, i.e., a single value is valid for any LTM candidate cell from that C-DU.

[0210] Another parameter may be the maximum transmit power increment for a UE to send uplink messages to a configured LTM candidate cell. In one option, the transmit power increment (e.g., in dB) and / or increment step size is provided to the UE in the uplink channel configuration for TA establishment. In another option, the transmit power increment (e.g., in dB) is provided to the S-DU (e.g., via the CU).

[0211] Another parameter may be the value of a supervision timer that the S-DU monitors to detect uplink signal transmission failure for TA setup / update. In one option, the S-DU detects preamble transmission failure for TA setup / update by expiration of the supervision timer.

[0212] When the S-DU sends a first downlink indication to the UE, the S-DU starts a supervision timer. While the timer is running, the S-DU expects to receive a message from the candidate DU directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or from the CU (via the F1AP interface, from the C-DU to the S-DU). This message includes the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). If the timer expires and the S-DU does not receive a message including the TA value, the S-DU considers the preamble transmission for TA establishment / update to have failed. This triggers the S-DU to initiate a fallback, i.e., send a second downlink indication to the UE, triggering the UE to send a second uplink signal / message to the C-DU at increased power or in another uplink channel resource selected based on the newly selected beam (e.g., SSB or CSI-RS).

[0213] Another parameter may include one or more parameters of the time window (C-DU response time window, start time, duration, etc.) that the S-DU monitors to detect a failure in uplink signal transmission for TA setup / update. In one option, the S-DU detects a failure in preamble transmission for TA setup / update by the end of the time window.

[0214] In other embodiments, the S-DU is expected to receive a message from the candidate DU directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or the CU (from the C-DU to the S-DU via the F1AP interface), wherein the message includes the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell) before the end of the time window. When the time window ends and the S-DU does not receive the message including the TA value, the S-DU considers that the preamble transmission for TA establishment / update has failed.

[0215] In one set of embodiments, the candidate DU accepts a request to configure LTM (for at least one LTM candidate cell) and a request to establish a TA for at least one LTM candidate cell (or multiple LTM candidate cells). In this case, the candidate DU responds to the request from the CU with a response message that includes the LTM candidate configuration (e.g., for LTM candidate cell X) and includes an uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., LTM candidate cell X). The UE then receives the uplink configuration (see step 4a).

[0216] In one embodiment, in addition to the uplink configuration, the response message also includes an indication that the candidate DU has accepted TA establishment, for example, as an IE in the F1AP message. This may be useful so that the serving DU does not need to parse the RRC fields in the response message to find the uplink configuration and determine whether to accept TA establishment. This may be required by the serving DU if triggering TA establishment later results in a message with the TA value from the candidate DU to the serving DU (via the CU).

[0217] In one embodiment, the response from the candidate DU may correspond to a UE context setup response (F1AP message).

[0218] In one embodiment, for example, if the candidate DU is a serving DU (which is the case when the requested target candidate cell is in the serving DU), the response from the candidate DU may correspond to a UE Context Modification Response (F1AP message).

[0219] In one embodiment, the uplink configuration used to establish a TA between the UE and an LTM candidate cell (eg, LTM candidate cell X) is valid for multiple uplink signal / message transmissions to cover a fallback case when the first uplink message is not successfully received in a C-DU.

[0220] In one embodiment, the response from the candidate DU includes one or more parameters for the S-DU and / or CU for controlling the fallback of the TA establishment / update process and / or enabling the S-DU to detect a preamble transmission failure for TA establishment. The one or more parameters may include at least the parameters disclosed in the aforementioned steps, such as the maximum number of uplink signal (e.g., RA preamble) transmission attempts by the UE for TA establishment, the maximum transmit power increment for the UE to send uplink messages to the configured LTM candidate cells, the value of the supervision timer monitored by the S-DU for detecting an uplink signal transmission failure for TA establishment / update, and / or one or more parameters of the time window monitored by the S-DU for detecting an uplink signal transmission failure for TA establishment / update (e.g., C-DU response time window, start time, duration, etc.).

[0221] Further details on establishing the uplink configuration of the TA between the UE and the target candidate cell will be provided later in steps 4 and 5, when the UE receives the uplink configuration.

[0222] The uplink configuration for TA establishment may include one or more parameters for TA establishment fallback, such as: i) the initial transmit power of the uplink signal / message; ii) the power step increment if the network triggers the fallback, i.e., when the UE receives the second downlink indication; iii) the association between the beam (e.g., SSB or CSI-RS) and the uplink channel resources (e.g., PRACH opportunity and / or time domain / frequency domain resources for preamble transmission, RA preamble, etc.).

[0223] In one set of embodiments, the candidate DU accepts a request to configure LTM (for at least one LTM candidate cell) but rejects a request to establish a TA for at least one LTM candidate cell (or multiple LTM candidate cells). In this case, the candidate DU responds to the request from the CU with a response message that includes the LTM candidate configuration (e.g., for LTM candidate cell X). This may include an indication of the rejection of TA establishment, which may include the inclusion or absence of parameters or configurations in the response message (e.g., the absence or presence of F1APIE). In this case, the serving DU is aware that when performing LTM on the target candidate cell, random access with the target candidate may be required during the execution to establish TA / uplink synchronization.

[0224] In one set of embodiments, the candidate DU rejects the request to configure the LTM and sends a message to the CU indicating the rejection, possibly including a cause value, such as overload.

[0225] In one set of embodiments, the candidate DU requests the establishment of a TA between the UE and a target candidate cell (for at least one target candidate cell) for LTM. In this case, the candidate DU responds to the L1 / L2 inter-cell mobility request from the CU with a response message that includes an LTM candidate configuration (e.g., for LTM candidate cell X) and includes an uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., LTM candidate cell X). This can serve as an indication that the candidate DU is requesting the establishment of a TA between the UE and one or more of its LTM candidate cells. The UE then receives the uplink configuration (see step 4a).

[0226] Steps 3a and 3b can be used to perform reconfiguration in the serving cell by the serving DU before the UE configures LTM, for example, to reconfigure CSI measurements. In this case, the CU generates an RRC reconfiguration (e.g., RRCReconfiguration) message that includes the cell group configuration generated by the serving DU. The CU also includes the LTM configuration with one or more LTM candidate cell configurations, as well as the configuration required for the UE to establish a TA with one or more target candidate cells for LTM.

[0227] In one embodiment, the S-DU determines the scheduling restrictions that it needs to apply when it anticipates that the UE will send uplink signals / messages to an LTM candidate cell for TA establishment / update and fallback to TA establishment / update. In other words, the scheduling restrictions mean that when the UE is sending uplink messages to the LTM candidate cell to establish and / or update the TA, the S-DU will not schedule the time slots / frames and subframes of the UE's serving cell.

[0228] In one set of embodiments, the UE receives an RRC reconfiguration (e.g., an RRCReconfiguration message, e.g., received from the CU via a serving DU) for configuring LTM, which includes an LTM configuration for configuring one or more LTM candidate cells, i.e., the LTM configuration includes one or more LTM candidate cell configurations, and an uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., candidate cell X), as described in step 2b.

[0229] In one embodiment, the UE receives an uplink configuration for establishing a TA for an LTM candidate cell. If fallback is required (when the first uplink message transmission is not successfully received in a C-DU, referred to herein as a preamble transmission failure during TA establishment), the uplink configuration may be used for more than a single uplink transmission.

[0230] In one embodiment, the UE receives multiple uplink configurations for establishing TAs for multiple LTM candidate cells, one for each LTM candidate cell.

[0231] In one embodiment, the UE receives an indication associated with an LTM candidate cell to indicate that this is the cell for which the UE should establish a TA, for example, by sending an uplink signal / message. The UE may have received at least one uplink configuration for each target candidate cell for which the TA should be established, and the UE sends a message to the target candidate cell based on the uplink configuration.

[0232] In one embodiment, the UE receives an indication associated with an LTM candidate cell to indicate that this is a possible LTM candidate cell to fall back to when the UE attempts to establish a TA.

[0233] In one embodiment, the target candidate cells configured by the UE for which the UE establishes a TA include a subset of the LTM candidate cells. In other words, the UE may be configured with a number 'N' of LTM candidates and be configured to establish a TA with a number 'N1' (N1 < N) of candidate cells. The reason may be that some of the target candidate cells may not require the establishment of a TA. For example, if they are in the same serving DU and / or are synchronized with one or more serving cells, and / or some of these candidate cells are co-located with one or more other serving cells, the same TA value can be assumed (i.e., it can be assumed that some of the target candidate cells are uplink synchronized with the UE).

[0234] In one embodiment, the UE receives an indication of the LTM candidate cells for which the UE does not need to establish a TA. Additionally, the UE receives an indication that the UE may use the same TA value as a given serving cell for the candidate cells. For example, the UE receives the serving cell index of one of its configured serving cells associated with the LTM candidate cell configuration. Then, when the UE receives an LTM cell handover command, in order to perform LTM (e.g., a MAC CE including a candidate cell configuration indication), the UE determines that this is a cell for which its TA value is considered the same as the TA value of the indicated serving cell, and the UE accordingly applies that TA value when accessing the LTM candidate cell.

[0235] In one embodiment, the UE receives an indication of the LTM candidate cells for which the UE does not need to establish a TA. Additionally, the UE receives the TA value of the candidate cells. For example, the UE receives the serving cell index of one of its configured serving cells associated with the target cell configuration. Then, when the UE receives an LTM cell handover command (e.g., a MAC CE including a candidate cell configuration indication), the UE applies the TA value provided in the LTM cell handover command.

[0236] In one embodiment, the UE receives an indication of the LTM candidate cells for which the UE does not need to establish a TA. Additionally, the UE receives the TA value 0 of the candidate cells. For example, the UE receives the serving cell index of one of its configured serving cells associated with the candidate cell configuration. Then, when the UE receives an LTM cell handover command (e.g., a MAC CE including a candidate cell configuration indication), the UE applies the TA value 0 provided in the LTM cell handover command.

[0237] In one embodiment, the UE receives an indication of the LTM candidate cells for which the UE does not need to establish a TA (e.g., there is no explicit indication in the uplink configuration for TA establishment or the LTM candidate cell configuration), and additionally, the UE receives an indication that the UE may need to perform random access with the LTM candidate cell when receiving an LTM cell handover command (e.g., a MAC CE including a candidate cell configuration indication).

[0238] In one embodiment, the UE receives an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X). The uplink configuration may include an indication (e.g., an uplink configuration of the LTM candidate cell), based on which the UE transmits one or more uplink signals or messages (e.g., one or more RA or PRACH preambles) to the LTM candidate cell, thereby enabling the candidate DU to establish a TA and indicate a TA value to the CU and serving DU. The uplink configuration may be valid for multiple uplink transmissions from the UE to establish a TA to cover a fallback case when the C-DU does not successfully detect the uplink message sent by the UE.

[0239] In one embodiment, the UE receives an uplink configuration (e.g., as a field, parameter, parameter set, and / or field set, IE, etc.) for establishing a TA between the UE and the LTM candidate cell (e.g., candidate cell X) within the LTM candidate configuration (e.g., in an RRCReconfiguration container and / or IE CellGroupConfig and / or SpCell configuration for candidate cell X). This can be, for example, one or more parameters in the random access configuration of the SpCell configuration in the target candidate configuration. The RA configuration can be valid for multiple uplink transmissions from the UE to establish a TA to cover the fallback case when the C-DU does not successfully detect the uplink message sent by the UE.

[0240] In one embodiment, the UE receives an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X), the uplink configuration being configured as an IE and / or field and / or IE set and field set in the LTM configuration, which may correspond to an IE of one or more LTM candidate cells for configuring LTM.

[0241] In one option, an uplink configuration is set for the LTM candidate cell, eg, the candidate cell has its uplink configuration for TA establishment.

[0242] In one option, the uplink configuration is set for a group of LTM candidate cells. The uplink configuration may still be used for a given LTM candidate cell, as the parameters are defined for a given uplink channel of a given cell, but when the UE establishes a TA for that single cell, it is valid for a group of cells, which is possible if multiple cells belong to the same candidate DU and / or the same TRP and / or have some common transceiver properties and / or are uplink synchronized.

[0243] In one embodiment, the UE receives an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X), the uplink configuration being configured as an IE and / or field and / or set of IEs and fields in an RRC reconfiguration message in which the UE receives the LTM configuration.

[0244] In one embodiment, the UE receives an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X), which includes a configuration of uplink signals / messages and / or a configuration of channels for the UE to transmit uplink signals / messages (to be received at the candidate DU). The uplink channel configuration (e.g., available time and / or frequency domain resources) may be valid for multiple uplink transmissions from the UE to establish the TA, covering a fallback case when the C-DU fails to successfully detect an uplink message transmitted by the UE.

[0245] The uplink signal / message may correspond to the random access preamble (or an equivalent sequence defined in the physical layer) indicated by the random access preamble index (eg, ra-PreambleIndex of IE INTEGER (0..63)) in the uplink configuration.

[0246] The uplink configuration may also include at least one beam identifier / index associated with the uplink signal, such as an SSB index and / or a CSI-RS resource identifier.

[0247] For example, when the uplink signal corresponds to a preamble, the uplink configuration may include at least one TA establishment resource as a pair (ssb of the IE SSB-Index, ra-PreambleIndex, or IE INTEGER (0..63)). The uplink configuration may include multiple such pairs because the candidate DU does not know which SSB and / or CSI-RS resource the UE will select to establish a TA. The configured beam (e.g., SSB) may be referred to as a candidate beam for TA establishment.

[0248] In the following example, a list of TA establishment resources of LTM candidate cells is provided to the UE, where each resource has an associated preamble index and SSB index.

[0249]

[0250] In another example, a list of TA establishment resources for LTM candidate cells is provided to the UE, where each resource has an associated preamble index and CSI-RS resource. In addition to the pair, there is also a list of random access opportunities for each resource. These random access opportunities are the RA opportunities that the UE should use when performing TA establishment with the LTM candidate cell (including possible subsequent preamble transmissions in the case of fallback when a preamble transmission failure is detected) when selecting a candidate beam identified by the corresponding CSI-RS.

[0251]

[0252] The candidate DU determines which beam identifiers / indices of the LTM candidate cells to configure for TA establishment based on the beam measurement information (e.g., measurement information about the SSB and / or CSI-RS of the target candidate cell) obtained from the CU in / via the LTM request. The network (e.g., the CU) may have configured the UE to report beam measurement information because it intends to trigger the UE to establish a TA with the LTM candidate cell when LTM is configured for the UE. For example, for the neighboring cells included in the measurement report, the UE may have reported SSB index X and SSB index Y and their corresponding RSRP values (e.g., above a threshold in the reporting configuration), indicating that these are suitable beams in the neighboring cell.

[0253] The uplink configuration may also include one or more of the following parameters:

[0254] Root Sequence Index: The PRACH root sequence index used for TA establishment in LTM, which may be defined in TS 38.211. This can be a field such as rootSequenceIndex of IE INTEGER (0..137).

[0255] RSRP threshold for SSB: The L1-RSRP threshold is used to determine whether the UE can use the candidate beam to attempt non-contention random access to establish a TA with the LTM candidate cell. This can be the field rsrp-ThresholdSSB.

[0256] SSBs per RACH opportunity: The number of SSBs per RACH opportunity for non-contention TA establishment with the LTM candidate cell. This can be the ssb-perRACH-Occasion field of the IE ENUMERATED {one eighth, one quarter, one half, one, two, four, eight, sixteen}.

[0257] RASSB Occasion Mask Index: Explicitly signaled PRACH mask index for RA resource selection, valid for one or more SSB resources. This can be the field ra-ssb-OccasionMaskIndex.

[0258] Subcarrier spacing for MSG1: The subcarrier spacing used to establish a non-contention TA with the target candidate cell, for example, 15kHz or 30kHz for FR1 and 60kHz or 120kHz for FR2. This can be the parameter msg1-SubcarrierSpacing of the IE SubcarrierSpacing.

[0259] • A trigger condition in the form of measurement events A2, A3, A4 or A5 to be met before triggering TA establishment with the LTM candidate cell.

[0260] The uplink configuration may correspond to non-contention resources and / or dedicated resources such that when a candidate DU receives a preamble in an uplink timeslot in a frequency resource, the candidate DU is able to determine which UE it has been configured for and / or which serving DU / CU is serving the UE.

[0261] The uplink configuration may also include one or more parameters of the random access configuration, for example, RACH parameters such as the preamble, time and frequency resources for PRACH, and / or one or more parameters, fields and / or IEs within the IEs RACH-Config, RACH-ConfigCommon, RACH-ConfigDedicated, RACH-ConfigGeneric as defined in TS 38.331. This may be a special RACH configuration that contains only transmission parameters (i.e., no random access response parameters) because the UE is not expected to receive a response from the target candidate in response to the preamble transmission.

[0262] In one embodiment, a UE receives an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X). This uplink configuration is included within one or more parameters in the beam failure recovery (BFR) configuration (e.g., IE BeamFailureRecoveryConfig) of the target candidate cell associated with the uplink bandwidth part (BWP), which can be assumed to be active when performing L1 / L2 inter-cell mobility. This allows the candidate DU to distinguish preambles and RACH messages used for TA establishment from other preambles and RACH attempts. BFR is not available to the UE in any way before accessing the target candidate during L1 / L2 inter-cell mobility, allowing this to be achieved without further detailed configuration.

[0263] In one embodiment, the UE derives its uplink configuration at least in part from the random access configuration of the LTM candidate configuration (e.g., the RACH configuration of the SpCell configuration of the LTM candidate configuration). The UE may receive a time / frequency resource partition for PRACH and / or a preamble partition indicating a subset of RACH resources to be used for this purpose, so that the candidate DU knows that it should not respond to the transmitted preamble in the RAR, but should calculate the TA and provide it to the serving DU. In this sense, in the case of multiple requests, the candidate DU may provide the UE with different PRACH resource partitions in different serving DUs.

[0264] In one embodiment, if fallback is required and is triggered by the network (e.g., via a second downlink indication), the uplink configuration for TA establishment contains one or more parameters for fallback for TA establishment / update, such as: i) the initial transmit power of the uplink signal / message; ii) the power step increment if fallback is triggered by the network, i.e., when the UE receives the second downlink indication; and iii) the association between beams (e.g., SSB or CSI-RS) and uplink channel resources (e.g., PRACH opportunities and / or time / frequency domain resources for preamble transmission, RA preamble, etc.).

[0265] The UE sends an RRC reconfiguration complete (eg, RRCReconfigurationComplete) message after it successfully applies the RRC reconfiguration (eg, RRCReconfiguration) message.

[0266] In one set of embodiments, a UE (e.g., from a CU via a serving DU) receives an RRC reconfiguration (e.g., RRCReconfiguration) message that includes an uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X) after the UE has received an LTM configuration that configures one or more LTM candidate cells. This means that the CU or serving DU can request TA establishment with a candidate DU after LTM has been configured at the UE. For example, the S-DU and / or CU can trigger TA establishment when it determines that a handover to an LTM cell to that candidate DU will occur. This also means that the serving DU has already received the uplink configuration before sending a low-layer handover command to the UE to perform LTM. The UE sends an RRCReconfigurationComplete message after it successfully applies the RRCReconfiguration message.

[0267] According to one set of embodiments, the S-DU is responsible for monitoring whether the UE successfully sends an uplink message / signal to the candidate DU to establish a TA. In other words, the S-DU determines whether a preamble transmission failure for TA establishment / update has occurred. There are different options for how to define these failure monitoring steps.

[0268] In one option, the S-DU detects a failure in the preamble transmission for TA establishment / update by the expiration of a timer (a supervision timer). When the S-DU sends the first downlink indication to the UE (e.g., an RRC reconfiguration including LTM configuration or a subsequent PDCCH command sent after the RRC reconfiguration including LTM configuration), the S-DU starts the supervision timer. While the timer is running, the S-DU expects to receive a message from the candidate DU directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or from the CU (from the C-DU to the S-DU via the F1AP interface). The message includes the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). Upon receiving the message including the TA value, the S-DU stops the timer and considers the TA establishment procedure successful. If the timer expires and the S-DU does not receive a message including the TA value, the S-DU considers the preamble transmission for TA establishment / update to have failed.

[0269] In one option, the S-DU detects a failure in the transmission of the preamble for TA establishment / update at the end of a time window (whose attributes include a start time point, duration, and / or end time point). The S-DU is expected to receive a message from the candidate DU directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or the CU (from the C-DU to the S-DU via the F1AP interface). This message includes the TA value calculated by the C-DU based on the received uplink message (the RA preamble sent by the UE to the LTM candidate cell). If this message including the TA value is received within the time window, the S-DU considers the TA establishment procedure successful. If the time window expires without the S-DU receiving a message including the TA value, the S-DU considers the transmission of the preamble for TA establishment / update to have failed.

[0270] In one option, the properties of the time window are the same as the properties of a random access response (RAR) time window configured as part of the uplink channel configuration provided to the UE for TA establishment.

[0271] In one option, the S-DU detects a failure in the preamble transmission for TA establishment / update by receiving a failure indication from a candidate DU (associated with the candidate cell in which the UE transmitted an uplink message) directly via the interface between the S-DU and C-DU (e.g., the E5 interface) and / or from the CU (via the F1AP interface, from the C-DU to the S-DU). The S-DU receives the first downlink indication sent to the UE (e.g., an RRC reconfiguration including an LTM configuration or a subsequent PDCCH order sent after the RRC reconfiguration including an LTM configuration) and anticipates receiving a message including the TA value calculated by the C-DU based on receipt of the first uplink message (the RA preamble sent by the UE to the LTM candidate cell). Upon receiving this message including the TA value, the S-DU considers the TA establishment procedure successful. Upon receiving a failure indication from the C-DU (e.g., via the CU), the S-DU considers the preamble transmission for TA establishment / update to have failed.

[0272] In one option, the failure indication from the C-DU to the S-DU (eg, via the CU) may correspond to a message lacking a TA value, so the S-DU considers the preamble transmission for TA establishment / update to have failed.

[0273] In one set of embodiments, the UE receives a subsequent message to trigger the UE to send a first uplink signal / message to the LTM candidate cell. The subsequent message may correspond to, for example, a MAC CE, a PDCCH command, a DCI, an RRC message received by the UE after an RRC reconfiguration (e.g., RRCReconfiguration) that configures LTM. The RRC reconfiguration that configures LTM may also include an indication of TA establishment for the LTM candidate cell, or the indication is in the subsequent message. The subsequent message is in Figure 5B This is shown as step 5.

[0274] In scenarios where the candidate DU accepts TA establishment from the CU, it may be useful for the UE to receive subsequent messages as described above. However, when the interruption time is not so critical, the serving DU has some freedom to trigger TA establishment to the UE because the UE may need to stop listening to the serving cell / serving DU to send the first uplink signal to the target candidate. Upon receiving the subsequent message (e.g., PDCCH order), the UE sends the first uplink signal / message based on the uplink configuration for TA establishment previously received in the LTM configuration.

[0275] The first downlink indication may correspond to a subsequent message (eg, MAC CE, PDCCH order, DCI, RRC message), as illustrated in step 5.

[0276] In one embodiment, the subsequent message (first downlink indication) includes one or more indications regarding how the UE should perform the transmission of the first uplink message / signal to the LTM candidate cell, such as parameters for RA preamble transmission and / or RA resources. The one or more indications may correspond to pointers or indications to one or more parameters in the uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., candidate cell X), as described in step 2b.

[0277] In one option, the UE may receive a set of RA preambles in the uplink configuration, such as p1, p2, p3, ..., pK. Therefore, a subsequent message (downlink indication) may indicate one or more of the configured RA preambles, such as p3 and p2. Based on this indication, the UE knows which preambles it can send / select / use for transmission to the LTM candidate cell.

[0278] In one option, the UE receives the RA preamble index (eg, ra-PreambleIndex) of the LTM candidate cell explicitly provided by the PDCCH in a subsequent message.

[0279] In one option, the UE may receive a set of RA resources, such as sequence and / or time-domain resources and / or frequency-domain resources, associated with an RS index or identifier (e.g., an SSB index) in the uplink configuration. Consequently, a subsequent message (downlink indication) may indicate one or more configured RA resources, for example, by indicating one or more SSBs. Based on this, the UE knows which SSBs (and therefore which RA resources) to select for transmission to the LTM candidate cell.

[0280] In one option, the UE may receive a set of RS indices, such as SSB indices, in the uplink configuration. Consequently, a subsequent message (downlink indication) may indicate one or more SSB indices associated with one or more RA resources, for example by indicating one or more SSBs. Based on this, the UE knows which SSBs (and therefore which RA resources) to select for transmission to the LTM candidate cell.

[0281] This subsequent message scheme can also be used for TA update / maintenance mechanism as shown in the following section.

[0282] Some embodiments include failure detection of the first uplink preamble at the C-DU and network-centric fallback. Steps 1 to 4b above are steps of configuring one or more LTM candidate cells to the UE and configuring TA establishment and / or update for at least one cell.

[0283] In the following steps, the embodiment group covers the situation where the C-DU fails to successfully detect the uplink signal / message for TA establishment and the actions taken by different nodes (e.g., UE, S-DU, C-DU, CU) in response thereto, which is referred to herein as the fallback procedure for TA establishment / update.

[0284] In one set of embodiments (see Figure 5B 6 of 6 （1） ), the UE sends a first uplink signal / message (e.g., PRACH preamble, RA preamble) to the LTM candidate cell (for which the UE needs to establish a TA) based on the uplink configuration described in step 4.

[0285] In one set of embodiments, the UE sends a first uplink signal in response to receiving an RRC reconfiguration (eg, RRCReconfiguration) configuring LTM (including an indication of establishing a TA for the LTM candidate cell), such as Figure 5A As shown in step 4a in.

[0286] In this case, the first downlink indication may correspond to an RRC reconfiguration (eg, RRCReconfiguration) message configuring the LTM.

[0287] This may be the case in the first uplink message, while subsequent messages may be used for fallback cases of TA establishment or TA update.

[0288] In one set of embodiments, the UE sends the first uplink signal in response to receiving a subsequent message (e.g., MAC CE, PDCCH command, DCI, RRC message), the subsequent message being received by the UE after the RRCReconfiguration message configuring LTM for the LTM candidate cell. Figure 5B Shown as step 5 （1） .

[0289] In this case, the first downlink indication may correspond to a subsequent message (eg, MAC CE, PDCCH order, DCI, RRC message).

[0290] In one embodiment, the uplink configuration is associated with a validity period (e.g., modeled as a time window, timer, etc.), so that the time after which the serving DU and / or CU can send subsequent messages to the UE is limited. This can be used to limit the use of uplink resources reserved by the C-DU for the TA, for example, when these resources are UE-dedicated / non-contention resources.

[0291] The validity time can be important when the S-DU triggers a fallback. For example, when the C-DU allocates uplink resources for TA establishment and performs a fallback, there are multiple uplinks to the C-DU / LTM candidate cells, which means that the resources may need to be used for a longer time than if a single uplink transmission was allowed. Therefore, the validity time can also be the time from the C-DU to the S-DU indication, which controls the fallback for TA establishment / update.

[0292] In one embodiment, upon triggering TA establishment with an LTM candidate cell (e.g., by receiving a subsequent message and / or a first downlink indication and / or sending a first uplink message), the UE initiates a procedure (e.g., in response to a first downlink indication, such as a subsequent message of an RRC reconfiguration with LTM configuration). Some steps in this procedure may be considered similar to those performed in the RA procedure, with some differences: for example, in the procedure for the TA establishment portion of the method disclosed herein, the UE sends a first uplink message (e.g., a first RA preamble) and does not expect a RAR from the LTM candidate cell in response to the RA preamble sent in the LTM candidate cell. The TA establishment procedure (particularly the initial attempt and any fallback-related steps that may be required) includes one or more of the following steps.

[0293] Some embodiments include performing one or more measurements on a beam, where a "beam" may also refer to a spatial direction in which a reference signal and / or a channel is being transmitted by the network (e.g., an S-DU or C-DU). In one option, the UE performing measurements on a beam corresponds to the UE performing measurements on a reference signal and / or synchronization signal associated with the spatial direction in which the reference signal and / or synchronization signal is being transmitted. A beam may be associated with a beam identifier (ID), which may be encoded by the reference signal or synchronization signal transmitted in the spatial direction associated with the beam.

[0294] Some embodiments include performing one or more measurements on the SSB and / or CSI-RS resources of the target candidate cell for which the UE needs to establish a TA, for example, performing SSB RSRP measurement on one or more SSBs, such as SS-RSRP with SSB index = 1, SS-RSRP with SSB index = 2, ..., SS-RSRP with SSB index = k; for example, CSI-RS RSRP measurement for one or more CSI-RSs.

[0295] Some embodiments include performing uplink channel resource selection, such as RACH resource selection, associated with SSBs and / or CSI-RS resources of LTM candidate cells for which the UE needs to establish a TA. For example, the UE selects an SSB or CSI-RS resource with a measured value above a threshold (possibly configured in the uplink configuration), such as SSB RSRP > rsrp-ThresholdSSB; and the UE selects uplink channel resources (e.g., time / frequency resources and preamble) associated with the selected SSB for TA establishment, wherein the association is also part of the uplink configuration.

[0296] Some embodiments include transmitting a first uplink signal / message to the LTM candidate cell in a selected RA resource (e.g., a preamble selected based on a selected SSB), wherein the first uplink message is transmitted using a first transmit power, wherein the selected RA resource corresponds to a first uplink resource (e.g., an RA resource in time and frequency).

[0297] In one option, the selected first uplink resource is associated with a first beam (eg, a selected SSB) that the UE has selected, eg, based on one or more beam measurements performed by the UE.

[0298] In one option, the UE sets a variable for preamble transmission to the signaled preamble, for example, setting the variable PREAMBLE_INDEX to the signaled ra-PreambleIndex. In one option, the UE selects an SSB signaled by the network, for example, via a PDCCH. In one option, the UE selects an SSB among the associated SSBs for which a measurement value (for example, SS-RSRP as defined in TS 38.215) is above a measurement threshold (for example, rsrp-ThresholdSSB).

[0299] In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB. In one option, the UE selects a CSI-RS signaled, for example, by the PDCCH. In one option, the UE selects a CSI-RS resource with a CSI-RSRP (as defined in TS 38.215) greater than rsrp-ThresholdCSI-RS among the associated CSI-RSs. In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0300] In one option, the UE selects an SSB, and when an SSB is selected, if the configuration is configured or indicated by PDCCH (e.g., ra-ssb-OccasionMaskIndex, part of the uplink configuration established by the TA), the UE determines the next available PRACH opportunity corresponding to the selected SSB from the PRACH opportunities allowed by the restrictions given by the configuration (the MAC entity at the UE randomly selects the PRACH opportunity corresponding to the selected SSB with equal probability among consecutive PRACH opportunities).

[0301] In one option, the UE (eg, a MAC entity at the UE) takes into account possible measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB.

[0302] In one option, the UE selects a CSI-RS and determines the next available PRACH opportunity corresponding to the selected CSI-RS from the PRACH opportunities in the configured RA opportunity list / set (e.g., ra-OccasionList). The UE (e.g., the MAC entity at the UE) randomly selects the PRACH opportunity corresponding to the selected CSI-RS with equal probability among the PRACH opportunities that occur simultaneously but are located on different subcarriers.

[0303] In one option, the UE (eg, a MAC entity at the UE) takes into account possible measurement gaps when determining the next available PRACH opportunity corresponding to the selected CSI-RS.

[0304] In one option, when the UE determines whether there is an SSB with an SS-RSRP higher than rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement.

[0305] In one option, the UE does not maintain a counter for preamble transmissions (e.g., PREAMBLE_TRANSMISSION_COUNTER), which is maintained during the RA procedure. The reason for this is that this should be controlled by the network (e.g., S-DU), which controls the need for the fallback procedure (i.e., RA preamble retransmission in the form of power ramping and / or beam / SSB / CSI-RS reselection if the maximum number of preamble transmission attempts has not been reached). Therefore, in such a network-controlled fallback, it is the network (e.g., S-DU) that monitors the number of preamble transmissions, for example by controlling a preamble transmission counter that is incremented each time the UE is instructed to send an RA preamble for TA establishment for LTM.

[0306] In one option, the UE sets the first transmit power (PREAMBLE_RECEIVED_TARGET_POWER) by adding one or more of: a value provided in the uplink configuration (e.g., preambleReceivedTargetPower); a delta value that depends on the RA preamble format (e.g., 0 dB for preamble format 0), such as DELTA_PREAMBLE; and / or a value indicated in a downlink indication or an indication in a downlink indication that enables the UE to derive a value to be added to the first transmit power.

[0307] In one option, the UE (eg, a MAC entity at the UE) instructs the physical layer at the UE to transmit the selected or indicated RA preamble using the selected PRACH opportunity and a first transmit power (eg, PREAMBLE_RECEIVED_TARGET_POWER).

[0308] This method is also applicable when the LTM candidate cell has a single beam, for example, when the LTM candidate cell has a single SSB associated with its physical cell identity. In this case, the step of selecting a beam (e.g., selecting an SSB or CSI-RS for the LTM candidate cell) for RA resource selection can be skipped.

[0309] In one set of embodiments, the candidate DU fails to successfully receive a first uplink message / signal (e.g., a PRACH preamble). Alternatively, the C-DU detects that the first uplink message was not successfully received, i.e., it detects that the transmission attempt failed. Consequently, the C-DU is unable to calculate the timing advance value for the UE and at least one LTM candidate cell. Thus, it can be said that the C-DU detects that the TA value cannot be calculated, which may have an associated cause value (e.g., detection timer expiration, weak signal strength resulting in inability to identify the uplink signal / preamble, etc.), and may indicate to the S-DU, for example, that the uplink signal transmission attempt failed. Different options may exist for the C-DU to determine that the first uplink message / signal was not successfully detected.

[0310] In one option, the C-DU starts a timer (e.g., a preamble reception timer) when it sends the uplink configuration for TA establishment to the CU and / or S-DU (e.g., step 2b, sending a UE context setup response). If the preamble reception timer does not receive the configured RA preamble for TA establishment while the preamble reception timer is running, the C-DU considers the preamble transmission attempt to have failed. In other words, when the preamble reception timer expires, the C-DU considers the preamble transmission attempt to have failed. If the preamble reception timer receives an RA preamble while the preamble reception timer is running, the timer is stopped, as the attempt is considered successful.

[0311] In response to preamble transmission failure detection, the C-DU may send a message to the CU and / or S-DU to indicate preamble transmission failure detection (in a sub-option, further input to enable fallback may be provided, such as a new SSB and / or parameter settings for further preamble retransmissions). This may be the same message, which may optionally include a TA value, but when this field is empty, it indicates that the C-DU cannot calculate the TA value because the RA preamble was not received correctly.

[0312] In one set of embodiments, the S-DU detects that the first uplink message / signal (e.g., PRACH preamble) was not successfully received at the C-DU, for example, by receiving a failure indication from the C-DU, the expiration of a time window, or by the expiration of a supervision timer (which may have been started when the S-DU sent the first downlink indication to the UE). Figure 5C The options shown are based on a supervision timer at the S-DU which is set in step 5. （1） or 4a (depending on which of these messages triggers the UE to send an uplink message / signal to the LTM candidate cell for LTM establishment). When the S-DU does not receive a message including the expected timing advance value from the C-DU (e.g., via the CU), or the S-DU receives an expected message from the C-DU (e.g., via the CU) but does not include the expected timing advance value, the RA preamble transmission attempt failure is detected upon expiration of the supervision timer (one advantage of this is that the S-DU can detect the failure more quickly without having to wait for the timer to expire).

[0313] In step 5 （2） In one set of embodiments, in response to detecting that the C-DU has not successfully received the first uplink message / signal (e.g., a PRACH preamble), i.e., in response to a failure in the attempt to send an RA preamble to the TLM candidate cell, the S-DU sends a second downlink indication to the UE. This can be detected at the S-DU, for example, upon expiration of a supervision timer, as described in the aforementioned steps. The S-DU sends the second downlink indication to the UE, triggering the UE to send a second uplink message / signal to the LTM candidate cell for TA establishment. This can be considered a fallback triggered by the S-DU upon detecting a failure in the UE's attempt to send an RA preamble.

[0314] 5 （2） Some of the steps in 5 can be combined with （1） The steps in are similar, for example assuming that the second downlink indication corresponds to a subsequent message, such as a PDCCH order.

[0315] In one option, the S-DU provides LTM configuration for RRC reconfiguration to trigger transmission of a first uplink signal / message at the UE, such that the first uplink indication corresponds to the RRC reconfiguration; and a subsequent message (e.g., a PDCCH order) is used to trigger the UE to send a second uplink signal / message (i.e., a second downlink indication corresponding to the subsequent message).

[0316] In one option, the S-DU provides the LTM configuration for configuring TA establishment / update for RRC reconfiguration, but it is a subsequent message (e.g., a first PDCCH order) that triggers the transmission of a first uplink signal / message at the UE, such that the first downlink indication corresponds to the first subsequent message after the RRC reconfiguration; and the second subsequent message (e.g., a second PDCCH order) is used to trigger the UE to send a second uplink signal / message (i.e., the second downlink indication corresponds to the second subsequent message, e.g., a second PDCCH order for RA preamble retransmission).

[0317] In one set of embodiments, the second downlink indication (e.g., a second subsequent message (e.g., a second PDCCH order)) includes one or more indications related to how the UE performs transmission of a second uplink message / signal to the LTM candidate cell, such as parameters for RA preamble transmission and / or RA resources. The one or more indications may correspond to pointers or indications to one or more parameters in the uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., candidate cell X), and in particular for retrying to transmit an RA preamble for TA establishment for LTM, as described in step 2b.

[0318] In one option, the UE may receive a set of RA preambles in the uplink configuration, such as p1, p2, p3, ..., pK. Consequently, a subsequent message (downlink indication) may indicate one or more of the configured RA preambles, such as p3 and p2. Based on the indication, the UE knows which preambles to send / select / use for transmission to the LTM candidate cell. This may be the same uplink configuration that the UE receives when it is configured for TA establishment.

[0319] In one option, the UE receives the RA preamble index (e.g., ra-PreambleIndex) of the LTM candidate cell explicitly provided via the PDCCH in a subsequent message. In another option, the UE may receive a set of RA resources, such as sequence and / or time-domain resources and / or frequency-domain resources, associated with an RS index or identifier (e.g., SSB index) in the uplink configuration. Thus, a subsequent message (downlink indication) may indicate one or more configured RA resources, for example, by indicating one or more SSBs. Based on this, the UE knows which SSBs (and therefore which RA resources) to select for transmission to the LTM candidate cell.

[0320] In one option, the UE may receive a set of RS indices, such as SSB indices, in the uplink configuration. Consequently, a subsequent message (downlink indication) may indicate one or more SSB indices associated with one or more RA resources, for example by indicating one or more SSBs. Based on this, the UE knows which SSBs (and therefore which RA resources) to select for transmission to the LTM candidate cell.

[0321] In one option, the UE may receive one or more LTM candidate cell IDs in its uplink configuration, to which the UE should send the second uplink message / signal. If multiple LTM candidate cell IDs are provided to the UE, each LTM candidate ID may be mapped to an RA preamble set, an RA preamble index, an RA resource, or an RS index (e.g., an SSB index). Based on this, the UE knows which parameters to use for each received LTM candidate cell. The UE may send a second uplink message / signal to each received LTM candidate cell, or it may select only one LTM candidate cell from the set of LTM candidate cells to which the UE is configured to send the first uplink message / signal.

[0322] Some embodiments include one or more parameters or indications based on which the UE determines how to set a second transmit power for sending a second uplink message / signal, for example, if the UE selects the same beam / SSB / CSI-RS selected in a previous failed preamble transmission attempt.

[0323] This scheme can also be used for TA update / maintenance mechanism as shown in the following section.

[0324] In one set of embodiments, in response to detecting that the C-DU has not successfully received the first uplink message / signal (e.g., a PRACH preamble) and when the maximum number of uplink signal (e.g., RA preamble) transmission attempts has not been reached (e.g., a parameter max_attemtps_TA_establishment_LTM set by the C-DU and indicated to the S-DU), the S-DU sends a second downlink indication to the UE. In other words, this is a prerequisite monitored at the S-DU to determine the transmission of the second downlink indication. When the maximum number has been reached, the S-DU does not send the second downlink indication to the UE, and instead the S-DU declares a TA establishment failure.

[0325] When the S-DU sends the first downlink indication to the UE, the S-DU initializes a counter for preamble transmission attempts as follows: PREAMBLE_TRANSMISSION_COUNTER = 1. Therefore, before sending the second downlink indication (or any other downlink indication after the first downlink indication), the S-DU determines whether the maximum number of uplink signal (e.g., RA preamble) transmission attempts has been reached. For example, the C-DU may have configured the maximum number of uplink signal (e.g., RA preamble) transmission attempts to be 5. Therefore, when the S-DU verifies that PREAMBLE_TRANSMISSION_COUNTER < 5, it sends the second downlink indication and increments the counter as follows: PREAMBLE_TRANSMISSION_COUNTER = PREAMBLE_TRANSMISSION_COUNTER + 1.

[0326] Based on the monitoring of the counter, the S-DU prevents an unlimited number of uplink signal retransmissions / uplink signal transmission attempts to LTM candidate cells that the UE may not be able to reach, thereby preventing unnecessary uplink interference in the LTM candidates. This may also provide an opportunity for the S-DU (or CU) to trigger the release of the candidate LTM that the UE cannot reach in the uplink (removing the LTM candidate at the UE and C-DU).

[0327] In one set of embodiments, upon detecting that the C-DU has not successfully received the first uplink message / signal (e.g., PRACH preamble), the S-DU sends a second downlink indication to the UE, but only if the maximum uplink signal (RA preamble) transmit power has not been reached after multiple transmissions by the UE.

[0328] According to this method, in one set of embodiments, since the UE does not expect a RAR from the LTM candidate cell in response to the first uplink signal / message, it is the S-DU that indicates to the UE that the UE should send a second uplink message if the first uplink message is not detected at the C-DU.

[0329] The difference compared to traditional RA with cells is that in traditional RA, when the UE does not receive a RAR within the RAR time window, the UE sends a preamble with power ramping (e.g., based on the same beam / SSB it had previously selected), or the UE selects a new beam / SSB / CSI-RS mapped to the second RA resource (e.g., no power ramping is required in this case).

[0330] The method includes different solutions for indicating to the UE whether the UE needs to perform a power ramp-up for a second uplink signal transmission triggered by a second downlink indication.

[0331] In one option, in response to the RA preamble attempt failing (e.g., the supervision timer expires), the S-DU indicates to the UE (e.g., in the second downlink indication) that the UE should resend the first uplink message and / or that the UE should send another uplink signal / message using an increased transmit power compared to the transmit power previously used for the first uplink signal / message according to the previously sent RA resource configuration.

[0332] In one option, in response to a failed RA preamble attempt (e.g., expiration of a supervision timer), the S-DU (e.g., in a second downlink indication) indicates to the UE that the UE should transmit a second uplink signal / message based on the previously transmitted RA resource configuration using an increased transmit power compared to the transmit power previously used for the first uplink signal / message. Here, the second uplink signal / message does not need to be identical to the first uplink signal / message, as long as the same SSB / CSI-RS / beam is selected and the mapped RA resource configuration (or configuration pool or set) is the same as that used for the first uplink signal / message transmission.

[0333] In one option, in response to a RA preamble attempt failure (e.g., expiration of a supervision timer), the S-DU (e.g., in a second downlink indication) indicates to the UE that the UE should select a beam (e.g., SSB or CSI-RS) different from the previously selected beam (e.g., SSB or CSI-RS) that resulted in the failed attempt of RA preamble transmission.

[0334] In one option, the S-DU indicates which SSB the UE needs to select and how to perform RA resource selection based on the indicated SSB. In one option, the S-DU indicates which CSI-RS the UE needs to select and how to perform RA resource selection based on the indicated CSI-RS.

[0335] In one option, the S-DU does not indicate the exact SSB that the UE needs to select, but it indicates that the SSB needs to be the SSB based on which RA resource selection is made. In one option, the S-DU does not indicate the exact CSI-RS that the UE needs to select, but it indicates that the CSI-RS needs to be the CSI-RS based on which RA resource selection is made.

[0336] In one option, the S-DU gives the UE some freedom, i.e., the S-DU does not indicate to the UE (e.g., in the second downlink indication) whether the UE should select a new beam / SSB / CSI-RS or perform a power ramp. Instead, the second downlink indication indicates the presence of an uplink signal preamble attempt, but the steps related to fallback are left to the UE.

[0337] In one option, the UE determines whether to perform power ramping based on RA resource selection. When the RA resource selection causes the UE to select the same SSB or CSI-RS or beam as that selected in the failed attempt, the UE performs power ramping. When the RA resource selection causes the UE to select a different SSB or CSI-RS or beam than that selected in the failed attempt, the UE does not perform power ramping.

[0338] In this option, the second downlink indication replaces the event that the UE detects that a RAR has not been received (within the RAR time window) in response to the first uplink signal / message transmission. In this context, it is the receipt of the second downlink indication that causes the UE to trigger a new attempt to send an RA preamble to the LTM candidate cell, rather than the failure to receive a RAR.

[0339] In step 6 （2） In one set of embodiments, the UE transmits a second uplink message / signal (e.g., a second RA preamble) to the candidate cell according to: i) an increased transmit power compared to the first transmit power (e.g., an initial RA preamble power that may be defined by the parameter / field preambleReceivedTargetPower); or ii) on second uplink resources (e.g., RA resources in time and frequency) associated with a second beam selected by the UE.

[0340] In one set of embodiments, the UE sends a second uplink message / signal (eg, a second RA preamble) to the candidate cell according to one or more indications included in the second downlink, eg, as defined in the above set of embodiments.

[0341] In one set of embodiments, before the UE sends the second uplink message / signal, the UE performs uplink resource selection for TA establishment / update fallback (eg, RA resource selection based on beam selection), which includes one or more of the following steps.

[0342] The UE may perform or update one or more measurements on the beam and / or SSB and / or CSI-RS resources of the fallback LTM candidate cell for which TA establishment needs to be performed, for example, performing SSB RSRP measurement on one or more SSBs, such as SS-RSRP with SSB index = 1, SS-RSRP with SSB index = 2, ..., SS-RSRP with SSB index = k; for example, CSI-RS RSRP measurement for one or more CSI-RSs.

[0343] The UE may perform uplink channel resource selection, such as RACH resource selection, associated with the SSB and / or CSI-RS resources of the LTM candidate cell for which the UE needs to establish a TA based on the selected beam / SSB / CSI-RS. For example, the UE selects an SSB or CSI-RS resource with a measurement value above a threshold (which may be configured in the uplink configuration), such as SSB RSRP >rsrp-ThresholdSSB; and the UE selects uplink channel resources (e.g., time / frequency resources and preamble) associated with the selected SSB for TA establishment, where the association is also part of the uplink configuration.

[0344] The UE may send a second uplink message (e.g., a second RA preamble) to the LTM candidate cell, wherein the second uplink message (e.g., a second RA preamble) is sent to the LTM candidate cell according to: i) an increased transmit power compared to the first transmit power; or ii) on second uplink resources (e.g., RA resources in time and frequency) associated with a second beam selected by the UE (e.g., an SSB or CSI-RS of the LTM candidate cell).

[0345] In one option, when an indication of a second uplink signal (e.g., RA preamble) is provided to the UE (ra-PreambleIndex of the PDCCH, or other uplink signal indication in the second downlink indication), the UE selects the SSB signaled by the second downlink indication (e.g., via the PDCCH) (so the UE uses RA resources mapped to the selected SSB).

[0346] In one option, the UE selects the indicated SSB when the RSRP of the indicated SSB is above the SSB threshold. This may be the case when the UE is sending a CSI report of the SSB of the LTM candidate cell to the S-DU, so the S-DU indicates in the downlink indication and SSB that the radio conditions of the S-DU are good enough.

[0347] In one option, the UE uses the indicated RA preamble for the second uplink signal / message transmission (eg, by setting PREAMBLE_INDEX to the signaled preamble).

[0348] In one option, the UE sets the variable used for preamble transmission to the signaled preamble, for example, setting the variable PREAMBLE_INDEX to the signaled ra-PreambleIndex.

[0349] In one option, the UE selects an SSB among the associated SSBs whose SS-RSRP (as defined in TS 38.215) is higher than rsrp-ThresholdSSB.

[0350] In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0351] In one option, the UE selects the CSI-RS signaled, for example, by the PDCCH.

[0352] In one option, the UE selects a CSI-RS resource with a CSI-RSRP (as defined in TS 38.215) higher than rsrp-ThresholdCSI-RS among the associated CSI-RSs.

[0353] In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0354] In one option, the UE selects an SSB, and when an SSB is selected, if the configuration is configured or indicated by PDCCH (e.g., ra-ssb-OccasionMaskIndex, part of the uplink configuration that establishes the TA), the UE determines the next available PRACH opportunity corresponding to the selected SSB from the PRACH opportunities allowed by the restrictions given by the configuration (the MAC entity at the UE randomly selects the PRACH opportunity corresponding to the selected SSB with equal probability among consecutive PRACH opportunities).

[0355] In one option, the UE (eg, a MAC entity at the UE) takes into account possible measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB.

[0356] In one option, the UE selects a CSI-RS and determines the next available PRACH opportunity corresponding to the selected CSI-RS from the PRACH opportunities in the configured RA opportunity list / set (e.g., ra-OccasionList). The UE (e.g., the MAC entity at the UE) randomly selects the PRACH opportunity corresponding to the selected CSI-RS with equal probability among the PRACH opportunities that occur simultaneously but are located on different subcarriers.

[0357] In one option, the UE (eg, a MAC entity at the UE) takes into account possible measurement gaps when determining the next available PRACH opportunity corresponding to the selected CSI-RS.

[0358] In one option, when the UE determines whether there is an SSB with an SS-RSRP higher than rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP higher than rsrp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement.

[0359] In one option, the UE does not maintain a counter for preamble transmissions (e.g., PREAMBLE_TRANSMISSION_COUNTER), which is maintained during the RA procedure. The reason for this is that this is controlled by the network (e.g., S-DU), which controls the need for the fallback procedure (i.e., RA preamble retransmission in the form of power ramping and / or beam / SSB / CSI-RS reselection if the maximum number of preamble transmission attempts has not been reached). Therefore, in such network-controlled fallback, it is the network (e.g., S-DU) that monitors the number of preamble transmissions, for example by controlling a preamble transmission counter that is incremented each time the UE is instructed to send an RA preamble for TA establishment for LTM.

[0360] In one set of embodiments, when the selected beam (e.g., SSB or CSI-RS) is the same beam selected by the UE during resource selection for sending the first uplink message / signal, the UE sends the second uplink message / signal for TA establishment / update fallback using an increased transmit power compared to the first transmit power (e.g., using a power ramp-up step).

[0361] In one option, the UE sets the transmit power (PREAMBLE_RECEIVED_TARGET_POWER(2)) of the second uplink message / signal to an increased power compared to the first transmit power, wherein the transmit power of the second uplink message / signal is set by adding one or more of: a value provided in the uplink configuration (e.g., preambleReceivedTargetPower); an incremental value that depends on the RA preamble format (e.g., 0 dB for preamble format 0), such as DELTA_PREAMBLE; a value indicated in the downlink indication or an indication in the downlink indication that enables the UE to derive a value to be added to the first transmit power; and / or an incremental step based on a preamble power ramping step (e.g., PREAMBLE_POWER_RAMPING_STEP) and a preamble power ramping counter (e.g., PREAMBLE_POWER_RAMPING_COUNTER). For example: Incremental step size = (PREAMBLE_POWER_RAMPING_COUNTER – 1) × PREAMBLE_POWER_RAMPING_STEP; therefore, the transmit power can be set, for example, to: PREAMBLE_RECEIVED_TARGET_POWER = preambleReceivedTargetPower + DELTA_PREAMBLE + incremental step size; set PREAMBLE_RECEIVED_TARGET_POWER to preambleReceivedTargetPower + DELTA_PREAMBLE + (PREAMBLE_POWER_RAMPING_COUNTER – 1) × PREAMBLE_POWER_RAMPING_STEP.

[0362] In one option, the UE monitors a power ramp-up counter (e.g., PREAMBLE_POWER_RAMPING_COUNTER). The power ramp-up counter is incremented by 1 when an RA preamble is transmitted / retransmitted as part of the same TA establishment / update procedure. The power ramp-up counter has a maximum value associated with it, and the UE may be configured with this maximum value as part of the uplink channel configuration.

[0363] In one option, the UE is configured with PREAMBLE_POWER_RAMPING_STEP, eg received in an RRC reconfiguration including LTM configuration and / or as part of uplink channel configuration.

[0364] In one option, the UE receives an indication of PREAMBLE_POWER_RAMPING_STEP, eg, a pointer to a certain value, in a downlink indication (eg, a second downlink indication that triggers RA preamble transmission for TA establishment).

[0365] In one set of embodiments, the UE sends a second uplink message / signal for TA establishment / update to the LTM candidate cell, and when the UE does not receive a downlink indication (e.g., a third downlink indication) in response from the serving cell (e.g., S-DU), the UE considers the TA establishment procedure successful.

[0366] In one set of embodiments, the UE sends an nth uplink message / signal for TA establishment / update to the LTM candidate cell, and when the UE does not receive an (n+1)th downlink indication from the serving cell (e.g., S-DU), the UE considers the TA establishment procedure successful. Based on this, the UE performs one or more actions, such as resetting at least one counter (setting it to zero) and stopping at least one timer related to the TA establishment procedure.

[0367] In one set of embodiments, the UE also receives a third downlink indication from the S-DU, based on which the UE sends a third uplink message (e.g., a third RA preamble) to the candidate cell, wherein the third uplink message (e.g., a third RA preamble) is sent to the candidate cell according to the following manner: i) an increased transmit power compared to the second transmit power; or ii) on a third uplink resource associated with a third beam selected by the UE (e.g., RA resources in time and frequency).

[0368] Some embodiments include a backoff repetition until a TA establishment failure is successful or detected. In one set of embodiments, the backoff for TA establishment is repeated until one or more conditions are met. The backoff for TA establishment includes: after the S-DU has sent an nth downlink indication to the UE that caused the nth preamble transmission failure for TA establishment / update, the S-DU sends to the UE (and the UE receives) an (n+1)th downlink indication, wherein the (n+1)th downlink indication indicates to the UE that the UE should perform transmission of the (n+1)th uplink message according to the following manner: with an increased or increased transmit power compared to the transmit power of the nth uplink message transmission; and / or indicates that the transmission of the (n+1)th uplink message will be towards an (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the (n+1)th beam selected by the UE.

[0369] The one or more conditions may correspond to: the S-DU detecting a preamble transmission failure for TA establishment / update; and / or the S-DU detecting a preamble transmission failure for TA establishment / update reaching a maximum number for a given LTM candidate cell and / or UE.

[0370] In one option, the maximum value may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0371] In one option, the S-DU increments a counter each time it detects a preamble transmission failure for TA establishment / update (e.g., based on one or more of the solutions proposed above). The S-DU checks whether the counter has reached a maximum value before sending a downlink indication to the UE. If the S-DU determines that the counter has reached the maximum value, the S-DU does not send a downlink indication and considers TA establishment to have failed, referred to as a TA establishment failure.

[0372] In other words, when the number of preamble transmission failures for TA establishment reaches its maximum value, the S-DU declares that TA establishment has failed.

[0373] In one option, the maximum number of preamble transmission failures for TA establishment may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0374] The S-DU detects that the maximum transmit power for the UE to send uplink messages to the LTM candidate cell has been reached.

[0375] After the preamble transmission established by the TA fails, the maximum value may be reached after multiple transmission power increases.

[0376] In one option, the maximum transmit power for TA establishment may have been configured by the candidate DU responsible for the LTM candidate cell, which is the C-DU that has been configured with uplink resources for TA establishment and / or TA update.

[0377] In one set of embodiments, the candidate DU successfully receives the first uplink message / signal (e.g., PRACH preamble), so it can calculate the timing advance value of the UE and at least one LTM candidate cell. The candidate DU sends a message including the at least one timing advance value to the CU.

[0378] In one embodiment, the candidate DU sends a message to the CU that includes a timing advance value and one or more associated LTM candidate cells to which the timing advance value is applicable. Based on this, the CU (and possibly the serving DU that also receives this information) knows that the given timing advance value is applicable to one or more LTM candidate cells configured for the UE and that the timing advance value may be required during an LTM execution (also known as LTM cell handover) to one of these candidate cells.

[0379] In one embodiment, the candidate DU sends a message to the CU using the UE signaling connection so that the CU knows that the timing advance value associated with the target candidate cell corresponds to the UE of the UE signaling connection.

[0380] In one embodiment, when a candidate DU sends a message to a CU, the candidate DU starts a timer, which may be referred to as a TA timer. Furthermore, while the TA timer is running, the candidate DU considers the timing advance value it has provided to the CU to be "valid," meaning that while the TA timer is running, the candidate DU may receive an incoming UE with LTM without random access, because the timing advance is still valid, assuming the TA value was provided to the UE via the CU and / or serving DU. When the TA timer expires, the candidate DU considers the TA value to be "invalid," and when the TA value is invalid, the candidate DU may trigger a TA update procedure.

[0381] In one embodiment, a CU receives a message including a TA value associated with a target candidate cell and a UE configured for LTM, and the CU starts a TA timer. While the TA timer is running, the CU considers the TA value "valid"; when the TA timer expires, the CU considers the TA value "invalid." When the TA value is invalid, the CU may trigger a TA update procedure.

[0382] In one option, the candidate DU also includes a TA timer value associated with the TA value (applicable to at least one target candidate cell) in the message sent to the CU, wherein the TA value is considered "valid" when the TA timer is running and is considered invalid when the TA timer expires. In this case, it may be an option for the candidate DU to also start a TA timer with the same or similar value so that it can also know when the TA value is invalid for the UE and the LTM candidate cell.

[0383] In one embodiment, the first uplink signal and / or RA resources (e.g., per-UE resources, non-contention preambles for TA establishment, and / or PRACH resources) may have been configured for a particular UE such that upon reception, the candidate DU knows which UE to associate with, and thus which CU to associate with, because there is a UE signaling connection for that UE (because the UE is the UE for which the candidate DU has accepted the request to configure LTM). The candidate DU calculates the TA value for the UE and the target candidate cell based on receipt of the first uplink signal / message, and sends the TA value to the serving DU (via the CU) for use by the UE when LTM is performed (i.e., later LTM cell handover).

[0384] In one set of embodiments, the CU sends a message including at least one TA value to the serving DU to which the UE is connected. Figure 5C As shown in step 7a of , the candidate DU receives a first uplink signal (e.g., a PRACH preamble) in an uplink channel (PRACH time / frequency resource slot) allocated for the purpose of TA establishment of LTM, calculates a TA value valid for the UE and at least one LTM candidate cell, and the candidate DU sends a message including at least one TA value to the CU so that the CU sends the TA value to the serving DU.

[0385] In one embodiment, the serving DU receives a message from the CU that includes a TA value and one or more associated LTM candidate cells for which the TA value is applicable. Based on this, the serving DU knows that a given TA value is applicable to one or more LTM candidate cells configured for the UE and that the TA value may be required during LTM execution (LTM cell handover) to one of these candidate cells.

[0386] In one embodiment, the serving DU receives a message from the CU in a UE signaling connection so that the serving DU knows that the TA value associated with the LTM candidate cell corresponds to the UE of the UE signaling connection.

[0387] In one embodiment, the serving DU receives a message including a TA value associated with an LTM candidate cell and a UE configured for LTM, and the serving DU starts a timer (which may be referred to as a TA timer). While the TA timer is running, the serving DU considers the TA value "valid"; when the TA timer expires, the serving DU considers the TA value "invalid." When the TA value is invalid, the serving DU may trigger a TA update procedure.

[0388] In one option, the serving DU receives a TA timer value associated with the TA value (applicable to at least one target candidate cell) in a message from the CU, wherein the TA value is considered "valid" when the TA timer is running and is considered invalid when the TA timer expires. In this case, it may be an option for the candidate DU and / or CU to also start a TA timer with the same or similar value so that it can also know when the TA value is invalid for the UE and the LTM candidate cell.

[0389] In one set of embodiments, the S-DU is responsible for monitoring whether the UE successfully sends an uplink message to the candidate DU for TA establishment. In other words, the S-DU determines whether there is a failure in the preamble transmission for TA establishment / update. There may be different options for how to define these failure monitoring steps.

[0390] In one option, upon receiving the message including the TA value, the S-DU stops the timer started when the S-DU instructs the UE to send the first uplink signal / message and considers the TA establishment procedure successful.

[0391] In one option, the S-DU considers the TA establishment procedure successful when receiving a message including a TA value.

[0392] In one set of embodiments, the UE may send measurement values (e.g., including CSI measurements of LTM candidate cells for which the UE has triggered TA establishment) to assist the serving DU and / or candidate DUs and / or CUs in triggering LTM execution (LTM cell handover).

[0393] In response to the reported measurement value (L1 RSRP) for a given LTM candidate cell, the network (eg, serving DU) may determine to trigger the UE's LTM cell handover to the LTM candidate cell for which the UE has triggered TA establishment.

[0394] In one embodiment, the serving DU performs one or more of the following actions. If the serving DU determines that the LTM candidate cell (e.g., cell X) that triggered LTM execution (cell handover) is a cell for which the serving DU has a valid TA value for the UE and the LTM candidate cell (e.g., the TA timer is running, the UE is considered time-aligned with the LTM candidate cell, and uplink synchronized), the serving DU sends low-layer signaling (e.g., MAC CE) to the UE indicating the LTM candidate cell and including a TA value to be used by the UE to communicate with the LTM candidate cell (which becomes the target cell). If the serving DU determines that the LTM candidate cell (e.g., cell X) that triggered LTM execution (LTM cell handover) is a cell for which the serving DU does not have a valid TA value for the UE and the target candidate cell (e.g., the TA timer has expired), the serving DU sends low-layer signaling (e.g., MAC CE) to the UE indicating the LTM candidate cell and not including a TA value.

[0395] In one embodiment, the serving DU performs one or more of the following actions: If the TA timer is running, the network (e.g., the serving DU) sends low-layer signaling (e.g., a MAC CE) to the UE indicating LTM candidate cells and including a TA value. If the TA timer has expired or stopped, the network (e.g., the serving DU) sends low-layer signaling (e.g., a MAC CE) to the UE indicating LTM candidate cells for L1 / L2 inter-cell mobility but not including a TA value.

[0396] In one embodiment, the serving DU performs one or more of the following actions: If the LTM candidate cell (e.g., cell X) in which the serving DU is performing LTM execution (LTM cell handover) is a cell for which the serving DU has a valid TA value for the UE (e.g., the TA timer is running) and the LTM candidate cell is a cell with the same TA value as the serving cell configured for the UE, the serving DU sends low layer signaling (e.g., MAC CE) indicating the LTM candidate cell and including the TA value of the serving cell configured for the UE to the UE, for the UE to use in communicating with the LTM candidate cell.

[0397] Another alternative is that instead of providing the TA value, the serving DU provides the serving cell index, thereby indicating to the UE that the UE should use the TA value between the UE and the serving cell, the index of which has been indicated as the TA value of the UE and the LTM candidate cell, which is also indicated in the low layer signaling.

[0398] The UE receives low-layer signaling (e.g., MAC CE) indicating an LTM candidate cell. When the signaling includes a TA value, the UE applies the TA value to the LTM candidate cell (for uplink transmission). When the signaling does not include a TA value, or the indicated LTM candidate cell is a cell with the same TA as the serving cell (and the UE is aware of this based on the LTM candidate configuration), the UE applies the TA value of the associated serving cell to the LTM candidate cell (for uplink transmission). When the signaling does not include a TA value, or the indicated LTM candidate cell is a cell with which time alignment (uplink synchronization) has not yet been established, the UE performs random access on the indicated LTM candidate cell. When the signaling includes a serving cell index, the UE uses the TA value between the UE and the serving cell, whose index is indicated as the TA value for the UE and the LTM candidate cell, which is also indicated in the low-layer signaling.

[0399] After having applied the indicated TA value for the LTM candidate cell according to this method, the UE sends an uplink message to the target candidate cell (eg, via PUCCH and / or PUSCH).

[0400] Some embodiments include fallback steps for TA update for LTM. In one set of embodiments, one or more of the disclosed steps for TA establishment fallback may be performed in the case of a TA update: when the TA value is invalid for the UE and the LTM candidate and the network and / or UE determines to calculate a new TA value before performing LTM with the LTM candidate cell.

[0401] According to certain embodiments, TA update may be triggered by: i) CU; ii) S-DU; iii) C-DU; and / or iv) UE.

[0402] The trigger may depend on which of these entities is managing the validity of the TA value that has been previously calculated by the C-DU and provided to the S-DU.

[0403] In one set of embodiments, a TA establishment between the UE and an LTM candidate is performed, for example, when a TA timer value expires, and the CU determines that the TA value is invalid. When the TA value is provided to the CU and / or S-DU, the TA timer may have been started. When the CU detects that the TA value is invalid (which may be equivalent to determining that the UE has lost synchronization with the LTM candidate cell in the uplink), the CU sends a request for a TA update to the C-DU (for the LTM candidate cell with which the UE has lost uplink synchronization, e.g., the LTM candidate cell for which the TA timer has expired). In response, the C-DU may reject or accept the request, possibly providing the UE with a new uplink channel configuration (e.g., RACH configuration) for uplink transmission, since the previously provided configuration may contain one or more invalid parameters. (3) The CU sends an indication of rejection or acceptance to the S-DU, for example by sending a first downlink indication, which triggers the TA establishment / update for the UE. From then on, the steps for the TA update are similar to those disclosed above, e.g., Figure 5A 、 Figure 5B and Figure 5C shown, and to some extent in the following Figure 6A 、 Figure 6B and Figure 6C Reappear in.

[0404] Figure 6A 、 Figure 6B and Figure 6C is a flow chart illustrating a fallback procedure for a TA update procedure (for CU-initiated TA update and network-based TA management). In one set of embodiments, for example, upon expiration of a TA timer value, a TA establishment between a UE and an LTM candidate is performed, and the S-DU determines that the TA value is invalid. When an uplink signal is received from the UE during the TA establishment procedure, for example, when a TA value is provided from the C-DU to the S-DU, the TA timer may have been started. When the S-DU detects that the TA value is invalid (which may be equivalent to determining that the UE has lost synchronization with the LTM candidate cell in the uplink), the S-DU sends (1) a TA update request to the CU, and (2) the CU sends the request to the C-DU (where the C-DU is responsible for the LTM candidate cell for which the UE has lost uplink synchronization, for example, the LTM candidate cell for which the TA timer has expired). In response, (2b) the C-DU may reject or accept the request, possibly providing the UE with a new uplink channel configuration (e.g., RACH configuration) for uplink transmission, because the previously provided configuration may contain one or more invalid parameters. The CU sends a rejection or acceptance indication to the S-DU, for example, by sending a first downlink indication, which triggers the TA establishment / update for the UE. From then on, the steps of TA update are similar to those disclosed above, such as Figure 5A 、 Figure 5B and Figure 5Cshown, and to some extent in the following Figure 7A 、 Figure 7B and Figure 7C Reappear in.

[0405] Figure 7A 、 Figure 7B and Figure 7C This is a flow chart illustrating an alternative fallback procedure for the TA update process (for both S-DU initiated TA updates and network-based TA management). Some embodiments include actions upon detecting a TA establishment / update failure. In one set of embodiments, the S-DU detects a TA establishment / update failure (e.g., when the maximum number of RA preamble transmission attempts for TA establishment / update is reached) and indicates this to the CU, which can then take one or more additional actions.

[0406] The CU cancels the LTM TA establishment / update for the C-DU of the LTM candidate cell where the UE has attempted to establish or update the TA but has failed. In one option, the CU sends a message (e.g., a UE Context Modification Request) to the C-DU to cancel the TA establishment. In response, the C-DU releases and / or cancels one or more uplink resources reserved for the TA establishment / update procedure. The C-DU may also stop monitoring uplink messages from the UE for TA establishment and / or update.

[0407] The CU cancels the TA establishment at the UE, for example, by generating and sending an RRC reconfiguration message to the UE, which removes / releases / cancels / deactivates one or more configurations for TA establishment / update of the LTM candidate cells.

[0408] The CU cancels LTM to the C-DU for the LTM candidate cell where the UE has attempted to establish or update a TA but has failed. In one example, the CU then considers the candidate target cell as a candidate for normal (L3) handover, or it configures a conditional handover (CHO) configuration for the UE, in which it is a candidate target cell. In an alternative approach, the CU then sends a message to the C-DU that cancels LTM for the LTM candidate cell and includes a request for CHO configuration (or configuration for normal handover) for the same cell.

[0409] The CU provides the C-DU (or another network node, such as OAM (Operation and Maintenance)) with information related to TA establishment failure, such as measurements of beams (e.g., SSB and / or CSI-RS) of LTM candidate cells where the UE has attempted to establish TA but has failed and / or beams that were not selected by the UE for TA establishment.

[0410] In one set of embodiments, when an S-DU detects a TA establishment failure (e.g., when the maximum number of RA preamble transmission attempts for TA establishment is reached), the S-DU may decide to initiate a new TA establishment using a new C-DU. In this case, the S-DU sends a new request for TA establishment using the new C-DU. In an alternative approach, the S-DU decides to initiate a new TA establishment for another candidate target cell in the same C-DU as the one that detected the TA establishment failure.

[0411] In an alternative approach, when the S-DU detects a TA establishment / update failure (e.g., when the maximum number of RA preamble transmission attempts for TA establishment has been reached), the S-DU decides not to trigger an LTM cell handover (LTM Execute) to the LTM candidate cell. In one example, the S-DU does not trigger any LTM handovers to candidate target cells for a certain period of time. After this period of time has elapsed, the S-DU may decide to initiate a new TA establishment / update procedure for the same candidate target cell first. In one option, the S-DU includes a timer to determine when an LTM cell handover (LTM Execute) to the LTM candidate cell can be triggered again, or when a new TA establishment / update procedure should be initiated for the same candidate target cell. This timer is started when the S-DU detects a TA establishment / update failure. In one example, a corresponding timer also exists in the UE.

[0412] In another example, when the S-DU has received measurement values for the same candidate target cell (which, for example, indicates that the radio conditions of the cell have improved for the UE), the S-DU initiates a new TA establishment / update procedure for the cell.

[0413] In another alternative, when the S-DU detects a TA establishment failure (e.g., when the maximum number of RA preamble transmission attempts for TA establishment is reached) and later triggers an LTM cell handover to the same LTM candidate cell (LTM Execute), the S-DU may include an indication (using an LTM Cell Handover Command) for the UE to perform a random access procedure as part of the LTM cell handover procedure to the candidate target cell. In one set of embodiments, the UE monitors for TA establishment failure: the UE detects that the maximum number of RA preamble transmission attempts has been reached, and upon detecting the failure, the UE releases one or more TA establishment resources, such as the uplink configuration used for TA establishment / update. Figure 8A and Figure 8B An example is shown in .

[0414] Figure 8A and Figure 8BThis is a flowchart illustrating an example of actions at the S-DU when a TA establishment failure is detected. In a conventional RA procedure, the UE detects the need for fallback (e.g., by the absence of an RAR in response to a preamble transmission) and detects RA failure (e.g., when the maximum number of transmission attempts is reached). When an RA failure is triggered, the UE performs one or more recovery actions, such as initiating an RRC re-establishment procedure (if the RA failure occurs on the primary cell group and MCG failure recovery is not supported) or initiating transmission of an SCG failure-related message (if the RA failure occurs on the secondary cell group). However, in the embodiment group described herein, the network detects the TA establishment failure, and since the UE is still connected to the serving cell, no recovery actions, such as a re-establishment procedure, need to be triggered.

[0415] As described herein, the network triggers the UE to re-initiate the TA establishment procedure to the same and / or another LTM candidate cell and / or cancel the TA establishment procedure.

[0416] Figure 9 An example of a communication system 100 according to some embodiments is shown. In this example, the communication system 100 includes a telecommunications network 102, which includes an access network 104 (such as a radio access network (RAN)) and a core network 106, which includes one or more core network nodes 108. The access network 104 includes one or more access network nodes, such as network nodes 110a and 110b (one or more of which may be generally referred to as network nodes 110), or any other similar Third Generation Partnership Project (3GPP) access nodes or non-3GPP access points. The network nodes 110 facilitate direct or indirect connection of user equipment (UE), such as connecting UEs 112a, 112b, 112c, and 112d (one or more of which may be generally referred to as UE 112) to the core network 106 via one or more wireless connections.

[0417] Example wireless communications over wireless connections include sending and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for sending information without the use of wires, cables, or other material conductors. Additionally, in various embodiments, the communication system 100 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 a wired or wireless connection). The communication system 100 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0418] The UE 112 may be any of a variety of communication devices, including wireless devices that are arranged, configured, and / or operable to wirelessly communicate with the network node 110 and other communication devices. Similarly, the network node 110 is arranged, capable, configured, and / or operable to communicate directly or indirectly with the UE 112 and / or with other network nodes or devices in the telecommunications network 102 to enable and / or provide network access (e.g., wireless network access) and / or to perform other functions (e.g., management) in the telecommunications network 102.

[0419] In the depicted example, core network 106 connects network node 110 to one or more hosts (such as host 116). These connections may be direct or indirect via one or more intermediate networks or devices. In other examples, the network node may be directly coupled to the host. Core network 106 includes one or more core network nodes (e.g., core network node 108) constructed using hardware and software components. The features of these components may be substantially similar to those described with respect to the UE, network nodes, and / or hosts, such that the descriptions generally apply to the corresponding components of core network node 108. Example core network nodes include one or more of the following functions: 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 dehiding function (SIDF), unified data management (UDM), security edge protection proxy (SEPP), network exposure function (NEF), and / or user plane function (UPF).

[0420] The host 116 may be owned or controlled by a service provider other than the operator or provider of the access network 104 and / or the telecommunications network 102, and may be operated by or on behalf of the service provider. The host 116 may host a variety of applications to provide one or more services. Examples of such applications include live and pre-recorded audio / video content, data collection services (e.g., retrieving and compiling data about various environmental conditions detected by multiple UEs), analytics functionality, social media, functionality for controlling or otherwise interacting with remote devices, functionality for an alarm and monitoring center, or any other such functionality performed by a server.

[0421] As a whole, Figure 9The communication system 100 enables connectivity between UEs, network nodes, and hosts. In this sense, the communication system can be configured to operate according to predefined rules or procedures such as specific standards, including but 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 standards (e.g., 6G); Wireless Local Area Network (WLAN) standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard (WiFi); and / or any other suitable wireless communication standards such as 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.

[0422] In some examples, telecommunication network 102 is a cellular network that implements 3GPP standardized features. Therefore, telecommunication network 102 can support network slicing to provide different logical networks to different devices connected to telecommunication network 102. For example, telecommunication network 102 can provide ultra-reliable low-latency communication (URLLC) services to some UEs while providing enhanced mobile broadband (eMBB) services to other UEs, and / or provide massive machine type communication (mMTC) / massive IoT services to yet other UEs.

[0423] In some examples, the UE 112 is configured to send and / or receive information without direct human interaction. For example, the UE can be designed to send information to the access network 104 according to a predetermined schedule when triggered by an internal or external event, or in response to a request from the access network 104. Additionally, the UE can be configured to operate in a single RAT mode, a multi-RAT mode, or a multi-standard mode. For example, the UE can operate using any one or a combination of Wi-Fi, NR (New Radio), and LTE, i.e., be configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) New Radio-Dual Connectivity (EN-DC).

[0424] In this example, hub 114 communicates with access network 104 to facilitate indirect communication between one or more UEs (e.g., UE 112c and / or UE 112d) and a network node (e.g., network node 110b). In some examples, hub 114 may be a controller, a router, a content source and analyzer, or any other communication device described herein with respect to UEs. For example, hub 114 may be a broadband router that enables UEs to access core network 106. As another example, hub 114 may be a controller that sends commands or instructions to one or more actuators in the UEs. The commands or instructions may be received from the UEs, network node 110, or via executable code, scripts, processes, or other instructions in hub 114. As another example, hub 114 may be a data collector that acts as a temporary storage device for UE data and, in some embodiments, may perform analysis or other processing on the data. As another example, hub 114 may be a content source. For example, for a UE that is a VR headset, display, speaker, or other media delivery device, the hub 114 can retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, and then the hub 114 provides it directly to the UE after performing local processing and / or adding additional local content. In another example, the hub 114 acts as a proxy server or orchestrator for the UE, especially if one or more UEs are low-energy IoT devices.

[0425] Hub 114 may have a constant / persistent or intermittent connection to network node 110b. Hub 114 may also allow for different communication schemes and / or schedules between hub 114 and UEs (e.g., UE 112c and / or UE 112d), as well as between hub 114 and core network 106. In other examples, hub 114 is connected to core network 106 and / or one or more UEs via a wired connection. Furthermore, hub 114 may be configured to connect to an M2M service provider via access network 104 and / or to another UE via a direct connection. In some scenarios, a UE may establish a wireless connection with network node 110 while still connected through hub 114 via a wired or wireless connection. In some embodiments, hub 114 may be a dedicated hub, i.e., a hub whose primary function is to route communications from network node 110b to UEs / from UEs to network node 110b. In other embodiments, the hub 114 may be a non-dedicated hub, ie, a device operable to route communications between UEs and the network node 110b, but which may also serve as a communications origin and / or destination for certain data channels.

[0426] Figure 10A UE 200 according to some embodiments is shown. As used herein, a UE refers to a device capable of, configured, arranged, and / or operable to wirelessly communicate with a network node and / or other UEs. Examples of UEs include, but are not limited to, smartphones, mobile phones, cellular phones, voice-over-IP (VoIP) phones, wireless local loop phones, desktop computers, personal digital assistants (PDAs), wireless cameras, gaming consoles or devices, music storage devices, playback devices, wearable terminal devices, wireless endpoints, mobile stations, tablet computers, laptop computers, laptop embedded devices (LEEs), laptop-mounted devices (LMEs), smart devices, wireless customer premises equipment (CPEs), vehicle-mounted or vehicle-embedded / integrated wireless devices, and the like. Other examples include any UE identified by the Third Generation Partnership Project (3GPP), including narrowband Internet of Things (NB-IoT) UEs, machine type communication (MTC) UEs, and / or enhanced MTC (eMTC) UEs.

[0427] A UE may support device-to-device (D2D) communication, for example, by implementing 3GPP standards 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 owning and / or operating the associated device. Alternatively, a UE may represent a device that is intended for sale to or operated by a human user but may not be associated with or initially 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 operated by an end user but may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0428] UE 200 includes processing circuitry 202 operatively coupled to input / output interface 206, power supply 208, memory 210, communication interface 212, and / or any other components or any combination thereof via bus 204. Some UEs may utilize Figure 10 All or a subset of the components shown. The level of integration between components may vary depending on the UE. In addition, some UEs may include multiple instances of components, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0429] Processing circuitry 202 is configured to process instructions and data and may be configured to implement any sequential state machine operable to execute instructions stored as a machine-readable computer program in memory 210. Processing circuitry 202 may be implemented as: one or more hardware-implemented state machines (e.g., implemented in discrete logic, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), etc.); programmable logic along with appropriate firmware; one or more stored computer programs, general-purpose processors (e.g., a microprocessor or a digital signal processor (DSP)) along with appropriate software; or any combination thereof. For example, processing circuitry 202 may include multiple central processing units (CPUs).

[0430] In this example, the input / output interface 206 can be configured to provide one or more interfaces to an input device, an output device, or one or more input and / or output devices. Examples of output devices include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, a transmitter, a smart card, another output device, or any combination thereof. An input device can allow a user to capture information into the UE 200. Examples of input devices include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a webcam, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smart card, etc. A presence-sensitive display can include a capacitive or resistive touch sensor to sense input from the user. The sensor can be, for example, 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. The output device can use the same type of interface port as the input device. For example, a Universal Serial Bus (USB) port can be used to provide both input and output devices.

[0431] In some embodiments, power source 208 is configured as a battery or battery pack. Other types of power sources may be used, such as an external power source (e.g., a power outlet), a photovoltaic device, or a battery. Power source 208 may also include power circuitry for delivering power from power source 208 itself and / or an external power source to various components of UE 200 via an input circuit or an interface such as a power cable. The delivered power may be used, for example, to charge power source 208. The power circuitry may perform any formatting, conversion, or other modifications on the power from power source 208 to make the power suitable for the respective components of UE 200 to which it is supplied.

[0432] The memory 210 may be or be configured to include a 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), a magnetic disk, an optical disk, a hard disk, a removable tape, a flash drive, etc. In one example, the memory 210 includes one or more application programs 214, such as an operating system, a web browser application, a widget, a gadget engine, or other applications, and corresponding data 216. The memory 210 may store any one of a variety of operating systems or a combination of operating systems for use by the UE 200.

[0433] Memory 210 may be configured to include multiple physical drive units, such as a Redundant Array of Independent Disks (RAID), flash memory, a USB flash drive, an external hard drive, a thumb drive, a pen drive, a key drive, a High-Density Digital Versatile Disc (HD-DVD) optical drive, an internal hard drive, a Blu-ray Disc drive, a Holographic Digital Data Storage (HDDS) optical drive, an external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), an external micro-DIMM SDRAM, smart card memory (e.g., a tamper-resistant module in the form of a Universal Integrated Circuit Card (UICC) including one or more Subscriber Identity Modules (SIMs), such as USIMs and / or ISIMs), other memory, or any combination thereof. The UICC may be, for example, an embedded UICC (eUICC), an integrated UICC (iUICC), or a removable UICC, commonly referred to as a "SIM card." Memory 210 may allow UE 200 to access instructions, applications, and the like stored on a volatile or non-volatile storage medium to offload or upload data. An article of manufacture, such as an article of manufacture utilizing a communication system, may be tangibly embodied as or in memory 210 , which may be or include a device-readable storage medium.

[0434] The processing circuit 202 can be configured to communicate with an access network or other network using a communication interface 212. The communication interface 212 may include one or more communication subsystems and may include an antenna 222 or be communicatively coupled to an antenna 222. The communication interface 212 may include one or more transceivers for communicating, for example, by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in the access network). Each transceiver may include a transmitter 218 and / or a receiver 220 suitable for providing network communications (e.g., optical, electrical, frequency allocation, etc.). In addition, the transmitter 218 and the receiver 220 may be coupled to one or more antennas (e.g., antenna 222) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0435] In the illustrated embodiment, the communication functionality of the communication interface 212 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communication such as Bluetooth, near-field communication, location-based communication (e.g., using a global positioning system (GPS) to determine location), another type of communication functionality, or any combination thereof. Communication may be implemented according to one or more communication protocols and / or standards (e.g., IEEE 802.11, code division multiple access (CDMA), wideband code division multiple access (WCDMA), GSM, LTE, new radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical network (SONET), asynchronous transfer mode (ATM), QUIC, hypertext transfer protocol (HTTP), etc.).

[0436] Regardless of the type of sensor, the UE can provide an output of the data captured by its sensor through its communication interface 212 via a wireless connection to a network node. The data captured by the UE's sensor can be transmitted via another UE via a wireless connection to a network node. The output can be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to balance the load of reports from several sensors), in response to a trigger event (e.g., sending an alert when humidity is detected), in response to a request (e.g., a user-initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0437] As another example, a UE includes an actuator, motor, or switch associated with a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input, the state of the actuator, motor, or switch can change. For example, the UE can include a motor that adjusts the control surfaces or rotors of a drone in flight based on the received input, or adjusts a robotic arm performing a medical procedure based on the received input.

[0438] When the UE is in the form of an Internet of Things (IoT) device, the UE may be used for devices in one or more application areas including, but not limited to, urban wearable technology, expanded industrial applications, and healthcare. Non-limiting examples of such IoT devices are or are embedded in: an internet-connected refrigerator or freezer, a television, internet-connected lighting, an electric meter, a robotic vacuum cleaner, a voice-controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door and window sensor, a flood / humidity sensor, an electronic door lock, an internet-connected doorbell, an air conditioning system (such as a heat pump), an autonomous vehicle, a monitoring system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smartwatch, a fitness tracker, a head-mounted display for augmented reality (AR) or virtual reality (VR), a wearable device for tactile enhancement or sensory enhancement, a sprinkler, an animal tracking or item tracking device, a sensor for monitoring plants or animals, an industrial robot, an unmanned aerial vehicle (UAV), and any kind of medical device (such as a heart rate monitor or a teleoperated surgical robot). In addition to the above, Figure 10 In addition to the other components depicted for the illustrated UE 200 , a UE in the form of an IoT device may also include circuitry and / or software depending on the intended application of the IoT device.

[0439] As another specific example, in an IoT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements and transmits the results of such monitoring and / or measurements to another UE and / or a network node. In this case, the UE may be an M2M device, which in the 3GPP context may be referred to as an MTC device. As a specific example, a UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle (e.g., a car, bus, truck, ship, or airplane) or other device capable of monitoring and / or reporting its operational status or other functions associated with its operation.

[0440] In practice, any number of UEs can be used together for a single use case. For example, a first UE could be a drone or integrated into a drone, and provide the drone's speed information (obtained via a speed sensor) to a second UE, acting as a remote controller for the drone. When the user makes changes via the remote controller, the first UE can adjust the drone's throttle (e.g., by controlling an actuator) to increase or decrease the drone's speed. The first and / or second UEs can also include more than one of the aforementioned functionalities. For example, a UE could include both a sensor and an actuator, and handle data communications for both the speed sensor and the actuator.

[0441] Figure 11 A network node 300 according to some embodiments is shown. As used herein, a network node refers to a device capable of, configured, arranged, and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or devices in a telecommunications 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, NodeBs, evolved NodeBs (eNBs), and NR NodeBs (gNBs)).

[0442] Base stations can be categorized based on the amount of coverage they provide (or, in other words, their transmit power level), and thus, depending on the amount of coverage provided, they can be referred to as femto, pico, micro, or macro base stations. A base station can be a relay node or a relay donor node that controls a relay. A network node can also include one or more (or all) parts of a distributed radio base station, such as a centralized digital unit and / or a remote radio unit (RRU), sometimes referred to as a remote radio head (RRH). These remote radio units may or may not be integrated with antennas as antenna-integrated radios. Parts of a distributed radio base station can also be referred to as nodes in a distributed antenna system (DAS).

[0443] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment (e.g., MSR BS), network controller (e.g., radio network controller (RNC) or base station controller (BSC)), base transceiver station (BTS), transmission point, transmission node, multi-cell / multicast coordination entity (MCE), operation and maintenance (O&M) node, operation support system (OSS) node, self-organizing network (SON) node, positioning node (e.g., evolved serving mobile location center (E-SMLC)) and / or minimization of drive tests (MDT).

[0444] Network node 300 includes processing circuitry 302, memory 304, a communication interface 306, and a power supply 308. Network node 300 may be comprised of multiple physically separate components (e.g., a Node B component and an RNC component, or a BTS component and a BSC component, etc.), each of which may have its own corresponding components. In some scenarios where network node 300 includes multiple separate components (e.g., a BTS and a BSC component), one or more of these separate components may be shared across multiple network nodes. For example, a single RNC may control multiple Node Bs. In such scenarios, each unique Node B and RNC pair may be considered a separate network node in some cases. In some embodiments, network node 300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 304 for different RATs), and some components may be reused (e.g., the same antenna 310 may be shared by different RATs). The network node 300 may also include various sets of components shown for different wireless technologies (e.g., GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, radio frequency identification (RFID), or Bluetooth wireless technologies) integrated into the network node 300. These wireless technologies may be integrated into the same or different chips or chipsets and other components within the network node 300.

[0445] The processing circuitry 302 may include a combination of one or more of the following: a microprocessor, a controller, a microcontroller, a central processing unit, a digital signal processor, an application specific integrated circuit, a field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software, and / or encoded logic operable to provide network node 300 functionality, alone or in combination with other network node 300 components (e.g., memory 304).

[0446] In some embodiments, processing circuitry 302 comprises a system on a chip (SOC). In some embodiments, processing circuitry 302 comprises one or more of radio frequency (RF) transceiver circuitry 312 and baseband processing circuitry 314. In some embodiments, radio frequency (RF) transceiver circuitry 312 and baseband processing circuitry 314 may be on separate chips (or chipsets), boards, or units (e.g., a radio unit and a digital unit). In alternative embodiments, some or all of RF transceiver circuitry 312 and baseband processing circuitry 314 may be on the same chip, chipset, board, or unit.

[0447] Memory 304 may include any form of volatile or non-volatile computer-readable memory, including, but not limited to, permanent storage devices, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (e.g., a hard drive), removable storage media (e.g., a flash drive, compact disc (CD), or digital video disc (DVD)), and / or any other volatile memory or non-volatile, non-transitory device-readable and / or computer-executable memory device that stores information, data, and / or instructions that can be used by processing circuitry 302. Memory 304 may store any suitable instructions, data, or information, including computer programs, software, applications including one or more of logic, rules, code, tables, and / or other instructions that can be executed by processing circuitry 302 and used by network node 300. Memory 304 may be used to store any computations performed by processing circuitry 302 and / or any data received via communication interface 306. In some embodiments, processing circuitry 302 and memory 304 are integrated.

[0448] Communication interface 306 is used for wired or wireless communication of signaling and / or data between network nodes, access networks, and / or UEs. As shown, communication interface 306 includes port / terminal 316 for sending and receiving data to and from the network, for example, via a wired connection. Communication interface 306 also includes radio front-end circuitry 318, which may be coupled to antenna 310 or, in some embodiments, be part of antenna 310. Radio front-end circuitry 318 includes filter 320 and amplifier 322. Radio front-end circuitry 318 may be connected to antenna 310 and processing circuitry 302. Radio front-end circuitry may be configured to condition signals transmitted between antenna 310 and processing circuitry 302. Radio front-end circuitry 318 may receive digital data to be transmitted to other network nodes or UEs via a wireless connection. Radio front-end circuitry 318 may use a combination of filter 320 and / or amplifier 322 to convert the digital data into a radio signal with appropriate channel and bandwidth parameters. The radio signal may then be transmitted via antenna 310. Similarly, when receiving data, antenna 310 may collect radio signals, which are then converted into digital data by radio front-end circuitry 318. The digital data may be passed to processing circuitry 302. In other embodiments, the communication interface may include different components and / or different combinations of components.

[0449] In certain alternative embodiments, network node 300 does not include separate radio front-end circuitry 318; instead, processing circuitry 302 includes the radio front-end circuitry and is connected to antenna 310. Similarly, in some embodiments, all or some of RF transceiver circuitry 312 is part of communication interface 306. In yet another embodiment, communication interface 306 includes one or more ports or terminals 316, radio front-end circuitry 318, and RF transceiver circuitry 312 as part of a radio unit (not shown), and communication interface 306 communicates with baseband processing circuitry 314 as part of a digital unit (not shown).

[0450] Antenna 310 may include one or more antennas or antenna arrays configured to transmit and / or receive wireless signals. Antenna 310 may be coupled to radio front-end circuitry 318 and may be any type of antenna capable of wirelessly transmitting and receiving data and / or signals. In some embodiments, antenna 310 is separate from network node 300 and may be connected to network node 300 via an interface or port.

[0451] Antenna 310, communication interface 306 and / or processing circuit 302 can be configured to perform any receiving operation and / or certain obtaining operations performed by a network node as described herein. Any information, data and / or signals can be received from a UE, another network node and / or any other network device. Similarly, antenna 310, communication interface 306 and / or processing circuit 302 can be configured to perform any transmitting operation performed by a network node as described herein. Any information, data and / or signals can be sent to a UE, another network node and / or any other network device.

[0452] Power supply 308 provides power to the various components of network node 300 in a form appropriate for the various components (e.g., at the voltage and current levels required by each corresponding component). Power supply 308 may also include or be coupled to power management circuitry to provide power to the components of network node 300 for performing the functions described herein. For example, network node 300 may be connected to an external power source (e.g., an electrical grid, a power outlet) via an input circuit or interface (e.g., a cable), whereby the external power source provides power to the power circuitry of power supply 308. As another example, power supply 308 may include a power source in the form of a battery or battery pack connected to or integrated into the power circuitry. The battery may provide backup power if the external power source fails.

[0453] An embodiment of the network node 300 may include Figure 11Additional components beyond those shown are used to provide certain aspects of the functionality of the network node, including any functionality described herein and / or any functionality required to support the subject matter described herein. For example, the network node 300 may include a user interface device to allow information to be input into the network node 300 and to allow information to be output from the network node 300. This may allow a user to perform diagnostic, maintenance, repair, and other management functions on the network node 300.

[0454] Figure 12 is a flow chart illustrating an example method in a wireless device according to certain embodiments. In certain embodiments, Figure 12 One or more steps may be performed by Figure 10 The user device 200 described here performs the following operations: The wireless device supports LTM.

[0455] The method begins at step 1212, where a wireless device (e.g., UE 200) obtains an uplink configuration of an LTM candidate cell. For example, the wireless device may obtain the uplink configuration of the LTM candidate cell via RRC. Examples of uplink configurations of LTM candidate cells will be described in more detail with reference to the above embodiments and examples.

[0456] At step 1214, the wireless device receives a first indication (eg, PDCCH command, RRC message, MAC CE, etc.) from the serving cell to perform uplink transmission in the LTM candidate cell. Examples of the first indication will be described in more detail with reference to the above embodiments and examples.

[0457] The wireless device transmits a first uplink transmission (eg, a random access preamble) in the LTM candidate cell using a first transmit power and on a first uplink time / frequency resource at step 1216. The wireless device does not expect a response (eg, a RAR) to the first uplink transmission.

[0458] In some embodiments, the wireless device selects a first beam, and based on the selected first beam, the UE selects a first uplink resource associated with the first beam to send a first uplink message.

[0459] Examples of sending uplink transmissions will be described in more detail with reference to the above embodiments and examples.

[0460] For example, the LTM candidate cell may not have received the first uplink transmission, or the LTM candidate cell may be unable to calculate the timing advance of the wireless device, in which case the serving cell can determine that a failure has occurred and the method continues to step 1218.

[0461] At step 1218, the wireless device receives a second indication (eg, PDCCH command, RRC message, MAC CE, etc.) from the serving cell to perform uplink transmission in the LTM candidate cell. Examples of the second indication will be described in more detail with reference to the above embodiments and examples.

[0462] At step 1220, the wireless device transmits a second uplink transmission (e.g., a random access preamble) in the LTM candidate cell. The second uplink transmission is transmitted using one or more of: a second transmit power different from the first transmit power, and a second uplink time / frequency resource different from the first time / frequency resource.

[0463] For example, in a particular embodiment, the first uplink transmission uses a first beam and in response to receiving a second indication to perform an uplink transmission, the method further includes: selecting a second beam for a second uplink transmission, and when the second beam is the same as the first beam, sending the second transmission using a second transmit power different from the first transmit power, and when the second beam is different from the first beam, sending the second transmission using a second uplink time / frequency resource different from the first time / frequency resource.

[0464] In a particular embodiment, the second indication to perform uplink transmission includes an indication of a second transmit power for the second uplink transmission or an indication of a second uplink time / frequency resource for the second uplink transmission.

[0465] In a specific embodiment, the uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

[0466] In a particular embodiment, at least one of the first indication and the second indication comprises an indication of an SSB associated with the first uplink transmission or the second uplink transmission, respectively.

[0467] In a particular embodiment, the uplink configuration of the uplink candidate cell includes more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication includes an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

[0468] Examples of sending the second uplink transmission will be described in more detail with reference to the above embodiments and examples.

[0469] At step 1222, based on the second uplink transmission, the wireless device receives a timing advance value for the LTM candidate cell from the serving cell (e.g., the S-DU). In certain embodiments, receiving the timing advance value from the serving cell includes receiving an LTM execution command. Examples of receiving the timing advance value will be described in more detail with reference to the above embodiments and examples.

[0470] Can Figure 12 Method 1200 may be modified, added, or omitted. Additionally, Figure 12 One or more steps in the method may be performed in parallel or in any suitable order.

[0471] Figure 13 is a flow chart illustrating an example method in a network node according to certain embodiments. In certain embodiments, Figure 13 One or more steps may be performed by Figure 11 The described network node 300 performs the following operations: The network node can act as an S-DU for TA management between a wireless device and at least one LTM candidate cell.

[0472] The method may start at step 1310, where a network node (eg, network node 300) sends an uplink configuration of uplink candidate cells to a wireless device. Examples of uplink configurations will be described in more detail with reference to the above embodiments and examples.

[0473] At step 1312, the network node sends a first indication to the wireless device to perform uplink transmission in the LTM candidate cell. Examples of the first indication will be described in more detail with reference to the above embodiments and examples.

[0474] At step 1314, the network node detects that uplink transmission in the LTM candidate cell is unsuccessful. For example, in certain embodiments, detecting that uplink transmission in the LTM candidate cell is unsuccessful includes: not receiving a response from the LTM candidate cell, or receiving an indication from the LTM candidate cell that uplink transmission in the LTM candidate cell is unsuccessful. Examples of detecting that uplink transmission in the LTM candidate cell is unsuccessful will be described in more detail with reference to the above embodiments and examples.

[0475] At step 1316, the network node sends a second indication to the wireless device to perform uplink transmission in the LTM candidate cell.

[0476] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmissions of random access preambles.

[0477] In certain embodiments, the second indication to perform an uplink transmission includes an indication of a transmit power or uplink time / frequency resources to be used for the second uplink transmission.

[0478] In a particular embodiment, the uplink configuration of the uplink candidate cell may include one or more random access parameters, and at least one of the first indication and the second indication includes an indication of which of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively. The uplink configuration of the uplink candidate cell may include more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication includes an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

[0479] In a particular embodiment, at least one of the first indication and the second indication comprises an indication of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

[0480] In certain embodiments, sending the second indication to the wireless device to perform an uplink transmission includes determining that a threshold number of uplink transmissions by the wireless device and the LTM candidate cell has not been exceeded.

[0481] Examples of the second indication will be described in more detail with reference to the above-described embodiments and examples.

[0482] The network node may receive a timing advance value from the candidate LTM cell at step 1318, and may send the timing advance value to the wireless device at step 1320. In certain embodiments, sending the timing advance value to the wireless device includes sending an LTM execution command to the wireless device.

[0483] Can Figure 13 Method 1300 may be modified, added, or omitted. Additionally, Figure 13 One or more steps in the method may be performed in parallel or in any suitable order.

[0484] The methods disclosed herein may be modified, added to, or omitted without departing from the scope of the invention. The methods may include more, fewer, or other steps. Additionally, the steps may be performed in any suitable order.

[0485] The foregoing description sets forth numerous specific details. However, it should be understood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description. Using the included description, one of ordinary skill in the art will be able to implement appropriate functionality without undue experimentation.

[0486] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment may include that particular feature, structure, or characteristic. Furthermore, these phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it should be understood that it is within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments (whether or not explicitly described).

[0487] Although the present disclosure has been described with reference to specific embodiments, modifications and permutations of the embodiments will be apparent to those skilled in the art. Therefore, the above description of the embodiments does not limit the present disclosure. Other changes, substitutions, and modifications may be made without departing from the scope of the present disclosure as defined by the appended claims.

[0488] Some example embodiments are included below.

[0489] Group A Examples

[0490] 1. A method for L1 / L2 triggered mobility (LTM) performed by a wireless device, the method comprising:

[0491] -Get uplink configuration of LTM candidate cells;

[0492] - receiving a first indication from the serving cell to perform uplink transmission in the LTM candidate cell;

[0493] - sending a first uplink transmission in the LTM candidate cell using a first transmit power and on a first uplink time / frequency resource;

[0494] - receiving a second indication from the serving cell to perform uplink transmission in the LTM candidate cell;

[0495] - sending a second uplink transmission in the second LTM candidate cell, wherein the second uplink transmission is sent using one or more of: a second transmit power different from the first transmit power, and a second uplink time / frequency resource different from the first time / frequency resource.

[0496] 2. The method of embodiment 1, wherein the second LTM candidate cell is the same cell as the first LTM candidate cell.

[0497] 3. The method of embodiment 1, wherein the second LTM candidate cell is a different cell than the first LTM candidate cell.

[0498] 4. A method performed by a wireless device, the method comprising:

[0499] -Any of the above wireless device steps, features, or functions, alone or in combination with any of the above other steps, features, or functions.

[0500] 5. The method according to any of the preceding embodiments further comprises one or more of the above-mentioned additional wireless device steps, features or functions.

[0501] 6. The method according to any one of the preceding embodiments, further comprising:

[0502] - provide user data; and

[0503] - Forwarding of user data to a host computer via transmission to a base station.

[0504] Group B Examples

[0505] 7. A method, performed by a base station acting as a service distributed unit (SDU), for timing advance (TA) management between a wireless device and at least one L1 / L2 triggered mobility (LTM) candidate cell, the method comprising:

[0506] -sending a first indication to the wireless device to perform uplink transmission in the LTM candidate cell;

[0507] - detecting that uplink transmission in the LTM candidate cell is unsuccessful; and

[0508] - Sending a second indication to the wireless device to perform uplink transmission in the LTM candidate cell.

[0509] 8. A method performed by a base station, the method comprising:

[0510] Any steps, features, or functions described above with respect to the base station (eg, serving DU, candidate DU, etc.), alone or in combination with other steps, features, or functions described above.

[0511] 9. The method according to the above embodiment further includes one or more of the above additional base station steps, features or functions.

[0512] 10. The method according to any one of the preceding embodiments, further comprising:

[0513] - obtain user data; and

[0514] -Forward user data to a host computer or wireless device.

[0515] Group C Examples

[0516] 11. A mobile terminal, comprising:

[0517] - a processing circuit configured to perform any of the steps according to any one of Group A embodiments; and

[0518] - A power circuit configured to supply power to the wireless device.

[0519] 12. A base station, comprising:

[0520] - a processing circuit configured to perform any of the steps according to any one of Group B embodiments;

[0521] - A power circuit configured to supply power to the wireless device.

[0522] 13. A user equipment (UE), comprising:

[0523] - an antenna configured to transmit and receive wireless signals;

[0524] - a radio front-end circuit connected to the antenna and the processing circuit and configured to condition signals transmitted between the antenna and the processing circuit;

[0525] - a processing circuit configured to perform any of the steps according to any one of Group A embodiments;

[0526] - an input interface connected to the processing circuitry and configured to allow information to be input into the UE for processing by the processing circuitry;

[0527] - an output interface connected to the processing circuit and configured to output information that has been processed by the processing circuit from the UE; and

[0528] - A battery connected to the processing circuit and configured to supply power to the UE.

[0529] 14. A communication system comprising a host computer, comprising:

[0530] - processing circuitry configured to provide user data; and

[0531] - a communication interface configured to forward user data to a cellular network for transmission to a user equipment (UE),

[0532] - wherein the cellular network comprises a base station having a radio interface and a processing circuit, the processing circuit of the base station being configured to perform any of the steps according to any one of Group B embodiments.

[0533] 15. The communication system according to the preceding embodiment further includes a base station.

[0534] 16. The communication system according to the two aforementioned embodiments further includes the UE, wherein the UE is configured to communicate with the base station.

[0535] 17. The communication system according to the three preceding embodiments, wherein:

[0536] - the processing circuitry of the host computer is configured to execute a host application, thereby providing user data; and

[0537] - The UE comprises a processing circuit configured to execute a client application associated with a host application.

[0538] 18. A method implemented in a communication system comprising a host computer, a base station, and a user equipment (UE), the method comprising:

[0539] - at the host computer, providing user data; and

[0540] - Initiating, at a host computer, transmission of bearer user data to a UE via a cellular network comprising a base station, wherein the base station performs any of the steps according to any of the embodiments in Group B.

[0541] 19. The method according to the preceding embodiment further includes: sending user data at the base station.

[0542] 20. The method of any preceding embodiment, wherein the user data is provided at the host computer by executing a host application, the method further comprising: executing, at the UE, a client application associated with the host application process.

[0543] 21. A user equipment (UE) configured to communicate with a base station, the UE comprising a radio interface and a processing circuit configured to perform any of the steps according to any one of the three preceding embodiments.

[0544] 22. A communication system comprising a host computer, comprising:

[0545] - processing circuitry configured to provide user data; and

[0546] - a communication interface configured to forward user data to a cellular network for transmission to a user equipment (UE),

[0547] - wherein the UE comprises a radio interface and a processing circuit, and the components of the UE are configured to perform any steps according to any embodiment of Group A.

[0548] 23. The communication system according to the preceding embodiment, wherein the cellular network further comprises a base station configured to communicate with the UE.

[0549] 24. The communication system according to the two preceding embodiments, wherein:

[0550] - the processing circuitry of the host computer is configured to execute a host application, thereby providing user data; and

[0551] - The processing circuitry of the UE is configured to execute a client application associated with the host application.

[0552] 25. A method implemented in a communication system comprising a host computer, a base station, and a user equipment (UE), the method comprising:

[0553] - at the host computer, providing user data; and

[0554] - Initiating, at a host computer, transmission of bearer user data to a UE via a cellular network including a base station, wherein the UE performs any of the steps according to any one of Group A of Embodiments.

[0555] 26. The method according to the preceding embodiment further includes: receiving user data from a base station at the UE.

[0556] 27. A communication system comprising a host computer, comprising:

[0557] - a communication interface configured to receive user data, the user data originating from a transmission from a user equipment (UE) to a base station,

[0558] - wherein the UE comprises a radio interface and a processing circuit, the processing circuit of the UE being configured to perform any of the steps according to any one of Group A embodiments.

[0559] 28. The communication system according to the aforementioned embodiment further includes the UE.

[0560] 29. The communication system according to the two aforementioned embodiments further includes the base station, wherein the base station includes: a radio interface configured to communicate with the UE; and a communication interface configured to forward user data carried by the transmission from the UE to the base station to the host computer.

[0561] 30. The communication system according to any of the preceding three embodiments, wherein:

[0562] - the processing circuitry of the host computer is configured to execute the host application; and

[0563] - The processing circuitry of the UE is configured to execute a client application associated with the host application, thereby providing user data.

[0564] 31. The communication system according to any of the preceding four embodiments, wherein:

[0565] - the processing circuitry of the host computer is configured to execute the host application, thereby providing the requested data; and

[0566] - The processing circuitry of the UE is configured to execute a client application associated with the host application, thereby providing user data in response to the request data.

[0567] 32. A method implemented in a communication system comprising a host computer, a base station, and a user equipment (UE), the method comprising:

[0568] - At a host computer, receiving user data sent from a UE to a base station, wherein the UE performs any of the steps according to any one of Group A embodiments.

[0569] 33. The method according to the aforementioned embodiment further includes: at the UE, providing user data to the base station.

[0570] 34. The method according to the two preceding embodiments, further comprising:

[0571] - At the UE, a client application is executed, thereby providing user data to be sent;

[0572] - At the host computer, executing a host application associated with the client application.

[0573] 35. The method according to the three preceding embodiments, further comprising:

[0574] - At the UE, executing the client application; and

[0575] - receiving, at the UE, input data to the client application, the input data being provided by executing a host application associated with the client application at a host computer,

[0576] The user data to be sent is provided by the client application in response to the input data.

[0577] 36. A communication system comprising a host computer, the host computer comprising a communication interface, the communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station, wherein the base station comprises a radio interface and processing circuitry, the processing circuitry of the base station being configured to perform any of the steps of any one of Group B embodiments.

[0578] 37. The communication system according to the aforementioned embodiment further includes the base station.

[0579] 38. The communication system according to the two aforementioned embodiments further includes the UE, wherein the UE is configured to communicate with the base station.

[0580] 39. The communication system according to the three preceding embodiments, wherein:

[0581] - the processing circuitry of the host computer is configured to execute a host application;

[0582] - The UE is configured to execute a client application in association with a host application, thereby providing user data to be received by the host computer.

[0583] 40. A method implemented in a communication system comprising a host computer, a base station, and a user equipment (UE), the method comprising:

[0584] - receiving, at a host computer, from a base station user data originating from a transmission that the base station has received from a UE, wherein the UE performs any of the steps according to any one of Group A of embodiments.

[0585] 41. The method according to the aforementioned embodiment further includes: receiving user data from the UE at the base station.

[0586] 42. The method according to the two preceding embodiments further comprises: at the base station, initiating transmission of the received user data to a host computer.

Claims

1. A method for layer 1 / layer 2 (L1 / L2 triggered mobility LTM) performed by a wireless device, the method comprising: Obtain (1212) the uplink configuration of the LTM candidate cell; receiving (1214) a first indication from a serving cell to perform uplink transmission in the LTM candidate cell; transmitting (1216) a first uplink transmission in the LTM candidate cell using a first transmit power and on a first uplink time / frequency resource; receiving (1218) a second indication from the serving cell to perform uplink transmission in the LTM candidate cell; transmitting (1220) a second uplink transmission in the LTM candidate cell, wherein the second uplink transmission is transmitted using one or more of: a second transmit power different from the first transmit power, and a second uplink time / frequency resource different from the first time / frequency resource; as well as Based on the second uplink transmission, a timing advance value of the LTM candidate cell is received (1222) from the serving cell.

2. The method according to claim 1, wherein The first uplink transmission and the second uplink transmission include transmission of a random access preamble.

3. The method according to claim 2, wherein: The wireless device does not expect a random access response (RAR) in response to the transmission of the random access preamble.

4. The method according to any one of claims 1 to 3, wherein The first uplink transmission uses a first beam and in response to receiving a second indication to perform the uplink transmission, the method further includes: selecting a second beam for the second uplink transmission, and when the second beam is the same as the first beam, sending the second uplink transmission using a second transmission power different from the first transmission power, and when the second beam is different from the first beam, sending the second uplink transmission using a second uplink time / frequency resource different from the first time / frequency resource.

5. The method according to any one of claims 1 to 4, wherein The second instruction to perform the uplink transmission includes an instruction of a second transmit power for the second uplink transmission or an instruction of a second uplink time / frequency resource for the second uplink transmission.

6. The method according to any one of claims 1 to 5, wherein The first indication and the second indication include a Physical Downlink Control Channel (PDCCH) order.

7. The method according to any one of claims 1 to 6, wherein Receiving the timing advance value from the serving cell includes receiving an LTM execution command.

8. The method according to any one of claims 1 to 7, wherein The uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively.

9. The method according to any one of claims 1 to 8, wherein At least one of the first indication and the second indication comprises an indication of a synchronization signal block SSB associated with the first uplink transmission or the second uplink transmission, respectively.

10. The method according to any one of claims 1 to 9, wherein The uplink configuration of the uplink candidate cell comprises more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication comprises an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

11. A wireless device (200) supporting Layer 1 / Layer 2 (L1 / L2 Triggered Mobility LTM), the wireless device comprising a processing circuit (202), the processing circuit (202) being operative to: Get the uplink configuration of the LTM candidate cell; receiving a first indication from a serving cell to perform uplink transmission in the LTM candidate cell; sending a first uplink transmission in the LTM candidate cell using a first transmit power and on a first uplink time / frequency resource; receiving a second indication from the serving cell to perform uplink transmission in the LTM candidate cell; sending a second uplink transmission in the LTM candidate cell, wherein the second uplink transmission is sent using one or more of: a second transmit power different from the first transmit power, and a second uplink time / frequency resource different from the first time / frequency resource; as well as Based on the second uplink transmission, a timing advance value of the LTM candidate cell is received from the serving cell.

12. The wireless device of claim 11, wherein: The first uplink transmission and the second uplink transmission include transmission of a random access preamble.

13. The wireless device of claim 12, wherein: The wireless device does not expect a random access response (RAR) in response to the transmission of the random access preamble.

14. The wireless device according to any one of claims 11 to 13, wherein: The first uplink transmission uses a first beam and in response to receiving a second indication to perform the uplink transmission, the processing circuit operates to: select a second beam for the second uplink transmission, and when the second beam is the same as the first beam, send the second uplink transmission using a second transmit power different from the first transmit power, and when the second beam is different from the first beam, send the second uplink transmission using a second uplink time / frequency resource different from the first time / frequency resource.

15. The wireless device according to any one of claims 11 to 14, wherein: The second instruction to perform the uplink transmission includes an instruction of a second transmit power for the second uplink transmission or an instruction of a second uplink time / frequency resource for the second uplink transmission.

16. The wireless device according to any one of claims 11 to 15, wherein: The first indication and the second indication include a Physical Downlink Control Channel (PDCCH) order.

17. The wireless device according to any one of claims 11 to 16, wherein: Receiving the timing advance value from the serving cell includes receiving an LTM execution command.

18. The wireless device according to any one of claims 11 to 17, wherein: The uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively.

19. The wireless device according to any one of claims 11 to 18, wherein: At least one of the first indication and the second indication comprises an indication of a synchronization signal block SSB associated with the first uplink transmission or the second uplink transmission, respectively.

20. The wireless device according to any one of claims 11 to 19, wherein The uplink configuration of the uplink candidate cell comprises more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication comprises an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

21. A method, performed by a network node as a Serving Distributed Unit (S-DU), for timing advance (TA) management between a wireless device and at least one Layer 1 / Layer 2 (L1 / L2 triggered mobility) candidate cell, the method comprising: sending (1312) a first indication to the wireless device to perform uplink transmission in the LTM candidate cell; as well as A second indication is sent (1316) to the wireless device to perform uplink transmission in the LTM candidate cell.

22. The method according to claim 21, further comprising: Upon detecting (1314) that the uplink transmission in the LTM candidate cell is unsuccessful, a second indication is sent to the wireless device to perform the uplink transmission in the LTM candidate cell.

23. The method according to claim 22, wherein Detecting that the uplink transmission in the LTM candidate cell is unsuccessful includes: not receiving a response from the LTM candidate cell.

24. The method according to claim 22, wherein Detecting that the uplink transmission in the LTM candidate cell is unsuccessful includes receiving an indication from the LTM candidate cell that the uplink transmission in the LTM candidate cell is unsuccessful.

25. The method according to any one of claims 21 to 24, wherein The first uplink transmission and the second uplink transmission include transmission of a random access preamble.

26. The method according to any one of claims 21 to 25, wherein The second instruction to perform the uplink transmission includes an instruction of a transmit power or an uplink time / frequency resource for the second uplink transmission.

27. The method according to any one of claims 21 to 26, wherein The first indication and the second indication include a Physical Downlink Control Channel (PDCCH) order.

28. The method according to any one of claims 21 to 27, further comprising: receiving (1318) a timing advance value from the candidate LTM cell; as well as The timing advance value is sent (1320) to the wireless device.

29. The method according to claim 28, wherein Sending the timing advance value to the wireless device includes sending an LTM execution command to the wireless device.

30. The method according to any one of claims 21 to 29, wherein Sending a second indication to the wireless device to perform the uplink transmission includes determining that a threshold number of uplink transmissions for the wireless device and the LTM candidate cell has not been exceeded.

31. The method according to any one of claims 21 to 30, further comprising: An uplink configuration of the uplink candidate cell is sent (1310) to the wireless device.

32. The method according to claim 31, wherein The uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively.

33. The method according to claim 31, wherein The uplink configuration of the uplink candidate cell comprises more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication comprises an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

34. The method according to any one of claims 21 to 33, wherein At least one of the first indication and the second indication comprises an indication of a synchronization signal block SSB associated with the first uplink transmission or the second uplink transmission, respectively.

35. A network node (300) capable of operating as a Serving Distributed Unit (S-DU) for timing advance (TA) management between a wireless device and at least one Layer 1 / Layer 2 (L1 / L2 triggered mobility) candidate cell, the network node comprising a processing circuit (302) operable to: sending a first indication to the wireless device to perform uplink transmission in the LTM candidate cell; detecting that the uplink transmission in the LTM candidate cell is unsuccessful; and A second indication is sent to the wireless device to perform uplink transmission in the LTM candidate cell.

36. The network node of claim 35, the processing circuit being operable to, upon detecting that the uplink transmission in the LTM candidate cell is unsuccessful, send a second indication to the wireless device to perform the uplink transmission in the LTM candidate cell.

37. The network node according to claim 36, wherein: The processing circuit is operable to detect that the uplink transmission in the LTM candidate cell is unsuccessful by not receiving a response from the LTM candidate cell.

38. The network node according to claim 36, wherein: The processing circuitry is operable to detect that the uplink transmission in the LTM candidate cell was unsuccessful by receiving an indication from the LTM candidate cell that the uplink transmission in the LTM candidate cell was unsuccessful.

39. The network node according to any one of claims 35 to 38, wherein: The first uplink transmission and the second uplink transmission include transmission of a random access preamble.

40. The network node according to any one of claims 35 to 39, wherein: The second instruction to perform the uplink transmission includes an instruction of a transmit power or an uplink time / frequency resource for the second uplink transmission.

41. The network node according to any one of claims 35 to 40, wherein: The first indication and the second indication include a Physical Downlink Control Channel (PDCCH) order.

42. The network node according to any one of claims 35 to 41, wherein: The processing circuit is further operable to: receiving a timing advance value from the candidate LTM cell; and The timing advance value is sent to the wireless device.

43. The network node according to claim 42, wherein: Sending the timing advance value to the wireless device includes sending an LTM execution command to the wireless device.

44. The network node according to any one of claims 35 to 43, wherein: The processing circuit is operable to send a second indication to the wireless device to perform the uplink transmission by determining that a threshold number of uplink transmissions for the wireless device and the LTM candidate cell has not been exceeded.

45. The network node according to any one of claims 35 to 44, the processing circuit is further operative to: send an uplink configuration of the uplink candidate cell to the wireless device.

46. The network node according to claim 45, wherein: The uplink configuration of the uplink candidate cell includes one or more random access parameters, and at least one of the first indication and the second indication includes: an indication of which random access parameter of the one or more random access parameters is used for the first uplink transmission or the second uplink transmission, respectively.

47. The network node according to claim 45, wherein: The uplink configuration of the uplink candidate cell comprises more than one uplink configuration for more than one uplink candidate cell, and at least one of the first indication and the second indication comprises an indication of in which uplink candidate cell the first uplink transmission or the second uplink transmission is sent, respectively.

48. The network node according to any one of claims 35 to 47, wherein: At least one of the first indication and the second indication comprises an indication of a synchronization signal block SSB associated with the first uplink transmission or the second uplink transmission, respectively.

Images