Time alignment fallback while moving

Abstract

The method is performed by a wireless device for Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM). The method includes obtaining an uplink configuration of the LTM candidate cell; receiving from a serving cell a first notification to perform an uplink transmission in the candidate cell; transmitting the first uplink transmission in the candidate cell with a first transmit power and first uplink time / frequency resources; receiving from the serving cell a second notification to perform an uplink transmission in the candidate cell; transmitting a second uplink transmission in the candidate cell, the second uplink transmission being transmitted with 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 from the serving cell a timing advance value for the candidate cell based on the second uplink transmission.

Description

[Technical Field]

[0001] FIELD Embodiments of the present disclosure relate to wireless communications, and more particularly to fallbacks for time alignment while in motion. [Background technology]

[0002] In general, all terms used herein should be interpreted according to their ordinary meaning in the relevant technical field unless a different meaning is clearly given and / or is implied from the context in which it is used. All references to a / an element, apparatus, component, means, step, etc. should be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc. unless expressly stated otherwise. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless a step is expressly described as following or preceding another step and / or it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, where appropriate. Similarly, any advantage of any embodiment may be applied to any other embodiment, and vice versa. Other objects, features, and advantages of the accompanying embodiments will become apparent from the following description.

[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 positions within the cell and may have different distances to the base station (e.g., NR gNodeB). Therefore, transmissions from different UEs experience different delays until they reach the base station. Therefore, an uplink timing control procedure is used to ensure that uplink (UL) transmissions from a UE arrive at the base station within the corresponding reception window for the base station. This avoids intra-cell interference, both 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, the main role of which is to counter different propagation delays between different UEs, as shown in the example below for an LTE eNodeB.

[0005] To achieve time alignment and obtain uplink synchronization, a base station (e.g., gNodeB, eNodeB) derives a TA value that the UE needs to use for uplink transmissions to reach the base station within the reception window and notifies the UE. When the UE first accesses a cell, the UE uses a random access procedure in which the received Msg1 (Physical Random Access Channel (PRACH) preamble) is used by the base station to determine the UE's initial TA to use for uplink transmissions in the cell. During the connection, the base station then continuously monitors whether the UE needs to advance / delay uplink transmissions to compensate for changes in propagation delay and notifies the UE if the TA value needs to be changed. The timing advance value, sometimes referred to as the TA value, can be either 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 has connections to several different serving cells, the same TA value may be used for two or more of the cells, for example, if the cells are co-located and therefore always have the same distance to the UE. Such cells may then be configured as belonging to the same Timing Advance Group (TAG). TAG configuration is done per cell group; for example, serving cells may be configured to belong to the same TAG only if they belong to the same cell group (master cell group (MCG) or secondary cell group (SCG)). Further details are provided below.

[0007] When a UE does not perform uplink transmissions on a serving cell for a certain 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 a different propagation delay. In that case, if the UE performs an uplink transmission using its most recently received TA value, the uplink transmission may arrive at the base station outside the reception window and therefore not be correctly received by the base station. The transmission may even interfere with other uplink transmissions (from other UEs). Therefore, a timer, timeAlignmentTimer (which may be referred to as the time alignment timer or TA timer), is configured for each TAG to indicate the length of time during which the UE can consider itself uplink time-aligned to the serving cell belonging to the associated TAG without receiving any updates to the TA value. Thus, timeAlignmentTimer indicates the length of time during which the UE can consider the received TA value valid. If the UE does not receive an updated value before timeAlignmentTimer expires, the UE is no longer uplink synchronized to the serving cell belonging to the corresponding TAG.

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

[0009] The UE transmits a selected preamble on the selected RACH resource and expects to receive an RA response (RAR) during the configured RAR time window. If the UE transmits the preamble and does not receive an RAR during the configured RAR time window, the UE performs what is called RA fallback, which consists of the UE performing RA resource reselection by selecting a new beam (e.g., a new SSB and / or CSI-RS) mapping to a new RA resource and / or preamble power ramping (e.g., increasing the transmit power for the preamble transmission). This may be done up to a maximum number of times configured by the network, after which the UE declares an RA failure.

[0010] This can be summarized as follows for the case of contention-based random access during reconfiguration with synchronization to the target cell: **************************************** [38.321] 5.1.4 Receiving a Random Access Response Once the random access preamble has been transmitted, regardless of the possible occurrence of measurement gaps, the MAC entity shall: [...] 1> If the ra-ResponseWindow configured in RACH-ConfigCommon expires and no random access response containing a random access preamble identifier matching the transmitted PREAMBLE_INDEX is received: 2> The reception of the random access response is considered unsuccessful; 2>Increase PREAMBLE_TRANSMISSION_COUNTER by 1; 2>If PREAMBLE_TRANSMISSION_COUNTER = preambleTransMax + 1: 3> When the random access preamble is sent on the SpCell: 4> Indicates random access problems to higher layers; [...] 2> If the random access procedure is not completed: 3>Select a random backoff time according to a uniform distribution between 0 and PREAMBLE_BACKOFF; 3> If the criteria for selecting a non-contentious random access resource (defined in Section 5.1.2) are met during the backoff time: 4> Perform the random access resource selection procedure (see section 5.1.2); 3>Others: 4> After the backoff period, the random access resource selection procedure (see Section 5.1.2) shall be performed. [...] [38.321] 5.1.2 Random Access Resource Selection The MAC entity: [...] 1> Otherwise (e.g., in the case of contention-based random access preamble selection): 2> If at least one SSB with SS-RSRP above rsrp-ThresholdSSB is available: 3) An SSB with SS-RSRP greater than rsrp-ThresholdSSB must be selected. 2>Others: 3> Any SSB must be selected [...] 2> A random access preamble shall be randomly selected with equal probability from the random access preambles associated with the selected SSB and the selected random access preamble group. 2> PREAMBLE_INDEX must be set to the selected random access preamble [...] 1>Otherwise, if SSB is selected above: 2>From the PRACH opportunities corresponding to the selected SSBs allowed by the restriction given by ra-ssb-OccasionMaskIndex, the MAC entity shall determine the next available PRACH opportunity, if configured or signaled by the PDCCH (the MAC entity shall randomly select a PRACH opportunity with equal probability among consecutive PRACH opportunities according to clause 8.1 of TS 38.213 corresponding to the selected SSB; the MAC entity may take into account the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB). 1>Otherwise, if CSI-RS is selected above: [...] 1> The random access preamble transmission procedure (see section 5.1.3) must be performed. NOTE: When the UE determines whether there is an SSB with an SS-RSRP above rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP above rsrp-ThresholdCSI-RS, the UE uses the most recent unfiltered L1-RSRP measurement. 5.1.3 Random Access Preamble Transmission For each random access preamble, the MAC entity: 1> PREAMBLE_TRANSMISSION_COUNTER is greater than 1, and 1> If no notification to stop the power ramping counter has been received from the lower layer, and 1> If the selected SSB or CSI-RS is unchanged from the selection in the last random access preamble transmission: 2> PREAMBLE_POWER_RAMPING_COUNTER must be increased by 1 1> Select a value for DELTA_PREAMBLE according to Section 7.3; 1>Set PREAMBLE_RECEIVED_TARGET_POWER to preambleReceivedTargetPower + DELTA_PREAMBLE + (PREAMBLE_POWER_RAMPING_COUNTER-1) × PREAMBLE_POWER_RAMPING_STEP; 1> Calculate the RA-RNTI associated with the PRACH opportunity on which the random access preamble is transmitted, excluding non-contentious random access preambles for beam failure recovery requests; 1> The physical layer must be instructed to transmit a random access preamble using the selected PRACH opportunity, the corresponding RA-RNTI (if available), PREAMBLE_INDEX, and PREAMBLE_RECEIVED_TARGET_POWER. [...] ****************************************

[0011] The 3rd Generation Partnership Project (3GPP) work includes work items on further NR mobility enhancements, particularly in the technology area entitled L1 / L2-based inter-cell mobility. For further details, see the Work Item Description (WID) of RP-213565.

[0012] According to WID, when a UE moves from the coverage area of ​​one cell to another, a serving cell change must be performed at some point. Currently, the serving cell change is triggered by Layer 3 (L3) measurements and triggered by Radio Resource Control (RRC) signaling, with synchronization for PCell and PSCell changes, and additional release for SCells, if applicable. All cases involve a full Layer 2 (L2) (and Layer 1 (L1)) reset, which leads to longer delays, greater overhead, and longer disruption times than beam-switched mobility. The goal of L1 / L2 mobility enhancements is to enable serving cell changes via L1 / L2 signaling to reduce delays, overhead, and disruption times.

[0013] One goal is that L1-L2 inter-cell mobility should be like inter-cell beam management, i.e., to support L1-L2 inter-cell mobility, the UE should be configured to perform measurements on cells other than the serving cell defined up to Rel-17. In Rel-17, a solution is standardized in which CSI resources can be associated with a primary cell identifier (PCI) of one of the serving cells that is not the same PCI, to support inter-PCI mTRP operation. In that solution, the UE receives explicit notification of which beam (SSB) and PCI should be measured for a given reporting configuration.

[0014] The goal is to identify mechanisms and procedures for L1 / L2 based inter-cell mobility to reduce mobility latency, including configuration and maintenance for multiple candidate cells to facilitate fast application of configuration for candidate cells, dynamic switching mechanisms between candidate serving cells (including SpCell and SCell) for potentially applicable scenarios based on L1 / L2 signaling, L1 extensions for inter-cell beam management and beam notification including L1 measurements and reporting, timing advance management, and CU-DU interface signaling to support L1 / L2 mobility as needed.

[0015] The L1 / L2-based inter-cell mobility procedure is 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 inter-DU cases within a CU (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 may be synchronized or asynchronous.

[0016] Currently, certain challenges exist. For example, one of the problems to be solved for L1 / L2 inter-cell mobility is timing advance management (which may include handling of time alignment timers). In legacy L3 handover, timing advance is established between the UE and the target cell using a random access procedure, where the UE sends a preamble to the target cell and receives a RAR from the target cell containing the time alignment value to be applied.

[0017] Performance improvements for L1 / L2-based inter-cell mobility to reduce handover interruption time include solutions for reducing the time for downlink and uplink synchronization after UE reconfiguration and handover decision. In one proposed solution, the UE transmits an RA preamble to a candidate cell, and unlike legacy RA procedures, the UE does not expect a RA containing a TA value from the candidate cell in response. Instead, the UE transmits the RA preamble to enable a candidate target network node (e.g., a candidate distributed unit - DU) to calculate a timing advance value (e.g., the amount of timing adjustment the UE needs to apply for uplink synchronization) and provide that value (or an index / notification of that value) to the source DU (S-DU). The S-DU may provide that value or a related value to the UE only when it is time to perform L1 / L2 triggered mobility (LTM) to the candidate cell. An example is shown in Figures 1A and 1B.

[0018] 1A and 1B are flowcharts illustrating an example of TA establishment based on RA preamble transmission and reception to a candidate, e.g., in a MAC CE for an LTM cell switch command, for an LTM-only TA value. In this solution, the UE can transmit a preamble to enable the network to calculate a timing advance value for the candidate cell without the UE having to wait for reception of an RAR in the candidate cell. This reduces transmission / reception interruptions in the source cell, because after the RA preamble transmission in the candidate cell, the UE must also monitor a control channel (such as the Physical Downlink Control Channel (PDCCH)) in the candidate cell for the possible reception of an RAR.

[0019] 3GPP work items include agreement on the following regarding LTM: **************************************** - The mechanism for obtaining TA for candidate cells in Rel-18 LTM shall at least support RACH commanded on PDCCH. PDCCH commands are triggered only by the source cell - Supports obtaining TA of candidate cells before receiving cell switch command in L1 / L2 based mobility - For RACH commanded by PDCCH in LTM, at least the following extensions are supported: o Introducing candidate cell notification and / or candidate cell RO in DCI RACH resource configuration for candidate cells is provided before PDCCH command - TA update (e.g., TA reacquisition) for candidate cells can be triggered by the NW o The same triggering mechanism reuses the initial TA acquisition, e.g. triggered RACH commanded by PDCCH in the candidate cell. ****************************************

[0020] The fact that the UE does not expect an RAR in the candidate cell after transmitting the RA preamble creates a problem because the receipt of the RAR acknowledges to the UE that the preamble transmission was successfully received by the network. Thus, without an RAR from the candidate cell, the UE does not know whether the preamble was successfully received and / or whether the UE needs to retransmit the preamble. At the same time, the presence of an RAR means that the terminal needs to monitor the control channel of the candidate cell, which increases interruptions between the terminal and the source cell. Summary of the Invention

[0021] As noted above, fallback for time alignment while in motion currently presents certain challenges. 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.

[0022] Some embodiments include a method in a user equipment (UE) capable of Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) and configured with at least one LTM candidate cell, the method including handling a failed attempt to perform TA establishment and / or TA update (e.g., by the UE performing another preamble transmission).

[0023] The method includes the UE (1) receiving a first downlink (DL) notification from a source network node (e.g., a source distribution unit (DU) (S-DU)); and (2) in response to the first downlink notification, the UE transmitting a first uplink (UL) message (e.g., a first random access (RA) preamble) to the LTM candidate cell, the uplink message being transmitted on a first uplink resource (e.g., an RA resource in time and frequency) using a first transmit power, the first uplink resource being associated with the LTM candidate cell.

[0024] 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 transmitting the first uplink message.

[0025] In some embodiments, the UE also receives a second downlink notification from the source network node (e.g., S-DU). In response to the second downlink notification, the UE also transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell, where the second uplink message (e.g., the second RA preamble) is transmitted to the LTM candidate cell by: i) an increased transmit power compared to the first transmit power; or ii) on a second uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell. Typically, the source network node (e.g., S-DU) transmits the second downlink notification to the UE when the first uplink message is not successfully received (in the candidate DU (C-DU)), although the UE may not necessarily recognize the failure in the C-DU.

[0026] In some embodiments, a second downlink notification is associated with the first downlink notification. Based on the second notification being associated with the first downlink notification, the UE transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell with either 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.

[0027] In some embodiments, in response to receiving the second downlink notification, 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 (e.g., an RA resource in time and frequency) associated with the LTM candidate cell for transmitting the second uplink message.

[0028] Generally speaking, the UE also receives an (n+1)th downlink notification from the source network node (e.g., S-DU). In response to the (n+1)th downlink notification, the UE also transmits an (n+1)th uplink message (e.g., an (n+1)th RA preamble) to the LTM candidate cell, which is transmitted to the LTM candidate cell by either i) an increased transmit power compared to the nth transmit power, or ii) on the (n+1)th uplink resource (e.g., an RA resource in time and frequency) associated with the LTM candidate cell. On the network side, the S-DU continues to transmit a downlink notification to trigger preamble transmission until one or more criteria are met, for example, until the maximum number of attempts is reached, or until an uplink signal / message is successfully received. In other words, this process is repeated until an uplink signal / message is successfully received at the candidate DU and the candidate DU can calculate a TA value, or until the maximum number of attempts is reached (see the network description for further details).

[0029] In some embodiments, the (n+1)th downlink notification is associated with the nth downlink notification. Based on the (n+1)th notification being associated with the nth downlink notification, the UE transmits the (n+1)th uplink message (e.g., the (n+1)th RA preamble) to the LTM candidate cell with either 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.

[0030] In a subordinate step, (3) in response to receiving the (n+1)th downlink notification, the UE selects a kth beam (e.g., SSB or CSI-RS of the LTM candidate cell), and based on the selected kth beam, the UE selects an (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell for transmitting the (n+1)th uplink message.

[0031] In some embodiments, the UE further receives a TA value (calculated by the network according to the second uplink message received at the candidate DU). Different sets of embodiments described herein disclose different ways to provide a TA value, for example, during LTM execution / cell switch to an LTM candidate cell (based on the received second uplink signal, the candidate DU could calculate a TA value for the UE associated with the LTM candidate cell).

[0032] In some embodiments, upon LTM cell switching to an LTM candidate cell (LTM execution), the UE transmits an uplink message on a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) based on the received TA value.

[0033] 2A and 2B are flow diagrams summarizing UE operation in network-based fallback for TA establishment.

[0034] Some embodiments include a method including: in a serving DU (S-DU), the S-DU sending a first downlink notification to a UE, and based thereon, the UE sending a first uplink message (e.g., a first RA preamble) to an LTM candidate cell, the uplink message being transmitted by the UE using a first transmit power and a first uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell; and the S-DU detecting that the first uplink message is not successfully received at a C-DU serving the LTM candidate cell, and in response, sending a second downlink notification associated with the first downlink notification to the UE, and based thereon, the UE also sending a second uplink message (e.g., a second RA preamble) to the LTM candidate cell, the second uplink message being transmitted to the candidate cell via i) an increased transmit power compared to the first transmit power, or ii) on a second uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell.

[0035] In some embodiments, the S-DU receives the TA value (calculated by the C-DU according to the second uplink signal received at the C-DU) from the candidate DU.

[0036] In some embodiments, the S-DU further transmits to the UE a TA value (calculated by the C-DU according to the second uplink signal received in the C-DU), e.g., included in an LTM cell switch command informing the UE to move to the LTM candidate cell.

[0037] In some embodiments, the S-DU determines that the first uplink message is not successfully received at the candidate DU when a supervision timer expires. The timer is started by the S-DU when it sends the first downlink notification to the UE. It 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. Although this is referred to herein as a supervision timer, its function may also be modeled as a time window during which a message from the C-DU is expected to be received, and if it is not received in that time window, the S-DU considers the attempt a failed attempt.

[0038] In some embodiments, the S-DU monitors a counter for the number of uplink signal / message transmission attempts (e.g., the maximum number of RA preamble transmission attempts). Thus, each time the S-DU provides a downlink notification to the UE after the first downlink notification, the counter is incremented. There is a maximum value that this counter can reach, and when it reaches that value, the S-DU declares a failure of the TA establishment procedure. Before the S-DU sends a second notification, it checks whether the maximum value has been reached. If it has, the S-DU declares a TA establishment failure.

[0039] In some embodiments, if the S-DU determines that the first uplink message is not successfully received at the candidate DU, when transmitting a second downlink message to trigger a second RA preamble transmission at the UE, the S-DU may also indicate (e.g., by indicating an LTM configuration ID) the new LTM candidate cell and / or the beam or transmission configuration indicator (TCI) state (from which the second RA preamble needs to be transmitted).

[0040] In some embodiments, the S-DU counts increases in the transmit power of uplink signals / messages. When the transmit power is indicated to be increased by the UE, the S-DU increments a variable. There is a maximum transmit power value, and if this value is reached after retransmissions, the S-DU declares the TA establishment procedure failed.

[0041] Some embodiments include a method including, in a candidate DU (C-DU), detecting whether a first uplink message is successfully received in the C-DU (serving an LTM candidate cell); when the uplink message is successfully received, calculating a TA value based on the received first uplink message and sending the TA value in a message to the S-DU; and when the first uplink message is not successfully received, performing one or more of: i) sending a message to the S-DU (e.g., via a CU) that does not include the TA value; and ii) not sending a message to the S-DU (e.g., via the CU).

[0042] In summary, a method in a UE capable of LTM and configured with at least one LTM candidate cell includes: (1) receiving a first downlink notification from a serving cell (e.g., of a source network node, e.g., a source DU (S-DU)); and (2) in response to the first downlink notification, the UE transmitting a first uplink message (e.g., a first RA preamble) to the first LTM candidate cell, the uplink message being transmitted on a first uplink resource (e.g., an RA resource in time and frequency) using a first transmit power. The method further includes receiving a second downlink notification from the source network node (e.g., the S-DU). In response to receiving the second downlink notification, the method includes transmitting a second uplink message (e.g., a second RA preamble) to the second LTM candidate cell, wherein the second uplink message (e.g., the second RA preamble) is transmitted to the LTM candidate cell with either 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.

[0043] 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.

[0044] 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 with transmitting the first uplink message.

[0045] According to some embodiments, a method is performed by a wireless device for LTM, the method including obtaining an uplink configuration for an LTM candidate cell, receiving from a serving cell a first notification to perform an uplink transmission at the LTM candidate cell, transmitting the first uplink transmission at the LTM candidate cell using a first transmit power and first uplink time / frequency resources, receiving from the serving cell a second notification to perform an uplink transmission at the LTM candidate cell, transmitting a second uplink transmission at the LTM candidate cell, the second uplink transmission being 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 from the serving cell a timing advance value for the LTM candidate cell based on the second uplink transmission.

[0046] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmission of a random access preamble.

[0047] In a particular embodiment, the wireless device does not expect an RAR in response to transmitting a random access preamble.

[0048] In a particular embodiment, the first uplink transmission uses the first beam, and in response to receiving a second notification to perform the uplink transmission, the method further includes selecting a second beam for use for the second uplink transmission, wherein when the second beam is the same as the first beam, the second transmission is transmitted at a second transmit power different from the first transmit power, and when the second beam is different from the first beam, the second transmission is transmitted on a second uplink time / frequency resource different from the first time / frequency resource.

[0049] In certain embodiments, the second notification to perform an uplink transmission comprises a notification of a second transmit power or a notification of a second uplink time / frequency resource to be used for the second uplink transmission.

[0050] In a particular embodiment, the first notification and the second notification comprise a PDCCH command.

[0051] In a particular embodiment, receiving a timing advance value from the serving cell includes receiving an LTM execution command.

[0052] In a particular embodiment, the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

[0053] In a particular embodiment, at least one of the first notification and the second notification includes a notification of an SSB associated with the first uplink transmission or the second uplink transmission, respectively.

[0054] In a particular embodiment, the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes a notification of an uplink candidate cell from which to transmit the first uplink transmission or the second uplink transmission, respectively.

[0055] According to some embodiments, a wireless device has processing circuitry operable to perform any of the wireless device methods described above.

[0056] Another computer program product includes a non-transitory computer-readable medium storing computer-readable program code, which, when executed by a processing circuit, is operable to perform any of the methods performed by the wireless device described above.

[0057] According to some embodiments, a method is performed by a network node operating as an S-DU for TA management between a wireless device and at least one LTM candidate cell, the method including: sending a first notification to the wireless device to perform an uplink transmission in the LTM candidate cell; and sending a second notification to the wireless device to perform an uplink transmission in the LTM candidate cell.

[0058] In a particular embodiment, the method further includes, upon detecting that the uplink transmission in the LTM candidate cell has failed, sending a second notification to the wireless device to perform the uplink transmission in the LTM candidate cell.

[0059] In certain embodiments, detecting that the uplink transmission at the LTM candidate cell has failed includes not receiving a response from the LTM candidate cell or receiving an indication from the LTM candidate cell that the uplink transmission at the LTM candidate cell has failed.

[0060] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmission of a random access preamble.

[0061] In a particular embodiment, the second notification to perform an uplink transmission includes notification of a transmit power or uplink time / frequency resources to use for the second uplink transmission.

[0062] In a particular embodiment, the first notification and the second notification include a PDCCH order.

[0063] In a particular embodiment, the method further includes receiving a timing advance value from the candidate LTM cell and transmitting the timing advance value to the wireless device.

[0064] In a particular embodiment, transmitting the timing advance value to the wireless device includes transmitting an LTM execution command to the wireless device.

[0065] In a particular embodiment, sending the second notification to the wireless device to perform the uplink transmission includes determining a threshold number of uplink transmissions for the wireless device, the LTM candidate cell not to be exceeded.

[0066] In certain embodiments, the method further includes transmitting an uplink configuration for the uplink candidate cell to the wireless device. The uplink configuration for the uplink candidate cell may have one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively. The uplink configuration for the uplink candidate cell may include two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes an indication of the uplink candidate cell from which to transmit the first uplink transmission or the second uplink transmission, respectively.

[0067] In a particular embodiment, at least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

[0068] According to some embodiments, the network node includes processing circuitry operable to perform any of the network node methods described above.

[0069] Another computer program product includes a non-transitory computer-readable medium storing computer-readable program code that, when executed by a processing circuit, is operable to perform any of the methods performed by the network node described above.

[0070] 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 is a cell that may not be uplink synchronized with the serving cell for which the UE is configured and, as a result, may not be uplink synchronized with the UE. Accordingly, certain embodiments enable the UE to perform an LTM cell switch (e.g., upon reception of a MAC CE for LTM) and transmit uplink information to the candidate cell (e.g., on a PUSCH or PUCCH) without first having to perform an RA procedure, which reduces interruption time during LTM execution and leads to more efficient use of network radio resources and better UE energy consumption.

[0071] Additionally, an advantage of certain embodiments is the possibility 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, so that when a candidate DU fails to detect a previous preamble transmission, it is possible to trigger a retransmission of an uplink message to the candidate LTM, making TA establishment and update more robust, efficient, and unambiguous in interoperable networks.

[0072] Certain embodiments include a network-based fallback for TA establishment. In one set of embodiments, the UE transmits an RA preamble to the LTM candidate cell but does not rely on receiving an RAR at the LTM candidate cell. Thus, the interruption time with the serving cell for the TA establishment and update procedures is minimized, which is beneficial to the data rate provided by the serving cell because more data can be scheduled (because there will be fewer scheduling restrictions imposed by the serving cell). At the same time, without an RAR, the UE could not determine whether the attempted transmission was successful. The advantage of network-based fallback is that the S-DU determines whether the attempt was successful and, if it was not successful, notifies the UE to transmit another uplink signal / message; for example, the S-DU notifies the UE of the need for a fallback, such as power ramping and / or beam selection.

[0073] In other words, some differences compared to the RA procedure are that i) the downlink notification 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), and ii) the receipt of the downlink notification indicates a failed attempt, as opposed to an RAR, which indicates a successful attempt. Another difference compared to the legacy RA procedure is that the monitoring of failed and successful attempts is performed on the network side rather than in the UE, offloading some responsibility from the UE. [Brief explanation of the drawings]

[0074] For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: [Figure 1A] FIG. 1A is a flowchart illustrating an example of timing advance (TA) establishment based on sending a random access (RA) preamble to a candidate and receiving a TA value only during Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) execution; [Figure 1B] FIG. 1B is a flowchart illustrating an example of timing advance (TA) establishment based on sending a random access (RA) preamble to a candidate and receiving a TA value only during Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) execution; [Figure 2A] Figure 2A is a flow diagram summarizing UE operations in network-based fallback for TA establishment; [Figure 2B] Figure 2B is a flow diagram summarizing UE operations in network-based fallback for TA establishment; [Figure 3] Fig. 3 is a block diagram showing the architecture of the central unit (CU) and distributed units (DU) in the radio access network (RAN); [Figure 4A] Figure 4A shows the Abstract Syntax Notation (ASN) for six examples of LTM candidate configurations; [Figure 4B] Figure 4B shows the Abstract Syntax Notation (ASN) for six examples of LTM candidate configurations; [Figure 5A] FIG. 5A is a flowchart illustrating an example of steps for LTM configuration and TA establishment / update, according to certain embodiments; [Figure 5B] FIG. 5B is a flowchart illustrating an example of steps for LTM configuration and TA establishment / update, according to certain embodiments; [Figure 5C] FIG. 5C is a flowchart illustrating an example of steps for LTM configuration and TA establishment / update, according to certain embodiments; [Figure 6A] FIG. 6A is a flowchart illustrating the fallback procedure for the TA update procedure; [Figure 6B] FIG. 6B is a flowchart illustrating the fallback procedure for the TA update procedure; [Figure 6C] FIG. 6C is a flowchart illustrating the fallback procedure for the TA update procedure; [Figure 7A] FIG. 7A is a flowchart illustrating another fallback procedure for the TA update procedure; [Figure 7B] FIG. 7B is a flowchart illustrating another fallback procedure for the TA update procedure; [Figure 7C] FIG. 7C is a flowchart illustrating another fallback procedure for the TA update procedure; [Figure 8A] FIG. 8A is a flowchart showing an example of the operation in the S-DU when detecting a TA establishment failure; [Figure 8B] FIG. 8B is a flowchart illustrating an example of an operation in the S-DU when a TA establishment failure is detected; [Figure 9] FIG. 9 illustrates an exemplary communication system, according to certain embodiments; [Figure 10] FIG. 10 illustrates an exemplary user equipment (UE) in accordance with certain embodiments; [Figure 11] FIG. 11 illustrates an exemplary network node according to certain embodiments; [Figure 12] FIG. 12 illustrates a method performed by a user equipment according to a particular embodiment; and [Figure 13] FIG. 13 illustrates a method performed by a network node according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0075] As noted above, fallback for time alignment while in motion currently presents certain challenges. 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.

[0076] Certain embodiments are more fully described with reference to the accompanying drawings. However, other embodiments are included within the scope of the subject matter disclosed herein. The disclosed subject matter should not be construed as limited to only the embodiments described herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

[0077] 3 is a block diagram illustrating an architecture of a central unit (CU) and distributed units (DUs) in a radio access network (RAN). In the illustrated example, the RAN is a next generation RAN (NG-RAN), which may be referred to as a fifth generation (5G) RAN, although certain embodiments are applicable to any RAN, such as a sixth generation (6G) RAN architecture.

[0078] The illustrated architecture (with both NG-RAN and 5GC) shows an NG-RAN split with CU and DU connected via an F1 interface. The RAN (e.g., NG-RAN) consists of a set of RAN nodes (e.g., gNBs) connected to a core network (e.g., 5GC) via a RAN / CN interface (e.g., NG interface). In the case of an NG-RAN, it may include one or more ng-eNBs, which may consist of an ng-eNB-CU and one or more ng-eNB-DUs. A gNB may consist of a gNB-CU and one or more gNB-DUs. The gNB-CU and gNB-DUs are connected via an F1 interface. A gNB-DU may be connected to multiple gNB-CUs, depending on the appropriate implementation.

[0079] NG, Xn, and F1 are logical interfaces. In NG-RAN, the NG and Xn-C interfaces for a gNB consisting of a gNB-CU and a gNB-DU terminate at the gNB-CU. In EN-DC, the S1-U and X2-C interfaces for a gNB consisting of a gNB-CU and a gNB-DU terminate at the gNB-CU. The gNB-CU and the connected gNB-DU are seen only as a gNB by other gNBs and 5GC.

[0080] Some embodiments refer to a Serving DU or a Source DU, the acronym of which is used interchangeably as S-DU. The S-DU may correspond to a gNode-DU responsible for one or more serving cells to which a user equipment (UE) is configured.

[0081] In some embodiments, the CU refers to the CU to which the UE is connected, e.g., the CU where higher layer protocols for communication with the UE (e.g., Radio Resource Control (RRC)) are terminated and where the UE Access Stratum (AS) context is stored.

[0082] Some embodiments refer to a candidate DU (C-DU) that refers to a DU (which may correspond to a gNodeB-DU) that is responsible for a Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) candidate cell on which a UE is configured. As part of the LTM configuration, the CU sends a request to the C-DU to configure an LTM candidate cell for the UE. In response, the CU receives at least an LTM candidate cell configuration, which is a configuration based on which the UE determines the configuration that the UE should use when switching to that LTM candidate cell during an LTM execution (also called an LTM cell switch).

[0083] The text refers to the term "L1 / L2-based inter-cell mobility" used in the 3GPP work item description, but also uses 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 interchangeably. The basic principle is that the UE receives lower layer signaling from the network that indicates to the UE a change (or switch or activation) of its serving cell (e.g., a change of PCell from source to target PCell), where the lower layer signaling is a message / signaling of a lower layer protocol that may be called an L1 / L2 inter-cell mobility execution command (or LTM cell switch command). A change of serving cell (e.g., a change of PCell) may result in a change of Scell ​​for 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 switch command, the UE is configured by the network with one or more LTM candidate cells (e.g., receiving an RRC Reconfiguration message with at least one candidate cell configuration). The candidate cell configuration may include parameters in an information element (IE) CellGroupConfig for each candidate cell and / or an embedded RRC Reconfiguration for each candidate cell.

[0084] A lower layer protocol refers to a lower layer protocol in the air interface protocol stack compared to the RRC protocol. For example, Medium Access Control (MAC) is considered a lower layer protocol because it is "below" RRC in the air interface protocol stack. In this case, the lower layer signaling / message may correspond to a MAC Control Element (MAC CE). Another example of a lower layer protocol is Layer 1 (or Physical Layer (L1)). In this case, the lower layer signaling / message may correspond to Downlink Control Information (DCI). Signaling information at a protocol layer lower than RRC reduces processing time and, as a result, reduces interruption time during transitions. In addition, it may also increase mobility robustness because the network can respond to faster changes in channel conditions.

[0085] Another related aspect in L1 / L2 inter-cell mobility is that in a multi-beam scenario, a cell may be associated with multiple synchronization signal blocks (SSBs), and during a half-frame, different SSBs may be transmitted in different spatial directions (e.g., using different beams across the cell's coverage area). Similar reasoning may be applicable to channel state information reference signal (CSI-RS) resources, which may also be transmitted in different spatial directions. Thus, in L1 / L2 inter-cell mobility (LTM), reception of lower layer signaling indicates that the UE should change from one beam in the serving cell to another beam in a neighboring cell (which is a configured candidate cell), and the change results in a change of serving cell.

[0086] The term LTM cell switch procedure refers to a process in which a UE changes its cell from a source cell to a target cell (which may be called 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 switch procedure may be referred to as dynamic switch, LTM switch, LTM cell switch, LTM serving cell change, or LTM cell change. Even when the term cell change is used, it may include changes to the configuration of an entire cell group, including changes in an SpCell (e.g., a PCell change or a PSCell change) and changes in the SCells of the cell group (e.g., adding, modifying, and / or releasing one or more SCells).

[0087] In some examples, the term target candidate configuration (or candidate cell configuration, or LTM candidate cell configuration, or LTM candidate cell configuration) is used to refer to the configuration of an "L1 / L2 inter-cell mobility candidate cell," which is a cell to which a UE is configured when configured for L1 / L2 inter-cell mobility. It is a cell to which the UE can move in an L1 / L2 inter-cell mobility procedure upon receiving lower layer signaling (e.g., a MAC CE containing an LTM candidate cell configuration identifier). These cells may be referred to as candidate cells, candidates, mobility candidates, non-serving cells, additional cells, target candidate cells, target candidates, etc. This is a cell on which the UE performs measurements (e.g., CSI measurements) so that the UE reports these measurements and the network can make an informed decision on which beam (e.g., transmission configuration indicator (TCI) state) and / or cell to which the UE should be switched. The L1 / L2 inter-cell mobility candidate cell may be a candidate for the target PCell or PSCell, or a SCell of a cell group (e.g., an MCG SCell).

[0088] The term "beam" may 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 the transmitted or received signal. Thus, transmitting signals on different beams may correspond to transmitting signals in different spatial directions. When the text refers to a "selected beam," it may refer to a beam index and / or a reference signal (RS) index or identifier (e.g., an SSB index, or a CSI-RS resource identifier). Thus, selecting a beam may correspond to selecting an SSB associated with an SSB index. Or, selecting a beam may correspond to selecting a CSI-RS associated with a CSI-RS resource identifier.

[0089] The actual LTM candidate configuration and its content and / or structure of this IE and / or embedded message may be referred to as the RRC model for candidate configuration, or simply the RRC model. The LTM candidate cell configuration includes the configuration that the UE needs to act upon when, upon receiving lower layer signaling indicating L1 / L2-based inter-cell mobility to that target candidate cell (which will be the target cell and the current (new) PCell or SCell in the serving frequency), the UE performs an L1 / L2 inter-cell mobility execution to that target candidate cell. A UE may be configured to multiple target candidate cells, and the candidate DU generates and sends multiple configurations to the CU. The target candidate configuration includes at least parameters of the serving cell (or multiple serving cells), including one or more of the group of parameters in the IE SpCellConfig (or the IE SCellConfig for secondary cells). The actual LTM candidate cell configuration that the UE receives during LTM configuration may be differential signaling to be applied on top of the reference configuration, and the actual configuration that the UE should use in the candidate cell upon LTM cell switch is a combination of the LTM candidate cell configuration and the reference configuration (e.g., signaled separately by the network to the UE).

[0090] Some examples of how signaling can be implemented in RRC for LTM candidate configurations are described as RRC models for L1 / L2-based inter-cell mobility, including the following: One example involves RRC reconfiguration per candidate cell. In this case, the UE receives multiple (list) RRC messages (e.g., RRC Reconfiguration messages) within a single RRC Reconfiguration message. Each RRC Reconfiguration message identifies target candidate configurations that are stored by the UE and applied / used / activated when receiving lower layer signaling for L1 / L2 inter-cell mobility. This model allows full flexibility, as in L3 reconfiguration, for the target node to modify / release / retain any parameters / fields in the RRC Reconfiguration message, such as measurement configuration, bearers, etc.

[0091] Another example includes a CellGroupConfig per candidate cell. In this model, the UE receives a list of CellGroupConfig IEs in the RRCReconfiguration, each one of which identifies a target candidate configuration. Each CellGroupConfig IE is stored in the UE and applied / used / activated when receiving lower layer signaling for L1 / L2 inter-cell mobility. This model makes it easy for the target node to modify / release / retain any parameters / fields that are part of the CellGroupConfig IE, while the rest of the RRCReconfiguration message (i.e., the part where the CellGroupConfig IE is received by the UE) remains unchanged. This means, for example, that measurement configurations, bearers, and security remain the same and are not changed by the target node.

[0092] Another example includes "K" SpCellConfigs or "K" ServingCellConfigCommons per cell, or both. In this model, the UE receives as target candidate configurations either "K" SpCellConfigs per cell, "K" ServingCellConfigCommons per cell, or "K" SpCellConfigs and "K" ServingCellConfigCommons per cell. This solution provides only minimal flexibility to the target node, as only cell-specific parameters (e.g., bandwidth fraction, downlink, and uplink configurations) can be modified / released / retained.

[0093] Another example includes "K" PCIs on the same PCell. In this model, multiple PCIs are configured for the same TCI state configuration, with each PCI identifying a target candidate configuration. This is an approach that offers less flexibility, as all parameters / fields used to configure the target candidate configuration are fixed, and the target node is only allowed to change the PCI, scrambling Id, and C-RNTI. Examples are shown in Figures 4A and 4B.

[0094] 4A and 4B show Abstract Syntax Notation (ASN) for six examples of LTM candidate configurations. The 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) having one or more target candidate cell configurations. The L1 / L2 inter-cell mobility configuration may include multiple target candidate cell configurations when the UE is configured with multiple target candidate cells for L1 / L2 inter-cell mobility. The L1 / L2 inter-cell mobility configuration may be included in an RRC Reconfiguration message (as defined in TS 38.331) or an RRC Resume message that the UE receives, for example, during a state transition to RRC_CONNECTED.

[0095] The L1 / L2 inter-cell mobility configuration may be generated by a CU (e.g., gNB-CU) and includes information generated and transmitted from a candidate DU, such as a target candidate cell configuration and / or a measurement configuration that indicates to the UE to perform measurements on the reference signaling (RS) (e.g., SSB and / or CSI-RS resources) of the target candidate cell, for reporting to the network to assist in the L1 / L2 inter-cell mobility execution decision.

[0096] The first, second, nth, or (n+1)th downlink notification that triggers the UE to send an uplink message to the LTM candidate cell to establish or update the TA may correspond to RRC signaling, such as an RRC message (RRC Reconfiguration) and / or IEs and / or fields associated with the LTM candidate cell, MAC signaling, such as a MAC CE (e.g., a 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 indicating, in some cases, notification of beam and / or count values ​​and / or power levels for transmission of uplink messages to the candidate cell.

[0097] The first, nth, or (n+1)th uplink message transmitted by the UE to the candidate cell to establish or update the TA may correspond to a random access (RA) preamble, a sequence having at least one similar property to the RA preamble (e.g., mutually orthogonal, semi-orthogonal, low correlation property, etc.), and / or a sequence that may be transmitted in the uplink channel of the LTM candidate cell that does not require the UE to be tightly synchronized with the uplink of the LTM candidate cell.

[0098] Some examples refer to a TA value, which may refer to a timing advance value. Some examples refer to a TA timer, which may correspond to a time alignment timer.

[0099] As used herein, a "TA value" may correspond to an actual TA value to be applied or a notification to a TA value, such as an integer value, received by a UE that maps to an actual TA value or shift to be applied for an uplink transmission. One example of a TA value is a timing advance command that includes multiple bits indicating an index value, TA, used to control the amount of timing adjustment that a MAC entity must apply to candidate uplink transmissions, e.g., on a sounding reference signal (SRS), a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), etc.

[0100] One set of embodiments includes an embodiment for a network-controlled fallback TA establishment / update procedure. In the set of embodiments, a UE that is LTM-capable and configured for at least one LTM candidate cell (1) receives a first downlink notification from a source network node (e.g., a source DU (S-DU)), which may correspond to a PDCCH command that may follow a previous configuration of the LTM candidate cell. In response to the first downlink notification, the UE transmits a first uplink message (e.g., a first RA preamble) to the LTM candidate cell, the uplink message being transmitted at a first transmit power, and the UE transmits the uplink message on 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 for transmitting the first uplink message.

[0101] The S-DU, which may be called the Serving DU (with the same acronym S-DU), detects when the first uplink message (e.g., RA preamble) is not successfully received at the Candidate DU, which is called a preamble transmission failure for TA establishment / update.

[0102] In one option, the S-DU detects the failure of the preamble transmission for TA establishment / update by the expiration of a timer. The S-DU starts the timer when it sends the first downlink notification to the UE, and while the timer is running, the S-DU expects a message from the candidate DU (C-DU) containing the TA value calculated by the C-DU based on the reception of an uplink message (RA preamble sent by the UE to the LTM candidate cell) via the interface directly between the S-DU and the C-DU (e.g., E5 interface) and / or CU (from the C-DU to the S-DU via the F1AP interface). When the timer expires and the S-DU does not receive a message containing the TA value, the S-DU considers the preamble transmission for TA establishment / update to be a failure.

[0103] In one option, the S-DU detects the failure of the preamble transmission for TA establishment / update by receiving a failure notification from a candidate DU (associated with the candidate cell to which the UE sends an uplink message) directly via the interface between the S-DU and the C-DU (e.g., E5 interface) and / or CU (C-DU to S-DU via F1AP interface). The S-DU sends a first downlink notification to the UE, expecting a message containing the TA value calculated by the C-DU based on the reception of the uplink message (RA preamble sent by the UE to the LTM candidate cell). When the S-DU receives the failure notification from the C-DU, the S-DU considers the preamble transmission for TA establishment / update to be a failure.

[0104] In one option, the S-DU detects a preamble transmission failure for TA establishment / update due to reception of a message from a candidate DU (associated with the candidate cell to which the UE transmits an uplink message) directly via the interface between the S-DU and the C-DU (e.g., the E5 interface) and / or the CU (via the F1AP interface from the C-DU to the S-DU) where the TA value is not present in the message. The S-DU sends a first downlink notification to the UE, expecting a message containing the TA value calculated by the C-DU based on reception of the uplink message (the RA preamble that the UE transmits to the LTM candidate cell). If the S-DU receives a message from the C-DU where the TA value is not present, the S-DU considers it a preamble transmission failure for TA establishment / update.

[0105] When the S-DU detects that the first uplink message (e.g., RA preamble) is not successfully received in the C-DU (preamble transmission failure for TA establishment / update), the S-DU sends a second downlink notification to the UE, which may be called a fallback for TA establishment triggered by the S-DU.

[0106] The UE further receives a second downlink notification from the S-DU, based on which the UE transmits a second uplink message (e.g., a second RA preamble) to the candidate cell, and the second uplink message (e.g., the second RA preamble) transmitted to the candidate cell is transmitted according to: i) an increased transmission power compared to the first transmission power; or ii) a second uplink resource (e.g., an RA resource in time and frequency) associated with the LTM candidate cell.

[0107] In some embodiments, a second downlink notification is associated with the first downlink notification. Based on the second downlink notification being associated with the first downlink notification, the UE transmits a second uplink message (e.g., a second RA preamble) to the LTM candidate cell with either 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.

[0108] In some embodiments, in response to receiving the second downlink notification, the UE selects a second beam (e.g., SSB or CSI-RS of the LTM candidate cell), and based on the selected second beam, the UE selects a second uplink resource (e.g., RA resource in time and frequency) associated with the LTM candidate cell for transmitting the second uplink message.

[0109] In some embodiments, the UE further receives a TA value (calculated according to the second uplink signal received at the candidate DU). Different sets of embodiments include, for example, different ways to provide a TA value to the LTM candidate cell during LTM execution / cell switching (based on the received second uplink signal, the candidate DU could calculate a TA value for the UE associated with the LTM candidate cell).

[0110] In some embodiments, in an LTM cell switch (LTM execution) to a candidate cell, the UE transmits an uplink message on the PUCCH or PUSCH based on the received TA value.

[0111] In some embodiments, the UE transmits a second uplink message to the candidate cell, and the S-DU detects another preamble transmission failure for TA establishment / update, and in response to the failure detection, the S-DU transmits a third downlink notification (e.g., a fallback for TA establishment triggered by the S-DU) to the UE.

[0112] The UE further receives a third downlink notification from the S-DU based on the UE transmitting a third uplink message (e.g., a third RA preamble) to the candidate cell, and the third uplink message (e.g., the third RA preamble) transmitted to the candidate cell is transmitted according to i) an increased transmission power compared to the second transmission power, or ii) a third uplink resource (e.g., an RA resource in time and frequency) associated with a third beam selected by the UE.

[0113] In some embodiments, attempts to establish a TA (fallback) are repeated until one or more conditions are met. The fallback for TA establishment includes transmitting an (n+1)th downlink notification to the UE after the S-DU provided an nth downlink notification that resulted in a preamble transmission failure for TA establishment / update, where the (n+1)th downlink notification indicates to the UE transmission of an (n+1)th uplink message with an increased or incremental transmit power compared to the transmit power of the nth uplink message transmission, or indicating that the transmission of the (n+1)th uplink message should be directed to the (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the (n+1)th beam selected by the UE.

[0114] 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 that the number of preamble transmission failures for TA establishment / update reaches a maximum value for a given LTM candidate cell and / or UE.

[0115] In one option, the maximum value may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0116] 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 its maximum value before sending a downlink notification to the UE. When the S-DU determines that the counter has reached its maximum value, it does not send a downlink notification and considers the TA establishment to be a failure: called a TA establishment failure.

[0117] In other words, when the number of failed preamble transmissions for TA establishment reaches a maximum value, the S-DU declares the TA establishment failure.

[0118] In one option, the maximum number of preamble transmission failures for TA establishment may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0119] In some embodiments, the S-DU detects that the UE has reached the maximum transmit power for transmitting uplink messages to the LTM candidate cell, which may be reached after multiple transmit power increases following failed preamble transmissions for TA establishment.

[0120] In one option, the maximum transmit power for TA establishment may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0121] 5A, 5B, and 5C are flowcharts illustrating example steps for LTM configuration and TA establishment / update, according to certain embodiments. This example illustrates a failed RA preamble transmission attempt for TA establishment for LTM. Steps 1 through 4b include configuring the UE with an LTM candidate cell and configuring TA establishment and / or update.

[0122] In one set of embodiments, the UE transmits, in frequency, an RRC Measurement Report message to the network (e.g., the CU) including measurements on one or more neighboring cells (e.g., cell-based Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and / or Signal-to-Interference-and-Noise Ratio (SINR)), potentially including beam measurement information (which is later used to configure the TA establishment procedure). The report is sent in response to a network configuration, and the UE is configured by the network (e.g., by the CU) to transmit an RRC Measurement Report including the neighboring cells and the serving cell (e.g., based on meeting conditions related to A3 and / or A5 measurement events, as defined in TS 38.331).

[0123] Depending on the reporting configuration, the UE includes beam measurement information (based on the measurement configuration) for one or more neighboring cells in the RRC measurement report, such as the RSRP and / or RSRQ and / or SINR of one or more beams (e.g., of one or more SSB and / or CSI-RS resources) of the neighboring cell with an associated beam identifier (e.g., SSB index and / or CSI-RS resource identifier) ​​or only the beam identifier.

[0124] The network (e.g., CU, gNB-CU) may decide to configure the UE for L1 / L2 inter-cell mobility and may decide to request the configuration of one or more neighboring cells included in the RRC measurement report as target candidate cells for L1 / L2 inter-cell mobility.

[0125] In one set of embodiments, a CU (e.g., gNB-CU, gNB) sends a request message to a candidate DU (e.g., via a candidate gNB-DU, 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 this is a request for cells of the same candidate DU. In one option, the CU sends requests for multiple candidate DUs in the same candidate DU, one per target candidate cell, and / or one for multiple target candidate cells. The requested target candidate cell may be one of the neighbor cells included in an RRC measurement report that the CU may have received.

[0126] In one set of embodiments, the CU further requests the candidate DU to establish a TA between the UE and at least one of its target candidate cells, for example by including the notification thereof in the above-mentioned request message. When the CU decides 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 in the uplink and decides to request a TA establishment to the candidate DU (serving the target candidate cell). This may be referred to as CU-initiated TA establishment for L1 / L2 inter-cell mobility.

[0127] In one embodiment, the CU includes a TA establishment request for each target candidate cell for which it wants a TA to be established, e.g., if they are in different candidate DUs or the same candidate DU but in different TRPs.

[0128] In one embodiment, the CU sends requests to establish TA to multiple candidate DUs, one for each target candidate cell.

[0129] In one embodiment, the CU sends a request to establish TA to a set of target candidate cells in the same candidate DU. In one embodiment, the CU further includes in the request to the candidate DU beam measurement information associated with the requested target candidate cells (e.g., beam measurements for one or more SSBs of the candidate DU's requested target candidate cells). This enables the candidate DU to generate an uplink configuration based on the beam measurement information, e.g., physical random access channel (PRACH) preambles mapped to one or more SSBs reported as sufficiently good / suitable in terms of RSRP and / or RSRQ and / or SINR.

[0130] In one embodiment, the request message from the CU to the candidate DU may correspond to a UE Context Setup Request (F1AP message).

[0131] In one embodiment, the request for establishment of a TA between the UE and at least one of its target candidate cells is signaled (encoded as an IE) in a UE Context Setup Request (F1AP message).

[0132] In one embodiment, the request message from the CU to the candidate DU may correspond to a UE Context Modification Request (F1AP message), for example, if the candidate DU is the same as the serving DU.

[0133] In one embodiment, the request for establishment of a TA between the UE and at least one of its target candidate cells is a notification (encoded as an IE) in a UE Context Modification Request (F1AP message), for example, if the candidate DU is the same as the serving DU.

[0134] In one embodiment, the request for establishment of a TA between the UE and at least one of its candidate cells includes a request for the S-DU to perform a TA establishment fallback when detecting a preamble transmission failure for TA establishment.

[0135] In one set of embodiments, when a CU decides to configure LTM for at least one target candidate cell in a candidate DU, this represents an implicit request for the candidate DU that TA establishment is necessary, and the candidate DU then decides by itself whether to provide one TA that is valid for all of the configured L1 / L2 inter-cell mobility target candidate cells, or one TA for each of the L1 / L2 inter-cell mobility target candidate cells.

[0136] In one set of embodiments, when a CU decides to configure TA establishment for an LTM candidate cell in a candidate DU, this represents an implicit request for the candidate DU that TA establishment fallback may be required. The candidate DU may respond by providing one or more parameters for the S-DU and / or CU to control the TA establishment fallback procedure and / or to enable the S-DU to perform detection of preamble transmission failures for TA establishment, such as the maximum number of uplink signal (e.g., RA preamble) transmission attempts by the UE for TA establishment, which is configured by the C-DU responsible for the LTM candidate cell, that is the C-DU that configured the uplink resources for TA establishment and / or update. In one option, this is configured per LTM candidate cell. In another option, this is configured per C-DU, e.g., a single value is valid for any LTM candidate cell from that C-DU.

[0137] Another parameter may be the maximum number of transmit power increments for uplink messages that the UE sends to configured LTM candidate cells. In one option, the transmit power increments (e.g., in dB) and / or increment steps are provided to the UE in the uplink channel configuration for TA establishment. In one option, the transmit power increments (e.g., in dB) are provided to the S-DU (e.g., via the CU).

[0138] Another parameter may be the value of a watchdog timer that the S-DU monitors to detect failures in uplink signal transmissions for TA establishment / update. In one option, the S-DU detects failures in preamble transmissions for TA establishment / update by the expiration of the watchdog timer.

[0139] When the S-DU sends the first downlink notification to the UE, it starts a watchdog timer. While the timer is running, the S-DU expects a message from the candidate DU containing the TA value calculated by the C-DU based on the reception of an uplink message (RA preamble sent by the UE to the LTM candidate cell) via the interface directly 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). When the timer expires and the S-DU does not receive a message containing the TA value, the S-DU considers the preamble transmission for TA establishment / update to be a failure. This triggers the S-DU to initiate a fallback, e.g., by sending a second downlink notification to the UE, which triggers the UE to transmit 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).

[0140] Another parameter may include one or more parameters of a time window (such as a C-DU response time window, start time, duration, etc.) that the S-DU monitors to detect an uplink signal transmission failure for TA establishment / update. In one option, the S-DU detects a preamble transmission failure for TA establishment / update by the end of the time window.

[0141] In another embodiment, the S-DU expects a message from the candidate DU directly via the interface between the S-DU and the C-DU (e.g., E5 interface) and / or CU (C-DU to S-DU via F1AP interface) containing the TA value calculated by the C-DU based on the reception of an uplink message (RA preamble sent by the UE to the LTM candidate cell) before the end of the time window. If the time window ends and the S-DU does not receive a message containing the TA value, the S-DU considers the preamble transmission for TA establishment / update to be a failure.

[0142] In one set of embodiments, the candidate DU accepts a request to configure LTM (for at least one LTM candidate cell) and accepts a request to establish a TA for at least one LTM candidate cell (or multiple LTM candidate cells). In that case, the candidate DU responds to the request from the CU with a response message that includes an LTM candidate configuration (e.g., for LTM candidate cell X) and an uplink configuration for establishing a TA between the UE and the LTM candidate cell (e.g., LTM candidate cell X). The UE later receives the uplink configuration (see step 4a).

[0143] In one embodiment, the response message also includes an indication that the TA establishment has been accepted by the candidate DU, e.g., as an IE in an F1AP message in addition to the uplink configuration. This may be needed so that the serving DU does not need to parse the RRC fields in the response message to discover the uplink configuration and determine acceptance for the TA establishment. The serving DU may need it if the trigger for TA establishment later leads to a message with the TA value from the candidate DU to the serving DU (via the CU).

[0144] In one embodiment, the response from the candidate DU may correspond to a UE Context Setup Response (F1AP message).

[0145] In one embodiment, the response from the candidate DU may correspond to a UE Context Modification Response (F1AP message), for example, if the candidate DU is the serving DU, which may be the case if the requested target candidate cell is within the serving DU.

[0146] In one embodiment, the uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., LTM candidate cell X) is valid for multiple uplink signal / message transmissions to cover fallback cases when the first uplink message is not successfully received in the C-DU.

[0147] In one embodiment, the response from the candidate DU includes one or more parameters for the S-DU and / or CU to control fallback for the TA establishment / update procedure and / or to enable the S-DU to perform detection of preamble transmission failure for TA establishment. The one or more parameters may include at least the parameters disclosed in the previous step, such as the maximum number of uplink signal (e.g., RA preamble) transmission attempts by the UE for TA establishment, the maximum number of transmit power increases for uplink messages sent by the UE to the configured LTM candidate cell, the value of a watchdog timer that the S-DU monitors to detect uplink signal transmission failure for TA establishment / update, and / or one or more parameters of a time window (C-DU response time window, start time, duration, etc.) that the S-DU monitors to detect uplink signal transmission failure for TA establishment / update.

[0148] Further details about the uplink configuration for establishing a TA between the UE and the target candidate cell are provided later in steps 4 and 5 when the UE receives the uplink configuration.

[0149] The uplink configuration for TA establishment may include one or more parameters for TA establishment fallback, such as i) initial transmit power for uplink signals / messages, ii) power step increment if fallback is triggered by the network, e.g., when the UE receives a second downlink notification, iii) 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.).

[0150] In one set of embodiments, a candidate DU accepts a request to configure LTM (for at least one LTM candidate cell) but rejects a request to establish TA for at least one LTM candidate cell (or multiple LTM candidate cells). In that case, the candidate DU responds to the request from the CU with a response message including an LTM candidate configuration (e.g., for LTM candidate cell X). It may potentially include a notification of the rejection of the TA establishment, which may include the inclusion or absence (e.g., absence or presence of an F1AP IE) of a parameter or configuration in the response message. In this scenario, the serving DU becomes aware that when LTM is performed for that target candidate cell, random access with the target candidate may be required during the execution to establish TA / uplink synchronization.

[0151] In one set of embodiments, the candidate DU rejects the request to set up the LTM and sends a message to the CU indicating the rejection, potentially including a cause value, for example, overload.

[0152] In one set of embodiments, it is the candidate DU that requests establishment of the target candidate cell for LTM and TA for the UE (for at least one target candidate cell). In that case, the candidate DU responds to the request from the CU for L1 / L2 inter-cell mobility with a response message that includes an LTM candidate configuration (e.g., for LTM candidate cell X) and includes an uplink configuration for establishing TA between the UE and the LTM candidate cell (e.g., LTM candidate cell X), which may serve as notification that the candidate DU is requesting TA establishment between the UE and one or more of the LTM candidate cells. The UE later receives the uplink configuration (see step 4a).

[0153] Steps 3a) and 3b) can be used by the serving DU to include reconfiguration of the serving cell, e.g., reconfiguring CSI measurements, before the UE is configured for LTM. In that case, the CU generates an RRC reconfiguration (e.g., RRC Reconfiguration) message including the Cell Group Configuration generated by the serving DU. The CU also includes an LTM configuration with one or more LTM candidate cell configurations and configurations necessary for the UE to establish a target association (TA) with one or more target candidate cells for LTM.

[0154] In one embodiment, the S-DU determines the scheduling restrictions that need to be applied when the UE expects to send uplink signals / messages to an LTM candidate cell for TA establishment / update and fall back to that TA establishment / update. In other words, the scheduling restrictions refer to the serving cell slots / frames and subframes in which the S-DU will not schedule the UE while the UE is sending uplink messages to an LTM candidate cell for TA establishment and / or update.

[0155] In one set of embodiments, the UE receives an RRC reconfiguration (e.g., an RRCReconfiguration message from the CU via the serving DU) to configure LTM, where the message includes an LTM configuration to configure one or more LTM candidate cells, e.g., an LTM configuration including one or more LTM candidate cell configurations, and an uplink configuration to establish a TA between the UE and the LTM candidate cell (e.g., candidate cell X), as described in step 2(b).

[0156] In one embodiment, a UE receives an uplink configuration for establishing a TA for an LTM candidate cell. The uplink configuration may be for more than a single uplink transmission if a fallback is required (when the first uplink message transmission is not successfully received in the C-DU, referred to herein as a preamble transmission failure during TA establishment).

[0157] In one embodiment, the UE receives, for each LTM candidate cell, one or a plurality of uplink configurations for establishing a TA for the plurality of LTM candidate cells.

[0158] In one embodiment, the UE receives, for example, by transmitting an uplink signal / message, a notification associated with an LTM candidate cell indicating that the cell is a cell for which the UE is to establish a TA. The UE may receive at least one uplink configuration for each target candidate cell for which a TA is to be established, and based thereon, the UE transmits a message to the target candidate cell.

[0159] In one embodiment, the UE receives a notification associated with an LTM candidate cell indicating that the LTM candidate cell is a cell for which fallback is possible when the UE attempts to establish a TA.

[0160] In one embodiment, the target candidate cells set for the UE (for which the UE is to establish a TA) include a subset of the LTM candidate cells. In other words, the UE may be set with the number “N” of LTM candidates and is set to establish a TA with a number “N1” (N1 < N) of candidate cells. The reason is that some target candidate cells may not require a TA to be established, 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 in the same location as one or more other serving cells and thus the same TA value may be assumed (for example, some target candidate cells may be assumed to be uplink synchronized with the UE).

[0161] In one embodiment, the UE receives notification of LTM candidate cells for which the UE does not need to establish a TA, and in addition, the UE receives notification for the candidate cells that the UE may assume the same TA value as used for a given serving cell. For example, the UE receives a serving cell index for one of the configured serving cells associated with the LTM candidate cell configuration. Then, when the UE receives an LTM cell switch command for LTM execution (e.g., a MAC CE including notification of candidate cell configuration), the UE determines that the TA value for this cell is the cell that is considered the same as the TA value for the indicated serving cell, and the UE applies the TA value accordingly when accessing the LTM candidate cell.

[0162] In one embodiment, the UE receives notification of LTM candidate cells for which the UE does not need to establish a TA, and in addition, the UE receives a TA value for the candidate cell. For example, the UE receives a serving cell index of one of the configured serving cells associated with a target cell configuration. Then, when the UE receives an LTM cell switch command (e.g., a MAC CE including notification of the candidate cell configuration), the UE applies the TA value provided in the LTM cell switch command.

[0163] In one embodiment, a UE receives a notification of an LTM candidate cell for which the UE does not need to establish a TA, and in addition, the UE receives a candidate cell TA value of 0. For example, the UE receives a serving cell index of one of the configured serving cells associated with the candidate cell configuration. Then, when the UE receives an LTM cell switch command (e.g., a MAC CE including the candidate cell configuration notification), the UE applies the TA value of 0 provided in the LTM cell switch command.

[0164] In one embodiment, the UE receives notification of an LTM candidate cell for which the UE does not need to establish a TA (e.g., there is no explicit notification in the uplink configuration for TA establishment or in the LTM candidate cell configuration), and in addition, upon receiving the LTM cell switch command (e.g., a MAC CE including notification of the candidate cell configuration), the UE receives notification for the candidate cell that the UE may need random access with the LTM candidate cell.

[0165] 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 may include a notification (e.g., uplink configuration for the LTM candidate cell), based on which the UE transmits one or more uplink signals or messages (e.g., one or more RAs or PRACH preambles) to the LTM candidate cell, enabling the candidate DU to establish the TA and notify the CU and serving DU of the TA value. The uplink configuration may be valid for multiple uplink transmissions from the UE for establishing the TA to cover fallback cases when the C-DU does not successfully detect an uplink message sent by the UE.

[0166] In one embodiment, the UE receives an uplink configuration (e.g., as a field, parameter, set of parameters and / or fields, IEs, etc.) for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X) in an LTM candidate configuration (e.g., in an RRCReconfiguration container and / or IEs CellGroupConfig and / or SpCell configuration for candidate cell X). This may be, for example, one or more parameters in a random access configuration of the SpCell configuration in the target candidate configuration. The RA configuration may be valid for multiple uplink transmissions from the UE for establishing a TA to cover fallback cases when the C-DU does not successfully detect an uplink message sent by the UE.

[0167] 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) configured as IEs and / or fields and / or sets of IEs and fields in the LTM configuration, which may correspond to IEs for configuring one or more LTM candidate cells for LTM.

[0168] In one option, an uplink configuration is configured for the LTM candidate cell, eg, the candidate cell has its uplink configuration for TA establishment.

[0169] In one option, the uplink configuration is configured for a set of LTM candidate cells. The uplink configuration may still be for a given LTM candidate cell, since parameters are defined for a given uplink channel of the given cell, but when the UE establishes a TA for that single cell, it is valid for a set of cells, which may be possible if the cells are of the same candidate DU and / or the same TRP, and / or have some common transceiver characteristics, and / or are uplink synchronized.

[0170] 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) 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.

[0171] In one embodiment, a UE receives an uplink configuration including a configuration of an uplink signal / message and / or a configuration of a channel for the UE to transmit an uplink signal / message (received at a candidate DU) to establish a TA between the UE and an LTM candidate cell (e.g., candidate cell X). 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 to cover a fallback case when the C-DU does not successfully detect an uplink message transmitted by the UE.

[0172] The uplink signal / message may correspond to a random access preamble (or an equivalent sequence defined in the physical layer) indicated by the random access preamble index (e.g., ra-PreambleIndex of IE INTEGER(0..63)) in the uplink configuration.

[0173] The uplink configuration may further include at least one beam identifier / index associated with the uplink signal, such as an SSB index and / or a CSI-RS resource identifier.

[0174] For example, when the uplink signal corresponds to a preamble, the uplink configuration may include at least one TA establishment resource as a pair (IE SSB-Index ssb, ra-PreambleIndex or IE INTEGER(0..63)). The uplink configuration may include multiple of these pairs because the candidate DU does not know which SSB and / or CSI-RS resource the UE will select to establish TA. The configured beam, e.g., SSB, may be referred to as a candidate beam for TA establishment.

[0175] In the following example, a UE is provided with a list of TA establishment resources for an LTM candidate cell, each resource having an associated preamble index and SSB index: TA-Config ::= SEQUENCE { [...] candidateBeamList SEQUENCE (SIZE(1..FFS)) OF TA-SSB-Resource OPTIONAL, [...] } [...] TA-SSB-Resource ::= SEQUENCE { ssb SSB-Index, ra-PreambleIndex INTEGER(0..63), ... }

[0176] In another example, the UE is provided with a list of TA establishment resources for an LTM candidate cell, each resource having an associated preamble index and CSI-RS resource. In addition to the pairs, there is also a list of random access opportunities per resource. These are the RA opportunities that the UE must use when performing TA establishment with the LTM candidate cell (including possible subsequent transmission of a preamble if fallback is required upon detection of a preamble transmission failure) when selecting the candidate beam identified by the corresponding CSI-RS. TA-CSI-Resource ::= SEQUENCE { csi-RS NZP-CSI-RS-ResourceId, ra-PreambleIndex INTEGER (0..63) OPTIONAL, -- Need R ra-OccasionList SEQUENCE (SIZE(1..maxRA-OccasionsPerCSIRS))OF INTEGER (0..maxRA-Occasions-1) OPTIONAL, --Need R ... }

[0177] The candidate DU determines the beam identifier / index of the LTM candidate cell to be configured for TA establishment based on beam measurement information (e.g., measurement information on SSB and / or CSI-RS of the target candidate cell) obtained from the CU in / with the LTM request. When the network (e.g., CU) configures the UE for LTM, it may configure the UE to report beam measurement information when it intends to trigger the UE to establish TA with the LTM candidate cell. For example, for neighboring cells included in the measurement report, the UE may report SSB index X and SSB index Y and their respective RSRP values ​​(e.g., above a threshold in the reporting configuration), indicating that these are suitable beams in the neighboring cells.

[0178] The uplink configuration may further include one or more of the following parameters: Root Sequence Index: The PRACH root sequence index for TA establishment in the LTM, which may be defined in TS 38.211. This may be a field, for example, rootSequenceIndex, of type IE INTEGER(0..137). RSRP threshold for SSB: The L1-RSRP threshold used to determine whether a candidate beam can be used by the UE to attempt contention-free random access to establish TA with an LTM candidate cell. This can be the field rsrp-ThresholdSSB ● SSBs per RACH opportunity: The number of SSBs per RACH opportunity for contention-free TA establishment with LTM candidate cells. This can be the field ssb-perRACH-Occasion of the IE ENUMERATED{oneEighth,oneFourth,oneHalf,one,two,four,eight,sixteen} ● RA SSB opportunity mask index: PRACH mask index explicitly signaled for RA resource selection, valid for one or more SSB resources. This can be the field ra-ssb-OccasionMaskIndex. ● Subcarrier spacing for MSG1: Subcarrier spacing for contention-free TA establishment with the target candidate cell, e.g., values ​​of 15 kHz or 30 kHz (FR1) and 60 kHz or 120 kHz (FR2). This can be the parameter msg1-SubcarrierSpacing of the IE SubcarrierSpacing. • A trigger condition in the form of measurement event A2, A3, A4, or A5 that must be met before triggering TA establishment with an LTM candidate cell.

[0179] The uplink configuration may correspond to non-conflicting resources and / or dedicated resources, so that when a candidate DU receives a preamble in an uplink slot in a frequency resource, it can determine which UE it is configured for and / or which serving DU / CU is serving that UE.

[0180] The uplink configuration may further include RACH parameters such as a preamble, time and frequency resources for the PRACH, and / or one or more parameters of the random access configuration, such as one or more parameters, fields and / or IEs in the IEs RACH-Config, RACH-ConfigCommon, RACH-ConfigDedicated, RACH-ConfigGeneric, as defined in TS 38.331. This may be a special RACH configuration that includes only transmission parameters, e.g., no random access response parameters, since the UE is not expected to receive a response from the target candidate in response to the preamble transmission.

[0181] 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) contained within one or more parameters in the beam failure recovery (BFR) configuration of the target candidate cell (e.g., IE BeamFailureRecoveryConfig) associated with an uplink bandwidth portion (BWP) that may be assumed active during L1 / L2 inter-cell mobility. Using this, the candidate DU can distinguish the preamble and RACH messages for the TA establishment from other preamble and RACH attempts. The BFR is not used for the UE before the target candidate is accessed during L1 / L2 inter-cell mobility, which makes this possible without the need for further detailed configuration.

[0182] In one embodiment, the UE derives the 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 preamble partition indicating the time / frequency resource partition for the PRACH and / or a subset of RACH resources used for that purpose, so that the candidate DU knows that the transmitted preamble will not be acknowledged in the RAR, but the TA is calculated and provided to the serving DU. In that sense, the candidate DU may provide different PRACH resource partitions for UEs in different serving DUs in case of multiple requests.

[0183] In one embodiment, if fallback is required and triggered by the network (e.g., by a second downlink notification), the uplink configuration for TA establishment includes one or more parameters for TA establishment / update fallback, such as i) initial transmit power for uplink signals / messages, ii) power step increment if fallback is triggered by the network, e.g., when the UE receives a second downlink notification, iii) 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.).

[0184] After successfully applying the RRC reconfiguration (eg, RRCReconfiguration) message, the UE sends an RRC reconfiguration complete (eg, RRCReconfigurationComplete) message.

[0185] In one set of embodiments, the UE receives an RRC reconfiguration (e.g., RRCReconfiguration) message (e.g., from a CU via a serving DU), where the message includes uplink configuration for establishing a TA between the UE and an LTM candidate cell (e.g., candidate cell X) after the UE receives an LTM configuration that configures one or more LTM candidate cells. This means that the CU or serving DU may request establishment of a TA to a candidate DU after LTM is configured in the UE. For example, the S-DU and / or CU may trigger TA establishment when there is some certainty that there will be an LTM cell switch to that candidate DU. This also means that the uplink configuration is received by the serving DU before sending a lower layer switch command to the terminal to perform LTM. The UE sends an RRCReconfigurationComplete message after successfully applying the RRCReconfiguration message.

[0186] According to one set of embodiments, the S-DU is responsible for monitoring whether the UE transmission of uplink messages / signals to the candidate DUs for TA establishment is successful. In other words, the S-DU determines whether there is a preamble transmission failure for TA establishment / update. There are different options how to define these failure monitoring steps.

[0187] In one option, the S-DU detects the failure of the preamble transmission for TA establishment / update by the expiration of a timer (monitoring timer). The S-DU starts the monitoring timer when it sends the first downlink notification (e.g., an RRC reconfiguration including LTM configuration or a subsequent PDCCH command transmitted after the RRC reconfiguration including LTM configuration) to the UE. While the timer is running, the S-DU expects a message from the candidate DU containing the TA value calculated by the C-DU based on the reception of the first uplink message (the RA preamble transmitted by the UE to the LTM candidate cell) 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). When the message containing the TA value is received, the S-DU stops the timer and considers the TA establishment procedure successful. When the timer expires and the S-DU does not receive a message containing the TA value, the S-DU considers the preamble transmission for TA establishment / update to be a failure.

[0188] In one option, the S-DU detects a preamble transmission failure for TA establishment / update at the end of a time window (whose characteristics are a start point, a duration, and / or an end point). The S-DU expects a message from the candidate DU containing the TA value calculated by the C-DU based on the reception of the first uplink message (the RA preamble sent by the UE to the LTM candidate cell) via the interface directly 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). When the message containing the TA value is received within the time window, the S-DU considers the TA establishment procedure successful. When the time window ends and the S-DU does not receive a message containing the TA value, the S-DU considers the preamble transmission failure for TA establishment / update.

[0189] In one option, the characteristics of the time window are the same as the characteristics of the random access response (RAR) time window configured as part of the uplink channel configuration for TA establishment provided to the UE.

[0190] In one option, the S-DU detects the failure of the preamble transmission for TA establishment / update by receiving a failure notification from a candidate DU (associated with the candidate cell to which the UE is transmitting an uplink message) 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). The S-DU sends the first downlink notification to the UE (e.g., an RRC reconfiguration including LTM configuration or a subsequent PDCCH command sent after the RRC reconfiguration including LTM configuration) and expects a message including the TA value calculated by the C-DU based on the reception of the first uplink message (the RA preamble sent by the UE to the LTM candidate cell). When the message including the TA value is received, the S-DU considers the TA establishment procedure successful. When the S-DU receives the failure notification from the C-DU (e.g., via the CU), the S-DU considers the preamble transmission for TA establishment / update to be a failure.

[0191] In one option, a failure notification from the C-DU to the S-DU (e.g., via the CU) may correspond to a message in which the TA value does not exist, and the S-DU considers this a preamble transmission failure for TA establishment / update.

[0192] In one set of embodiments, the UE receives a subsequent message to trigger the UE to transmit a first uplink signal / message to the LTM candidate cell. The subsequent message may correspond to, for example, a MAC CE, PDCCH command, DCI, or RRC message received by the UE after an RRC reconfiguration (e.g., RRCReconfiguration) to configure LTM. The RRC reconfiguration to configure LTM may also include a notification for TA establishment for that LTM candidate cell, or the notification may be in a subsequent message. The subsequent message is shown in FIG. 5B as step 5.

[0193] Since a UE receiving the subsequent message as described above may need to stop listening to the serving cell / serving DU to transmit the first uplink signal to the target candidate, this may be useful in scenarios where the candidate DU accepts TA establishment from the CU and the serving DU has some freedom to trigger TA establishment to the UE when the interruption time is not very critical. Upon receiving the subsequent message (e.g., PDCCH command), the UE transmits the first uplink signal / message based on the previously received uplink configuration for TA establishment in the LTM configuration.

[0194] The first downlink notification may correspond to a subsequent message (eg, MAC CE, PDCCH command, DCI, RRC message) as illustrated in step 5.

[0195] In one embodiment, the subsequent message (first downlink notification) includes one or more notifications regarding how the UE performs the first uplink message / signal transmission to the LTM candidate cell, e.g., parameters for RA preamble transmission and / or RA resources. The one or more notifications may correspond to a pointer to or notification of 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 2(b).

[0196] In one option, the UE may receive a set of RA preambles, e.g., p1, p2, p3, ..., pK, in uplink configuration. Thus, a subsequent message (downlink notification) may indicate one or more of the configured RA preambles, e.g., p3 and p2. Based on the notification, the UE knows which preambles to transmit / select / use for transmission to the LTM candidate cell.

[0197] In one option, the UE receives the RA preamble index (eg, ra-PreambleIndex) of the LTM candidate cell in a subsequent message, which is explicitly provided by the PDCCH.

[0198] In one option, the UE may receive in the uplink configuration a set of RA resources, such as sequences and / or time-domain and / or frequency-domain resources, associated with an RS index or identifier, e.g., an SSB index. A subsequent message (downlink notification) may then indicate one or more of the configured RA resources, e.g., by indicating one or more SSBs. Based thereon, the UE knows which SSBs (and therefore which RA resources) it may select for transmission to the LTM candidate cell.

[0199] In one option, the UE may receive a set of RS indices, e.g., SSB indices, in the uplink configuration. A subsequent message (downlink notification) may then indicate one or more of the SSB indices associated with one or more RA resources, e.g., by indicating one or more SSBs. Based thereon, the UE knows which SSBs (and therefore which RA resources) it may select for transmission to the LTM candidate cell.

[0200] This scheme of subsequent messages can also be used for the TA update / maintenance mechanism shown in the following section.

[0201] Some embodiments include steps for first uplink preamble failure detection in C-DU and network-centric fallback. Steps 1 to 4b above are steps for configuring one or more LTM candidate cells for the UE and configuring TA establishment and / or update for at least one cell.

[0202] In the following steps, a set of embodiments covers the case where an uplink signal / message for TA establishment is not successfully detected by the C-DU and the actions from different nodes (e.g., UE, S-DU, C-DU, CU) in response thereto, in what is referred to herein as a fallback procedure for TA establishment / update.

[0203] In one set of embodiments (see 6(1) in Figure 5B), the UE transmits a first uplink signal / message (e.g., PRACH preamble, RA preamble) to the LTM candidate cell (with which the UE needs to establish TA) based on the uplink configuration described in step 4.

[0204] In one set of embodiments, the UE transmits a first uplink signal (including a notification for TA establishment for the LTM candidate cell) in response to receiving an RRC reconfiguration (e.g., RRCReconfiguration) that configures the LTM, as shown in step 4(a) of FIG. 5A.

[0205] In this case, the first downlink notification may correspond to an RRC reconfiguration (eg, RRCReconfiguration) message that configures the LTM.

[0206] This may be the case in the first uplink message, and subsequent messages may be used in the fallback case for TA establishment or TA update.

[0207] In one set of embodiments, the UE transmits the first uplink signal in response to receiving a subsequent message (e.g., MAC CE, PDCCH command, DCI, RRC message) received by the UE after an RRC Reconfiguration that configures LTM for that LTM candidate cell. The subsequent message is shown in Figure 5B as step 5(1).

[0208] In this case, the first downlink notification may correspond to a subsequent message (eg, MAC CE, PDCCH order, DCI, RRC message).

[0209] In one embodiment, the uplink configuration is associated with a validity time (e.g., modeled as a time window, timer, etc.), so the serving DU and / or CU has a limited time to send subsequent messages to the UE. This can be used, for example, to limit the use of uplink resources reserved for TA establishment by the C-DU, if these are UE-dedicated / non-contentious resources.

[0210] The validity time may be important when fallback is triggered by the S-DU. For example, if the C-DU allocates uplink resources for TA establishment and fallback is performed, there may be multiple uplink transmissions to the C-DU / LTM candidate cell, which means that resources may need to be used longer than if a single uplink transmission were allowed. Therefore, the validity time may also be signaled from the C-DU to the S-DU, which controls the fallback for TA establishment / update.

[0211] In one embodiment, upon triggering TA establishment with the LTM candidate cell (e.g., by receiving a subsequent message and / or a first downlink notification and / or transmitting a first uplink message), the UE initiates the procedure (e.g., in response to the first downlink notification, as well as a subsequent message for RRC reconfiguration with LTM configuration). Some steps in such a procedure may be considered similar to some steps performed in an RA procedure, but there are some differences: for example, in the procedure for the TA establishment portion of the method disclosed herein, the UE transmits a first uplink message (e.g., a first RA preamble) and does not expect an RAR from the LTM candidate cell in response to the RA preamble transmitted at the LTM candidate cell. The procedure for TA establishment (particularly some related steps for the initial attempt and, possibly, for fallback when necessary) includes one or more of the following steps:

[0212] Some embodiments include performing one or more measurements on a beam, where a "beam" may also be referred to as a spatial direction in which a reference signal and / or channel is being transmitted by the network, e.g., by an S-DU or C-DU. In one option, a UE performing measurements on a beam corresponds to a 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 that beam.

[0213] Some embodiments include performing one or more measurements on SSB and / or CSI-RS resources of a target candidate cell with which the UE needs to establish a TA, e.g., SSB RSRP measurements for one or more SSBs such as SS-RSRP for SSB index=1, SS-RSRP for SSB index=2, ..., SS-RSRP for SSB index=k; e.g., CSI-RS RSRP measurements for one or more CSI-RSs;

[0214] Some embodiments include performing uplink channel resource selection, e.g., RACH resource selection, associated with SSB and / or CSI-RS resources of an LTM candidate cell with which the UE needs to establish TA. For example, the UE selects an SSB or CSI-RS resource for which a measurement value exceeds a threshold (which may be configured in the uplink configuration), e.g., SSB RSRP > rsrp-ThresholdSSB, and the UE selects uplink channel resources (e.g., time / frequency resources and preambles) for TA establishment associated with the selected SSB, where association is also part of the uplink configuration.

[0215] Some embodiments include transmitting a first uplink signal / message (e.g., a preamble selected based on a selected SSB) in a selected RA resource to the LTM candidate cell, the first uplink message being transmitted using a first transmit power, and the selected RA resource corresponding to the first uplink resource (e.g., an RA resource in time and frequency).

[0216] In one option, the selected first uplink resource is associated with a first beam (e.g., a selected SSB) selected by the UE, for example, based on one or more beam measurements performed by the UE.

[0217] In one option, the UE sets a variable for preamble transmission to the signaled preamble, e.g., sets the variable PREAMBLE_INDEX to the signaled ra-PreambleIndex. In one option, the UE selects an SSB signaled by the network, e.g., signaled by the PDCCH. In one option, the UE selects an SSB among its associated SSBs that has a measurement value, such as SS-RSRP (defined in TS 38.215), above a measurement threshold, e.g., rsrp-ThresholdSSB.

[0218] In one option, the UE sets PREAMBLE_INDEX to ra-PreambleIndex corresponding to the selected SSB. In another option, the UE selects a CSI-RS signaled, for example, by PDCCH. In one option, the UE selects a CSI-RS resource from the associated CSI-RSs that has a CSI-RSRP (defined in TS 38.215) above rsrp-ThresholdCSI-RS. In one option, the UE sets PREAMBLE_INDEX to ra-PreambleIndex corresponding to the selected CSI-RS.

[0219] In one option, the UE selects an SSB, and once the SSB is selected, the UE determines the next available PRACH opportunity from the PRACH opportunities corresponding to the selected SSB that are allowed by the restrictions given by the configuration (e.g., ra-ssb-OccasionMaskIndex, part of the uplink configuration for TA establishment), if configured or signaled by the PDCCH (the MAC entity in the UE randomly selects a PRACH opportunity with equal probability among consecutive PRACH opportunities corresponding to the selected SSB).

[0220] In one option, the UE (eg, a MAC entity in the UE) takes into account the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB.

[0221] In one option, the UE selects a CSI-RS and determines the next available PRACH opportunity from the PRACH opportunities in a configured RA opportunity list / set (e.g., ra-OccasionList) corresponding to the selected CSI-RS. The UE (e.g., a MAC entity in the UE) randomly selects a PRACH opportunity with equal probability among PRACH opportunities that occur simultaneously but on different subcarriers corresponding to the selected CSI-RS.

[0222] In one option, the UE (eg, a MAC entity in the UE) takes into account the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected CSI-RS.

[0223] In one option, when the UE determines whether there is an SSB with an SS-RSRP above rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP above rsrp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement.

[0224] In one option, the UE does not maintain a counter for preamble transmissions (e.g., PREAMBLE_TRANSMISSION_COUNTER) maintained in the RA procedure, since this should be controlled by the network (e.g., S-DU), which controls the need for a fallback procedure (e.g., RA preamble retransmissions with power ramping and / or beam / SSB / CSI-RS reselection without reaching the maximum number of preamble transmission attempts). Thus, in this 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, which is incremented each time the UE is notified to send an RA preamble for TA establishment for LTM.

[0225] In one option, the UE sets the first transmit power (PREAMBLE_RECEIVED_TARGET_POWER) by adding one or more of the following: a value provided in the uplink configuration (e.g., preambleReceivedTargetPower), a difference value that depends on the RA preamble format, e.g., DELTA_PREAMBLE (e.g., 0 dB for preamble format 0), and / or a value indicated in the downlink notification or downlink notification that allows the UE to derive a value to be added to the first transmit power.

[0226] In one option, the UE (e.g., a MAC entity in the UE) notifies the physical layer in the UE to transmit the selected or indicated RA preamble using the selected PRACH opportunity and a first transmit power (e.g., PREAMBLE_RECEIVED_TARGET_POWER).

[0227] This method is also applicable when an LTM candidate cell has a single beam, such as when the LTM candidate cell has a single SSB associated with its physical cell identity, in which case the step of selecting a beam for RA resource selection (e.g., selecting an SSB or CSI-RS for that LTM candidate cell) may be skipped.

[0228] In one set of embodiments, the candidate DU does not successfully receive the first uplink message / signal (e.g., PRACH preamble). Or, in other words, the C-DU detects that the first uplink message was not successfully received, e.g., detects a failed transmission attempt. As a result, the C-DU is unable to calculate timing advance values ​​for the UE and at least one LTM candidate cell. Therefore, it can be said that the C-DU detects that it is not possible to calculate a TA value and that there may be an associated cause value (e.g., expiration of a detection timer, weak signal strength that does not allow identification of the uplink signal / preamble, etc.) that may inform the S-DU, for example, that an attempt to transmit an uplink signal has failed. There may be different options for the C-DU to determine that the first uplink message / signal was not successfully detected.

[0229] In one option, when the C-DU sends the uplink configuration for TA establishment (e.g., step 2(b), sending UE Context Setup Response) to the CU and / or S-DU, it starts a timer (e.g., a preamble reception timer), and if the configured RA preamble for TA establishment is not received 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 preamble transmission attempt is considered to have failed in the C-DU. If an RA preamble is received while the preamble reception timer is running, the attempt is considered to have been successful, and the timer is stopped.

[0230] In response to the preamble transmission failure detection, the C-DU may send a message to the CU and / or S-DU to inform them of the preamble transmission failure detection (one sub-option may provide further inputs to allow fallback, e.g., new SSB and / or parameter settings for further preamble retransmissions). This may be the same message that may optionally contain a TA value, but when that field is empty, it indicates that the C-DU was not able to calculate the TA value because the RA preamble was not properly received.

[0231] In one set of embodiments, the S-DU detects that the first uplink message / signal (e.g., a PRACH preamble) is not successfully received at the C-DU, for example, by receiving a failure notification from the C-DU, the end of a time window, or the expiration of a supervision timer (which the S-DU may start when it sends the first downlink notification to the UE). In Figure 5C, the options shown are based on a supervision timer in the S-DU that is started in step 5(1) or 4(a) (depending on which of these messages triggers the UE to send an uplink message / signal to the LTM candidate cell for LTM establishment). A failed RA preamble transmission attempt is detected when the S-DU does not receive a message from the C-DU (e.g., via the CU) containing the expected timing advance value, or when the S-DU receives an expected message from the C-DU (e.g., via the CU) but does not contain the expected timing advance value, and the monitoring timer expires (one advantage of which is that the S-DU may detect the failure faster without having to wait for the timer to expire).

[0232] In step 5(2), in one set of embodiments, the S-DU sends a second downlink notification to the UE in response to detecting that the C-DU does not successfully receive the first uplink message / signal (e.g., a PRACH preamble), e.g., in response to a failed attempt to transmit an RA preamble to the LTM candidate cell. This can be detected in the S-DU, e.g., upon expiration of a supervision timer, as described in the previous step. The S-DU sends the second downlink notification to the UE to trigger the UE to transmit 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 failed attempt by the UE to transmit an RA preamble.

[0233] Some of the steps in 5(2) may be similar to steps in 5(1), for example, assuming that the second downlink notification corresponds to a subsequent message such as a PDCCH command.

[0234] In one option, the S-DU provides an RRC reconfiguration with LTM setting to trigger the transmission of a first uplink signal / message in the UE, such that the first uplink notification corresponds to the RRC reconfiguration, while a subsequent message (e.g., a PDCCH command) is used to trigger the UE to transmit a second uplink signal / message (e.g., a second downlink notification corresponding to the subsequent message).

[0235] In one option, the S-DU provided an RRC reconfiguration with LTM configuration for configuring TA establishment / update, but it is a subsequent message (e.g., a first PDCCH command) that triggers the transmission of a first uplink signal / message in the UE; thus, the first downlink notification corresponds to the first subsequent message after the RRC reconfiguration, while the second subsequent message (e.g., a second PDCCH command) is used to trigger the UE to transmit a second uplink signal / message (e.g., a second downlink notification corresponding to the second subsequent message, e.g., a second PDCCH command for RA preamble retransmission).

[0236] In one set of embodiments, the second downlink notification (e.g., a second subsequent message (e.g., a second PDCCH command) includes one or more notifications regarding how the UE performs the second uplink message / signal transmission to the LTM candidate cell, e.g., parameters for RA preamble transmission and / or RA resources. The one or more notifications may correspond to a pointer to or notification of 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), in particular for retrying transmission of an RA preamble for TA establishment for LTM, as described in step 2(b).

[0237] In one option, the UE may receive a set of RA preambles, e.g., p1, p2, p3, ..., pK, in uplink configuration. Thus, a subsequent message (downlink notification) may indicate one or more of the configured RA preambles, e.g., p3 and p2. Based on that notification, 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.

[0238] In one option, the UE receives in a subsequent message the RA preamble index (eg, ra-PreambleIndex) of the LTM candidate cell that is explicitly provided by the PDCCH.

[0239] In one option, the UE may receive in the uplink configuration a set of RA resources, such as sequences and / or time-domain resources and / or frequency-domain resources, associated with an RS index or identifier, e.g., an SSB index. A subsequent message (downlink notification) may then indicate one or more of the configured RA resources, e.g., by indicating one or more SSBs. Based thereon, the UE knows which SSBs (and therefore which RA resources) it may select for transmission to the LTM candidate cell.

[0240] In one option, the UE may receive a set of RS indices, e.g., SSB indices, in the uplink configuration. Thus, a subsequent message (downlink notification) may indicate one or more of the 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) it may select for transmission to the LTM candidate cell. In one option, the UE may receive one or more LTM candidate cell IDs in the uplink configuration from which the UE should transmit the second uplink message / signal. If multiple LTM candidate cell IDs are provided to the UE, each LTM candidate ID may be mapped to a set of RA preambles, RA preamble indices, RA resources, or RS indices (e.g., SSB indices). Based on this, the UE knows which parameters to use for each received LTM candidate cell. The UE may transmit one second uplink message / signal to each of the received LTM candidate cells, or may select only one LTM candidate cell from the set of LTM candidate cells configured as the destination for the first uplink message / signal.

[0241] Some embodiments include one or more parameters or indications, such as if the UE selects the same beam / SSB / CSI-RS that was selected in a previous failed preamble transmission attempt, based on which the UE determines how to set the second transmit power for transmitting the second uplink message / signal.

[0242] This method may also be used for the TA update / maintenance mechanism described in the following section.

[0243] In one set of embodiments, the S-DU sends a second downlink notification to the UE in response to detecting that the C-DU does not successfully receive the first uplink message / signal (e.g., PRACH preamble) and when the maximum number of transmission attempts of the uplink signal (e.g., RA preamble) (e.g., parameter max_attemtps_TA_establishment_LTM set by the C-DU and indicated in the S-DU) has not been reached. In other words, this is a precondition monitored in the S-DU to decide to send the second downlink notification. When the maximum number is reached, the S-DU does not send the second downlink notification to the UE; instead, the S-DU declares a TA establishment failure.

[0244] When the S-DU sends the first downlink notification to the UE, the S-DU initializes a counter for preamble transmission attempts as PREAMBLE_TRANSMISSION_COUNTER=1. Thus, before sending the second downlink notification (or any other downlink notification after the first downlink notification), 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 set the maximum number of uplink signal (e.g., RA preamble) transmission attempts to 5. Thus, when the S-DU verifies that PREAMBLE_TRANSMISSION_COUNTER<5, it sends the second downlink notification and increments the counter as follows: PREAMBLE_TRANSMISSION_COUNTER = PREAMBLE_TRANSMISSION_COUNTER +1

[0245] Based on the counter monitoring, the S-DU prevents an infinite amount of uplink signal retransmissions / uplink signal transmission attempts to LTM candidate cells that may not be reachable by the UE, and unnecessary uplink interference is prevented in the LTM candidates. This may also give the S-DU (or CU) an opportunity to trigger the release of candidate LTMs that cannot be reached by the UE in the uplink (delete the LTM candidates in the UE and C-DU).

[0246] In one set of embodiments, the S-DU transmits a second downlink notification to the UE in response to detecting that the C-DU does not successfully receive the first uplink message / signal (e.g., PRACH preamble), but only if the maximum uplink signal (RA preamble) transmit power has not been reached after multiple transmissions by the UE.

[0247] According to this method, in one set of embodiments, if the UE fails to detect in the C-DU for the first uplink message because the UE does not expect an RAR from the LTM candidate cell in response to the first uplink signal / message, it is the S-DU that informs the UE that the UE will transmit a second uplink message.

[0248] Difference compared to legacy RA in one cell: In legacy RA, when the UE does not receive an RAR within the RAR time window, the UE either transmits a preamble with power ramping (e.g., based on the same beam / SSB previously selected) or the UE selects a new beam / SSB / CSI-RS to map to the second RA resource (e.g., in this case, no power ramping is used).

[0249] The method includes different solutions for informing the UE whether the UE needs to perform power ramping for the second uplink signal transmission triggered by the second downlink notification.

[0250] In one option, the S-DU, in response to an RA preamble attempt failure (e.g., expiration of a supervision timer), indicates to the UE (e.g., in a second downlink notification) that the UE should retransmit the first uplink message and / or that the UE should transmit another uplink signal / message in accordance with the previously transmitted RA resource configuration with an increased transmit power compared to the previously used transmit power for the first uplink signal / message.

[0251] In one option, the S-DU, in response to an RA preamble attempt failure (e.g., expiration of a supervision timer), indicates to the UE (e.g., in a second downlink notification) that the UE should transmit a second uplink signal / message according to the previously transmitted RA resource configuration with an increased transmit power compared to the previously used transmit power for the first uplink signal / message, where the second uplink signal / message does not need to be the same as 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 for the first uplink signal / message transmission.

[0252] In one option, the S-DU, in response to a failed RA preamble attempt (e.g., expiration of a supervision timer), indicates to the UE (e.g., in a second downlink notification) that it 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 RA preamble transmission attempt.

[0253] In one option, the S-DU indicates which SSB the UE should select and thus how the RA resource selection is made based on the indicated SSB. In one option, the S-DU indicates which CSI-RS the UE should select and thus how the RA resource selection is made based on the indicated CSI-RS.

[0254] In one option, the S-DU does not indicate the exact SSB that the UE should select, but indicates that it should be an SSB for RA resource selection based on that. In one option, the S-DU does not indicate the exact CSI-RS that the UE should select, but indicates that it should be an CSI-RS for RA resource selection based on that.

[0255] In one option, the S-DU gives the UE some freedom, e.g., the S-DU does not inform the UE (e.g., in the second downlink notification) whether the UE should select a new beam / SSB / CSI-RS or perform power ramping. Instead, the second downlink notification indicates that there has been an uplink signal preamble attempt, but leaves the steps related to fallback to the UE.

[0256] In one option, the UE determines whether to perform power ramping based on the RA resource selection. The UE performs power ramping when the RA resource selection leads to the UE selecting the same SSB or CSI-RS or beam selected in the failed attempt. The UE does not perform power ramping when the RA resource selection leads to the UE selecting a different SSB or CSI-RS or beam than the one selected in the failed attempt.

[0257] In this option, the second downlink notification replaces the event where the UE detects that no RAR was received (within the RAR time window) in response to the first uplink signal / message transmission, where it is the receipt of the second downlink notification, rather than the lack of reception of the RAR, that triggers the UE to make a new attempt to transmit an RA preamble to the LTM candidate cell.

[0258] In step 6(2), in one set of embodiments, the UE transmits a second uplink message / signal (e.g., a second RA preamble, transmitted to the candidate cell) according to either i) an increased transmit power compared to the first transmit power (e.g., an initial RA preamble power, which may be defined by the parameter / field preambleReceivedTargetPower), or ii) a second uplink resource (e.g., an RA resource in time and frequency) associated with the second beam selected by the UE.

[0259] In one set of embodiments, the UE transmits a second uplink message / signal (e.g., a second RA preamble, transmitted to the candidate cell) according to one or more notifications included in the second downlink notification, e.g., as defined in the set of embodiments above.

[0260] In one set of embodiments, before the UE transmits the second uplink message / signal, the UE performs uplink resource selection for TA establishment / update fallback (e.g., RA resource selection based on beam selection), which includes one or more of the following steps:

[0261] The UE may perform or update one or more measurements of beams and / or SSBs and / or CSI-RS resources of an LTM candidate cell for which the UE needs to perform TA establishment fallback, e.g., SSB RSRP measurements for one or more SSBs such as SS-RSRP for SSB index=1, SS-RSRP for SSB index=2, ..., SS-RSRP for SSB index=k, e.g., CSI-RS RSRP measurements for one or more CSI-RSs.

[0262] The UE may perform uplink channel resource selection based on the selected beam / SSB / CSI-RS, e.g., RACH resource selection, associated with the SSB and / or CSI-RS resources of the LTM candidate cell with which the UE needs to establish TA. For example, the UE selects an SSB or CSI-RS resource whose measurement value exceeds a threshold (which may be configured in the uplink configuration), e.g., SSB RSRP > rsrp-ThresholdSSB, and the UE selects uplink channel resources (e.g., time / frequency resources and preambles) for TA establishment associated with the selected SSB, where the association is also part of the uplink configuration.

[0263] The UE may transmit a second uplink message (e.g., a second RA preamble) to the LTM candidate cell, where the second uplink message (e.g., the second RA preamble) is transmitted to the LTM candidate cell by either 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 a second beam (e.g., an SSB or CSI-RS of the LTM candidate cell) that the UE selects. In one option, when notification of the second uplink signal (e.g., the RA preamble) is provided to the UE (ra-PreambleIndex via PDCCH or other uplink signal notification in the second downlink notification), the UE selects the SSB signaled by the second downlink notification, e.g., via PDCCH (and the UE uses the RA resource mapped to the selected SSB).

[0264] In one option, when notification of a second uplink signal (e.g., RA preamble) is provided to the UE (ra-PreambleIndex via PDCCH or other uplink signal notification in the second downlink notification), the UE selects the SSB signaled by the second downlink notification, e.g., via PDCCH (and the UE uses the RA resource mapped to the selected SSB).

[0265] 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 CSI reports to the S-DU for the SSBs of the LTM candidate cells, and therefore the S-DU indicates in the downlink notification the SSBs for which the S-DU is known to have sufficiently good radio conditions.

[0266] 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).

[0267] In one option, the UE sets a variable for preamble transmission to the signaled preamble, eg, sets the variable PREAMBLE_INDEX to the signaled ra-PreambleIndex.

[0268] In one option, the UE selects an SSB with an SS-RSRP (defined in TS 38.215) above rsrp-ThresholdSSB from among the associated SSBs.

[0269] In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected SSB.

[0270] In one option, the UE selects the CSI-RS that is signaled, for example, by the PDCCH.

[0271] In one option, the UE selects a CSI-RS resource from among its associated CSI-RS with a CSI-RSRP (defined in TS 38.215) above rsrp-ThresholdCSI-RS.

[0272] In one option, the UE sets PREAMBLE_INDEX to the ra-PreambleIndex corresponding to the selected CSI-RS.

[0273] In one option, the UE selects an SSB, and once the SSB is selected, the UE determines the next available PRACH opportunity from the PRACH opportunities corresponding to the selected SSB that are allowed by the restrictions given by the configuration (e.g., ra-ssb-OccasionMaskIndex, part of the uplink configuration for TA establishment), if configured or signaled by the PDCCH (the MAC entity in the UE randomly selects a PRACH opportunity with equal probability among consecutive PRACH opportunities corresponding to the selected SSB).

[0274] In one option, the UE (eg, a MAC entity in the UE) takes into account the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected SSB.

[0275] In one option, the UE selects a CSI-RS and determines the next available PRACH opportunity from the PRACH opportunities in a configured RA opportunity list / set (e.g., ra-OccasionList) corresponding to the selected CSI-RS. The UE (e.g., a MAC entity in the UE) randomly selects a PRACH opportunity with equal probability among PRACH opportunities that occur simultaneously but on different subcarriers corresponding to the selected CSI-RS.

[0276] In one option, the UE (eg, a MAC entity in the UE) takes into account the possible occurrence of measurement gaps when determining the next available PRACH opportunity corresponding to the selected CSI-RS.

[0277] In one option, when the UE determines whether there is an SSB with an SS-RSRP above rsrp-ThresholdSSB or a CSI-RS with a CSI-RSRP above rsrp-ThresholdCSI-RS, the UE uses the latest unfiltered L1-RSRP measurement.

[0278] In one option, the UE does not maintain a counter for preamble transmissions (e.g., PREAMBLE_TRANSMISSION_COUNTER) that is maintained in the RA procedure, because this is controlled by the network (e.g., S-DU), which controls the need for a fallback procedure (e.g., RA preamble retransmissions with power ramping and / or beam / SSB / CSI-RS reselection without reaching the maximum number of preamble transmission attempts). Thus, in this network-controlled fallback, it is the network (e.g., S-DU) that monitors the number of preamble transmissions, for example, by controlling the preamble transmission counter, which is incremented each time the UE is notified to send an RA preamble for TA establishment for LTM.

[0279] In one set of embodiments, the UE transmits a second uplink message / signal for TA establishment / update fallback at an increased power (e.g., with a power ramping step) compared to the first transmit power transmission when the selected beam (e.g., SSB or CSI-RS) is the same beam that the UE selected during resource selection for transmission of the first uplink message / signal.

[0280] In one option, the UE sets the transmit power for the second uplink message / signal (PREAMBLE_RECEIVED_TARGET_POWER(2)) to an increased power compared to the first transmit power, where the transmit power for the second uplink message / signal is set by adding one or more of the following: a value provided in the uplink configuration (e.g., preambleReceivedTargetPower); a difference value that depends on the RA preamble format, e.g., DELTA_PREAMBLE (e.g., 0 dB for preamble format 0); a downlink notification or notification in the downlink notification that allows the UE to derive a value to be added to the first transmit power; and / or an increase 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, Increment step=(PREAMBLE_POWER_RAMPING_COUNTER-1)*PREAMBLE_POWER_RAMPING_STEP; therefore, the transmission power is set, for example, as follows: PREAMBLE_RECEIVED_TARGET_POWER=preambleReceivedTargetPower+DELTA_PREAMBLE+Increment step; → PREAMBLE_RECEIVED_TARGET_power is set as preambleReceivedTargetPower+DELTA_PREAMBLE+(PREAMBLE_POWER_RAMPING_COUNTER-1)*PREAMBLE_POWER_RAMPING_STEP.

[0281] In one option, the UE monitors a power ramping counter (e.g., PREAMBLE_POWER_RAMPING_COUNTER), which is incremented by one when an RA preamble is transmitted / retransmitted as part of the same TA establishment / update procedure. The power ramping counter has a maximum value associated with it, and the UE may be configured with that maximum value as part of the uplink channel configuration.

[0282] In one option, the UE is configured with PREAMBLE_POWER_RAMPING_STEP, received, for example, in an RRC reconfiguration including LTM configuration and / or as part of uplink channel configuration.

[0283] In one option, the UE receives notification of PREAMBLE_POWER_RAMPING_STEP, eg, a pointer to a value, in a downlink notification (eg, a second downlink notification that triggers an RA preamble transmission for TA establishment).

[0284] In one set of embodiments, the UE considers the TA establishment procedure successful when the UE transmits a second uplink message / signal for TA establishment / update to the LTM candidate cell and in response the UE does not receive a downlink notification (e.g., a third downlink notification) from the serving cell (e.g., from an S-DU).

[0285] In one set of embodiments, when the UE transmits the nth uplink message / signal for TA establishment / update to the LTM candidate cell and the UE does not receive the (n+1)th downlink notification from the serving cell (e.g., from an 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 them to zero) and stopping at least one timer associated with the TA establishment procedure.

[0286] In one set of embodiments, the UE further receives a third downlink notification from the S-DU, based on which the UE transmits a third uplink message (e.g., a third RA preamble) to the candidate cell, and the third uplink message (e.g., the third RA preamble) transmitted to the candidate cell is transmitted by i) an increased transmit power compared to the second transmit power, or ii) a third uplink resource (e.g., an RA resource in time and frequency) associated with a third beam selected by the UE.

[0287] Some embodiments include fallback iterations until success or detection of TA establishment failure. In one set of embodiments, the fallback for TA establishment is repeated until one or more conditions are met. The fallback for TA establishment includes, after the S-DU transmits the nth downlink notification to the UE resulting in the nth preamble transmission failure for TA establishment / update, the S-DU transmitting (and the UE receiving) the (n+1)th downlink notification to the UE, where the (n+1)th downlink notification indicates to the UE that the UE should perform the (n+1)th uplink message transmission at any increased transmit power compared to the transmit power of the nth uplink message transmission and / or indicates that the (n+1)th uplink message transmission should be directed to the (n+1)th uplink resource (e.g., RA resource in time and frequency) associated with the (n+1)th beam selected by the UE.

[0288] 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 that the number of preamble transmission failures for TA establishment / update for a given LTM candidate cell and / or UE has reached a maximum value.

[0289] In one option, the maximum value may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0290] 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 its maximum value before sending a downlink notification to the UE. If the S-DU determines that the counter has reached its maximum value, it does not send a downlink notification and considers the TA establishment as a failure, which is called a TA establishment failure.

[0291] In other words, when the number of failed preamble transmissions for TA establishment reaches a maximum value, the S-DU declares the TA establishment failure.

[0292] In one option, the maximum number of failed preamble transmissions for TA establishment may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0293] The S-DU detects when the UE has reached the maximum transmit power for transmitting uplink messages to an LTM candidate cell.

[0294] The maximum value may be reached after multiple transmit power increases after a failed preamble transmission for TA establishment.

[0295] In one option, the maximum transmit power for TA establishment may be configured by the candidate DU serving the LTM candidate cell, which is the C-DU that configured the uplink resources for TA establishment and / or TA update.

[0296] In one set of embodiments, a candidate DU successfully receives a first uplink message / signal (e.g., a PRACH preamble) and can therefore calculate timing advance values ​​for 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.

[0297] In one embodiment, a candidate DU sends a message to a CU containing a timing advance value and one or more associated LTM candidate cells for which the TA value is applicable, based on which the CU (and possibly the serving DU, which also receives the information) knows that a given timing advance value is applicable to one or more LTM candidate cells to which the UE is configured, which may be needed during an LTM execution (also called an LTM cell switch) to one of the candidate cells.

[0298] In one embodiment, the candidate DU sends a message to the CU using a UE signaling connection so that the CU knows that the timing advance value associated with the target candidate cell corresponds to the UE for that UE signaling connection.

[0299] 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. Also, while the TA timer is running, the candidate DU considers the timing advance value it provided to the CU to be "valid," which means that, assuming the TA value is provided to the UE via the CU and / or serving DU, while the TA timer is running, the candidate DU can receive incoming UEs with LTM without random access because the timing advance is still valid. When the TA timer expires, the candidate DU considers the TA value to be "invalid," and if the TA value is not valid, the candidate DU may trigger a TA update procedure.

[0300] 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 to be "valid," and when the TA timer expires, the CU considers the TA value to be "invalid." When the TA value is not valid, the CU may trigger a TA update procedure.

[0301] In one option, the candidate DU further includes in the message to the CU a TA timer value associated with the TA value (applicable to at least one target candidate cell), the TA value being considered "valid" while the TA timer is running and not valid when the TA timer expires. In that case, it may be an option for the candidate DU to also start a TA timer with the same or a similar value so that it is also aware when the TA value is not valid for that UE and LTM candidate cell.

[0302] In one embodiment, a first uplink signal and / or RA resource may be configured for a particular UE (e.g., per UE resource, per contention-free preamble and / or PRACH resource for TA establishment), so that upon reception, the candidate DU knows which UE, and therefore which CU, it is associated with since there is a UE signaling connection for that UE (because the candidate DU is the UE that accepted the request to configure LTM). Based on reception of the first uplink signal / message, the candidate DU calculates TA values ​​for that UE and the target candidate cell and transmits the TA values ​​to the serving DU (via the CU) to be used by the UE in LTM execution (e.g., subsequent LTM cell switch).

[0303] 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. Similar to step (7a) in Figure 5C, 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 for LTM, calculates valid TA values ​​for the UE and at least one LTM candidate cell, and sends a message to the CU including the at least one TA value for the CU to transmit to the serving DU.

[0304] In one embodiment, a serving DU receives a message from a CU containing a TA value and one or more associated LTM candidate cells for which the TA value is applicable, based on which the serving DU knows that a given TA value is applicable to one or more UE-configured LTM candidate cells, which may be needed during LTM execution (LTM cell switch) to one of these candidate cells.

[0305] 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 for that UE signaling connection.

[0306] In one embodiment, a serving DU receives a message containing TA values ​​associated with LTM candidate cells and UEs 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 to be "valid," and when the TA timer expires, the serving DU considers the TA value to be "invalid." When the TA value is not valid, the serving DU may trigger a TA update procedure.

[0307] In one option, the serving DU receives in a message from the CU a TA timer value associated with a TA value (applicable to at least one target candidate cell), which is considered "valid" while the TA timer is running and is not valid when the TA timer expires. In that case, it may be an option for the candidate DU and / or CU to also start a TA timer with the same or a similar value so that they can also recognize when the TA value is not valid for that UE and LTM candidate cell.

[0308] In one set of embodiments, the S-DU is responsible for monitoring whether the UE transmission of uplink messages to the candidate DUs for TA establishment is successful. In other words, the S-DU determines whether there is a preamble transmission failure for TA establishment / update. There can be different options for defining these failure monitoring steps.

[0309] In one option, when a message containing the TA value is received, the S-DU stops the timer that was started when the S-DU indicated to the UE that the first uplink signal / message is to be transmitted, and the TA establishment procedure is considered successful.

[0310] In one option, the S-DU considers the TA establishment procedure successful when a message containing a TA value is received.

[0311] In one set of embodiments, the UE may send measurements to assist the serving DU and / or candidate DU and / or CU in triggering LTM execution (LTM cell switch), including, for example, CSI measurements regarding the LTM candidate cell for which the UE triggered the establishment of a TA.

[0312] In response to the reported measurements (L1 RSRP) for a given LTM candidate cell, the network (e.g., the serving DU) may decide to trigger an LTM cell switch for the UE to the LTM candidate cell for which the UE triggered the establishment of a TA.

[0313] In one embodiment, the serving DU performs one or more of the following actions: If the LTM candidate cell (e.g., cell X) for which the serving DU determines to trigger LTM execution (cell switch) 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 is uplink synchronized), the serving DU sends lower layer signaling (e.g., MAC CE) to the UE indicating the LTM candidate cell and including the TA value to be applied by the UE for communication with the LTM candidate cell (which will become the target cell). If the LTM candidate cell (e.g., cell X) for which the serving DU determines to trigger LTM execution (LTM cell switch) 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 lower layer signaling (e.g., MAC CE) to the UE indicating the LTM candidate cell and not including a TA value.

[0314] In one embodiment, the serving DU performs one or more of the following actions: If the TA timer is running, the network (e.g., serving DU) sends lower layer signaling (e.g., MAC CE) to the UE indicating LTM candidate cells and including the TA value. If the TA timer expires or is stopped, the network (e.g., serving DU) sends lower layer signaling (e.g., MAC CE) to the UE indicating LTM candidate cells for L1 / L2 inter-cell mobility without including the TA value.

[0315] In one embodiment, the serving DU performs one or more of the following actions: If the LTM candidate cell (e.g., cell X) of the serving DU LTM execution (LTM cell switch) is a cell with a valid TA value for the UE and the LTM candidate cell (e.g., the TA timer is running) that is the same as the TA value of the serving cell the serving DU is configured with, the serving DU sends lower layer signaling (e.g., MAC CE) to the UE indicating the LTM candidate cell, including the TA value of the serving cell the UE is configured with, to be applied by the UE for communication with the LTM candidate cell.

[0316] Another alternative is that instead of providing a TA value, the serving DU provides a serving cell index and indicates to the UE that the UE should use the TA value between the UE and the serving cell with the indicated index as the TA value for the UE and the LTM candidate cell, which is also indicated in the lower layer signaling.

[0317] The UE receives lower layer signaling (e.g., MAC CE) indicating an LTM candidate cell. When the signaling includes a TA value, the UE applies the TA value for the LTM candidate cell (for uplink transmission). If the signaling does not include a TA value or the notified LTM candidate cell is a cell whose TA is the same as that of the serving cell (and the UE recognizes it based on the LTM candidate configuration), the UE applies the TA value of the serving cell associated with the LTM candidate cell (for uplink transmission). If the signaling does not include a TA value or the notified LTM candidate cell is a cell with which time alignment (uplink synchronization) is not established, the UE performs random access to the notified LTM candidate cell. When the signaling includes a serving cell index, the UE uses the TA value between the UE and the serving cell with the index indicated in the lower layer signaling as the TA value for the LTM candidate cell.

[0318] The UE may transmit an uplink message to the target candidate (eg, via a PUCCH and / or a PUSCH) after applying the indicated TA value for the LTM candidate cell according to the method.

[0319] Some embodiments include a fallback step for TA update for LTM. In one set of embodiments, one or more steps disclosed for TA establishment fallback may be performed in the case of TA update, where when the TA value is not valid for the UE and the LTM candidate, the network and / or UE decides to calculate a new TA value before LTM execution with that LTM candidate cell.

[0320] According to certain embodiments, the TA update may be triggered by i) the CU, ii) the S-DU, iii) the C-DU, and / or iv) the UE.

[0321] The trigger may depend on which of these entities is in control of the validity of the TA value previously calculated by the C-DU and provided to the S-DU.

[0322] In one set of embodiments, TA establishment between the UE and an LTM candidate is performed, and the CU determines that the TA value is not valid, e.g., upon expiration of the TA timer value. The TA timer may be started when the TA value is provided to the CU and / or S-DU. When the CU detects that the TA value is not valid (which may be equivalent to determining that the UE has lost synchronization in the uplink with the LTM candidate cell), the CU sends a request for TA update to the C-DU (e.g., for the LTM candidate cell for which the UE has lost uplink synchronization, for which the TA timer has expired). In response, the C-DU may reject or accept the request, potentially with a new uplink channel configuration (e.g., RACH configuration) for uplink transmissions for the UE, since the previously provided configuration may include one or more parameters that are not valid. (3) The CU sends a notification of rejection or acceptance to the S-DU, which triggers TA establishment / update to the UE, e.g., by sending a first downlink notification. In that regard, the steps for TA update are similar to those disclosed above, as shown in Figures 5A, 5B, and 5C, and reproduced to some extent below in Figures 6A, 6B, and 6C.

[0323] 6A, 6B, and 6C are flowcharts illustrating fallback procedures for the TA update procedure (for CU-initiated TA update and network-based TA management). In one set of embodiments, TA establishment between a UE and an LTM candidate is performed, and the S-DU determines that the TA value is not valid, e.g., upon expiration of the TA timer value. The TA timer may have been started upon receiving an uplink signal from the UE in the TA establishment procedure, e.g., when the TA value was provided to the S-DU from the C-DU. When the S-DU detects that the TA value is not valid (which may be equivalent to determining that the UE has lost synchronization in the uplink with the LTM candidate cell), the S-DU (1) sends a request for TA update to the CU, and (2) it sends a request to the C-DU (the C-DU serving the LTM candidate cell for which the UE has lost uplink synchronization, e.g., the TA timer expired). In response (2b), the C-DU may reject or accept the request, potentially with a new uplink channel configuration (e.g., RACH configuration) for uplink transmissions for the UE, since the previously provided configuration may include one or more parameters for which it is not valid. The CU sends a notification of rejection or acceptance to the S-DU, which triggers a TA establishment / update to the UE, for example, by sending a first downlink notification. From that point on, the steps for TA update are similar to those disclosed above, as shown in Figures 5A, 5B, and 5C and reproduced to some extent below in Figures 7A, 7B, and 7C.

[0324] 7A, 7B, and 7C are flowcharts illustrating alternative fallback procedures for the TA update procedure (for S-DU initiated TA update 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 to the CU that the CU may take one or more further actions.

[0325] The CU cancels the TA establishment / update for the LTM toward the C-DU for an LTM candidate cell for which the UE attempted and failed to establish or update the TA. 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.

[0326] The CU cancels the TA establishment in the UE, for example, by generating and sending to the UE an RRC reconfiguration message that removes / releases / cancels / deactivates one or more settings for TA establishment / update for the LTM candidate cell.

[0327] The CU cancels LTM towards the C-DU for LTM candidate cells for which the UE has attempted and failed to establish / update TA. In one example, the CU then considers the candidate target cell as a candidate for normal (L3) handover instead, or configures the UE with conditional handover (CHO) configuration for which it is a candidate target cell. In one alternative, the CU then cancels LTM for the LTM candidate cell and sends a message to the C-DU containing a request for CHO configuration (or configuration for normal handover) for the same cell.

[0328] The CU provides the C-DU (or another network node, e.g., Operation and Maintenance (OAM)) with information related to the failure to establish a TA, such as the beams (e.g., SSB and / or CSI-RS) of the LTM candidate cells on which the UE attempted to establish a TA and failed, and / or measurements on beams that were not selected by the UE for TA establishment.

[0329] In one set of embodiments, 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), the S-DU may decide to initiate a new TA establishment with a new C-DU. In such a case, the S-DU sends a new request for TA establishment with the new C-DU.

[0330] In one alternative, the S-DU decides to initiate a new TA establishment for another candidate target cell in the same C-DU where the TA establishment failure was detected. In one alternative, when the S-DU detects a TA establishment / update failure (e.g., when the maximum number of RA preamble transmission attempts for TA establishment is reached), the S-DU decides not to trigger an LTM cell switch (LTM execution) to that LTM candidate cell. In one example, the S-DU then does not trigger any LTM switch to the candidate target cell for a certain period of time. When that time has elapsed, the S-DU may first decide to initiate a new TA establishment / update procedure toward the same candidate target cell. In one option, the S-DU has a timer to determine when an LTM cell switch (LTM execution) to that LTM candidate cell can be triggered again or when a new TA establishment / update procedure toward the same candidate target cell should be initiated. The timer is started when the S-DU detects a TA establishment / update failure. In one example, there is also a corresponding timer in the UE.

[0331] In another example, the S-DU initiates a new TA establishment / update procedure towards the same candidate target cell when it receives measurements for that cell that indicate, for example, that the radio conditions towards that cell have improved for the UE.

[0332] 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 when an LTM cell switch (LTM execution) is later triggered towards the same LTM candidate cell, the S-DU may include a notification to the UE (with an LTM cell switch command) to perform a random access procedure as part of the LTM cell switch procedure to that candidate target cell. In one set of embodiments, the UE monitors for TA establishment failures, and the UE detects that the maximum number of RA preamble transmissions has been reached, and upon detecting the failure, the UE releases one or more TA establishment resources, such as uplink configuration, for TA establishment / update. An example is shown in Figures 8A and 8B.

[0333] 8A and 8B are flowcharts illustrating an example of operations in an S-DU upon detecting a TA establishment failure. In a legacy RA procedure, it is the UE that detects the need for fallback (e.g., by the absence of an RAR in response to a preamble transmission) and detects an RA failure, for example, when a 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 is on the master cell group and MCG failure recovery is not supported) or initiating the transmission of an SCG failure-related message (if the RA failure is on a secondary cell group). However, in the set of embodiments described herein, the network detects the TA establishment failure, and since the UE is still connected with the serving cell, there is no need to trigger a recovery action such as a re-establishment procedure.

[0334] As described herein, the network triggers the UE to either re-initiate the TA establishment procedure to the same and / or another LTM candidate cell and / or to cancel the TA establishment procedure.

[0335] 9 illustrates an example of a communications system 100 according to some embodiments. In this example, the communications system 100 includes a telecommunications network 102 including an access network 104, such as a radio access network (RAN), and a core network 106 including 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 3GPP access nodes or non-3GPP access points. The network nodes 110 facilitate direct or indirect connectivity of user equipment (UE), such as connecting UEs 112a, 112b, 112c, and 112d (one or more of which may be generally referred to as UEs 112), to the core network 106 over one or more wireless connections.

[0336] Exemplary wireless communications over wireless connections include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for carrying information without the use of wires, cables, or other material conductors. Moreover, in various embodiments, communications 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 wired or wireless connections. Communications system 100 may include and / or interface with any type of communications, telecommunications, data, cellular, wireless networks, and / or other similar types of systems.

[0337] The UE 112 may be any of a wide variety of communication devices, including wireless devices, that are positioned, configured, and / or operable to communicate wirelessly with the network node 110 and other communication devices. Similarly, the network node 110 is positioned, capable, configured, and / or operable to communicate, directly or indirectly, with the UE 112 and / or with other network nodes or equipment within the telecommunications network 102 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as management within the telecommunications network 102.

[0338] In the illustrated example, the core network 106 connects the network node 110 to one or more hosts, such as the host 116. The connections may be direct or indirect through one or more intermediate networks or devices. In other examples, the network nodes may be directly coupled to the hosts. The core network 106 includes one or more core network nodes (e.g., the core network node 108) structured with hardware and software components. The functionality of those components may be substantially similar to that described with respect to the UEs, network nodes, and / or hosts, and thus those descriptions are generally applicable to the corresponding components of the core network node 108. Exemplary core network nodes include one or more of a Mobile Switching Center (MSC), a Mobility Management Entity (MME), a Home Subscriber Server (HSS), an Access and Mobility Management Function (AMF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Subscription Identifier Deciphering Function (SIDF), a Unified Data Management (UDM), a Security Edge Protection Proxy (SEPP), a Network Publishing Function (NEF), and / or a User Plane Function (UPF).

[0339] The host 116 may be owned or controlled by, and operated by or on behalf of, a non-operator service provider or provider of the access network 104 and / or telecommunications network 102. 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 such as acquiring and compiling data about various ambient conditions sensed by multiple UEs, analytics functionality, social media, functionality for controlling or otherwise interacting with remote devices, functionality for alarm and monitoring centers, or any other such functionality performed by a server.

[0340] 9 enables connectivity between UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as a particular standard, 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 standard (e.g., 6G), a wireless local area network (WLAN) standard, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard (WiFi), and / or any other suitable wireless communication standard, 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) standard, such as LoRa and Sigfox.

[0341] In some examples, the telecommunications network 102 is a cellular network that implements functions standardized by 3GPP. Thus, the telecommunications network 102 may support network slicing to provide different logical networks to different devices connected to the telecommunications network 102. For example, the telecommunications network 102 may provide Ultra-Reliable Low Latency Communications (URLLC) services to some UEs, while providing enhanced Mobile Broadband (eMBB) services to other UEs and massive machine type communications (mMTC) / massive IoT services to still further UEs.

[0342] In some examples, the UE 112 is configured to transmit and / or receive information without direct human interaction. For example, the UE may be designed to transmit information to the access network 104 on 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 may be configured to operate in a single or multi-RAT or multi-standard mode. For example, the UE may be configured and operate in any one or combination of Wi-Fi, NR (New Radio), and LTE, i.e., for Multi-Radio Dual Connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio-Dual Connectivity (EN-DC).

[0343] In the above example, the hub 114 communicates with the access network 104 to facilitate indirect communication between one or more UEs (e.g., UEs 112c and / or 112d) and a network node (e.g., network node 110b). In some examples, the hub 114 may be a controller, a router, a content source, an analytics, or any of the other communication devices described herein with respect to UEs. For example, the hub 114 may be a broadband router that enables access to the core network 106 for the UE. As another example, the hub 114 may be a controller that sends commands or instructions to one or more actuators in the UE. The commands or instructions may be received from the UE or the network node 110 or may be accepted by executable code, scripts, processes, or other instructions in the hub 114. As another example, the hub 114 may be a data collector that acts as a temporary storage for UE data and, in some embodiments, may perform analysis or other processing of that data. As another example, the hub 114 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker, or other media delivery device, the hub 114 may obtain media or data related to VR assets, video, audio, or other sensory information via a network node, and then provide it to the UE either directly, after performing local processing, and / or adding additional local content. In yet another example, the hub 114 acts as a proxy server or orchestrator for the UEs, particularly if one or more of the UEs are low-energy IoT devices.

[0344] The hub 114 may have a constant / permanent or intermittent connection to the network node 110b. The hub 114 may also enable different communication schemes and / or schedules between the hub 114 and the UEs (UEs 112c and / or 112d) and between the hub 114 and the core network 106. In other examples, the hub 114 is connected to the core network 106 and / or one or more UEs via a wired connection. Additionally, the hub 114 may be configured to connect to an M2M service provider over the access network 104 and / or to other UEs over a direct connection. In some scenarios, a UE may establish a wireless connection with the network node 110b while still being connected via the hub 114 via a wired or wireless connection. In some embodiments, the hub 114 may be a dedicated hub, i.e., a hub whose primary function is to route communications between UEs and the network node 110b. In other embodiments, the hub 114 may be a non-dedicated hub, i.e., a device that is operable to route communications between the UE and the network node 110b, but that is also operable as an origin and / or terminator of communications for any data channel.

[0345] 10 illustrates a UE 200 according to some embodiments. As used herein, a UE refers to a device capable of, configured, arranged, and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a UE include, but are not limited to, a smartphone, a mobile phone, a cell phone, a Voice over IP (VoIP) phone, a wireless local loop phone, a desktop computer, a personal digital assistant (PDA), a wireless camera, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, a laptop embedded equipment (LEE), a laptop mounted equipment (LME), a smart device, a wireless customer premises equipment (CPE), an in-vehicle or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3GPP, including a Narrowband Internet of Things (NB-IoT) UE, a Machine Type Communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0346] A UE may support device-to-device (D2D) communications, for example, by implementing 3GPP standards for sidelink communications, dedicated short-range communications (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the associated device. Instead, a UE may represent a device (e.g., a smart sprinkler controller) that is intended for sale to or operation by a human user, but that may not, at least initially, be associated with a particular human user. Alternatively, a UE may represent a device (e.g., a smart power meter) that is not intended for sale to or operation by an end user, but that may be associated with or operated for the benefit of a user.

[0347] UE 200 includes processing circuitry 202, a power source 208, memory 210, a communication interface 212, and / or any other components, or any combination thereof, operably coupled via bus 204 to input / output interface 206. A given UE may utilize all or a subset of the components shown in FIG. 10. The level of integration between components may vary from one UE to another. Furthermore, a given UE may include multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0348] 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., in discrete logic, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), etc.), programmable logic with appropriate firmware, one or more stored computer programs, a general-purpose processor such as a microprocessor or digital signal processor (DSP) with appropriate software, or any combination of the above. For example, processing circuitry 202 may include multiple central processing units (CPUs).

[0349] In the above example, the input / output interface 206 may be configured to provide one or more interfaces for an input device, an output device, or one or more input / output devices. Examples of output devices include speakers, sound cards, video cards, displays, monitors, printers, actuators, emitters, smart cards, other output devices, or any combination thereof. An input device may enable a user to capture information from the UE 200. Examples of input devices include touch-sensitive or presence-sensitive displays, cameras (e.g., digital cameras, digital video cameras, webcams, etc.), microphones, sensors, mice, trackballs, directional pads, trackpads, scroll wheels, and smart cards. A presence-sensitive display may include a capacitive or resistive touch sensor for sensing input from a user. The sensor may be, for example, an accelerometer, gyroscope, tilt sensor, force sensor, magnetic sensor, optical sensor, proximity sensor, biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as the input device. For example, a universal serial bus (USB) port may be used to provide input and output devices.

[0350] In some embodiments, the power source 208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electrical outlet), a photovoltaic device, or a battery, may also be used. The power source 208 may further include power circuitry for transferring power from the power source 208 itself and / or the external power source to various portions of the UE 200 via interfaces, such as input circuits or power cables. The power transfer may be for charging the power source 208, for example. The power circuitry may perform some shaping, conversion, or other modification of the power from the power source 208 to make it suitable for the respective components of the UE 200 that it powers.

[0351] The memory 210 may be or be configured to include random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk, optical disk, hard disk, removable cartridge, 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, widgets, gadget engine, or other applications, and corresponding data 216. The memory 210 may store any of a wide variety of operating systems or combinations of operating systems for use by the UE 100.

[0352] The 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 disk drive, a thumb drive, a pen drive, a key drive, a high-density digital versatile disc (HD-DVD), an optical disk drive, an internal hard disk drive, a Blu-ray optical disk drive, a holographic digital data storage (HDDS) optical disk drive, an external mini-DIMM (Dual In-Line Memory Module), a synchronous dynamic random access memory (SDRAM), an external micro-DIMM (SDRAM), a smart card memory such as a tamper-resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs) such as a USIM and / or an ISIM, 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 known as a "SIM card." Memory 210 may enable UE 200 to access instructions, application programs, and the like stored on temporary or non-transitory storage media to offload or upload data. An item of manufacture, such as one utilizing a communication system, may be tangibly embodied as or within memory 210, which may be or include a device-readable storage medium.

[0353] The processing circuit 202 may be configured to communicate with an access network or other networks using a communication interface 212. The communication interface 212 may include one or more communication subsystems and may include or be communicatively coupled to an antenna 222. The communication interface 212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of other devices capable of wireless communication (e.g., other UEs or network nodes within the access network). Each transceiver may include a transmitter 218 and / or a receiver 220 appropriate for providing network communications (e.g., optical, electrical, frequency-assigned, etc.). Moreover, the transmitter 218 and receiver 220 may be coupled to one or more antennas (e.g., antenna 222), which may share circuit components, software, or firmware, or may alternatively be implemented separately.

[0354] In the illustrated embodiment, the communication capabilities of 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 such as using the Global Positioning System (GPS) to determine location, other similar communication capabilities, or any combination thereof. Communications may be implemented according to one or more communication protocols and / or standards, such as, for example, 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 Networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), etc.

[0355] Regardless of the type of sensor, the UE may provide an output of data captured by its sensors to a network node via a wireless connection through its communications interface 212. Data captured by the UE's sensors may be communicated via other UEs to the network node via a wireless connection. The output may be periodic (e.g., once every 15 minutes when reporting sensed temperature), random (e.g., to balance the load of notifications from multiple sensors), in response to a triggering event (e.g., moisture is detected and an alert is sent), on request (e.g., a user-initiated request), or as a continuous stream (e.g., a live video feed of a patient).

[0356] As another example, the UE may include an actuator, motor, or switch associated with a communications interface configured to receive wireless input from a network node via a wireless connection. The actuator, motor, or switch may change state in response to the received wireless input. For example, the UE may include a motor that adjusts a control surface or rotor of a drone in flight in accordance with the received input, or a robotic arm that performs a medical procedure in accordance with the received input.

[0357] If the UE is in the form of an Internet of Things (IoT) device, it may be a device for use in one or more application domains, including but not limited to wearable technology in the city, extended industrial applications, and healthcare. Non-limiting examples of such IoT devices include, or are incorporated into, devices such as a connected refrigerator or freezer, a TV, a connected lighting fixture, an electric meter, a robot vacuum cleaner, a voice-controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electric door lock, a connected doorbell, an air conditioning system such as a heat pump, an autonomous vehicle, a surveillance system, a weather monitor, a vehicle parking monitor, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for augmented reality (AR) or virtual reality (VR), a wearable for haptic augmentation or sensory enhancement, a water sprinkler, an animal or object tracker, a sensor for monitoring plants or animals, an industrial robot, an unmanned aerial vehicle (UAV), and any type of medical device such as a heart rate monitor or a remote-controlled surgical robot. A UE in the form of an IoT device comprises other components such as those described in connection with the UE 200 shown in FIG. 10, in addition to circuitry and / or software depending on the intended application of the IoT device.

[0358] As yet 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 other UEs and / or network nodes. The UE, in this case, may be an M2M device, which may also be referred to as an MTC device in the 3GPP context. As one example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a car, truck, ship, or aircraft, or other equipment that can monitor and / or report on its operational status or other functionality associated with its operation.

[0359] In practice, any number of UEs may be used together for a single use case. For example, a first UE may be a drone or integrated into a drone and provide drone speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When a user makes changes from the remote controller, the first UE may adjust the drone's throttle (e.g., by controlling an actuator) to increase or decrease the drone's speed. The first and / or second UE may also include more than one of the above-described functionalities. For example, a UE may include a sensor and an actuator and handle communication of data for both the speed sensor and the actuator.

[0360] 11 illustrates a network node 300 according to some embodiments. As used herein, a network node refers to a device that is capable of, configured, arranged, and / or operable to communicate directly or indirectly with UEs and / or other network nodes or devices in a telecommunications network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., wireless access points) and base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs), and NR Node Bs (gNBs)).

[0361] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power levels), and thus may be referred to as femto, pico, micro, or macro base stations, depending on the amount of coverage provided. A base station may also be a relay node or a relay donor node that controls a relay. A network node may 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). Such remote radio units may or may not be integrated with an antenna, such as an antenna-integrated radio. Some distributed radio base stations may also be referred to as nodes in a distributed antenna system (DAS).

[0362] Other examples of network nodes include multi-transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as an MSR BS, a network controller such as a radio network controller (RNC) or base station controller (BSC), a base transceiver station (BTS), a transmission point, a transmitting node, a multi-cell / multicast coordination entity (MCE), an operation and maintenance (O&M) node, an operation support system (OSS) node, a self-organizing network (SON) node, a positioning node (e.g., an evolved serving mobile location center (E-SMLC) and / or a minimized drive test (MDT).

[0363] The network node 300 includes processing circuitry 302, memory 304, a communications interface 306, and a power source 308. The 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), each of which may have its own respective components. In some scenarios in which the network node 300 includes multiple separate components (e.g., a BTS and a BSC component), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple Node Bs. In such scenarios, each unique pair of Node B and RNC may, in some examples, be considered a single separate network node. In some embodiments, the network node 300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be redundant (e.g., separate memories 304 for different RATs) and some components may be reused (e.g., the same antenna 310 may be shared by different RATs). Network node 300 may also include multiple sets of the various illustrated components for different wireless technologies, such as GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, RFID (Radio Frequency Identification), or Bluetooth wireless technologies, that are integrated into network node 300. The wireless technologies may be integrated into the same or different chips or chipsets and other components within network node 300.

[0364] The processing circuitry 302 may include one or more combinations of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or other suitable computing device, resources, or combination of hardware, software, and / or coded logic operable, alone or in conjunction with other network node 300 components, such as memory 304, to provide the functionality of the network node 300.

[0365] In some embodiments, the processing circuitry 302 comprises a system-on-chip (SOC). In some embodiments, the processing circuitry 302 includes one or more of a radio frequency (RF) transceiver circuitry 312 and a baseband processing circuitry 314. In some embodiments, the radio frequency (RF) transceiver circuitry 312 and the baseband processing circuitry 314 may be on separate chips (or chipsets), boards, or units, such as a radio unit and a digital unit. In alternative embodiments, some or all of the RF transceiver circuitry 312 and the baseband processing circuitry 314 may be on the same chip or chipset, board, or unit.

[0366] The memory 304 may include any type of volatile or non-volatile computer-readable memory, including, but not limited to, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (e.g., hard disks), removable storage media (e.g., flash drives, compact discs (CDs), or digital video discs (DVDs)), and / or any other volatile or non-volatile non-transitory device-readable and / or computer-executable memory device that stores information, data, and / or instructions that may be used by the processing circuitry 302. The memory 304 may store any suitable instructions, data, or information, including applications, including one or more of computer programs, software, logic, rules, code, tables, and / or other instructions, executable by the processing circuitry 302 and usable by the network node 300. The memory 304 may be used to store any computational results produced by the processing circuitry 302 and / or any data received via the interface 306. In some embodiments, the processing circuitry 302 and the memory 304 are integrated.

[0367] The 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, the communication interface 306 includes a port / terminal 316 for transmitting and receiving data to and from a network, for example, over a wired connection. The communication interface 306 also includes a radio front-end circuit 318 that is coupled to an antenna 310 or, in some embodiments, may be part of the antenna 310. The radio front-end circuit 318 includes a filter 320 and an amplifier 322. The radio front-end circuit 318 may be connected to the antenna 310 and the processing circuit 302. The radio front-end circuit may be configured to condition signals communicated between the antenna 310 and the processing circuit 302. The radio front-end circuit 318 may accept digital data to be sent to another network node or UE via a wireless connection. The radio front-end circuit 318 may convert the digital data into a radio signal having appropriate channel and bandwidth parameters using a combination of a filter 320 and / or an amplifier 322. The wireless signal may then be transmitted via antenna 310. Similarly, if data is to be received, antenna 310 collects the wireless signal, which may then be converted to digital data by wireless 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.

[0368] In an alternative embodiment, the network node 300 may not include a separate radio front-end circuit 318; rather, the processing circuit 302 may include the radio front-end circuitry and may be connected to the antenna 310. Similarly, in some embodiments, all or some of the RF transceiver circuitry 312 is part of the communications interface 306. In yet another embodiment, the communications interface 306 includes one or more ports or terminals 316, the radio front-end circuitry 318, and the RF transceiver circuitry 312 as part of a radio unit (not shown), and the communications interface 306 communicates with baseband processing circuitry 314 that is part of a digital unit (not shown).

[0369] Antenna 310 may include one or more antennas or an antenna array 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 connectable to network node 300 through an interface or port.

[0370] The antenna 310, the communication interface 306, and / or the processing circuitry 302 may be configured to perform any receiving operation and / or any acquiring operation described herein as being performed by a network node. Any information, data, and / or signals may be received from a UE, another network node, and / or any other network equipment. Similarly, the antenna 310, the communication interface 306, and / or the processing circuitry 302 may be configured to perform any transmitting operation described herein as being performed by a network node. Any information, data, and / or signals may be transmitted to a UE, another network node, and / or any other network equipment.

[0371] The power source 308 provides power to the various components of the network node 300 in a manner appropriate for each component (e.g., at the voltage and current levels required for each component). The power source 308 may include or be coupled to power management circuitry for providing power to the components of the network node 300 to perform the functionality described herein. For example, the network node 300 may be connectable to an external power source (e.g., a power grid, an electrical outlet) via an input circuit or interface, such as an electrical cable, whereby the external power source provides power to the power circuitry of the power source 308. As a further example, the power source 308 may include a source of power in the form of a battery or battery pack connected to or integrated into the power circuitry. The battery may provide backup power in case of failure of the external power source.

[0372] Embodiments of network node 300 may include additional components other than those shown in Figure 11 to provide certain aspects of the network node's functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, network node 300 may include user interface devices that allow information to be input into network node 300 and information to be output from network node 300. This may enable a user to perform diagnostic, maintenance, repair, and other administrative functions on network node 300.

[0373] 12 is a flowchart illustrating an exemplary method in a wireless device according to a particular embodiment, in which one or more steps of the method may be performed by the user equipment 200 described with respect to FIG. 10. The wireless device is LTM-capable.

[0374] The method begins in step 1212, where a wireless device (e.g., UE 200) obtains an uplink configuration for an LTM candidate cell. For example, the wireless device may obtain the uplink configuration for the LTM candidate cell via RRC. Examples of uplink configurations for the LTM candidate cell are described in more detail with respect to the embodiments and examples described above.

[0375] In step 1214, the wireless device receives a first notification (e.g., a PDCCH command, an RRC message, a MAC CE, etc.) from the serving cell to perform uplink transmission on the LTM candidate cell. Examples of the first notification are described in more detail with respect to the above-mentioned embodiments and examples.

[0376] In step 1216, the wireless device transmits a first uplink transmission (e.g., a random access preamble) in the LTM candidate cell at a first transmit power and on a first uplink time / frequency resource. The wireless device does not expect a response (e.g., an RAR) to the first uplink transmission.

[0377] 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 for transmitting a first uplink message.

[0378] Examples of sending uplink transmissions are described in more detail with respect to the embodiments and examples described above.

[0379] The first uplink transmission may not have been received by the LTM candidate cell, or the LTM candidate cell may have been unable to calculate a timing advance for the wireless device, for example, in which case the serving cell may determine that a failure has occurred, and the method continues at step 1218.

[0380] In step 1218, the wireless device receives a second notification (e.g., a PDCCH command, an RRC message, a MAC CE, etc.) from the serving cell to perform uplink transmission on the LTM candidate cell. Examples of the second notification are described in more detail with respect to the above-mentioned embodiments and examples.

[0381] In 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 being transmitted at 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.

[0382] For example, in a particular embodiment, the first uplink transmission uses a first beam, and in response to receiving a second notification to perform the uplink transmission, the method further includes selecting a second beam for use for the second uplink transmission, wherein when the second beam is the same as the first beam, the second transmission is transmitted at a second transmit power different from the first transmit power, and when the second beam is different from the first beam, the second transmission is transmitted on a second uplink time / frequency resource different from the first time / frequency resource.

[0383] In certain embodiments, the second notification to perform the uplink transmission includes notification of a second transmit power or notification of second uplink time / frequency resources to use for the second uplink transmission.

[0384] In a particular embodiment, the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

[0385] In a particular embodiment, at least one of the first notification and the second notification includes a notification of an SSB associated with the first uplink transmission or the second uplink transmission, respectively.

[0386] In a particular embodiment, the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes a notification of an uplink candidate cell from which to transmit the first uplink transmission or the second uplink transmission, respectively.

[0387] Examples of transmitting the second uplink transmission are described in more detail with respect to the embodiments and examples described above.

[0388] In step 1222, the wireless device receives a timing advance value for the LTM candidate cell based on the second uplink transmission from the serving cell (e.g., S-DU). In a particular embodiment, receiving the timing advance value from the serving cell includes receiving an LTM execution command. Examples of receiving a timing advance value are described in more detail with respect to the above-mentioned embodiments and examples.

[0389] Modifications, additions, or omissions may be made to the method 1200 of Figure 12. Additionally, one or more steps in the method of Figure 12 may be performed in parallel or in any suitable order.

[0390] 13 is a flowchart illustrating an exemplary method in a network node according to a particular embodiment. In a particular embodiment, one or more steps of FIG. 13 may be performed by the network node 300 described with respect to FIG. 11. The network node may act as an S-DU for TA management between a wireless device and at least one LTM candidate cell.

[0391] The method may begin in step 1310, where a network node (e.g., network node 300) transmits an uplink configuration for an uplink candidate cell to a wireless device. Examples of uplink configurations are described in more detail with respect to the embodiments and examples described above.

[0392] In step 1312, the network node sends a first notification to the wireless device to perform uplink transmission in the LTM candidate cell. Examples of the first notification are described in more detail with respect to the above embodiments and examples.

[0393] In step 1314, the network node detects that the uplink transmission at the LTM candidate cell has failed. For example, in certain embodiments, detecting that the uplink transmission at the LTM candidate cell has failed includes not receiving a response from the LTM candidate cell or receiving an indication from the LTM candidate cell that the uplink transmission at the LTM candidate cell has failed. Examples of failed detection of uplink transmission at the LTM candidate cell are described in more detail with respect to the embodiments and examples above.

[0394] In step 1316, the network node sends a second indication to the wireless device to perform an uplink transmission in the LTM candidate cell.

[0395] In a particular embodiment, the first uplink transmission and the second uplink transmission include transmission of a random access preamble.

[0396] In a particular embodiment, the second notification to perform an uplink transmission includes notification of a transmit power or uplink time / frequency resources to use for the second uplink transmission.

[0397] In certain embodiments, the uplink configuration for the uplink candidate cell may include one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively. The uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes an indication of the uplink candidate cell from which to transmit the first uplink transmission or the second uplink transmission, respectively.

[0398] In a particular embodiment, at least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

[0399] In a particular embodiment, sending the second notification to the wireless device to perform the uplink transmission includes determining a threshold number of uplink transmissions for the wireless device, the threshold number being not exceeded for the LTM candidate cell.

[0400] The second notification example is described in more detail with respect to the above embodiments and examples.

[0401] In step 1318, the network node may receive a timing advance value from the candidate LTM cell, and in step 1320, the network node may transmit the timing advance value to the wireless device. In a particular embodiment, transmitting the timing advance value to the wireless device includes transmitting an LTM execution command to the wireless device.

[0402] Modifications, additions, or omissions may be made to the method 1300 of Figure 13. Additionally, one or more steps in the method of Figure 13 may be performed in parallel or in any suitable order.

[0403] Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the invention. Methods may include more, fewer, or other steps. Further, steps may be performed in any suitable order.

[0404] The foregoing description sets forth numerous specific details. However, it is 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 an understanding of this description. Those skilled in the art will be able to implement the appropriate functionality without undue experimentation using the included description.

[0405] References herein to "one embodiment," "embodiment," "exemplary embodiment," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is asserted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0406] While the present disclosure has been described with respect to particular embodiments, modifications and substitutions of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain the present disclosure. Other modifications, substitutions, and alterations are possible without departing from the scope of the present disclosure, as defined by the following claims.

[0407] Some exemplary embodiments are included below. Group A Embodiments 1. A method performed by a wireless device for L1 / L2 triggered mobility (LTM), the method comprising: - obtaining uplink configurations of LTM candidate cells; - receiving a first notification from a serving cell to perform uplink transmission in an LTM candidate cell; - transmitting a first uplink transmission in the LTM candidate cell at a first transmit power and on a first uplink time / frequency resource; - receiving a second notification from the serving cell to perform uplink transmission in the LTM candidate cell; - transmitting a second uplink transmission in a second LTM candidate cell, wherein the second uplink transmission is transmitted at 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. 2. The method of embodiment 1, wherein the second LTM candidate cell is the same cell as the first LTM candidate cell. 3. The method of embodiment 1, wherein the second LTM candidate cell is a different cell from the first LTM candidate cell. 4. A method performed by a wireless device, the method comprising: - Including any of the steps, features, or functions of the wireless device described above, alone or in combination with other steps, features, or functions described above. 5. The method of the foregoing embodiment further includes one or more additional wireless device steps, features, or functions described above. 6. The method of any of the above embodiments, further comprising: - Providing user data; and - Transferring user data to a host computer via transmission to a base station Group B Embodiments 7. A method performed by a base station acting as a serving distribution 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: - sending a first notification to a wireless device to perform an uplink transmission in an LTM candidate cell; - detecting that uplink transmission in an LTM candidate cell has failed; and - transmitting a second notification to the wireless device to perform uplink transmission in the LTM candidate cell. 8. A method performed by a base station, the method comprising: - Including any of the steps, features, or functions described above with respect to a base station (e.g., serving DU, candidate DU, etc.), alone or in combination with other steps, features, or functions described above. 9. The method of the foregoing embodiment further includes one or more additional base station steps, features, or functions described above. 10. The method of any of the above embodiments, further comprising: - Obtaining user data; and - Transferring user data to a host computer or wireless device Group C Embodiments 11. For mobile devices: - a processing circuit configured to perform any of the steps of any of the embodiments of Group A; and - includes a power supply circuit configured to power a wireless device 12. The base station: - a processing circuit configured to perform any of the steps of any of the embodiments of Group B; - includes a power supply circuit configured to power a wireless device 13. The User Equipment (UE) shall: - an antenna configured to transmit and receive radio signals; - a radio front-end circuit coupled to the antenna and the processing circuit and configured to condition signals communicated between the antenna and the processing circuit; - a processing circuit configured to perform any of the steps of any of the embodiments of group A; - an input interface connected to the processing circuit and configured to allow input of information into the UE to be processed by the processing circuit; - an output interface connected to the processing circuit and configured to output information from the UE that has been processed by the processing circuit; and - including a battery connected to the processing circuit and configured to power the UE 14. A communications system including a host computer: - processing circuitry configured to provide user data; and - a communications interface configured to transfer user data to a cellular network for transmission to a user equipment (UE); - the cellular network includes a base station having a radio interface and processing circuitry, the processing circuitry of the base station configured to perform any of the steps of any of the Group B embodiments 15. The communication system of the above embodiment further includes a base station. 16. The communication system of the two preceding embodiments further includes a UE, and the UE is configured to communicate with the base station. 17. In the communication system of the three preceding embodiments: - processing circuitry of the host computer is configured to execute the host application and thereby provide user data; and - the UE includes processing circuitry configured to execute a client application associated with the host application 18. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: - providing user data at the host computer; and initiating, at the host computer, a transmission carrying user data to the UE over a cellular network including a base station, the base station performing any of the steps of any of the Group B embodiments; 19. The method of the preceding embodiment further includes, at the base station, transmitting user data. 20. In the method of the two preceding embodiments, the user data is provided at the host computer by executing a host application, and the method further includes executing, at the UE, a client application associated with the host application. 21. A user equipment (UE) configured to communicate with a base station, the UE including a radio interface and processing circuitry configured to perform any of the three preceding embodiments. 22. A communications system including a host computer: - processing circuitry configured to provide user data; and - a communications interface configured to transfer user data to a cellular network for transmission to a user equipment (UE); - the UE includes a radio interface and processing circuitry, and the elements of the UE are configured to perform any of the steps of any of the embodiments of Group A. 23. In the communication system of the foregoing embodiment, the cellular network further includes a base station configured to communicate with the UE. 24. In the communication system of the two preceding embodiments: - processing circuitry of the host computer configured to execute a host application, thereby providing user data; and the processing circuitry of the UE is configured to execute a client application associated with the host application; 25. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: - providing user data at the host computer; and - initiating, at the host computer, a transmission carrying user data to the UE over a cellular network including a base station, the UE performing any of the steps of any of the embodiments of Group A. 26. The method of the preceding embodiment further includes, at the UE, receiving user data from the base station. 27. A communications system including a host computer: - a communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station; - a UE including a radio interface and processing circuitry, the processing circuitry of the UE configured to perform any of the steps of any of the embodiments of Group A 28. The communication system of any preceding embodiment, further including a UE. 29. The communication system of the two preceding embodiments further includes a base station, the base station including a radio interface configured to communicate with the UE and a communication interface configured to transfer user data carried by transmissions from the UE to the base station to a host computer. 30. In the communication system of the three preceding embodiments: - processing circuitry of the host computer configured to execute a host application; and - the processing circuitry of the UE is configured to execute a client application associated with the host application, thereby providing user data; 31. In the communication system of any of the preceding four embodiments: - processing circuitry of the host computer configured to execute the host application and thereby provide the requested data; and - 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; 32. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: receiving, at the host computer, user data transmitted from the UE to the base station, the UE performing any of the steps of any of the embodiments of Group A; 33. The method of the preceding embodiment further includes, at the UE, providing user data to the base station. 34. The method of the two preceding embodiments further comprises: - running, in the UE, a client application thereby providing user data to be transmitted; and - executing, on the host computer, a host application associated with the client application. 35. The method of the preceding three embodiments further comprises: - running, in the UE, a client application; and - receiving, at the UE, input data for the client application, the input data being provided at the host computer by executing a host application associated with the client application; - The user data to be sent is provided by the client application in response to the input data 36. A communications system including a host computer including a communications interface configured to receive user data originating from a transmission from user equipment (UE) to a base station, the base station including a wireless interface and processing circuitry, the processing circuitry of the base station configured to perform any of the steps of any of the Group B embodiments. 37. The communication system of the above embodiment further includes a base station. 38. The communication system of the two preceding embodiments further includes a UE, and the UE is configured to communicate with the base station. 39. In the communication system of the three preceding embodiments: - processing circuitry of the host computer configured to execute a host application; The UE is configured to execute a client application associated with the host application, thereby providing user data to be received by the host computer. 40. A method implemented in a communications system including a host computer, a base station, and a user equipment (UE), the method comprising: receiving, at the host computer, from a base station, user data originating from a transmission received by the base station from the UE, the UE performing any of the steps of any of the embodiments of Group A; 41. The method of the foregoing embodiment further includes, at the base station, receiving user data from the UE. 42. The method of the two preceding embodiments further includes initiating, at the base station, transmission of the received user data to the host computer.

Claims

1. 1. A method performed by a wireless device for Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM), comprising: Obtaining an uplink configuration for an LTM candidate cell (1212); receiving a first notification from a serving cell to perform uplink transmission in the LTM candidate cell (1214); Transmitting 1216 a first uplink transmission in the LTM candidate cell at a first transmit power and on a first uplink time / frequency resource; receiving a second notification from the serving cell to perform uplink transmission in the LTM candidate cell (1218); transmitting 1220 a second uplink transmission in the LTM candidate cell, the second uplink transmission being transmitted with 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; receiving, from the serving cell, a timing advance value for the LTM candidate cell based on the second uplink transmission (1222). method.

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

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

4. The first uplink transmission uses a first beam, and in response to receiving the second notification to perform the uplink transmission, the method further includes selecting a second beam for use in the second uplink transmission, wherein when the second beam is the same as the first beam, the second transmission is transmitted at a second transmit power different from the first transmit power, and when the second beam is different from the first beam, the second transmission is transmitted on a second uplink time / frequency resource different from the first time / frequency resource.

4. The method according to any one of claims 1 to 3.

5. the second notification for performing the uplink transmission includes notification of a second transmit power or notification of a second uplink time / frequency resource to be used for the second uplink transmission.

5. The method according to any one of claims 1 to 4.

6. the first notification and the second notification include a Physical Downlink Control Channel (PDCCH) command.

6. The method according to any one of claims 1 to 5.

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

8. the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

8. The method according to any one of claims 1 to 7.

9. At least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

9. The method according to any one of claims 1 to 8.

10. the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes an indication of an uplink candidate cell to transmit the first uplink transmission or the second uplink transmission, respectively.

10. The method according to any one of claims 1 to 9.

11. A Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) capable wireless device (200), comprising: Obtaining uplink configuration of LTM candidate cells; receiving a first notification from a serving cell to perform uplink transmission in the LTM candidate cell; Transmitting a first uplink transmission in the LTM candidate cell at a first transmit power and on a first uplink time / frequency resource; receiving a second notification from the serving cell to perform uplink transmission in the LTM candidate cell; transmitting a second uplink transmission in the LTM candidate cell, the second uplink transmission being transmitted with 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; a processing circuit (202) operable to receive, from the serving cell, a timing advance value for the LTM candidate cell based on the second uplink transmission; Wireless devices.

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

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

14. the first uplink transmission uses a first beam, and in response to receiving the second notification to perform the uplink transmission, the processing circuitry is operable to select a second beam for use in the second uplink transmission, wherein when the second beam is the same as the first beam, the second transmission is transmitted at a second transmit power different from the first transmit power, and when the second beam is different from the first beam, the second transmission is transmitted on a second uplink time / frequency resource different from the first time / frequency resource. A wireless device according to any one of claims 11 to 13.

15. the second notification for performing the uplink transmission includes notification of a second transmit power or notification of a second uplink time / frequency resource to be used for the second uplink transmission. A wireless device according to any one of claims 11 to 14.

16. the first notification and the second notification include a Physical Downlink Control Channel (PDCCH) command.

16. A wireless device according to any one of claims 11 to 15.

17. receiving the timing advance value from the serving cell includes receiving an LTM execution command; 17. A wireless device according to any one of claims 11 to 16.

18. the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

18. A wireless device according to any one of claims 11 to 17.

19. At least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

19. A wireless device according to any one of claims 11 to 18.

20. the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes a notification of an uplink candidate cell to transmit the first uplink transmission or the second uplink transmission, respectively.

20. A wireless device according to any one of claims 11 to 19.

21. 1. A method performed by a network node acting as a Serving Distribution Unit (S-DU) for Timing Advance (TA) management between a wireless device and at least one Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell, the method comprising: transmitting a first notification to the wireless device to perform an uplink transmission in the LTM candidate cell (1312); and transmitting a second notification to the wireless device to perform uplink transmission in the LTM candidate cell (1316). method.

22. and, upon detecting that the uplink transmission in the LTM candidate cell has failed (1314), transmitting the second notification to the wireless device to perform the uplink transmission in the LTM candidate cell.

22. The method of claim 21.

23. Detecting that the uplink transmission in the LTM candidate cell has failed includes not receiving a response from the LTM candidate cell.

23. The method of claim 22.

24. Detecting that the uplink transmission in the LTM candidate cell has failed includes receiving a notification from the LTM candidate cell that the uplink transmission in the LTM candidate cell has failed.

23. The method of claim 22.

25. the first uplink transmission and the second uplink transmission include transmission of a random access preamble.

25. The method of any one of claims 21 to 24.

26. the second notification to perform the uplink transmission includes notification of a transmit power or an uplink time / frequency resource to be used for the second uplink transmission.

26. The method of any one of claims 21 to 25.

27. the first notification and the second notification include a Physical Downlink Control Channel (PDCCH) command.

27. The method of any one of claims 21 to 26.

28. receiving a timing advance value from the candidate LTM cell (1318); and transmitting the timing advance value to the wireless device (1320).

28. The method of any one of claims 21 to 27.

29. transmitting the timing advance value to the wireless device includes transmitting an LTM execution command to the wireless device.

29. The method of claim 28.

30. transmitting the second notification to the wireless device to perform the uplink transmission includes determining a threshold number of uplink transmissions for the wireless device, the threshold number being not exceeded; 30. The method of any one of claims 21 to 29.

31. transmitting 1310 an uplink configuration for the uplink candidate cell to the wireless device.

31. The method of any one of claims 21 to 30.

32. the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

32. The method of claim 31 .

33. the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes an indication of an uplink candidate cell to transmit the first uplink transmission or the second uplink transmission, respectively.

32. The method of claim 31 .

34. at least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively; 34. The method of any one of claims 21 to 33.

35. 1. A network node (300) operable as a Serving Distribution Unit (S-DU) for Timing Advance (TA) management between a wireless device and at least one Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell, comprising: sending a first notification to a wireless device to perform an uplink transmission in the LTM candidate cell; Detecting an uplink transmission failure in the LTM candidate cell; a processing circuit (302) operable to transmit a second notification to a wireless device to perform an uplink transmission in the LTM candidate cell; Network node.

36. the processing circuitry is operable to, upon detecting that the uplink transmission in the LTM candidate cell has failed, send the second notification to the wireless device to perform the uplink transmission in the LTM candidate cell.

36. A network node according to claim 35.

37. the processing circuitry is operable to detect that the uplink transmission in the LTM candidate cell has failed by not receiving a response from the LTM candidate cell.

37. A network node according to claim 36.

38. the processing circuitry is operable to detect that the uplink transmission at the LTM candidate cell has failed by receiving a notification from the LTM candidate cell that the uplink transmission at the LTM candidate cell has failed.

37. A network node according to claim 36.

39. the first uplink transmission and the second uplink transmission include transmission of a random access preamble.

39. A network node according to any one of claims 35 to 38.

40. the second notification to perform the uplink transmission includes notification of a transmit power or an uplink time / frequency resource to be used for the second uplink transmission.

40. A network node according to any one of claims 35 to 39.

41. the first notification and the second notification include a Physical Downlink Control Channel (PDCCH) command. A network node according to any one of claims 35 to 40.

42. The processing circuitry receiving a timing advance value from the candidate LTM cell; and further operable to transmit the timing advance value to the wireless device.

42. A network node according to any one of claims 35 to 41.

43. transmitting the timing advance value to the wireless device includes transmitting an LTM execution command to the wireless device.

43. A network node according to claim 42.

44. the processing circuitry is operable to transmit the second notification to the wireless device to perform the uplink transmission by determining a threshold number of uplink transmissions for the wireless device, the threshold number being not exceeded; 44. A network node according to any one of claims 35 to 43.

45. The processing circuitry is further operable to transmit an uplink configuration for the uplink candidate cell to the wireless device.

45. A network node according to any one of claims 35 to 44.

46. the uplink configuration for the uplink candidate cell includes one or more random access parameters, and at least one of the first notification and the second notification includes an indication of which of the one or more random access parameters to use for the first uplink transmission or the second uplink transmission, respectively.

46. ​​A network node according to claim 45.

47. the uplink configuration for the uplink candidate cell includes two or more uplink configurations for two or more uplink candidate cells, and at least one of the first notification and the second notification includes a notification of an uplink candidate cell to transmit the first uplink transmission or the second uplink transmission, respectively.

46. ​​A network node according to claim 45.

48. At least one of the first notification and the second notification includes notification of a synchronization signal block (SSB) associated with the first uplink transmission or the second uplink transmission, respectively.

48. A network node according to any one of claims 35 to 47.

Images