Enhanced l1 / l2 triggered mobility (LTM)-related data logging

Abstract

This invention relates to LTM (L1 / L2 Triggered Mobility)-related data logging, wherein a terminal logs and reports the data after experiencing HOF or RLF (handover failure or radio link failure) occurring during a LTM cell switch procedure, wherein the logged data comprises at least one of an RACH (Random Access Channel) type indicator indicating an RACH procedure, a TA (Timing Advance) type applied in an RACH-less procedure, the RACH type indicator indicating one of a CFRA (Contention Free Random Access) procedure or a CBRA (Contention Based Random Access) procedure, the TA type indicating at least one of a terminal-based TA, a PDCCH-ordered TA provided by a serving cell, or a configured TA provided by the serving cell.

Description

TUTL 00404 PCENHANCED L1 / L2 TRIGGERED MOBILITY (LTM)-RELATED DATA LOGGINGCLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No. 63 / 680,950 entitled “Logged data for LTM enhancement” and filed August 08, 2024, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.FIELD

[0002] This invention generally relates to wireless communications and more particularly to LTM-related data logging.BACKGROUND

[0003] Wireless communication systems include several base stations (network nodes) to provide service to terminals (user equipment (UE) devices) where each base station provides wireless communication services within geographical areas of one or more cells. As a terminal moves, service is provided by different cells. Procedures for switching service from one cell to another may include procedures referred to as handovers, handoffs, cell switches, and others. Communication specifications define the information, signaling, protocol, and timing for switching cells. Some communication specifications include techniques designed to reduce mobility latency. For example, the Third Generation Partnership Project (3GPP) Release 18 (Rel-18), the first release of 5G Advanced, first standardized L1 / L2 Triggered Mobility (LTM) to reduce latency. With LTM, a network node (base station, gNB) receives L1 measurement report(s) from a terminal (UE) and changes the serving cell of the terminal based on the measurements. A current serving network node, providing the original serving cell, sends a cell switch command to the terminal via Medium Access Control (MAC) layer signaling in a MAC Control Element (MAC-CE). The cell switch command indicates an LTM candidate configuration that the base station (gNB) previously prepared and provided to theTUTL 00404 PC terminal through Radio Resource Control (RRC) signaling. In response, the terminal switches to the target configuration in accordance with the cell switch command.SUMMARY

[0004] A terminal logs data related to L1 / L2 Triggered Mobility (LTM) cell switch procedure as logged LTM-related data. The terminal reports the LTM-related data to the network after experiencing a Handover Failure (HOF) or Radio Link Failure (RLF) occurring during the LTM cell switch procedure. The LTM-related data can be reported in a Radio Link Failure (RLF) report and provides parameters and other information related to the LTM cell switch procedure allowing the network to improve performance. The logged and reported information includes any combination of parameters, indicators, and / or values including a Random Access Channel (RACH) type indicator indicating a RACH procedure used for the LTM cell switch procedure, a Timing Advance (TA) type applied in a RACH-less procedure used for the LTM cell switch procedure where the RACH type indicator indicates one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure and where the TA type indicates at least one of a terminal-based TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 is a block diagram of a communication system for an example where a terminal logs LTM-related data.

[0006] FIG. 2 is a message flow diagram for an example of logging LTM-related data.

[0007] FIG. 3 is a block diagram of an example of a base station suitable for use as a network node.

[0008] FIG. 4 is a block diagram of an example of a UE device suitable for use as a terminal device.TUTL 00404 PC

[0009] FIG. 5A is a first portion of a flow chart of an example of a method of logging and reporting LTM-related data.

[0010] FIG. 5B is a second portion of the flow chart of the example of the method of logging and reporting LTM-related data.

[0011] FIG. 6 is a flow chart of an example of a method of receiving LTM-related data from a terminal.DETAILED DESCRIPTION

[0012] Wireless communication systems operating in accordance with various standards employ minimization drive tests (MDT) and Self-Organizing Network (SON) reporting to improve wireless communication coverage. When new base stations are deployed, drive tests are performed before and after service activation of the new cell (base station). Initially, downlink / uplink (DL / UL) coverage measurements of the new cell and neighbor cells are made in the intended area of coverage improvement. During this phase, initial area tuning is performed (e.g. selection of an appropriate antenna for the new cell, adjustment of antenna tilting of the new cell and neighbor cells, etc.). Service with the new cell will be started after such initial tuning. Drive tests are performed to collect more extensive data of DL / UL coverage measurements in the intended area to confirm that adequate DL / UL coverage is being provided. In order to reduce the rigorous drive tests that are needed to collect downlink / uplink coverage measurements Minimization of Drive Test (MDT) are used to gather data. Using an MDT procedure, measurements can be collected from user equipment (UEs) (mobile devices) without the need for the extensive drive tests. As a result, the MDT can reduce network maintenance costs for operators, ensure a faster optimization cycle resulting in higher customer satisfaction and help to reduce the carbon emission to protect the environment. Furthermore, MDT enables operators to collect measurements from areas which are not accessible for drive tests (e.g. narrow roads, forests, private land / house / office). Other uses of MDT include mobility, capacity, QoS optimizations. In order to collect measurements from the mobile communication device, the device must be configured with the MDT parameters. The MDT configuration parameters typically include indicators of what parameters to measure, the time stamp of the log, how longTUTL 00404 PC the measurement should last and what parameters to report. The terminal logs the data and reports the requested information in a UElnformationResponse message (RRC message which is typically in response to a UElnformationRequest Message.

[0013] Conventional systems and communication specifications (such as 3GPP), however, do not provide for logged or reported information related to the LTM procedures discussed above. Accordingly, the network does not receive information regarding conditions or measurements related to an LTM cell switch radio link failure (RLF) or Handover Failure (HO). Even if the network realizes that handover failure occurred, it may not know the reason behind the handover failure. It may be due to RLF or it may be related to a multitude of parameters that are improperly configured to the UE. For the examples herein, however, the terminal logs and reports information related to the LTM cell switch procedure that resulted in a HOF or RLF. For at least one example, the logged and reported information related to the LTM cell switch procedure as logged LTM-related data comprises at least one of a Random Access Channel (RACH) type indicator indicating a RACH procedure used for the LTM cell switch procedure or a Timing Advance (TA) type applied in a RACH-less procedure used for the LTM cell switch procedure, where the RACH type indicator indicates one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure and where the TA type indicates at least one of a terminalbased TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell. The logged LTM-related data may also include at least one of a terminal-based TA value, a PDCCH-ordered TA value, or a configured TA value. The logged LTM-related data may also include a TA acquisition to CSC elapsed time value indicative of an elapsed time from the terminal-based TA value is acquired to reception of the CSC. In the examples, the logged LTM-related data further comprises a cell identifier (Cell ID) of an attempted destination cell to which the LTM cell switch procedure was directed where the attempted destination cell may be the target cell or another configured candidate cell.

[0014] In some situations, the logged LTM-related data may include other parameters related to LTM including conditional-LTM (C-LTM). Some examples of such parameters are discussed on International Patent Application NumberTUTL 00404 PCPCT / US2025 / 020337, entitled “L1 / L2 TRIGGERED MOBILITY (LTM)-RELATED DATA LOGGING”, filed on March 18, 2025 and hereby expressly incorporated by reference in its entirety.

[0015] For the examples discussed herein, a network node is any apparatus, equipment, device, or combination of devices, on the network side of the communication system that is connected to the communication network or is part of communication network. Some examples of a network node include a base station, a node B, an E-UTRA Node B, Evolved Node B, eNodeB, eNB, a New Generation eNB (ng-eNB), a gNodeB (also known as a gNB) in new radio (NR) technology, a macro station, pico station, and a femto station. Each network node provides at least one cell where each cell provides wireless service to terminal in a geographic area. The network node may form, or be a part of, the radio access network (RAN) that provides a connection between the core network and terminal communication devices. A RAN may be organized into three functional blocks including a Radio Unit (RU), a Distributed Unit (DU) and a Centralized Unit (CU). The RU transmits, receives, amplifies, and digitizes radio frequency signals and is typically located near, or integrated into, the antenna. The DU and CU perform computations and / or processing to send and receive digitalized radio signals to and from the core network. The DU is typically located at or near the RU and the CU may be closer to the core network. The infrastructure or connection between the RU and the DU is often referred to as fronthaul and the infrastructure or connection between the DU and the CU is often referred to as a midhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0016] A terminal communication device (terminal), such as a remote terminal and a relay terminal, is a communication device on the terminal side of the communication system and is sometimes referred to as user equipment (UE), a UE device, a terminal device, wireless mobile device, wireless communication device and other terms. Some examples of a terminal communication device include a mobile phone, a smart phone, a personal digital assistant (PDA), tablet, and laptop computer. In some situations, the terminal communication device is a machine type communication (MTC) communication device or Internet-of-Things (IOT) device. In addition, the terminal communicationTUTL 00404 PC device may be, or may be a part of, a wearable device or a vehicle where the vehicle may be terrestrial vehicle, watercraft, or aircraft (including unmanned aerial vehicles). The terminal communication device, therefore, is any fixed, mobile, or portable equipment that performs the functions of the terminal device described herein.

[0017] FIG. 1 is a block diagram of a communication system 100 for an example where a terminal 102 logs LTM-related data 104. The LTM-related data 104 includes data related to an LTM cell switch and is part of MDT / SON logging in the example. For the example, a network node 106 providing the serving cell 108 of the terminal 102 and the terminal 102 perform LTM preparation and early sync procedures before the network node 106 transmits a cell switch command 110 to the terminal 102 instructing the terminal 102 to switch from the serving cell 108 to a target cell 112 provided by a target network node 114. The LTM preparation, early sync, and switch procedures are in accordance with known techniques except that the terminal 102 logs LTM related data 104 that can be reported to the network, either via the original serving cell 108 or a new serving cell.

[0018] The communication system 100 includes communication system infrastructure that provides wireless communication service to terminals including the terminal 102. The communication system infrastructure includes multiple network nodes (e.g., base stations) 106, 114-116 connected to a core network 118 through a backhaul (not shown) to provide wireless communication services to the multiple terminals. The network nodes can communicate with each other via the backhaul which may be wired and / or wireless. An example of a suitable communication technique includes using X2 or Xn messaging. Accordingly, each network node (base station) also includes communication interface equipment for communicating with other base stations and network entities. For the examples discussed herein, the system operates in accordance with at least one revision of the 3rd Generation Partnership Project (3GPP) 5G specification, such as New Radio (NR), standards and protocols. Each network node provides wireless service through one or more cells.

[0019] While in the Radio Resource Configuration (RRC) Connected (RRC_CONNECTED) state, the terminal 102 provides measurement reports 120 to the network node 106. After receiving one or more reports, the network node 106TUTL 00404 PC determines that an LTM cell switch should be completed and performs LTM preparation. The network node 106 transmits an RRC configuration message 122 providing an LTM candidate cell configuration to the terminal 102. The terminal acknowledges the configuration message 122 with a configuration complete message. After the network node receives an L1 measurement report, the network node 106 may transmit a Physical Downlink Control Channel ordered (PDCCH-ordered) early timing advance (TA) message. In response, the terminal 102 invokes early synchronization (early sync) which includes downlink (DL) synchronization and uplink (UL) synchronization. The terminal 102 performs DL synchronization for the candidate cells 112, 124, 126 of the network nodes 114-116. As described in further detail below, the UL synchronization may include each of the cells calculating an early timing advance (TA) value or may include the terminal calculating and storing the early TA value for each candidate cell. Where the PDCCH-ordered early TA message includes UL TA parameters, the candidate cells calculate the UL early TA. A candidate cell calculating the UL early TA provides the UL early TA value to the serving cell which is provided to the terminal 102. Such a procedure is typically referred to as a PDCCH-ordered early TA procedure. For an LTM cell switch, the UL early TA value(s) is / are provided to the terminal 102 in the LTM cell switch command. In some situations, the terminal 102 may also determine UE-based early TA values when the PDCCH-ordered early TA procedure is performed. The terminal 102 may also determine UE-based early TA values without receiving a PDCCH-order. When the PDCCH-ordered early TA values are successfully received, the terminal typically overrides the UE-based values and applies the PDCCH-ordered values.

[0020] Although the example of FIG. 1 includes three candidate cells 112, 124, 126, any number of candidate cells may be identified. In some situations, for example, a single candidate cell 112 may be the only candidate cell and, therefore, is the cell selected as the target cell when an LTM switch is initiated.

[0021] After receiving an L1 measurement report from the terminal 102, the network node 106 of the serving cell 108 determines that an LTM cell switch should be performed and sends the cell switch command 110 to the terminal 102. The cell switch command 110 identifies one of the candidate cells as the target cell 112 of the cellTUTL 00404 PC switch. In response, the terminal discontinues communication with the serving cell 108 and attempts to establish communication with the target cell 112. Where the LTM cell switch is successful, the terminal 102 continues communication with the network via the target cell 112 which becomes the new serving cell of the terminal 102. In some situations, however, the cell switch (handover to the target cell) may fail. An LTM handover failure (HOF) or radio link failure (RLF) (LTM RLF / HOF) 128 may occur requiring the terminal 102 to reestablish communication using a reestablishment procedure or perform subsequent LTM if configured.

[0022] With conventional techniques, the terminal does not log information related specifically to the cell switch RLF / HOF 128 and, as a result, the network 118 does not receive MDT / SON reports with such information. For the examples herein, however, the terminal 102 logs the LTM-related data (logged LTM-related data) 104 in order to report some or all of the LTM-related data 104 to the network 118 if and when requested. The data 104 provides the network 118 with information that can be used to improve performance. For the example, the logged LTM-related data 104 is data logged as part of the MDT or SON logging process and is stored in an MDT / SON log 130 on memory 132 in the terminal 102. In some situations, the logged LTM-related data 104 may be logged as a part of separate process.

[0023] The LTM related data 104 may include any number of parameters, indicators, and values and combinations of parameters, indicators, and values depending on the particular implementation, terminal configuration, and network configuration. For the example of FIG. 1 , the LTM-related logged data 104 includes at least one of a Random Access Channel (RACH) type indicator 141 or a Timing Advance (TA) type indicator 143, at least one of a terminal-based TA value 145, a PDCCH-ordered TA value 147, or a configured TA value 149, a TA acquisition to CSC elapsed time value 151 , a cell identifier (Cell ID) 153 of an attempted destination cell, and a switch attempt type 155.

[0024] The information of each of the indicators, parameters and / or values may be modified, filtered, or otherwise be different from the descriptions herein and the information as depicted as a single indicator, parameter and / or value may be categorized as different information in some implementations. One or more of theTUTL 00404 PC indicators, parameters and / or values shown in FIG. 1 may be omitted or combined with other indicators, parameters and / or values. For example, some of the logged data fields may include more than one indicator in situations where a cell switch was attempted multiple times. In another example, the TA type indicator 143, TA value 147, terminalbased TA value 145 and the conjured TA value 149 may be omitted where the switch attempt employed CFRA or CBRA and received a TA value from the target cell in a Random Access Response (i.e. , MSG 2). The indicators, parameters and values are discussed briefly below and are discussed in more detail with reference to FIG. 2.

[0025] For the example, the LTM-related data 104 includes a type of RACH indicator 141 indicating RACH procedure used for the attempted LTM cell switch procedure. The RACH type indicator indicates one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure

[0026] The Timing Advance (TA) type indicator 143 indicated the TA Type applied in a RACH-less procedure used for the LTM cell switch attempt. TA type indicator 143 indicates at least one of a terminal-based TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell. The TA type indicator may also indicate that no TA value was available for the switch attempt.

[0027] The logged LTM-related data may also include at least one of a terminalbased TA value, a PDCCH-ordered TA value, or a configured TA value. The terminalbased TA value indicator 145 indicates the value early TA that was acquired by the terminal 102. The terminal-based TA (UE-based TA) may be determined in response to a PDCCH-order received from the serving cell in some situations.

[0028] The TA value provided in the CSC is indicated by the CSC TA value indicator 147. The TA value indicator 147, therefore, indicates the value of the PDCCH-ordered TA that was acquired by the serving cell 108 from the candidate cell and provided to the terminal 102 in the CSC 110.

[0029] The configured TA value indicator 149 indicates the configured TA value provided in an RRC Reconfiguration message from the serving cell. For the example, the configured TA value is either 0 or the TA value of the source cell. A TA=0 is typically provided when the target cell is a small cell such that there is no difference in a TA value for any terminal within the cell. A source cell TA value is typically provided whenTUTL 00404 PC the target cell and the source cell are provided by the same network node (gNB) or generated from the same physical location. The configured TA value was introduced to facilitate conditional Handovers (CHO) when no mechanism was defined for a terminal to obtain an early TA and UE-based early TA was not yet defined. The configured TA allows the terminal to access the target cell for a CHO by sending a RRC Configuration Complete message (Msg 3) without receiving a Random Access Response message (Msg 2). Accordingly, by logging and reporting the configured TA value, the network is notified of the TA value that was used but also that the cell switch failure was a result of failed legacy CHO procedure and not an LTM procedure.

[0030] The logged LTM-related data also includes a TA acquisition to CSC elapsed time value 151 that is indicative of an elapsed time from the time the terminal-based TA value is acquired to reception of the CSC. In other words, the TA acquisition to CSC elapsed time value 151 indicates the age of the value at the time the CSC was received.

[0031] In the examples, the logged LTM-related data further also includes a cell identifier (Cell ID) 153 of an attempted destination cell to which the LTM cell switch procedure was directed where the attempted destination cell may be the target cell or another configured candidate cell. Accordingly, where the terminal attempts to perform a switch to a configured cell that is not the specified target cell, the configured cell is identified to the network.

[0032] FIG. 2 is a message flow diagram 200 for an example of logging LTM-related data 104. One or more of the events and / or transmissions may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 2. In still further examples, additional events and / or transmissions may be added that are not explicitly described in connection with the example discussed with reference to FIG. 2.

[0033] At transmission 202, the terminal 102 transmits a measurement report to the serving cell of the serving network node (gNB) 106. Based at least partially on the measurement report, the network node 106 initiates LTM preparation at event 204.

[0034] At transmission 206, the network node 106 transmits an RRC Reconfiguration message to the terminal where the message includes LTM candidate configurations. The terminal stores the LTM candidate configurations received in the RRCTUTL 00404 PCReconfiguration message and transmits an RRC Reconfiguration Complete message to the serving cell of the network node (gNB) 106 at transmission 208.

[0035] At transmission 209, a PDCCH-ordered early TA message is transmitted from the network node to the terminal 102. The PDCCH-ordered early TA message invokes the DL synchronization leading to UL synchronization. As discussed below, the early UL TA values can be provided to the terminal via an RRC message or via a MAC CE.

[0036] At event 210, the terminal performs downlink (DL) synchronization with the candidate cell(s) identified in the LTM candidate cell configuration. The DL synchronization is triggered by the reception of the early TA PDCCH-order from the serving cell.

[0037] At event 212, uplink (UL) synchronization is performed for the candidate cell(s) and the terminal 102. The UL TA acquisition, referred to as early TA, may be performed with the PDCCH-ordered early TA acquisition procedure using a Contention- Free Random Access (CFRA) procedure or by a UE-based measurement procedure in accordance with an RRC configuration. Where UE-based TA measurement is configured, the network node 106 instructs the terminal to perform early TA acquisition with the candidate cell(s) 112, 124, 126 by measuring signals. With the CFRA procedure, the network node instructs the terminal via the PDCCH-ordered early TA acquisition message over PDCCH to perform the CFRA procedure where the terminal sends a preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the terminal does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command transmitted by the serving cell. The terminal does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity. For the terminal-determined TA (UE-based TA), the terminal receives an RRC configuration from the serving cell and measures the TA. The timing of the TA measurement, however, is based on the terminal implementation. The TA value for each candidate cell 112, 124, 126 is stored in memory 132 at the terminal 102 for the UE-based TA. For the example of FIG. 2, the terminal performs UE-based TA in addition to the PDCCH-ordered early TA acquisition and logs data associated with bothTUTL 00404 PC procedures even though a TA value resulting from only one of the procedures is applied to the RACH-less cell switch attempt. In addition, data associated with both procedures may be logged even though a RACH procedure was attempted.

[0038] At transmission 214, the terminal 102 performs L1 measurements on the configured candidate cell(s) and transmits L1 measurement report(s) to the network node 106. L1 measurement should be performed as long as the RRC reconfiguration received at transmission 206 is applicable.

[0039] At event 218, the network node (gNB) 106 decides to execute a cell switch to a target cell 112. At transmission 220, the network node 106 transmits an LTM cell switch command. A Medium Access Control - Control Element (MAC CE) including the candidate configuration index of the target cell is transmitted to the terminal triggering the LTM cell switch procedure. For the PDCCH ordered early TA procedure, the TA value may be included in the Cell Switch Command, and it is up to network implementation whether the TA value is included in the Cell Switch Command (even if the PDCCH order was performed in step 210). If the early TA value is not provided in the LTM cell switch command, the terminal either relies on the UE-based TA value for RACH-less cell switch or attempts the cell switch using a RACH procedure. Accordingly, the terminal may perform UE-based TA acquisition and PDCCH-ordered early TA acquisition.

[0040] At event 224, the terminal logs the TA related data. For the example, the early TA values for all the candidate cells including the target cell are logged. In some examples, only the early TA value for the target cell is logged. Where the early TA values are determined by the terminal, for example, the TA values for all the candidate cells should be available. Where the TA value for the target cell is provided by the cell switch command, the other candidate cell TA values may not be available to the terminal and only the target cell TA value is logged. Logging the target cell TA value, although known to the network, may be beneficial because a RACH-less cell switch may fail if an incorrect TA value is applied. Accordingly, the target cell TA value provided by the network node is still logged and reported in an RLF-Report even thoughTUTL 00404 PC the network may have the calculated TA value provided by the candidate cell that was selected as the target cell.

[0041] At event 226, the elapsed time from TA acquisition to receipt of the CSC is logged. Since the PDCCH-ordered TA value is provided in the CSC, the elapsed time is always zero for such a value and is not logged in the example. For other values such as terminal-based TA value or configured TA value, however, the elapsed time is logged.

[0042] At event 228, the terminal detaches from the serving cell and begins the process of switching to the target cell. Depending on the availability of a TA value (either via the Cell Switch Command or via UE-based TA measurement), the terminal performs either a RACH-less LTM or RACH-based LTM cell switch. The RACH-based LTM cell switch may include a CFRA procedure where the CFRA resource (e.g., RACH preamble) has been provided by the serving cell from the target cell.

[0043] For CFRA, the terminal sends a preamble transmission (Msg1 ), receives a Random Access Response (RAR) (Msg2) and transmits an RRC Configuration Complete (Msg 3). The UE initiates the process by sending a random access preamble to the target cell of the network node on the Physical Random Access Channel (PRACH). The target cell responds to the preamble with the RAR message which facilitates UL synchronization and provides initial resources and a temporary identifier (RA-RNTI) for further communication. The terminal transmits the RRC Configuration Complete message to indicate the successful completion of the Radio Resource Control (RRC) configuration.

[0044] Where a TA value for the target cell and RACH resource are unavailable, the a CBRA RACH process is used to access the target cell for the cell switch. In some situations, where a TA value for the target cell and RACH resource are unavailable or where the CBRA RACH process fails, the terminal may attempt the cell switch to a configured candidate cell that is not the specified target cell using a RACH-less process. The terminal may attempt such access where a TA value is available for the configured candidate cell. In some situations, the terminal may attempt the RACH-less cell switch to the configured candidate cell where the RACH-less cell switch to the target cell has failed. Both TA values may be logged in such situations.TUTL 00404 PC

[0045] At event 230, the terminal attempts a RACH-less cell switch to the target cell 112. If the TA value is provided in the cell switch command, the terminal 102 applies the TA value as instructed by the network. In the case where UE-based TA measurement is configured, but no TA value is provided in the cell switch command, the terminal applies the terminal-determined TA value, if available. If RACH is not required, therefore, the terminal switches to the target cell and applies the configuration indicated by the candidate configuration index.

[0046] If no valid TA value is available, the UE attempts RACH-based LTM cell switch at event 232. Where the cell switch is successfully performed, either by RACH- based or RACH-less procedures, the terminal completes the LTM cell switch procedure by sending a RRC Reconfiguration Complete message to the target cell. If the terminal has performed the Random Access procedure in event 232, the terminal determines the LTM cell switch execution is successfully completed when the random access procedure is successfully completed. As discussed above, the RACH procedure may include CBRA in some situations. For RACH-less LTM, the terminal considers that LTM cell switch execution is successfully completed when the terminal determines that the first UL data has been successfully received by the network. For the example of FIG. 2, however, the cell switch is not successfully competed due to either a HOF or RLF. At event 234 an RLF / HOF occurs. Event 230 and event 232 in FIG. 2 are illustrated with dashed lines to indicate that only one of the events may be attempted.

[0047] At event 236, the other TA information and the cell ID of the destination cell (target cell or other configured candidate cell) are logged. Where multiple cell switch attempts are made using the different TA values, information related to each attempt are logged. For example, where a RACH-less cell switch attempt to the target cell fails and a subsequent RACH-less cell switch attempt is made to a configured candidate cell, both TA values are logged and associated with the corresponding attempt. The cell IDs of both destination cells are also logged.

[0048] At event 238, the RACH types are logged. Accordingly, for each cell switch attempt (if more than one), the terminal logs whether the attempt used RACH-less or RACH access and where RACH was used, whether the cell switch attempt used CFRA or CBRA for access to the target cell.TUTL 00404 PC

[0049] At event 240, the terminal reestablished an RRC connection with a network node 242. Since the terminal experienced an RLF or HOF, the terminal performs an RRC re-establishment procedure to attempt to re-establish a connection with the network. The terminal initiates the RRC re-establishment procedure by sending an RRC Connection Re-establishment Request message to the original serving cell or another suitable cell within the network. The network node 242 may be the serving network node, one of the network nodes 115, 116 providing a cell that was candidate cell 124, 126 for the LTM cell switch, or another network node providing a suitable cell for reconnection.

[0050] At transmission 244, the new serving cell of the network node 242 sends a UE Information Request message to the terminal 102.

[0051] At transmission 246, the terminal 102 sends a UE Information Response message to the new serving cell provided the network node 242. In response to the UE Information Request message, the terminal 102 sends a UE Information Response message to the network node 242 that includes the logged LTM-related data. For the example, the UE Information Response message includes an RLF report that includes the logged LTM-related data. In some situations, the RLF report may only indicate that an RLF / HOF occurred during an LTM cell switch. The network may request additional LTM logged information in some situations. In other situations, additional logged LTM- related data is included and may include any of the parameters, indicators, or values discussed above.

[0052] FIG. 3 is a block diagram of an example of a base station 300 suitable for use as a network node 108. The base station 300 includes an antenna system 302, electronics 304, a transmitter 306, and a receiver 308, as well as other electronics, hardware, and code. The base station 300 is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to the base station 300 and network node 106 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. The baseTUTL 00404 PC station 300 may be a fixed device or apparatus that is installed at a particular location at the time of system deployment. Examples of such equipment include fixed base stations or fixed transceiver stations. Although the base station may be referred to by different terms, the base station is typically referred to as a gNodeB or gNB when operating in accordance with one or more revisions of the 3GPP communication specification. In some situations, the base station 300 may be mobile equipment that is temporarily installed at a particular location. Some examples of such equipment include mobile transceiver stations that may include power generating equipment such as electric generators, solar panels, and / or batteries. Larger and heavier versions of such equipment may be transported by trailer. In still other situations, the base station 300 may be a portable device that is not fixed to any particular location.

[0053] The electronics 304 include any combination of hardware, software, and / or firmware for communicating with and controlling other base station components to execute the functions described herein as well as facilitating the overall functionality of the base station 300. The electronics 304, therefore, cooperatively operate with other base station 300 components to initiate tasks and perform the operations and functions of the base station 300. An example of suitable electronics 304 includes code running on a microprocessor or processor arrangement connected to memory 314. The transmitter 306 includes electronics configured to transmit wireless signals. In some situations, the transmitter 306 may include multiple transmitters. The receiver 308 includes electronics configured to receive wireless signals. In some situations, the receiver 308 may include multiple receivers. The receiver 308 may receive signals through multiple antennas or through a selected antenna of the antenna system 302. The antenna system 302 may include separate transmit and receive antennas in some situations.

[0054] The transmitter 306 and receiver 308 in the example of FIG. 3 perform radio frequency (RF) processing including modulation and demodulation. The receiver 308, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 306 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the base station functions.TUTL 00404 PCThe required components may depend on the particular functionality required by the base station 300.

[0055] The transmitter 306 includes a modulator (not shown), and the receiver 308 includes a demodulator (not shown). The modulator modulates the signals to be transmitted as part of the downlink signals and can apply any one of a plurality of modulation orders. The demodulator demodulates any uplink signals received at the base station 300 in accordance with one of a plurality of modulation orders.

[0056] The base station 300 includes a communication interface 312 for communicating with other base stations and other network components, and other entities, such as servers and databases. The communication interface 312 may be connected to a backhaul or network enabling communication with other base stations. In some situations, the link between base stations may include at least some wireless portions. The communication interface 312, therefore, may include wireless communication functionality and may utilize some of the components of the transmitter 306 and / or receiver 308.

[0057] The electronics 304, in conjunction with the receiver 308, measure and evaluate signals transmitted by UE devices. The electronics 304 and the receiver 308, therefore, can receive, measure, and evaluate uplink signals including reference signals transmitted by UE devices. Signal measurements and evaluations can be stored in a memory 314.

[0058] The electronics 304, in conjunction with the transmitter 306 and antenna system 302, process outgoing signals to precode signals transmitted to terminals (UE devices). Accordingly, the electronics 304 and transmitter 306 apply the appropriate MU-MIMO precoder to signals transmitted to a specific UE device. As discussed herein, the base station 300 may transmit reference signals and receive feedback from the terminals in order to determine the appropriate precoders, antenna system settings, and other transmission parameters.

[0059] FIG. 4 is a block diagram of an example of a UE device 400 suitable for use as a terminal device 102. In some examples, the UE device 400 is any wireless communication device such as a mobile phone, a transceiver modem, a personal digital assistant (PDA), a tablet, or a smartphone. In other examples, the UE device 400 is aTUTL 00404 PC machine type communication (MTC) communication device or Internet-of-Things (IOT) device. The UE device 400, therefore is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to UE device 400 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices.

[0060] The UE device 400 includes at least electronics 402, a transmitter 404 and a receiver 406. The electronics 402 include any combination of hardware, software, and / or firmware for communicating with and controlling other UE device components to execute the functions described herein as well as facilitating the overall functionality of a communication device. The electronics 402, therefore, cooperatively operate with other UE device components to initiate tasks and perform the operations and functions of the UE device 400. An example of suitable electronics 402 includes code running on a microprocessor or processor arrangement connected to memory 132. The transmitter 404 includes electronics configured to transmit wireless signals. In some situations, the transmitter 404 may include multiple transmitters. The receiver 406 includes electronics configured to receive wireless signals. In some situations, the receiver 406 may include multiple receivers. The receiver 406 and transmitter 404 receive and transmit signals, respectively, through antenna 408. The antenna 408 may include separate transmit and receive antennas. In some circumstances, the antenna 408 may include multiple transmit and receive antennas.

[0061] The transmitter 404 and receiver 406 in the example of FIG. 4 perform radio frequency (RF) processing including modulation and demodulation. The receiver 406, therefore, may include components such as low noise amplifiers (LNAs) and filters. The transmitter 404 may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.TUTL 00404 PC

[0062] The transmitter 40 includes a modulator (not shown), and the receiver 406 includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted as part of the uplink signals. The demodulator demodulates the downlink signals in accordance with one of a plurality of modulation orders.

[0063] The UE device 400 is capable of transmitting and receiving sidelink signals to and from other UE devices as well as communicating with base stations. The electronics 402, in conjunction with the receiver 406, measure an evaluate signals transmitted by other devices, such as base stations and UE devices. The electronics 402 and the receiver 406, therefore, can receive, measure, and evaluate downlink reference signals transmitted by a base station (e.g. candidate cells). Signal measurements and evaluations can be stored in the memory 132.

[0064] FIG. 5A and FIG. 5B are portions of a flow chart of an example of a method of logging and reporting LTM -related data. The method may be performed in a system such the system 100 discussed herein. For the example, the method is performed by a terminal such as terminal 102 or the UE device 400. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the terminal may facilitate the generation, formatting, reception, and transmission of signals and messages as well as facilitating measurements, evaluations and determinations. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 5A and FIG. 5B. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 5A and FIG. 5B.

[0065] At step 502, the terminal 102 transmits a measurement report to the serving cell of the serving network node (gNB) 106.

[0066] At step 504, the terminal received from the network node 106 an RRC Reconfiguration message including LTM candidate configurations. The terminal stores the LTM candidate configurations received in the RRC Reconfiguration message andTUTL 00404 PC transmits an RRC Reconfiguration Complete message to the network node (gNB) 106 at step 506.

[0067] At step 507, a PDCCH-ordered early TA message is received from the network node to the terminal 102. The PDCCH-ordered early TA message invokes the DL synchronization leading to UL synchronization. The PDCCH-ordered early TA message may be used to invoke the PDCCH-ordered procedure for C-LTM as well as for LTM. For C-LTM, however, the early UL TA values are provided to the terminal using a mechanism other than the LTM cell switch command. The early UL TA values can be provided to the terminal via an RRC message or via a MAC CE.

[0068] At step 508, the terminal performs downlink (DL) synchronization with the candidate cell(s) identified in the LTM candidate cell configuration.

[0069] At step 510, the uplink (UL) synchronization is performed for the candidate cell(s) and the terminal 102. The UL early TA acquisition may be performed with a CFRA procedure or by a UE-based measurement procedure in accordance with an RRC configuration. Where UE-based TA measurement is configured, the network node 106 instructs the terminal to perform early TA acquisition with the candidate cell(s) 112, 124, 126. For the CFRA procedure, the network node instructs the terminal via a command over PDCCH to perform the CFRA procedure where the terminal sends a preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the terminal does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. For the terminal-determined TA (UE-based TA), the terminal receives an RRC configuration from the serving cell and measures the TA. The timing of the TA measurement, however, is based on the terminal implementation. The TA value for each candidate cell 112, 124, 126 is stored in memory 132 at the terminal 102 for the UE-based TA.

[0070] At step 512, the terminal 102 performs L1 measurements on the configured candidate cell(s) and transmits L1 measurement report(s) to the network node 106. L1TUTL 00404 PC measurement should be performed as long as the RRC reconfiguration received at transmission 206 is applicable.

[0071] At step 516, the terminal receives, from the network node 106, an LTM cell switch command. A Medium Access Control - Control Element (MAC CE) including the candidate configuration index of the target cell is transmitted to the terminal to initiate the LTM cell switch procedure.

[0072] At step 518, the terminal logs any available LTM data such as early TA value data. For the example, the early TA values for all the candidate cells including the target cell are logged. In some examples, only the early TA value for the target cell is logged. Where the early TA values are determined by the terminal, for example, the TA values for all the candidate cells should be available. Where the TA value for the target cell is provided by the cell switch command, the other candidate cell TA values may not be available to the terminal and only the target cell TA value is logged. Logging the target cell TA value known to the network may be beneficial since a RACH-less cell switch may fail if an incorrect TA value was applied. Accordingly, the target cell TA value provided by the network node is still logged and reported in an RLF-Report even though the network may have the calculated TA value provided by the candidate cell. The terminal may also log CP data related to the CP used to calculate the early TA value since the CP used by each cell impacts the accuracy of the early TA value. The CP data includes at least data indicating whether the CP is a Normal CP (NCP) or an Extended CP (ECP). The associated numerology may also be logged. The terminal typically uses the CP to determine the TA value.

[0073] At step 520, the terminal detaches from the serving cell 108 and begins the process of switching to the target cell.

[0074] At step 522, it is determined whether a valid TA is available for target cell 112. Depending on the availability of a valid TA value, the terminal performs either a RACH- less LTM or RACH-based LTM cell switch. If a valid TA is not available, the method proceeds to step 523. If a valid TA is available for the target cell, the terminal performs a RACH-less cell switch procedure at step 526.TUTL 00404 PC

[0075] At step 526, the terminal attempts a RACH-less cell switch procedure to the target cell 112. If the TA value is provided in the cell switch command, the terminal 102 applies the TA value as instructed by the network. In the case where UE-based TA measurement is configured, but no TA value is provided in the cell switch command, the terminal applies the terminal-determined TA value, if available. If RACH is not required, therefore, the terminal switches to the target cell and applies the configuration indicated by the candidate configuration index.

[0076] At step 527, it is determined whether the cell switch to the target cell was successful. If the cell switch was successful, the terminal continues data communication via the target cell at step 529. If the cell switch failed, the method continues at step 523.

[0077] At step 523, the terminal determines whether a CFRA resource for the target cell is available. If the CFRA resource (preamble) was successfully received in the CSC, the terminal attempts CFRA RACH to the target cell at step 531. If a CFRA resource is not available for the target cell, the method continues at step 533.

[0078] At step 535, it is determined whether the cell switch to the target cell was successful. If the cell switch failed, the method continues at step 533. Otherwise, the method continues at step 537.

[0079] At step 537, the terminal logs the LTM-related data before continuing data communication via the target cell at step 529. The terminal logs data related to all failed cell switch attempts. Accordingly, if a RACH-less cell switch was attempted, the terminal logs the TA values, the types of TA values, at the elapsed time from TA acquisition to receipt of the CSC, and the indicator that a RACH-less attempt was made. The terminal also logs values related to the failed cell switch attempted using CFRA if one was attempted at step 533 and failed. The logged vales, therefore, may include indicator indicating the CFRA was attempted.

[0080] At step 533, the terminal attempts access to the target cell using the CBRA procedure. Accordingly, the terminal transmits the preamble transmission (Msg1 ) using a preamble of the resource pool for contention based random access.TUTL 00404 PC

[0081] At step 539, it is determined whether the cell switch to the target cell was successful. If the cell switch failed, the method continues at step 541 . Otherwise, the method continues at step 537.

[0082] At step 541 , the terminal determines whether a TA value is available for another configured candidate cell other than the target cell. If a TA value is available, the terminal attempts a RACH-less cell switch to the destination cell (configured candidate cell) at step 543. Otherwise, the method continues at step 545.

[0083] At step 547, it is determined whether the cell switch to the destination cell (configured candidate cell) was successful. If the cell switch failed, the method continues at step 545. Otherwise, the method continues at step 549.

[0084] At step 549, the terminal logs the LTM-related data before continuing data communication via the configured candidate cell at step 551. The terminal logs data related to all failed cell switch attempts. Accordingly, if a RACH-less cell switch was attempted, the terminal logs the TA values, the types of TA values, at the elapsed time from TA acquisition to receipt of the CSC, and the indicator that a RACH-less attempt was made. The terminal also logs values related to the failed cell switch attempted using CFRA if one was attempted at step 533 and failed. The logged values, therefore, may include indicator indicating the CFRA was attempted. Logged data also includes values and parameters related to the CBRA attempt.

[0085] At step 545, the terminal logs the LTM-related data establishing an RRC session with a new serving cell at step 553. The terminal logs data related to all failed cell switch attempts. Accordingly, if a RACH-less cell switch was attempted, the terminal logs the TA values, the types of TA values, at the elapsed time from TA acquisition to receipt of the CSC, and the indicator that a RACH-less attempt was made. The terminal also logs values related to the failed cell switch attempted using CFRA if one was attempted at step 533 and failed. The logged values, therefore, may include indicator indicating the CFRA was attempted. Logged data also includes values and parameters related to the CBRA attempt and a RACH-less switch attempt to another configured candidate cell if one was attempted at step 543.TUTL 00404 PC

[0086] At step 553, the terminal reestablished an RRC connection with a network node 242. For the example of FIG. 5A and FIG. 5B, all RACH-less procedures and the RACH-based procedures resulted in a HOF or RLF to reach step 553. The terminal performs an RRC re-establishment procedure to attempt to re-establish a connection with the network. The terminal initiates the RRC re-establishment procedure by sending an RRC Connection Re-establishment Request message to the original serving cell or another suitable cell within the network. The re-establishment, therefore, may be with the original serving cell 108, the target cell 112, one of the other candidate cells 115, 116 for the LTM cell switch, or another suitable cell for reconnection.

[0087] At step 554, the terminal transmits an indicator indicating that logged data is available. The availability indicator may be an rlf-InfoAvailable indicator indicating the terminal has an RLF report available. The terminal may send the availability indicator in any one of the following RRC message, such as RRCSetupComplete, RRCReestablishmentComplete, RRCResumeComplete, or RRCReconfigurationComplete message. For the example herein, the terminal also transmits the availability indicator after successfully switch to a candidate cell or the target cell when at least one previous cell switch failed. Accordingly, for the method of FIG. 5A and FIG. 5B, step 554 follows steps 529 and 551 .

[0088] At step 555, a UE Information Request message is received from the new serving cell which may be the target cell, candidate cell, original serving cell or another cell depending on how method arrives at step 554. At step 557, the terminal sends a UE Information Response message to the new serving cell in response to the UE Information Request message where the UE Information Response message includes the logged LTM-related data. For the example, the UE Information Response message includes an RLF report that includes the logged LTM-related data. In some situations, the RLF report may only indicate that an RLF / HOF occurred during an LTM cell switch. Accordingly, the RLF report may include a last HO-type that indicates LTM or C-LTM. In other situations, additional logged LTM-related data is included and may include any of the parameters, indicators, or values discussed above for each failed cell switch attempt.TUTL 00404 PC

[0089] FIG. 6 is a flow chart of an example of a method of receiving LTM-related data from a terminal. The method may be performed in a system such the system 100 discussed herein. For the example, the method is performed by a network node such as the network node 106 and or the base station 300. The method may be performed using any of several techniques involving any combination of software, hardware, and firmware. For example, software code running on electronics including a processor, computer or other processor arrangement within the network node may facilitate the generation, formatting, reception, and transmission of signals and messages as well as facilitating measurements, evaluations and determinations. One or more of the steps may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in FIG. 6. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 6.

[0090] At step 602, the network node establishes RRC establishment with a terminal that has experiences an RLF of HOF. The RRC re-establishment procedure is initiated by a receiving an RRC Connection Re-establishment Request message from the terminal.

[0091] At step 604, the network node transmits a UE Information Request message is to the terminal.

[0092] At step 606, the network node receives form the terminal, a UE Information Response message that includes logged LTM-related data. For the example, the UE Information Response message includes an RLF report that includes logged LTM- related data. In some situations, the RLF report may only indicate that an RLF / HOF occurred during an LTM cell switch. Accordingly, the RLF report may include a last HO- type that indicates LTM or C-LTM. In other situations, additional logged LTM-related data is included and may include any of the parameters, indicators, or values discussed above.

[0093] To clearly illustrate this interchangeability of hardware, firmware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality isTUTL 00404 PC implemented as hardware, firmware or software, or a combination of these techniques, depends upon the particular application and design constraints imposed on the overall system. The described functionality may be implemented in various ways for each particular application, but such implementation decisions do not cause a departure from the scope of the present disclosure. In accordance with various embodiments, a processor, device, component, circuit, structure, machine, module, etc. can be configured to perform one or more of the functions described herein. The term "configured to" or "configured for" as used herein with respect to a specified operation or function refers to processors, devices, components, circuits, electronics, and equipment that are physically constructed, programmed, instructed and / or arranged to perform the specified operation or function. Furthermore, the various illustrative logical blocks, modules, devices, components and circuits described herein can be implemented within or performed by an integrated circuit (IC) that can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), other electronics or combinations thereof. (ASIC), a field programmable gate array (FPGA) or other programmable logic device, or any combination thereof. The logical blocks, electronics, and circuits can further include antennas and / or transceivers to communicate with various components within the network or within the device. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any conventional processor, controller, or state machine. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other suitable configuration to perform the functions described herein.

[0094] When implemented in software, the functions can be stored as one or more instructions or code on a computer-readable medium. Thus, the steps of a method or algorithm disclosed herein can be implemented as software stored on a computer- readable medium. Computer readable media includes both computer storage media and communication media, including any medium that can be enabled to transfer a computer program or code from one place to another. A storage media can be any available media that can be accessed by a computer. By way of example, and notTUTL 00404 PC limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0095] Therefore, the methods and apparatus of this invention may take the form, at least partially, of program logic or program code (i.e. , instructions) embodied in tangible media, such as a machine-readable storage medium. When the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. The methods and apparatus of the present invention may also be embodied in the form of program code that is transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via any other form of transmission. When the program code is received and loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0096] Additionally, memory or other storage, as well as communication components, may be employed in embodiments of the present disclosure. It will be appreciated that, for clarity purposes, the above description has described embodiments of the present disclosure with reference to different functional units and processors. However, it will be apparent that any suitable distribution of functionality between different functional units, processing logic elements or domains may be used without detracting from the present disclosure. For example, functionality illustrated to be performed by separate processing logic elements, or controllers, may be performed by the same processing logic element, or controller. Therefore, references to specific functional units are only references to a suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organization.

[0097] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed inTUTL 00404 PC conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims

TUTL 00404 PCCLAIMS1 . A method comprising: receiving an L1 / L2 Triggered Mobility (LTM) candidate configuration from a serving cell; receiving a Cell Switch Command (CSC); attempting an LTM cell switch procedure in response to the CSC; logging data related to the LTM cell switch procedure as logged LTM-related data, the logged LTM-related data comprising at least one of a Random Access Channel (RACH) type indicator indicating a RACH procedure used for the LTM cell switch procedure or a Timing Advance (TA) type applied in a RACH-less procedure used for the LTM cell switch procedure, the RACH type indicator indicating one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure, the TA type indicating at least one of a terminal-based TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell; and reporting the LTM-related data to a network after the LTM cell switch procedure fails.

2. The method of claim 1 , the logged LTM-related data further comprising at least one of a terminal-based TA value, a PDCCH-ordered TA value, or a configured TA value.

3. The method of claim 2, wherein the logged LTM-related data comprises the terminal-based TA value and the PDCCH-ordered value.

4. The method of claim 1 , the logged LTM-related data further comprising: a TA acquisition to CSC elapsed time value indicative of an elapsed time from the terminal-based TA value is acquired to reception of the CSC.TUTL 00404 PC5. The method of claim 1 , the logged LTM-related data further comprising a cell identifier (Cell ID) of an attempted destination cell to which the LTM cell switch procedure was directed.

6. The method of claim 1 , wherein the LTM cell switch procedure comprises: receiving, from the serving cell, the PDCCH-ordered TA value for a target cell; receiving, from the serving cell, a CFRA resource for accessing the target cell; attempting a cell switch to the target cell using a RACH-less procedure with thePDCCH-ordered TA value; and in response to a failed attempt to cell switch to the target cell using the RACH- less procedure with the PDCCH-ordered TA value, attempting the cell switch to the target cell using a CFRA procedure with the CFRA resource.

7. The method of claim 6, wherein receiving the CSC comprises receiving the PDCCH-ordered TA value and the CFRA resource in the CSC.

8. The method of claim 6, further comprising: in response to a failed attempt to cell switch to the target cell using the CFRA procedure with the CFRA resource, attempting a cell switch to the target cell using a CBRA procedure.

9. The method of claim 8, further comprising: in response to a failed attempt to cell switch to the target cell using a CBRA procedure, attempting a cell switch to a candidate cell identified in the LTM candidate configuration using a RACH-less procedure with a candidate cell terminal-based early TA.TUTL 00404 PC10. The method of claim 9, further comprising: in response to a failed attempt to cell switch to the candidate cell, establishing a Radio Resource Configuration (RRC) connection with a new serving cell and transmitting a UE information response message including the logged LTM data.11 . The method of claim 1 , further comprising: receiving the configured TA in the LTM candidate configuration; and attempting to cell switch to a target cell identified in the CSC using a RACH-less procedure with the configured TA.

12. A method comprising: establishing Radio Resource Configuration (RRC) connection with a terminal that experienced failure of an L1 / L2 Triggered Mobility (LTM) cell switch procedure; and receiving, from the terminal, a report comprising logged LTM-related data comprising information related to the LTM cell switch procedure, the logged LTM-related data comprising at least one of a Random Access Channel (RACH) type indicator indicating a RACH procedure used for the LTM cell switch procedure or a Timing Advance (TA) type applied in a RACH-less procedure used for the LTM cell switch procedure, the RACH type indicator indicating one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure, the TA type indicating at least one of a terminal-based TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell.

13. The method of claim 12, the logged LTM-related data further comprising at least one of a terminal-based TA value, a PDCCH-ordered TA value, or a configured TA value.TUTL 00404 PC14. The method of claim 13, wherein the logged LTM-related data comprises the terminal-based TA value and the PDCCH-ordered value.

15. The method of claim 12, the logged LTM-related data further comprising: a TA acquisition to CSC elapsed time value indicative of an elapsed time from the terminal-based TA value is acquired to reception of the CSC.

16. The method of claim 12, the logged LTM-related data further comprising a cell identifier (Cell ID) of an attempted destination cell to which the LTM cell switch procedure was directed.

17. A terminal comprising: a receiver configured to receive an L1 / L2 Triggered Mobility (LTM) cell switch candidate cell configuration from a serving cell of a network and to receive a Cell Switch Command (CSC); a memory configured to store data related to an LTM cell switch procedure as logged LTM-related data, the logged LTM-related data comprising at least one of a Random Access Channel (RACH) type indicator indicating a RACH procedure used for the LTM cell switch procedure or a Timing Advance (TA) type applied in a RACH-less procedure used for the LTM cell switch procedure, the RACH type indicator indicating one of a Contention Free Random Access (CFRA) procedure or a Contention Based Random Access (CBRA) procedure, the TA type indicating at least one of a terminalbased TA, a PDCCH-ordered TA provided by the serving cell, or a configured TA provided by the serving cell; electronics configured to attempt the LTM cell switch procedure; and a transmitter configured to transmit a report reporting the LTM-related data to the network after the LTM cell switch procedure fails.

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