L1 / l2 triggered mobility (LTM)-related data logging

Abstract

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 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 last handover type (Last_HO-type) indicator identifying LTM as the last HO based, L1 parameters, L3 parameters, a target timing advance (TA) value, candidate TA values, a cyclic prefix (CP) indicator, a reconfiguration elapsed time, a TA type indicator, and a TA acquisition elapsed time.

Description

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

[0001] The present application claims priority to Provisional Application No. 63 / 574,807 entitled “Logged Data for LTM”, filed April 04, 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 theterminal 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 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 last handover type (HO-type) indicator identifying LTM as the last HO based, L1 parameters, L3 parameters, a target timing advance (TA) value, candidate TA values, a cyclic prefix (CP) indicator, a reconfiguration elapsed time, a TA type indicator, and a TA acquisition elapsed time.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.

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

[0010] FIG. 6 is a flow chart of an example of a method of receiving LTM-related data from a terminal.DETAILED DESCRIPTION

[0011] 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 long 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.Conventional systems and communication specifications (such as 3GPP), however, do not provide for logged or reported information related to the LTM procedures discussedabove. 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 indicates that the last handover type (Last_HO-type) performed was LTM based. Other logged and reported information may include L1 parameters, L3 parameters, a target timing advance (TA) value, candidate TA values, a cyclic prefix (CP) indicator, a reconfiguration elapsed time, a TA type indicator, and a TA acquisition elapsed time.

[0012] 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 amidhaul. The communication node, therefore, may perform the functions of one or more of the RU, DU and / or CU depending on the particular implementation.

[0013] 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 communication 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.

[0014] 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.

[0015] 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 wiredand / 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.

[0016] 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 106 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 transmits 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. For a conditional-LTM (C-LTM) procedure where the PDCCH-ordered early procedure is used, the UL early TA values may be provided to the UE via a new RRC message or via MAC CE. In some situations, the terminal 102 may also determine UE-based early TA values when the PDCCH-ordered early TAprocedure is performed. When the PDCCH-ordered early TA values are successfully received, the terminal typically overrides the UE-based values and applies the PDCCH- ordered values.

[0017] 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.

[0018] 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 cell 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.

[0019] 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.

[0020] 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 an LTM HO-type indicator 134, L1 parameters 136, L3 parameters 138, a target timing advance (TA) value 140, candidate TA values 142, a cyclic prefix (CP) indicator 144, a reconfiguration to RACH elapsed time 146, a TA type indicator 148, a TA acquisition to RACH-less switch elapsed time 150, command to RACH-less switch elapsed time 152, an early TA acquisition to RACH 154 elapsed time, a command to RACH elapsed time 156, and RACH indicator 158 indicating whether the cell switch attempt was RACH-based or RACH-less. 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 the indicators, parameters and / or values shown in FIG. 1 may be omitted or combined with other indicators, parameters and / or values. For example, the target TA value 140 may be included in the candidate TA values 142. The indicators, parameters and values are discussed briefly below and are discussed in more detail with reference to FIG. 2.

[0021] The LTM-related data 104 includes a last handover type (HO-type) indicator 134 indicating that the failed handover or RLF occurred during, or immediately after, an LTM cell switch. The HO-type indicator 134 may further specify that the LTM cell switch was a conditional-LTM (C-LTM) cell switch where the terminal determines the timing for the LTM cell switch. The HO-type indicator 134 may be in addition to, or may be a part of any conventional HO-type indicators. For example, a conventional HO type indicator can be expanded to include an LTM HO-type and a C-LTM HO-type.

[0022] The LTM-related data 104 may include L1 parameters 136 and / or L3 parameters 138. The L1 and L3 parameters that are measured or otherwise determined by the terminal 102 for reporting to the serving cell 108 as part of the LTM process prior to the LTM cell switch are logged.

[0023] A target TA value 140 is the early TA value used by the terminal when attempting the LTM cell switch to the target cell and may be a terminal-calculated value(LIE determined TA) or may be a TA value provided by the network node 106 in the LTM cell switch command 110.

[0024] The candidate TA value(s) 142 are the early TA values of all of the candidate cells that were determined by the terminal. The candidate TA values 142, therefore, are the UE determined TAs for the candidate cells identified by the LTM candidate cell configuration received from the serving cell in the RRC reconfiguration message. For the example, the cell IDs of the candidate cells are included with the TA values.

[0025] Cyclic prefix (CP) indicator 144 provides information regarding the CP used by the terminal to determine the early TA values (UE-based TA). In some situations, the CP indicator indicates whether a normal CP (NCP) or an extended CP (ECP) was used by the terminal. The CP indicator 144 may also provide the associated numerology related to the structure of the radio frame which is dependent on the subcarrier spacing (inversely proportional to the OFDM symbol duration), cyclic prefix, and the slot structure (i.e. , the number of slots per subframe).

[0026] The reconfiguration elapsed time 146 is a value indicative of the elapsed time from when the terminal 102 receives a reconfiguration message including the LTM cell candidate cell configuration to when the RACH process is initiated. The reconfiguration elapsed time 146, therefore, is the elapsed time from reception of the LTM candidate cell configuration to initiation of the RACH process in situations when the RACH process must be invoked because an early TA is not available. The TA type indicator 148 indicates the TA type of the early TA that was used for the RACH-less cell switch process or that no early TA was available. For the example, the TA type indicator 148 may indicate that no TA was available, that the TA was determined by the terminal (UE- based TA), or was determined by the candidate cells (e.g. via a Contention-Free Random Access (CFRA) procedure initiated by the PDCCH-order).

[0027] The TA acquisition elapsed time indicator 150 indicates the elapsed time from the time the terminal acquired the early TA to the time the RACH-less cell switch was initiated. Therefore, the TA acquisition elapsed time indicator 150 may be from the measurement of the early TA or from the reception of the LTM cell switch command to the LTM cell switch attempt.

[0028] The command to attempt elapsed time 152 is the elapsed time from the time the LTM cell switch command is received to the time the cell switch is attempted.

[0029] The early TA acquisition to RACH elapsed time 154 is the elapsed time from the time the early TA values were determined or received to the time the RACH-based cell switch is attempted.

[0030] The switch command-to-RACH elapsed time 156 is a value indicative of the elapsed time from when the terminal 102 receives an LTM cell switch command to when the RACH process is initiated. The switch command-to-RACH elapsed time 156, therefore, is the elapsed time from reception of the LTM cell switch command VIA MAC CE to initiation of the RACH process in situations when the RACH process must be invoked because an early TA is not available.

[0031] The RACH type indicator 158 indicates whether the attempted cell switch was RACH-based or RACH-less. In some situations, the RACH type indicator 158 may not be needed since the RACH-type may be inherent from other parameters.

[0032] The selection of the parameters that are logged may be based on any of numerous factors where at least some of the parameters selected may be preconfigured. The network node may send a logging configuration message to configure the terminal with the parameters to the logged. In some situations, the selected logged parameters may be based on conditions or circumstances at the terminal. For example, the terminal may log different parameters for C-LTM procedure as compared to an LTM procedure. The timing of the cell switch attempt in the LTM procedure is triggered by reception of the LTM cell switch command. The cell switch attempt in the C-LTM procedure is triggered when certain conditions are met. The terminal monitors and measures signals from the candidate cells and when measurement meet criteria, the cell switch is triggered. For example, the terminal may continuously measure L1 parameters of the candidate cells to determine when the cell switch should be performed. Accordingly, the logged parameters may omit the parameters related to the timing of the LTM cell switch command when the last HO-type was C-LTM since the cell switch command was not received. On the other hand, some parameters may be logged even though those parameters were not used in the cell switch attempt. Forexample, the terminal may log UE-based early TA values even though PDCCH-ordered TA values were received and used for the cell switch attempt.

[0033] An example of a suitable set of parameters to be logged in the logged LTM- related data 104 include values RACH-type 158, elapsed time from early TA acquisition to the RACH attempt 154, CP parameters (CP 144), TA type 148, and candidate TA values with cell IDs 142.

[0034] 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.

[0035] 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.

[0036] 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 RRC Reconfiguration message and transmits an RRC Reconfiguration Complete message to the network node (gNB) 106 at transmission 208.

[0037] 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. 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. As discussed below, the early UL TA values can be provided to the terminal via an RRC message or via a MAC CE.

[0038] At event 210, the terminal performs downlink (DL) synchronization with the candidate cell(s) identified in the LTM candidate cell configuration. The DLsynchronization is triggered by the reception of the early TA PDCCH-order from the serving cell.

[0039] 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. 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 both procedures even though 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.

[0040] 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. At event 216, the L1 measurements are logged as part of the LTM-related data logging procedure. For the example, the LTM-related data logging procedure is part of the MDT / SON logging procedure and the data is stored in memory at the terminal 102. In some situations, L3 values may be logged.

[0041] 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 NW 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 the RACH procedure. Accordingly, the terminal may perform UE-based TA acquisition and PDCCH-ordered early TA acquisition.

[0042] Event 222 may be performed where the cell switch is a C-LTM cell switch. At event 222, the network node sends the early TA values acquired by the PDCCH- ordered early TA procedure to the terminal for use in the C-LTM cell switch.

[0043] At event 223, the terminal determines that LTM cell switch should be performed. For C-LTM, the determination is based on L1 measurements of one or more candidate cells and the determination that conditions for the C-LTM have been met. Otherwise, the LTM cell switch is triggered by the receipt of the LTM cell switch command.

[0044] At event 224, the terminal logs the TA 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 thenetwork 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 that was selected as the target cell.

[0045] At event 226, the terminal logs the CP data. The terminal logs 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. The CP is typically determined based on different frequency bands and deployment scenarios. For example, macrocell typically use larger CP to account for a larger delay spread.

[0046] The choice of SCS (Sub-carrier Spacing) will impact the duration of the slot where the larger the SCS the shorter the slot duration. There are 14 OFDM symbols per slot, which is kept the same regardless of slot duration. As a result, the CP length for the OFDM symbol will decrease when the slot duration is decreased. For example, at a 15kHz SCS, the CP length is 7 micro seconds and the CP length will decrease when a higher SCS (e.g., 60kHz SCC) is sued. ECP (12 OFDM symbol / slot) allows the OFDM symbol duration to increase for a given slot duration allowing the CP length to increase, proportionally. This impacts the TA values. When the terminal sends Msg 1 (Preamble) to the candidate cell which is used by the candidate cell to calculate TA, the Msg 1 itself already consists of the CP. As a result, the TA values provided to the terminal are at best within the CP uncertainty. Depending on the terminal implementation, the terminal may still track the TA value of the candidate cell based on its internal clock associated with the source cell. Even when the source cell and candidate cell are “synched” there remains up to 3 micro seconds of time difference which adds to the uncertainly of the derived TA value. The difference is in addition to the potential delay before the terminal performs the cell switch resulting in a potential inaccurate TA value leading to HOF. This may especially be problematic with a C-LTM cell switch.

[0047] 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.

[0048] 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.

[0049] 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. 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 be 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 is attempted in the example depending on whether a valid TA is available.

[0050] At event 236, the elapsed time from TA acquisition to initiation of the RACH- less cell switch is logged. In some situations, the start time for the TA acquisition is the measurement time of the terminal determined (UE-based) TA measurement. In other situations, the start time is the CFRA trigger in the PDCCH order towards a candidate cell. In still other situations, or the start time is the time of reception of the cell switch command (MAC CE). The information of the elapsed time from the TA acquisition to the RACH-less cell switch may be especially beneficial where a C-LTM cell switch was attempted.

[0051] At event 238, the elapsed time from reconfiguration to initiation of the RACH procedure is logged. Where the terminal attempts the RACH-based cell switch, the elapsed time from reception of the reconfiguration at transmission 206 to the initiation of the RACH procedure is logged.

[0052] 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.

[0053] At transmission 244, the new serving cell of the network node 242 sends a UE Information Request message to the terminal 102.

[0054] 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. 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.

[0055] 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 ofthe 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 base 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.

[0056] 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.

[0057] 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. The required components may depend on the particular functionality required by the base station 300.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] FIG. 4 is a block diagram of an example of a LIE 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 a 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.

[0063] 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 410. 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.

[0064] 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 incombination or cooperation with other components perform the communication device functions. The required components may depend on the particular functionality required by the communication device.

[0065] The transmitter 404 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.

[0066] 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 410.

[0067] FIG. 5 is 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. 5. In still further examples, additional steps may be added that are not explicitly described in connection with the example discussed with reference to FIG. 5.

[0068] At step 502, the terminal 102 transmits a measurement report to the serving cell of the serving network node (gNB) 106.

[0069] 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 and transmits an RRC Reconfiguration Complete message to the network node (gNB) 106 at step 506.

[0070] 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.

[0071] At step 508, the terminal performs downlink (DL) synchronization with the candidate cell(s) identified in the LTM candidate cell configuration.

[0072] 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.

[0073] 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. L1 measurement should be performed as long as the RRC reconfiguration received at transmission 206 is applicable.

[0074] At step 514, the L1 measurements are logged as part of the LTM-related data logging procedure. For the example, the LTM-related data logging procedure is part of the MDT / SON logging procedure and the data is stored in memory at the terminal 102. In some situations, L3 parameters are also logged.

[0075] 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.

[0076] At step 518, the terminal logs the TA data and the CP 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 also logs 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.

[0077] At step 520, the terminal detaches from the serving cell 108 and begins the process of switching to the target cell.

[0078] 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 terminal performs a Radom Access (RACH) procedure at step 524. If a valid TA is available for the target cell, the terminal performs a RACH-less cell switch procedure at step 526.

[0079] 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.

[0080] At step 528, the terminal logs the elapsed time from receiving the reconfiguration message to the time RACH was initiated. Where the terminal attempts the RACH-based cell switch, therefore, the elapsed time from reception of the reconfiguration at step 504 to the time of RACH is logged.

[0081] At step 530, the elapsed time from TA acquisition to initiation of the RACH- less cell switch is logged. In some situations, the start time for the TA acquisition is the measurement time of the terminal determined (UE-based) TA measurement. In other situations, the start time is the CFRA trigger in the PDCCH order towards a candidate cell. In still other situations, or the start time is the time of reception of the cell switch command (MAC CE). The information of the elapsed time from the TA acquisition to the RACH-less cell switch may be especially beneficial where a C-LTM cell switch was attempted.

[0082] At step 532, the terminal reestablished an RRC connection with a network node 242. For the example of FIG. 5, both the RACH-less procedure and the RACH- based procedure result in a HOF or RLF. 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 Reestablishment Request message to the original serving cell or another suitable cellwithin 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.

[0083] At step 534, a UE Information Request message is received from the new serving cell. At step 536, 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. An example of a suitable set of parameters to be logged in the logged LTM-related data 104 include values RACH-type 158, elapsed time from early TA acquisition to the RACH attempt 154, CP parameters (CP 144), TA type 148, and candidate TA values with cell IDs 142.

[0084] 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.

[0085] 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 initiatedby a receiving an RRC Connection Re-establishment Request message from the terminal.

[0086] At step 604, the network node transmits a UE Information Request message is to the terminal.

[0087] 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.

[0088] 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 is 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) orother 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.

[0089] 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 not 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.

[0090] 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-purposeprocessor, the program code combines with the processor to provide a unique apparatus that operates analogously to specific logic circuits.

[0091] 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.

[0092] 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 in 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

CLAIMS1 . A method comprising: receiving an L1 / L2 Triggered Mobility (LTM) candidate configuration from a serving cell; and logging data related to an LTM cell switch procedure as logged LTM-related data; attempting the LTM cell switch procedure; and reporting the LTM-related data to a network after the LTM cell switch procedure fails.

2. The method of claim 1 , further comprising receiving an LTM cell switch command from the serving cell; and attempting the LTM cell switch procedure in response to the LTM cell switch command.

3. The method of claim 2, wherein the logged LTM-related data comprises an LTM last Handover-type (HO-type) indicator indicating a last attempted handover by the terminal was the LTM cell switch procedure.

4. The method of claim 1 , further comprising: determining conditions have been met for executing a conditional LTM (C-LTM) procedure, the LTM cell switch procedure comprising the C-LTM procedure, the attempting the LTM cell switch procedure comprising attempting the C-LTM procedure in response to the determining the conditions have been met for executing the C-LTM procedure.

5. The method of claim 4, wherein the logged LTM-related data comprises an LTM last Handover-type (HO-type) indicator indicating a last attempted handover by the terminal was the C-LTM procedure.

6. The method of claim 4, wherein the C-LTM procedure comprises: determining a terminal-based early uplink (UL) timing advance (TA) value for a target cell based on measured signals from the target cell, the logged LTM-related data comprising the terminal-based early UL TA value and a target cell ID of the target cell.

7. The method of claim 4, wherein the C-LTM procedure comprises: receiving a Physical Downlink Control Channel ordered (PDCCH-ordered) early timing advance (TA) message; and performing a PDCCH-ordered uplink (UL) TA procedure to determine a PDCCH- ordered early UL TA value for a target cell, the logged LTM-related data comprising PDCCH-ordered early UL TA value and a target cell ID of the target cell.

8. The method of claim 7, receiving the PDCCH-ordered early TA message comprising receiving the PDCCH-ordered early TA message in a Radio Resource Configuration (RRC) message.

9. The method of claim 7, receiving the PDCCH-ordered early TA message comprising receiving the PDCCH-ordered early TA message via a Medium Access Control - Control Element (MAC CE).

10. The method of claim 3, wherein the logged LTM-related data comprises: a target early uplink (UL) timing advance (TA) value indicating an early UL target TA applied to the LTM cell switch procedure to a target cell; and a target cell ID of the target cell.11 . The method of claim 10, wherein the logged LTM-related data comprises:a candidate UL early TA value indicating a candidate early TA measured for a candidate cell for the LTM cell switch procedure; and a candidate cell ID of the candidate cell.

12. The method of claim 11 , wherein the logged LTM-related data comprises at least one of:L1 parameters reported to the serving cell as part of the LTM cell switch procedure,L3 parameters reported to the serving cell as part of the LTM cell switch procedure, a target cyclic prefix (CP) indicator providing information regarding a target CP used by the terminal to determine the target early TA, a candidate CP indicator providing information regarding the candidate CP used by the terminal to determine the candidate early TA, a reconfiguration elapsed time value indicative of the elapsed time from reception of the LTM cell switch candidate cell configuration message to initiation of a random access process to the target cell using a random-access channel (RACH), a command to RACH-less switch elapsed time indicative of an elapsed time from reception of the LTM cell switch command to a RACH-less cell switch attempt, a TA type indicator indicating whether a TA was unavailable, was determined by the terminal, or was determined by a candidate cell, a Physical Downlink Control Channel ordered (PDCCH-ordered) early TA reception to RACH-less switch elapsed time indicating an elapsed time from the reception of the target PDCCH-ordered early TA value to initiation of a RACH-less cell switch, or a TA acquisition elapsed time indicator indicating an elapsed time from acquisition of a target UE-based early TA to initiation of a RACH-less cell switch.

13. 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.

14. The method of claim 13, wherein the logged LTM-related data comprises an LTM last Handover-type (HO-type) indicator indicating a last attempted handover by the terminal was the LTM cell switch procedure.

15. The method of claim 13, wherein the LTM HO-type indicator indicates the last attempted handover by the terminal was a conditional LTM (C-LTM) cell switch where the terminal determined a time to initiate the LTM cell switch procedure.

16. The method of claim 15, wherein the logged LTM-related data comprises a target early uplink (UL) timing advance (TA) value indicating an early UL target TA applied to the LTM cell switch procedure to a target cell.

17. The method of claim 16, wherein the logged LTM-related data comprises a candidate UL early TA value indicating a candidate early TA measured for a candidate cell for the LTM cell switch procedure.

18. The method of claim 17, wherein the logged LTM-related data comprises at least one of:L1 parameters reported to an original serving cell as part of the LTM cell switch procedure,L3 parameters reported to the original serving cell as part of the LTM cell switch procedure,a target cyclic prefix (CP) indicator providing information regarding a target CP used by the terminal to determine the target early TA, a candidate CP indicator providing information regarding the candidate CP used by the terminal to determine the candidate early TA, a reconfiguration elapsed time value indicative of the elapsed time from reception of the LTM cell switch command to initiation of a random access process to the target cell using a random-access channel (RACH), a TA type indicator indicating whether a TA was unavailable, was determined by the terminal, or was determined by a candidate cell, a command to RACH-less switch elapsed time indicative of an elapsed time from reception of the LTM cell switch command to a RACH-less cell switch attempt, a Physical Downlink Control Channel ordered (PDCCH-ordered) early TA reception to RACH-less switch elapsed time indicating an elapsed time from the reception of the target PDCCH-ordered early TA value to initiation of a RACH-less cell switch, or a TA acquisition elapsed time indicator indicating an elapsed time from acquisition of a target UE-based early TA to initiation of a RACH-less cell switch.

19. 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; a memory configured to store data related to an LTM cell switch procedure as logged LTM-related data; 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.

Images