Method of fault processing in condition handover

Abstract

The invention relates to a method of fault handling in conditional handover. A method performed by a user equipment (UE) includes receiving a conditional handover (CHO) configuration; initiating a reconstruction process if one of a plurality of first conditions is satisfied; performing a cell selection procedure; performing a CHO procedure if the cell selected by the cell selection procedure is configured with the CHO configuration; and performing the reestablishment procedure if the selected cell is not configured with the CHO configuration.

Description

[0001] Divisional Application Information

[0002] This application is a divisional application of the invention patent application with the application date of January 10, 2020, application number "202080092539.8", and invention name "Method for fault handling in conditional handover". Technical Field

[0003] The present application relates generally to wireless communications and, more particularly, to failure handling in conditional handover (CHO). Background Art

[0004] A base station (BS) may have some cells (or areas) to provide communication services. In 3GPP Release 17, when a UE needs to hand over from a serving cell of a source base station (BS) to a target cell of a target BS, a handover process (e.g., a fault handling mechanism, a conditional handover (CHO) process, etc.) and a cell selection process before the handover process are performed. CHO is defined as a handover performed by a UE when one or more handover execution conditions are met.

[0005] 3GPP 5G NR adopts the fault handling mechanism in CHO. However, the details of the fault handling mechanism in CHO have not yet been discussed in 3GPP 5G NR technology. Summary of the invention

[0006] One aspect of the present disclosure provides a method performed by a user equipment (UE), wherein the method includes: receiving a conditional handover (CHO) configuration; initiating a reestablishment process if one of a plurality of first conditions is satisfied; performing a cell selection process; performing a CHO process if a cell selected by the cell selection process is configured with the CHO configuration; and performing the reestablishment process if the selected cell is not configured with the CHO configuration.

[0007] Another aspect of the present disclosure provides a method performed by a user equipment (UE), wherein the method includes: receiving a conditional handover (CHO) configuration of a secondary node (SN) change; initiating a process of reporting information indicating a CHO failure from a source SN to a target SN if one of the following conditions is met: a CHO-based SN change failure; and a CHO-based SN addition failure; and reporting the information indicating the CHO failure to a master node (MN).

[0008] Another aspect of the present disclosure provides a method performed by a network node, wherein the method includes: receiving a request from a source secondary node (SN) to perform a CHO-based SN change process from the source SN to a target SN; transmitting a CHO configuration for the CHO-based SN change process to a user equipment (UE); receiving information indicating a failure of the CHO-based SN change process from the UE; and transmitting the information indicating a failure of the CHO-based SN change process to the source SN.

[0009] Another aspect of the present disclosure provides a method performed by a source secondary node (SN), wherein the method includes: transmitting to a master node (MN) a request to perform a conditional handover (CHO)-based SN change process from the source SN to a target SN having one or more conditional handover (CHO) conditions; and receiving information from the MN indicating a failure of the CHO-based SN change process.

[0010] Another aspect of the present disclosure provides a method performed by a user equipment (UE), wherein the method includes: receiving a conditional handover (CHO) configuration for a secondary node (SN) change; performing a CHO-based SN change once an execution condition associated with the CHO configuration is met; and starting a timer once the CHO configuration is applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to describe the manner in which the advantages and features of the present application can be obtained, the present application is described with reference to specific embodiments illustrated in the accompanying drawings. These drawings depict only example embodiments of the present application and therefore should not be considered limiting of its scope.

[0012] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0013] Figure 2 A block diagram illustrating an MR-DC wireless communication system according to some embodiments of the present application.

[0014] Figure 3 The following describes the conditional handover process within the AMF / UPF according to some embodiments of the present application.

[0015] Figure 4 The following describes a CHO-based SN change process initiated by an SN according to some embodiments of the present application.

[0016] Figure 5 A flow chart illustrating a method for wireless communication according to some embodiments of the present application.

[0017] Figure 6 An example of transmission of fault information according to some embodiments of the present application is described.

[0018] Figure 7 Another example of transmission of a fault information message according to some embodiments of the present application is described.

[0019] Figure 8 A flow chart illustrating another method for wireless communication according to some embodiments of the present application.

[0020] Fig. 9 A flow chart illustrating another method for wireless communication according to some embodiments of the present application.

[0021] Fig.10 A block diagram illustrating an exemplary apparatus according to some embodiments of the present application. DETAILED DESCRIPTION

[0022] The detailed description of the accompanying drawings is intended as a description of the preferred embodiments of the present application and is not intended to represent the only form in which the present application can be implemented. It should be understood that the same or equivalent functions can be accomplished by different embodiments that are intended to be included in the spirit and scope of the present application.

[0023] Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided in specific network architectures and new service scenarios, such as 3GPP 5G, 3GPP LTE Release 8, etc. It is conceivable that, with the development of network architectures and new service scenarios, all embodiments in the present application are also applicable to similar technical issues; and in addition, the terms cited in the present application may change, which should not affect the principles of the present application.

[0024] Multi-Radio Dual Connectivity (MR-DC)

[0025] With the development of the fifth generation mobile communication technology (5G), in the development of operators, base stations working in the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA) system and base stations working in the 5G New Radio (NR) system can be configured to communicate with user equipment (EP) together, that is, UE can be connected to the base station (eNB) working in the E-UTRA system and the base station (gNB) working in the NR system at the same time, and we can use the frequency of the E-UTRA system and the frequency of the NR system to transmit data at the same time, so as to improve the throughput of the UE. This type of UE is connected to two different base stations at the same time, which can be called multi-radio dual connection (MR-DC).

[0026] In the MR-DC architecture, a multi-Rx / Tx-capable UE can be configured to utilize resources provided by two different nodes connected via a non-ideal backhaul, one providing NR access and the other providing E-UTRA or NR access. One node acts as a master node (MN) and the other node acts as a secondary node (SN). The MN and SN are connected via a network interface and at least the MN is connected to the core network.

[0027] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present application.

[0028] like Figure 1 As described and shown in FIG. 1 , the wireless communication system 100 includes at least one multi-Rx / Tx UE 101 and at least one BS 102. In particular, for illustrative purposes, the wireless communication system 100 includes one UE 101 (e.g., UE 101a) and four BSs 102 (e.g., BS 102a, BS 102b, BS 102c, BS 102d), and BS 102a is a gNB as a MN, and BS 102b is an eNB as a SN. That is, Figure 1 Demonstrating NR-E-UTRA Dual Connectivity (NE-DC). Figure 1 Although a specific number of UEs 101 and BSs 102 are depicted in FIG. 1 , it is contemplated that any number of UEs 101 and BSs 102 may be included in wireless communication system 100 .

[0029] UE 101 may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (such as a TV connected to the Internet), a set-top box, a game console, a security system (including a security camera), a car computer, a network device (such as a router, a switch and a modem), an Internet of Things (IoT) device, etc. According to some embodiments of the present application, UE 101 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a selective call receiver, or any other device capable of sending and receiving communication signals on a wireless network. In some embodiments of the present application, UE 101 includes a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, etc. In addition, UE 101 may be referred to as a subscriber unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device or described using other terms used in the present technology. UE 101 may communicate directly with BS 102 via an uplink (UL) communication signal.

[0030] In some embodiments of the present application, each of UE 101 may be deployed as an IoT application, an eMBB application, and / or a URLLC application. It is contemplated that the specific type of application deployed in UE 101 may vary and is not limited.

[0031] BS102 may be distributed over a geographic area. In certain embodiments of the present application, each of BS102 may also be referred to as an access point, an access terminal, a base station, a base station unit, a macro cell, a Node-B, an evolved Node B (eNB), a gNB, a NG-RAN (next generation radio access network) node, a home node-B, a relay node or a device or described using other terms used in the present technology. BS102 is typically part of a radio access network, which may include one or more controllers communicatively coupled to one or more corresponding BS102. BS102 may communicate directly with each other. For example, BS102 may communicate directly with each other via an Xn interface or an X2 interface.

[0032] The wireless communication system 100 may be compatible with any type of network capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a network based on time division multiple access (TDMA), a network based on code division multiple access (CDMA), a network based on orthogonal frequency division multiple access (OFDMA), an LTE network, a network based on 3GPP, a 3GPP5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0033] In some embodiments of the present application, the wireless communication system 100 is compatible with the 5G NR of the 3GPP protocol, wherein the BS 102 uses an OFDM modulation scheme to transmit data on the DL and the UE 101 uses a single carrier frequency division multiple access (SC-FDMA) or OFDM scheme to transmit data on the UL. However, more generally, the wireless communication system 100 may implement some other open or proprietary communication protocols, such as WiMAX and other protocols.

[0034] In some embodiments of the present application, BS102 can communicate using other communication protocols, such as IEEE802.11 wireless communication protocol family. In addition, in some embodiments of the present application, BS102 can communicate via licensed spectrum, while in other embodiments, BS102 can communicate via unlicensed spectrum. The present application is not intended to be limited to any specific wireless communication system architecture or protocol implementation. In some further embodiments of the present application, BS102 can communicate with UE 101 using 3GPP 5G protocol.

[0035] Control Plane of DC

[0036] like Figure 2It is described in MR-DC that the UE has a single radio resource control (RRC) state based on the MN RRC and a single C-plane connection towards the core network. Figure 2 The control plane architecture of MR-DC is illustrated. Each radio node has its own RRC entity (E-UTRA version if the node is an eNB, or NR version if the node is a gNB) which can generate RRC PDUs to be sent to the UE.

[0037] The RRC PDU generated by the SN may be transmitted to the UE via the MN. The MN always sends the initial SNRRC configuration via the MCG SRB (SRB1), but subsequent reconfigurations may be transmitted via the MN or the SN. When transmitting the RRC PDU from the SN, the MN does not modify the UE configuration provided by the SN.

[0038] In MR-DC, the master cell group is a group of serving cells associated with the master node, including the SpCell (PCell) and optionally one or more SCells.

[0039] In MR-DC, the master node is the radio access node that provides the control plane connection to the core network. It can be a master eNB (in EN-DC), a master ng-eNB (in NGEN-DC), or a master gNB (in NR-DC and NE-DC).

[0040] Multi-radio dual connectivity is dual connectivity between E-UTRA and an NR node or between two NR nodes.

[0041] PCell is the SpCell of the primary cell group.

[0042] PSCell is the SpCell of the secondary cell group.

[0043] In MR-DC, the secondary cell group is a group of serving cells associated with the secondary node, including the SpCell (PSCell) and optionally one or more SCells.

[0044] In MR-DC, the secondary node is a radio access node with no control plane connection to the core network, providing additional resources to the UE. It can be an en-gNB (in EN-DC), secondary ng-eNB (in NE-DC) or secondary gNB (in NR-DC and NGEN-DC).

[0045] SpCell is the primary cell of a primary or secondary cell group.

[0046] Conditional Handover (Pcell Change in MN)

[0047] Conditional Handover (CHO) is defined as a handover performed by the UE when one or more handover execution conditions are met. The UE starts evaluating the execution conditions after receiving the CHO configuration and stops evaluating the execution conditions during CHO execution once the execution conditions are met.

[0048] The following principles apply to CHO:

[0049] -CHO configuration contains the configuration of the CHO candidate cells generated by the candidate gNB and the execution conditions generated by the source gNB.

[0050] - The execution condition can consist of one or two trigger conditions (A3 / 5). Only a single RS type is supported and up to two different execution quantities (such as RSRP and RSRQ, RSRP and SINR, etc.) can be configured simultaneously to evaluate the CHO execution condition of a single candidate cell.

[0051] - Before any CHO execution conditions are met, upon receiving a HO Command (without CHO configuration), the UE performs the HO procedure described in clause 9.2.3.2, regardless of any previously received CHO configuration.

[0052] - When performing CHO, that is, from the time the UE starts synchronizing with the target cell, the UE does not monitor the source cell.

[0053] C-plane processing

[0054] As with Intra-NR RAN Handover, in Intra-NR RAN CHO, the preparation and execution phases of the conditional handover procedure are performed without involving the 5GC; i.e., the preparation messages are exchanged directly between the gNBs. During the conditional handover completion phase, the release of resources at the source gNB is triggered by the target gNB.

[0055] Figure 3 Describe the basic condition handover scenario where neither AMF nor UPF has changed. Figure 3 The process is explained in detail as follows:

[0056] Step 300: The UE context in the source gNB contains information about roaming and access restrictions, which is provided at connection establishment or at the last TA update.

[0057] Step 301: The source gNB configures the UE measurement process and the UE reports according to the measurement configuration.

[0058] Step 302: The source gNB decides to use CHO.

[0059] Step 303: The source gNB sends a CHO request message to one or more candidate gNBs.

[0060] Step 304: Admission control may be performed by the target gNB.

[0061] Step 305: The candidate gNB sends a CHO response containing the configuration of the CHO candidate cell to the source gNB.

[0062] Step 306: The source gNB sends an RRCReconfiguration message to the UE, which contains the configuration of the CHO candidate cells and the CHO execution conditions.

[0063] Step 307: The UE sends an RRCReconfigurationComplete message to the source gNB.

[0064] Step 308: After receiving the CHO configuration, the UE maintains the connection with the source gNB and starts to evaluate the CHO execution conditions of the candidate cells. If at least one CHO candidate cell meets the corresponding CHO execution condition, the UE is separated from the source gNB and the stored corresponding configuration is applied.

[0065] Conditional handover (MN / SN initiated SN change)

[0066] Same as in CHO for PCell mobility, multiple PScells are configured to the UE in conditional PScell ​​add / change. In CHO, it is unlikely that a PScell ​​supports secondary connections between the UE and the network. In rel-15, only one SN is allowed to be active at a time. Similarly, even if multiple configured PScells can satisfy conditional PScell ​​add / change, the UE should only be allowed to connect to a single active PScell ​​at a time.

[0067] SN change can be triggered by MN or SN in regular SN change. SN change initiated by MN (only for inter-frequency SN change), MN can make decision based on measurements configured by MN. This scenario is similar to SN addition.

[0068] For SN changes initiated by the SN, the RRM measurement configuration is maintained by the SN and the SN also processes the measurement reports without providing measurement results to the MN. The MN is also unaware of the measurement configuration by the SN. In order to support conditional SN changes to intra-RAT measurements on serving and non-serving frequencies configured by the SN, the SN shall decide the conditional SN change execution conditions and they shall be defined by the measurement identifier configured by the source SN. Otherwise, major changes to the measurement coordination between the MN and the SN shall be introduced. We believe that such major specification changes should be avoided.

[0069] Figure 4 Describes the CHO-based SN change scenario initiated by SN. Figure 4 The process is explained in detail as follows:

[0070] Step 401. The source SN initiates the CHO-based SN change process by sending an SgNB Change Required message, which contains the target SN ID information and may include the SCG configuration and measurement results related to the target SN.

[0071] - Also contains the CHO execution conditions for each candidate T-SN.

[0072] Step 402. The MN requests the target SN to allocate resources to the UE through the SgNB Addition process, including the measurement results related to the target SN received from the source SN.

[0073] - In step 2, the CHO indicator will be included.

[0074] Step 403. If forwarding is required, the target SN provides the forwarding address to the MN. The target SN includes an indication of a complete or incremental RRC configuration.

[0075] Step 404. The MN indicates the new configuration to the UE in the RRCConnectionReconfiguration message containing the NR RRC configuration message generated by the target SN.

[0076] - In step 404, the CHO execution condition of each candidate T-SN is also included.

[0077] Step 405. If necessary, the UE stores the new configuration and sends an RRCConnectionReconfigurationComplete message, containing the encoded NR RRC Response message of the target SN. If the UE cannot comply with (part of) the configuration contained in the RRCConnectionReconfiguration message, it performs the Reconfiguration Failure procedure.

[0078] Step 406. If the allocation of target SN resources is successful, the MN confirms the CHO-based SgNB change request.

[0079] Step 407. If the RRC connection reconfiguration procedure is successful, the MN notifies the target SN via the SgNB ReconfigurationComplete message: if received from the UE, then the encoded NR RRC response message with the target SN.

[0080] Step 408. Once the conditions are met, the UE synchronizes to the target SN.

[0081] Step 409: After the UE accesses the T-SN, data forwarding and path switching will be performed.

[0082] Step 410: The MN transmits a UE Context Release message to the source SN to release the radio and C-plane related resources associated with the UE context.

[0083] Scenario A: PCell CHO Failure Handling in the Master Node (MN)

[0084] Currently, the RAN2 working group has agreed to start a new reestablishment procedure before CHO recovery, which is used for RLF / CHO failure / HO failure recovery as follows:

[0085] 1. Start the reconstruction based on the old version trigger conditions (5.3.7.2).

[0086] 2.UE should release spCellConfig and other parameters (according to the old version 5.3.7.2)

[0087] 3. T311 starts and the UE performs cell selection;

[0088] 4. If the selected cell is a CHO cell, then perform CHO. Otherwise, perform the reestablishment process. (According to the CR agreed in RAN2#108)

[0089] Step 4 above includes performing CHO, and the performed CHO includes the UE applying the CHO configuration for the selected candidate cell. However, in the case where the incremental configuration (which only indicates the difference from the original CHO configuration) is configured with the CHO configuration, the behavior of "UE applying CHO configuration" should refer to the source configuration (spCellConfig). However, according to step 2 above, spCellConfig has been released when the UE applies the CHO configuration.

[0090] To solve the above problems, the present invention provides three options:

[0091] Option 1: When the UE initiates reestablishment, the UE shall release the spCellConfig if one of the following conditions is met:

[0092] Condition 1-1: attemptCHO is not configured

[0093] Condition 1-2: No CHO candidate cells are configured

[0094] Condition 1-3: It is not the first cell selection after a failure

[0095] Option 2: Another description of Option 1: When the UE initiates reestablishment, the UE shall maintain (or store) spCellConfig if one of the following conditions is met:

[0096] Condition 2-1: It is the first cell selection after a failure and attemptCHO is configured

[0097] Condition 2-2: It is the first cell selection after the failure and configures at least one CHO candidate cell

[0098] Condition 2-3: It is the first cell selection after a failure, attemptCHO is configured, and at least one CHO candidate cell is configured

[0099] Option 3: When the UE receives a CHO configuration for a cell, it stores the corresponding source configuration;

[0100] If spCellConfig is not released when starting reconstruction, spCellConfig can be released once an NR cell without CHO configuration is selected and / or CHO configuration is applied, and the UE should release spCellConfig.

[0101] Figure 5 A flow chart illustrating a method for wireless communication according to some embodiments of the present application. Figure 5 The exemplary method 500 described and illustrated in FIG. 5 is performed by a UE intended to be handed over from the PCell of MN1 to the PCell of MN2.

[0102] In exemplary method 500, in operation 501, a UE (e.g., Figure 1 101a) receives a CHO configuration. The CHO configuration may be transmitted from a MN (e.g., gNB 102a). Thereafter, if one of a plurality of first conditions is satisfied in operation 502, the UE initiates a reestablishment process. The plurality of first conditions may be RLF, HO failure, and CHO failure.

[0103] In operation 503 , the UE performs cell selection, and if the selected cell through the cell selection process is configured with a CHO configuration in operation 504 , the UE performs a CHO process in operation 505 , and if not, the UE performs a reestablishment process in operation 506 .

[0104] According to one aspect of the present invention, when the UE initiates reestablishment, the UE shall release the spCellConfig if one of the following conditions is met:

[0105] Condition 1-1: attemptCHO is not configured

[0106] Condition 1-2: No CHO candidate cells are configured

[0107] Condition 1-3: It is not the first cell selection after a failure

[0108] In addition, when the UE initiates reestablishment, the UE shall retain (or store) spCellConfig if one of the following conditions is met:

[0109] Condition 2-1: It is the first cell selection after a failure and attemptCHO is configured

[0110] Condition 2-2: It is the first cell selection after the failure and configures at least one CHO candidate cell

[0111] Condition 2-3: It is the first cell selection after a failure, attemptCHO is configured, and at least one CHO candidate cell is configured

[0112] According to another aspect of the present disclosure, the UE stores the CHO configuration and the corresponding source configuration.

[0113] According to another aspect of the present disclosure, once an NR cell without CHO configuration is selected and / or CHO configuration is applied, the UE should release the spCellConfig. The UE releases the spCellConfig.

[0114] Scenario B: SN initiates CHO SN change

[0115] For SCG, the SCG Failure Information procedure is used to notify the MN of SCG failures due to S-RLF, reconfiguration of synchronization failures, SCG configuration failures, and integrity check failures. When an SCG failure occurs, the UE suspends SCG transmission, resets SCGMAC, and stops T304 (if running). The MN takes action after receiving the SCG failure information. In traditional specifications, the SCG failure information will not be transmitted to the source SN.

[0116] For mobility failure scenarios in LTE, the UE will report, for example, an RLF report to the new serving cell. The serving cell will transmit an RLF report from the UE to the source gNB, which is used for network optimization purposes. (See 36.300 MRO section) For example, the RLF report can be used to optimize the "handover boundary". Similarly, the failure information can be transmitted to the SN that initiated the CHO SN change, which can be used to optimize, for example, the CHO execution conditions.

[0117] Therefore, the present invention provides the following solutions:

[0118] First, the UE reports SCGfailureinformation to the MN. SCGfailureinformation may include at least one of the following four items:

[0119] (1) One or more triggering conditions for this CHO-based SN change.

[0120] One or more trigger conditions may include RS type and trigger quantity. For example, the trigger quantity may be reference signal received power (RSRP) and reference signal received quality (RSRQ), or RSRP and signal to interference plus noise ratio (SINR).

[0121] (2) The beam index associated with the preamble transmission.

[0122] The beam ID can be a selected synchronization signal block (SSB) index or a channel state information reference signal (CSI-RS) index.

[0123] (3) Configuration set contained in failureDetectionResources

[0124] For each BWP in the serving cell, a set of Periodic CSI-RS resource configuration index.

[0125] UE Desired Group Contains up to two RS indices. UE expects group A single port in RS.

[0126] (4) The time from SN change initialization to connection failure.

[0127] This information is used by the MN or SN to determine whether to handover prematurely. Optionally, information about the elapsed time may also be stored by the MN. If so, the UE does not need to report the elapsed time.

[0128] Next, the MN indicates the fault information to the source SN for the purpose of MRO. The fault information may include at least one of the following four items:

[0129] (1) SCG failure information.

[0130] SCGfailureinformation can be a container included in the Xn message.

[0131] (2) The T-SN ID where the CHO SN change failure occurred.

[0132] (3) UE ID in SN or C-RNTI in SN.

[0133] (4) The type of SN change problem detected.

[0134] The types of SN change problems detected may be premature change or change to a wrong cell.

[0135] Information is used for a recently completed SN change when the target cell (in T-SN) fails shortly after sending a UE CONTEXT RELEASE message to the source SN A. This information is also used in the case of a RLF that occurs before sending a UE CONTEXT RELEASE message if the Random Access procedure in the target cell completes successfully.

[0136] Figure 6 and 7 An example of transmission of fault information according to some embodiments of the present application is described. In particular, Figure 6 In the embodiment, the UE transmits the CHO-based SN change failure and / or the CHO-based SN addition failure to the MN, and Figure 7 In the process, the MN transmits a CHO-based SN change failure and / or a CHO-based SN addition failure to the source SN.

[0137] Scenario C: MN or SN initiates CHO SN change

[0138] It is possible that the UE may receive a normal handover (i.e., PCell CHO in the MN) request during a CHO SN change, so there is a situation where a PCell handover and a CHO SN change may occur simultaneously. Traditionally, the MN can avoid this situation because when to perform the SN change is under the control of the MN. However, the CHO SN change is a UE autonomous HO, so the situation cannot be avoided. Therefore, a new UE behavior should be specified in this new situation.

[0139] To solve the above problems, the present invention provides the following solutions:

[0140] The timer T304 of the RRC layer can be reused for the SN change based on CHO.

[0141] Once the UE applies the CHO SN change, T304 is started. The UE stops this T304 for the CHO SN change after receiving the RRCReconfiguration message containing reconfigurationWithSync for MCG. That is, the UE stops T304 after learning about the MN change. Therefore, the definition of T304 should be changed as follows:

[0142]

[0143] Table 1

[0144] like Figure 8In the method 800 of FIG. 1 , the UE receives a conditional handover (CHO) configuration for a secondary node (SN) change from a MN or a SN in operation 801. Once the execution condition is met, the UE performs a CHO-based SN change in operation 802. Once the CHO configuration for the SN change is applied, the UE starts a timer in operation 802. The timer may be T304.

[0145] like Fig. 9 In method 900 of , if a timer corresponding to a CHO SN change is running, the UE receives a request for a PCell change in operation 901 , and then the UE stops the timer in operation 902 .

[0146] Fig.10 A block diagram illustrating an exemplary device according to some embodiments of the present application. Fig.10 , apparatus 1000 includes receiving circuitry 1002, transmitting circuitry 1004, a processor 1006, and a non-transitory computer-readable medium 1008. Processor 1006 is coupled to non-transitory computer-readable medium 1008, receiving circuitry 1002, and transmitting circuitry 1004.

[0147] It can be imagined that, for simplicity, Fig.10 In some embodiments, the receiving circuit system 1002 and the transmitting circuit system 1004 may be integrated into a single component (eg, a transceiver).

[0148] In some embodiments, the non-transitory computer-readable medium 1008 may have stored thereon computer-executable instructions to enable the processor to implement the operations related to the UE as described above. For example, after executing the computer-executable instructions stored in the non-transitory computer-readable medium 1008, the processor 1006 and the receiving circuit system 1002 perform Figure 5 The method includes: receiving a conditional handover (CHO) configuration by the receiving circuit system 1002; if one of a plurality of first conditions is satisfied by the processor 1006, then initiating a reestablishment process; executing a cell selection process by the processor 1006; if the cell selected by the cell selection process is configured with the CHO configuration by the processor 1006, then executing the CHO process; and if the selected cell is not configured with the CHO configuration by the processor 1006, then executing the reestablishment process. In some embodiments, after executing the computer executable instructions stored in the non-transitory computer readable medium 1008, the processor 1006 and the receiving circuit system 1002 execute Fig. 9 The method comprises: if a timer corresponding to a CHO SN change is running, receiving a request for a PCell change; and stopping the timer.

[0149] In some embodiments, the non-transitory computer-readable medium 1008 may have computer-executable instructions stored thereon to cause the processor to perform the operations related to the BS as described above. For example, after executing the computer-executable instructions stored in the non-transitory computer-readable medium 1008, the processor 1006 and the receiving circuit system 1002 perform Figure 8 The method comprises: receiving a conditional handover (CHO) configuration for a secondary node (SN) change by a receiving circuit system 1002; executing a CHO-based SN change once an execution condition associated with the CHO configuration is satisfied by a processor 1006; and starting a timer once the CHO configuration is applied by the processor 1006.

[0150] The method of the present application can be implemented on a programmed processor. However, the controller, flow chart and module can also be implemented on a general or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit components, an integrated circuit, a hardware electronic or logic circuit (such as a discrete component circuit), a programmable logic device, etc. In general, any device on which there is a finite state machine capable of implementing the flow chart shown in the figure can be used to implement the processor function of the present application.

[0151] Those of ordinary skill in the art will appreciate that the steps of the methods described in conjunction with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the steps of the methods may reside as one or any combination or set of codes and / or instructions on a non-transitory computer-readable medium, which may be incorporated into a computer program product.

[0152] Although the present disclosure has been described by its specific embodiments, it is apparent that many alternatives, modifications and variations may be understood by those skilled in the art. For example, the various components of the embodiments may be interchanged, added or replaced in other embodiments. In addition, all elements of each of the accompanying drawings are not necessary for the operation of the disclosed embodiments. For example, a person of ordinary skill in the art of the disclosed embodiments will be able to make and use the teachings of the present disclosure by simply adopting the elements of the independent claims. Therefore, the embodiments of the present disclosure as described herein are intended to be illustrative, not restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.

[0153] In this document, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device that includes a list of elements includes not only those elements, but may include other elements that are not explicitly listed or inherent to such processes, methods, articles or devices. In the absence of more constraints, elements beginning with "one", "an", etc. do not exclude the presence of additional identical elements in the process, method, article or device that includes the elements. In addition, the term "another" is defined as at least a second or more. As used herein, the terms "include", "have", etc. are defined as "include".

Claims

1. A method performed by a user equipment UE, comprising: Receive the conditional handover CHO configuration of the secondary node SN change; The process of reporting information indicating a CHO failure from the source SN to the target SN is initiated if one of the following conditions is met: CHO-based SN change failure; and CHO-based SN addition failure; and The information indicating the CHO failure is reported to a master node MN.

2. The method of claim 1 , wherein the information indicating the CHO failure comprises: one or more conditions that trigger the CHO process; a beam index, which is associated with the preamble transmission; The serving beam index that belongs to the configuration set contained in failureDetectionResources; and The time period from the initialization of the SN change to the connection failure.

3. The method according to claim 2, wherein the beam index is a synchronization signal SS / physical broadcast channel PBCH block SSB index or a channel state information-reference signal CSI-RS index. The method of claim 2 , wherein the one or more conditions triggering the CHO process include a RS type and a trigger amount.

5. The method of claim 4, wherein the triggering amount comprises one of the following: Reference signal received power RSRP and reference signal received quality RSRQ; and RSRP and signal-to-interference-and-noise ratio SINR.

6. A method performed by a network node, comprising: receiving, from a source secondary node SN, a request to perform a CHO-based SN change procedure from said source SN to a target SN; Transmitting a CHO configuration for the CHO-based SN change procedure to a user equipment UE; receiving, from the UE, information indicating a failure of the CHO-based SN change procedure; The information indicating a failure of the CHO-based SN change procedure is transmitted to the source SN.

7. The method of claim 6, wherein the information indicating a failure of the SN change process comprises: One or more conditions that trigger the CHO-based SN change process; a beam index, which is associated with the preamble transmission; The serving beam index that belongs to the configuration set contained in failureDetectionResources; and The time period from the initialization of the SN change to the connection failure.

8. The method according to claim 7, wherein the beam index is a synchronization signal SS / physical broadcast channel PBCH block SSB index or a channel state information-reference signal CSI-RS index.

9. The method of claim 7, wherein the one or more conditions triggering the CHO-based SN change process include RS type and trigger amount.

10. The method of claim 9, wherein the triggering amount comprises one of the following: Reference signal received power RSRP and reference signal received quality RSRQ; and RSRP and signal-to-interference-and-noise ratio SINR.

11. The method of claim 6, wherein additional information is transmitted to the source SN together with the information indicating the failure of the CHO-based SN process, and the additional information comprises: T-SN ID, where a CHO-based SN change failure occurs; UEID in SN and / or C-RNTI in SN; and The type of SN change problem has been detected.

12. The method of claim 11, wherein the type of detected SN change problem includes changing too early or changing to a wrong cell.

13. The method of claim 6, wherein the information indicating the failure of the CHO-based SN change procedure is transmitted to the source SN by being included in an Xn message.

14. A method performed by a source secondary node SN, comprising: transmitting to the master node MN a request to perform a CHO-based SN change procedure from the source SN to a target SN having one or more conditional handover CHO conditions; and Information indicating a failure of the CHO-based SN change procedure is received from the MN.

15. The method of claim 14, wherein the information indicating a failure of the CHO-based SN change procedure comprises: One or more conditions that trigger the CHO-based SN change process; a beam index, which is associated with the preamble transmission; The serving beam index that belongs to the configuration set contained in failureDetectionResources; and The time period from the initialization of the SN change to the connection failure.

16. The method according to claim 15, wherein the beam index is a synchronization signal SS / physical broadcast channel PBCH block SSB index or a channel state information-reference signal CSI-RS index.

17. A device for wireless communication, comprising: at least one memory; as well as at least one processor coupled to the at least one memory and configured to cause the apparatus to: receiving, from a source secondary node SN, a request to perform a CHO-based SN change procedure from said source SN to a target SN; Transmitting a CHO configuration for the CHO-based SN change procedure to a user equipment UE; receiving, from the UE, information indicating a failure of the CHO-based SN change procedure; The information indicating a failure of the CHO-based SN change procedure is transmitted to the source SN.

18. A processor for communication, comprising: at least one controller coupled to at least one memory and configured to cause the processor to: receiving, from a source secondary node SN, a request to perform a CHO-based SN change procedure from said source SN to a target SN; Transmitting a CHO configuration for the CHO-based SN change procedure to a user equipment UE; receiving, from the UE, information indicating a failure of the CHO-based SN change procedure; The information indicating a failure of the CHO-based SN change procedure is transmitted to the source SN.

19. A device for wireless communication, comprising: at least one memory; as well as at least one processor coupled to the at least one memory and configured to cause the apparatus to: transmitting to the master node MN a request to perform a CHO-based SN change procedure from the device to a target secondary node SN having one or more conditional handover CHO conditions; and Information indicating a failure of the CHO-based SN change procedure is received from the MN.

20. A processor for wireless communication, comprising: at least one controller coupled to at least one memory and configured to cause the processor to: transmitting to the master node MN a request to perform a CHO-based SN change procedure from the processor to a target secondary node SN having one or more conditional handover CHO conditions; and Information indicating a failure of the CHO-based SN change procedure is received from the MN.

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