Wireless link failure recovery method and corresponding user equipment

Abstract

The present disclosure provides a method for link failure recovery during handover and a corresponding user equipment. The method executed in the user equipment includes: after a handover process in which a UE is configured with a dual-active protocol stack is successful, if a radio link failure (RLF) of a primary cell group occurs in the UE, then during a radio resource control re-establishment process for restoring a connection or when an RLF occurs in a source link, the UE performs an operation of falling back from the dual-active protocol stack to a single-active protocol stack, releasing the protocol stack and configuration associated with the source base station; when the link quality of the source base station is good, the UE releases the protocol stack and configuration associated with the target base station, recovers the single connection state with the source base station, and reports the failure information to the base station.

Description

Technical Field

[0001] The present disclosure relates to the technical field of wireless communications, and more particularly, to a handover method and corresponding user equipment. Background Art

[0002] In June 2018, the 3rd Generation Partnership Project (3GPP) RAN#80 plenary meeting approved a new research project for 5G technical standards (see non-patent document: RP-181433: New WID on NR (New Radio) mobility enhancements) and a new research project for Long Term Evolution (LTE) Release 16 (see non-patent document: RP-181544). One of the research objectives of these two projects is to find a solution to meet one of the mobility requirements: seamless handover, that is, achieving zero or near-zero millisecond handover interruption time during the handover process when changing the UE's serving cell. Among the solutions being studied to reduce handover interruption time is the Dual Active Protocol Stack mechanism. In the DAPS mechanism, after receiving the handover command, the UE does not cut off the link (data transmission) with the source base station during the handover process to the target base station. Instead, it can simultaneously maintain the connection and data transmission between the target base station and the source base station, thereby avoiding the delay caused by service interruption due to disconnection from the source base station before accessing the target base station during the handover process.

[0003] This disclosure proposes a solution to the problem of how to implement the DAPS mechanism in an LTE system or a NR system. Summary of the Invention

[0004] The purpose of the embodiments of the present disclosure is to propose a solution to the problem of implementing the DAPS mechanism in the LTE / NR system. More specifically, the present disclosure proposes a solution to the problem of how the UE falls back to the traditional single-activation protocol stack when a radio link failure (RLF) of the target cell link occurs after successfully accessing the target cell after performing a DAPS handover in the LTE / NR system. The embodiments of the present disclosure provide a method for radio link failure recovery when DAPS is configured and executed in a user equipment, and a corresponding user equipment.

[0005] According to a first aspect of the present disclosure, a method performed in a user equipment (UE) is proposed, including: when a radio link failure (RLF) of a master cell group (MCG) occurs in the user equipment (UE), the UE initiates a radio resource control (RRC) connection re-establishment process to restore the connection with the network side; during the RRC connection re-establishment process, if the UE is configured with a dual-activation protocol stack (DAPS) bearer, the UE performs a change operation from the dual-activation protocol stack to a single-activation protocol stack, and releases the protocol stack and configuration associated with the source base station.

[0006] In the radio link failure recovery method of the first aspect, the UE performs a change operation from a dual-active protocol stack to a single-active protocol stack, including one or more of the following:

[0007] Operation 1: Reset the Medium Access Control (MAC) entity corresponding to the source base station and release the MAC configuration of the source base station;

[0008] Operation 2: For each DAPS bearer, release the Radio Link Control (RLC) entity of the source base station and its associated logical channels, and reconfigure the Packet Data Convergence Protocol (PDCP) entity to release the DAPS (i.e., reconfigure the DAPS-configured PDCP entity (called a DAPS PDCP entity) to a normal non-PDCP entity (a PDCP entity not configured with DAPS)).

[0009] Operation 3: For each signaling radio bearer (SRB), release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0010] Operation 4: Release the physical channel configuration of the source base station;

[0011] Operation 5: discard the security key used in the source base station.

[0012] In the radio link failure recovery method of the first aspect above, when the UE configured with the DAPS bearer determines that the link between the UE and the source base station does not detect a radio link failure RLF, the UE falls back to a single active protocol stack state in which only the connection with the source base station is maintained, including performing one or more of the following operations:

[0013] Operation 1: Release the configuration of the target base station;

[0014] Operation 2: Reset the MAC address corresponding to the target base station and release the MAC configuration of the target base station;

[0015] Operation 3: For each DAPS bearer, release the RLC entity of the target base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the DAPS PDCP entity to a normal non-PDCP entity);

[0016] Operation 4: For each SRB, release the PDCP entity of the target base station, release the RLC entity of the target base station and its associated logical channels, and if no master key update indication (such as the masterKeyUpdate information element indication) is received, configure the PDCP entity of the source base station to be the continuation of the state variables of the PDCP entity of the target base station (cotinuation);

[0017] Operation 5: For each Data Radio Bearer (DRB) that is not configured as a DAPS bearer, if no master key update indication (e.g., masterKeyUpdate information element indication) is received, configure the PDCP entity of the source base station to be a continuation of the state variables of the PDCP entity of the target base station;

[0018] Operation 6: Release the physical channel configuration of the target base station;

[0019] Operation 7: discard the security key used in the target base station;

[0020] Action 8: Lose any saved RRC messages; resume the suspended SRB at the source base station;

[0021] Operation 9: For each non-DAPS bearer, fall back to the UE configuration used in the DRB of the source base station (including PDCP and RLC state variables, security configuration, and data stored in the transmit and receive buffers of the PDCP and RLC entities);

[0022] Operation 10: Fall back to the measurement configuration used by the UE at the source base station.

[0023] Operation 11: Initiate a failure information procedure to report to the network side that an RLF has occurred in the target base station when DAPS is configured. Preferably, in the failure information procedure, the UE sets the failure reason included in the RRC message (such as the FailureInformation message) used to report the failure information to MCG RLF configured with DAPS.

[0024] In the radio link failure recovery method of the first aspect, the occurrence of MCG RLF in the UE occurs after the UE successfully completes DAPS handover to the target base station.

[0025] In the radio link failure recovery method of the first aspect above, when the UE configured with the DAPS bearer detects that an RLF has occurred in the link between the UE and the source base station, the UE initiates an RRC connection re-establishment process.

[0026] In the radio link failure recovery method of the first aspect above, the UE performs a change operation from a dual-active protocol stack to a single-active protocol stack when the UE receives an RRC message containing indication information for releasing the source base station from the network side.

[0027] In the radio link failure recovery method of the first aspect above, the UE sends an RRC message containing DAPS indication information to the network side, where the DAPS indication information is used to indicate that the UE is configured with a DAPS bearer; preferably, the RRC message is an RRC re-establishment request message or an RRC re-establishment request completion message.

[0028] In the radio link failure recovery method of the first aspect, the UE is configured with a DAPS bearer, which means that one or more DRBs of the UE are configured with a DAPS configuration information element for instructing to perform a DAPS switching operation.

[0029] In the radio link failure recovery method of the first aspect above, when the UE detects that an RLF occurs in the link of the source base station, the UE performs one or more of the following operations:

[0030] Operation 1: Reset the MAC address corresponding to the source base station and release the MAC configuration of the source base station;

[0031] Operation 2: For each DAPS bearer, release the RLC entity of the source base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the PDCP entity configured with DAPS (called DAPS PDCP entity) to a normal non-PDCP entity (PDCP entity not configured with DAPS)).

[0032] Operation 3: For each SRB, release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0033] Operation 4: Release the physical channel configuration of the source base station;

[0034] Operation 5: discard the security key used in the source base station.

[0035] According to a second aspect of the present disclosure, a user equipment is provided, comprising: a processor; and a memory storing instructions; wherein the instructions, when executed by the processor, execute the radio link failure recovery method according to the context. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] For a more complete understanding of the present disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0037] Figure 1 This is a sequence diagram showing how a connected user equipment UE changes its serving cell through a handover procedure.

[0038] Figure 2 The diagram is a schematic diagram showing the protocol stack associated with a DAPS bearer in a dual-active protocol stack configuration.

[0039] Figure 3 This is a flowchart showing the wireless link failure recovery method of embodiment 1.

[0040] Figure 4 A block diagram showing a user equipment UE involved in the present disclosure.

[0041] In the drawings, the same or similar structures are marked with the same or similar reference numerals. DETAILED DESCRIPTION

[0042] Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description of exemplary embodiments of the disclosure, taken in conjunction with the accompanying drawings.

[0043] In this disclosure, the terms "include" and "including" and their derivatives mean inclusion without limitation; the term "or" is inclusive, meaning and / or.

[0044] In this specification, the various embodiments described below for describing the principles of the present disclosure are merely illustrative and should not be construed in any way as limiting the scope of the disclosure. The following description with reference to the accompanying drawings is intended to assist in a comprehensive understanding of the exemplary embodiments of the present disclosure as defined by the claims and their equivalents. The following description includes a variety of specific details to aid understanding, but these details should be considered merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, for the sake of clarity and brevity, descriptions of well-known functions and structures have been omitted. In addition, throughout the drawings, the same reference numerals are used for similar functions and operations.

[0045] The following describes multiple embodiments of the present disclosure using the Long Term Evolution (LTE) / NR mobile communication system and its subsequent evolutionary versions as example application environments. However, it should be noted that the present disclosure is not limited to the following embodiments, but is applicable to many other wireless communication systems. Unless otherwise specified, in the present disclosure, the concepts of cell and base station can be interchangeable; the LTE system is also used to refer to 5G and subsequent LTE systems (such as the eLTE system, or the LTE system that can be connected to the 5G core network), and LTE can be replaced by Evolved Universal Terrestrial Radio Access (E-UTRA) or Evolved Universal Terrestrial Radio Access Network E-UTRAN. In the present disclosure, handover refers to the change of the primary cell initiated by the network side, including the primary cell change between cells and the primary cell change within the cell, that is, the primary cell of the UE is changed from the source cell to the target cell, where the source cell and the target cell can be the same cell or different cells. During this process, the key or security algorithm used for access layer security may also be updated or not. The security includes encryption and decryption and integrity protection. The source cell may also be referred to as the source base station, or the source beam, the source transmission point (Transmission point, TRP), the source primary cell (Primary Cell, PCell), the source primary cell group MCG; the target cell may also be referred to as the target base station, or the target beam, the target transmission point, the target primary cell PCell, the target cell group MCG. The source cell refers to the cell serving the UE to which the handover process is connected before the handover process is initiated, that is, the cell that sends an RRC message containing a handover command to the UE. The target cell refers to the cell serving the UE to which the UE is connected after the handover process is successfully completed, or the cell indicated by the target cell identifier contained in the handover command. The handover command described in the present disclosure is used to trigger the UE to perform a handover, and in the NR system it is an RRC reconfiguration message containing a synchronous reconfiguration (Reconfiguration with sync) information element, and further, it is an RRC reconfiguration message containing a synchronous reconfiguration (Reconfiguration with sync) information element for the master cell group (Master Cell Group, MCG). At this time, the handover may also be referred to as a synchronous reconfiguration of the MCG. In the LTE system, it is an RRC connection reconfiguration message including a Mobility Control Information (MobilityControlInformation) information element.Among them, the synchronization reconfiguration information element or the mobile control information information element may include configuration information of the target cell, such as the target cell identifier, the target cell frequency, the public configuration of the target cell such as system information, the random access configuration used by the UE to access the target cell, the security parameter configuration of the UE in the target cell, the radio bearer configuration of the UE in the target cell, etc. For the convenience of description, the RRC reconfiguration message and the RRC connection reconfiguration message are equivalent in the present disclosure; similarly, its response message RRC reconfiguration completion message and the RRC connection reconfiguration completion message are equivalent. The handover command and the RRC message containing the handover command are equivalent, which refers to the RRC message that triggers the UE to perform the handover or the configuration in the RRC message. The handover configuration refers to all or part of the configuration in the handover command. Cancellation, release, deletion, clearing and removal can be replaced. Execution, use and application can be replaced. Configuration and reconfiguration can be replaced. Monitoring (monitor) and detection (detect) can be replaced.

[0046] The following describes processes or concepts in the prior art to which this disclosure relates.

[0047] Handover configuration in NR system:

[0048] In the NR system, the RRC reconfiguration message for the handover command carries the RRC configuration from the target base station, including but not limited to the following RRC configuration (see section 6.2.2 of 3GPP technical standard agreement 38.331 for details):

[0049] - Measurement configuration (measconfig information element): used to configure the intra-frequency, inter-frequency, and inter-radio access technology measurements performed by the UE, such as measurement object configuration, measurement reporting configuration, and measurement gap configuration.

[0050] -Cell group configuration (cellGroupConfig information element), used to configure the primary cell group or secondary cell group. Including the RLC bearer configuration corresponding to DRB / SRB

[0051] (rlc-bearerToAddModList information element and rlc-bearerToreleaselist information element), MAC configuration (MAC-cellgroupconfig information element), physical layer configuration, secondary cell addition / modification / release configuration, special cell (SpCell) configuration, etc. Among them, the spcell configuration includes the cell index number, switching information (reconfigurationWithSync information element), radio link failure related timer and constant configuration, radio link detection (Radio Link Monitoring, RLM) configuration, special cell dedicated configuration, etc. Among them, the reconfigurationwithsync information element is similar to the mobile control information in the LTE system, and contains switching related information to achieve mobility, which includes serving cell configuration public information, UE's C-RNTI in the target cell, switching process monitoring timer T304 configuration, random access dedicated configuration for the random access process to the target cell, etc.

[0052] - Non-access stratum dedicated information (dedicatedInfoNASList information element).

[0053] -Radio bearer configuration (radiobearerConfig information element), used to configure the Service Data Application Protocol (SDAP) and PDCP layer of the radio bearer DRB and / or SRB.

[0054] -Master key update configuration (masterKeyupdate information element).

[0055] -Other configurations (otherconfig information element), used to configure proximity reporting configuration (reportproximityconfig information element), in-device coexistence (IDC) configuration, energy selection indication configuration (powerprefindicationconfig information element), location acquisition configuration (obtainlocationconfig information element), etc.

[0056] General handover process in LTE / NR system:

[0057] User mobility in a connected state is mainly achieved through a handover process, where the handover refers to a process in which a UE in an RRC connected state changes a serving cell (primary cell). Figure 1 This is a sequence diagram showing how a connected user equipment UE changes its serving cell through a handover process. Figure 1 As shown in Figure 1, the switching process generally includes the following stages:

[0058] Phase 1: Measurement Phase. The base station sends a measurement configuration to the user equipment (UE). Based on this measurement configuration, the UE measures the radio link corresponding to the serving cell or neighboring cell. When the configured measurement reporting conditions are met, the UE sends a measurement report to the base station. The measurement phase is optional; the base station can also perform a blind handover of the UE when it does not have a valid measurement report.

[0059] Phase 2: Handover preparation phase. The base station determines whether to trigger a handover for the UE based on the received measurement report and other factors such as base station load. If a handover is determined to be triggered for the UE, the source base station initiates the handover preparation process by sending a handover request message to the target base station. The target base station decides whether to accept the handover request for the UE based on factors such as the UE context in the handover request message and the available resources of the target base station. If accepted, it replies to the source base station with a handover confirmation message, which contains an inter-node RRC message, namely the handover command.

[0060] Phase 3: Handover Execution. The source eNB issues a handover command to the UE and begins forwarding the UE's data to the target eNB. Upon receiving the handover command, the UE immediately applies the configuration specified in the handover command and executes the handover. It then accesses the target eNB through a random access procedure and sends a confirmation message to the target eNB. The random access procedure is optional.

[0061] Phase 4: Handover completion phase. After the target base station confirms that the UE has successfully accessed, it sends a handover completion message to the source base station. The source base station can then release the UE context stored on it.

[0062] DAPS Switching:

[0063] The DAPS handover introduced in version 16 refers to a handover process in which the UE maintains the connection with the source base station after receiving the RRC message for handover until the source base station is released after the random access process to the target is successfully performed. During this process, the UE continues to receive downlink data from the source base station until the source base station is released, and the user continues to send uplink data to the source base station until the random access process to the target base station is successfully completed. After the random access process to the target base station is completed, the MAC layer indicates to the upper layer that the random access process is completed. After receiving the indication, the RRC layer instructs the lower layer (such as the PDCP layer) to perform an uplink data change and change the uplink path from the source base station to the target base station. When the PDCP layer is requested to change the uplink data, the PDCP data protocol data unit (PDU) of the PDCP layer is delivered to the RLF entity associated with the target base station, the PDCP control PDU associated with the source base station is delivered to the RLC entity associated with the source base station, and the PDCP control PDU associated with the target base station is delivered to the RLC entity associated with the target base station.

[0064] In the case of DAPS switching, after receiving the switching command, the UE establishes a MAC entity for the target base station. If a DRB is configured as a DAPS bearer, an RLC entity and a dedicated traffic channel (DTCH) logical channel associated with the target base station are established for the DRB, and the PDCP entity associated with the DAPS bearer is reconfigured as a DAPS PDCP entity. The DAPS PDCP entity has security and robustness header compression (RObust Header Compression, ROHC) functions associated with the source base station and the target base station respectively in the PDCP entity, and the security and ROHC functions are associated with the corresponding RLC entities configured by the source base station and the target base station respectively. In the above manner, during the DAPS switching process, the UE maintains the activation protocol stacks for the source base station and the target base station at the same time, see Figure 2 .

[0065] During the DAPS process, if the source base station experiences a radio link failure, the UE will suspend the transmission of all DRBs of the source base station and release the connection of the source base station. When the DAPS handover is completed, the UE receives an RRC reconfiguration message sent from the target base station, which carries indication information for instructing the release of the source base station (such as identified by the daps-SourceRelease information element). After receiving the indication, the UE performs the operation of releasing the source base station configuration and protocol stack. The operation includes one or more of the following: resetting the MAC corresponding to the source base station, releasing the MAC configuration of the source base station; for each DAPS bearer, releasing the RLC entity of the source base station and its associated logical channels, reconfiguring the PDCP release to release the DAPS (i.e., reconfiguring the PDCP entity configured with DAPS (called DAPSPDCP entity) to a normal non-PDCP entity (PDCP entity not configured with DAPS)); for each SRB, releasing the PDCP entity of the source base station, releasing the RLC entity of the source base station and its associated logical channels; releasing the physical channel configuration of the source base station; and discarding the security keys used in the source base station.

[0066] When the DAPS handover fails, that is, the T304 timer used to monitor the handover process times out, if the source base station does not detect a radio link failure, the UE returns to the connection with the source base station and reports the DAPS handover failure through the source base station without triggering the RRC connection re-establishment process. In the process of returning to the connection with the source base station, the UE falls back from the DAPS state to the single-activated protocol stack state that only maintains communication with the source base station by performing one or more of the following operations: releasing the configuration of the target base station; resetting the MAC corresponding to the target base station and releasing the MAC configuration of the target base station; for each DAPS bearer, releasing the RLC entity of the target base station and its associated logical channels, and reconfiguring the PDCP release to release the DAPS (i.e., releasing the DAPS PDCP entity is reconfigured to a normal non-PDCP entity); for each SRB, the PDCP entity of the target base station is released, the RLC entity of the target base station and its associated logical channels are released, and if no master key update indication is received, the PDCP entity of the source base station is configured as a continuation of the state variables of the PDCP entity of the target base station (cotinuation); the physical channel configuration of the target base station is released; the security keys used in the target base station are discarded; any saved RRC messages are lost; the suspended SRB in the source base station is restored; for each non-DAPS bearer, fall back to the UE configuration used in the DRB of the source base station (including PDCP, RLC state variables, security configuration, data saved in the send and receive buffers of PDCP and RLC entities); fall back to the measurement configuration used by the UE in the source base station.

[0067] Radio Link Failure (RLF):

[0068] The UE considers that RLF has occurred when the following situations occur: timer T310 for RLF monitoring times out, timer T312 for fast RLF monitoring times out, random access question received from the MAC layer, and indication received from the RLC entity indicating that the maximum number of retransmissions has been reached. During DAPS switching, if the above timers, MAC entity and RLC are associated with the source base station MCG, it is considered that the source base station MCG RLF has been monitored; if the above timers, MAC entity and RLC are associated with the target base station MCG, it is considered that the target base station MCG RLF has been monitored. In dual connectivity (DC), the UE is configured with a secondary cell group (SCG). If the above timers, MAC entity and RLC are associated with the SCG, it is considered that the SCG RLF has been monitored.

[0069] The following two scenarios are considered in this disclosure:

[0070] Scenario 1: After a successful DAPS handover, a radio link failure (RLF) occurs in the UE. The RLF refers to the link failure of the PCell after the handover is successful, or the link failure of the target cell of the DAPS handover. At this time, the link between the UE and the source base station is also in the RLF state. The RLF of the source link can occur during the DAPS handover process (T304 is running) or after the DAPS handover process is successfully completed, that is, the UE's random access process to the target base station is successfully completed.

[0071] Scenario 2: After a successful DAPS handover, the UE experiences a radio link failure (RLF). This refers to a link failure in the PCell after the handover, or a link failure in the target cell of the DAPS handover. At this point, the link between the UE and the source eNB is not in the RLF state, meaning the link quality of the source link is good.

[0072] In the above two cases, the UE needs to fall back from the DAPS state, i.e., the dual-activated protocol stack state, to the single-activated protocol stack state to continue the next operation, such as executing the RRC connection re-establishment process. Otherwise, when the UE in the DAPS state performs the connection recovery process with the network side under the RLF in the above two scenarios, the network side cannot know whether the UE is in the DAPS state. The state mismatch between the UE and the network side may cause the RRC reconfiguration to fail after the UE's connection recovery process fails. The present disclosure provides a solution to the above problem based on the above scenario, but is not limited to the above scenario.

[0073] Example 1:

[0074] This embodiment provides a method for a UE to autonomously execute fallback from the DAPS state to the single active protocol stack (non-DAPS) state during the RRC connection re-establishment process (e.g. Figure 3 shown).

[0075] Step 1: UE initiates RRC re-establishment procedure.

[0076] Preferably, the UE can initiate the RRC re-establishment process when one of the following conditions is met: that is, in step 0, when the RLF of the MCG is detected; when the RLF of the MCG is detected and the timer 316 is not configured; when the synchronous reconfiguration of the MCG fails, that is, the handover fails. When the UE is configured with DAPS, the RLF of the MCG refers to the RLF of the target base station after receiving the handover command or after the handover is successful. As mentioned above, the successful handover refers to the successful completion of the random access between the MAC layer and the target base station. The timer T316 is used to monitor the MCG failure information process (or fast MCG recovery process). When the UE sends an MCG failure information message or triggers the MCG failure information process, T316 is started. When a response message from the network side is received, such as an RRC reconfiguration message or an RRC release message, or when the RRC connection re-establishment process is initiated, T316 is stopped. When T316 times out, the UE considers that the MCG failure information process has failed and the UE can perform the RRC re-establishment process.

[0077] Step 2: During the RRC re-establishment process, such as the initialization phase of the RRC re-establishment process, the UE performs an operation of falling back from the DAPS state to the single active protocol stack (non-DAPS) state, releasing the protocol stack and configuration associated with the source base station. The operation may include one or more of the following:

[0078] Operation 1: Reset the MAC address corresponding to the source base station and release the MAC configuration of the source base station;

[0079] Operation 2: For each DAPS bearer, release the RLC entity of the source base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the PDCP entity configured with DAPS (called DAPS PDCP entity) to a normal non-PDCP entity (PDCP entity not configured with DAPS)).

[0080] Operation 3: For each SRB, release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0081] Operation 4: Release the physical channel configuration of the source base station;

[0082] Operation 5: discard the security key used in the source base station.

[0083] The UE performs the above operations when DAPS is configured. The DAPS configured by the UE can also be described as the UE being configured with any one or more DAPS bearers; or any one or more DRBs of the UE being configured with DAPS (such as identified by the daps-Config information element). The DAPS bearer means that the bearer DRB is configured with an information element for indicating the daps configuration, such as the daps-config information element. Preferably, the daps-config information element is configured for each DRB separately.

[0084] Example 2:

[0085] This embodiment provides a method for the network side to instruct the UE to perform a fallback from the DAPS state to the single active protocol stack (non-DAPS) state during the RRC connection re-establishment process through explicit RRC signaling based on the DAPS information reported by the UE.

[0086] Step 1: UE initiates RRC re-establishment procedure.

[0087] The triggering of the UE initiating the RRC re-establishment process is the same as described in Example 1.

[0088] Step 2: During the RRC re-establishment process, the UE carries a DAPS indication message in the RRC connection re-establishment request message or the RRC connection re-establishment complete message to indicate to the network side that the UE is configured with DAPS, or that the UE is configured with any one or more DAPS bearers.

[0089] Step 3: Receive an RRC message from the base station containing an information element for indicating the release of the source base station. The RRC message may be an RRC connection re-establishment message or an RRC reconfiguration message. Preferably, the RRC reconfiguration message is the first RRC reconfiguration message after the RRC re-establishment process is completed. Preferably, the information element for indicating the release of the source base station is a daps-sourcerelease information element, which is used to instruct the UE to release the source base station, including the source cell part for stopping the DAPS operation and the source cell part for releasing the DAPS configuration. Preferably, the information element containing the information element for indicating the release of the source base station may also be described as an information element for indicating the release of the source base station set to TRUE or 1.

[0090] In this step, after receiving the RRC message containing the above information element, the UE performs an operation of falling back from the DAPS state to the single active protocol stack (non-DAPS) state, releasing the protocol stack and configuration associated with the source base station. The operation includes one or more of the following:

[0091] Operation 1: Reset the MAC address corresponding to the source base station and release the MAC configuration of the source base station;

[0092] Operation 2: For each DAPS bearer, release the RLC entity of the source base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the PDCP entity configured with DAPS (called DAPS PDCP entity) to a normal non-PDCP entity (PDCP entity not configured with DAPS)).

[0093] Operation 3: For each SRB, release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0094] Operation 4: Release the physical channel configuration of the source base station;

[0095] Operation 5: discard the security key used in the source base station.

[0096] The UE performs the above operations when DAPS is configured. The DAPS configured by the UE can also be described as the UE being configured with any one or more DAPS bearers; or any one or more DRBs of the UE being configured with DAPS (such as identified by the daps-Config information element). The DAPS bearer means that the bearer DRB is configured with an information element for indicating the daps configuration, such as the daps-config information element. Preferably, the daps-config information element is configured for each DRB separately.

[0097] Example 3:

[0098] This embodiment provides a method in which, in the above scenario 2, the UE performs a fallback from the DAPS state to the single active protocol stack (non-DAPS) state, and falls back to the connection with the source base station, so as to avoid initiating the RRC connection re-establishment process.

[0099] Step 1: The UE detects that an MCG RLF occurs.

[0100] The MCG refers to the target MCG during DAPS switching.

[0101] Step 2: If the source base station does not detect RLF, the UE releases the target base station portion of the DAPS operation and performs an operation to fall back from the DAPS state to the single active protocol stack (non-DAPS) state. The operation may include one or more of the following:

[0102] Operation 1: Release the configuration of the target base station;

[0103] Operation 2: Reset the MAC address corresponding to the target base station and release the MAC configuration of the target base station;

[0104] Operation 3: For each DAPS bearer, release the RLC entity of the target base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the DAPS PDCP entity to a normal non-PDCP entity);

[0105] Operation 4: For each SRB, release the PDCP entity of the target base station, release the RLC entity of the target base station and its associated logical channels, and if no master key update indication (such as the masterKeyUpdate information element indication) is received, configure the PDCP entity of the source base station to be the continuation of the state variables of the PDCP entity of the target base station (cotinuation);

[0106] Operation 5: For each DRB that is not configured as a DAPS bearer, if no master key update indication (such as a masterKeyUpdate information element indication) is received, configure the PDCP entity of the source base station to be a continuation of the state variables of the PDCP entity of the target base station;

[0107] Operation 6: Release the physical channel configuration of the target base station;

[0108] Operation 7: discard the security key used in the target base station;

[0109] Action 8: Lose any saved RRC messages; resume the suspended SRB at the source base station;

[0110] Operation 9: For each non-DAPS bearer, fall back to the UE configuration used in the DRB of the source base station (including PDCP and RLC state variables, security configuration, and data stored in the transmit and receive buffers of the PDCP and RLC entities);

[0111] Operation 10: Fall back to the measurement configuration used by the UE at the source base station.

[0112] Operation 11: Initiate a failure information procedure to report to the network side that an RLF has occurred in the target base station when DAPS is configured. Preferably, in the failure information procedure, the UE sets the failure reason included in the RRC message (such as the FailureInformation message) used to report the failure information to MCG RLF configured with DAPS.

[0113] Prior to step 1, the UE successfully completes the DAPS handover, i.e., when the UE is configured with any DAPS bearer, the MAC layer successfully completes the random access procedure to the target base station, at which point T304 is not in the running state. That is, step 2 is executed when the UE is configured with any one or more DAPS bearers.

[0114] Example 4:

[0115] This embodiment provides a method for a UE to roll back from a DAPS state to a single active protocol stack (non-DAPS) state when an RLF occurs in a source base station.

[0116] Step 1: A source RLF occurs during the DAPS process, that is, when the UE is configured with any DAPS bearer, the UE detects the RLF of the source MCG.

[0117] Step 2: Roll back from the DAPS state to the single active protocol stack (non-DAPS) state, releasing the configuration and protocol stack of the source base station. The operation may include one or more of the following:

[0118] Operation 1: Suspend the transmission of DRBs of all source base stations;

[0119] Operation 2: Release the connection with the source base station;

[0120] Operation 3: Reset the MAC address corresponding to the source base station and release the MAC configuration of the source base station;

[0121] Operation 4: For each DAPS bearer, release the RLC entity of the source base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the PDCP entity configured with DAPS (called DAPS PDCP entity) to a normal non-PDCP entity (a PDCP entity not configured with DAPS)).

[0122] Operation 5: For each SRB, release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0123] Operation 6: Release the physical channel configuration of the source base station;

[0124] Operation 7: Discard the security key used in the source base station.

[0125] It is worth noting that this embodiment is not limited to the aforementioned scenarios 1 and 2 of the present disclosure, and is also applicable to the case where the source base station RLF occurs when DAPS has not been completed, that is, T304 is running.

[0126] Example 5:

[0127] This embodiment corresponds to embodiment 2, and provides a corresponding method on the base station side.

[0128] Step 1: During the RRC re-establishment process, an RRC connection re-establishment request message or an RRC connection re-establishment complete message received from the UE carries a DAPS indication message, which is used by the UE to indicate to the network side that the UE is configured with DAPS, or that the UE is configured with any one or more DAPS bearers.

[0129] Step 2: Send an RRC message to the UE containing an information element for indicating the release of the source base station. The RRC message may be an RRC connection re-establishment message or an RRC reconfiguration message. Preferably, the RRC reconfiguration message is the first RRC reconfiguration message after the RRC re-establishment process is completed. Preferably, the information element for indicating the release of the source base station is a daps-sourcerelease information element, which is used to instruct the UE to release the source base station, including the source cell part for stopping the DAPS operation and the source cell part for releasing the DAPS configuration. Preferably, the information element containing the information element for indicating the release of the source base station can also be described as an information element for indicating the release of the source base station set to TRUE or 1.

[0130] In this step, the information element indicating the release of the source base station is used so that after receiving the information element, the UE performs an operation of falling back from the DAPS state to the single active protocol stack (non-DAPS) state, releasing the protocol stack and configuration associated with the source base station. The operation includes one or more of the following:

[0131] Operation 1: Reset the MAC address corresponding to the source base station and release the MAC configuration of the source base station;

[0132] Operation 2: For each DAPS bearer, release the RLC entity of the source base station and its associated logical channels, and reconfigure the PDCP release to release the DAPS (i.e., reconfigure the PDCP entity configured with DAPS (called DAPS PDCP entity) to a normal non-PDCP entity (PDCP entity not configured with DAPS)).

[0133] Operation 3: For each SRB, release the PDCP entity of the source base station, release the RLC entity of the source base station and its associated logical channels;

[0134] Operation 4: Release the physical channel configuration of the source base station;

[0135] Operation 5: discard the security key used in the source base station.

[0136] The UE performs the above operations when DAPS is configured. The DAPS configured by the UE can also be described as the UE being configured with any one or more DAPS bearers; or any one or more DRBs of the UE being configured with DAPS (such as identified by the daps-Config information element). The DAPS bearer means that the bearer DRB is configured with an information element for indicating the daps configuration, such as the daps-config information element. Preferably, the daps-config information element is configured for each DRB separately.

[0137] Example 6

[0138] This embodiment describes the user equipment UE of the present disclosure. Figure 4 1 is a block diagram showing a user equipment UE involved in the present invention. Figure 4 As shown, the user equipment UE40 includes a processor 401 and a memory 402. The processor 401 may include, for example, a microprocessor, a microcontroller, an embedded processor, etc. The memory 402 may include, for example, a volatile memory (such as a random access memory RAM), a hard disk drive (HDD), a non-volatile memory (such as a flash memory), or other memory. The memory 402 stores program instructions. When the instructions are executed by the processor 401, the various methods for radio link failure recovery when carrying DAPS bearers described in detail in the present invention may be executed.

[0139] The method and related devices of the present disclosure have been described above in conjunction with preferred embodiments. Those skilled in the art will appreciate that the method shown above is merely exemplary. The method of the present disclosure is not limited to the steps and sequence shown above. The base station and user equipment shown above may include more modules, for example, modules that can be developed or will be developed in the future and can be used for the base station, MME, or UE, etc. The various identifiers shown above are merely exemplary and not restrictive, and the present disclosure is not limited to the specific information elements used as examples of these identifiers. Those skilled in the art may make many changes and modifications based on the teachings of the illustrated embodiments.

[0140] The program running on the device according to the present disclosure may be a program that controls a central processing unit (CPU) to enable a computer to implement the functions of the embodiments of the present disclosure. The program or the information processed by the program may be temporarily stored in a volatile memory (such as a random access memory RAM), a hard disk drive (HDD), a non-volatile memory (such as a flash memory), or other memory systems.

[0141] The program for realizing each embodiment function of the present disclosure can be recorded on a computer-readable recording medium. The corresponding function can be realized by making a computer system read the program recorded on the recording medium and executing these programs. The so-called "computer system" herein can be a computer system embedded in the device, and can include an operating system or hardware (such as a peripheral device). "Computer-readable recording medium" can be a semiconductor recording medium, an optical recording medium, a magnetic recording medium, a short-term dynamic storage program recording medium or any other recording medium that is computer-readable.

[0142] The various features or functional modules of the devices used in the above embodiments can be implemented or executed by circuits (e.g., single-chip or multi-chip integrated circuits). The circuits designed to perform the functions described in this specification may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination of the above devices. The general-purpose processor may be a microprocessor, or any existing processor, controller, microcontroller, or state machine. The above circuits may be digital circuits or analog circuits. In the case where new integrated circuit technologies have emerged to replace existing integrated circuits due to advances in semiconductor technology, one or more embodiments of the present disclosure may also be implemented using these new integrated circuit technologies.

[0143] Furthermore, the present disclosure is not limited to the above-described embodiments. Although various examples of the embodiments have been described, the present disclosure is not limited thereto. Fixed or non-mobile electronic devices installed indoors or outdoors can be used as terminal devices or communication devices, such as AV equipment, kitchen equipment, cleaning equipment, air conditioners, office equipment, vending machines, and other household appliances.

[0144] As described above, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. However, the specific structure is not limited to the above-mentioned embodiments, and the present disclosure also includes any design changes that do not deviate from the main purpose of the present disclosure. In addition, various modifications can be made to the present disclosure within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. In addition, components with the same effect described in the above-mentioned embodiments can be replaced with each other.

Claims

1. A radio link failure recovery method performed by a user equipment (UE), the radio link failure recovery method comprising: Based on the handover failure, initiate the radio resource control RRC connection re-establishment process; as well as performing a plurality of operations during the RRC connection re-establishment process based on any dual-active protocol stack (DAPS) bearer configured for the UE, The multiple operations include: Reset the medium access control (MAC) of the source base station; Releasing the MAC configuration of the source base station; For each DAPS bearer, releasing the Radio Link Control (RLC) entity and associated logical channels of the source base station, and reconfiguring the Protocol Data Convergence Protocol (PDCP) entity to release the DAPS; For each signaling radio bearer (SRB), release the PDCP entity of the source base station, and release the RLC entity and related logical channels of the source base station; releasing the physical channel configuration of the source base station; and The security key used in the source base station is discarded.

2. A user equipment (UE), comprising: processor; as well as A memory having instructions stored therein, wherein, based on the instructions, the processor is configured to: Initiating a radio resource control (RRC) connection re-establishment process based on a handover failure; and performing a plurality of operations during the RRC connection re-establishment process based on any dual-active protocol stack (DAPS) bearer configured for the UE, The multiple operations include: Reset the medium access control (MAC) of the source base station; Releasing the MAC configuration of the source base station; For each DAPS bearer, releasing the Radio Link Control (RLC) entity and associated logical channels of the source base station, and reconfiguring the Protocol Data Convergence Protocol (PDCP) entity to release the DAPS; For each signaling radio bearer (SRB), release the PDCP entity of the source base station, and release the RLC entity and related logical channels of the source base station; releasing the physical channel configuration of the source base station; and The security key used in the source base station is discarded.

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