Managing MCG fast recovery

Abstract

The UE communicating with the MN and the SN with the DC detects a primary cell group (MCG) failure associated with the MN. In response to detecting the MCG failure, the UE performs an MCG recovery procedure by sending an MCG failure information message to the SN, receiving an MCG failure recovery message from the SN, and sending an MCG failure recovery completion message to the MN.

Description

[0001] This application is a divisional application of the invention patent application with application date of September 29, 2020, application number 202080028227.0, and invention name “Managing MCG Quick Recovery”. Technical Field

[0002] The present disclosure relates generally to wireless communications, and more particularly to fast recovery with a master node due to an integrity check failure or a reconfiguration failure. Background Art

[0003] This background description is provided to generally present the context of the present disclosure. To the extent described in this background section, the work of the presently named inventors and aspects of the description that may not qualify as prior art at the time of filing are neither explicitly nor implicitly admitted as prior art in this disclosure.

[0004] The evolution of wireless communications to fifth generation (5G) standards and technologies delivers higher data rates and greater capacity, as well as improved reliability and lower latency, enhancing mobile broadband services. 5G technology also enables new service categories for in-vehicle, fixed wireless broadband, and the Internet of Things (IoT). The specifications for the 5G air interface characteristics are defined as 5G New Radio (5GNR).

[0005] In order to communicate wirelessly with the network, a user equipment (UE) may establish a connection to the network via at least one node (e.g., a base station or a serving cell) supporting a fifth generation core network (5GC). In some cases, the UE is able to connect to multiple nodes at once using a multi-node connection (e.g., a dual connection). By connecting to multiple nodes, performance improvements in user throughput, mobility robustness, or load balancing can be achieved. Multiple nodes can be associated with the same radio access technology (RAT) or different RATs. As an example, the UE is able to establish communication with two nodes (e.g., a primary node (MN) and a secondary node (SN)) using multi-RAT dual connection (MR-DC) or new radio dual connection (NR-DC).

[0006] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as user plane data transmission, encryption, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP TS 36.323) and New Radio (NR) (see TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (from user equipment (UE) to base station) and in the downlink direction (from base station to UE). In addition, the PDCP sublayer provides signaling radio bearers (DRBs) and data radio bearers (DRBs) to the radio resource control (RRC) sublayer. Typically, the UE and the base station can exchange RRC messages and non-access stratum (NAS) messages using SRBs, and use DRBs to transmit data on the user plane.

[0007] The UE is able to use several types of SRBs and DRBs. When operating in dual connectivity (DC), cells associated with a base station operating a primary node (MN) define a primary cell group (MCG), while cells associated with a base station operating as a secondary node (SN) define a secondary cell group (SCG). The so-called SRB1 resources carry RRC messages, including non-access stratum (NAS) messages over a dedicated control channel (DCCH) in some cases, and SRB2 resources support RRC messages including logged measurement information or NAS messages, also over the DCCH, but with a lower priority than SRB1 resources. More generally, SRB1 and SRB2 resources allow the UE and MN to exchange RRC messages related to the MN and embed RRC messages related to the SN, and may also be referred to as MCG SRBs. SRB3 resources allow the UE and SN to exchange RRC messages related to the SN, and may be referred to as SCG SRBs. Split SRBs allow the UE to exchange RRC messages directly with the MN via the lower layer resources of the MN and SN. In addition, a DRB that terminates at the MN and uses only the lower layer resources of the MN can be called an MCG DRB, a DRB that terminates at the SN and uses only the lower layer resources of the SN can be called an SCG DRB, and a DRB that terminates at the MCG but uses the lower layer resources of the MN or SN, or both can be called a split DRB.

[0008] 3GPP specification TS 37.340 (v15.7.0) describes the process of adding or changing SN in a dual connectivity (DC) scenario. These processes involve messaging (e.g., RRC signaling and preparation) between RAN nodes (e.g., components of a base station or a distributed base station), which typically results in delays, thereby increasing the probability of failure of the SN addition or SN change process. These processes do not involve conditions associated with the UE and can be referred to as "immediate" SN addition and change processes. On the other hand, according to the "conditional" SN addition process, the UE receives the configuration of the candidate SN (C-SN) and the conditions from the base station, and initiates a connection to the C-SN only when the conditions are met (e.g., by performing a random access process).

[0009] To further enhance DC operation, the 3GPP organization has also proposed a so-called fast MCG recovery procedure. According to this procedure, when a UE operating in DC detects an MCG failure, the UE notifies the SN, which in turn notifies the MN. Then, the MN sends a recovery message to the UE via the SN.

[0010] Certain interactions between the Conditional SN Addition procedure and Fast MCG Recovery may cause one or both procedures to fail. As a result, the UE loses dual connectivity and, in some cases, all network connectivity. Summary of the invention

[0011] In order to perform fast recovery in response to detecting a master cell group (MCG) failure at the UE, the UE performs a fast MCG recovery procedure, including sending an MCG failure information message to the SN, which in turn forwards the MCG failure information message to the MN. The MN then sends an MCG failure recovery message to the SN, which in turn forwards the MCG failure recovery message to the UE. The UE then sends an MCG failure recovery complete message to the MN. The MCG failure may include an MCG radio link failure, a handover failure, an MCG reconfiguration with a synchronization failure, an integrity failure on an RRC message received from the MN 104, or a reconfiguration failure on an RRC message (e.g., an RRC reconfiguration message) received from the MN 104.

[0012] These techniques allow the UE and the base station to prevent data transmission between the UE and the MN. In response to the MCG failure, the SN is interrupted by the RRC re-establishment procedure, and these techniques avoid having to perform the time-consuming RRC reconfiguration procedure and measurement reporting procedure to recover.

[0013] An example embodiment of the technology of the present disclosure is a method for performing fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC). The method includes detecting, by the UE communicating with the MN and the SN in DC, a master cell group (MCG) fault associated with the MN. In response to detecting the MCG fault, the method includes performing an MCG recovery procedure, including sending an MCG fault information message to the SN, receiving an MCG fault recovery message from the SN, and sending an MCG fault recovery complete message to the MN.

[0014] Another example embodiment of the disclosed technology is a method for performing fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC). The method includes receiving a handover command from the MN by the UE communicating with the MN and the SN in DC, the handover command including a first time value of a first timer for performing a first random access procedure with the MN and a second time value of a second timer for performing a second random access procedure with the SN, starting the first timer and the second timer, performing the first random access procedure with the MN, stopping the first timer in response to completing the second random access procedure, performing the second random access procedure with the SN, and stopping the second timer in response to completing the second random access procedure, wherein the first timer and the second timer are configured to prevent the second timer from expiring before the second random access procedure is completed.

[0015] Another example embodiment of the disclosed technology is a method for fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC). The method includes detecting a primary cell group (MCG) radio link failure associated with the MN by the UE communicating with the MN and the SN in DC, sending an MCG fault information message to the SN, receiving a radio resource control (RRC) reconfiguration message from the SN, and determining whether the RRC reconfiguration message configures a cell associated with the MN to be connected to the UE. In response to determining that the RRC reconfiguration message includes a cell associated with the MN, the method includes sending an RRC reconfiguration complete message to the MN.

[0016] Another example embodiment of the techniques is a UE including processing hardware and configured to implement the above methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a block diagram of an example system in which a radio access network (RAN) and a user equipment can implement the disclosed techniques for managing conditional procedures associated with a secondary node (SN);

[0018] Figure 2 is based on Figure 1A block diagram of an example protocol stack for UE communicating with a base station;

[0019] Figure 3 is a message passing diagram for an example scenario in which a UE notifies a master node (MN) of a master cell group (MCG) failure that a UE operating with a dual connectivity (DC) with the MN has been detected and the UE, MN and SN perform a known procedure for fast recovery of the MCG link;

[0020] Figure 4 is a message passing diagram for an example scenario in which a UE configured with maximum transmit power for a secondary cell group (SCG) detects an MCG radio link failure;

[0021] Figure 5 is a message transfer diagram for an example scenario in which the UE receives a handover command from the MN, performs a random access procedure on a PCell configured by the handover command, and a timer expires before completing the random access procedure;

[0022] Figure 6 is a message passing diagram of an example scenario in which a UE receives a Radio Resource Control (RRC) message from a MN and detects an integrity check failure or a configuration failure on the RRC message;

[0023] Figure 7 is a message transfer diagram of an example scenario, in which the UE receives a handover command from the MN, and for a first random access procedure on a PCell configured by the handover command and a second random access procedure on a PSCell configured by the handover command, the handover command includes a first timer value and a second timer value for the first timer and the second timer, respectively;

[0024] Figure 8 is a message passing diagram for an example scenario, in which the UE detects an MCG radio link failure and sends an MCGFailureInformation message to the SN;

[0025] Fig. 9 is a message passing diagram for an example scenario in which a UE configured with a maximum transmit power for a secondary cell group (SCG) detects an MCG radio link failure and sends a MCGFailureInformation message using a transmit power higher than the maximum transmit power configured for the SCG;

[0026] Fig.10 is a message passing diagram for an example scenario in which the UE receives a handover command from the MN, performs a random access procedure on a PCell configured by the handover command, a timer expires before completing the random access procedure, and the UE, the MN, and the SN perform a known procedure for quickly recovering an MCG link;

[0027] Fig.11 is a message passing diagram for an example scenario in which a UE receives a radio resource control (RRC) message from a MN, detects an integrity check failure or a configuration failure on the RRC message, and the UE, MN, and SN perform a known procedure for fast recovery of an MCG link;

[0028] Fig.12 is a message transfer diagram of an example scenario, in which the UE receives a handover command from the MN, and for a first random access procedure on a PCell configured by the handover command and a second random access procedure on a PSCell configured by the handover command, the handover command includes a first timer value and a second timer value for a first timer and a second timer, respectively, wherein the second timer value is greater than the first timer value;

[0029] Fig.13 is a message transfer diagram of an example scenario, in which the UE receives a handover command from the MN, and for a first random access procedure on a PCell configured by the handover command and a second random access procedure on a PSCell configured by the handover command, the handover command includes a first timer value and a second timer value for a first timer and a second timer, respectively, wherein the first random access procedure and the second random access procedure are performed simultaneously;

[0030] Fig.14A is a message transfer diagram of an example scenario, in which the UE receives a handover command from the MN, and for a first random access procedure on a PCell configured by the handover command and a second random access procedure on a PSCell configured by the handover command, the handover command includes a first timer value and a second timer value of a first timer and a second timer, respectively, wherein the second timer is started after the first timer;

[0031] Fig. 14B is a message transfer diagram for an example scenario, in which the UE receives a handover command from the MN, and for a first random access procedure on a PCell configured by the handover command and a second random access procedure on a PSCell configured by the handover command, the handover command includes a first timer value and a second timer value of a first timer and a second timer, respectively, wherein the first timer expires before the first random access procedure is completed, the second random access procedure is completed, and the UE, the MN, and the SN perform a known procedure for quickly recovering an MCG link;

[0032] Fig.15 is a message transfer diagram for an example scenario in which a UE detects an MCG radio link failure, sends an MCGFailureInformation message to a SN, receives an RRC message from the SN, and determines whether the RRC message configures a PCell belonging to the MN;

[0033] Fig.16 is a message transfer diagram for an example scenario in which the UE detects an MCG radio link failure and sends an MCGFailureInformation message to the SN, and the MN generates an RRC message to configure a PCell belonging to the MN;

[0034] Fig.17A is a flow chart of an example method including releasing a maximum transmit power configuration for an SCG (P-Max-SCG) after detecting an MCG radio link failure, which can be Figure 1 Implementation in UE;

[0035] Fig. 17B is another flow chart of an example method including not using a maximum transmit power configuration of an SCG (P-Max-SCG) after detecting an MCG radio link failure, which can be Figure 1 Implementation in UE;

[0036] Fig. 17C is a flow chart of an example method including releasing a maximum transmit power configuration for an SCG (P-Max-SCG) after detecting an MCG radio link failure, which can be Figure 1 is implemented in the MN or SN;

[0037] Fig.17D is another flow chart of an example method including not using a maximum transmit power configuration of an SCG (P-Max-SCG) after detecting an MCG radio link failure, which can be Figure 1 is implemented in the MN or SN;

[0038] Fig.18A is a flow chart of an example method for handling the expiration of a handover-related timer during a handover procedure, which can be Figure 1 Implementation in UE;

[0039] Fig.18B is another flow chart of an example method for handling the expiration of a handover-related timer during a handover procedure, which can be Figure 1 Implementation in UE;

[0040] Fig.19 is a flow chart of an example method for processing a configuration from an RRC message, which can be Figure 1 Implementation in UE;

[0041] Fig. 20A is a flow chart of an example method for handling a configuration failure from an RRC message, which can be Figure 1 Implementation in UE;

[0042] Fig. 20B is a flow chart of an example method for handling an integrity check failure from an RRC message, which can be Figure 1 Implementation in UE;

[0043] Fig.21A is a flow chart of an example method for processing a handover-related timer during a handover process, which can be Figure 1 is implemented in MN;

[0044] Fig. 21B is a flow chart of an example method for processing a handover-related timer during a handover process, which can be Figure 1 Implementation in UE;

[0045] Fig. 21C is another flow chart of an example method for handling handover-related timers during a handover process, which can be Figure 1 Implementation in UE;

[0046] Fig.21D is another flow chart of an example method for handling handover-related timers during a handover process, which can be Figure 1 Implementation in UE;

[0047] Fig. 22 is a flow chart of an example method for processing an RRC reconfiguration message, which can be Figure 1 Implementation in UE;

[0048] Fig.23 is a flow chart of an example method for processing an RRC reconfiguration message, which can be Figure 1 ; and

[0049] Fig.24 is a flow chart of an example method for processing an RRC reconfiguration message, which can be Figure 1 is implemented in the UE. DETAILED DESCRIPTION

[0050] Figure 1 An exemplary wireless communication system 100 is depicted in which a communication device can implement these techniques. Wireless communication system 100 includes UE 102, base station 104, base station 106A, base station 106B, and core network (CN) 110. UE 102 initially connects to base station 104.

[0051] In some scenarios, base station 104 can perform an immediate SN addition to configure UE 102 to operate in dual connectivity (DC) with base station 104 and base station 106A. Base stations 104 and 106A serve as the MN and SN, respectively, of UE 102. Later, while UE 102 is in DC with MN 104 and S-SN 106A, MN 104 can perform an immediate SN change to change the SN of UE 102 from base station 106A (source SN, or “S-SN”) to base station 106B (target SN, or “T-SN”).

[0052] In other scenarios, base station 104 can perform a conditional SN addition process to first configure base station 106A as a candidate SN (C-SN) for UE 102. At this point, UE 102 can be in a single connection (SC) with base station 104, or in a DC with base station 104 and another base station 106B. In contrast to the immediate SN addition case discussed above, UE 102 does not immediately attempt to connect to C-SN 106A. In this scenario, base station 104 again operates as a MN, but base station 106A initially operates as a C-SN instead of a SN.

[0053] More specifically, when UE 102 receives the configuration of C-SN 106A, UE 102 does not connect to C-SN 106A until UE 102 determines that a certain condition is satisfied (UE 102 can consider multiple conditions in some cases, but for convenience, the following discussion refers to only a single condition). When UE 102 determines that the condition is satisfied, UE 102 connects to candidate SN 106A, so that C-SN 106A begins to operate as SN 106A for UE 102. Therefore, when base station 106A operates as a C-SN instead of an SN, base station 106A is not yet connected to UE 102, and therefore is not yet serving UE 102.

[0054] In some scenarios, the condition associated with conditional SN addition can be that the signal strength / quality detected by UE 102 on the candidate primary and secondary cells (PSCells) of C-SN 106A exceeds a certain threshold or corresponds to an acceptable measurement. For example, when one or more measurement results obtained by UE 102 on the candidate PSCell (C-PSCell) are higher than a threshold configured by MN 104 or higher than a predetermined or pre-configured threshold, UE 102 determines that the condition is met. When UE 102 determines that the signal strength / quality on the C-PSCell of C-SN 106A is good enough (again, measured relative to one or more quantitative thresholds or other quantitative metrics), UE 102 can use C-SN 106A to perform a random access procedure to connect to the candidate SN 106A. Once UE 102 successfully completes the random access procedure, base station 106A begins to operate as an SN, and C-PSCell becomes the PSCell of UE 102. SN 106A can then begin to communicate data with UE 102.

[0055] In some scenarios, while the UE 102 is in DC with the MN 104 and the SN (e.g., base station 106A / B), the UE 102 may detect a primary cell group (MCG) failure in communication with the MN 104. In response to the detection, the UE 102 may send an MCG failure indication message to the SN via the radio resources of the SN (i.e., via the secondary cell group (SCG) radio resources). In one implementation, if the MN 104 understands the MCG failure indication message, the SN may forward the MCG failure indication message to the MN 104 in an interface message (e.g., an RRC transport message). In another implementation, the SN may indicate the MCG failure in an interface message (e.g., an RRC transport message), and if the MN 104 does not understand the MCG failure indication message, the interface message is delivered to the MN 104. In response to receiving the MCG failure indication message or an indication of the MCG failure, the MN 104 may deliver an MCG failure recovery message to the UE 102 for recovering the MCG failure via the SCG radio resources. The SN may allocate SCG radio resources to the UE 102. For example, the SCG radio resources include one or more physical resource blocks, resource elements, or subcarriers in a time unit. The time unit can be one or more ODFM symbols, time slots, or subframes.

[0056] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106A or 106B can be implemented as a secondary gNB (SgNB) or a candidate SgNB (C-SgNB). The UE 102 can communicate with the base station 104 and the base station 106A or 106B (106A / B) via the same RAT or different RATs such as EUTRA or NR. When the base station 104 is a MeNB and the base station 106A is an SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB. In this scenario, the MeNB 104 may or may not configure the base station 106B as a C-SgNB for the UE 102. When the base station 104 is a MeNB and the base station 106A is a C-SgNB for the UE 102, the UE 102 can be in SC with the MeNB. In this scenario, MeNB 104 may or may not configure base station 106B as another C-SgNB for UE 102.

[0057] In some cases, the MeNB, SeNB, or C-SgNB is implemented as an ng-eNB instead of an eNB. When the base station 104 is a master ng-eNB (Mng-eNB) and the base station 106A is an SgNB, the UE 102 can be in a next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. In this scenario, the MeNB 104 may or may not configure the base station 106B as the C-SgNB of the UE 102. When the base station 104 is a Mng-NB and the base station 106A is the C-SgNB of the UE 102, the UE 102 can be in a SC with the Mng-NB. In this scenario, the Mng-eNB 104 may or may not configure the base station 106B as another C-SgNB of the UE 102.

[0058] When the base station 104 is a MgNB and the base stations 106A / B are SgNBs, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. In this scenario, the MeNB 104 may or may not configure the base station 106B as a C-SgNB for the UE 102. When the base station 104 is a MgNB and the base station 106A is a C-SgNB for the UE 102, the UE 102 may be in SC with the MgNB. In this scenario, the MgNB 104 may or may not configure the base station 106B as another C-SgNB for the UE 102.

[0059] When the base station 104 is a MgNB and the base station 106A / B is a secondary ng-eNB (Sng-eNB), the UE 102 may be in NR-EUTRADC (NE-DC) with the MgNB and the Sng eNB. In this scenario, the MgNB 104 may or may not configure the base station 106B as a C-Sng-eNB for the UE 102. When the base station 104 is a MgNB and the base station 106A is a candidate Sng-eNB (C-Sng-eNB) for the UE 102, the UE 102 may be in SC with the MgNB. In this scenario, the MgNB 104 may or may not configure the base station 106B as another C-Sng-eNB for the UE 102.

[0060] The base stations 104, 106A, and 106B can be connected to the same core network (CN) 110, which can be an evolved packet core (EPC) 111 or a fifth generation core (5GC) 160. The base station 104 can be implemented as an eNB supporting an S1 interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a base station supporting an NR radio interface and an NG interface for communicating with the 5GC 160. The base station 106A can be implemented as an EN-DC gNB (en-gNB) having an S1 interface to the EPC 111, an en-gNB not connected to the EPC 111, a gNB supporting an NR radio interface and an NG interface to the 5GC 160, or an ng-eNB supporting an EUTRA radio interface and an NG interface to the 5GC 160. To directly exchange messages in the scenarios discussed below, base stations 104, 106A, and 106B may support an X2 or Xn interface.

[0061] Among other components, the EPC 111 can include a serving gateway (S-GW) 112 and a mobility management entity (MME) 114. The S-GW 112 is typically configured to transfer user plane packets associated with audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, addressing, and other related functions. The 5GC 160 includes a user plane function (UPF) 162, an access and mobility management (AMF) 164, and / or a session management function (SMF) 166. In general, the UPF 162 is configured to transfer user plane packets associated with audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, addressing, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0062] like Figure 1As shown, base station 104 supports cell 124, base station 106A supports cell 126A, and base station 106B supports cell 126B. Cells 124 and 126A can partially overlap, and cells 124 and 126B can also partially overlap, so that UE 102 can communicate with base station 104 (operating as MN) and base station 106A (operating as SN) in DC, and when the SN change is completed, communicate with base station 104 (operating as MN) and SN 106B in DC. More specifically, when UE 102 is in DC with base station 104 and base station 106A, base station 104 operates as MeNB, Mng-eNB, or MgNB, and base station 106A operates as SgNB or Sng-eNB. When UE 102 is in SC with base station 104, base station 104 operates as MeNB, Mng-eNB, or MgNB, and base station 106A operates as C-SgNB or C-Sng-eNB.

[0063] In general, the wireless communication network 100 can include any appropriate number of base stations supporting NR cells and / or EUTRA cells. More specifically, the EPC 111 or 5GC 160 can be connected to any appropriate number of base stations supporting NR cells and / or EUTRA cells. Although the following examples specifically refer to specific CN types (EPC, 5GC) and RAT types (5G NR and EUTRA), in general, the techniques of the present disclosure may also be applied to other suitable radio access and / or core network technologies, such as sixth generation (6G) radio access and / or 6G core network or 5G NR-6G DC.

[0064] Continue to refer Figure 1 The base station 104 is equipped with processing hardware 130, which can include one or more general-purpose processors such as a CPU and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or a dedicated processing unit. The processing hardware 130 in the example implementation includes a MN RRC controller 132, which is configured to manage or control one or more RRC configurations or RRC procedures when the base station 104 operates as a MN.

[0065] The base station 106A is equipped with processing hardware 140, which can also include one or more general-purpose processors such as a CPU and non-transitory computer-readable memory storing machine-readable instructions executable on one or more general-purpose processors, and / or a dedicated processing unit. The processing hardware 140 in the example implementation includes a (C-)SN RRC controller 142, which is configured to manage or control one or more RRC configurations and / or RRC processes when the base station 106A operates as a SN or a candidate SN (C-SN). The base station 106B may have the same or similar hardware as the base station 106A.

[0066] although Figure 1 The RRC controllers 132 and 142 are shown to operate in the MN and SN, respectively, but in different scenarios, the base station can generally operate as a MN, SN, or candidate SN. Therefore, the MN 104, SN 104A, and SN 106B can implement a similar set of functions and support MN, SN, and conditional SN operations.

[0067] Still reference Figure 1 , the UE 102 is equipped with processing hardware 150, which can include one or more general-purpose processors such as a CPU and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or a dedicated processing unit. The processing hardware 150 in the example implementation includes a UE RRC controller 152, which is configured to manage or control one or more RRC configurations and / or RRC procedures.

[0068] In operation, UE 102 can use radio bearers (e.g., DRBs or SRBs) that terminate at different times at MN 104 or SN 106A. UE 102 can apply one or more security keys when communicating on the radio bearers in uplink (from UE 102 to base station) and / or downlink (from base station to UE 102) directions.

[0069] Next, Figure 2 The radio protocol stack according to which the UE 102 can communicate with an eNB / ng-eNB or a gNB is illustrated in a simplified manner. Each of the base stations 104, 106A, or 106B can be an eNB / ng-eNB or a gNB.

[0070] The physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA medium access control (MAC) sublayer 204A, which in turn provides logical channels to the EUTRA radio link control (RLC) sublayer 206A, and the EUTRA RLC sublayer in turn provides RLC channels to the EUTRA PDCP sublayer 208, and in some cases, provides RLC channels to the NR PDCP sublayer 210. Similarly, the PHY 202B of NR provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B, and the NR RLC sublayer 206B in turn provides RLC channels to the NR PDCP sublayer 210. In some implementations, the UE 102 supports both EUTRA and NR stacks to support handover between EUTRA and NR base stations and / or DC over the EUTRA and NR interfaces. In addition, as Figure 2 As shown, UE 102 is capable of supporting layering of NR PDCP 210 on EUTRARLC 206A.

[0071] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets that can be referred to as service data units (SDUs) (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly on the PDCP layer 208 or 210), and output packets that can be referred to as protocol data units (PDUs) (e.g., to the RLC layer 206A or 206B). Except for the difference between SDUs and PDUs, for simplicity, this disclosure refers to both SDUs and PDUs as "packets".

[0072] On the control plane, for example, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 provide SRBs to exchange radio resource control (RRC) messages. On the user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 provide DRBs to support data exchange.

[0073] When the UE 102 operates in EUTRA / NR DC (EN-DC) with the BS 104A operating as a MeNB and the BS 106A operating as an SgNB, the network can provide the UE 102 with a MN terminated bearer using EUTRA PDCP 208 or a MN terminated bearer using NR PDCP 210. In various scenarios, the network can also provide the UE 102 with an SN terminated bearer using NR PDCP 210. The MN terminated bearer can be an MCG bearer or a split bearer. The SN terminated bearer can be an SCG bearer or a split bearer. The MN terminated bearer can be an SRB (e.g., SRB1 or SRB2) or a DRB. The SN terminated bearer can be an SRB (e.g., SRB2) or a DRB.

[0074] First reference Figure 3 , base station 104 operates as a MN and base station 106B operates as a SN. At the beginning, UE 102 is in DC 302 with MN 104 and SN 106B. UE 102 detects 304 an MCG radio link failure (i.e., a radio link failure on an MCG link configured by MN 104). In response to detection 304, UE 102 sends 306 an MCG failure information (MCGFailureInformation) message to SN 106B. SN 106B sends 308 an MCGFailureInformation message to MN 104. In response to the MCGFailureInformation message, MN 104 generates an MCG failure recovery message for UE 102 to recover the MCG radio link failure detected by the UE at event 304. The MN 104 then delivers 310 a MCG fault recovery message (e.g., an RRC reconfiguration message) to the SN 106, which in turn delivers 312 the MCG fault recovery message to the UE 102. The UE 102 recovers 314 the MCG fault according to the MCG fault recovery message, and sends 316 a MCG fault recovery complete message (e.g., an RRC reconfiguration complete message) to the MN 104 in response to the MCG fault recovery message.

[0075] Events 306 , 308 , 310 , 312 , 314 , 316 collectively may be considered to define an MCG fast recovery process 350 .

[0076] Figure 4 Scenario 400 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 402 with MN 104 and SN 106B and is configured with a maximum transmit power for SCG (P-Max-SCG). P-Max-SCG limits the maximum transmit power that UE 102 can use to send uplink transmissions to SN 106B on the SCG. P-Max-SCG is lower than the maximum transmit power that UE 102 can achieve.

[0077] UE 102 detects 404 an MCG radio link failure and decides to send an MCG failure information (MCGFailureInformation) message to SN 106B. In response to the decision, UE 102 sends 408 an MCGFailureInformation message to SN 106B. UE 102 sends the MCGFailureInformation message using P-Max-SCG power, which is insufficient for SN 106B to receive the MCGFailureInformation message. UE 102 then disconnects 410 from the SN in response to failing to send the MCGFailureInformation message and performs 416 an RRC re-establishment procedure with MN 104. After successfully performing the RRC re-establishment procedure, MN 104 may perform 418 multiple RRC reconfiguration procedures and measurement reporting procedures with UE 102 to configure 420 UE 102 to be in DC with MN 104 and SN 106B again, or to configure UE 102 to be in DC with MN 104 and SN 106A ( Figure 4 4). Then, the UE is in DC with MN 104 and SN 106B (or 106A). However, during this process, since UE 102 suspends the data radio bearer for data communication between UE 102 and MN 104 / SN 106B, data transmission between UE 102 and MN 104 / SN 106B is interrupted by RRC re-establishment process 416. In addition, MN 104 performs 418 RRC reconfiguration process and measurement report process with UE 102 to return UE 102 to DC. It takes time to configure UE 102 in DC to provide a higher data rate for data communication.

[0078] Figure 5 Scenario 500 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 502 with MN 104 and SN 106B.

[0079] UE 102 receives 504 a handover command from MN 104. In response to the handover command, UE 102 starts 506 a timer T304 and performs 508 a random access procedure on the PCell configured by the handover command. Timer T304 expires 510 before completing the random access procedure. In response to the expiration of T304, UE 102 disconnects 512 from SN 106B and performs 516 an RRC re-establishment procedure. After successfully performing the RRC re-establishment procedure 516, MN 104 may perform 518 a plurality of RRC reconfiguration procedures and measurement reporting procedures with UE 102 to configure 520 UE 102 to be in DC with MN 104 and SN 106B again, or to configure UE 102 to be in DC with MN 104 and SN 106A ( Figure 5 516). The UE is then in DC with the MN 104 and the SN 106B (or 106A). However, since the UE 102 suspends the data radio bearer for data communication between the UE 102 and the MN 104 / SN 106B, data transmission between the UE 102 and the MN 104 / SN 106B is interrupted by the RRC re-establishment procedure 516. In addition, the MN 104 performs 518 an RRC reconfiguration procedure and a measurement report procedure with the UE 102 to return the UE 102 to the DC. This takes time to configure the UE 102 in the DC to provide a higher data rate for data communication.

[0080] Figure 6 Scenario 600 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 602 with MN 104 and SN 106B.

[0081] UE 102 receives 604 an RRC message from MN 104. UE 102 then detects 606 an integrity check failure or a reconfiguration failure on the RRC message. In response to the integrity check failure or the reconfiguration failure, UE 102 disconnects 612 from SN 106B and performs 616 an RRC reestablishment procedure with MN 104. After successfully performing the RRC reestablishment procedure 616, MN 104 may perform 618 multiple RRC reconfiguration procedures and measurement reporting procedures with UE 102 to configure 620 UE 102 to be in DC with MN 104 and SN 106B again, or to configure UE 102 to be in DC with MN 104 and SN 106A ( Figure 66A). Then, the UE is in DC with MN 104 and SN 106B (or 106A). However, since UE 102 suspends the data radio bearer for data communication between UE 102 and MN 104 / SN 106B, data transmission between UE 102 and MN 104 / SN 106B is interrupted by RRC re-establishment procedure 616. In addition, MN 104 performs 618 an RRC reconfiguration procedure and a measurement report procedure with UE 102 to return UE 102 to DC. This takes time to configure UE 102 in DC to provide a higher data rate for data communication.

[0082] Figure 7 Scenario 700 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 702 with MN 104 and SN 106B.

[0083] UE 102 receives 704 a handover command including a first T304 timer value and a second T304 timer value from MN 104. In response to the handover command, UE 102 starts 706 a first timer T304 having a first T304 timer value and a second timer T304 having a second T304 timer value upon receiving the handover command. UE 102 performs 708 a random access procedure on the PCell configured by the handover command and sends 710 a handover complete message to MN 104 in response to the handover command. UE 102 stops 712 the first timer T304 after completing the first random access procedure. Then, UE 102 performs a second random access procedure on the PSCell configured by the handover command after completing the first random access procedure. However, the second timer T304 expires 714 before completing the second random access procedure. In response to the expiration of the second timer T304, UE 102 disconnects 716 from SN 106B and sends 718 a SCGFailureInformation message to MN 104. In response to the SCGFailureInformation message, MN 104 may perform 720 multiple RRC reconfiguration and measurement reporting procedures with UE 102 to configure 722 UE 102 to be in DC with MN 104 and SN 106B again, or to configure UE 102 to be in DC with MN 104 and SN 106A ( Figure 7716). The UE is then in DC with the MN 104 and the SN 106B (or 106A). However, since the UE 102 suspends the data radio bearer for data communication between the UE 102 and the MN 104 / SN 106B, data transmission between the UE 102 and the MN 104 / SN 106B is interrupted by the RRC re-establishment procedure 716. In addition, the MN 104 performs 718 an RRC reconfiguration procedure and a measurement report procedure with the UE 102 to return the UE 102 to the DC. This takes time to configure the UE 102 in the DC to provide a higher data rate for data communication.

[0084] Figure 8 Scenario 800 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 802 with MN 104 and SN 106B. UE 102 detects 804 an MCG radio link failure (i.e., a radio link failure on an MCG link configured by MN 104). In response to detection 804, UE 102 sends 806 an MCGFailureInformation message to SN 106B. SN 106B sends 808 an MCGFailureInformation message to MN 104. In response to the MCGFailureInformation message, MN 104 generates an MCG failure recovery message for UE 102 to recover the MCG radio link failure detected by the UE at event 804. MN 104 then delivers 810 an RRC reconfiguration message to SN 106B, which in turn delivers 812 an RRC reconfiguration message to UE 102. UE 102 generates 814 an RRC reconfiguration complete message in response to the RRC reconfiguration message and intends to send the RRC reconfiguration complete message to MN 104. However, since UE 102 has not yet recovered the MCG radio link failure, UE 102 cannot send the RRC reconfiguration complete message to MN 104. Before the MCG radio link failure is recovered, UE 102 may not send the RRC reconfiguration complete message. Because MN 104 does not receive the RRC reconfiguration complete message from UE 102, MN 104 may determine 816 to retransmit the RRC reconfiguration message. In response to determining 816, MN 104 delivers 818 the RRC reconfiguration message to SN 106B, and then SN 106B delivers 820 the RRC reconfiguration message to UE 102. UE 102 may perform 814 again, which causes a deadlock between UE 102 and MN 104.

[0085] In order to solve the above reference Figure 4-Figure 8The problems described herein, such as interruption of data transmission between UE 102 and MN 104 / SN 106B, the amount of time required to perform the RRC reconfiguration procedure and the measurement reporting procedure, and deadlock between UE 102 and MN 104, are described below with reference to Figure 9-Figure 16 The processes are described. These processes may include performing an MCG fast recovery process in response to detecting an MCG failure, expiration of a timer before completing a random access process, or an integrity check failure or reconfiguration failure of an RRC message. These processes may also include configuring a timer for a first random access process between UE 102 and MN 104 and a second random access process between UE 102 and SN 106B, so that the second timer value is greater than the first timer value, performing the first random access process and the second random access process at the same time, or starting the timer at different times. In addition, these processes may include determining whether the RRC reconfiguration message configures the PCell, sending an RRC configuration complete message to MN 104 if the RRC reconfiguration message configures the PCell, and sending the RRC configuration complete message to SN 106B if the RRC reconfiguration message does not configure the PCell, or generating an RRC reconfiguration message including the PCell by MN 104.

[0086] Fig. 9 A scenario 900 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 902 with MN 104 and SN 106B. UE 102 detects 904 an MCG failure, and UE 102 decides to send a MCGFailureInformation message to SN 106B and ignore P-Max-SCG in response to detecting the MCG failure. UE 102 sends 906 an MCGFailureInformation message to SN 106B using a transmit power higher than P-Max-SCG. Then, UE 102 performs 908 an MCG fast recovery procedure 350. Since UE 102 ignores P-Max-SCG, UE 102 is able to send an MCGFailureInformation message 906 to SN 106B using a transmit power higher than P-Max-SCG.

[0087] P-Max-SCG is the maximum total transmit power used by the UE 102 in the SCG. In some implementations, P-Max-SCG is the maximum total transmit power used by the UE 102 in the SCG across all serving cells in frequency range 1 (FR1). For example, P-Max-SCG can be p-MaxUE-FR1 defined in 3GPP Technical Specification (TS) 36.331 or p-NR-FR1 defined in 3GPP TS 38.331.

[0088] In some implementations, before detecting the MCG failure, the UE 102 may be configured by the MN 104 to have a maximum total transmit power (e.g., p-UE-FR1) that the UE 102 can use to transmit on the MCG and SCG. The UE 102 may maintain the maximum total transmit power in response to the MCG failure, and send uplink transmissions on the SCG at a transmit power not exceeding the maximum total transmit power before recovering from the MCG failure. In some implementations, the MN 104 may configure a new P-Max-SCG to the UE 102 in an MCG failure recovery message, and the UE 102 may send uplink transmissions on the SCG at a transmit power not exceeding the new P-Max-SCG after recovering from the MCG failure.

[0089] In some implementations, the MN 104 or SN 106B may configure a time division multiplexing (TDM) pattern for the UE 102. The TDM pattern configuration includes a UL / DL reference configuration indicating the time when the UE 102 configured with (NG) EN-DC or NE-DC is allowed to transmit. For example, the TDM pattern can be tdm-PatternConfig or tdm-PatternConfigNE-DC defined in 3GPP TS 36.331.

[0090] In some implementations, the UE 102 may release the TDM mode configuration in response to detecting an MCG failure. In response to releasing the TDM mode configuration, the UE 102 may transmit in a time slot on the SCG when the corresponding subframe on the MCG is a UL subframe in the TDM mode configuration. In response to receiving the MCGFailureInformation message, the SN 106B in one implementation may release the TDM mode configuration and configure the UE 102 to transmit in a time slot on the SCG when the corresponding subframe on the MCG (i.e., corresponding to the time slot) is a UL subframe in the TDM mode configuration. In another implementation, the MN 104 may deliver an interface message to request the SN 104B to release the TDM mode configuration. In response to receiving the interface message, the SN 106B in one implementation may release the TDM mode configuration and configure the UE 102 to transmit in a time slot on the SCG when the corresponding subframe on the MCG is a UL subframe in the TDM mode configuration.

[0091] In other implementations, the UE 102 may maintain (or keep) the TDM mode configuration configured by the MN 102 or the SN 106B in response to detecting an MCG failure. According to the TDM mode configuration, the UE 102 may not transmit in the time slot on the SCG when the corresponding subframe on the MCG is a UL subframe in the TDM mode configuration. In response to receiving the MCGFailureInformation message, the SN 106B in one implementation may maintain the TDM mode configuration. In response to maintaining the TDM mode configuration, the SN 106B configures the UE 102 to transmit in the time slot on the SCG when the corresponding subframe on the MCG is a DL subframe in the TDM mode configuration. That is, the SN 106B and the UE 102 still follow the TDM mode configuration to communicate with each other when the UE 102 encounters an MCG failure.

[0092] In some implementations, the MCG failure can be an MCG radio link failure, a handover failure, an MCG reconfiguration with a synchronization failure, an integrity failure on an RRC message received from the MN 104, or a reconfiguration failure on an RRC message received from the MN 104 (e.g., an RRC reconfiguration message).

[0093] Next, Fig.10 A scenario 1000 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in a DC 1002 with MN 104 and SN 106B.

[0094] UE 102 receives 1004 a handover command from MN 104. In response to the handover command, UE 102 starts 1006 a timer T304 and performs 1008 a random access procedure on the PCell configured by the handover command to handover to the PCell. Timer T304 expires 1010 before completing the random access procedure. In response to the expiration of T304, UE 102 performs 1012 an MCG fast recovery procedure 350 instead of disconnecting from SN 106B and performing an RRC re-establishment procedure. Thus, UE 102 can recover connection with MN 104 through connection with SN 106B to avoid having to perform a time-consuming RRC reconfiguration procedure and a measurement reporting procedure.

[0095] In some implementations, the handover command may include a T304 timer value for the UE 102 to use when starting the T304 timer. In some implementations, the handover command may include one or more configurations for the UE 102 to perform a random access procedure.

[0096] In some implementations, the handover command may be an RRC reconfiguration message including a ReconfigurationWithSync IE. In other implementations, the handover command may be an RRC reconfiguration message including a MobilityControlInfo IE.

[0097] Fig.11 A scenario 1100 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in a DC 1102 with MN 104 and SN 106B.

[0098] UE 102 receives 1104 an RRC message from MN 104. UE 102 then detects 1106 an integrity check failure or a reconfiguration failure on the RRC message. In response to the integrity check failure or the reconfiguration failure, UE 102 performs 1112 an MCG fast recovery procedure 350 instead of disconnecting from SN 106B and performing an RRC reestablishment procedure. Thus, UE 102 can recover connection with MN 104 through connection with SN 106B to avoid having to perform a time-consuming RRC reconfiguration procedure and a measurement reporting procedure.

[0099] In some implementations, UE 102 receives an RRC message from MN 104 on SRB1. In some implementations, the RRC message may be a DL-DCCH-Message specified in 3GPP TS 36.331 or TS 38.331. In some implementations, SN 106B configures SRB3 for UE 102, and then sends MCGFailureInformation to SN 106B when performing the MCG fast recovery procedure 350 on SRB3. SN 106B then forwards the MCGFailureInformation message to MN 104.

[0100] Fig.12 A scenario 1200 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in a DC 1202 with MN 104 and SN 106B.

[0101] SN 106B configures 1203 a second T304 timer value to be longer than the first T304 timer value, and delivers 1205 the second T304 timer value to MN 104. Then, UE 102 receives 1204 a handover command including the first T304 timer value and the second T304 timer value from MN 104. In response to the handover command, UE 102 starts 1206 a first timer T304 having the first T304 timer value and a second timer T304 having the second T304 timer value upon receiving the handover command. UE 102 performs 1208 a first random access procedure on the PCell configured by the handover command, and sends 1210 a handover complete message to MN 104 in response to the handover command. UE 102 stops 1212 the first timer T304 after completing the first random access procedure. UE 102 performs 1214 a second random access procedure on the PSCell configured by the handover command after completing the first random access procedure. The UE 102 stops 1216 the second timer T304 in response to completing the second random access procedure. Since the second T304 timer value is greater than the first T304 timer value, the UE 102 is able to complete the second random access procedure before the second timer T304 expires. Therefore, the UE 102 is able to complete the handover and the PSCell change configured by the handover command to avoid having to perform time-consuming RRC reconfiguration and measurement reporting.

[0102] In some implementations, the handover command can be an RRC reconfiguration message including a ReconfigurationWithSync IE. In other implementations, the handover command can be an RRC reconfiguration message including a MobilityControlInfo IE. The handover complete message can be an RRC reconfiguration complete message. The UE 102 can send the handover complete message during or after the first random access procedure.

[0103] In some implementations, MN 104 delivers an SN Request message (e.g., SN AdditionRequest or SN Modification Request) to SN 106B. SN 106B delivers an SN Request Acknowledge message (e.g., SN Addition Request Acknowledge or SN ModificationRequest Acknowledge) to MN 104 in response to the SN Request message. SN 106B includes the RRC reconfiguration message (including the second T304 timer value) in the SN Request Acknowledge message and delivers the SN Request Acknowledge message at event 1205.

[0104] In other implementations, MN 104 may receive the second T304 timer value from SN 106A instead of SN 106B. In this case, SN 106A configures the second T304 timer value to be greater than the first T304 timer value. In one implementation, MN 104 delivers an SN Request message (e.g., SN Addition Request or SN Modification Request) to SN 106A instead of SN 106B. SN 106A delivers an SN RequestAcknowledge message (e.g., SN Addition RequestAcknowledge or SN Modification RequestAcknowledge) to MN 104 in response to the SN Request message. SN 106A includes an RRC reconfiguration message including the second T304 timer value in the SN Request Acknowledge message, and delivers the SN Request Acknowledge message to MN 104 instead of event 1205. In this case, after completing the first random access procedure, UE 102 performs a second random access procedure with SN 106A instead of SN 106B.

[0105] In yet another implementation, during the handover preparation process, the MN 104 may receive a request from the base station (ie, Fig.12 106A receives the handover command from a new MN (not shown in FIG. 1 ). The new MN receives a second T304 timer value from SN 106A, and SN 106A configures the second T304 timer value to be longer than the first T304 timer value. In one implementation, the new MN delivers an SN Request message (e.g., SN Addition Request or SN Modification Request) to SN 106A. SN 106A delivers an SN RequestAcknowledge message (e.g., SN Addition Request Acknowledge or SN Modification RequestAcknowledge) to the new MN in response to the SN Request message. SN 106A includes an RRC reconfiguration message including the second T304 timer value in the SN Request Acknowledge message, and delivers the SN Request Acknowledge message to the new MN. In this case, UE 102 performs a first random access procedure with the new MN instead of MN 104, and performs a second random access procedure with SN 106A instead of SN 106B after completing the first random access procedure.

[0106] In a further implementation, during the handover preparation process, the MN 104 may receive a message from the base station (ie, Figure 1106B receives the handover command from a new MN (not shown in FIG. 1 ). The new MN receives a second T304 timer value from SN 106B, and SN 106B configures the second T304 timer value to be longer than the first T304 timer value. In one implementation, the new MN delivers an SN Request message (e.g., SN Addition Request or SN Modification Request) to SN 106B. SN 106B delivers an SN Request Acknowledge message (e.g., SN Addition RequestAcknowledge or SN Modification Request Acknowledge) to the new MN in response to the SN Request message. SN 106B includes an RRC reconfiguration message including the second T304 timer value in the SN Request Acknowledge message, and delivers the SN Request Acknowledge message to the new MN. In this case, UE 102 performs a first random access procedure with the new MN instead of MN 104, and performs a second random access procedure with SN 106B after completing the first random access procedure.

[0107] Fig.13 Scenario 1300 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. Fig.13 Similar to Fig.12 , wherein the MN 104 sends 1304 a handover command to the UE 102, including a first T304 timer value and a second T304 timer value.

[0108] UE 102 receives 1304 a handover command including a first T304 timer value and a second T304 timer value from MN 104. In response to the handover command, UE 102 starts 1306 a first timer T304 having a first T304 timer value and a second timer T304 having a second T304 timer value upon receiving the handover command. UE 102 simultaneously performs 1308 a first random access procedure with MN 104 on a PCell (configured by the handover command) and performs a second random access procedure with SN 106B on a PSCell (configured by the handover command). UE 102 sends 1310 a handover complete message to MN 104 in response to the handover command. UE 102 stops 1316 the first timer T304 in response to completing the first random access procedure, and stops the second timer T304 in response to completing the second random access procedure. Since the UE 102 performs the first random access procedure and the second random access procedure simultaneously, the UE 102 can complete the second random access procedure before the second timer T304 expires, regardless of whether the second T304 timer value is greater than the first T304 timer value. Therefore, the UE 102 can complete the handover and the PSCell change configured by the handover command to avoid having to perform a time-consuming RRC reconfiguration process and a measurement report process.

[0109] In some implementations, the UE 102 may perform the first random access procedure and the second random access procedure in an interleaved manner. For example, the UE 102 may send a first random access preamble on the PCell and send a second random access preamble on the PSCell at different times (e.g., time slots or subframes). Then, the UE 102 may receive a first random access response (in response to the first random access preamble) on the PCell and a second random access response (in response to the second random access preamble) on the PSCell at the same or different times (e.g., time slots or subframes).

[0110] Fig.14A Scenario 1400 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. Fig.13 Same, Fig.14A Similar to Fig.12 , the MN 104 sends 1404 a handover command to the UE 102, the handover command including a first T304 timer value and a second T304 timer value.

[0111] In this example scenario, the UE 102 starts 1413 a second timer T304 having a second T304 timer value at a time later than the first timer T304 having the first T304 timer value was started. Fig.14AIn one example shown, the UE 102 starts 1406 a first timer T304 upon receiving the handover command and performs 1408 a first random access procedure. After completing the first random access procedure, the UE 102 starts a second timer T304 with a second T304 timer value. Since the UE 102 starts the second timer T304 after the first timer T304, the UE 102 is able to complete the second random access procedure before the second timer T304 expires, regardless of whether the second T304 timer value is greater than the first T304 timer value. Therefore, the UE 102 is able to complete the handover and the PSCell change configured by the handover command to avoid having to perform a time-consuming RRC reconfiguration procedure and a measurement reporting procedure.

[0112] Fig. 14B Scenario 1450 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. Fig.13 and Fig.14A Same, Fig. 14B and Fig.12 Similarly, MN 104 sends 1454 a handover command to UE 102, the handover command including a first T304 timer value and a second T304 timer value. Fig.12 In the example scenario described, the second T304 timer value may be longer than the first T304 timer value, as described in reference Fig.13 In the example scenario described, UE 102 may perform the first random access procedure and the second random access procedure simultaneously, or as described in reference Fig.14A As shown in the described example scenario, the UE 102 may start a second timer T304 after the first timer T304.

[0113] In any event, the UE performs 1456 a first random access procedure upon receiving the handover command. Then, due to a failure in the first random access procedure, the first timer T304 expires 1458. When the first timer T304 expires, the UE 102 also performs (or continues to perform) 1460 a second random access procedure with the SN 106B. The UE 102 stops the second T304 timer 1462 in response to completing the second random access procedure. Then, the UE 102 performs 1464 an MCG fast recovery procedure 350 instead of disconnecting from the SN 106B and performing an RRC re-establishment procedure. Therefore, the UE 102 can recover the connection with the MN 104 through the connection with the SN 106B to avoid having to perform a time-consuming RRC reconfiguration procedure and a measurement reporting procedure.

[0114] Fig.15Scenario 1500 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. UE 102 is in DC 1502 with MN 104 and SN 106B. UE 102 then detects an MCG failure 1504. In response to detecting the MCG failure 1504, UE 102 sends 1506 a MCGFailureInformation message to SN 106B. SN 106B delivers 1508 the MCGFailureInformation message to MN 104. UE 102 receives 1512 an RRC reconfiguration message from SN 106B after sending the MCGFailureInformation message. UE 102 may determine 1514 whether the RRC reconfiguration message configures a PCell belonging to MN 104. If the RRC reconfiguration message does not configure 1516 the PCell, UE 102 sends 1518 an RRC reconfiguration complete message to SN 104 in response to the RRC reconfiguration message. If the RRC reconfiguration message configures 1520 the PCell belonging to the MN 104, the UE 102 sends 1522 an RRC reconfiguration complete message to the MN 104 in response to the RRC reconfiguration message.

[0115] In some implementations, the MCG failure can be an MCG radio link failure, a handover failure, an MCG reconfiguration with a synchronization failure, an integrity failure on an RRC message received from the MN 104, or a reconfiguration failure on an RRC message received from the MN 104.

[0116] In some implementations, the RRC reconfiguration message may include a ReconfigurationWithSync IE that configures the PCell. In other implementations, the RRC reconfiguration message may include a MobilityControlInfo IE that configures the PCell. In this case, the UE 102 sends an RRC reconfiguration complete message on the PCell.

[0117] In some implementations, the RRC reconfiguration message may configure the PCell belonging to the new MN ( Fig.15 In this case, UE 102 sends an RRC reconfiguration complete message to the new MN instead of MN 104 on the PCell.

[0118] If the RRC reconfiguration message configures the PCell, in some implementations, the RRC reconfiguration message may include one or more configurations for the UE 102 to perform a random access procedure on the PCell. The UE 102 performs a random access procedure on the PCell according to the one or more configurations. The UE 102 sends an RRC reconfiguration complete message on the PCell during or after the random access procedure.

[0119] In some implementations, the RRC reconfiguration message may be generated by the MN 104, the SN 106B, or the new MN. In some implementations, the RRC reconfiguration message 1512 may be associated with SRB1 or SRB3. That is, the UE 102 may receive the RRC reconfiguration message 1512 on SRB1 or SRB3. In the case of SRB1, the MN 104 in one implementation may generate the RRC reconfiguration message, generate a packet data convergence protocol (PDCP) protocol data unit (PDU) including the RRC reconfiguration message, and send the PDCP PDU to the SN 106B. The SN 106B in turn delivers the PDCP PDU to the UE 102. In another implementation, the MN 104 may include the RRC reconfiguration message in a DL-DCCH-Message, generate a PDCP PDU including the DL-DCCH-Message, and send the PDCP PDU to the SN 106B. The SN 106B in turn delivers the PDCP PDU to the UE 102.

[0120] When the RRC reconfiguration message is associated with SRB1, the new MN in another implementation may generate an RRC reconfiguration message and deliver the RRC reconfiguration message to the MN 104, for example, in a Handover Request Acknowledge message in response to a Handover Request message received by the new MN from the MN 104. Then, in one implementation, the MN 104 may generate a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU) including the RRC reconfiguration message and deliver the PDCP PDU to the SN 106B. The SN 106B, in turn, sends the PDCP PDU to the UE 102. In another implementation, the MN 104 may include the RRC reconfiguration message in a DL-DCCH-Message message, generate a PDCP PDU including the DL-DCCH-Message, and send the PDCP PDU to the SN 106B. The SN 106B, in turn, delivers the PDCP PDU to the UE 102.

[0121] When the RRC reconfiguration message is associated with SRB3, the MN 104 in one implementation may generate an RRC reconfiguration message and deliver the RRC reconfiguration message to the SN 106B. The SN 106B includes the RRC reconfiguration message in an RRC container message and generates a PDCP PDU including the RRC container message. The SN 106B then delivers the PDCP PDU to the UE 102. In another implementation, the MN 104 may include the RRC reconfiguration message in a DL-DCCH-Message message and deliver the DL-DCCH-Message message to the SN 106B. The SN 106B includes the DL-DCCH-Message message in the RRC container message and generates a PDCP PDU including the RRC container message. The SN 106B then delivers the PDCP PDU to the UE 102. In these implementations, the RRC container message can be a DLInformationTransferMRDC message.

[0122] When the RRC reconfiguration message is associated with SRB3, the new MN in one implementation may generate the RRC reconfiguration message and deliver the RRC reconfiguration message to the MN 104, for example, in a Handover Request Acknowledge message in response to a Handover Request message received by the new MN from the MN 104. The MN 104 may then deliver the RRC reconfiguration message to the SN 106B. The SN 106B includes the RRC reconfiguration message in an RRC container message and generates a PDCP PDU including the RRC container message. The SN 106B then delivers the PDCP PDU to the UE 102. In another implementation, the MN 104 may include the RRC reconfiguration message in a DL-DCCH-Message message and deliver the DL-DCCH-Message message to the SN 106B. The SN 106B includes the DL-DCCH-Message in the RRC container message and generates a PDCP PDU including the RRC container message. The SN 106B then delivers the PDCP PDU to the UE 102. In these implementations, the RRC container message can be a DLInformationTransferMRDC message.

[0123] When the RRC reconfiguration message is associated with SRB3, the SN 106B in another implementation may generate the RRC reconfiguration message, generate a PDCP PDU including the RRC reconfiguration message, and deliver the PDCP PDU to the UE 102.

[0124] Fig.16Scenario 1600 is illustrated in which base station 104 operates as a MN and base station 106B operates as a SN. Fig.16 Similar to Fig.15 , where UE 102 detects 1604 an MCG failure, in response to detecting the MCG failure 1604, UE 102 sends 1606 an MCGFailureInformation message to SN 106B, SN 106B delivers 1608 an MCGFailureInformation message to MN 104, and UE 102 receives 1612 an RRC reconfiguration message from SN 106B after sending the MCGFailureInformation message.

[0125] In addition, the SN 106B may suspend 1607 its RRC function in response to the MCGFailureInformation message 1606. When the SN 106B suspends the RRC function 1607, the SN 106B does not generate an RRC reconfiguration message to configure or reconfigure SN radio resources to the UE 102. The MN 104 does not generate 1609 an RRC reconfiguration message that does not configure the PCell in response to the MCGFailureInformation message 1608. Instead, the MN 104 generates 1609 an RRC reconfiguration message that configures the PCell and delivers the RRC reconfiguration message to the SN 106B in response to the MCGFailureInformation message 1608. The SN 106B then sends 1612 an RRC reconfiguration message to the UE 102 including the PCell. The UE 102 then sends 1616 an RRC reconfiguration complete message in response to the RRC reconfiguration message. Since SN 106B suspends the RRC function and MN 104 does not generate an RRC reconfiguration message that does not configure the PCell, UE 102 only needs to process the RRC reconfiguration message that configures the PCell. Therefore, UE 102 sends an RRC reconfiguration complete message to MN 104 on the PCell. Fig.15 As described above, if the PCell belongs to a new MN, the UE 102 can send an RRC reconfiguration complete message to the new MN instead of the MN 104 on the PCell.

[0126] Fig.17A is a flow chart depicting an example method 1700 implemented in a UE (e.g., UE 102) for releasing a maximum transmit power configuration of an SCG (P-Max-SCG). For convenience, the method 1700 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0127] At block 1702, UE 102 in DC with MN 104 and SN 106B is configured with a maximum transmit power for SCG (P-Max-SCG). At block 1704, UE 102 detects an MCG failure. In response to detecting the MCG failure, at block 1706, UE 102 releases P-Max-SCG and sends a MCGFailureInformation message to SN 106B at a transmit power exceeding P-Max-SCG.

[0128] Fig. 17B 17 is a flow chart depicting an example method 1720 implemented in a UE (e.g., UE 102) for removing a maximum transmit power configuration requirement for an SCG (P-Max-SCG). For convenience, the method 1720 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0129] At box 1722, UE 102 in DC with MN 104 and SN 106B is configured with a maximum transmit power for SCG (P-Max-SCG). At box 1724, UE 102 detects an MCG failure. In response to detecting the MCG failure, at box 1726, UE 102 stops (or suspends) using P-Max-SCG as the maximum transmit power for SCG and sends an MCGFailureInformation message to SN 106B. At box 1728, UE 102 receives an MCG recovery message from SN 106B. Then at box 1730, UE 102 continues (or recovers) using P-Max-SCG in response to the MCG recovery message.

[0130] Fig. 17C 1 is a flow chart depicting an example method 1750 implemented in a MN (e.g., MN 104) or a SN (e.g., SN 106) for releasing a maximum transmit power configuration of an SCG (P-Max-SCG). For convenience, the method 1750 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0131] At block 1752, MN 104 or SN 106B configures a maximum transmit power for SCG (P-Max-SCG) for UE 102 in DC with MN 104 and SN 106B. At block 1754, MN 104 or SN 106B receives a MCGFailureInformation message from UE 102. Then at block 1756, in response to receiving the MCGFailureInformation message, MN 104 or SN 106B releases P-Max-SCG as the maximum transmit power for UE 102 to transmit to SCG.

[0132] Fig.17D 1 is a flow chart depicting an example method 1780 implemented in a MN (e.g., MN 104) or SN (e.g., SN 106) for removing a maximum transmit power configuration requirement for a SCG (P-Max-SCG). For convenience, the method 1780 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0133] At block 1782, MN 104 or SN 106B configures a maximum transmit power for SCG (P-Max-SCG) for UE 102 that is in DC with MN 104 and SN 106B. At block 1784, MN 104 or SN 106B receives a MCGFailureInformation message from UE 102. In response to receiving the MCGFailureInformation message, at block 1786, MN 104 or SN 106B stops (or suspends) using P-Max-SCG as the maximum transmit power for SCG. At block 1788, MN 104 or SN 106B sends an MCG failure recovery message to UE 102 in response to the MCGFailureInformation message. At block 1790, MN 104 or SN 106B, after sending the MCG failure recovery message to UE 102, continues (or resumes) using P-Max-SCG as the maximum transmit power for SCG.

[0134] Fig.18A 1 is a flow chart depicting an example method 1800 implemented in a UE (e.g., UE 102) for handling the expiration of a handover-related timer (e.g., timer T304 for MCG) during a handover procedure. For convenience, the method 1800 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0135] At block 1802, UE 102, which is in DC with MN 104 and SN 106B, receives a handover command from MN 104. At block 1804, UE 102 starts timer T304 in response to the handover command. At block 1806, UE 102 determines whether timer T304 has expired. If timer T304 has expired, UE 102 determines 1808 whether MCG fast recovery is configured by MN 104. If MCG fast recovery is configured, UE 102 performs 1810 a MCG fast recovery procedure. If MCG fast recovery is not configured, UE 102 performs 1812 a RRC re-establishment procedure.

[0136] Fig.18B 1 is a flow chart depicting another example method 1850 implemented in a UE (e.g., UE 102) for handling the expiration of a handover-related timer (e.g., timer T304 for MCG) during a handover procedure. For convenience, the method 1500 is discussed below with reference to the MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0137] At block 1852, UE 102, which is in DC with MN 104 and SN 106B, receives a handover command from MN 104. At block 1854, UE 102 starts timer T304 in response to the handover command. At block 1856, UE 102 determines whether timer T304 has expired. If timer T304 has expired, UE 102 determines 1858 whether the handover command is to restore an MCG failure. If the handover command is to restore an MCG failure, UE 102 performs 1860 an RRC re-establishment procedure. If the handover command is not to restore an MCG failure, UE 102 performs 1862 an MCG fast recovery procedure.

[0138] Fig.19 1 is a flow chart depicting an example method 1900 implemented in a UE (e.g., UE 102) for processing a configuration from a received RRC message (e.g., RRCReconfiguration message). For convenience, the method 1900 is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0139] At block 1902, UE 102, which is in DC with MN 104 and SN 106B, receives an RRC message including at least one configuration from MN 104. At block 1904, UE 102 determines whether it cannot comply with at least one configuration in the received RRC message. If UE 102 cannot comply with the configuration (i.e., UE 102 detects a reconfiguration failure), UE 102 determines 1906 whether MCG fast recovery is configured by MN 104. If MCG fast recovery is configured, UE 102 performs 1910 an MCG fast recovery procedure. If MCG fast recovery is not configured, UE 102 performs 1908 an RRC reestablishment procedure. If the UE is able to comply with all configurations, UE 1912 applies the configurations from the RRC message.

[0140] Fig. 20A 2 is a flow chart depicting an example method 2000a implemented in a UE (e.g., UE 102) for handling a reconfiguration failure from receiving an RRC message (e.g., an RRC configuration message). For convenience, the method 2000a is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0141] At block 2002a, UE 102 in DC with MN 104 and SN 106B receives a first RRC message from MN 104 or SN 106B and detects a reconfiguration failure on the first RRC message. At block 2004a, UE 102 determines whether the first RRC message is received from SRB3. If the first RRC message is not received from SRB3, UE 102 determines 2006a whether SRB3 is configured. If SRB3 is configured, UE 102 performs 2008a MCG fast recovery procedure 350. If SRB3 is not configured, UE 102 performs 2010a RRC re-establishment procedure.

[0142] If the first RRC message is received from SRB3, UE 102 determines 2012a whether the first RRC message is included in the second RRC message. If the first RRC message is included in the second RRC message (e.g., DLInformationTransferMRDC message), UE 102 performs 2010a RRC re-establishment procedure. If the first RRC message is not included in the second RRC message, UE 102 performs 2014a SCG failure information procedure (i.e., UE 102 sends SCGFailureInformation message to MN 104).

[0143] To perform the MCG fast recovery procedure, in one implementation, UE 102 includes the MCGFailureInformation message in the ULInformationTransferMRDC message, and if SRB3 is configured, sends the ULInformationTransferMRDC message via SRB3. To perform the RRC re-establishment procedure, UE 102 sends an RRC re-establishment request message to MN 104 or a new MN. UE 102 may receive an RRC re-establishment message in response to the RRC re-establishment request message from MN 104 or a new MN.

[0144] Fig. 20B 2 is a flow chart depicting an example method 2000b implemented in a UE (e.g., UE 102) for handling an integrity check failure from a received RRC message (e.g., ULInformationTransferMRDC message). For convenience, the method 2000b is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0145] At block 2002b, UE 102 in DC with MN 104 and SN 106B receives a first RRC message from MN 104 or SN 106B and detects an integrity check failure on the first RRC message. At block 2004b, UE 102 determines whether the first RRC message is received from SRB3. If the first RRC message is not received from SRB3, UE 102 determines 2006b whether SRB3 is configured. If SRB3 is configured, UE 102 performs 2008b an MCG fast recovery procedure. If SRB3 is not configured, UE 102 performs 2010b an RRC re-establishment procedure.

[0146] If the first RRC message is received from SRB3, UE 102 determines 2012b whether the first RRC message (e.g., DLInformationTransferMRDC message) includes the second RRC message. If the first RRC message includes the second RRC message, UE 102 performs 2010b the RRC re-establishment procedure. If the first RRC message does not include the second RRC message, UE 102 performs 2014b the SCG failure information procedure (e.g., UE 102 sends a SCGFailureInformation message to MN 104).

[0147] To perform the MCG fast recovery procedure, in one implementation, UE 102 includes the MCGFailureInformation message in the ULInformationTransferMRDC message, and if SRB3 is configured, sends the ULInformationTransferMRDC message via SRB3. To perform the RRC re-establishment procedure, UE 102 sends an RRC re-establishment request message to MN 104 or a new MN. UE 102 may receive an RRC re-establishment message in response to the RRC re-establishment request message from MN 104 or a new MN.

[0148] Fig.21A 2 is a flow chart depicting an example method 2100a implemented in a MN (e.g., MN 104) for handling a handover procedure (also referred to as a reconfiguration with synchronization procedure). For convenience, the method 2100a is discussed below with reference to MN 104, SN 106B, and UE 102 operating in wireless communication system 100.

[0149] At block 2102a, SN 106B decides to configure UE 102 to connect to PSCell. In response to configuring UE 102 to connect to PSCell, SN 106B sets 2104a a second T304 timer value (e.g., for a second timer T304 for SCG) that is greater than the first T304 timer value (e.g., for a first timer T304 for MCG). At block 2016a, SN 106B sends an RRC reconfiguration message to UE 102, which configures UE 102 to connect to PSCell and includes the second T304 timer value.

[0150] Fig. 21B 2 is a flow chart depicting an example method 2100b implemented in a UE (e.g., UE 102) for handling a handover process (or also known as reconfiguration using a synchronization process). For convenience, the method 2100b is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0151] In box 2102b, UE 102 receives an RRC reconfiguration message, which configures the UE to be connected to the PCell and the PSCell and includes a first T304 timer value (e.g., for a first timer T304 for the MCG) and a second T304 timer value (e.g., for a second timer T304 for the SCG).

[0152] In response to the RRC reconfiguration message, the UE 102 starts a first timer T304 with a first T304 timer value and performs a first random access procedure on the PCell. In block 2106b, the UE 102 starts a second timer T304 with a second T304 timer value and performs a second random access procedure on the PSCell after completing the first random access procedure (e.g., after successfully performing the first random access procedure on the PCell or failing to perform the first random access procedure on the PCell).

[0153] Fig. 21C 2 is a flowchart depicting another example method 2100c implemented in a UE (e.g., MN 102) for processing a handover process (or also known as reconfiguration using a synchronization process). For convenience, the method 2100c is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0154] In box 2102c, UE 102 receives an RRC reconfiguration message, which configures the UE to be connected to the PCell and the PSCell and includes a first T304 timer value (e.g., for a first timer T304 for the MCG) and a second T304 timer value (e.g., for a second timer T304 for the SCG).

[0155] In response to the RRC reconfiguration message, the UE 102 starts 2104c a first timer T304 having a first T304 timer value and performs a first random access procedure on the PCell. In block 2106c, the UE 102 starts a second timer T304 using a second T304 timer value and performs a second random access procedure on the PSCell while performing the first random access procedure.

[0156] Fig.21D 2 is a flowchart depicting another example method 2100d implemented in a UE (e.g., MN 102) for processing a handover process (or referred to as reconfiguration using a synchronization process). For convenience, the method 2100d is discussed below with reference to MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0157] In box 2102d, UE 102 receives an RRC reconfiguration message, which configures the UE to be connected to the PCell and the PSCell and includes a first T304 timer value (e.g., for the first timer T304 for the MCG) and a second T304 timer value (e.g., for the second timer T304 for the SCG).

[0158] In response to the RRC reconfiguration message, the UE 102 starts 2104d a second timer T304 having a second T304 timer value and performs a second random access procedure on the PSCell. In block 2106d, the UE 102 starts the first timer T304 using the first T304 timer value and performs a second random access procedure on the PCell while performing the second random access procedure.

[0159] Fig. 22 is a flow chart depicting an example method 2200 implemented in a UE (eg, UE 102) for processing an RRC reconfiguration message. For convenience, the method 2200 is discussed below with reference to the MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0160] At block 2202, UE 102 in DC with MN 104 and SN 106B detects an MCG failure. At block 2204, after UE 102 detects the MCG failure, UE 102 receives an RRC reconfiguration message from SN 106B. At block 2206, UE 102 determines whether the RRC reconfiguration message configures the PCell (i.e., requests the UE to perform a handover or synchronization reconfiguration).

[0161] If the RRC reconfiguration message does not configure the PCell, the UE 102 sends 2208 an RRC reconfiguration complete message to the SN 106B. If the RRC reconfiguration message configures the PCell, the UE 102 connects 2210 to the PCell (e.g., performs a random access procedure on the PCell) and sends the RRC reconfiguration complete message via the PCell.

[0162] Fig.23 is a flow chart depicting another example method 2300 implemented in a UE (eg, UE 102) for processing an RRC reconfiguration message. For convenience, the method 2300 is discussed below with reference to the MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0163] At block 2302, UE 102 in DC with MN 104 and SN 106B detects an MCG failure. At block 2304, after UE 102 detects the MCG failure, UE 102 receives an RRC reconfiguration message from SN 106B. At block 2306, UE 102 determines whether the RRC reconfiguration message configures the PCell (i.e., requests UE 102 to perform a handover).

[0164] If the RRC reconfiguration message does not configure the PCell, the UE 102 determines 2308 whether the RRC reconfiguration message is included in a DL RRC container message. In one implementation, the DL-RRC container message can be a DLInformationTransferMRDC message. If the RRC reconfiguration message is included in the DL RRC container message, the UE 102 includes 2310 an RRC reconfiguration complete message in a UL RRC container message and sends the UL RRC container message to the SN. In one implementation, the UL RRC container message is a ULInformationTransferMRDC message. If the RRC reconfiguration message is not included in the DL RRC container message, the UE 102 sends 2312 an RRC reconfiguration complete message to the SN 106B without using the UL RRC container message.

[0165] If the RRC reconfiguration message configures the PCell, the UE 102 connects 2314 to the PCell (eg, performs a random access procedure on the PCell) and sends an RRC reconfiguration complete message via the PCell without using a UL RRC container message.

[0166] Fig.24 is a flow chart depicting yet another example method 2400 implemented in a UE (eg, UE 102) for processing an RRC reconfiguration message. For convenience, the method 2400 is discussed below with reference to the MN 104, SN 106B, and UE 102 operating in the wireless communication system 100.

[0167] At block 2402, UE 102 in DC with MN 104 and SN 106B detects an MCG failure. At block 2404, after UE 102 detects the MCG failure, UE 102 receives an RRC reconfiguration message from SN 106B. At block 2406, UE 102 determines whether the RRC reconfiguration message configures the PCell (i.e., requests the UE to perform a handover or synchronization reconfiguration).

[0168] If the RRC reconfiguration message does not configure the PCell, the UE 102 determines 2408 whether the RRC reconfiguration message is received on SRB3. If the RRC reconfiguration message is not received on SRB3, the UE 102 sends 2410 an RRC reconfiguration complete message to the SN via SRB1 without using an RRC container message. If the RRC reconfiguration message is received on SRB3, the UE 102 determines 2412 whether the RRC reconfiguration message is included in a DL RRC container message. In one implementation, the DL-RRC container message may be a DLInformationTransferMRDC message. If the RRC reconfiguration message is not included in the DL RRC container message, the UE 102 sends 2414 an RRC reconfiguration complete message via SRB3 without using an UL RRC container message. In one implementation, the UL RRC container message may be a ULInformationTransferMRDC message. If the RRC reconfiguration message is contained in a DL RRC container message, the UE 102 includes 2416 an RRC reconfiguration complete message in the UL RRC container message and sends the RRC container message via SRB3.

[0169] If the RRC reconfiguration message configures the PCell, the UE 102 connects 2414 to the PCell and sends an RRC reconfiguration complete message via the PCell without using an UL RRC container message. In some implementations, the UE 102 performs a random access procedure on the PCell to connect to the PCell. The UE 102 may send the RRC reconfiguration complete message during or after the random access procedure.

[0170] The following additional considerations apply to the above discussion.

[0171] In some implementations, the RRC reconfiguration message can be an RRCReconfiguration message, and the RRC reconfiguration complete message can be an RRCReconfigurationComplete message. In other implementations, the RRC reconfiguration message can be an RRCConnectionReconfiguration message, and the RRC reconfiguration complete message can be an RRCConnectionReconfigurationComplete message.

[0172] In some implementations, the RRC reconfiguration message can be generated by MN 104 or the new MN. In other implementations, the RRC reconfiguration can be generated by SN 106B or SN 106A.

[0173] In some implementations, the handover command may include an RRC reconfiguration message configuring the PSCell and a second T304 timer value, and the handover completion message may include an RRC reconfiguration completion message. In the case of NR-NR DC, the handover command and the RRC reconfiguration message can be an RRCReconfiguration message, and the handover completion message and the RRC reconfiguration completion message can be an RRCReconfigurationComplete message. In the case of NE-DC, the handover command can be an RRCReconfiguration message and the RRC reconfiguration message can be an RRCConnectionReconfiguration message, the handover completion message can be an RRCReconfigurationComplete message and the RRC reconfiguration completion message can be an RRCConnectionReconfigurationComplete message. In the case of (NG)EN-DC, the handover command can be an RRCConnectionReconfiguration message and the RRC reconfiguration message can be an RRCConnectionReconfiguration message, the handover completion message can be an RRCConnectionReconfigurationComplete message and the RRC reconfiguration completion message can be an RRCReconfigurationComplete message. In other implementations, the handover command may not include an RRC reconfiguration message configuring the PSCell and the second T304 timer value, and the handover completion does not include an RRC reconfiguration complete message.

[0174] In some implementations, the UE 102 may include a failure cause in the MCG failure indication message. If the MCG failure is a radio link failure, the UE 102 indicates a radio link failure as the failure cause. If the MCG failure is an integrity check failure, the UE 102 indicates an integrity check failure as the failure cause. If the MCG failure is a handover failure, the UE 102 indicates a handover failure as the failure cause. If the MCG failure is a reconfiguration failure, the UE 102 indicates a reconfiguration failure as the failure cause. If the MCG failure is a reconfiguration with synchronization failure, the UE 102 indicates a reconfiguration with synchronization failure or a handover failure as the failure cause.

[0175] In some implementations, UE 102 may include one or more measurement results associated with one or more different cells in the MCGFailureInformation message. In one implementation, MN 104 may generate an MCG fault recovery message based on the one or more measurement results. MN 104 configures the target cell (i.e., target PCell) in the MCG fault recovery message. The target cell is associated with one or more specific measurement results in the MCGFailureInformation message. MN 104 may include one or more configurations for UE 102 to perform a random access procedure on the target cell in the MCG fault recovery message. In response to the MCG fault recovery message, UE 102 performs a random access procedure via the target cell according to the one or more configurations. In another implementation, MN 104 may determine the target cell based on one or some measurement results. For example, one or some measurement results of the target cell indicate that the target cell has good signal strength / quality for UE 102. Then, MN 104 may send a request to the new MN ( Figure 1 The new MN 104 (not shown) delivers a Handover Request message indicating the target cell (i.e., the target PCell). The new MN generates an MCG fault recovery message and includes the MCG fault recovery message in the Handover RequestAcknowledge message. The new MN may include one or more configurations for UE 102 to perform a random access procedure on the target cell in the MCG fault indication message. In response to the MCG recovery message, UE 102 performs a random access procedure via the target cell according to the one or more configurations. Then, the new MN delivers a Handover Request Acknowledge message to MN 104. Finally, MN 104 extracts the MCG fault recovery message from the Handover Request Acknowledge message and sends the MCG fault recovery message to UE 102 via SN 106B.

[0176] In some implementations, one or more configurations for the UE 102 to perform a random access procedure may configure a 2-step random access procedure. In another implementation, the random access configuration may configure a 4-step random access procedure. In yet another embodiment, the random access configuration may configure a contention-based random access procedure or a contention-free random access procedure. The UE 102 may send an MCG failure recovery response message to the cell during the random access procedure or after successfully completing the random access procedure. The cell may be the same or different from the cell in which the UE detected the MCG failure.

[0177] In some implementations, the RRC reestablishment request is an RRCConnectionReestablishmentRequest message or an RRCReestablishmentRequest message. The RRC reestablishment is an RRCConnectionReestablishment message or an RRCReestablishment message. The UE may send an RRC reestablishment complete message to the MN or the new MN in response to the RRC reestablishment message. The RRC reestablishment complete is an RRCConnectionReestablishmentComplete message or an RRCReestablishmentComplete message.

[0178] The user equipment (e.g., UE 102) in which the technology of the present disclosure can be implemented can be any suitable device capable of wireless communication, such as a smart phone, a tablet computer, a laptop computer, a mobile game console, a point of sale (POS) terminal, a health monitoring device, a drone, a camera, a media streaming dongle or other personal media device, a wearable device such as a smart watch, a wireless hotspot, a femtocell or a broadband router. In addition, in some cases, the user equipment can be embedded in an electronic system, such as a head unit or an advanced driver assistance system (ADAS) of a vehicle. Further, the user equipment can operate as an Internet of Things (IoT) device or a mobile Internet device (MID). Depending on the type, the user equipment can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0179] Embodiments of the technology described in this disclosure may include any number of the following aspects, alone or in combination:

[0180] 1. A method for performing fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the method comprising: detecting, by processing hardware in the UE communicating with the MN and the SN in DC, a primary cell group (MCG) radio link failure associated with the MN; sending, by the processing hardware, an MCG fault information message to the SN in response to the MCG radio link failure; receiving, by the processing hardware, an MCG fault recovery message from the SN; sending, by the processing hardware, an MCG fault recovery completion message to the MN; detecting, by the processing hardware, a timer expiration, an integrity check failure, or a reconfiguration failure; and sending, by the processing hardware, a radio connection reestablishment request message to the MN in response to the timer expiration, the integrity check failure, or the reconfiguration failure.

[0181] 2. The method according to aspect 1 also includes: obtaining, by processing hardware, an indication of a maximum transmit power for communicating with a secondary cell group (SCG) associated with the SN; and in response to detecting an MCG radio link failure, sending an MCG failure information message to the SN with a power output exceeding the maximum transmit power for communicating with the SCG.

[0182] 3. The method according to any of the above aspects also includes: receiving an MCG recovery message from the SN by the processing hardware; and in response to receiving the MCG recovery message, adjusting the power output used for subsequent communication with the SCG by the processing hardware to not exceed the maximum transmission power.

[0183] 4. A method according to any of the above aspects, wherein the expiration of the detection timer is the expiration of a timer for switching, and includes: receiving a switching command from the MN by processing hardware; starting a timer by the processing hardware, the timer being used to configure a maximum amount of time for performing a random access procedure with the MN; performing random access sensing with the MN by the processing hardware; and detecting a switching failure by the processing hardware in response to the timer expiring before the random access sensing has been completed.

[0184] 5. The method according to any one of the above aspects, wherein sending the radio connection re-establishment request message to the MN comprises sending the radio connection re-establishment request message in response to determining that a timer expires before the random access procedure is completed.

[0185] 6. The method according to any of the above aspects also includes: receiving a switching command from the MN by the processing hardware, including a first time value of a first timer for performing a first random access process with the MN and a second time value of a second timer for performing a second random access process with the SN; starting the first timer and the second timer by the processing hardware; performing the first random access process with the MN by the processing hardware; detecting a switching failure by the processing hardware in response to the expiration of the first timer before the random access process is completed; performing the second random access process with the SN by the processing hardware; stopping the second timer by the processing hardware in response to completing the second random access process; and sending a radio connection re-establishment request message to the MN in response to determining that the first timer expires before the first random access process is completed.

[0186] 7. The method according to any one of the above aspects, wherein the second time value is greater than the first time value.

[0187] 8. The method according to any of the above aspects, wherein starting the first timer and the second timer comprises: starting the first timer and the second timer simultaneously by processing hardware; and executing the first random access procedure and the second random access procedure simultaneously by processing hardware.

[0188] 9. The method according to any one of the above aspects, wherein starting the first timer and the second timer comprises: starting the second timer by processing hardware when the first random access procedure is completed or when the first timer expires.

[0189] 10. The method according to any of the above aspects, wherein detecting the integrity check failure or the reconfiguration failure comprises detecting the integrity check failure or the reconfiguration failure in response to a radio resource control (RRC) message from the MN.

[0190] 11. The method according to any one of the preceding aspects, wherein in response to detecting an integrity check failure or a reconfiguration failure, a radio connection re-establishment request message is sent.

[0191] 12. A method for fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the method comprising: receiving, by processing hardware in the UE communicating with the MN and the SN in DC, a switching command from the MN, comprising a first time value of a first timer for performing a first random access procedure with the MN, and a second time value of a second timer for performing a second random access procedure with the SN; starting, by the processing hardware, the first timer and the second timer; performing, by the processing hardware, the first random access procedure with the MN; stopping, by the processing hardware, the first timer in response to completion of the first random access procedure; performing, by the processing hardware, the second random access procedure with the SN; and stopping, by the processing hardware, the second timer in response to completion of the second random access procedure, wherein the first timer and the second timer are configured to prevent the second timer from expiring before completion of the second random access procedure.

[0192] 13. A method according to aspect 12, wherein the second time value is greater than the first time value, starting the first timer and the second timer includes starting the first timer and the second timer simultaneously, and performing the second random access procedure when the first random access procedure is completed.

[0193] 14. The method according to aspect 12 or aspect 13, wherein starting the first timer and the second timer comprises starting the first timer and the second timer simultaneously, and performing the first random access procedure and the second random access procedure simultaneously.

[0194] 15. The method according to any one of aspects 12-14, wherein starting the first timer and the second timer comprises starting the second timer when the first random access procedure is completed or the first timer expires.

[0195] 16. A method for fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the method comprising: detecting, by processing hardware in the UE communicating with the MN and SN in DC, a primary cell group (MCG) fault associated with the MN; sending, by the processing hardware, an MCG fault information message to the SN; receiving, by the processing hardware, a radio resource control (RRC) reconfiguration message from the SN; determining, by the processing hardware, whether the RRC reconfiguration message configures a cell associated with the MN for connection with the UE; and sending, by the processing hardware, an RRC reconfiguration completion message to the SN in response to determining that the RRC reconfiguration message does not include a cell associated with the MN.

[0196] 17. The method according to aspect 16, wherein detecting an MCG failure comprises at least one of: detecting an MCG radio link failure; detecting a handover failure; or detecting an integrity check failure or a reconfiguration failure.

[0197] 18. The method according to aspect 16 or aspect 17 further comprises: in response to determining that the RRC reconfiguration message includes a cell associated with the MN, sending, by the processing hardware, an RRC reconfiguration complete message to the MN.

[0198] 19. A method according to any of aspects 16-18, wherein: determining that the RRC reconfiguration message includes a cell associated with the MN includes determining that the RRC reconfiguration message includes a cell associated with a new MN, and sending the RRC reconfiguration message to the MN includes sending an RRC reconfiguration complete message to the new MN by processing hardware.

[0199] 20. A user equipment (UE) comprising processing hardware and configured to implement the method according to any of aspects 1-18.

[0200] 21. A method for fault recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the method comprising: detecting, by processing hardware in the UE communicating with the MN and the SN in DC, a master cell group (MCG) fault associated with the MN; in response to detecting the MCG fault, attempting to send, by the processing hardware, an MCG fault information message to the SN; and in response to failing to send the MCG fault information message to the SN: disconnecting, by the processing hardware, from the SN; and in response to the MCG fault, sending, by the processing hardware, a radio connection re-establishment request to the MN.

[0201] 22. The method according to aspect 21, wherein detecting an MCG failure comprises at least one of: detecting an MCG radio link failure; detecting a handover failure; or detecting an integrity check failure or a reconfiguration failure.

[0202] 23. The method according to aspect 21 or aspect 22 also includes: obtaining, by processing hardware, an indication of a maximum transmit power for communicating with a secondary cell group (SCG) associated with the SN; and in response to detecting an MCG radio link failure, sending an MCG failure information message to the SN with a power output not exceeding the maximum transmit power for communicating with the SCG.

[0203] 24. The method according to any one of aspects 21-23 further includes: performing a radio connection reestablishment procedure with the MN by the processing hardware; and performing a radio connection reconfiguration procedure and a measurement reporting procedure with the MN by the processing hardware to reconfigure the UE in the DC with the MN and the SN.

[0204] In the present disclosure, certain embodiments are described as including logic or multiple components or modules. A module may be able to be a software module (e.g., a code or machine-readable instruction stored on a non-temporary machine-readable medium) or a hardware module. A hardware module is a tangible unit that can perform a specific operation and can be configured or arranged in some way. A hardware module can include dedicated circuits or logic that are permanently configured to perform certain operations (e.g., as a dedicated processor, such as a field programmable gate array (FPGA) or application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.). A hardware module may also include programmable logic or circuits (e.g., contained in a general-purpose processor or other programmable processor) that are temporarily configured by software to perform certain operations. The decision to implement a hardware module in a dedicated and permanently configured circuit or in a temporarily configured circuit (e.g., configured by software) can be driven by cost and time factors.

[0205] When implemented in software, the techniques can be provided as part of an operating system, a library used by multiple applications, a specific software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

Claims

1. A method for performing failure recovery in a user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the method comprising: detecting, by a UE communicating with the MN and the SN in DC, a master cell group (MCG) radio link failure associated with the MN; In response to an MCG radio link failure, the UE sends an MCG failure information message to the SN; The UE receives an MCG failure recovery message from the SN; The UE sends an MCG fault recovery completion message to the MN; Detection by the UE of a timer expiration, integrity check failure or reconfiguration failure; and In response to timer expiration, integrity check failure or reconfiguration failure, a radio connection reestablishment request message is sent by the UE to the MN.

2. The method according to claim 1, wherein: Detecting timer expiration is when the timer switches to expiration, and: The UE receives a handover command from the MN; A timer is started by the UE to configure a maximum amount of time in which a random access procedure is performed with the MN; The UE and the MN perform a random access procedure; and In response to the timer expiring before the random access procedure is completed, the handover failure is detected by the UE.

3. The method according to claim 2, wherein: In response to determining that the timer expires before the random access procedure is completed, sending the radio connection reestablishment request message to the MN includes sending the radio connection reestablishment request message.

4. The method according to claim 2, further comprising: Receiving, by the UE from the MN, a handover command, the handover command including a first time value of a first timer for performing a first random access procedure with the MN and a second time value of a second timer for performing a second random access procedure with the SN; The UE starts the first timer and the second timer; The UE and the MN perform a first random access procedure; In response to expiration of a first timer before completion of the random access procedure, detecting, by the UE, a handover failure; The UE and the SN perform a second random access procedure; In response to completing the second random access procedure, stopping, by the UE, the second timer; as well as In response to determining that the first timer expires before the first random access procedure is completed, a radio connection reestablishment request message is sent to the MN.

5. The method according to claim 4, wherein: The second time value is greater than the first time value.

6. The method according to claim 4, wherein: Starting the first timer and the second timer includes: The UE starts the first timer and the second timer simultaneously; and The first random access procedure and the second random access procedure are performed simultaneously by the UE.

7. The method according to claim 4, wherein: Starting the first timer and the second timer includes: When the first random access procedure is completed or the first timer expires, the UE starts the second timer.

8. The method according to claim 1, wherein: Detecting the integrity check failure or the reconfiguration failure includes detecting the integrity check failure or the reconfiguration failure in response to a radio resource control (RRC) message from the MN.

9. The method according to claim 8, wherein: In response to detecting an integrity check failure or a reconfiguration failure, a radio connection reestablishment request message is sent.

10. A user equipment (UE) communicating with a primary node (MN) and a secondary node (SN) in dual connectivity (DC), the UE comprising processing hardware and configured to: detecting a master cell group (MCG) radio link failure associated with the MN; In response to an MCG radio link failure, sending an MCG failure information message to the SN; Receive MCG fault recovery message from SN; Send an MCG fault recovery completion message to the MN; Detecting timer expiration, integrity check failure, or reconfiguration failure; and In response to timer expiration, integrity check failure, or reconfiguration failure, a radio connection reestablishment request message is sent to the MN.

11. The UE according to claim 10, wherein: The timer expiration is the timer switching to expiration, and the UE is further configured to: receiving a handover command from the MN; Starting a timer for configuring a maximum amount of time in which a random access procedure is performed with the MN; performing a random access procedure with the MN; and In response to the timer expiring before the random access procedure is completed, a handover failure is detected.

12. The UE according to claim 11, wherein: In response to determining that the timer expires before the random access procedure is completed, a radio connection reestablishment request message is sent to the MN.

13. The UE according to claim 11, wherein: The UE is further configured to: receiving a handover command from the MN, the handover command including a first time value of a first timer for performing a first random access procedure with the MN and a second time value of a second timer for performing a second random access procedure with the SN; Start the first timer and the second timer; Performing a first random access procedure with the MN; In response to a first timer expiring before the random access procedure is completed, detecting a handover failure; Performing a second random access procedure with the SN; In response to completing the second random access procedure, stopping the second timer; as well as In response to determining that the first timer expires before the first random access procedure is completed, a radio connection reestablishment request message is sent to the MN.

14. The UE according to claim 13, wherein: The second time value is greater than the first time value.

15. The UE according to claim 13, wherein: The first timer and the second timer are started simultaneously, and the UE is further configured to perform the first random access procedure and the second random access procedure simultaneously. 16 . The UE according to claim 13 , wherein the second timer is started when the first random access procedure is completed or the first timer expires.

17. The UE according to claim 10, wherein: An integrity check failure or a reconfiguration failure is detected in response to a Radio Resource Control (RRC) message from the MN.

18. The UE according to claim 13, wherein: In response to detecting an integrity check failure or a reconfiguration failure, a radio connection reestablishment request message is sent.

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