Method and apparatus for MRO mechanism for inter-rat handover program

Abstract

Embodiments of the present application relate to methods and apparatus for a mobility robustness optimization (MRO) mechanism for an inter-radio access technology (RAT) handover procedure. In accordance with an embodiment of the present application, a method may include receiving a mobility command message from a source new radio (NR) cell, where the mobility command message includes an identifier (ID) of a target cell, and the target cell is at least one of an evolved universal terrestrial radio access network (E-UTRAN) cell and a universal terrestrial radio access network (UTRAN) cell; determining whether a timer (e.g., a timer T312) for initiating failure recovery based on the triggered measurement report is running; and in response to the fact that the timer is running, stopping the timer. In addition, radio link failure report (RLF) information is transmitted to the network in response to an inter-RAT handover failure from the NR to the E-UTRAN and the UTRAN.

Description

[0001] Relevant information of divisional application

[0002] This application is a divisional application, and its parent application is a patent application for an invention named "Method and Device for MRO Mechanism for RAT - to - RAT Handover Procedure" with an application date of July 28, 2020, an application number of 202080103088.3. Technical Field

[0003] Embodiments of the present application generally relate to wireless communication technologies. Specifically, they relate to methods and devices for a mobility robustness optimization (MRO) mechanism for radio access technology (RAT) - to - RAT handover procedures. Background Art

[0004] A base station (BS) may have some cells (or areas) to provide communication services. When a user equipment (UE) moves from a serving cell of a source BS to a target cell of a target BS, a handover procedure is performed.

[0005] When a UE experiences a radio link failure (RLF) or a handover failure (HOF), the UE may perform a radio resource control (RRC) re - establishment procedure. The UE can access a cell through a successful RRC re - establishment procedure. The access network will request UE information including the RLF report of the UE, so that the network can optimize mobility problems based on the UE information from the UE. Therefore, the UE will transmit a failure report to the network.

[0006] The 3rd Generation Partnership Project (3GPP) 5G New Radio (NR) adopts an MRO mechanism. However, the details of the MRO mechanism for RAT - to - RAT handover procedures have not been discussed in 3GPP 5G NR technology. Summary of the Invention

[0007] Some embodiments of the present application provide a method that can be executed by a UE. The method includes: receiving a mobility command message from a source NR cell, where the mobility command message includes an identifier (ID) of a target cell, and the target cell is at least one of an evolved universal terrestrial radio access network (E - UTRAN) cell and a universal terrestrial radio access network (UTRAN) cell; determining whether a timer (e.g., timer T312) for starting failure recovery based on a triggered measurement report is running; and in response to the timer being running, stopping the timer.

[0008] Some embodiments of the present application also provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the method performed by the UE mentioned above.

[0009] Some embodiments of the present application provide another method that can be performed by a UE. The method includes: receiving an RRC release message from a source NR cell, wherein the RRC release message includes a voice fallback indication, and wherein the voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation; entering the RRC idle state; performing a cell selection procedure; selecting an NR cell in response to being unable to establish a connection with the E-UTRAN cell after selecting an evolved universal terrestrial radio access network (E-UTRAN) cell or in response to being unable to select an E-UTRAN cell; and transmitting radio link failure (RLF) report information to the serving cell.

[0010] Some embodiments of the present application also provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the method performed by the UE mentioned above.

[0011] Some embodiments of the present application provide another method that can be performed by a BS. The method includes: transmitting a mobility command message to a UE, wherein the mobility command message includes the ID of the target cell of the UE, and the target cell is at least one of an E-UTRAN cell and a UTRAN cell; and receiving RLF report information.

[0012] Some embodiments of the present application also provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement the method performed by the BS mentioned above.

[0013] Some embodiments of the present application provide another method that can be performed by a BS. The method includes: transmitting an RRC release message including a voice fallback indication to a UE, wherein the voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation; and receiving RLF report information.

[0014] Some embodiments of the present application also provide a device for wireless communication. The device includes: a non-transitory computer-readable medium having computer-executable instructions stored thereon; a receiving circuit system; a transmitting circuit system; and a processor coupled to the non-transitory computer-readable medium, the receiving circuit system, and the transmitting circuit system, wherein the computer-executable instructions cause the processor to implement another method performed by the BS as mentioned above.

[0015] Details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To describe the manner in which the advantages and features of the present application can be obtained, a description of the present disclosure is presented by reference to specific embodiments of the present application illustrated in the accompanying drawings. These figures only depict example embodiments of the present application and are thus not considered to limit the scope of the present application.

[0017] Figure 1 Schematic diagram illustrating a wireless communication system according to some embodiments of the present application;

[0018] Figure 2 Exemplary flowchart illustrating movement from an NR procedure according to some embodiments of the present application;

[0019] Figure 3 Another exemplary flowchart illustrating movement from an NR procedure according to some embodiments of the present application;

[0020] Figure 4 Exemplary flowchart illustrating a UE information procedure according to some embodiments of the present application;

[0021] Figure 5 Flowchart illustrating a method for a handover procedure according to some embodiments of the present application;

[0022] Figure 6 Another flowchart illustrating a method for a fault information procedure according to some embodiments of the present application;

[0023] Figure 7 Flowchart illustrating a method for receiving RLF report information according to some embodiments of the present application;

[0024] Figure 8 Another flowchart illustrating a method for receiving RLF report information according to some embodiments of the present application; and

[0025] Figure 9 Exemplary block diagram illustrating a device according to some embodiments of the present application. Detailed Implementation Modes

[0026] The detailed description of the accompanying drawings is intended as a description of the preferred embodiments of the present application and is not intended to represent the only form in which the present application can be practiced. It should be understood that the same or equivalent functions can be accomplished by different embodiments that are intended to be covered by the spirit and scope of the present application.

[0027] Some embodiments of the present application will now be described in detail, and their examples are illustrated in the accompanying drawings. For the sake of promoting understanding, the embodiments are provided under specific network architectures and new service scenarios (such as 3GPP 5G, 3GPP LTE Release 8, etc.). After consideration, with the development of network architectures and new service scenarios, all embodiments in the present application are also applicable to similar technical problems; and in addition, the terms cited in the present application may change, which should not affect the principles of the present application.

[0028] Figure 1 Schematic diagram of a wireless communication system according to some embodiments of the present application.

[0029] As Figure 1 illustrated and shown, the wireless communication system 100 includes at least one user equipment (UE) 101 and at least one base station (BS) 102. Specifically, for illustrative purposes, the wireless communication system 100 includes one UE 101 (such as UE101a) and three BSs 102 (such as BS102a, BS102b, and BS102c). Although a specific number of UEs 101 and BSs 102 are depicted in Figure 1 , it is considered that any number of UEs 101 and BSs 102 can be included in the wireless communication system 100.

[0030] The UE 101 may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a gaming console, a security system (including security cameras), an in-vehicle computer, a network device (e.g., a router, a switch, and a modem), an Internet of Things (IoT) device, or the like. According to some embodiments of the present application, the UE 101 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a pager, or any other device capable of transmitting and receiving communication signals over a wireless network. In some embodiments of the present application, the UE 101 includes a wearable device, such as a smart watch, a fitness bracelet, an optical head-mounted display, or the like. Additionally, the UE 101 may be referred to as a user unit, a mobile device, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a user station, a user terminal, or a device, or other terms used in the art to describe it. The UE 101 may communicate directly with the BS102 via an uplink (UL) communication signal.

[0031] In some embodiments of the present application, each of the UEs 101 may be deployed with IoT applications, eMBB applications, and / or URLLC applications. It is contemplated that the specific types of applications deployed in the UEs 101 may vary and are not limited.

[0032] The BS102 may be distributed throughout a geographical area. In certain embodiments of the present application, each of the BS102s may also be referred to as an access point, an access terminal, a base station, a base unit, a macro cell, a Node B, an evolved Node B (eNB), a gNB, an NG-RAN (Next Generation Radio Access Network) node, a home Node B, a relay node, or a device, or other terms used in the art to describe it. The BS102 is generally part of a radio access network that may include one or more controllers communicatively coupled to one or more corresponding BS102s.

[0033] The wireless communication system 100 may be compatible with any type of network capable of transmitting and receiving wireless communication signals. For example, the wireless communication system 100 may be compatible with: a wireless communication network, a cellular phone network, a time-division multiple access (TDMA)-based network, a code-division multiple access (CDMA)-based network, an orthogonal frequency-division multiple access (OFDMA)-based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communication network, a high-altitude platform network, and / or other communication networks.

[0034] In some embodiments of the present application, the wireless communication system 100 is compatible with 5G NR of the 3GPP protocol, where BS102 transmits on the DL using an OFDM modulation scheme, and UE 101 transmits data on the UL using a single-carrier frequency-division multiple access (SC-FDMA) or OFDM scheme. However, more generally, the wireless communication system 100 may implement some other open or proprietary communication protocols, such as WiMAX and other protocols.

[0035] In some embodiments of the present application, BS102 may communicate using other communication protocols, such as wireless communication protocols of the IEEE 802.11 series. Additionally, in some embodiments of the present application, BS102 may communicate via licensed spectrum, while in other embodiments, BS102 may communicate via unlicensed spectrum. The present application is not intended to be limited to the implementation of any specific wireless communication system architecture or protocol. In still other embodiments of the present application, BS102 may communicate with UE 101 using the 3GPP 5G protocol.

[0036] Each BS102 may include one or more cells. Each UE 101 may perform a cell selection procedure between different cells of different BSs. Each UE 101 may switch from the serving cell of the source BS to the target cell of the target BS. For example, in the wireless communication system 100 illustrated and described as in Figure 1 , BS102a may be used as the source BS, and each of BS102b and BS102c may be used as the target BS. If a handover is required, then as illustrated and described in Figure 1 , UE101a may perform a handover procedure from the serving cell of BS102a to the target cell of BS102b or the target cell of BS102c, depending on the result of the cell selection procedure. The handover procedure performed by UE 101a may be a CHO procedure.

[0037] According to some protocols of the 3GPP standard documents, during the handover procedure from 5G to LTE (i.e., 4G), the inter-RAT handover is characterized by the following:

[0038] - The source RAT BS configures measurement information and the reporting configuration of the target RAT BS.

[0039] - The source RAT BS decides the handover procedure and provides the necessary information to the target RAT BS.

[0040] - Radio resources are reserved in the target RAT BS before the UE accesses the target RAT BS.

[0041] - The RRC reconfiguration message from the target RAT BS is delivered to the source RAT BS as a transparent container and transmitted by the source RAT BS to the UE in the handover command. For example, the source BS transmits a MobilityFromNRCommand message to the UE, and the MobilityFromNRCommand message contains the RRC reconfiguration message provided by the target RAT BS.

[0042] According to some protocols of the 3GPP standard document, during the handover procedure from 5G to 3G, a Single Radio Voice Call Continuity (SRVCC) operation is performed. The source NR node decides to hand over the UE that is having an Internet Protocol Multimedia Subsystem (IMS) voice call from NR to UTRAN based on the following principles:

[0043] - The source NR node configures the measurement information and the reporting configuration of the target UTRAN node.

[0044] - The source NR node determines that the handover procedure to the target UTRAN node should be initiated.

[0045] - The source NR node only initiates the handover procedure for the ongoing IMS voice call and provides an indication to the Access and Mobility Management Function (AMF) indicating the handover towards UTRAN together with the identifier (ID) of the target UTRAN node. The source NR node also indicates to the target UTRAN node that the incoming handover originates from the 5G system.

[0046] - Radio resources are reserved in the target RAT BS (i.e., the target UTRAN node) before the UE accesses the target RAT BS.

[0047] - The RRC reconfiguration message from the target RAT BS is delivered to the source NR node via a transparent container and passed by the source NR node to the UE in the handover command. For example, the source BS transmits a MobilityFromNRCommand message containing the RRC reconfiguration message provided by the target RAT BS to the UE.

[0048] In addition, 3GPP TS 38.331 defines the mobility procedure from NR to 4G or 3G. The purpose of the mobility procedure is to move the UE in the RRC_CONNECTED state to a cell using another RAT, such as an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) cell or a UTRAN - Frequency Division Duplex (FDD) cell. The specific content is described in Figures 2 to 4 .

[0049] Figure 2 Illustrate an exemplary flowchart of the movement from the NR procedure according to some embodiments of the present application. Figure 2The embodiment is performed by a UE that aims to handover from the serving cell of a source BS to a candidate cell of a target BS.

[0050] As Figure 2 shown in, in step 201, a BS (e.g., BS102a, BS102b, or BS102c as described and shown in Figure 1 ) initiates a move from the NR procedure to the UE (e.g., UE 101a as described and shown in Figure 1 ) by transmitting a MobilityFromNRCommand message to the UE. The BS is the source BS that controls the serving cell of the UE. The UE may be in the RRC_CONNECTED state. For example, the MobilityFromNRCommand message includes radio resources that have been allocated to the UE in a candidate cell of the target BS.

[0051] Figure 3 Illustrates another exemplary flowchart of a move from the NR procedure according to some embodiments of the present application. Similar to Figure 2 , Figure 3 the embodiment is performed by a UE that aims to handover from the serving cell of a source BS to a candidate cell of a target BS.

[0052] As Figure 3 shown in, in step 301, a BS that is of the NR RAT type (e.g., BS102a, BS102b, or BS102c as described and shown in Figure 1 ) initiates a move from the NR procedure to the UE (e.g., UE 101a as described and shown in Figure 1 ) by transmitting a MobilityFromNRCommand message to the UE. The BS is the source BS that controls the serving cell of the UE. The UE may be in the RRC_CONNECTED state. For example, the MobilityFromNRCommand message includes radio resources that have been allocated to a candidate cell of the target BS of the UE.

[0053] If a failure occurs during the inter-RAT handover procedure of the UE, the UE re-establishes to a cell, which may be the source cell, the target cell, or an additional cell. For example, as shown in step 302, if no failure occurs during the inter-RAT handover procedure, then the UE may perform an RRC re-establishment procedure to the source cell of the BS that sent the MobilityFromNRCommand message. Alternatively, if a failure occurs during the inter-RAT handover procedure, then the UE may perform an RRC re-establishment procedure to a candidate cell of the target BS or the UE may perform an RRC re-establishment procedure to a cell different from the source cell or the candidate target cell.

[0054] Figure 4Exemplary flowchart of a UE information procedure according to some embodiments of the present application.

[0055] Figure 4 In an embodiment, the UE information procedure is used by a BS that aims to request the UE to report information. Specifically, the UE may re - establish connection to a cell after an RLF or HOF occurs. The UE may access a cell after the UE enters the RRC idle state due to an RRC re - establishment failure. The UE may transmit an indication to the source BS, which indicates RLF information available to the source BS. After the source BS receives the failure information that can be obtained from the UE, the source BS transmits a UE information request message to the UE.

[0056] As Figure 4 shown, in step 401, the source BS (e.g., BS102a, BS 102b, or BS102c as described and shown in Figure 1 starts the UE information procedure by transmitting a UE Information Request message to the UE (e.g., UE101a as described and shown in Figure 1 . The source BS should start this UE information procedure only after successful security activation. In step 402, after receiving the UE Information Request message, the UE reports the UE Information Request message to the source BS. For example, the UE transmits a UE Information Request message containing an RLF report to the source BS. When an RLF occurs, the UE Information Request message may contain an RLF report.

[0057] Generally, the MEO mechanism aims to detect and enable problem correction for RLF, HOF, or ping - pong problems. In 3GPP Release 16, during the inter - RAT handover procedure, an RLF or HOF may occur. However, an MRO mechanism for the inter - RAT handover procedure has not been designed. Embodiments of the present application provide a solution regarding the MRO mechanism for the inter - RAT handover procedure.

[0058] The following table shows an introduction to some timers as specified in 3GPP standard documents, including the start condition, stop condition, operation upon expiration, and possible common names for each of these timers.

[0059]

[0060] Figure 5 Flowchart of a method for a handover procedure according to some embodiments of the present application. Method 500 may be performed by a UE (e.g., UE 101 as shown and described in Figure 1 or as shown and described in Figures 2 to 4performed by one of the UEs shown and described herein. Although described with respect to a UE, it should be understood that other devices may be configured to perform methods similar to the Figure 5 method.

[0061] In an exemplary method 500 as shown in Figure 5 , at operation 502, the UE receives a mobility command message from a source NR cell. The mobility command message may include the ID of the target cell. The target cell is at least one of an E-UTRAN cell and a UTRAN cell. In an embodiment, the mobility command message is a MobilityFromNRCommand message as specified in a 3GPP standard document.

[0062] In an embodiment, the UE performs a handover procedure to the target cell indicated in the mobility command message. In an embodiment, the UE further receives an RRC reconfiguration message containing CHO configuration information associated with one or more candidate cells. The UE may determine whether the selected candidate cell is configured with CHO configuration information. If the UE determines that the selected candidate cell is configured with CHO configuration information, then the UE may perform a CHO procedure to the selected candidate cell.

[0063] If a handover failure occurs during a handover procedure (e.g., a CHO procedure), then the UE performs a cell selection procedure and selects a suitable candidate cell. Then, the UE may initiate an RRC reestablishment procedure to the selected candidate cell.

[0064] For example, the selected candidate cell may be an NR cell, an E-UTRAN cell, or a UTRAN cell. In an embodiment, if the UE finds one or more candidate cells during the cell selection procedure, and if the one or more found candidate cells include at least one UTRAN cell, then the UE selects the UTRAN cell as the selected candidate cell.

[0065] If a handover failure occurs during the handover procedure, then the UE may transmit RLF report information. In an embodiment, if the mobility command message includes a voice fallback indication, then the RLF report information includes an indicator for indicating that the handover procedure is for a voice fallback operation.

[0066] In an embodiment, the RLF report information includes an indicator for indicating: (1) no E-UTRAN cell was found for voice fallback operation; or (2) no UTRAN cell was found for voice fallback operation.

[0067] In an embodiment, the RLF report information includes the ID of the target cell. In an embodiment, if the handover procedure is performed between different radio access technologies (RATs), then the RLF report information includes the RAT type of the target cell. The RAT type may be E-UTRAN or UTRAN-FDD.

[0068] In an embodiment, if the selected candidate cell is a UTRAN cell, then the RLF report information is transmitted to the BS serving the UE (e.g., one of BS102a, BS102b, or BS102c as illustrated and described in Figure 1 or one of the BSs as illustrated and described in Figures 2 to 4 ). The BS serving the UE may forward the message containing the RLF report information to the source BS associated with the source NR cell. For example, the BS serving the UE transmits the message containing the RLF report information to the AMF, and the AMF is associated with the source NR cell. Then, the AMF transmits the message containing the RLF report information to the source BS associated with the source NR cell.

[0069] Return to reference Figure 5 , in operation 504, the UE determines whether a timer for initiating fault recovery based on a triggered measurement report is running. In operation 506, if the UE determines that the timer is running, the UE stops the timer. In an embodiment, the timer is timer T312 as specified in the 3GPP standard document. The UE determines whether timer T312 is running and stops timer T312 when it is running.

[0070] The following text describes Figure 5 four specific embodiments of the method illustrated and described in

[0071] Embodiment 1

[0072] According to Embodiment 1, the UE (e.g., one of UE 101 as illustrated and described in Figure 1 or one of the UEs as illustrated and described in Figures 2 to 4 ) and the BS (e.g., one of BS102a, BS102b, or BS102c as illustrated and described in Figure 1 or one of the BSs as illustrated and described in Figures 2 to 4 ) perform the following operations:

[0073] (1) The source BS decides to move the UE to an LTE cell (e.g., an E-UTRAN cell) for voice services.

[0074] (2) The UE receives a MobilityFromNRCommand message from the source BS.

[0075] ● After receiving the MobilityFromNRCommand message, if timer T312 is running, the UE stops the timer.

[0076] ● The MobilityFromNRCommand message contains a voice fallback indication.

[0077] (3) The UE accesses the target LTE cell (e.g., an E-UTRAN cell) indicated in the MobilityFromNRCommand message.

[0078] ● The UE starts timer T304.

[0079] (4) The UE fails to establish a connection to the target LTE cell, e.g., after timer T304 expires.

[0080] (5) The UE performs a cell selection procedure. The cell selection procedure may be as follows.

[0081] a) If a suitable LTE cell (e.g., an E-UTRAN cell) is selected during the cell selection procedure, the UE transitions to the RRC_IDLE state and performs a connection establishment procedure to the selected LTE cell.

[0082] b) After accessing the selected LTE cell (i.e., an E-UTRAN cell), the UE transmits an RLF report to the BS of the LTE cell serving the UE (i.e., the LTE serving cell (i.e., an E-UTRAN cell)).

[0083] i. The UE reports the RLF report to the LTE serving cell. The RLF report may contain additional auxiliary information indicating whether voiceFallbackIndication is included in the MobilityFromNRCommand message. That is, the RLF report may contain an indicator for indicating whether this handover procedure is performed for voice fallback purposes. For example, the voice fallback indication is included in the RLF report.

[0084] c) The BS of the LTE serving cell receives the RLF report from the UE and then forwards the RLF report to the source BS.

[0085] A. If no suitable LTE cell (e.g., an E-UTRAN cell) is selected during the cell selection procedure, the UE may select an NR cell to perform an RRC reconstruction procedure.

[0086] B. The UE reports the RLF report to the BS of the selected NR. The RLF report may contain at least one of the following additional auxiliary information:

[0087] ii. Supplementary information indicating whether voiceFallbackIndication is included in the MobilityFromNRCommand message. That is, the RLF report may include an indicator for indicating whether this handover procedure is performed for voice fallback purposes. For example, the voice fallback indication is included in the RLF report.

[0088] iii. Supplementary information indicating that no suitable E-UTRAN cell is found for voice fallback purposes when voiceFallbackIndication is configured.

[0089] C. The BS of the selected NR cell receives the RLF report from the UE and then forwards the RLF report to the target BS associated with the failed handover procedure.

[0090] Example 2

[0091] According to Example 2, the UE (e.g., one of the UEs 101 shown and described as Figure 1 or one of the UEs shown and described as Figures 2 to 4 ) and the BS (e.g., one of the BSs 102a, 102b, or 102c described and shown as Figure 1 or one of the BSs shown and described as Figures 2 to 4 ) perform the following operations:

[0092] (1) The source NR BS decides to hand over the UE to a UTRAN cell for voice services.

[0093] (2) The UE receives a MobilityFromNRCommand message from the source NR BS.

[0094] ● After receiving the MobilityFromNRCommand message, if the timer T312 is running, the UE stops the timer T312.

[0095] ● The MobilityFromNRCommand message includes voiceFallbackIndication.

[0096] (3) The UE accesses the target UTRAN cell indicated in the MobilityFromNRCommand message.

[0097] ● The UE starts the timer T304.

[0098] (4) The UE fails to establish a connection to the target UTRAN cell, e.g., after the timer T304 expires. Alternatively, after the UE succeeds in the handover procedure within one cycle, RLF occurs in 3G.

[0099] (5) The UE performs a cell selection procedure for RRC reconstruction purposes.

[0100] ● If the UE fails to perform the handover procedure from 5G to 3G or RLF occurs in 3G, then the UE shall perform an RRC reconstruction procedure. If a suitable UTRAN cell is available during the cell selection procedure, the UE shall select the suitable UTRAN cell for the RRC reconstruction procedure. Otherwise, the UE may select another suitable cell (e.g., an NR cell) for RRC reconstruction purposes.

[0101] (6) After accessing the UTRAN cell or the NR cell, the UE transmits the RLF report to the serving cell. The RLF report may include at least one of the following additional auxiliary information:

[0102] ● Auxiliary information indicating whether the handover procedure is an inter-RAT handover procedure. That is, the auxiliary information indicates whether the handover procedure is of the inter-RAT type.

[0103] ● If the handover procedure is an inter-RAT handover procedure, auxiliary information indicating whether the target cell is E-UTRAN or UTRAN-FDD.

[0104] i. For example, the RLF report includes a targetRAT-Type IE, which indicates the RAT type of the target cell. The targetRAT-Type IE can be one of E-UTRAN and UTRAN-FDD. In an embodiment, the targetRAT-Type can be enumerated as {eutran, utran-fdd}.

[0105] ● Auxiliary information indicating the ID of the target cell.

[0106] i. For example, the RLF report may include the ID of the target UTRAN cell of the failed handover procedure. In an embodiment, the field "FailedPCellid-UTRAN" or "FailedPCellid-UTRA" is used to indicate the ID of the target UTRAN cell where the RLF is detected.

[0107] (7) The UTRAN cell receives the RLF report from the UE. Then, the UTRAN cell transmits the RLF report as a container to the core network (CN). The node of the UTRAN CN will forward the information containing the RLF report to the AMF associated with the source NR cell.

[0108] (8) The AMF will transmit the received information containing the RLF report to the source NR BS.

[0109] Embodiment 3

[0110] According to Embodiment 3, a UE (e.g., one of the UEs 101 shown and described as in Figure 1 or one of the UEs shown and described as in Figures 2 to 4 ) and a BS (e.g., one of the BSs 102a, 102b, or 102c described and shown as in Figure 1 or one of the BSs shown and described as in Figures 2 to 4 ) perform the following operations:

[0111] (1) The source BS transmits target RAT measurement and reporting configuration information to the UE.

[0112] (2) The source BS determines the target cell of the target BS in another RAT and sends a handover request including necessary information (e.g., the context of the UE) to the target BS.

[0113] (3) The target BS transmits an RRC reconfiguration message to the source BS.

[0114] (4) The source BS transmits a MobilityFromNRCommand message to the UE. The MobilityFromNRCommand message contains the RRC reconfiguration message transmitted from the target BS.

[0115] (5) The UE receives the MobilityFromNRCommand message from the network. The MobilityFromNRCommand message indicates information about the target cell of the target BS.

[0116] ● After receiving the MobilityFromNRCommand message, if the timer T312 is running, the UE stops the timer.

[0117] (6) The UE accesses the target cell of the target BS.

[0118] Embodiment 4

[0119] According to Embodiment 4, a UE (e.g., one of the UEs 101 shown and described as in Figure 1 or one of the UEs shown and described as in Figures 2 to 4 ) and a BS (e.g., one of the BSs 102a, 102b, or 102c described and shown as in Figure 1 or one of the BSs shown and described as in Figures 2 to 4 ) perform the following operations:

[0120] (1) The UE receives CHO configuration information.

[0121] (2) The UE receives a MobilityFromNRCommand message from the source NR BS.

[0122] ● After receiving the MobilityFromNRCommand message, if timer T312 is running, the UE stops the timer T312.

[0123] (3) The UE accesses the target cell indicated in the MobilityFromNRCommand message.

[0124] ● The UE starts timer T304.

[0125] (4) The UE fails to successfully establish a connection to the target cell, for example, after timer T304 expires.

[0126] (5) The UE initiates the RRC reconstruction procedure and starts timer T311 for the cell selection procedure.

[0127] (6) The UE performs the cell selection procedure and selects a suitable NR cell.

[0128] ● The UE stops timer T311.

[0129] (7) The UE applies the associated stored CHO configuration information to the selected suitable NR cell, and if the selected cell is configured with CHO configuration information, then performs the CHO procedure.

[0130] ● In an example, the attemptCondReconfig IE is used to indicate that CHO configuration information is allowed for the UE. For example, the UE is allowed to perform the CHO procedure to the selected cell through the following conditions:

[0131] - "Cell selection is triggered by the failure of the inter-RAT handover procedure from NR",

[0132] - "The attemptCondReconfig IE is configured", and

[0133] - "The selected cell has been configured with CHO configuration information".

[0134] Details described in all other embodiments of the present application (for example, details of the MRO mechanism of the inter-RAT handover procedure and auxiliary information in the RLF report information) may be applicable to Figure 5 the embodiments of. In addition, Figure 5 Details described in the embodiments of may be applicable to Figures 1 to 4 and all embodiments of 6 to 9.

[0135] Figure 6 Another flowchart illustrating a method for a fault information procedure according to some embodiments of the present application. The method 600 may be performed by a UE (for example, the UE 101 as shown and described in Figure 1 or as shown inFigures 2 to 4 performed by one of the UEs shown and described in Figure 6 . Although described with respect to a UE, it should be understood that other devices may be configured to perform a method similar to the method of

[0136] In the exemplary method 600 shown in Figure 6 , at operation 602, the UE receives an RRC release message from a source NR cell. The RRC release message includes a voice fallback indication. The voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation. At operation 604, the UE enters the RRC idle state.

[0137] At operation 606, the UE performs a cell selection procedure. At operation 608, if the UE is unable to establish a connection with an E-UTRAN cell after selecting an E-UTRAN cell or if the UE is unable to select an E-UTRAN cell, then the UE selects an NR cell. At operation 610, the UE transmits RLF report information to the serving cell of the UE.

[0138] In an embodiment, the serving cell is the same as the source NR cell. In other words, the UE may reselect back to the source NR cell as its serving cell. In another embodiment, the serving cell is a cell different from the source NR cell. In other words, the UE may select a different cell as its serving cell.

[0139] In an embodiment, the RLF report information includes an indicator for indicating that the RRC release message includes a voice fallback indication. In another embodiment, the RLF report information includes an indicator for indicating that no E-UTRAN cell was found during the cell selection procedure. In another embodiment, the RLF report information includes the ID of the source NR cell.

[0140] The following text describes a specific embodiment 5 of the method shown and described in Figure 6 .

[0141] According to embodiment 5, a UE (e.g., one of the UEs 101 shown and described in Figure 1 or one of the UEs shown and described in Figures 2 to 4 ) and a BS (e.g., one of the BSs 102a, 102b, or 102c shown and described in Figure 1 or one of the BSs shown and described in Figures 2 to 4 ) perform the following operations:

[0142] (1) The NR BS decides to move the UE to an E-UTRAN cell for voice services.

[0143] (2) The UE receives an RRC release message containing voiceFallbackIndication from the source cell of the NR BS.

[0144] (3) The UE attempts to select an E-UTRAN cell that it can access, but a failure occurs during the handover procedure to the selected E-UTRAN cell.

[0145] (4) The UE can reselect back to the source cell. Alternatively, the UE can select a cell different from both the source cell and the selected E-UTRAN cell. When the UE can access the source cell or a different cell, the UE needs to report RLF report information. More specifically, the RLF report information may include the following potential auxiliary information:

[0146] ● An indicator indicating that the UE receives an RRC release message containing voiceFallbackIndication;

[0147] ● After receiving the RRC release message containing voiceFallbackIndication, no suitable E-UTRAN cell for voice fallback purposes is found.

[0148] ● The ID of the source cell that transmits the RRC release message containing voiceFallbackIndication.

[0149] The details described in all other embodiments of the present application (e.g., the details of the MRO mechanism for the inter-RAT handover procedure and the auxiliary information in the RLF report information) may be applicable to Figure 6 the embodiments. In addition, Figure 6 the details described in the embodiments of Figures 1 to 5 may be applicable to all embodiments of

[0150] Figure 7 A flowchart illustrating a method for receiving RLF report information according to some embodiments of the present application. Method 700 may be executed by a BS or a source BS (e.g., one of BS102a, BS102b, or BS102c as illustrated and described in Figure 1 or a BS as illustrated and described in Figures 2 to 4 ). Although described with respect to a BS, it should be understood that other devices may be configured to execute a method similar to Figure 7 the method.

[0151] In an exemplary method 700 as illustrated in Figure 7 , at operation 702, the source BS transmits a mobility command message to the UE (e.g., one of UE 101 as illustrated and described in Figure 1 or a UE as illustrated and described in Figures 2 to 4 ). The mobility command message contains the ID of the target cell of the UE. The target cell is at least one of an E-UTRAN cell and a UTRAN cell.

[0152] In an embodiment, the mobility command message is a MobilityFromNRCommand message as specified in the 3GPP standard document. The mobility command message may include a voice fallback indication (e.g., voiceFallbackIndication as specified in the 3GPP standard document).

[0153] In operation 704, the source BS receives RLF report information from the UE, for example.

[0154] In an embodiment, if the mobility command message includes a voice fallback indication (e.g., voiceFallbackIndication as specified in the 3GPP standard document), then the RLF report information includes an indicator for indicating that the handover procedure is for a voice fallback operation.

[0155] In another embodiment, the RLF report information includes an indicator for indicating that no E-UTRAN cell has been found for the voice fallback operation. In another embodiment, the RLF report information includes an indicator for indicating that no UTRAN cell has been found for the voice fallback operation.

[0156] In another embodiment, the BS serving the UE forwards a message to the source BS, and the message includes the RLF report information. In an example, the serving BS transmits a message including the RLF report information to the AMF, and the AMF forwards the message to the source BS.

[0157] In an embodiment, the RLF report information includes the ID of the target cell of the UE.

[0158] The details described in all other embodiments of this application (e.g., the details of the MRO mechanism for the inter-RAT handover procedure and the auxiliary information in the RLF report information) may be applicable to Figure 7 the embodiments. In addition, Figure 7 the details described in the embodiments of Figures 1 to 6 may be applicable to all embodiments of

[0159] Figure 8 Another flowchart illustrating a method for receiving RLF report information according to some embodiments of the present application. Method 800 may be executed by a BS or a source BS (e.g., one of BS102a, BS102b, or BS102c as illustrated and shown in Figure 1 or a BS as illustrated and shown in Figures 2 to 4 ). Although described with respect to a BS, it should be understood that other devices may be configured to execute a method similar to Figure 8 's method.

[0160] In as Figure 8In the exemplary method 800 shown, at operation 802, the BS may transmit an RRC release message to the UE (e.g., to one of the UEs 101 shown and described in Figure 1 or to one of the UEs shown and described in Figures 2 to 4 ). The RRC release message includes a voice fallback indication (e.g., voiceFallbackIndication as specified in the 3GPP standard document). The voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation. In some cases, the UE is unable to select a suitable E-UTRAN cell or the UE is unable to establish a connection with the E-UTRAN cell after selecting the E-UTRAN cell. Thus, in these cases, the UE selects an NR cell. The UE may transmit RLF report information to the serving cell after the UE accesses the selected NR cell.

[0161] At operation 804, the source BS receives the RLF report. In an example, if the selected NR cell is the source cell of the UE, then the UE will transmit the RLF report information to the source BS. In another example, if the selected NR cell is not the source cell, then the UE will transmit the RLF report information to the serving BS. Then, the serving BS will forward the received RLF report information to the source BS.

[0162] In an embodiment, the RLF report information includes an indicator for indicating that the RRC release message includes a voice fallback indication.

[0163] In another embodiment, the RLF report information includes an indicator for indicating that no E-UTRAN cell was found during the UE's cell selection procedure.

[0164] In another embodiment, the RLF report information includes the ID of the UE's source NR cell.

[0165] The details described in all other embodiments of the present application (e.g., details of the MRO mechanism for the inter-RAT handover procedure and the auxiliary information in the RLF report information) may be applicable to the embodiments of Figure 8 . In addition, Figure 8 The details described in the embodiments of may be applicable to all embodiments of Figures 1 to 7 and 9.

[0166] Figure 9 Exemplary block diagrams illustrating devices according to some embodiments of the present application. In some embodiments of the present application, the device 900 may be a UE, which may at least execute the method described in Figure 5 or Figure 6 . In some embodiments of the present application, the device 900 may be a BS (e.g., a source BS), which may at least execute the method described in Figure 7 or Figure 8 .

[0167] As Figure 9 shown in Figure 9 , device 900 may include at least one receiver 902, at least one transmitter 904, at least one non-transitory computer-readable medium 906, and at least one processor 908 coupled to the at least one receiver 902, the at least one transmitter 904, and the at least one non-transitory computer-readable medium 906.

[0168] Although in Figure 9 , elements such as the at least one receiver 902, the at least one transmitter 904, the at least one non-transitory computer-readable medium 906, and the at least one processor 908 are described in the singular form, the plural form is contemplated unless explicitly stated to be limited to the singular form. In some embodiments of the present application, the at least one receiver 902 and the at least one transmitter 904 are combined into a single device, such as a transceiver. In certain embodiments of the present application, device 900 may further include an input device, a memory, and / or other components.

[0169] In some embodiments of the present application, computer-executable instructions may be stored on the at least one non-transitory computer-readable medium 906, which may be programmed to implement the operations of a method with the at least one receiver 902, the at least one transmitter 904, and the at least one processor 908, such as described in any of Figures 5 to 8 .

[0170] Those of ordinary skill in the art will understand that the operations of the methods described in connection with the aspects disclosed herein may be embodied directly in hardware, in software modules executed by a processor, or in a combination of both. Software modules may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the operations of the methods may reside on a non-transitory computer-readable medium as one or any combination of a code set and / or an instruction set that may be incorporated into a computer program product.

[0171] Although the present disclosure has been described with reference to specific embodiments of the present disclosure, it is apparent that many alternatives, modifications, and variations will be obvious to those skilled in the art. For example, the various components of the embodiments may be interchanged, added, or substituted in other embodiments. Also, all elements of each figure are not necessarily required for the operation of the disclosed embodiments. For example, those of ordinary skill in the art will be able to make and use the teachings of the present disclosure by simply employing the elements of the independent claims. Therefore, the embodiments of the present disclosure set forth herein are intended to be illustrative rather than restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.​​​​

[0172] In this document, the term "includes" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to the process, method, article, or apparatus. An element that begins with "a" or the like does not, without further limitation, preclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element. Moreover, the term "another" is defined as at least a second or more. As used herein, the terms "has" and the like are defined as "includes".

Claims

1. A device, comprising: At least one non - transitory computer - readable medium storing computer - executable instructions; At least one receiving circuit system; At least one transmitting circuit system; And At least one processor coupled to the at least one non - transitory computer - readable medium, the at least one receiving circuit system, and the at least one transmitting circuit system, wherein the computer - executable instructions cause the at least one processor to implement a method, the method comprising: Receiving a Radio Resource Control (RRC) release message from a source New Radio (NR) cell, wherein the RRC release message includes a voice fallback indication, and wherein the voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation; Entering an RRC idle state; Performing a cell selection procedure; Selecting an NR cell in response to being unable to establish a connection with an Evolved Universal Terrestrial Radio Access Network (E - UTRAN) cell after selecting the E - UTRAN cell or in response to being unable to select an E - UTRAN cell; and Transmitting Radio Link Failure (RLF) report information to a serving cell.

2. The device according to claim 1, wherein the serving cell is the source NR cell.

3. The device according to claim 1, wherein the serving cell is a cell different from the source NR cell.

4. The device according to claim 1, wherein the RLF report information includes an indicator for indicating that the RRC release message includes the voice fallback indication.

5. The device according to claim 1, wherein the RLF report information includes an indicator for indicating that no E-UTRAN cell is found during the cell selection procedure.

6. The device according to claim 1, wherein the RLF report information includes the ID of the source NR cell.

7. A device, comprising: At least one non - transitory computer - readable medium storing computer - executable instructions; At least one receiving circuit system; At least one transmitting circuit system; And At least one processor coupled to the at least one non - transitory computer - readable medium, the at least one receiving circuit system, and the at least one transmitting circuit system, wherein the computer - executable instructions cause the at least one processor to implement a method, the method comprising: Transmitting a mobility command message to a User Equipment (UE), wherein the mobility command message includes an identifier (ID) of a target cell of the UE, and the target cell is at least one of an Evolved Universal Terrestrial Radio Access Network (E - UTRAN) cell and a Universal Terrestrial Radio Access Network (UTRAN) cell; And Receiving Radio Link Failure (RLF) report information.

8. The device according to claim 7, wherein in response to the handover command message including the voice fallback indication, the RLF report information includes an indicator for indicating that the handover procedure is for the voice fallback operation.

9. The device according to claim 7, wherein the RLF report information includes an indicator for indicating one of the following: No E-UTRAN cell is found for the voice fallback operation; and No UTRAN cell found for the voice fallback operation.

10. The apparatus according to claim 7, wherein the RLF report information is included in a message, and the message is forwarded from a base station BS serving the UE.

11. The apparatus according to claim 10, wherein the message is transmitted from the BS serving the UE to an access and mobility management function AMF, and then forwarded by the AMF.

12. The apparatus according to claim 7, wherein the RLF report information includes an ID of the target cell of the UE.

13. An apparatus, comprising: At least one non - transitory computer - readable medium storing computer - executable instructions; At least one receiving circuit system; At least one transmitting circuit system; And At least one processor coupled to the at least one non - transitory computer - readable medium, the at least one receiving circuit system, and the at least one transmitting circuit system, wherein the computer - executable instructions cause the at least one processor to implement a method, the method comprising: Transmitting a mobility command message to a User Equipment (UE), wherein the mobility command message includes an identifier (ID) of a target cell of the UE, and the target cell is at least one of an Evolved Universal Terrestrial Radio Access Network (E - UTRAN) cell and a Universal Terrestrial Radio Access Network (UTRAN) cell; And Receiving Radio Link Failure (RLF) report information.

14. The apparatus according to claim 13, wherein in response to the mobility command message including a voice fallback indication, the RLF report information includes an indicator for indicating that the handover procedure is for a voice fallback operation.

15. The apparatus according to claim 13, wherein the RLF report information includes an indicator for indicating one of the following: No E-UTRAN cell found for the voice fallback operation; and No UTRAN cell found for the voice fallback operation.

16. The apparatus according to claim 13, wherein the RLF report information is included in a message, and the message is forwarded from a base station BS serving the UE.

17. The apparatus according to claim 16, wherein the message is transmitted from the BS serving the UE to an access and mobility management function AMF, and then forwarded by the AMF.

18. The apparatus according to claim 13, wherein the RLF report information includes an ID of the target cell of the UE.

19. A method, comprising: Receiving a Radio Resource Control (RRC) release message from a source New Radio (NR) cell, wherein the RRC release message includes a voice fallback indication, and wherein the voice fallback indication indicates that the RRC release message is triggered by a voice fallback operation; Entering an RRC idle state; Performing a cell selection procedure; Select an NR cell in response to being unable to establish a connection with the evolved universal terrestrial radio access network (E-UTRAN) cell after selecting the E-UTRAN cell or in response to being unable to select an E-UTRAN cell; and Transmit radio link failure (RLF) report information to the serving cell.

20. The method according to claim 19, wherein the serving cell is the source NR cell.

21. The method according to claim 19, wherein the serving cell is a cell different from the source NR cell.

22. The method according to claim 19, wherein the RLF report information includes an indicator for indicating that the RRC release message includes the voice fallback indication.

23. The method according to claim 19, wherein the RLF report information includes an indicator for indicating that no E-UTRAN cell is found during the cell selection procedure.

24. The method according to claim 19, wherein the RLF report information includes the ID of the source NR cell.

25. A method, comprising: Transmit a mobility command message to a user equipment (UE), wherein the mobility command message includes an identifier (ID) of a target cell of the UE, and the target cell is at least one of an evolved universal terrestrial radio access network (E-UTRAN) cell and a universal terrestrial radio access network (UTRAN) cell; and Receive radio link failure (RLF) report information.

26. The method according to claim 25, wherein in response to the mobility command message including the voice fallback indication, the RLF report information includes an indicator for indicating that the handover procedure is used for the voice fallback operation.

27. The method according to claim 25, wherein the RLF report information includes an indicator for indicating one of the following: No E-UTRAN cell is found for the voice fallback operation; and No UTRAN cell is found for the voice fallback operation.

28. The method according to claim 25, wherein the RLF report information is included in a message, and the message is forwarded from the base station BS serving the UE.

29. The method according to claim 28, wherein the message is transmitted from the BS serving the UE to the access and mobility management function AMF and then forwarded by the AMF.

30. The method according to claim 25, wherein the RLF report information includes the ID of the target cell of the UE.

31. A method, comprising: Transmit a mobility command message to a user equipment (UE), wherein the mobility command message includes an identifier (ID) of a target cell of the UE, and the target cell is at least one of an evolved universal terrestrial radio access network (E-UTRAN) cell and a universal terrestrial radio access network (UTRAN) cell; and Receive radio link failure (RLF) report information.

32. The method according to claim 31, wherein in response to the mobility command message including a voice fallback indication, the RLF report information includes an indicator for indicating that the handover procedure is used for the voice fallback operation.

33. The method according to claim 31, wherein the RLF report information includes an indicator for indicating one of the following: No E-UTRAN cell is found for the voice fallback operation; and No UTRAN cell is found for the voice fallback operation.

34. The method according to claim 31, wherein the RLF report information is included in a message, and the message is forwarded from the base station BS serving the UE.

35. The method according to claim 34, wherein the message is transmitted from the BS serving the UE to the access and mobility management function AMF, and then forwarded by the AMF.

36. The method according to claim 31, wherein the RLF report information includes the ID of the target cell of the UE.

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