Device and method for handling a recovery of a radio resource control connection of a non-terrestrial network

Abstract

A communication device for handling the recovery of a Radio Resource Control (RRC) connection of a non-terrestrial network (NTN) comprises one or more storage devices and one or more processing circuits. The one or more storage devices store commands, and the one or more processing circuits are configured to execute a command (302) for establishing an RRC connection with a first cell of the NTN; a command (304) for receiving a cooperating cell configuration message from the first cell, wherein the cooperating cell configuration message includes one or more cooperating cell configurations associated with one or more cells of the NTN; a command (306) for initiating an RRC connection recovery procedure after receiving the cooperating cell configuration message; a command (308) for selecting a second cell for the RRC connection recovery procedure when the RRC connection recovery procedure is initiated; and a command (310) for performing the RRC connection recovery procedure with the second cell.

Description

Technology Field

[0001] The present invention relates to a device and method used in a wireless communication system, and in particular to a device and method for handling the recovery of a wireless resource control connection of a non-terrestrial network. Background Technology

[0002] Long-term evolution (LTE) systems supporting 3rd Generation Partnership Project (3GPP) Rel-8 and / or 3GPP Rel-9 standards were developed by 3GPP as a successor to the Universal Mobile Telecommunication System (UMTS) to further enhance the performance of UMTS in order to meet the growing demands of users. LTE systems include new radio interfaces and new radio network architectures that provide high data rates, low latency, packet optimization, and improved system capacity and coverage.

[0003] As the name suggests, LTE-A (LTE-advanced) systems are the product of the evolution of LTE systems. LTE-A systems aim for faster transitions between power states, improve performance at the coverage edge of evolved Node-B (eNB), increase peak data rates and throughput, and include advanced technologies such as Carrier Aggregation (CA), Coordinated Multipoint (CoMP) Transceive, Uplink (UL) Multiple-Input Multiple-Output (UL-MIMO), and Licensed-Assisted Access (LAA) (e.g., LTE usage).

[0004] To further enhance LTE-A systems, the next-generation radio access network (NG-RAN) was developed. The NG-RAN includes one or more next-generation Node-Bs (gNBs) and features a wider operating band, different numerologies for different frequency ranges, massive MIMO, and advanced channel coding.

[0005] New advancements in NG (e.g., 5th generation (5G) NR (new radio)) standards create opportunities to integrate non-terrestrial networks (NTN) into a globally interoperable and standardized wireless experience. NTNs can meet connection requests anytime, anywhere by providing wide coverage and ensuring service availability, continuity, and scalability. However, the distances between gNBs or gNB cells in NTNs are long. In the event of a radio resource control (RRC) connection failure, it is difficult for communication devices to switch from the source gNB / cell to the target gNB / cell (e.g., from one gNB cell to another gNB cell, or from one gNB cell to another gNB cell). Therefore, improving the performance of recovering RRC connections in NTNs is a critical issue that needs to be addressed.

[0006] With this in mind, the present invention aims to provide a communication device and a method for handling the recovery of a wireless resource control (RRC) connection of a non-terrestrial network (NTN) in order to solve the aforementioned problem.

[0007] This is achieved by a communication device for handling the recovery of the NTN's RRC connection according to the independent clause. The dependent clause concerns corresponding further development and improvement.

[0008] As can be more clearly understood from the detailed description below, the claimed communication device comprises one or more storage devices; and one or more processing circuits coupled to the one or more storage devices, wherein the one or more storage devices store instructions; and the one or more processing circuits are configured to execute instructions for establishing an RRC connection with a first cell of the NTN; instructions for receiving a collaborator cell configuration message from the first cell, wherein the collaborator cell configuration message includes one or more collaborator cell configurations associated with one or more cells of the NTN; instructions for initiating an RRC connection recovery procedure after receiving the collaborator cell configuration message; instructions for selecting a second cell for the RRC connection recovery procedure when the RRC connection recovery procedure is initiated; and instructions (310) for performing the RRC connection recovery procedure with the second cell. Brief explanation of the drawing

[0009] The present invention will be further explained below with reference to the following drawings. FIG. 1 is a schematic diagram of a wireless communication system according to an example of the present invention. FIG. 2 is a schematic diagram of a communication device according to an example of the present invention. Figure 3 is a flowchart of a process according to an embodiment of the present invention. FIG. 4 is a flowchart of a process according to an example of the present invention. FIG. 5 is a flowchart of a process according to an example of the present invention. FIG. 6 is a flowchart of a process according to an example of the present invention. FIG. 7 is a flowchart of a process according to an example of the present invention. FIG. 8 is a flowchart of a process according to an example of the present invention. FIG. 9 is a flowchart of a process according to an example of the present invention. FIG. 10 is a flowchart of a process according to an example of the present invention. FIG. 11 is a flowchart of a process according to an example of the present invention. FIG. 12 is a flowchart of a process according to an example of the present invention. FIG. 13 is a flowchart of a process according to an example of the present invention. FIG. 14 is a flowchart of a process according to an example of the present invention. FIG. 15 is a flowchart of a process according to an example of the present invention. FIG. 16 is a flowchart of a process according to an example of the present invention. FIG. 17 is a flowchart of a process according to an example of the present invention. FIG. 18 is a flowchart of a process according to an example of the present invention. Specific details for implementing the invention

[0010] FIG. 1 is a schematic diagram of a wireless communication system (10) according to an example of the present invention. The wireless communication system (10) is simply composed of a network (12) and a plurality of communication devices (14). The wireless communication system (10) may support time-division duplexing (TDD) mode, frequency-division duplexing (FDD) mode, TDD-FDD joint operation mode, non-terrestrial network (NTN) mode, or licensed-assisted access (LAA) mode. That is, the network (12) and the communication devices (14) may communicate with each other via FDD carrier(s), TDD carrier(s), licensed carrier(s) (licensed serving cell(s)) and / or unlicensed carrier(s) (unlicensed serving cell(s)). Additionally, the wireless communication system (10) can support carrier aggregation (CA). That is, the network (12) and the communication device (14) can communicate with each other through a plurality of serving cells (e.g., a plurality of serving carriers) comprising a primary cell (e.g., a primary component carrier) and one or more secondary cells (e.g., a secondary component carrier).

[0011] In FIG. 1, the network (12) and the communication device (14) are used simply to describe the configuration of the wireless communication system (10). Substantially, the network (12) may be a universal terrestrial radio access network (UTRAN) comprising at least one Node-B (NB) in a universal mobile communication system (UMTS). In one example, the network (12) may be an evolved UTRAN (E-UTRAN) comprising at least one relay node and / or at least one evolved NB (eNB) in a long term evolution (LTE) system, an LTE-A (LTE-Advanced) system, an evolution of LTE-A, etc. In one example, the network (12) may be a next-generation radio access network (NG-RAN) comprising at least one next-generation Node-B (gNB) or at least one fifth-generation (5G) base station (BS). In one example, the gNB or 5G BS of the network (12) may include an NTN gateway and an NTN payload. In one example, the network (12) may be any BS that follows a specific communication standard to communicate with a communication device (14).

[0012] New Radio (NR) is a standard defined to provide a unified air interface with better performance in 5G systems (or 5G networks). gNBs are deployed to implement 5G systems that support advanced features such as enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLC), and massive Machine Type Communications (mMTC). eMBB provides broadband services with wider bandwidth and low to moderate latency. URLLC provides characteristics of higher reliability and low latency for applications (e.g., end-to-end communication). Examples of applications include the Industrial Internet, smart grids, infrastructure protection, remote surgery, and intelligent transportation systems (ITS). mMTC can support the Internet of Things (IoT) in 5G systems, which include billions of connected devices and / or sensors.

[0013] Additionally, the network (12) may include at least one of UTRAN / E-UTRAN / NG-RAN and a core network, wherein the core network may include network entities such as MME (Mobility Management Entity), S-GW (Serving Gateway), P-GW (Packet Data Network (PDN) Gateway), SON (Self-Organizing Networks) server and / or RNC (Radio Network Controller), AMF (Access and Mobility Management Function), SMF (Session Management Function), UPF (User, Plane Function), AUSF (Authentication Server Function), etc. In one example, after the network (12) receives information transmitted by a communication device (14), the information may be processed only by UTRAN / E-UTRAN / NG-RAN, and a decision corresponding to the information is made in UTRAN / E-UTRAN / NG-RAN. In one example, UTRAN / E-UTRAN / NG-RAN can forward information to the core network, and a decision corresponding to the information is made in the core network after the core network processes the information. In one example, information can be processed by both UTRAN / E-UTRAN / NG-RAN and the core network, and a decision is made after coordination and / or cooperation is performed by UTRAN / E-UTRAN / NG-RAN and the core network.

[0014] The communication device (14) may be user equipment (UE), VSAT (Very Small Aperture Terminal), low-cost devices (e.g., machine type communication (MTC) devices), device-to-device (D2D) communication devices, narrow-band internet of things (IoT, NB-IoT), mobile phones, laptops, tablet computers, e-books, portable computer systems, or a combination thereof. Additionally, the network (12) and the communication device (14) may be viewed as either a transmitter or a receiver depending on the direction (i.e., the direction of transmission). For example, in the case of an uplink (UL), the communication device (14) is a transmitter and the network (12) is a receiver, and in the case of a downlink (DL), the network (12) is a transmitter and the communication device (14) is a receiver.

[0015] FIG. 2 is a schematic diagram of a communication device (20) according to an example of the present invention. The communication device (20) may be the communication device (14) or network (12) shown in FIG. 1, but is not limited thereto. The communication device (20) may include at least one processing circuit (200), such as a microprocessor or an ASIC (Application Specific Integrated Circuit), at least one storage device (210), and at least one communication interface device (220). The at least one storage device (210) may be any data storage device capable of storing program code (214) accessed and executed by the at least one processing circuit (200). Examples of at least one storage device (210) include, but are not limited to, a subscriber identity module (SIM), read-only memory (ROM), flash memory, random-access memory (RAM), CD-ROM (Compact Disc Read-Only Memory), digital versatile disc-ROM (DVD-ROM), BD-ROM (Blu-ray Disc-ROM), magnetic tape, hard disk, optical data storage device, non-volatile storage device, computer-readable non-transient media (e.g., tangible media). At least one communication interface device (220) is preferably at least one transceiver and is used to transmit and receive signals (e.g., data, messages and / or packets) according to the processing result of at least one processing circuit (200).

[0016] FIG. 3 is a flowchart of a process (30) according to an example of the present invention. The process (30)

[0017] It can be used in a communication device (e.g., the communication device (20) of FIG. 2) to handle the recovery of a radio resource control (RRC) connection of a non-terrestrial network (NTN). The process (30) can be compiled into program code (214) and includes the following steps:

[0018] Step 300: Start.

[0019] Step 302: Establish an RRC connection with the first cell of the NTN.

[0020] Step 304: Receive a collaborator cell configuration message from the first cell, wherein the collaborator cell configuration message includes at least one collaborator cell configuration associated with at least one cell of the NTN.

[0021] Step 306: After receiving the collaborator cell configuration message, initiate the RRC connection recovery procedure.

[0022] Step 308: When initiating the RRC connection recovery procedure, select the second cell for the RRC connection recovery procedure.

[0023] Step 310: Perform the RRC connection recovery procedure with the second cell.

[0024] Step 314: Exit.

[0025] According to process (30), the communication device (20) establishes an RRC connection with the first cell of the NTN. The communication device (20) triggers a state transition to the connection mode and enters the connection mode (i.e., the access stratum of the mobile device (20) is in the RRC_CONNECTED state). The communication device (20) receives a cooperating cell configuration message from the first cell. The cooperating cell configuration message includes at least one cooperating cell configuration associated with at least one cell of the NTN (e.g., at least one cooperating cell). The cooperating cell is an NTN cell associated with one of the at least one cooperating cell configurations. After receiving the cooperating cell configuration message, the communication device (20) initiates an RRC connection recovery procedure. When initiating the RRC connection recovery procedure (e.g., when initiating), the communication device (20) selects a second cell for the RRC connection recovery procedure. The communication device (20) performs the RRC connection recovery procedure with the second cell.

[0026] The implementation of the process (30) is not limited to the above description. To implement the process (30), the following examples may be applied.

[0027] In one example, the first cell and the second cell are configured (e.g., serving) by the same network entity (e.g., gNB). In one example, the first cell and the second cell are configured by different network entities (e.g., different gNBs).

[0028] In one example, at least one cell of the NTN receives a cooperator cell request message from the first cell and transmits a cooperator cell response message to the first cell in response to the cooperator cell request message. Then, the first cell transmits a cooperator cell configuration message containing information included in the cooperator cell response message to a communication device (20).

[0029] In one example, a collaborator cell request message includes required information and optional information. The required information includes the IDentity of the first cell, the ID of the communication device (20) (e.g., the cell radio network temporary identifier (C-RNTI) of the communication device (20), security verification information for the communication device (20) (e.g., Message Authentication Code - Integrity (MAC-I) or short MAC-I), and at least one of the access stratum (AS) security configurations configured and applied by the first cell. The optional information includes at least one SRB configuration (e.g., SRB1 and / or SRB2) and / or at least one DRB configuration (e.g., default DRB configuration).

[0030] In one example, the cooperator cell response message includes at least one of cell access information for at least one cell of the NTN (e.g., random access resource configuration information for the communication device (20) to perform random access with the cooperator cell, system information associated with the cooperator cell) or a move-in ID of the communication device (20) (e.g., an identity to be used in the cooperator cell to identify the communication device (20)).

[0031] In one example, at least one cell of the NTN receives a handover request message from the first cell and sends a handover acknowledgment (ACK) message to the first cell in response to the handover request message. Upon receiving the handover ACK message, the first cell generates at least one handover configuration and transmits at least one handover configuration to a communication device (20). In one example, the communication device (20) is configured with the handover configuration among the at least one handover configuration.

[0032] There are various alternatives for performing the RRC connection recovery procedure. In one example, the communication device (20) performs an RRC connection re-establishment procedure as an RRC connection recovery procedure. Specifically, if the communication device (20) is configured with a cooperating cell configuration among at least one cooperating cell configuration, the communication device (20) performs an RRC connection re-establishment procedure with the second cell according to the cooperating cell configuration associated with the second cell. In one example, the communication device (20) performs an RRC connection re-establishment procedure (e.g., handover or conditional handover) as an RRC connection recovery procedure. In detail, if the communication device (20) is configured with a handover configuration among at least one handover configuration, the communication device (20) performs an RRC connection re-establishment procedure with the second cell according to the handover configuration associated with the second cell. In one example, if the second cell is not associated with at least one collaborator cell configuration associated with at least one cell of the NTN (e.g., a cell that is not at least one cell of the NTN) and the communication device is not configured with a valid handover configuration associated with the second cell, the communication device (20) performs an RRC connection re-establishment procedure with the second cell according to system information associated with the second cell. In one example, the communication device (20) performs a random access procedure with the second cell. In one example, the communication device (20) sends an RRC connection recovery request message to the second cell during the random access procedure.

[0033] In one example, the collaborator cell configuration associated with the second cell is a collaborator cell configuration among at least one collaborator cell configuration included in the collaborator cell configuration message. In one example, the collaborator cell configuration is a handover configuration, and the handover configuration includes "ReconfigurationWithSync" associated with the NTN cell (e.g., at least one cell of the NTN). In one example, at least one handover configuration includes at least one execution condition associated with at least one cell of the NTN. That is, at least one execution condition is each associated with at least one handover configuration. In one example, the RRC connection recovery request message includes at least one of the ID of the communication device (20) to be applied in the second cell, the ID of the first cell, or the ID to be used by the second cell to perform authentication of the communication device (20). In one example, the random access procedure is a two-stage random access procedure or a four-stage random access procedure.

[0034] In one example, if the communication device (20) fails to select a second cell, it enters from connection mode to idle mode (i.e., the access layer portion of the communication device (20) is in the RRC_IDLE state).

[0035] In one example, a collaborator cell configuration message includes a validity time associated with at least one collaborator cell configuration associated with at least one cell of the NTN. The validity time may be indicated by a start time, a period including a start time and a time duration, a period including a start time and an end time, a period including a start time and a timer, or a timer. A collaborator cell configuration associated with at least one cell of the NTN is considered valid within the validity time.

[0036] In one example, a collaborator cell configuration among at least one collaborator cell configuration includes the validity period during which the collaborator cell configuration is considered valid within the validity period, or the validity area during which the collaborator cell configuration is considered valid within the validity area. The validity period may be a period including a start time and a duration, a period including a start time and an end time, a period including a start time and a timer, or indicated by a timer. A collaborator cell configuration associated with at least one cell of the NTN is considered valid within the validity period. The validity area may be indicated by a first cell and may be included in the collaborator cell configuration message by at least one ID associated with at least one geographic area, at least one ID associated with at least one NTN tracking area, at least one ID associated with at least one N cell (e.g., at least one cell of the NTN), or at least one ID associated with at least one ID of at least one NTN cell (e.g., a list or set of at least one cell of the NTN). A mapping of at least one ID with at least one geographical area is configured by the NTN and provided (e.g., transmitted) to a communication device (20) via an NTN cell. A collaborator cell configuration associated with at least one cell of the NTN is considered valid in the valid area.

[0037] In one example, the cooperating cell configuration of at least one cooperating cell configuration includes at least one cell ID associated with a cell (e.g., a second cell) of at least one cell of the NTN, at least one frequency associated with a cell of at least one cell of the NTN, at least one frequency associated with at least one reference signal of a cell of at least one cell of the NTN, or at least one of information for accessing a cell of at least one cell of the NTN. In one example, the information for accessing a cell includes at least one configuration of a random access resource associated with a cell for the communication device (20) to perform a random access procedure with the cell.

[0038] In one example, at least one collaborator cell configuration includes at least one synchronization signal block (SSB)-based radio resource management (RRM) measurement timing configuration (SMTC) associated with a frequency associated with the cell, an ID of a communication device (20) to be applied to the cell, or at least one ID to be used by the cell to perform authentication for the communication device (20).

[0039] In one example, the communication device (20) can select a second cell by performing at least one evaluation (or by performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the first cell. In one example, the communication device (20) selects a second cell by performing at least one evaluation (or by performing at least one evaluation and at least one measurement) according to at least one cooperating cell configuration associated with at least one cell of the NTN included in the cooperating cell configuration message. In one example, the communication device (20) selects a second cell by performing at least one evaluation (or by performing at least one evaluation and at least one measurement) according to a handover configuration among at least one handover configuration.

[0040] Additionally, there is another alternative for selecting a second cell for the RRC connection recovery procedure. In one example, the communication device (20) performs at least one evaluation (or performs at least one evaluation and at least one measurement) according to at least one collaborator cell configuration associated with at least one cell of the NTN, where the communication device is configured with at least one collaborator cell configuration associated with at least one cell of the NTN and the communication device is configured with at least one handover configuration among at least one handover configuration. In one example, the communication device (20) performs at least one evaluation (or performs at least one evaluation and at least one measurement) according to at least one handover configuration among at least one handover configuration, where the communication device is configured with at least one collaborator cell configuration associated with at least one cell of the NTN and the communication device is configured with at least one handover configuration among at least one handover configuration and the handover configuration is considered valid.

[0041] In one example, the communication device (20) initiates an RRC connection recovery procedure after failing to perform a handover according to the handover configuration. In one example, the communication device (20) initiates an RRC connection recovery procedure before any one of at least one execution condition is satisfied.

[0042] FIG. 4 is a flowchart of a process (40) according to an example of the present invention. The process (40) is performed by a communication device (4000) (e.g., the communication device (20) of FIG. 2), a cell (4002) (e.g., the first cell in process (30)), and a cell (4004) (e.g., the second cell in process (30)). The cells (4002, 4004) are configured by a gNB (4006), and the cell (4002) is a serving cell of the communication device (4000). First, the communication device (4000) in connected mode transmits an RRC re-establishment request message to the cell (4004) (step 400). If the UE context of the communication device (4000) is not available in the cell (4004), the cell (4004) sends a UE context request message to the cell (4002) (step 402) and receives a UE context response message from the cell (4002) (step 404). If the UE context of the communication device (4000) is available in the cell (4004), the cell (4004) sends an RRC re-establishment message to the communication device (4000) (step 406) to resume AS security and wireless bearer for the communication device (4000). The communication device (4000) sends an RRC re-establishment completion message to the cell (4004) (step 408). Accordingly, the communication device (4000) transmits UL data to the cell (4004) when the UL resource is instructed by the cell (4004) for UL transmission (step 410), and can receive an RRC reconstruction message from the cell (4004) (step 412). The cell (4002) and the cell (4004) perform a path switch procedure that may include a core network entity (not shown) (step 414).

[0043] In FIG. 4, cell (4002) and cell (4004) are configured by the same gNB. Steps 402 and 404 are intra-gNB actions that result in a short delay. In one example, after cell (4004) authenticates the communication device (4000), it retrieves the UE context of the communication device (4000) stored in the gNB (4006).

[0044] FIG. 5 is a flowchart of a process (50) according to an example of the present invention. The process (50) is performed by a communication device (5000) (e.g., the communication device (20) of FIG. 2), a cell (5002) (e.g., the first cell in process (30)), and a cell (5004) (e.g., the second cell in process (30)). The cell (5002) is configured by a gNB (5006) and is a serving cell of the communication device (5000). The cell (5004) is configured by a gNB (5008). First, the cell (5002) transmits UE information of the communication device (5000) to the cell (5004) (step 500).

[0045] The communication device (5000) in connection mode transmits an RRC re-establishment request message to the cell (5004) (step 506). The cell (5004) transmits an RRC re-establishment message to the communication device (5000) (step 508). The RRC re-establishment message is used to re-establish AS security and establish at least one signaling radio bearer (SRB), and may additionally be used to establish at least one data radio bearer (DRB). The communication device (5000) transmits an RRC re-establishment completion message to the cell (5004) (step 510). The cell (5002) and the cell (5004) may perform a route switching procedure (step 512) that may include a core network entity (not shown). Before performing the path switching procedure between cell (5002) and cell (5004), if cell (5002) decides to modify (e.g., update) UE information (step 502), cell (5002) may transmit the modified (e.g., updated) UE information to cell (5004) (step 504). When UL resources for UL transmission are indicated by cell (4004), the communication device (5000) transmits UL data to cell (5004) after transmitting an RRC re-establishment completion message (step 514) and may receive an RRC reconfiguration message from cell (5004) (step 506).

[0046] In FIG. 5, cell (5002) and cell (5004) are configured by different gNBs. Cell (5002) transmits UE information to cell (5004) in advance. In one example, when cell (5004) is selected by a communication device (5000) and cell (5004) receives an RRC re-establishment request message from the communication device (5000), cell (5004) activates AS security according to the UE information and establishes an RRC connection to the communication device (5000).

[0047] In FIG. 5, cell (5002) and cell (5004) perform a route switching procedure that may include a core network entity (not shown) to switch connections to a communication device (5000) (e.g., packet data unit (PDU) and / or packet data network (PDN) connections). In one example, during the route switching procedure, cell (5004) informs the core network entity (not shown) to communicate (e.g., transmit or receive) packets to the communication device (5000) (e.g., user plane packet, packet data unit) with cell (5004) (e.g., to or from cell (5004)) and stops communicating packets to the communication device (5000) with cell (5002).

[0048] FIG. 6 is a flowchart of a process (60) according to an example of the present invention. The process (60) is performed by a communication device (6000) (e.g., the communication device (20) of FIG. 2), a cell (6002) (e.g., the first cell in process (30)), and a cell (6004) (e.g., the second cell in process (30)). The cell (6002) is configured by a gNB (6006) and is a serving cell of the communication device (6000). The cell (6004) is configured by a gNB (6008). Steps 600-610 may refer to steps 500-510 in FIG. 5, which are not described herein for brevity. Cell (6004) may send a notification to Cell (6002) after successfully receiving an RRC re-establishment request message from the communication device (6000) (step 606), after successfully transmitting an RRC re-establishment message to the communication device (6000) (step 608), or after successfully receiving an RRC re-establishment completion message from the communication device (6000) (step 610) (step 612). Before receiving the notification from Cell (6004) (step 602), Cell (6002) may transmit modified UE information to Cell (6004) (step 604). After receiving the notification transmitted from Cell (6004) (step 612), Cell (6002) stops modifying (e.g. updating) the UE information and releases the UE information in response to the notification (step 614). When the communication device (6000) is instructed by the cell (6004) to send an RRC re-establishment completion message (step 616), it can send UL data to the cell (6004) and receive an RRC re-establishment message from the cell (6004) (step 618). The cell (6002) and the cell (6004) perform a path switching procedure (step 620) that may include a core network entity (not shown).

[0049] In FIG. 6, cell (6002) and cell (6004) are configured by different gNBs. Cell (6002) transmits the UE to cell (6004) in advance. In one example, when cell (6004) is selected by a communication device (6000) and cell (6004) receives an RRC re-establishment request message from the communication device (6000), cell (6004) activates AS security according to the UE information and establishes an RRC connection to the communication device (6000). In one example, cell (6004) receives the RRC re-establishment request message and, after successfully authenticating the communication device (6000), transmits a notification to cell (6002) to stop modifying / transmitting the UE information.

[0050] In FIG. 6, cell (6002) and cell (6004) perform a route switching procedure to switch connections (e.g., PDU sessions and / or PDN connections) to a communication device (6000). In one example, during the route switching procedure, cell (6004) informs a core network entity (not shown) to communicate (e.g., transmit or receive) packets (e.g., user plane packets) to the communication device (6000) with cell (6004) (e.g., to or from cell (6004)) and stops communicating packets to the communication device (6000) with cell (6002).

[0051] FIG. 7 is a flowchart of a process (70) according to an example of the present invention. The process (70) may be performed by a communication device (7000) (e.g., the communication device (20) of FIG. 2), a cell (7002) (e.g., the first cell in process (30)), and a cell (7004) (e.g., at least one cell of NTN in process (30)), and may be further performed by a cell (7006) (e.g., at least one cell of NTN in process (30). The cell (7002) is an NTN serving cell of the communication device (7000). First, the communication device (7000) establishes an RRC connection (successfully) with the cell (7002) (step 700). Cell (7002) can negotiate with Cell (7004) (or Cell (7004) and Cell (7006)) by sending a collaborator cell request message to Cell (7004) (step 702) and sending a collaborator cell request message to Cell (7006) (step 704). Cell (7004) and Cell (7006) each send one collaborator cell response message to Cell (7002) in response to the collaborator cell request message (steps 706 and 708, respectively). After receiving a collaborator cell response message(s) from cell (7004) (or cell (7004) and cell (7006)), cell (7002) transmits a collaborator cell configuration message to the communication device (7000) (step 710). The communication device (7000) initiates an RRC connection recovery procedure with cell (7002) (step 712).

[0052] In one example, the cell (7002) includes SRB0 and SRB1. In one example, the cell (7002) further includes at least one other SRB or at least one DRB. In one example, the cell (7002) determines the collaborator cell(s) (e.g., cell (7004) and cell (7006)) for the communication device (7000) based on, for example, network deployment, network policy, or UE information or measurement report(s) received from the communication device (7000), and performs an RRC connection recovery procedure.

[0053] In one example, cell (7002) generates a cooperator cell configuration message containing the cooperator cell configurations of cell (7004) and cell (7006) according to a cooperator cell response message. In one example, cell (7002) modifies the cooperator cell configurations of cell (7004) and cell (7006) (e.g., adding, changing, or removing all or part of the contents of the cooperator cell configurations) by transmitting another cooperator cell configuration message to a communication device (7000).

[0054] FIG. 8 is a flowchart of a process (80) according to an example of the present invention. The process (80) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (7000) of FIG. 7). The process (80) includes the following steps:

[0055] Step 800: Start.

[0056] Step 802: Initiate the RRC connection recovery procedure.

[0057] Step 804: Does the communication device select a cooperating cell (e.g., one of cell (7004) and cell (7006) of FIG. 7) as a suitable cell (a cell where the communication device can stay, e.g., a second cell of process (30))? If Yes, perform Step 806. If No, perform Step 808.

[0058] Step 806: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with the collaborator cell according to the collaborator cell configuration associated with the collaborator cell, and perform Step 816.

[0059] Step 808: Select the appropriate cell.

[0060] Step 810: Does the communication device successfully select a suitable cell? If Yes, perform Step 812. If No, perform Step 814.

[0061] Step 812: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell, and perform Step 816.

[0062] Step 814: Enter idle mode from connected mode.

[0063] Step 816: Exit.

[0064] In step 802, if the communication device is configured with at least one cooperating cell configuration associated with at least one cell of the NTN and at least one cooperating cell configuration is considered valid, the communication device performs an evaluation of a suitable cell (a cell where the communication device can stay, e.g., a second cell in process (30)) according to the at least one cooperating cell configuration and selects a suitable cell (e.g., performs an evaluation of only the suitable cell among the cells in which the cell ID, the cell frequency, or the frequency of the cell reference signal(s) is included in one of the at least one cooperating cell configurations).

[0065] Before performing a suitable cell evaluation, the communication device can perform cell search and measurement according to at least one collaborator cell configuration.

[0066] If a suitable cell is selected in step 802 and the suitable cell is a cooperator cell, the process proceeds to step 806. In step 806, the communication device initiates an RRC re-establishment procedure as an RRC connection recovery procedure with the suitable cell, depending on the cooperator cell configuration associated with the suitable cell. The RRC re-establishment procedure may include a random access procedure between the communication device and the suitable cell.

[0067] In step 804, the communication device determines whether a suitable cell is one of the cooperating cells based on the cooperating cell configuration(s).

[0068] If a suitable cell is not selected in step 802, step 808 is performed. In step 808, the communication device selects a suitable cell. The selection of a suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)), or according to a stored cell selection configuration configured by the communication device's serving cell or a previous serving cell.

[0069] In step 810, if a suitable cell is found according to the process in step 808, the communication device performs step 812. Otherwise, the communication device performs step 814. In step 812, the communication device initiates an RRC re-establishment procedure as an RRC connection recovery procedure with the suitable cell. The RRC re-establishment procedure may include a random access procedure between the communication device and the suitable cell. Information required to access the suitable cell may be obtained from system information associated with the suitable cell obtained by the communication device (e.g., the communication device may obtain system information of the suitable cell from system information broadcast by the suitable cell), or may be configured from a previous serving cell and stored by the communication device. In step 814, the communication device enters from connection mode to idle mode. An idle mode procedure may be initiated by the communication device accordingly.

[0070] In process (80), if a suitable cell is successfully selected and the suitable cell is a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the cooperator cell according to the cooperator cell configuration associated with the cooperator cell. If a suitable cell is successfully selected and the suitable cell is not a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to, for example, system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0071] FIG. 9 is a flowchart of a process (90) according to an example of the present invention. The process (90) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (7000) of FIG. 7). The process (90) includes the following steps:

[0072] Step 900: Start.

[0073] Step 902: Initiate the RRC connection recovery procedure.

[0074] Step 904: Select a suitable cell (a cell where a communication device can stay, e.g., a second cell in process (30)).

[0075] Step 906: Does the communication device successfully select a suitable cell? If Yes, perform Step 910. If No, perform Step 908.

[0076] Step 908: Enter idle mode from connected mode and perform Step 916.

[0077] Step 910: Is the suitable cell a collaborator cell (e.g., one of cell (7004) and cell (7006) in FIG. 7)? If Yes, perform Step 912. If No, perform Step 914.

[0078] Step 912: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell, and perform Step 916.

[0079] Step 914: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell.

[0080] Step 916: Exit.

[0081] In step 904, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the communication device's serving cell or a previous serving cell.

[0082] In step 912, an RRC re-establishment procedure is initiated as an RRC connection recovery procedure with a suitable cell according to the collaborator cell configuration associated with the suitable cell. The RRC re-establishment procedure may include a random access procedure between the communication device and the suitable cell.

[0083] In step 914, the RRC re-establishment procedure may include a random access procedure between the communication device and the suitable cell. Information required to access the suitable cell may be obtained from system information associated with the suitable cell obtained by the communication device (e.g., the communication device may obtain system information of the suitable cell from system information broadcast by the suitable cell), or may be configured from a previous serving cell and stored by the communication device.

[0084] In process (90), if a suitable cell is successfully selected and the suitable cell is a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the cooperator cell according to the cooperator cell configuration associated with the cooperator cell. If a suitable cell is successfully selected and the suitable cell is not a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to, for example, system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0085] FIG. 10 is a flowchart of a process (100) according to an example of the present invention. The process (100) is performed by a communication device (10000) (e.g., the communication device (20) of FIG. 2), a cell (10002) (e.g., the first cell in process (30)), and a cell (10004) (e.g., at least one cell of NTN in process (30)), and may be further performed by a cell (10006) (e.g., at least one cell of NTN in process (30). The cell (10002) is an NTN serving cell of the communication device (10000). First, the communication device (7000) establishes an RRC connection (successfully) with the cell (10002) (step 1000). Cell (10002) transmits a cooperating cell request message to Cell (10004) (step 1002) and negotiates with Cell (10004). Cell (10004) transmits a cooperating cell response message to Cell (10002) (step 1004). Cell (10002) transmits a cooperating cell configuration message to a communication device (10000) (step 1006). The communication device (10000) stores at least one cooperating cell configuration included in the cooperating cell configuration message. Cell (10002) determines a handover of the communication device (10000) (step 1008) and transmits a handover request message to Cell (10006) to negotiate with Cell (10006) (step 1010). Cell (10002) receives a handover request ACK message from Cell (10006) (step 1012) and transmits an RRC reconfiguration message associated with Cell (10006) to the communication device (10000) (step 1014). The communication device (10000) performs a handover procedure according to the RRC reconfiguration message associated with Cell (10006).If the communication device (10000) determines that it has failed to complete the handover procedure for a handover from cell (10002) to cell (10006) (e.g., if the communication device (10000) fails to detect cell (10006), fails to perform a random access procedure with cell (10006), or fails to transmit an RRC reconfiguration completion message to cell (10006) (step 1016)), the communication device (10000) initiates an RRC connection recovery procedure (step 1020).

[0086] In one example, the cell (10002) includes SRB0 and SRB1. In one example, the cell (10002) further includes at least one other SRB or at least one DRB. In one example, the cell (10002) determines a cooperating cell(s) (e.g., cell (10004)) for a communication device (10000) based on, for example, network deployment, network policy, or UE information or measurement report(s) received from the communication device (10000), and performs an RRC connection recovery procedure. In one example, the cell (10002) generates a cooperating cell configuration message containing the cooperating cell configuration of the cell (10004) based on a cooperating cell response message.

[0087] In one example, the cell (10002) modifies the cooperator cell configuration of the cell (10004) by transmitting another cooperator cell configuration message to the communication device (10000) (e.g., adding, changing, or removing all or part of the contents of the cooperator cell configuration). In one example, the cell (10002) determines the handover of the communication device (10000) and determines the handover cell(s) for the communication device (10000) based on measurement report(s) received from the communication device (10000), orbit information associated with the first cell and / or cell (10006), or service time and / or area information associated with the first cell and / or cell (10006). (The cell of the NTN is associated with at least one handover configuration included in the RRC reconstruction message associated with the cell (10006) of step 1014, e.g., cell (10006). In one example, the RRC reconfiguration message is a deover configuration consisting of "ReconfigurationWithSync".

[0088] In FIG. 10, cell (10002) can send a collaborator cell request message to cell (10004) and send a collaborator cell request message to other collaborator cell(s), and cell (10004) and other collaborator cell(s) can each send one collaborator cell response message to cell (10002) in response to the collaborator cell request message. Cell (10002) sends a handover request message to cell (10006) and other handover cell(s), and cell (10006) and other handover cell(s) each send one handover request ACK message to cell (10002) in response to the handover request message (not shown). Thus, the RRC reconfiguration message may include the handover configuration of cell (10006) and other handover cell(s). In one example, other collaborator cell(s) and other handover cell(s) are the same cell(s). In one example, the other collaborator cell(s) and the other handover cell(s) are different cells.

[0089] FIG. 11 is a flowchart of a process (110) according to an example of the present invention. The process (110) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (10000) of FIG. 10). The process (110) includes the following steps:

[0090] Step 1100: Start.

[0091] Step 1102: Initiate the RRC connection recovery procedure.

[0092] Step 1104: Does the communication device select the collaborator cell as a suitable cell (a cell where the communication device can stay, e.g., the second cell 30 of the process)? If Yes, perform Step 1106. If No, perform Step 1112.

[0093] Step 1106: Is the suitable cell selected by the communication device a handover cell (e.g., cell (10006) of FIG. 10 and one of the other handover cell(s))? If Yes, perform Step 1108. If No, perform Step 1110.

[0094] Step 1108: Perform an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the appropriate cell according to the handover configuration associated with the appropriate cell. After successfully performing Step 1108, the communication device performs Step 1120.

[0095] Step 1110: Perform an RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell. After successfully performing Step 1110, the communication device performs Step 1120.

[0096] Step 1112: Select the appropriate cell.

[0097] Step 1114: Does the communication device successfully select a suitable cell? If Yes, perform Step 1116. If No, perform Step 1118.

[0098] Step 1116: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with a suitable cell. After successfully performing Step 1116, the communication device performs Step 1120.

[0099] Step 1118: Enter idle mode from connected mode.

[0100] Step 1120: Exit.

[0101] In step 1102, if the communication device is configured with at least one cooperating cell configuration associated with at least one cell of the NTN and at least one cooperating cell configuration is deemed valid, it is configured with at least one handover configuration associated with at least one cell of the NTN and at least one handover configuration is deemed valid. The communication device performs a suitable cell evaluation based on the at least one cooperating cell configuration and selects a suitable cell (e.g., the cell ID, the cell frequency, or the frequency of the cell's reference signal(s) is included in one of the at least one cooperating cell configuration).

[0102] In step 1104, the communication device determines whether the suitable cell is one of the cooperating cell(s) (e.g., cell (10004) of FIG. 10 and other cooperating cell(s)) depending on whether the suitable cell is associated with at least one cooperating cell configuration.

[0103] In step 1106, the communication device determines whether the suitable cell is a handover cell.

[0104] In step 1112, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the serving cell or a previous serving cell.

[0105] In step 1116, the RRC re-establishment procedure may include a random access procedure between the communication device and the suitable cell. Information required to access the suitable cell may be obtained from system information associated with the suitable cell obtained by the communication device (e.g., the communication device may obtain system information of the suitable cell from system information broadcast by the suitable cell), or may be configured from a previous serving cell and stored by the communication device.

[0106] In process (110),

[0107] (a) If a suitable cell is successfully selected and the suitable cell is a handover cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0108] (b) If a suitable cell is successfully selected and the suitable cell is a cooperator cell rather than a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to the cooperator cell configuration associated with the cooperator cell;

[0109] (c) If a suitable cell is successfully selected and the suitable cell is neither a handover cell nor a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0110] FIG. 12 is a flowchart of a process (120) according to an example of the present invention. The process (120) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (10000) of FIG. 10). The process (120) includes the following steps:

[0111] Step 1200: Start.

[0112] Step 1202: Initiate the RRC connection recovery procedure.

[0113] Step 1204: Select a suitable cell (a cell where a communication device can stay, e.g., a second cell in process (30)).

[0114] Step 1206: Does the communication device successfully select a suitable cell? If Yes, perform Step 1210. If No, perform Step 1208.

[0115] Step 1208: Enter idle mode from connected mode, and perform Step 1216.

[0116] Step 1210: Is the appropriate cell a collaborator cell? If Yes, perform Step 1212. If No, perform Step 1214.

[0117] Step 1212: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell, and perform Step 1216.

[0118] Step 1214: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell.

[0119] Step 1216: Exit.

[0120] In step 1204, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the serving cell or a previous serving cell.

[0121] In step 1206, the communication device determines whether a suitable cell has been successfully selected. In step 1210, the communication device determines whether the suitable cell is a cooperator cell.

[0122] In process (120),

[0123] (a) If a suitable cell is successfully selected and the suitable cell is a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the cooperator cell according to the cooperator cell configuration associated with the cooperator cell;

[0124] (b) If a suitable cell is successfully selected and the suitable cell is not a cooperating cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0125] FIG. 13 is a flowchart of a process (130) according to an example of the present invention. The process (130) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (10000) of FIG. 10). The process (130) includes the following steps:

[0126] Step 1300: Start.

[0127] Step 1302: Initiate the RRC connection recovery procedure.

[0128] Step 1304: Select a suitable cell (a cell where a communication device can stay, e.g., the second cell of process (30)).

[0129] Step 1306: Does the communication device successfully select a suitable cell? If Yes, perform Step 1310, and if No, perform Step 1308.

[0130] Step 1308: Enter idle mode from connected mode and perform Step 1320.

[0131] Step 1310: Is the appropriate cell a handover cell? If Yes, perform Step 1312. If No, perform Step 1314.

[0132] Step 1312: Perform the RRC connection reconstruction procedure as the RRC connection recovery procedure with the appropriate cell according to the handover configuration associated with the appropriate cell, and perform Step 1320.

[0133] Step 1314: Is the appropriate cell a collaborator cell? If Yes, perform Step 1316. If No, perform Step 1318.

[0134] Step 1316: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell, and perform Step 1320.

[0135] Step 1318: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell.

[0136] Step 1320: Exit.

[0137] In step 1304, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the communication device's serving cell or a previous serving cell.

[0138] In step 1306, the communication device determines whether a suitable cell has been successfully selected. In step 1310, the communication device determines whether the suitable cell is a handover cell. In step 1314, the communication device determines whether the suitable cell is a cooperator cell.

[0139] In process (130),

[0140] (a) If a suitable cell is successfully selected and the suitable cell is a handover cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0141] (b) If a suitable cell is successfully selected and the suitable cell is a cooperator cell rather than a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the cooperator cell according to the cooperator cell configuration associated with the cooperator cell;

[0142] (c) If a suitable cell is successfully selected and the suitable cell is neither a handover cell nor a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0143] FIG. 14 is a flowchart of a process (140) according to an example of the present invention. The process (140) is performed by a communication device (14000) (e.g., the communication device (20) of FIG. 2), a cell (14002) (e.g., the first cell in process (30)), a cell (14004) (e.g., at least one cell of NTN in process (30)), and a cell (14006) (e.g., at least one cell of NTN in process (30). The cell (14002) is an NTN serving cell of the communication device (14000). Steps 1400-1406 may refer to steps 1000-1006 of FIG. 10, which are not described herein for brevity. Cell (14002) determines a handover (e.g., conditional handover) of the communication device (14000) (step 1408), transmits a handover request message to Cell (14006) (step 1410), and negotiates with Cell (14006). Afterward, Cell (14002) receives a handover request ACK message from Cell (10006) (step 1412) and transmits an RRC reconfiguration message associated with Cell (14006) to the communication device (14000) (step 1414). The communication device (14000) performs a handover procedure according to the RRC reconfiguration message associated with Cell (14006). If the communication device (14000) determines that it has failed to complete the handover procedure for a handover from cell (14002) to cell (14006) (e.g., if the communication device (14000) fails to detect cell (14006), fails to perform a random access procedure with cell (14006), or fails to send an RRC reconfiguration completion message to cell (14006)) (step 1416)), the communication device (14000) initiates an RRC connection recovery procedure (step 1418).

[0144] In one example, the cell (14002) includes SRB0 and SRB1. In one example, the cell (14002) further includes at least one other SRB or at least one DRB. In one example, the cell (14002) determines a cooperating cell(s) (e.g., cell (14004)) for the communication device (14000) based on, for example, network deployment, network policy, or UE information or measurement report(s) received from the communication device (14000), and performs an RRC connection recovery procedure. In one example, the cell (14002) generates a cooperating cell configuration message containing the cooperating cell configuration of the cell (14004) based on a cooperating cell response message.

[0145] In one example, the cell (14002) modifies the cooperator cell configuration of the cell (14004) (e.g., adding, changing, or removing all or part of the contents of the cooperator cell configuration) by transmitting another cooperator cell configuration message to the communication device (14000). In one example, the cell (14002) determines the handover (e.g., conditional handover) of the communication device (14000) and determines the handover cell(s) (e.g., cell (14006)) for the communication device (14000) based on measurement report(s) received from the communication device (14000), orbit information associated with the first cell and / or cell (14006), or service time and / or area information associated with the first cell and / or cell (14006). In one example, the RRC reconfiguration message includes a handover configuration with "ReconfigurationWithSync". In one example, the RRC reconfiguration message may further include a handover configuration having execution conditions of the cell (14006).

[0146] In one example, the communication device (14000) initiates an RRC connection recovery procedure before the execution condition of the cell (14006) is satisfied. In one example, the communication device (14000) initiates an RRC connection recovery procedure after failing to perform a handover from cell (14002) to cell (14006).

[0147] In FIG. 14, cell (14002) sends a collaborator cell request message to cell (14004) (or cell (14006) and other collaborator cell(s), and cell (14004) and other collaborator cell(s) each send one collaborator cell response message to cell (14002) in response to the collaborator cell request message (not shown). Cell (14002) sends a handover request message to cell (14006) (or cell (14006) and other handover cell(s), and cell (14006) and other handover cell(s) each send one handover request ACK message to cell (14002) in response to the handover request message (not shown). The RRC reconfiguration message may include a handover configuration having execution conditions of cell (14006) and other handover cell(s). In one example, the other collaborator cell(s) and the other handover cell(s) are the same cell(s). In one example, the other collaborator cell(s) and the other handover cell(s) are different cells.

[0148] FIG. 15 is a flowchart of a process (150) according to an example of the present invention. The process (150) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (14000) of FIG. 14). The process (150) includes the following steps:

[0149] Step 1500: Start.

[0150] Step 1502: Initiate the RRC connection recovery procedure.

[0151] Step 1504: Does the communication device select the handover cell as a suitable cell (a cell where the communication device can stay, e.g., the second cell in process (30))? If Yes, perform Step 1506. If No, perform Step 1508.

[0152] Step 1506: Perform an RRC connection reconfiguration procedure as an RRC connection recovery procedure with a suitable cell according to a handover configuration having the execution conditions of a suitable cell. After successfully performing Step 1506, the communication device performs Step 1520.

[0153] Step 1508: Does the communication device select the cooperator cell as a suitable cell? If Yes, perform Step 1510. If No, perform Step 1512.

[0154] Step 1510: Perform an RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell. After successfully performing Step 1510, the communication device performs Step 1520.

[0155] Step 1512: Select the appropriate cell.

[0156] Step 1514: Does the communication device successfully select a suitable cell? If Yes, perform Step 1516. If No, perform Step 1518.

[0157] Step 1516: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with a suitable cell. After successfully performing Step 1506, the communication device performs Step 1520.

[0158] Step 1518: Enter idle mode from connected mode.

[0159] Step 1520: Exit.

[0160] In step 1502, if the communication device (1500) is configured with at least one cooperating cell configuration associated with at least one cell of the NTN and at least one cooperating cell configuration is considered valid, then the communication device is configured with at least one handover configuration associated with at least one cell of the NTN and at least one handover configuration is considered valid. The communication device may select a suitable cell by performing a suitable cell evaluation and performing at least one measurement according to at least one cooperating cell configuration (e.g., performing a suitable cell evaluation only among cells in which the cell ID, the cell frequency, or the frequency of the cell reference signal(s) is included in at least one cooperating cell configuration).

[0161] In step 1504, the communication device determines whether the suitable cell is a handover cell. In step 1508, the communication device determines whether the suitable cell is a cooperator cell.

[0162] In process (150),

[0163] (a) If a suitable cell is successfully selected and the suitable cell is a handover cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0164] (b) If a suitable cell is successfully selected and the suitable cell is a cooperator cell rather than a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to the cooperator cell configuration associated with the suitable cell;

[0165] (c) If a suitable cell is successfully selected and the suitable cell is neither a handover cell nor a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0166] FIG. 16 is a flowchart of a process (160) according to an example of the present invention. The process (160) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (14000) of FIG. 14). The process (160) includes the following steps:

[0167] Step 1600: Start.

[0168] Step 1602: Initiate the RRC connection recovery procedure.

[0169] Step 1604: Does the communication device select the collaborator cell as a suitable cell (a cell where the communication device can stay, e.g., a second cell in process (30))? If Yes, perform Step 1606. If No, perform Step 1612.

[0170] Step 1606: Does the communication device select the handover cell as a suitable cell? If Yes, perform Step 1608. If No, perform Step 1610.

[0171] Step 1608: Perform an RRC connection reconfiguration procedure as an RRC connection recovery procedure with a suitable cell according to a handover configuration having the execution conditions of a suitable cell. After successfully performing Step 1608, the communication device performs Step 1620.

[0172] Step 1610: Perform an RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell. After successfully performing Step 1610, the communication device performs Step 1620.

[0173] Step 1612: Select the appropriate cell.

[0174] Step 1614: Does the communication device successfully select a suitable cell? If Yes, perform Step 1616. If No, perform Step 1618.

[0175] Step 1616: Perform the RRC connection re-establishment procedure as an RRC connection recovery procedure with a suitable cell. After successfully performing Step 1616, the communication device performs Step 1620.

[0176] Step 1618: Enter idle mode from connected mode.

[0177] Step 1620: Exit.

[0178] In step 1602, if the communication device (1600) is configured with at least one cooperating cell configuration associated with at least one cell of the NTN and at least one cooperating cell configuration is considered valid, then the communication device is configured with at least one handover configuration associated with at least one cell of the NTN and at least one handover configuration is considered valid. The communication device may perform a suitable cell evaluation and perform at least one measurement according to at least one cooperating cell configuration to select a suitable cell (e.g., perform a suitable cell evaluation only among cells in which the cell ID, the cell frequency, or the frequency of the cell reference signal(s) is included in at least one cooperating cell configuration).

[0179] In step 1604, the communication device determines whether the suitable cell is a cooperator cell. In step 1606, the communication device determines whether the suitable cell is a handover cell.

[0180] In process (160),

[0181] (a) If a suitable cell is successfully selected and the suitable cell is a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to the cooperator cell configuration associated with the suitable cell;

[0182] (b) If a suitable cell is successfully selected and the suitable cell is a handover cell rather than a cooperator cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0183] (c) If a suitable cell is successfully selected and the suitable cell is neither a cooperator cell nor a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0184] FIG. 17 is a flowchart of a process (170) according to an example of the present invention. The process (170) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (14000) of FIG. 14). The process (170) includes the following steps:

[0185] Step 1700: Start.

[0186] Step 1702: Initiate the RRC connection recovery procedure.

[0187] Step 1704: Select a suitable cell (a cell where a communication device can stay, e.g., a second cell in process (30)).

[0188] Step 1706: Does the communication device successfully select a suitable cell? If Yes, perform Step 1710. If No, perform Step 1708.

[0189] Step 1708: Enter idle mode from connected mode.

[0190] Step 1710: Is the appropriate cell a handover cell (e.g., cell (14006) in FIG. 14 and one of the other handover cell(s))? If Yes, perform Step 1712. If No, perform Step 1714.

[0191] Step 1712: Perform an RRC connection reconfiguration procedure as an RRC connection recovery procedure with a suitable cell according to a handover configuration having the execution conditions of a suitable cell. After successfully performing Step 1712, the communication device performs Step 1720.

[0192] Step 1714: Is the suitable cell a collaborator cell (e.g., cell (14004) in FIG. 14 and one of the other collaborator cell(s))? If Yes, perform Step 1716. If No, perform Step 1718.

[0193] Step 1716: Perform an RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell. After successfully performing Step 1716, the communication device performs Step 1720.

[0194] Step 1718: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell.

[0195] Step 1720: Exit.

[0196] In step 1704, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the communication device's serving cell or a previous serving cell.

[0197] In process (170),

[0198] (a) If a suitable cell is successfully selected and the suitable cell is a handover cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0199] (b) If a suitable cell is successfully selected and the suitable cell is a cooperator cell rather than a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to the cooperator cell configuration associated with the suitable cell;

[0200] (c) If a suitable cell is successfully selected and the suitable cell is neither a cooperator cell nor a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0201] FIG. 18 is a flowchart of a process (180) according to an example of the present invention. The process (180) may be used in a communication device (e.g., the communication device (20) of FIG. 2 or the communication device (14000) of FIG. 14). The process (180) includes the following steps:

[0202] Step 1800: Start.

[0203] Step 1802: Initiate the RRC connection recovery procedure.

[0204] Step 1804: Select a suitable cell (a cell where a communication device can stay, e.g., a second cell in process (30)).

[0205] Step 1806: Does the communication device successfully select a suitable cell? If Yes, perform Step 1810. If No, perform Step 1808.

[0206] Step 1808: Enter idle mode from connected mode.

[0207] Step 1810: Is the appropriate cell a collaborator cell? If Yes, perform Step 1812. If No, perform Step 1814.

[0208] Step 1812: Perform an RRC connection re-establishment procedure as an RRC connection recovery procedure with the appropriate cell according to the collaborator cell configuration associated with the appropriate cell. After successfully performing Step 1812, the communication device performs Step 1820.

[0209] Step 1814: Is the appropriate cell a handover cell? If Yes, perform Step 1816. If No, perform Step 1818.

[0210] Step 1816: Perform an RRC connection reconfiguration procedure as an RRC connection recovery procedure with a suitable cell according to a handover configuration having the execution conditions of a suitable cell. After successfully performing Step 1816, the communication device performs Step 1720.

[0211] Step 1818: Perform the RRC connection re-establishment procedure as the RRC connection recovery procedure with the appropriate cell.

[0212] Step 1820: Exit.

[0213] In step 1804, the communication device selects a suitable cell. The selection of the suitable cell may include performing at least one evaluation (or performing at least one evaluation and at least one measurement) according to a cell selection configuration configured by system information of the communication device's serving cell (i.e., the first cell in process (30)) or according to a stored cell selection configuration configured by the communication device's serving cell or a previous serving cell.

[0214] In process (180),

[0215] (a) If a suitable cell is successfully selected and the suitable cell is a cooperator cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell according to the cooperator cell configuration associated with the suitable cell;

[0216] (a) If a suitable cell is successfully selected and the suitable cell is a handover cell rather than a cooperator cell, the communication device performs an RRC connection reconfiguration procedure as an RRC connection recovery procedure with the suitable cell according to the handover configuration associated with the suitable cell;

[0217] (c) If a suitable cell is successfully selected and the suitable cell is neither a cooperator cell nor a handover cell, the communication device performs an RRC connection re-establishment procedure as an RRC connection recovery procedure with the suitable cell, for example, based on system information associated with the suitable cell, or stored information that may be configured by the serving cell or the previous serving cell.

[0218] The aforementioned action "determine" may be replaced with the actions "compute," "calculate," "obtain," "generate," "output," "use," "choose / select," "decide," or "is configured to." The aforementioned action "detect" may be replaced with the actions "monitor," "receive," "sense," or "obtain." The aforementioned phrase "according to" may be replaced with "in response to." The phrase "associated with" described above may be replaced with "of" or "corresponding to." The aforementioned term "via" can be replaced with "on, in, or at." The term "when" explained above can be replaced with "upon" and "after."

[0219] A person skilled in the art should be able to easily perform combinations, modifications, and / or changes to the descriptions and embodiments mentioned above. A process including the descriptions, steps, and / or proposed steps mentioned above may be realized by means having hardware, software, firmware (known as a combination of computer instructions and data residing as read-only software on a hardware device), an electronic system, or a combination thereof. An example of such means may be a communication device (20).

[0220] Examples of hardware may include analog circuit(s), digital circuit(s) and / or mixed circuit(s). For example, hardware may include ASIC(s), field programmable gate array(s), FPGA(s), programmable logic device(s), combined hardware components, or a combination thereof. In other examples, hardware may include general-purpose processor(s), microprocessor(s), controller(s), digital signal processor(s), DSP(s), or a combination thereof.

[0221] Examples of software may include a storage unit, e.g., a code set(s), an instruction set(s), and / or a function set(s) maintained (e.g., stored) on a computer-readable medium. A computer-readable medium may include a SIM, ROM, flash memory, RAM, CD-ROM / DVD-ROM / BD-ROM, magnetic tape, a hard disk, an optical data storage device, a non-volatile storage unit, or a combination thereof. A computer-readable medium (e.g., a storage unit) may be connected internally (e.g., integrated) or externally (e.g., detached) to at least one processor. At least one processor, which may include one or more modules, may execute (e.g., be configured to execute) the software within the computer-readable medium. The code set(s), instruction set(s), and / or function set(s) may enable at least one processor, module(s), hardware, and / or electronic system to perform the associated steps.

[0222] Examples of electronic systems may include SoC (System on Chip), SiP (System in Package), CoM (Computer on Module), computer program products, devices, mobile phones, laptops, tablet computers, e-books or portable computer systems, and communication devices (20).

[0223] In summary, embodiments of the present invention provide a communication device and a method for handling the recovery of an RRC connection of an NTN. The initiation of an RRC connection recovery procedure is considered a trigger event for recovering the RRC connection of the NTN. Additionally, the communication device performs the RRC connection recovery procedure according to a collaborator cell configuration associated with a target cell (e.g., a second cell in process (30)), a handover cell configuration associated with the target cell, or system information associated with the target cell. Under different conditions / environments, the RRC connection recovery procedure is performed in a different manner. Thus, the performance of the RRC connection recovery of the NTN can be improved.

Claims

Claim 1 A communication device (20) for handling the recovery of a radio resource control (RRC) connection of a non-terrestrial network (NTN), comprising: one or more storage devices; and one or more processing circuits coupled to the one or more storage devices, wherein the one or more storage devices store commands; and wherein the one or more processing circuits are configured to execute: a command (302) for establishing an RRC connection with a first cell of the NTN; a command (304) for receiving a cooperating cell configuration message from the first cell, wherein the cooperating cell configuration message includes one or more cooperating cell configurations associated with one or more cells of the NTN; a command (306) for initiating an RRC connection recovery procedure after receiving the cooperating cell configuration message; a command (308) for selecting a second cell for the RRC connection recovery procedure when the communication device initiates the RRC connection recovery procedure; and a command (310) for performing the RRC connection recovery procedure with the second cell. Claim 2 In claim 1, the command for performing the RRC connection recovery procedure includes a command for performing an RRC connection re-establishment procedure as the RRC connection recovery procedure; the command for performing the RRC connection re-establishment procedure as the RRC connection recovery procedure includes a command for performing an RRC connection re-establishment procedure with the second cell according to the cooperating cell configuration associated with the second cell when the communication device is configured with a cooperating cell configuration among the one or more cooperating cell configurations; and the cooperating cell configuration associated with the second cell is a cooperating cell configuration among the one or more cooperating cell configurations included in the cooperating cell configuration message, the communication device (20). Claim 3 In claim 1 or 2, the command for performing the RRC connection recovery procedure includes a command for performing the RRC connection reconfiguration procedure as the RRC connection recovery procedure; the command for performing the RRC connection reconfiguration procedure as the RRC connection recovery procedure includes a command for performing the RRC connection reconfiguration procedure with the second cell according to the handover configuration associated with the second cell when the communication device is configured with one or more handover configurations; the handover configuration includes "ReconfigurationWithSync" associated with the NTN cell; or the one or more handover configurations each include one or more execution conditions associated with one or more cells of the NTN, communication device (20). Claim 4 In claim 1, the command for performing the RRC connection recovery procedure includes a command for performing an RRC connection re-establishment procedure with the second cell according to system information associated with the second cell when the second cell is not associated with one or more collaborator cell configurations associated with one or more cells of the NTN and the communication device is not configured with a valid handover configuration associated with the second cell. (20). Claim 5 In claim 1, the command for performing the RRC connection recovery procedure includes a command for performing a random access procedure with the second cell; the command for performing the random access procedure includes a command for transmitting an RRC connection recovery request message to the second cell; and the RRC connection recovery request message includes at least one of the ID of a communication device to be applied in the second cell, the ID of the first cell, or an ID to be used by the second cell to perform authentication of the communication device, the communication device (20). Claim 6 In paragraph 1, the communication device (20) enters idle mode from connection mode when the selection of the second cell fails. Claim 7 In paragraph 1, the communication device (20) wherein the collaborator cell configuration message includes a valid time associated with one or more collaborator cell configurations associated with one or more cells of the NTN. Claim 8 In claim 1, the one or more collaborator cell configurations include a valid period in which the collaborator cell configuration is considered valid within a valid period, or a valid area in which the collaborator cell configuration is considered valid within a valid area, the communication device (20). Claim 9 In claim 1, the cooperating cell configuration among the one or more cooperating cell configurations comprises at least one of a cell ID (IDentity) associated with a cell among one or more cells of the NTN, one or more frequencies associated with said cell, one or more frequencies associated with one or more reference signals of said cell, or information for accessing said cell, a communication device (20). Claim 10 In claim 9, the information for accessing the cell comprises one or more configurations of random access resources associated with the cell for the communication device to perform a random access procedure with the cell, the communication device (20). Claim 11 In claim 9, the one or more collaborator cell configurations include at least one of an SSB-based radio resource management (RRM) measurement timing configuration (SMTC) associated with a frequency associated with the cell, an ID of a communication device to be applied in the cell, or an ID to be used by the cell to perform authentication for the communication device, the communication device (20). Claim 12 In claim 1, the communication device (20) selects the second cell by performing one or more evaluations according to a cell selection configuration configured by the system information of the first cell. Claim 13 In claim 1, the communication device (20) selects the second cell by performing one or more evaluations according to one or more cooperating cell configurations associated with one or more cells of the NTN included in the cooperating cell configuration message. Claim 14 In paragraph 1, the communication device (20) selects the second cell by performing one or more evaluations according to one or more handover configurations among one or more handover configurations. Claim 15 In claim 1, the step of selecting the second cell for the RRC connection recovery procedure comprises the step of performing one or more evaluations according to one or more collaborator cell configurations associated with one or more cells of the NTN when the communication device is configured with one or more collaborator cell configurations associated with one or more cells of the NTN, wherein the communication device is configured with one or more collaborator cell configurations among one or more handover configurations. Claim 16 In claim 1, the step of selecting the second cell for the RRC connection recovery procedure comprises the step of performing one or more evaluations according to the handover configuration among the handover configurations when the communication device is configured with one or more collaborator cell configurations associated with one or more cells of the NTN, and the communication device is configured with a handover configuration among the one or more handover configurations, and when the handover configuration is considered valid.

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