Communication control method

Abstract

A communication control method according to one aspect is employed in a cellular communication system. The communication control method includes a step in which a base station broadcasts a first message including non-public network (NPN) service provision availability information indicating whether the base station provides an NPN service, for each entry of an NPNID information list that includes information relating to NPN services. The communication control method also includes a step in which a user device receives the first message. Here, at least one of the entries includes NPN service provision availability information indicating that the base station does not provide an NPN service.

Description

Communication Control Method

[0001] The present disclosure relates to a communication control method for use in a cellular communication system.

[0002] In the Third Generation Partnership Project (3GPP), a standardization project for cellular communication systems, the introduction of a new relay node called an Integrated Access and Backhaul (IAB) node is being considered (see, for example, Non-Patent Documents 1 and 2). One or more relay nodes intervene in communication between a base station and a user device and relay this communication.

[0003] 3GPP TS 38.300 V17.5.0 (2023-06)3GPP TS 38.331 V17.5.0 (2023-06)

[0004] A communication control method according to a first aspect is a communication control method for use in a cellular communication system. The communication control method includes a step of a network node broadcasting a first message including NPN (Non-Public Network) service provision status information indicating whether the network node provides NPN service for each entry of an NPN ID information list including information on NPN service. The communication control method also includes a step of a user equipment receiving the first message. Here, at least one of the entries includes NPN service provision status information indicating that the network node does not provide NPN service.

[0005] A network node according to a second aspect is a network node in a cellular communication system, the network node having a transmitter configured to broadcast a first message including NPN service provision status information indicating whether the network node provides the NPN service for each entry in an NPN ID information list including information on the NPN service, wherein at least one of the entries includes NPN service provision status information indicating that the network node does not provide the NPN service.

[0006] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system according to the first embodiment. FIG. 2 is a diagram showing the relationship between an IAB node, parent nodes, and child nodes. FIG. 3 is a diagram showing an example of the configuration of a gNB (base station) according to the first embodiment. FIG. 4 is a diagram showing an example of the configuration of an IAB node (relay node) according to the first embodiment. FIG. 5 is a diagram showing an example of the configuration of a UE (user equipment) according to the first embodiment. FIG. 6 is a diagram showing an example of a protocol stack related to IAB-MT RRC connection and NAS connection. FIG. 7 is a diagram showing an example of a protocol stack related to the F1-U protocol. FIG. 8 is a diagram showing an example of a protocol stack related to the F1-C protocol. FIG. 9 is a diagram for explaining problems according to the first embodiment. FIG. 10 is a diagram showing an example of the configuration of SIB4 according to the first embodiment. FIG. 11 is a diagram showing an example of the configuration of SIB1 according to the first embodiment. FIG. 12 is a diagram showing an example of the configuration of SIB1 according to the first embodiment. FIG. 13 is a diagram showing an example of an operation according to the first embodiment. Figure 14 shows a diagram illustrating a UE's mobile IAB cell reselection. Figure 15 shows a diagram illustrating an HSDN cell list for each entry in the inter-frequency carrier frequency list of SIB4. Figure 16 shows an NPN Identity Info List of SIB1. Figure 17 shows a diagram illustrating a UE's macro cell reselection.

[0007] A cellular communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0008] [First embodiment] (Configuration of cellular communication system) An example configuration of a cellular communication system according to one embodiment will be described. A cellular communication system 1 according to one embodiment is a 3GPP 5G system. Specifically, the radio access method in the cellular communication system 1 is NR (New Radio), which is a 5G radio access method. However, LTE (Long Term Evolution) may be applied at least partially to the cellular communication system 1. Furthermore, future cellular communication systems such as 6G may also be applied to the cellular communication system 1.

[0009] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system 1 according to an embodiment.

[0010] 1, the cellular communication system 1 includes a 5G core network (5GC) 10, user equipment (UE) 100, base station devices (hereinafter sometimes referred to as "base stations") 200-1 and 200-2, and IAB nodes 300-1 and 300-2. The base station 200 may be referred to as a gNB.

[0011] In the following, we will mainly describe an example in which base station 200 is an NR base station, but base station 200 may also be an LTE base station (i.e., eNB).

[0012] In the following, base stations 200-1 and 200-2 may be referred to as gNB 200 (or base station 200), and IAB nodes 300-1 and 300-2 may be referred to as IAB node 300.

[0013] The 5GC 10 has an Access and Mobility Management Function (AMF) 11 and a User Plane Function (UPF) 12. The AMF 11 is a device that performs various mobility controls for the UE 100. The AMF 11 manages information about the area in which the UE 100 is located by communicating with the UE 100 using Non-Access Stratum (NAS) signaling. The UPF 12 is a device that performs transfer control of user data, etc.

[0014] Each gNB 200 is a fixed wireless communication node and manages one or more cells. A cell is used as a term indicating the smallest unit of a wireless communication area. A cell may also be used as a term indicating a function or resource for performing wireless communication with a UE 100. One cell belongs to one carrier frequency. Hereinafter, there may be cases where a cell and a base station are used interchangeably.

[0015] Each gNB 200 is interconnected with the 5GC 10 via an interface called an NG interface. In FIG. 1, two gNBs 200-1 and 200-2 connected to the 5GC 10 are illustrated.

[0016] Each gNB 200 may be divided into a central unit (CU) and a distributed unit (DU). The CU and DU are connected to each other via an interface called an F1 interface. The F1 protocol is a communication protocol between the CU and DU, and includes the F1-C protocol, which is a control plane protocol, and the F1-U protocol, which is a user plane protocol.

[0017] The cellular communication system 1 supports IAB, which enables wireless relay of NR access using NR for backhaul. The donor gNB 200-1 (or donor node, hereinafter sometimes referred to as the "donor node") is the terminal node of the NR backhaul on the network side and is a donor base station with additional functions that support IAB. The backhaul can be multi-hopped via multiple hops (i.e., multiple IAB nodes 300).

[0018] FIG. 1 shows an example in which IAB node 300-1 wirelessly connects with donor node 200-1, IAB node 300-2 wirelessly connects with IAB node 300-1, and the F1 protocol is transmitted over two backhaul hops.

[0019] The UE 100 is a mobile wireless communication device that performs wireless communication with a cell. The UE 100 may be any device that performs wireless communication with the gNB 200 or the IAB node 300. For example, the UE 100 is a mobile phone terminal or a tablet terminal, a laptop PC, a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle, or an aircraft or a device provided in an aircraft. The UE 100 wirelessly connects to the IAB node 300 or the gNB 200 via an access link. FIG. 1 shows an example in which the UE 100 is wirelessly connected to the IAB node 300-2. The UE 100 indirectly communicates with the donor node 200-1 via the IAB node 300-2 and the IAB node 300-1.

[0020] FIG. 2 is a diagram showing an example of the relationship between the IAB node 300, parent nodes, and child nodes.

[0021] As shown in FIG. 2, each IAB node 300 has an IAB-DU corresponding to a base station function unit and an IAB-MT (Mobile Termination) corresponding to a user equipment function unit.

[0022] An adjacent node (i.e., an upper node) on the NR Uu radio interface of the IAB-MT is called a parent node. The parent node is the parent IAB node or the DU of the donor node 200. The radio link between the IAB-MT and the parent node is called a backhaul link (BH link). FIG. 2 shows an example in which the parent nodes of the IAB node 300 are IAB nodes 300-P1 and 300-P2. The direction toward the parent node is called upstream. From the perspective of the UE 100, the upper node of the UE 100 may correspond to the parent node.

[0023] Adjacent nodes (i.e., lower nodes) on the NR access interface of the IAB-DU are called child nodes. The IAB-DU manages the cell, similar to the gNB 200. The IAB-DU terminates the NR Uu radio interface to the UE 100 and lower IAB nodes. The IAB-DU supports the F1 protocol to the CU of the donor node 200-1. In FIG. 2, an example is shown in which the child nodes of the IAB node 300 are IAB nodes 300-C1 to 300-C3, but the child nodes of the IAB node 300 may also include the UE 100. The direction toward the child nodes is called downstream.

[0024] Furthermore, all IAB nodes 300 connected to the donor node 200 via one or more hops form a directed acyclic graph (DAG) topology (hereinafter sometimes referred to as "topology") with the donor node 200 as the root. In this topology, as shown in FIG. 2, adjacent nodes on the IAB-DU interface are child nodes, and adjacent nodes on the IAB-MT interface are parent nodes. The donor node 200 centralizes, for example, resource, topology, and route management of the IAB topology. The donor node 200 is a gNB that provides network access to the UE 100 via a network of backhaul links and access links.

[0025] (Configuration of base station) Next, the configuration of the gNB 200, which is a base station according to the embodiment, will be described. Fig. 3 is a diagram showing an example configuration of the gNB 200. As shown in Fig. 3, the gNB 200 has a wireless communication unit 210, a network communication unit 220, and a control unit 230.

[0026] The wireless communication unit 210 performs wireless communication with the UE 100 and wireless communication with the IAB node 300. The wireless communication unit 210 has a receiving unit 211 and a transmitting unit 212. The receiving unit 211 performs various receptions under the control of the control unit 230. The receiving unit 211 includes an antenna, and converts (down-converts) a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 230. The transmitting unit 212 performs various transmissions under the control of the control unit 230. The transmitting unit 212 includes an antenna, and converts (up-converts) a baseband signal (transmitted signal) output by the control unit 230 into a wireless signal, and transmits the signal from the antenna.

[0027] The network communication unit 220 performs wired communication (or wireless communication) with the 5GC10 and wired communication (or wireless communication) with other adjacent gNBs 200. The network communication unit 220 has a receiving unit 221 and a transmitting unit 222. The receiving unit 221 performs various receptions under the control of the control unit 230. The receiving unit 221 receives a signal from the outside and outputs the received signal to the control unit 230. The transmitting unit 222 performs various transmissions under the control of the control unit 230. The transmitting unit 222 transmits the transmission signal output by the control unit 230 to the outside.

[0028] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs processing of each layer, which will be described later. Note that the control unit 230 may perform each process or operation in the gNB 200 in each of the embodiments shown below.

[0029] (Configuration of Relay Node) Next, a configuration of an IAB node 300, which is a relay node (or relay node device; hereinafter, may be referred to as a "relay node") according to an embodiment, will be described. FIG. 4 is a diagram showing an example configuration of the IAB node 300. As shown in FIG. 4, the IAB node 300 has a wireless communication unit 310 and a control unit 320. The IAB node 300 may have multiple wireless communication units 310.

[0030] The wireless communication unit 310 performs wireless communication (BH link) with the gNB 200 and wireless communication (access link) with the UE 100. The wireless communication unit 310 for BH link communication and the wireless communication unit 310 for access link communication may be provided separately.

[0031] The wireless communication unit 310 has a receiving unit 311 and a transmitting unit 312. The receiving unit 311 performs various types of reception under the control of the control unit 320. The receiving unit 311 includes an antenna, and converts (down-converts) a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 320. The transmitting unit 312 performs various types of transmission under the control of the control unit 320. The transmitting unit 312 includes an antenna, and converts (up-converts) a baseband signal (transmitted signal) output by the control unit 320 into a wireless signal, and transmits the signal from the antenna.

[0032] The control unit 320 performs various controls in the IAB node 300. The control unit 320 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs processing of each layer, which will be described later. Note that the control unit 320 may perform each process or operation in the IAB node 300 in each of the embodiments described below.

[0033] (Configuration of User Device) Next, a configuration of the UE 100, which is a user device according to the embodiment, will be described. Fig. 5 is a diagram showing an example configuration of the UE 100. As shown in Fig. 5, the UE 100 includes a radio communication unit 110 and a control unit 120.

[0034] The wireless communication unit 110 performs wireless communication in an access link, i.e., wireless communication with the gNB 200 and wireless communication with the IAB node 300. The wireless communication unit 110 may also perform wireless communication in a side link, i.e., wireless communication with other UEs 100. The wireless communication unit 110 has a receiving unit 111 and a transmitting unit 112. The receiving unit 111 performs various receptions under the control of the control unit 120. The receiving unit 111 includes an antenna, and converts (down-converts) a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 120. The transmitting unit 112 performs various transmissions under the control of the control unit 120. The transmitting unit 112 includes an antenna, and converts (up-converts) a baseband signal (transmitted signal) output by the control unit 120 into a wireless signal, and transmits the signal from the antenna.

[0035] The control unit 120 performs various controls in the UE 100. The control unit 120 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs processing of each layer, which will be described later. Note that the control unit 120 may be configured to perform each process in the UE 100 in each of the embodiments described below.

[0036] (Protocol Stack Configuration) Next, a description will be given of the configuration of a protocol stack according to the embodiment. Fig. 6 is a diagram showing an example of a protocol stack related to an IAB-MT RRC connection and a NAS connection.

[0037] As shown in FIG. 6, the IAB-MT of IAB node 300-2 has a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) layer, and a non-access stratum (NAS) layer.

[0038] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the IAB-MT of IAB node 300-2 and the PHY layer of the IAB-DU of IAB node 300-1 via a physical channel.

[0039] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted via transport channels between the MAC layer of the IAB-MT of IAB node 300-2 and the MAC layer of the IAB-DU of IAB node 300-1. The MAC layer of the IAB-DU includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the allocated resource blocks.

[0040] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the IAB-MT of IAB node 300-2 and the RLC layer of the IAB-DU of IAB node 300-1 via logical channels.

[0041] The PDCP layer performs header compression / decompression, and encryption / decryption. Data and control information are transmitted between the PDCP layer of the IAB-MT of the IAB node 300-2 and the PDCP layer of the donor node 200 via a radio bearer.

[0042] The RRC layer controls logical channels, transport channels, and physical channels in response to the establishment, re-establishment, and release of radio bearers. RRC signaling for various settings is transmitted between the RRC layer of the IAB-MT of the IAB node 300-2 and the RRC layer of the donor node 200. When there is an RRC connection with the donor node 200, the IAB-MT is in an RRC connected state. When there is no RRC connection with the donor node 200, the IAB-MT is in an RRC idle state.

[0043] The NAS layer, which is positioned above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the IAB-MT of the IAB node 300-2 and the AMF 11.

[0044] Figure 7 shows a protocol stack for the F1-U protocol. Figure 8 shows a protocol stack for the F1-C protocol. Here, an example is shown in which the donor node 200 is divided into a CU and a DU.

[0045] As shown in Figure 7, the IAB-MT of IAB node 300-2, the IAB-DU of IAB node 300-1, the IAB-MT of IAB node 300-1, and the DU of donor node 200 each have a BAP (Backhaul Adaptation Protocol) layer above the RLC layer. The BAP layer is a layer that performs routing processing and bearer mapping / demapping processing. In the backhaul, the IP layer is transmitted via the BAP layer, enabling routing over multiple hops.

[0046] In each backhaul link, PDUs (Protocol Data Units) of the BAP layer are transmitted by a backhaul RLC channel (BH NR RLC channel). By configuring multiple backhaul RLC channels in each BH link, traffic prioritization and QoS (Quality of Service) control are possible. The association between BAP PDUs and backhaul RLC channels is performed by the BAP layer of each IAB node 300 and the BAP layer of the donor node 200.

[0047] As shown in FIG. 8, the protocol stack of the F1-C protocol has an F1AP layer and an SCTP layer instead of the GTP-U layer and UDP layer shown in FIG.

[0048] In the following, the processing or operations performed by the IAB-DU and IAB-MT of the IAB may be simply described as the processing or operations of the "IAB." For example, the transmission of a BAP layer message from the IAB-DU of IAB node 300-1 to the IAB-MT of IAB node 300-2 will be described as the IAB node 300-1 sending the message to IAB node 300-2. In addition, the processing or operations of the DU or CU of the donor node 200 may also be simply described as the processing or operations of the "donor node."

[0049] Also, the upstream direction and the uplink (UL) direction may be used interchangeably, and the downstream direction and the downlink (DL) direction may be used interchangeably.

[0050] (Mobile IAB Node) Currently, 3GPP has begun discussions toward the introduction of mobile IAB nodes. A mobile IAB node is, for example, an IAB node that is moving. A mobile IAB node may be an IAB node that is capable of moving. Alternatively, a mobile IAB node may be an IAB node that is currently stationary but is certain to move in the future (or is expected to move in the future).

[0051] The mobile IAB node enables, for example, a UE 100 under the mobile IAB node to receive services from the mobile IAB node while moving in accordance with the movement of the mobile IAB node. For example, a case is envisioned in which a user (or UE 100) on a vehicle receives services via a mobile IAB node installed on the vehicle.

[0052] On the other hand, in contrast to mobile IAB nodes, there are also IAB nodes that do not move. Such IAB nodes are sometimes referred to as intermediate IAB nodes. An intermediate IAB node is, for example, an IAB node that does not move. Alternatively, the intermediate IAB node may be a stationary IAB node. Alternatively, the intermediate IAB node may be an IAB node that remains stationary (or does not move) and remains installed at its installation location. Alternatively, the intermediate IAB node may be a stationary IAB node that does not move. The intermediate IAB node may also be a fixed IAB node.

[0053] A mobile IAB node can also be connected to an intermediate IAB node. Also, a mobile IAB node can be connected to a donor node 200. A mobile IAB node can also change its connection destination due to movement (migration or handover). The connection source may be an intermediate IAB node. The connection source may be the donor node 200. Also, the connection destination may be an intermediate IAB node. The connection destination may be the donor node 200.

[0054] In the following, the terms "migration" of a mobile IAB node and "handover" of a mobile IAB node may be used interchangeably.

[0055] In the following description, a mobile IAB node may be referred to as a "mobile IAB node." The mobile IAB node may also be referred to as a "migrating IAB node." In either case, the mobile IAB node may also be referred to as a mobile IAB node. The mobile IAB node may also be a mobile relay node.

[0056] (Cell Reselection Procedure According to First Embodiment) Next, a cell reselection procedure according to the first embodiment will be described.

[0057] A UE 100 in an RRC idle state or an RRC inactive state performs a cell reselection procedure to transition from a current serving cell to a neighboring cell as it moves. Specifically, the UE 100 identifies a neighboring cell on which it should camp by the cell reselection procedure and reselects the identified neighboring cell. When the frequency (carrier frequency) of the current serving cell and the neighboring cell is the same, this is called an intra-frequency, and when the frequency (carrier frequency) of the current serving cell and the neighboring cell is different, this is called an inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB 200 or may be managed by different gNBs 200.

[0058] Cell reselection procedures include intra-frequency cell reselection procedures and inter-frequency cell reselection procedures.

[0059] In the intra-frequency cell reselection procedure, cell reselection is performed based on the cell ranking. In the intra-frequency cell reselection procedure, for example, the following processing is performed.

[0060] First, the UE 100 performs a measurement process to measure radio quality for each of the serving cell and the neighboring cell. Specifically, the UE 100 measures RSRP and RSRQ of CD-SSB (Cell Defining-Synchronization Signal and PBCH block) for each of the serving cell and the neighboring cell.

[0061] Second, the UE 100 calculates a ranking criterion (Rs) for the serving cell and a ranking criterion (Rn) for the neighboring cell for all cells that satisfy the cell selection criterion S. The cell selection criterion S is a criterion for selecting a cell whose RSRP exceeds the RSRP minimum required level and whose RSRQ exceeds the RSRQ minimum required level.

[0062] The UE 100 basically reselects the cell with the highest rank from among the two ranking criteria Rs and Rn.

[0063] On the other hand, in the inter-frequency cell reselection procedure, cell reselection is performed based on absolute frequency priority. The frequency priority is provided from the gNB 200 to the UE 100 by broadcast signaling (e.g., a system information block) or dedicated signaling (e.g., an RRC Release message). In the inter-frequency cell reselection procedure, for example, the following processing is performed.

[0064] First, the UE 100 performs a measurement process (measurement) to measure the radio quality of each of the serving cell and the neighboring cell. Specifically, the UE 100 always measures the radio quality of a frequency having a higher priority than the priority of the frequency of the current serving cell. Furthermore, for a frequency having a priority equal to or lower than the priority of the frequency of the current serving cell, the UE 100 measures the radio quality of the frequency having the same priority or a lower priority when the radio quality of the current serving cell falls below a predetermined quality.

[0065] Second, the UE 100 performs a cell reselection process to reselect a cell on which the UE 100 camps based on the measurement result. Specifically, when the frequency priority of the neighboring cell is higher than the priority of the current serving cell and the neighboring cell satisfies a predetermined quality standard (i.e., a minimum required quality standard) for a predetermined period, the UE 100 may perform cell reselection to the neighboring cell. When the frequency priority of the neighboring cell is the same as the priority of the current serving cell, the UE 100 may rank the radio qualities of the neighboring cells and perform cell reselection to a neighboring cell having a higher rank than the rank of the current serving cell for a predetermined period. When the frequency priority of the neighboring cell is lower than the priority of the current serving cell, and when the radio quality of the current serving cell is lower than a radio quality threshold and the radio quality of the neighboring cell continues to be higher than another radio quality threshold for a predetermined period, the UE 100 may perform cell reselection to the neighboring cell.

[0066] Although the above example describes an example in which the UE 100 performs the cell reselection procedure, it is also possible for the IAB-MT of the IAB node 300 to perform the cell reselection procedure.

[0067] (Communication Control Method According to First Embodiment) Currently, the 3GPP is discussing the following issues regarding the cell reselection procedure of a mobile IAB node.

[0068] (Problem) In a situation where UE 100 is physically located in a moving vehicle but is not yet camped on a mobile IAB cell managed by a mobile IAB node (i.e., UE 100 is camped on a fixed cell that does not move), how can UE 100 identify neighboring mobile IAB cells, how can the priority of the mobile IAB cell (frequency and cell) be increased, and how can UE 100 be attracted to the mobile IAB cell? In particular, in a scenario of an inter-frequency cell reselection procedure, what should be done when the frequency priority of the mobile IAB cell is lower than others? Figure 9 is a diagram for explaining this problem according to the first embodiment.

[0069] As shown in Fig. 9, the UE 100 is located in a mobile vehicle. The vehicle is provided with a mobile IAB node 300M. The UE 100 is located in a cell managed by the mobile IAB node 300M. The cell managed by the mobile IAB node 300M may be referred to as a mobile IAB cell 300S. In the following, the mobile IAB node 300M and the mobile IAB cell 300S may be used interchangeably.

[0070] However, UE100 is camped on a cell (stationary cell or macro cell) managed by a fixed, non-moving gNB200. The gNB200 can be a serving cell for UE100. Hereinafter, the gNB200 may be referred to as a serving cell 200S. UE100 is camped on the serving cell 200S and is located in a vehicle, but has not yet camped on the mobile IAB cell 300S. However, the frequency used in the serving cell 200S and the frequency used in the mobile IAB cell 300S are different.

[0071] In such a situation, a problem has been pointed out as to how to camp the UE 100 on the moving IAB cell 300S when the UE 100 performs an inter-frequency cell reselection procedure.

[0072] To address the above problem, 3GPP has also discussed broadcasting the frequency used in the mobile IAB cell 300S by including it in assistance information in SIB4 (System Information Block type 4), and having the UE 100 identify the mobile IAB cell 300S using the assistance information in SIB4. That is, according to this discussion, by acquiring the frequency used in the mobile IAB cell 300S from SIB4, the UE 100 may be able to camp on the mobile IAB cell 300S by, for example, regarding the frequency as having the highest priority and performing an inter-frequency cell reselection procedure.

[0073] Meanwhile, 3GPP has also agreed to apply a Closed Access Group (CAG) to restrict access to the mobile IAB cell 300S. CAG is a technology that, for example, allows CAG subscribers to access the CAG cell and prevents non-CAG subscribers from accessing the CAG cell. The CAG is identified by a CAG ID, which indicates a unique identifier within a PLMN (Public Land Mobile Network). The CAG ID is used to control access of the UE 100 via the mobile IAB node 300M. The AMF 11 checks whether access of the UE 100 via the mobile IAB node 300M is permitted by the CAG ID.

[0074] The current 3GPP specifications regarding CAG will now be described. Fig. 10 shows an example of the configuration of SIB4, and Figs. 11 and 12 show examples of the configuration of SIB1.

[0075] The UE 100 basically acquires information required for performing an inter-frequency cell reselection procedure using SIB4 and SIB1. As shown in Fig. 10 , the SIB4 includes an inter-frequency list (interFreqCarrierFreqList). The inter-frequency list (interFreqCarrierFreqList) includes a list of frequencies used in neighboring cells. By checking the frequencies, the UE 100 can perform an inter-frequency cell reselection procedure, such as performing measurements on the frequencies.

[0076] 10, SIB4 also includes an inter-frequency CAG cell list (interFreqCAG-CellList-r16). The inter-frequency CAG cell list (interFreqCAG-CellList-r16) includes a PLMN ID index (plmn-IdentityIndex-r16). The PLMN ID index (plmn-IdentityIndex-r16) indicates the indexes (or entry numbers) of both the PLMN ID information list (PLMN-IdentityInfoList) and the NPN ID information list (NPN-IdentityInfoList) included in SIB1. In other words, the index (or entry number) indicated by the PLMN ID index indicates one of the entries included in the PLMN ID information list (PLMN-IdentityInfoList) and also indicates one of the entries included in the NPN ID information list (NPN-IdentityInfoList).

[0077] FIG. 11 shows an example of the configuration of the NPN ID information list (NPN-IdentityInfoList-r16) included in SIB1. The NPN ID information list (NPN-IdentityInfoList-r16) includes, for example, information about NPN (Non-Public Network) services. An NPN service is, for example, a service provided by a network for non-public use. An NPN is sometimes referred to as a private network. Each entry (NPN ID information (NPN-IdentityInfo-r16)) in the NPN ID information list (NPN-IdentityInfoList-r16) includes a CAG ID (cag-Identity-r16).

[0078] For example, when #1 is included as the PLMN ID index (plmn-IdentityIndex-r16) of SIB4, the first entry (NPN ID information (NPN-IdentityInfo-r16)) included in the NPN ID information list (NPN-IdentityInfoList-r16) of SIB1 is referenced. By referring to this entry, the UE 100 can confirm the CAG-ID (for example, CAG-ID #1) used in the neighboring cell.

[0079] 12 shows an example of the configuration of the PLMN ID information list (PLMN-IdentityInfoList) included in SIB1. Each entry (PLMN ID information (PLMN-IdentityInfo)) of the PLMN ID information list (PLMN-IdentityInfoList) can also be referenced by the PLMN ID index (plmn-IdentityIndex-r16) included in SIB4. The UE 100 can confirm the PLMN ID used in neighboring cells by referring to the entry of the specified PLMN ID information list (PLMN-IdentityInfoList).

[0080] However, the total number of entries in the NPN ID information list (NPN-IdentityInfoList-r16) and PLMN ID information list (PLMN-IdentityInfoList) included in SIB1 is currently limited to "12."

[0081] The NPN ID information list (NPN-IdentityInfoList-r16) included in SIB1 basically includes information about the NPN service of the serving cell. For example, in FIG. 9, when the serving cell 200S broadcasts SIB1, the NPN ID information list (NPN-IdentityInfoList-r16) is used to broadcast the NPN service provided by the serving cell 200S. Even if the serving cell 200S attempts to add an NPN ID information list related to the mobile IAB cell 300S, which is not the serving cell, to SIB1, as described above, currently, the total number of entries in the NPN ID information list (NPN-IdentityInfoList-r16) and the PLMN ID information list (PLMN-IdentityInfoList) is limited to "12", so the total number of entries may exceed "12". For this reason, the serving cell 200S may not be able to broadcast the CAG ID related to the mobile IAB cell in the NPN ID information list (NPN-IdentityInfoList-r16). When the mobile IAB cell 300S restricts access to the UE 100 by the CAG ID and the UE 100 is unable to acquire the CAG ID, even if the UE 100 camps on the mobile IAB cell 300S by the inter-frequency cell reselection procedure, the UE 100 may be restricted from accessing the mobile IAB cell 300S, and the inter-frequency cell reselection procedure itself may become a useless operation.

[0082] Therefore, the first embodiment aims to enable the UE 100 to appropriately perform the inter-frequency cell reselection procedure.

[0083] Therefore, in the first embodiment, first, a base station (e.g., serving cell 200S) broadcasts a first message (e.g., SIB1) including NPN service provision information indicating whether the base station provides the NPN service for each entry of an NPN ID information list including information on the NPN service. Second, a user equipment (e.g., UE 100) receives the first message. Third, at least one of the entries includes NPN service provision information indicating that the base station does not provide the NPN service.

[0084] As a result, for example, the UE 100 can check an entry in the NPN ID information list for which the serving cell 200S does not provide an NPN service, and can confirm that the entry is not an entry for the serving cell 200S but is (implies) an entry for the mobile IAB cell 300S. Furthermore, the serving cell 200S can also refer to the entry for the mobile IAB cell 300S using the PLMN ID index (plmn-IdentityIndex-r16) of SIB4. Therefore, the UE 100 can obtain the entry using SIB1 and SIB4 and obtain the CAG-ID used in the mobile IAB cell 300S from the entry. By checking the CAG-ID, the UE 100 can confirm whether or not the mobile IAB cell 300S is accessible. The UE 100 can then perform the inter-frequency cell reselection procedure if the mobile IAB cell 300S is accessible, and can also not perform the inter-frequency cell reselection procedure if the mobile IAB cell 300S is not accessible. Thus, the UE 100 can appropriately perform the inter-frequency cell reselection procedure.

[0085] (Example of Operation According to First Embodiment) Next, an example of operation according to the first embodiment will be described.

[0086] Fig. 13 is a diagram illustrating an example of operation according to the first embodiment. The example of operation illustrated in Fig. 13 will be described assuming that, for example, as illustrated in Fig. 9 , the UE 100 is camped on the serving cell 200S and is not camped on the moving IAB cell 300S.

[0087] As shown in FIG. 13, in step S10, the UE 100 is in an RRC idle state or an RRC inactive state.

[0088] In step S11, the serving cell 200S broadcasts SIB1 including an NPNID information list (NPN-IdentityInfoList) that includes, as an entry, NPNID information (NPN-IdentityInfo) for the mobile IAB cell 300S.

[0089] First, the total number of entries in the NPNID information list and the PLMNID information list (PLMN-IdentityInfoList) included in the message may exceed 12. For example, the 13th entry may be an entry (NPNID information) for the mobile IAB cell 300S.

[0090] Second, each entry in the NPNID information list includes NPN service provision availability information indicating whether the serving cell 200S provides the NPN service. For example, the first entry (NPNID information) in the NPNID information list includes "1" as the NPN service provision availability information (indicating, for example, that the serving cell 200S provides the NPN service and that the NPNID information can be used for the serving cell 200S), and the second entry in the NPNID information list includes "0" as the NPN service provision availability information (indicating that the serving cell 200S does not provide the NPN service and that the NPNID information cannot be used by the serving cell 200S). The meanings of "0" and "1" may be reversed.

[0091] In the first embodiment, the entries in the NPN ID information list include at least one entry including NPN service provision information indicating that the serving cell 200S does not provide the NPN service. This entry (implicitly) indicates that the serving cell 200S does not provide the NPN service, that is, that this entry is for the mobile IAB cell 300S used in the mobile IAB cell 300S. The UE 100 may recognize this entry as invalid in the serving cell 200S and ignore the CAG ID ( FIG. 11 ) included in this entry. The UE 100 may recognize this entry as an entry for the mobile IAB cell 300S.

[0092] The NPN service provision information may be expressed as an "identifier" indicating whether the serving cell 200S provides the NPN service.

[0093] Furthermore, SIB1 is an example of a first message. SIB1 is broadcast from, for example, the transmitter 212 of the serving cell 200S. UE 100 receives SIB1. For example, receiver 111 of UE 100 receives SIB1.

[0094] In step S12, the serving cell 200S broadcasts SIB4. SIB4 includes a list of frequencies (inter-frequencies) used by the UE 100 in the inter-cell reselection procedure. Furthermore, SIB4 includes an index (PLMNID index) to the NPNID information list included in SIB1. The index refers to an entry (NPNID information) in the NPNID information list included in SIB1, which is an entry for the mobile IAB cell 300S (i.e., an entry including NPN service provision status information indicating that the serving cell 200S does not provide the NPN service). By checking the entry, the UE 100 can check the CAG ID used for access restriction in the mobile IAB cell 300S. The CAG ID can be identification information used for access restriction in the mobile IAB cell 300S.

[0095] Note that SIB4 is an example of a second message. For example, the transmitter 212 of the serving cell 200S broadcasts SIB4. The UE 100 receives SIB4. For example, the receiver 111 of the UE 100 receives SIB4.

[0096] In step 13, UE 100 performs an inter-frequency cell reselection procedure using SIB1 and SIB4. That is, UE 100 checks an entry (NPNID information) of the NPNID information list included in SIB1 using the PLMNID index included in SIB4. Then, UE 100 confirms that the entry includes NPN service provision / non-provision information indicating that the serving cell 200S does not provide the NPN service, and therefore (implicitly) indicates that the entry is an entry for the mobile IAB cell 300S. UE 100 obtains a CAG ID from the entry and confirms that the CAG ID is a CAG ID that restricts access in the mobile IAB cell 300S. UE 100 may perform an inter-frequency cell reselection procedure if the CAG ID set for itself matches the access-restricted CAG ID, or may not perform the procedure if they do not match.

[0097] (Another Operation Example 1 According to the First Embodiment) In the first embodiment, the CAG-ID has been mainly described as an example of identification information used for access restriction in the mobile IAB cell 300S, but the identification information used for access restriction in the mobile IAB cell 300S is not limited to the CAG-ID. As shown in FIG. 11 , the NPNID (NPN-Identity) included in the NPNID information (NPN-IdentityInfo-r16) also includes the PNI-NPN ID. In addition, the NPNID information (NPN-IdentityInfo-r16) also includes the TAC (Tracking Area Code). Therefore, the identification information used for access restriction in the mobile IAB cell 300S may be the PNI-NPN ID. This identification information may also be the TAC. The same implementation as in the first embodiment is possible by replacing the CAG ID described in the first embodiment with the PNI-NPN ID or the TAC. The identification information used for access restriction may be an SNPN ID. The SNPN ID is composed of a PLMN ID and an NID. The same implementation as in the first embodiment can be achieved by replacing the CAG ID described in the first embodiment with the SNPN ID.

[0098] (Another Operation Example 2 According to First Embodiment) In the first embodiment, an example has been described in which the first message is SIB1. The first message may be a system information block other than SIB1. Alternatively, the first message may be transmitted by dedicated signaling (for example, an RRC message such as an RRCRelease message) rather than broadcast signaling. Similarly, the second message may be a system information block other than SIB4, or may be transmitted by dedicated signaling (for example, an RRC message such as an RRCRelease message) rather than broadcast signaling.

[0099] [Other Embodiments] The above-described operational flows are not limited to being implemented independently, but can be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0100] In the above-described embodiments and examples, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node.

[0101] That is, the UE 100 may be a terminal function unit (a type of communication module) for a base station to control a repeater that relays signals. Such a terminal function unit is referred to as an MT. Examples of the MT include, in addition to the IAB-MT, an NCR (Network Controlled Repeater)-MT and a RIS (Reconfigurable Intelligent Surface)-MT.

[0102] The term "network node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU). A network node may also be configured by a combination of at least a part of a core network device and at least a part of a base station.

[0103] A program may be provided that causes a computer to execute each process performed by the UE 100, the gNB 200, or the mobile IAB node 300M. The program may be recorded on a computer-readable medium. Using a computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the UE 100 or the gNB 200 may be integrated, and at least a portion of the UE 100, the gNB 200, or the mobile IAB node 300M may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0104] The functions performed by the UE 100, the gNB 200 (network node), or the mobile IAB node 300M may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (Central Processing Unit), conventional circuitry, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may be a programmed processor that executes programs stored in memory. In this specification, a circuitry, unit, or means is hardware that is programmed to realize or executes a described function. The hardware may be any hardware disclosed herein or any hardware known to be programmed to realize or execute the described function. If the hardware is a processor, which is considered to be a type of circuitry, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0105] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0106] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made within the scope of the gist. Furthermore, the embodiments, operation examples, and processes can be appropriately combined within the scope of not being inconsistent.

[0107] This application claims priority to U.S. Provisional Application No. 63 / 531,369 (filed August 8, 2023), the entire contents of which are incorporated herein by reference.

[0108] (Supplementary Note 1) (Supplementary Note 1) A communication control method used in a cellular communication system, comprising: a step of a network node broadcasting a first message including NPN (Non-Public Network) service provision status information indicating whether the network node is providing the NPN service for each entry of an NPN ID information list including information on the NPN service; and a step of a user equipment receiving the first message, wherein at least one of the entries includes the NPN service provision status information indicating that the network node is not providing the NPN service.

[0109] (Supplementary Note 2) The communication control method according to Supplementary Note 1, wherein the entry including the NPN service provision information indicating that the NPN service is not provided indicates an entry for a mobile IAB cell managed by a mobile IAB node.

[0110] (Supplementary Note 3) The communication control method according to Supplementary Note 1 or Supplementary Note 2, further comprising: the network node broadcasting a second message including an index of the NPNID information list; and the user equipment receiving the second message.

[0111] (Supplementary Note 4) The communication control method according to any one of Supplementary Notes 1 to 3, further comprising: the entry in the NPN ID information list indicated by the index is an entry for the mobile IAB cell; and the user equipment performs an inter-frequency cell reselection procedure using information about the NPN service included in the entry for the mobile IAB cell.

[0112] (Supplementary Note 5) The communication control method according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the first message is SIB1 and the second message is SIB4.

[0113] (Supplementary Note 6) A network node in a cellular communication system, comprising: a transmitter that broadcasts a first message including NPN service provision status information indicating whether the network node is providing the NPN service for each entry of an NPN ID information list including information related to an NPN service, wherein at least one of the entries includes the NPN service provision status information indicating that the network node is not providing the NPN service.

[0114] (Second Appendix) Introduction WID for Mobile IAB aims to specify the procedures for UE mobility and IAB-MT mobility as follows:

[0115] The detailed objectives of WI are as follows: Define mobility / topology adaptation procedures to enable IAB node mobility, including inter-donor mobility (full mobility) of a mobile IAB node [RAN3, RAN2]. Mobile IAB nodes can be attached to fixed (intermediate) IAB nodes. Optimizations specific to scenarios where a mobile IAB node connects to a stationary (intermediate) IAB node or directly connects to an IAB donor DU are deprioritized. Mobility of dual-connected IAB nodes is deprioritized. Enhancements for IAB nodes to move with their UEs, including aspects related to group mobility. There are no optimizations for targeting surrounding UEs [RAN3, RAN2]. Note: Solutions should avoid touching on topics already discussed in Rel-17 or excluded from Rel-17, except for enhancements specific to IAB node mobility. Mitigation of interference due to IAB node movement, including avoidance of potential reference and control signal collisions (PCI, RACH, etc.) [RAN3, RAN2].

[0116] The following principles should be respected: - Mobile IAB nodes should be able to serve legacy UEs. - Solutions providing optimization for mobile IAB may involve enhancements to Rel-18 UEs.

[0117] This appendix discusses the details of the mobility enhancements for the mobile IAB.

[0118] Discussion Enhancement of UE cell reselection functionality Regarding the cell reselection functionality enhancement, RAN2#119bis-e agreed to the following confirmations, observations and assumptions: RAN2 confirms that mobile IAB needs to work with legacy UEs. RAN2 observes that if a UE camps on / attaches to a mobile IAB cell for an extended period of time, the UE may be considered to be onboarded on the mobile IAB cell (i.e., the UE needs to know that the mobile IAB cell is such a cell). The time period requires further study. Whether this is necessary requires further study.

[0119] RAN2 makes the following assumptions (which may be trivial) about UEs operating in mobile IAB cells: Assumption 1: From the viewpoint of the network of the mobile IAB cell, the configuration principles of legacy parameters (including cell (re)selection, cell reservation, and access restriction) are the same as for legacy IAB cells. Assumption 2: There is no impact on the operation of legacy UEs in terms of specifications. Assumption 3: The information of mobile IAB cells newly broadcast by R18 (if agreed) does not prohibit / control access for legacy UEs. Assumption 4: Non-enhancement capable UEs (including legacy UEs and non-enhancement capable R18 UEs) simply ignore the information of mobile IAB cells newly broadcast by R18 (if agreed).

[0120] RAN2 Assumptions: Mobile IAB Cell Broadcast Information: To support mobility in inactive / idle state for Rel-18 UEs, a 1-bit Mobile IAB Cell Type Indicator is introduced (further study is needed on whether this needs to be known to prove the UE is onboard). How this is used needs further study (may be implementation dependent).

[0121] RAN2 has not specified any modifications to prevent surrounding UEs from accessing mobile IAB nodes from the perspective of mobile IAB WI, but believes SA2 may be working on an applicable Rel-18 solution (wait for SA2).

[0122] RAN2#120 further agreed to the following assumptions: RAN2 assumes that the assumed mobile IAB cell type indication may be specified if the behavior of the associated UE is specified.

[0123] RAN2#121 further agreed on the following assumptions and considerations: Working Assumption: Cell reselection to mIAB cells supports UE prioritization, at least for inter-frequency cell reselection. Further consideration is needed for the case where a UE is unspecified in searching and measuring mIAB cells on different frequencies (autonomous search). Further consideration is needed for the case where such a search is possible without assistance frequency information.

[0124] RAN2#122 has agreed on these two issues and their solution directions as follows: RAN2 believes that if the UE is camped on an mIAB cell, the UE can prioritize (cell and / or frequency) using the mIAB cell indication, and if the UE is not yet camped on an mIAB cell, it can prioritize. If the detailed conditions for applying such prioritization can be specified (in either case), RAN2 will consider conditions based on the cell residence timer or mobility state.

[0125] R2 direction (a matter of agreement at a later stage; other directions are not considered): RAN2 recognizes that for idle / inactive UEs, the following two problems need to be addressed: - Problem 1: For a UE that is physically on a moving vehicle but not yet camped on a mobile IAB cell (i.e., the UE is camped on a stationary cell), how can such a UE identify nearby mobile IAB cells, prioritize the mobile IAB cell (frequency and cell), and be "pulled" to this mobile IAB cell (especially in inter-frequency scenarios where the mobile IAB cell has a low frequency priority)? - Problem 2: How can a UE physically on a moving vehicle avoid reselecting other non-IAB (stationary) cells after camping on a mobile IAB cell? - Such a UE can prioritize the highest ranked cell on frequency when broadcasting the mIAB cell type indicator in SIB1 for cell reselection. The UE can use the SIB4 assistance information, when broadcast, to identify the presence of such a mobile IAB cell. The SIB4 assistance information can include the frequency of the mIAB cell. Further discussion is needed to clarify the UEs for Problem 1 and Problem 2.

[0126] Solution to Problem 1 Regarding problem 1 of the RAN2#122 agreement, as shown in Figure 1, the UE is located in a moving vehicle but is camped on an outer stationary cell. According to this statement, it is assumed that the outer fixed cell is operating at F1 while the moving IAB cell is operating at F2. Since the vehicle is moving, the UE is assumed to be in a high-mobility state.

[0127] To solve this problem, RAN2 assumes that such a UE can prioritize the highest ranked cell on a frequency when broadcasting the mIAB cell type indicator in SIB1 for cell reselection, but the UE behavior is exactly the same as the existing HSDN mechanism.

[0128] When an HSDN-capable UE is in a high-mobility state, the UE always considers the HSDN cell as the highest priority (i.e., higher than any other network-configured priority). When an HSDN-capable UE is not in a high-mobility state, the UE always considers the HSDN cell as the lowest priority (i.e., lower than any other network-configured priority).

[0129] The HSDN mechanism specifies another behavior to deprioritize HSDN cells when the UE is in a low mobility state. If considered a potential problem, a mobile IAB cell can always remove the HSDN indication from its SIB when the mobile IAB (or train) is in a low mobility or stationary state.

[0130] Therefore, RAN2 should again discuss whether it can reuse the existing HSDN indication in SIB1 instead of introducing a new mobile IAB cell type indication.

[0131] Proposal 1: Regarding Problem 1, before deciding to introduce mobile IAB cell type indication in SIB1, RAN2 should discuss whether the existing HSDN indication in SIB1 can be reused for mobile IAB frequency / cell prioritization.

[0132] Another issue captured in the RAN2#122 agreement is how the UE identifies the frequency on which the mobile IAB cell operates. The solution is for the UE to use SIB4 assistance information, which lists the mobile IAB frequencies. As a starting point, in the HSDN mechanism, SIB4 provides an HSDN cell list for each entry in the inter-frequency carrier frequency list, as follows: With this information, the UE can know on which frequency the HSDN cell is operating without a blind / full search.

[0133] Meanwhile, SA2 decided to reuse CAGs to restrict access to mobile IAB cells, and RAN2 is currently discussing how to implement this in its specifications. SA2 also decided to reuse prohibited TAs for UEs that cannot use NPNs. This means that "premium" mobile IAB cells are accessible only to "premium" UEs, while "standard" mobile IAB cells are accessible to all UEs (e.g., special subscription fees for enterprise and residential customers for a premium vehicular 5G experience). In this sense, providing only frequency information in SIB4 is insufficient because "standard" UEs cannot access "premium" mobile IAB cells even if they prioritize mobile IAB frequencies / cells. As a result, these UEs not only waste battery power due to inter-frequency measurements, but also degrade the user experience. Therefore, it is worth considering whether SIB4 also provides CAG and TA information for each frequency.

[0134] Observation 1: Some UEs are not allowed to access some mobile IAB cells (i.e., due to CAG access restrictions), so these UEs do not need to prioritize mobile IAB frequencies / cells.

[0135] According to the current specification, the interFreqCAG-CellList is available in SIB4 for the Rel-16 NPN feature. This list provides the CAG and TA information for each frequency with an "index" of the PLMN ID (i.e., not "PLMN ID + CAG ID"). The index refers to the NPN Identity Info List in SIB1, as follows:

[0136] Therefore, if the serving cell (i.e., the external fixed cell) does not broadcast the PNI-NPN ID (i.e., "PLMN ID + CAG ID") of the mobile IAB cell on a different frequency, the current SIB4 may not function because the required PNI-NPN ID index is not present. Therefore, it is necessary to consider whether the serving cell must always broadcast the PNI-NPN ID of the mobile IAB cell, especially when the serving cell does not provide NPN service, and the limited number of PLMNs, PNI-NPNs, and SNPNs (maximum 12 in total). Therefore, it is necessary to discuss whether RAN2 can assume such network limitations. If not, a method can be considered to broadcast explicit CAG and TAC information of the mobile IAB cell in SIB4.

[0137] Proposal 2: Regarding problem 1, RAN2 should agree that the SIB4 assistance information includes CAG and TA information in addition to frequency information.

[0138] Proposal 3: If Proposal 2 is agreeable, RAN2 should further discuss whether the existing interFreqCAG-CellList in SIB4 really works in all deployment scenarios.

[0139] Solution to Problem 2 According to the RAN2#122 agreement, the UE is located in a moving vehicle and is camped on an external stationary cell as shown in Figure 2, but the UE should avoid reselecting the external stationary cell.

[0140] In this case, the solution to problem 1 above can be reused to prioritize operation of UEs with mobile IAB frequencies / cells, i.e., either the existing HSDN cell indication or the new mobile IAB cell type indication.

[0141] Proposal 4: For Problem 2, RAN2 should agree that the common solution to Problem 1 in Proposal 1 is applicable.

[0142] IAB-MT Access Restriction Enhancements Fixed IAB Node Access WID states that a mobile IAB node shall only serve UEs, which means that a mobile IAB node should not serve other IAB nodes as child nodes: - A mobile IAB node has no descendant IAB nodes and serves only UEs.

[0143] To ensure this requirement, RAN2#119e has agreed to the following: Not broadcasting the "iab-Support" indication is sufficient to prevent other IAB nodes from accessing the mobile IAB (with no further impact on the specification).

[0144] However, the agreement has not been fully discussed. In particular, the part "(without being affected by further specifications)" leaves open the question of whether it is truly sufficient to leave it up to the implementation. Since WID explicitly requires that mobile IAB nodes cannot access other mobile IAB nodes, it is considered necessary to clarify this assumption in the specification to avoid confusion in mobile IAB implementations. Therefore, it is desirable for the Stage 2 specification to incorporate the above agreement or clarify that "in this release, mobile IAB nodes cannot access other mobile IAB nodes."

[0145] Proposal 5: RAN2 should agree to include in the Stage 2 specification that if an IAB node acts as a mobile IAB node in this release, it will not set the IAB support IE in the SIB.

[0146] Mobile IAB Node Access In RAN2 #120, the following agreements have been reached for mobile IAB node access to parent nodes: Mobile IAB nodes can camp on and connect to legacy Rel-16 / Rel-17 IAB-capable cells. R2 assumes that a "supporting mobile-IAB" indication is provided by the Rel-18 mobile IAB-capable parent cell.

[0147] Based on the agreement, the correspondence between display availability and IAB node behavior is summarized in Table 1.

[0148] (Table 1) SIB indications and IAB node behavior

[0149] For Cases 1 and 4, the behavior of the mobile IAB node is clear, as shown in Table 1.

[0150] Proposal 6: RAN2 should agree to prohibit mobile IABs from accessing parent nodes that do not broadcast both the legacy IAB support IE and the new "supporting mobile-IAB" IE.

[0151] Proposal 7: RAN2 should agree that the mobile IAB evaluates parent nodes that broadcast both the legacy IAB-support IE and the new "supporting mobile-IAB" IE.

[0152] Regarding Case 2, it is unclear whether a mobile IAB node can access the parent node if the legacy IAB support IE is not present and a new indication is provided. Furthermore, it should be discussed whether it is valid for the parent node to broadcast only the new indication without the legacy IE. It is considered typical for a parent node to accept access from both legacy and mobile IAB nodes. However, it is also possible that the parent node is deployed solely to provide services to mobile IAB nodes. Therefore, maintaining configuration flexibility is a good idea.

[0153] Proposal 8: RAN2 should discuss whether it is a valid configuration for the new "supporting mobile IAB-node" IE to be broadcast while the legacy IAB-support IE is not provided (i.e., the case in Table 1).

[0154] In Case 3, i.e., when the legacy IAB-support IE is provided but the new indication is not, the mobile IAB node can access the parent node because, as cited above, RAN2 has agreed that "mobile IAB nodes can camp on and connect to legacy Rel-16 / Rel-17 IAB-capable cells." However, the expected behavior of the IAB node is the same as in Case 4. In Case 3, the mobile IAB node can access the parent node under certain conditions, while in Case 4, it can always access the parent node. For example, the mobile IAB node can access only if no cell broadcasting the new indication is found. As another example, the mobile IAB node may be configured, for example, by the AMF or OAM, in the authorization / validation process as to whether it is allowed to access a cell that does not broadcast the new indication. Therefore, RAN2 needs to clarify under what conditions a mobile IAB node can access a parent cell that does not broadcast the new indication.

[0155] Proposal 9: RAN2 needs to discuss under what conditions a mobile IAB node broadcasting the legacy IA supporting IE (case 3 in Table 1) but not providing the new "supporting mobile IAB-node" IE should be allowed to access the parent node (e.g., only if no cell broadcasting the new indication is found, access to the parent node should be allowed).

Claims

1. A communication control method used in a cellular communication system, comprising: a network node broadcasting a first message including NPN service provision status information indicating whether the network node provides the NPN service for each entry of an NPN ID information list including information regarding NPN services; and a user device receiving the first message, wherein at least one of the entries includes the NPN service provision status information indicating that the network node does not provide the NPN service.

2. The communication control method according to claim 1, wherein the entry including the NPN service provision information indicating that the NPN service is not provided indicates an entry for a mobile IAB cell managed by a mobile IAB node.

3. The communication control method according to claim 2, further comprising: the network node broadcasting a second message including an index of the NPNID information list; and the user equipment receiving the second message.

4. The communication control method according to claim 3, further comprising: the entry of the NPN ID information list indicated by the index is an entry for the mobile IAB cell; and the user equipment performs an inter-frequency cell reselection procedure using information on the NPN service included in the entry for the mobile IAB cell.

5. The communication control method according to claim 3, wherein the first message is SIB1 and the second message is SIB4.

6. A network node in a cellular communication system, comprising: a transmitting unit that broadcasts a first message including NPN service provision information indicating whether the network node provides the NPN service for each entry of an NPN ID information list including information regarding an NPN service, wherein at least one of the entries includes the NPN service provision information indicating that the network node does not provide the NPN service.

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