Communication method, user equipment, and network node

Abstract

A communication method according to a first aspect of the present disclosure is executed by a user equipment in a cellular communication system, and comprises a step for receiving, from a network node different from a mobile relay node, a system information block for inter-frequency cell reselection performed by the user equipment in an RRC idle state or an RRC inactive state. The system information block includes frequency information indicating a mobile relay node frequency that is a frequency to which a mobile relay node cell managed by the mobile relay node belongs, a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell, and additional information relating to the list.

Description

COMMUNICATION METHOD, USER EQUIPMENT, AND NETWORK NODE

[0001] The present disclosure relates to a communication method, a user equipment, and a network node for use in a cellular communication system.

[0002] In the 3GPP (Third Generation Partnership Project) (registered trademark, the same applies hereinafter), a standardization project for cellular communication systems, a relay node called an IAB (Integrated Access and Backhaul) node has been introduced (see, for example, Non-Patent Document 1). Specifically, one or more relay nodes intervene in communication between a base station and a user device and perform relay operations for this communication.

[0003] 3GPP TS 38.300 V17.6.0 (2023-09)

[0004] The present disclosure relates to a technique for improving the efficiency of inter-frequency cell reselection performed by a user equipment in a radio resource control (RRC) idle state or an RRC inactive state in a cellular communication system in which a mobile relay node may exist.

[0005] A communication method according to a first aspect of the present disclosure is a communication method executed by a user equipment in a cellular communication system, comprising a step of receiving, from a network node other than a mobile relay node, a system information block for inter-frequency cell reselection performed by the user equipment in an RRC idle state or an RRC inactive state, wherein the system information block includes frequency information indicating a mobile relay node frequency that is a frequency to which a mobile relay node cell managed by the mobile relay node belongs, a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell, and additional information related to the list.

[0006] A user equipment according to a second aspect of the present disclosure is a user equipment used in a cellular communication system, and includes a receiver that receives, from a network node other than a mobile relay node, a system information block for inter-frequency cell reselection performed by the user equipment in an RRC idle state or an RRC inactive state, wherein the system information block includes frequency information indicating a mobile relay node frequency that is a frequency to which a mobile relay node cell managed by the mobile relay node belongs, a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell, and additional information related to the list.

[0007] A network node according to a third aspect of the present disclosure is used in a cellular communication system, and is a network node different from a mobile relay node, and includes a transmitter for transmitting a system information block for inter-frequency cell reselection performed by user equipment in an RRC idle state or an RRC inactive state, wherein the system information block includes frequency information indicating a mobile relay node frequency that is a frequency to which a mobile relay node cell managed by the mobile relay node belongs, a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell, and additional information related to the list.

[0008] 1 is a diagram illustrating an example of a configuration of a cellular communication system according to an embodiment. A diagram illustrating an example of a relationship between an IAB node, a parent node, and a child node. A diagram illustrating an example of a configuration of a gNB that is a network node according to an embodiment. A diagram illustrating an example of a configuration of an IAB node that is a relay node according to an embodiment. A diagram illustrating an example of a configuration of a UE that is a user equipment according to an embodiment. A diagram illustrating an example of a protocol stack related to an IAB-MT RRC connection and a NAS connection. A diagram illustrating a protocol stack related to an F1-U protocol. A diagram illustrating a protocol stack related to an F1-C protocol. A diagram for explaining an operation scenario according to an embodiment. A diagram illustrating an overview of an operation of a cellular communication system according to an embodiment. A diagram illustrating an example of an operation of a UE according to an embodiment. A diagram illustrating an example of a change in specifications of SIB4 according to a first specific example. A diagram illustrating an example of a change in specifications of SIB4 according to a first specific example. A diagram illustrating an example of a change in specifications of SIB4 according to a second specific example. A diagram illustrating an example of a change in specifications of SIB4 according to a third specific example. A diagram illustrating an example of a change in specifications of SIB4 according to a fourth specific example. A diagram illustrating another example of a change in specifications of SIB4 according to a fourth specific example. A diagram illustrating another example of a change in specifications of SIB4 according to a fifth specific example. A diagram illustrating another example of a change in specifications of SIB4 according to the fifth specific example. FIG. 13 is a diagram showing an example of a change in the specifications of SIB4 according to a sixth specific example.

[0009] 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.

[0010] (1) System Configuration An example configuration of a cellular communication system according to an embodiment will be described. The cellular communication system 1 according to an 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 at least partially applied to the cellular communication system 1. Furthermore, future cellular communication systems such as 6G may also be applied to the cellular communication system 1.

[0011] 1 is a diagram showing an example of the configuration of a cellular communication system 1 according to an embodiment. 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.

[0012] In the following, an example in which the base station 200 is an NR base station will be mainly described, but the base station 200 may also be an LTE base station (i.e., an eNB). Note that, in the following, the base stations 200-1 and 200-2 may be referred to as gNB 200 (or base station 200), and the IAB nodes 300-1 and 300-2 may be referred to as IAB nodes 300.

[0013] The 5GC 10 has an AMF (Access and Mobility Management Function) 11 and a UPF (User Plane Function) 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 NAS (Non-Access Stratum) signaling. The UPF 12 is a device that performs user data transfer control, etc.

[0014] Each gNB200 is a fixed wireless communication node and manages one or more cells. Cell is used as a term indicating the smallest unit of a wireless communication area. Cell is sometimes used as a term indicating a function or resource for wireless communication with UE100. One cell belongs to one carrier frequency. Hereinafter, cells and base stations may be used interchangeably. Each gNB200 is interconnected with 5GC10 via an interface called an NG interface. Figure 1 illustrates two gNBs, 200-1 and 200-2, connected to 5GC10. Each gNB200 may be divided into a central unit (CU) and a distributed unit (DU). The CU and DU are interconnected 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.

[0015] 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). Figure 1 shows an example in which the IAB node 300-1 is wirelessly connected to the donor node 200-1, the IAB node 300-2 is wirelessly connected to the IAB node 300-1, and the F1 protocol is transmitted over two backhaul hops.

[0016] 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, 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.

[0017] FIG. 2 is a diagram showing an example of the relationship between the IAB node 300, parent nodes, and child nodes.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] In addition, 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.

[0022] (2) Configuration of the Network Node Next, the configuration of the gNB 200, which is a network node according to the embodiment, will be described. Fig. 3 is a diagram showing an example configuration of the gNB 200. The gNB 200 has a wireless communication unit 210, a network communication unit 220, and a control unit 230.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] (3) Configuration of Relay Node Next, the configuration of the IAB node 300, which is a relay node according to the embodiment, will be described. Fig. 4 is a diagram showing an example configuration of the IAB node 300. 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] (4) Configuration of User Equipment Next, a configuration of the UE 100, which is a user equipment according to the embodiment, will be described. Fig. 5 is a diagram showing an example configuration of the UE 100. The UE 100 includes a radio communication unit 110 and a control unit 120.

[0031] 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.

[0032] 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.

[0033] (5) Protocol Stack Configuration Next, a description will be given of the configuration of the protocol stack according to the embodiment. Fig. 6 is a diagram showing an example of a protocol stack related to the RRC connection and NAS connection of the IAB-MT.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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 as a 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.

[0043] 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.

[0044] 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.

[0045] 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 transmitting the message to the 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." In addition, the upstream direction and the uplink (UL) direction may be used without distinction. In addition, the downstream direction and the downlink (DL) direction may be used without distinction.

[0046] (6) 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).

[0047] 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.

[0048] 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.

[0049] 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.

[0050] In the following, there may be no distinction between the movement of a mobile IAB node (migration) and the handover of a mobile IAB node (handover). In the following, a mobile IAB node may be referred to as a "mobile IAB node" or a "migrating IAB node." In either case, the mobile IAB node may be referred to as a mobile IAB node. The mobile IAB node may also be a mobile relay node.

[0051] (7) Cell Reselection Procedure Next, a cell reselection procedure according to the embodiment will be described.

[0052] 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.

[0053] Cell reselection procedures include intra-frequency cell reselection procedures and inter-frequency cell reselection procedures.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The UE 100 basically reselects the cell with the highest rank from among the two ranking criteria Rs and Rn.

[0058] 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.

[0059] 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.

[0060] Second, the UE 100 performs a cell reselection process to reselect a cell (serving 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 the radio quality of the current serving cell is lower than a radio quality threshold and the radio quality of the neighboring cell is higher than another radio quality threshold, the UE 100 may perform cell reselection to the neighboring cell.

[0061] 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.

[0062] (8) Operation Related to Inter-Frequency Cell Reselection in a Scenario Where a Mobile IAB Node May Exist Next, an operation according to the embodiment will be described. The operation according to the embodiment relates to inter-frequency cell reselection in a scenario where a mobile IAB node (also referred to as an "mIAB node" or "mIAB") may exist. Figure 9 is a diagram for explaining an operation scenario according to the embodiment.

[0063] A UE 100 in an RRC idle state or an RRC inactive state 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 (mIAB cell). In the following, the mobile IAB node 300M and the mobile IAB cell 300S may be used interchangeably.

[0064] However, UE100 is camped on a cell (stationary cell or macro cell) managed by a fixed, non-moving gNB200. The cell of gNB200 can be a serving cell for UE100. Hereinafter, the cell of gNB200 may be referred to as serving cell 200S. UE100 is camped on serving cell 200S and is located in a vehicle, but has not yet camped on mobile IAB cell 300S. Here, the frequency used in serving cell 200S and the frequency used in mobile IAB cell 300S are assumed to be different.

[0065] In such a situation, when the UE 100 performs an inter-frequency cell reselection procedure, there is a problem of how to camp the UE 100 on the mobile IAB cell 300S. To address this problem, in 3GPP, it has been agreed that the gNB 200 broadcasts information indicating the frequency to which the mobile IAB cell 300S belongs (also referred to as the "mIAB frequency") (also referred to as the "mIAB frequency information") in a system information block type 4 (SIB4). This makes it easy for the UE 100 to perform cell reselection to the mobile IAB cell 300S using the mIAB frequency information.

[0066] Specifically, the UE 100 acquires the mIAB frequency information from SIB4, performs cell search and measurements (measures RSRP and / or RSRQ) on the mIAB frequency, and identifies the cell with the best measurement result (also referred to as the "best cell"). The best cell may be a cell that satisfies a predetermined condition, for example, the cell with the highest rank. The UE 100 determines whether the identified best cell is an mIAB cell. For example, the UE 100 receives (acquires) System Information Block Type 1 (SIB1) broadcast in the best cell, and determines that the best cell is an mIAB cell if an indicator indicating that the best cell is an mIAB cell (mIAB cell indicator) is included in SIB1. Then, if the UE 100 determines that the best cell is an mIAB cell, the UE 100 performs an inter-frequency cell reselection procedure, regarding the mIAB frequency as the highest priority for cell reselection. As a result, the UE 100 may be able to reselect and camp on the moving IAB cell 300S.

[0067] Furthermore, in 3GPP, in order to facilitate the determination of an mIAB cell by UE 100, in addition to including mIAB frequency information in SIB4, it is being discussed to include in SIB4 a physical cell identifier (PCI) list used by UE 100 to identify a mobile IAB node 300M cell. Such a PCI list may include the PCI of the mIAB cell. For example, UE 100 identifies the PCI of the best cell on the mIAB frequency from the SSB of the cell (specifically, a synchronization signal in the SSB), and determines whether the PCI of the best cell is the PCI of the mIAB cell based on the PCI list. This allows UE 100 to determine whether the cell is an mIAB cell when it detects the PCI of the cell (i.e., by simply receiving the SSB), and does not need to acquire (decode) SIB1. Therefore, the cell reselection operation of the UE 100 can be made more efficient.

[0068] However, 3GPP has not yet determined whether a PCI list is an exclusive PCI list. An exclusive PCI list means that the PCI list includes only PCIs of mIAB cells. In other words, if the PCI list includes PCIs of normal cells (fixed cells) other than mIAB cells, the PCI list is not exclusive.

[0069] Furthermore, 3GPP has not yet determined whether a PCI list is a complete PCI list. A complete PCI list means that the PCI list includes the PCIs of all available mIAB cells. In other words, if the PCI list includes only the PCIs of some of the available mIAB cells, the PCI list is not complete.

[0070] Because the mIAB node 300 may move, the network (gNB 200) may not necessarily be able to provide an exclusive and complete PCI list to the UE 100. The operation to be performed by the UE 100 may change depending on whether the PCI list is exclusive or not and whether the PCI list is complete or not. Therefore, in an embodiment, additional information regarding the PCI list is further included in the SIB 4, thereby making inter-frequency cell reselection more efficient in a scenario where an mIAB node may be present.

[0071] (8.1) Operation Flow Next, an operation flow according to the embodiment will be described. Fig. 10 is a diagram showing an overview of the operation of the cellular communication system 1 according to the embodiment. In the following description of the embodiment, it is assumed that the UE 100 is in an RRC idle state or an RRC inactive state in the cell of the gNB 200. In other words, the serving cell of the UE 100 in the RRC idle state or the RRC inactive state is the cell of the gNB 200.

[0072] In step S1, the gNB 200 transmits (broadcasts) an SIB for inter-frequency cell reselection performed by the UE 100 in an RRC idle state or an RRC inactive state. The SIB for inter-frequency cell reselection is SIB4 in 5G / NR. The UE 100 receives SIB4. However, in future cellular communication systems such as 6G, the SIB for inter-frequency cell reselection may be an SIB with a different type number from SIB4.

[0073] In an embodiment, SIB4 includes: 1) mIAB frequency information indicating the mIAB frequency to which the mIAB cell belongs; 2) a PCI list used by UE100 to identify the mIAB cell; and 3) additional information regarding the PCI list (also referred to as "PCI list additional information").

[0074] SIB4 may include an mIAB frequency list, which is a list of mIAB frequencies, and each entry in the mIAB frequency list may be mIAB frequency information. The PCI list and PCI list additional information may be included in SIB4 on a mIAB frequency basis. For example, the PCI list and PCI list additional information may be in one-to-one correspondence with each entry in the mIAB frequency list. Note that gNB200 may include the PCI list and PCI list additional information corresponding to the mIAB frequency information in SIB4 only when the mIAB frequency information is included in SIB4.

[0075] The UE 100 may perform the operation shown in Fig. 10 only when the UE 100 recognizes that it is in an on-boarding state. The on-boarding state is a state in which the UE 100 is on a vehicle (for example, a train and / or a bus).

[0076] In step S2, UE 100 identifies a best cell belonging to the mIAB frequency based on the mIAB frequency information included in SIB 4 received from gNB 200. Then, UE 100 determines whether to acquire SIB 1 from the identified best cell based on the PCI list addition information included in SIB 4 received from gNB 200.

[0077] If it is determined not to acquire SIB1 from the best cell, UE100 determines whether the best cell is an mIAB cell (specifically, whether the PCI of the best cell is the PCI of the mIAB cell) based on the PCI list included in SIB4 received from gNB200 without acquiring SIB1 from the best cell. On the other hand, if it is determined to acquire SIB1 from the best cell, UE100 acquires SIB1 from the best cell, and determines whether the best cell is an mIAB cell based on whether the acquired SIB1 includes an "mIAB cell indicator".

[0078] FIG. 11 is a diagram illustrating an example of the operation of the UE 100 according to the embodiment.

[0079] In step S10, the UE 100 recognizes that it is in an onboarding state. For example, the UE 100 may detect the onboarding state using at least one of its own moving speed, a change in the propagation environment, and information managed by a higher-level application. The moving speed of the UE 100 can be known by positioning that the UE 100 periodically performs, for example, by positioning using a GNSS (Global Navigation Satellite System) receiver. The UE 100 may recognize that it is in an onboarding state based on the fact that its moving speed is high (for example, the moving speed exceeds a threshold). The UE 100 may estimate its moving speed from Doppler measurement values. The UE 100 may recognize that the user of the UE 100 has boarded a vehicle from application information. For example, an application may recognize boarding of a vehicle using near field communication (NFC).

[0080] In step S11, UE 100 acquires SIB 4 from gNB 200 (serving cell). The SIB 4 includes mIAB frequency information indicating the mIAB frequency to which the mIAB cell belongs, a PCI list used by UE 100 to identify the mIAB cell, and PCI list addition information related to the PCI list.

[0081] In step S12, UE100 performs a cell search (e.g., attempts to receive SSB) at the mIAB frequency based on the mIAB frequency information contained in SIB4 received from gNB200, measures the reception quality (RSRP and / or RSRQ) of each discovered cell based on the SSB, and identifies the best cell.

[0082] In step S13, the UE 100 determines whether to acquire the SIB1 from the best cell, based on the PCI list addition information.

[0083] If it is determined to acquire SIB1 (step S14: YES), in step S15, UE 100 acquires SIB1 from the best cell. In this case, in step S16, UE 100 determines whether or not the best cell is an mIAB cell based on the acquired SIB1. Specifically, if the acquired SIB1 includes an "mIAB cell indicator," UE 100 determines that the best cell is an mIAB cell. On the other hand, if the acquired SIB1 does not include an "mIAB cell indicator," UE 100 determines that the best cell is a cell that is not an mIAB cell (a normal cell (fixed cell)).

[0084] On the other hand, if it is determined not to acquire SIB1 (step S14: NO), in step S17, UE 100 determines whether or not the best cell is an mIAB cell based on the PCI list without acquiring SIB1 from the best cell. Specifically, UE 100 determines whether or not the PCI identified based on the SSB of the best cell is the PCI of the mIAB cell based on the PCI list.

[0085] If it is determined that the best cell is an mIAB cell (step S18: YES), in step S19, the UE 100 regards the mIAB frequency as the highest priority for cell reselection. Specifically, the UE 100 sets the frequency priority of the mIAB frequency as the highest priority for cell reselection. The highest priority may be a frequency priority higher than the frequency priority signaled from the gNB 200. As a result, in step S20, the UE 100 performs cell reselection to the best cell (i.e., the mIAB cell) on the mIAB frequency by the above-described inter-frequency cell reselection procedure, and camps on the best cell (mIAB cell).

[0086] On the other hand, if it is determined that the best cell is not an mIAB cell (step S18: NO), UE100 may select the next candidate mIAB frequency and resume processing from step S12 for the selected mIAB frequency.

[0087] (8.2) Specific Examples of Additional Information Next, specific examples of PCI list additional information according to the embodiment will be described.

[0088] (8.2.1) First Specific Example In the first specific example, the PCI list additional information is information for specifying whether the PCI list includes only the PCI of the mIAB cell, i.e., the PCI list additional information is information for specifying whether the corresponding PCI list is exclusive.

[0089] When the PCI list additional information indicating exclusive (Exclusive) is associated with the PCI list, the PCI list includes only the PCI of the mIAB cell. Therefore, when the PCI identified by the SSB of the best cell on the mIAB frequency is included in the PCI list, the UE 100 regards the mIAB frequency as the highest priority for cell reselection without acquiring the SIB1 of the best cell.

[0090] On the other hand, if the PCI list additional information indicating exclusive (Exclusive) is not associated with the PCI list, the PCI list may include not only the PCI of the mIAB cell but also the PCI of a fixed cell (normal cell). Therefore, when the PCI identified by the SSB of the best cell on the mIAB frequency is included in the PCI list, the UE 100 acquires the SIB1 of the best cell, and when the "mIAB cell indicator" is included in the SIB1, the UE 100 regards the mIAB frequency as the highest priority for cell reselection. Note that, when the PCI of the best cell is not included in the PCI list, the UE 100 regards that no mIAB cell exists on the mIAB frequency and does not perform the operation of regarding the mIAB frequency as the highest priority.

[0091] 12 and 13 are diagrams illustrating an example of a change in the SIB4 specification according to a first specific example. In the example of a change in the specification in the following embodiment, an example of a change in the SIB4 specification in TS38.331, which is a 3GPP technical specification for RRC, will be described.

[0092] As shown in Fig. 12, in this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18," which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq). Note that "-r18" indicates that this is an information element (IE) introduced in Release 18 of the 3GPP standard.

[0093] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18(ARFCN-ValueNR)," which is information indicating the corresponding mIAB frequency (mIAB frequency information), "mobileIAB-PCI-List," which is a PCI list of mIAB cells belonging to the mIAB frequency, and "mobileIAB-PCI-List-Exclusive," which is PCI list additional information related to the PCI list. Note that "mobileIAB-PCI-List" includes the PCI (PCI-Range) of the number of mIAB cells up to the maximum number (maxmIABcell).

[0094] As shown in FIG. 13, when the "mobileIAB-PCI-List-Exclusive" field is present, the "mobileIAB-PCI-List" includes only the PCIs of mobile IAB cells (mIAB cells), and the UE 100 can skip acquiring the SIB1 of each listed cell for frequency prioritization.

[0095] On the other hand, if this field is not present, the "mobileIAB-PCI-List" may contain the PCI of a non-mobile IAB cell (a normal cell (fixed cell)), and the UE 100 must check whether a mobile IAB node indicator (mIAB cell indicator) is broadcast by each listed cell. If the UE 100 cannot find a cell that matches the PCI in the list, the UE 100 assumes that no mobile IAB cell (mIAB cell) exists on that frequency.

[0096] (8.2.2) Second Specific Example In the second specific example, the PCI list additional information is information for specifying whether the PCI list includes the PCIs of all possible mIAB cells, i.e., whether the corresponding PCI list is complete.

[0097] When PCI list addition information indicating completeness is associated with the PCI list, the PCI list includes all PCIs that the mIAB cell can take (for example, PCIs of all mIAB cells in the cell of gNB200). Therefore, if the PCI identified by the SSB of the best cell on the mIAB frequency is included in the PCI list, UE100 does not acquire SIB1 of the best cell, and the mIAB frequency is considered to be the highest priority for cell reselection.

[0098] On the other hand, if the PCI list addition information indicating completeness is not associated with the PCI list, an mIAB cell not included in the PCI list may exist, for example, in a cell of gNB200. Therefore, when the PCI identified by the SSB of the best cell on the mIAB frequency is included in the PCI list, UE100 acquires SIB1 of the best cell, and if the "mIAB cell indicator" is included in SIB1, the mIAB frequency is considered to be the highest priority for cell reselection. Note that if the PCI of the best cell is not included in the PCI list, UE100 considers that there is no mIAB cell on the mIAB frequency and does not perform the operation of considering it to be the highest priority.

[0099] FIG. 14 is a diagram showing an example of a change in the specifications of SIB4 according to the second specific example.

[0100] In this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18" which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq).

[0101] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18(ARFCN-ValueNR)," which is information indicating the corresponding mIAB frequency (mIAB frequency information), "mobileIAB-PCI-List," which is a PCI list of mIAB cells belonging to the mIAB frequency, and "mobileIAB-PCI-List-Complete," which is PCI list additional information related to the PCI list. Note that "mobileIAB-PCI-List" includes the PCI (PCI-Range) of the number of mIAB cells up to the maximum number (maxmIABcell).

[0102] If the "mobileIAB-PCI-List-Complete" field is present, the "mobileIAB-PCI-List" contains all possible PCIs of mobile IAB cells (mIAB cells), and the UE 100 can skip acquiring SIB1s of each listed cell for frequency prioritization purposes. On the other hand, if the "mobileIAB-PCI-List" field is not present, the "mobileIAB-PCI-List" may contain some PCIs of mobile IAB cells (mIAB cells), and the UE 100 must check whether a mobile IAB node indicator (mIAB cell indicator) is broadcast by a cell that is not listed.

[0103] (8.2.3) Third Specific Example In the third specific example, the PCI list addition information is information for identifying whether UE100 needs to acquire SIB1 from the best cell identified on the mIAB frequency.

[0104] When PCI list addition information indicating that the SIB1 of the best cell on the mIAB frequency should be acquired is associated with the PCI list, the UE 100 needs to acquire the SIB1 of the best cell on the mIAB frequency corresponding to the PCI list. Therefore, when the PCI identified by the SSB of the best cell on the mIAB frequency is included in the PCI list, the UE 100 acquires the SIB1 of the best cell, and when an "mIAB cell indicator" is included in the SIB1, the UE 100 considers the mIAB frequency to be the highest priority for cell reselection. Note that when the PCI of the best cell is not included in the PCI list, the UE 100 considers that no mIAB cell exists on the mIAB frequency and does not perform the operation of considering the mIAB frequency to be the highest priority.

[0105] On the other hand, if the PCI list additional information indicating that the SIB1 of the best cell on the mIAB frequency should be acquired is not associated with the PCI list, the UE 100 does not need to acquire the SIB1 of the best cell on the mIAB frequency corresponding to the PCI list. Therefore, if the PCI specified by the SSB of the best cell on the mIAB frequency is included in the PCI list, the UE 100 does not acquire the SIB1 of the best cell, and regards the mIAB frequency as the highest priority for cell reselection.

[0106] FIG. 15 is a diagram showing an example of a change in the specifications of SIB4 according to the third specific example.

[0107] In this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18" which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq).

[0108] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18(ARFCN-ValueNR)," which is information indicating the corresponding mIAB frequency (mIAB frequency information), "mobileIAB-PCI-List," which is a PCI list of mIAB cells belonging to the mIAB frequency, and "NeedsForSIB1-check," which is PCI list additional information related to the PCI list. Note that "mobileIAB-PCI-List" includes the PCIs (PCI-Range) of mIAB cells up to the maximum number (maxmIABcell).

[0109] "NeedsForSIB1-check": If this field is not present, the UE 100 can skip acquiring SIB1 of each listed cell for frequency prioritization. On the other hand, if this field is present, the UE 100 needs to check whether a mobile IAB node indicator (mIAB cell indicator) is broadcast by each listed cell.

[0110] (8.2.4) Fourth Specific Example In the fourth specific example, the PCI list additional information is information for identifying whether the PCI indicated in each entry of the PCI list is the PCI of an mIAB cell. The PCI list additional information is included in the SIB4 for each entry of the PCI list. In other words, the PCI list additional information is in one-to-one correspondence with the entries of the PCI list.

[0111] When PCI list additional information indicating the PCI of the mIAB cell corresponds to an entry in the PCI list, if the PCI of the best cell on the mIAB frequency matches the entry, UE100 considers the mIAB frequency to be the highest priority for cell reselection without acquiring SIB1 of the best cell.

[0112] On the other hand, when the PCI list additional information indicating the PCI of the mIAB cell does not correspond to an entry in the PCI list, if the PCI of the best cell on the mIAB frequency matches the entry, the UE 100 acquires the SIB1 of the best cell. Then, if the SIB1 includes an "mIAB cell indicator," the UE 100 regards the mIAB frequency as the highest priority for cell reselection.

[0113] FIG. 16 is a diagram showing an example of a change in the specifications of SIB4 according to the fourth specific example.

[0114] In this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18" which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq).

[0115] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18(ARFCN-ValueNR)," which is information indicating the corresponding mIAB frequency (mIAB frequency information), and "mobileIAB-PCI-List," which is a PCI list of mIAB cells belonging to the mIAB frequency. "mobileIAB-PCI-List" includes PCI information (MobileIAB-PCI-info) of up to the maximum number (maxmIABcell) of mIAB cells.

[0116] Each "MobileIAB-PCI-info" includes a PCI (PhysCellId (PCI-Range)) and "MobileIABCell", which is PCI list additional information for specifying whether the PCI is the PCI of an mIAB cell. When this field "MobileIABCell" exists, the PCI on the same entry is a mobile IAB cell (mIAB cell), and the UE 100 can skip acquiring SIB1 of this cell for frequency prioritization. On the other hand, when this field does not exist, the PCI on the same entry is a non-mobile IAB cell (normal cell (fixed cell)), and the UE 100 can skip acquiring SIB1 of this cell for frequency prioritization. Alternatively, if this field is not present, the PCI on the same entry may or may not be a mobile IAB cell (mIAB cell), and the UE 100 needs to check whether a mobile IAB node indicator (mIAB cell indicator) is broadcast by this cell.

[0117] 17 is a diagram showing another example of specification changes to SIB4 according to the fourth specific example, in which differences from the specification change example shown in FIG.

[0118] In this modified specification example, each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18 (ARFCN-ValueNR)," which is information indicating the corresponding mIAB frequency (mIAB frequency information). Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "mobileIAB-PCI-List" and / or "mobileIAB-PCI-List-Exclusive." The "mobileIAB-PCI-List" includes PCI information (MobileIAB-PCI-info) for up to the maximum number (maxmIABcell) of mIAB cells.

[0119] Each "MobileIAB-PCI-info" includes a PCI (PhysCellId (PCI-Range)) and "MobileIABCell," which is PCI list additional information for specifying whether the PCI is the PCI of an mIAB cell. If this field exists for "MobileIABCell," the PhysCellId of the same entry is the PCI of a mobile IAB cell (mIAB cell), and the UE 100 can skip acquiring SIB1 of this cell for frequency prioritization purposes. On the other hand, if this field does not exist, the PhysCellId of the same entry is the PCI of a non-mobile IAB cell, and the UE 100 needs to check whether a mobile IAB node indicator (mIAB cell indicator) is broadcast by this cell. If the UE 100 does not find a cell that matches the PCI in the list, the UE 100 assumes that there is no mobile IAB cell (mIAB cell) on that frequency.

[0120] Alternatively, each "Mobile-IAB-PCI-info" may alternatively include either "Mobile-IAB-PCI" or "Stationary-PCI." "Mobile-IAB-PCI" includes a PCI (PCI-Range) and indicates that the PCI is the PCI of a mobile IAB cell (mIAB cell). In contrast, "Stationary-PCI" includes a PCI (PCI-Range) and indicates that the PCI is the PCI of a non-mobile IAB cell (normal cell (fixed cell)).

[0121] (8.2.5) Fifth Specific Example In the fifth specific example, the PCI list additional information is information for specifying whether the PCI list is expressed in the PCI range of the mIAB cell. Here, the "PCI range" refers to the range of PCIs that the mIAB cell can have.

[0122] When PCI list addition information indicating that the PCI range of the mIAB cell is expressed is associated with the PCI list, if the PCI of the best cell on the mIAB frequency is within the PCI range, the UE 100 regards the mIAB frequency as the highest priority for cell reselection without acquiring the SIB1 of the best cell.

[0123] If a PCI list contains only the first and second entries of a PCI list, this may implicitly indicate that the PCI list is a PCI range.

[0124] Furthermore, if there are multiple PCI ranges (for example, if there are two PCI ranges, A to C and F to H), the first and second entries in the PCI list may indicate the first PCI range (A to C), and the third and fourth entries may indicate the second PCI range (F to H). Although an example is given here of two PCI ranges, there may be three or more ranges.

[0125] FIG. 18 is a diagram showing an example of a change in the specifications of SIB4 according to the fifth specific example.

[0126] In this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18" which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq).

[0127] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18 (ARFCN-ValueNR)", which is information indicating the corresponding mIAB frequency (mIAB frequency information), "mobileIAB-PCI-List", which is a PCI list of mIAB cells belonging to the mIAB frequency, and "mobileIAB-PCI-Range", which is PCI list additional information related to the PCI list.

[0128] If the "mobileIAB-PCI-Range" field exists, the first entry in the "mobileIAB-PCI-List" indicates the lower limit of the PCI of the mobile IAB cell (mIAB cell), and the second entry in the "mobileIAB-PCI-List" indicates the upper limit of the PCI of the mobile IAB cell (mIAB cell). There are no entries after the third. For the purpose of frequency prioritization, the UE 100 may skip acquiring the SIB1 of a cell (best cell) having a PCI within the range indicated by the lower limit and the upper limit.

[0129] Alternatively, "mobileIAB-PCI-Range" may be information indicating the number of PCI ranges. Fig. 19 is a diagram showing another example of a modification of the specifications of SIB4 according to the fifth specific example. In this example of a modification, "mobileIAB-PCI-Range" is set to any value from 1 to 8 as the number of PCI ranges.

[0130] (8.2.6) Sixth Specific Example In the sixth operation example, the PCI list additional information is information for identifying whether the PCI indicated in the PCI list is the PCI of a cell (normal cell (fixed cell)) different from the mIAB cell. In other words, the PCI list additional information is information for identifying whether each entry in the PCI list is the PCI of a fixed cell.

[0131] When PCI list additional information indicating that each entry of the PCI list is the PCI of a fixed cell is associated with the PCI list, the UE 100 can estimate that a cell having a PCI not included in the PCI list is an mIAB cell. When the PCI of the best cell on the mIAB frequency is not included in the PCI list, the UE 100 regards the mIAB frequency as the highest priority for cell reselection without acquiring the SIB1 of the best cell.

[0132] FIG. 20 is a diagram showing an example of a change in the specifications of SIB4 according to the sixth specific example.

[0133] In this modified example of the specification, SIB4 includes "mobileIAB-InterFreqCarrierFreqList-r18" which is a list of mIAB frequencies. "mobileIAB-InterFreqCarrierFreqList-r18" includes "MobileIAB-InterFreqCarrierFreqInfo-r18" up to the maximum number (maxFreq).

[0134] Each "MobileIAB-InterFreqCarrierFreqInfo-r18" includes "targetFrequency-r18 (ARFCN-ValueNR)", which is information indicating the corresponding mIAB frequency (mIAB frequency information), "mobileIAB-PCI-List", which is a PCI list of mIAB cells belonging to the mIAB frequency, and "non-MobileIAB-PCI-List", which is PCI list additional information related to the PCI list.

[0135] If the "non-MobileIAB-PCI-List" field exists, the "mobileIAB-PCI-List" includes only PCIs of non-mobile IAB cells (fixed cells). In this case, the UE 100 can skip acquiring the SIB1 of the best cell whose PCI is not included in the "mobileIAB-PCI-List" for the purpose of frequency prioritization.

[0136] (9) Other Embodiments In the above embodiment, an example in which the relay node is an IAB node has been described, but the relay node may be a network-controlled repeater device. Such a repeater device is also called an NCR (Network Controlled Repeater).

[0137] The above-described operational flows are not limited to being implemented independently, but can also 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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 and / 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).

[0142] The functions performed by the UE 100, the gNB 200, 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 (a Central Processing Unit), conventional circuits, 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 also be a programmed processor that executes a program stored in memory. In this specification, circuitry, unit, or means refers to hardware that is programmed to perform the described functions or that executes the described functions. The hardware may be any hardware disclosed herein or any hardware known to be programmed or capable of performing the described functions. If the hardware is a processor, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0143] 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.

[0144] 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.

[0145] This application claims priority to U.S. Provisional Application No. 63 / 594,311 (filed October 30, 2023), the entire contents of which are incorporated herein by reference.

[0146] (10) First Supplementary Note The following is a supplementary note regarding the features of the above-described embodiment.

[0147] (Supplementary Note 1) A communication method executed by a user equipment in a cellular communication system, comprising a step of receiving, from a network node other than a mobile relay node, a system information block for inter-frequency cell reselection performed by the user equipment in a Radio Resource Control (RRC) idle state or an RRC inactive state, wherein the system information block includes: frequency information indicating a mobile relay node frequency, which is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information related to the list.

[0148] (Supplementary Note 2) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether the list includes only physical cell identifiers of mobile relay node cells.

[0149] (Supplementary Note 3) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether the list includes physical cell identifiers of all available mobile relay node cells.

[0150] (Supplementary Note 4) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether the user equipment needs to acquire a system information block type 1 (SIB1) from a best cell detected on the mobile relay node frequency.

[0151] (Supplementary Note 5) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether or not a physical cell identifier indicated in each entry of the list is a physical cell identifier of a mobile relay node cell.

[0152] (Supplementary Note 6) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether the list is expressed in a range of physical cell identifiers of mobile relay node cells.

[0153] (Supplementary Note 7) The communication method according to Supplementary Note 1, wherein the additional information is information for identifying whether or not a physical cell identifier indicated in the list is a physical cell identifier of a cell different from a mobile relay node cell.

[0154] (Supplementary Note 8) The communication method according to any one of Supplementary Notes 1 to 7, further comprising the step of determining whether to acquire a System Information Block Type 1 (SIB1) from a best cell detected on the mobile relay node frequency based on the additional information.

[0155] (Supplementary Note 9) A user equipment used in a cellular communication system, comprising: a receiving unit that receives, from a network node other than a mobile relay node, a system information block for inter-frequency cell reselection performed by the user equipment in a radio resource control (RRC) idle state or an RRC inactive state, the system information block including: frequency information indicating a mobile relay node frequency that is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information related to the list.

[0156] (Supplementary Note 10) A network node used in a cellular communication system, different from a mobile relay node, comprising: a transmitter unit for transmitting a system information block for inter-frequency cell reselection performed by user equipment in a radio resource control (RRC) idle state or an RRC inactive state, wherein the system information block includes: frequency information indicating a mobile relay node frequency, which is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information related to the list.

[0157] (11) Supplement 2 1. Introduction To support the mobile IAB feature, RAN2 has decided that a UE in idle / inactive mode may select a frequency on which a mobile IAB cell is available in preference to other frequencies and may be provided with SIB4 assistance information. RAN2 has further agreed that the SIB4 assistance information may provide a mobile IAB PCI list for each mobile IAB frequency in addition to the mobile IAB frequency information as follows:

[0158] P1: The mIAB PCI list is optional (i.e., not required) for the indicated mIAB frequencies (ensure that the mIAB PCI list is implemented). P7: It is left to the UE implementation to decide which frequencies are actually prioritized among those that can prioritize mIAB cells / HSDN / MBS / SL / V2X. P8: Existing Note 0c in TS 38.304 is applicable to prioritization between mIAB cells / HSDN / MBS / SL / V2X. Therefore, no or very little additional specification work is required. Items requiring further consideration: - P2: Further discuss cases where the mIAB PCI list is not necessarily exclusive, i.e., where the PCI list may or may not include PCIs of non-mIAB cells. - P3: Further discussion of cases where the mIAB PCI list is not necessarily complete, i.e., the PCI list may or may not include all possible mIAB PCIs.

[0159] This appendix discusses the remaining issues regarding idle / inactive UE mobility to complete work items.

[0160] 2. Discussion 2.1 Remaining Issues Regarding Cell Reselection Priority Handling 2.1.1 Relationship with HSDN and Priority Release Requests At the previous meeting, RAN2 agreed to the following statements: P7: Of the frequencies that can be prioritized for mIAB cells / HSDN / MBS / SL / V2X, it is up to the UE implementation to decide which frequencies are actually prioritized. P8: Existing Note 0c in TS 38.304 is applicable to prioritization between mIAB cells / HSDN / MBS / SL / V2X. Therefore, no or very little additional specification work is required.

[0161] One of the omissions identified in the latest CR is whether mIAB frequency prioritization can override HSDN or de-prioritization request frequency prioritization. A similar issue was discussed in Release 17 (Rel-17) regarding the introduction of slice-based cell reselection. At that time, HSDN and de-prioritization requests, which were designated as mandatory operations, always took precedence over MBS broadcast, NR sidelink, and V2X sidelink, which were designated as optional operations. The same principle applies here. That is, mobile IAB frequency prioritization is optional, and the current CR states that "a UE on a vehicle to which a mobile IAB cell is assigned may detect and determine that the mobile IAB cell is the most prioritized cell." This is based on the corresponding RAN2 agreement. Therefore, it is necessary to confirm that mobile IAB frequency prioritization cannot override HSDN or de-prioritization request prioritization, and NOTE 1a needs to be revised.

[0162] Proposal 1: RAN2 should agree that the mobile IAB function does not replace the cell reselection priority with HSDN or priority release requests.

[0163] Proposal 2: RAN2 should agree to amend NOTE 1a of TS 38.304 to the following proposed text:

[0164] NOTE 1a: The UE does not expect MBS broadcast, NR sidelink communication, V2X sidelink communication, or mobile IAB functionality to supersede the cell reselection priority triggered by the HSDN or deprioritizationReq functionality.

[0165] 2.1.2 Relationship with Slice-Based Cell Reselection Another point that should be clarified is the relationship with slice-based cell reselection. In the current specification, it is up to the UE implementation to decide which frequency to prioritize among MBS broadcast, NR sidelink, V2X sidelink, and slice-based cell reselection, i.e., according to NOTE 0i. RAN2 has already agreed that "the existing NOTE 0c in TS 38.304 is applicable to prioritization between mIAB cell / HSDN / MBS / SL / V2X." Therefore, NOTE 0i should be amended accordingly.

[0166] Proposal 3: RAN2 should agree that it is implementation-dependent whether the frequency priority of the mobile IAB overrides the cell reselection priority of the slice-based cell reselection.

[0167] Proposal 4: RAN2 should agree to amend NOTE 0i of TS 38.304 as per the following proposed text:

[0168] NOTE 0i: The frequency priority of MBS broadcast, NR sidelink communication, or V2X sidelink communication, or mobile IAB may override the reselection priority of slice-based cell reselection.

[0169] 2.2. Open Issues Regarding SIB4 Supporting Information 2.2.1. Details of PCI List In the previous meeting, RAN2 agreed to introduce a PCI list for each mobile IAB frequency in SIB4, and whether the PCI list is exclusive / complete needs further consideration.

[0170] P1: The mIAB PCI list is optionally present (i.e., not required) for the indicated mIAB frequency (ensure that the mIAB PCI list is implemented). [...] Issues requiring further consideration: P2: Further discussion is needed regarding the case where the mIAB PCI list is not necessarily exclusive, i.e., the PCI list may or may not include PCIs of non-mIAB cells. P3: Further discussion is needed regarding the case where the mIAB PCI list is not necessarily complete, i.e., the PCI list may or may not include all possible mIAB PCIs.

[0171] The definitions of exclusive / complete were provided in the offline discussion as follows:

[0172] A) Exclusive PCI List: The mIAB PCI list is a dedicated PCI list reserved exclusively for mIAB cells on that frequency (i.e., the PCIs indicated by the list must be PCIs of mIAB cells). B) Non-Exclusive PCI List: The mIAB PCI list is a PCI list that may be shared on that frequency (i.e., the PCIs indicated by the list may be PCIs of mIAB cells or fixed cells). C) Complete List: The mIAB PCI list is an exhaustive list that includes all possible / detectable mIAB cells on that frequency (i.e., there are no other mIAB cells whose PCIs are not included in the PCI list). D) Incomplete List: The mIAB PCI list is not an exhaustive list; therefore, the list may contain only a subset of possible mIAB cells on that frequency (i.e., there may be other mIAB cells whose PCIs are not included in the PCI list).

[0173] In general, PCI lists should be "exclusive," i.e., they should only contain PCIs of mIAB cells, since there is no incentive for a gNB to include PCIs of fixed cells in a new list. For some deployments, RAN3 has agreed to use OAM-based PCI space partitioning for PCI collision avoidance purposes. However, as some companies have commented, this assumption may not be true for some deployments, depending on the network implementation. In this regard, PCI lists should be flexible enough to support both deployment scenarios. For example, a PCI list could have a one-bit indicator to inform the UE whether the PCI list is "exclusive" or "non-exclusive." Alternatively, each entry in a "non-exclusive" PCI list could have a one-bit indicator indicating whether the PCI of this entry is for a mobile IAB cell. This indication allows smart UE implementations to optimize inter-frequency measurements for mobile IAB frequency prioritization, e.g., by skipping decoding of SIB1.

[0174] On the other hand, although it is simple to have a "complete" PCI list, the UE behavior does not change significantly whether the PCI list is "complete" or "incomplete" because the UE can be aware that a mobile IAB cell is available if the PCIs of the best cells on different frequencies are listed in the PCI list. One advantage of a "complete" PCI list is that it is efficient for inter-frequency measurements because the UE can skip decoding SIB1s of cells on each mobile IAB frequency.

[0175] Another option for achieving a "complete" list (and at the same time an "exclusive" list) is to support PCI ranges proposed by some companies. This is in line with the PCI space partitioning agreed upon by RAN3. The question is whether to support PCI ranges as an option to the PCI list already agreed upon by RAN2. For example, if the PCI list includes a one-bit indicator conveying PCI range information, the PCI range is determined by setting the first entry as the lowest PCI and the second entry as the highest PCI. For further extension, it is also considered whether multiple PCI ranges can be supported if required for network deployment.

[0176] Alternatively, the PCI list can be considered to contain only the PCIs of fixed cells. This is the same as a conventional neighbor cell list. Because the PCs of fixed cells are static, the network may be able to provide an "exclusive" and "complete" list of PCs of fixed cells. If the PC of the best cell on that frequency is not listed in this list, the UE can identify a mobile IAB cell. However, considering that the number of PCs in NR has doubled compared to LTE, the disadvantage is that the size of the PC list may become large, resulting in signaling overhead.

[0177] In summary, it is desirable to minimize specific deployment prerequisites from the network perspective and to allow smart and efficient cell reselection behavior as much as possible from the UE perspective. Therefore, the PCI list should be flexible for all the above aspects.

[0178] Proposal 5: RAN2 should discuss the possibility that the agreed PCI list could consist of only PCIs of fixed cells as options, i.e., not including PCIs of mobile IAB cells. Note that this is very similar to the existing neighbor cell list.

[0179] Proposal 6: RAN2 should discuss whether the agreed PCI list can indicate the PCI range of the mobile IAB cell as an option, for example, by using only the first two entries of the list.

[0180] Proposal 7: RAN2 should discuss whether to introduce a one-bit indicator in the agreed PCI list that indicates whether the list is "exclusive" or not.

[0181] 2.2.2 CAG Processing It was discussed whether the UE could apply Rel-18 mobile IAB frequency prioritization to CAG mobile IAB cells, or whether the UE should follow the traditional principle (i.e., dedicated priority only). For Alt. 1 and Alt. 2 of Proposal 5, five companies supported Alt. 1 and seven companies supported Alt. 2. As a result, the e-mail discussion reporters, although RAN2 has not yet reached a conclusion, proposed the following:

[0182] Proposal 5: Decide on one of the alternatives: Alt. 1) The UE may prefer a mobile IAB cell configured as a CAG cell regardless of the cell reselection priority; Alt. 2) The UE shall only follow the network configured frequency priority.

[0183] SA2 decided to reuse the CAG for restricting access to mobile IAB cells. The main motivation is to enable the mobile IAB to offer "premium" services to "gold" users, i.e., special subscription plans [...], e.g., business or residential customers for a premium in-vehicle 5G experience. In other words, "regular" services via the mobile IAB can allow all UEs access, including "bronze" users, without a CAG.

[0184] Alt. 2 does not produce the expected results if dedicated priorities are not configured, because it means that "Gold" UEs cannot prioritize mobile IAB frequencies independently (because they only follow dedicated priorities for such frequency prioritization), whereas "Bronze" UEs are allowed to do so. Therefore, Alt. 1 is straightforward and preferred.

[0185] Proposal 8: RAN2 should agree that a UE can prefer a mobile IAB cell configured as a CAG cell regardless of the cell reselection priority.

[0186] If Proposal 8 is acceptable, it is worth considering whether the auxiliary information in SIB4 can provide CAG information for mobile IAB cells on each mobile IAB frequency. Given that RAN2 has agreed to introduce a PCI list useful to UEs, the CAG information in SIB4 is useful for inter-frequency measurements (i.e., the UE can omit decoding SIB1).

[0187] Proposal 9: RAN2 should discuss whether the CAG information of the mobile IAB cell should also be provided in SIB4.

Claims

1. A communication method executed by a user equipment in a cellular communication system, comprising receiving a system information block for inter-frequency cell reselection performed by the user equipment in a radio resource control (RRC) idle state or an RRC inactive state from a network node other than a mobile relay node, the system information block including: frequency information indicating a mobile relay node frequency, which is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information related to the list.

2. The communication method according to claim 1, wherein the additional information is information for specifying whether the list includes only physical cell identifiers of mobile relay node cells.

3. The communication method according to claim 1, wherein the additional information is information for specifying whether the list includes physical cell identifiers of all available mobile relay node cells.

4. The communication method according to claim 1, wherein the additional information is information for identifying whether the user equipment needs to acquire a system information block type 1 (SIB1) from a best cell detected on the mobile relay node frequency.

5. The communication method according to claim 1, wherein the additional information is information for identifying whether or not a physical cell identifier indicated in each entry of the list is a physical cell identifier of a mobile relay node cell.

6. The communication method according to claim 1, wherein the additional information is information for identifying whether the list is expressed in a range of physical cell identifiers of mobile relay node cells.

7. The communication method according to claim 1, wherein the additional information is information for identifying whether or not a physical cell identifier indicated in the list is a physical cell identifier of a cell different from a mobile relay node cell.

8. The method of any one of claims 1 to 7, further comprising: determining whether to acquire a System Information Block type 1 (SIB1) from a best cell detected on the mobile relay node frequency based on the additional information.

9. A user equipment for use in a cellular communication system, comprising: a receiving unit that receives a system information block for inter-frequency cell reselection performed by the user equipment in a radio resource control (RRC) idle state or an RRC inactive state from a network node other than a mobile relay node, the system information block including: frequency information indicating a mobile relay node frequency, which is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information related to the list.

10. A network node used in a cellular communication system and different from a mobile relay node, comprising: a transmitter for transmitting a system information block for inter-frequency cell reselection performed by user equipment in a radio resource control (RRC) idle state or an RRC inactive state, the system information block including: frequency information indicating a mobile relay node frequency, which is a frequency to which a mobile relay node cell managed by the mobile relay node belongs; a list of physical cell identifiers used by the user equipment to identify the mobile relay node cell; and additional information regarding the list.

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