Communication methods, user devices, processors, programs, and systems

Abstract

This provides a method for re-selecting slice-specific cells. [Solution] The method involves a user device in an RRC idle or inactive state identifying cells belonging to frequencies that support selected network slice groups according to the priority provided by the NAS layer as candidate cells for cell re-selection, determining whether the candidate cells support them, receiving a System Information Block (SIB) from the serving cell containing information indicating each identifier of the network slice group and the cell identifier of cells that do not support them, determining whether the candidate cells support them, receiving another SIB from the candidate cell indicating whether an SIB containing an identifier of an unavailable network slice group is broadcast by the candidate cell, and if it is determined that an SIB containing an identifier of an unavailable network slice group is not broadcast by the candidate cell, sending a message to the candidate cell requesting an SIB containing that identifier.

Description

Technical Field

[0001] The present invention relates to a communication method and a user device used in a mobile communication system.

Background Art

[0002] In the specifications of 3GPP (Third Generation Partnership Project), which is a standardization project for mobile communication systems, network slicing is defined (see, for example, Non-Patent Document 1). Network slicing is a technology for creating a plurality of virtual networks (network slices) by logically dividing the physical network constructed by a communication carrier.

[0003] A user device in the radio resource control (RRC) idle state or the RRC inactive state executes a cell reselection procedure. In 3GPP, slice-specific cell reselection is being considered. In such slice-specific cell reselection, it is assumed that the user device preferentially reselects (i.e., camps on) a cell belonging to a frequency with a high frequency priority associated with the network slice that the user device desires to use.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

[0005] The first aspect of the communication method is a communication method performed on a user device that is in an RRC idle state or an RRC inactive state. The communication method includes identifying cells belonging to frequencies that support selected network slice groups selected according to the priority provided by the NAS layer as candidate cells for cell reselection, and determining whether the candidate cells support the selected network slice groups. The determination includes receiving a system information block from the serving cell of the user device, for each of a plurality of network slice groups, which includes information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group, and determining whether the candidate cells support the selected network slice group based on the information.

[0006] The user device according to the second embodiment includes a processor. The processor performs the following processes: identifying cells belonging to frequencies that support selected network slice groups selected according to the priority provided by the NAS layer as candidate cells for cell reselection; and determining whether the candidate cells support the selected network slice groups. The determination process includes receiving a system information block from the serving cell of the user device, for each of a plurality of network slice groups, which includes information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group; and determining whether the candidate cells support the selected network slice group based on the information. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram shows the configuration of a mobile communication system according to an embodiment. [Figure 2] This diagram shows the configuration of the UE (User Equipment) according to the embodiment. [Figure 3]This diagram shows the configuration of the gNB (base station) according to the embodiment. [Figure 4] This diagram shows the protocol stack configuration of the user plane wireless interface that handles data. [Figure 5] This diagram shows the protocol stack configuration of the wireless interface of the control plane that handles signaling (control signals). [Figure 6] This diagram illustrates the overview of the cell reselection procedure. [Figure 7] This diagram shows a general overview of a typical cell reselection procedure. [Figure 8] This figure shows an example of network slicing. [Figure 9] This diagram shows an overview of the slice-specific cell reselection procedure. [Figure 10] This figure shows an example of slice frequency information. [Figure 11] This diagram shows the basic flow of the slice-specific cell reselection procedure. [Figure 12] This figure shows an example of operation of the first embodiment. [Figure 13] This figure shows an example of slice availability information in a modified version of the first embodiment. [Figure 14] This figure shows an example of a modification to the operation example of the first embodiment. [Figure 15] This figure shows an example of operation of the second embodiment. [Figure 16] This figure shows an example of a modified operation of the second embodiment. [Modes for carrying out the invention]

[0008] While a desired network slice should be provided by cells belonging to the frequency associated with that slice, there may be cases where a cell temporarily fails to provide some or all of the network slice due to reasons such as congestion. In other words, even if a slice support frequency is capable of providing a certain network slice, some cells within that frequency may not provide that network slice. In this case, the user's device may select a cell that does not provide the desired network slice (i.e., is unusable) as a serving cell.

[0009] Therefore, the present disclosure aims to provide a communication method and user device that enable the re-selection of an appropriate cell in slice-specific cell re-selection.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals.

[0011] [First Embodiment]

[0012] (Configuration of mobile communication systems) Figure 1 shows the configuration of a mobile communication system according to the first embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. In the following explanation, 5GS will be used as an example, but the mobile communication system may also have at least a portion of an LTE (Long Term Evolution) system or at least a portion of a 6th Generation (6G) system.

[0013] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. Also, the 5GC 20 may be simply referred to as the core network (CN) 20.

[0014] The UE 100 is a movable wireless communication device. The UE 100 can be any device used by a user. For example, the UE 100 can be a mobile phone terminal (including smartphones), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device provided on the sensor, a vehicle or a device provided on the vehicle (Vehicle UE), an aircraft or a device provided on the aircraft (Aerial UE).

[0015] The NG-RAN 10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via an Xn interface which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its cell. The gNB 200 has functions such as a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, etc. A "cell" is a term used to indicate the smallest unit of a wireless communication area. A "cell" is also used as a term to indicate a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0016] Note that the gNB can also be connected to the EPC (Evolved Packet Core), which is the core network of LTE. The base station of LTE can also be connected to the 5GC. The base station of LTE and the gNB can also be connected via an interface between base stations.

[0017] The 5GC 20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0018] FIG. 2 is a diagram showing the configuration of the UE 100 (user equipment) according to the first embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0019] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts the wireless signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0020] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmitted signal) output by the control unit 130 into a wireless signal and transmits it from the antenna.

[0021] The control unit 130 performs various control and processing operations in the UE 100. Such processing includes processing in each layer described later. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing operations.

[0022] Figure 3 shows the configuration of the gNB200 (base station) according to the first embodiment. The gNB200 comprises a transmitter 210, a receiver 220, a control unit 230, and a backhaul communication unit 240. The transmitter 210 and receiver 220 constitute a wireless communication unit that performs wireless communication with the UE100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN20.

[0023] The transmitting unit 210 performs various types of transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts the baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0024] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts the radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 230.

[0025] The control unit 230 performs various control and processing in the gNB200. Such processing includes processing in each layer described later. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processing.

[0026] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface, which is an inter-base station interface. The backhaul communication unit 240 is connected to the AMF / UPF300 via the NG interface, which is an inter-base station-core network interface. The gNB200 may consist of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally separated), and the two units may be connected by the F1 interface, which is a fronthaul interface.

[0027] Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data.

[0028] The user plane radio interface protocol consists of a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0029] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the UE100's PHY layer and the gNB200's PHY layer via a physical channel. The UE100's PHY layer receives downlink control information (DCI) transmitted from the gNB200 over the physical downlink control channel (PDCCH). Specifically, the UE100 performs blind decoding of the PDCCH using a Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from the gNB200 has a CRC parity bit added, which is scrambled by the RNTI.

[0030] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of the UE100 and the MAC layer of the gNB200 via the transport channel. The MAC layer of the gNB200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to the UE100.

[0031] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the UE100's RLC layer and the gNB200's RLC layer via a logical channel.

[0032] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0033] The SDAP layer maps IP flows, which are the units under which the core network performs QoS control, to wireless bearers, which are the units under which the AS (Access Stratum) performs QoS control. Note that if the RAN is connected to the EPC, the SDAP layer may not be necessary.

[0034] Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals).

[0035] The control plane's wireless interface protocol stack includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer, instead of the SDAP layer shown in Figure 4.

[0036] RRC signaling for various settings is transmitted between the RRC layer of the UE100 and the RRC layer of the gNB200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the radio bearer. If there is a connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of the UE100 and the RRC of the gNB200, the UE100 is in the RRC idle state. If the connection between the RRC of the UE100 and the RRC of the gNB200 is suspended, the UE100 is in the RRC inactive state.

[0037] The NAS, located above the RRC layer, handles session management and mobility management, among other things. NAS signaling is transmitted between the UE100's NAS and the AMF300A's NAS. The UE100 also has application layers in addition to the wireless interface protocol. Layers below the NAS are called AS (Access Stratum).

[0038] (Overview of the cell reselection procedure) Figure 6 is a diagram illustrating the overview of the cell reselection procedure.

[0039] A UE100 in an RRC idle or RRC inactive state performs a cell reselection procedure to move from its current serving cell (cell #1) to an adjacent cell (one of cells #2 through #4) upon movement. Specifically, the UE100 identifies the adjacent cell to which it should camp on using the cell reselection procedure and reselects the identified adjacent cell. When the current serving cell and the adjacent cell have the same frequency (carrier frequency), it is called an intra-frequency, and when the current serving cell and the adjacent cell have different frequencies (carrier frequencies), it is called an inter-frequency. The current serving cell and the adjacent cell may be managed by the same gNB200, or they may be managed by different gNB200s.

[0040] Figure 7 shows a schematic flow of a typical cell reselection procedure.

[0041] In step S10, UE100 performs frequency prioritization based on the frequency-specific priority (also called "absolute priority") specified by gNB200, for example, in a system information block or RRC release message. Specifically, UE100 manages the frequency priority specified by gNB200 for each frequency.

[0042] In step S20, the UE100 performs a measurement process to measure the radio quality for both the serving cell and the adjacent cell. The UE100 measures the received power and received quality of the reference signal transmitted by each of the serving cell and the adjacent cell, specifically the CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, the UE100 always measures the radio quality for frequencies with a higher priority than the current serving cell's frequency priority, and for frequencies with the same or lower priority as the current serving cell's frequency priority, it measures the radio quality of frequencies with the same or lower priority only if the current serving cell's radio quality falls below a predetermined quality.

[0043] In step S30, UE100 performs a cell reselection process to reselect the cell to which it will camp on, based on the measurement results in step S20. For example, UE100 may reselect a cell to an adjacent cell if the frequency priority of the adjacent cell is higher than the priority of the current serving cell, and the adjacent cell meets a predetermined quality standard (i.e., the minimum required quality standard) for a predetermined period. If the frequency priority of the adjacent cell is the same as the priority of the current serving cell, UE100 may rank the wireless quality of the adjacent cell and reselect a cell to an adjacent cell that has a higher rank than the current serving cell for a predetermined period. If the frequency priority of the adjacent cell is lower than the priority of the current serving cell, and the wireless quality of the current serving cell remains below a certain threshold, and the wireless quality of the adjacent cell remains above another threshold for a predetermined period, UE100 may reselect a cell to that adjacent cell.

[0044] (Overview of network slicing) Network slicing is a technique that creates multiple virtual networks by virtually dividing a physical network built by an operator (for example, a network consisting of NG-RAN10 and 5GC20). Each virtual network is called a network slice. In the following, a network slice may be simply referred to as a "slice."

[0045] Network slicing allows telecommunications carriers to implement technologies such as eMBB (Enhanced Mobile Broadband) and URLLC (Ultra-Reliable Network). It is possible to create slices according to the service requirements of different service types, such as low-latency communications and massive machine type communications (mMTC), thereby optimizing network resources.

[0046] Figure 8 shows an example of network slicing.

[0047] Three slices (slice #1 to slice #3) are configured on network 50, which consists of NG-RAN10 and 5GC20. Slice #1 is associated with the service type eMBB, slice #2 is associated with the service type URLLC, and slice #3 is associated with the service type mMTC. Note that more than three slices may be configured on network 50. A single service type may be associated with multiple slices.

[0048] Each slice is assigned a slice identifier to identify it. An example of a slice identifier is S-NSSAI (Single Network Slice Selection Assistance Information). S-NSSAI includes an 8-bit SST (slice / service type). S-NSSAI may further include a 24-bit SD (slice differentiator). SST is information indicating the service type to which the slice is associated. SD is information used to differentiate multiple slices associated with the same service type. Information containing multiple S-NSSAIs is called NSSAI (Network Slice Selection Assistance Information).

[0049] Alternatively, one or more slices may be grouped together to form a slice group. A slice group is a group containing one or more slices, and a slice group identifier is assigned to such a slice group. A slice group may be configured by a core network (e.g., AMF300) or by a wireless access network (e.g., gNB200). The configured slice group may be notified to the UE100.

[0050] In the following, the term "network slice (slice)" may mean an S-NSSAI, which is the identifier of a single slice, or an NSSAI, which is a collection of S-NSSAIs, or a slice group, which is a group of one or more S-NSSAIs or NSSAIs.

[0051] (Overview of the slice-specific cell reselection procedure) Figure 9 shows an overview of the slice-specific cell reselection procedure.

[0052] In the slice-specific cell reselection procedure, UE100 performs cell reselection based on slice frequency information provided from network 50. The slice frequency information may be provided to UE100 from gNB200 via broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message).

[0053] Slice frequency information is information that shows the correspondence between network slices, frequencies, and frequency priorities. For example, slice frequency information shows, for each slice (or slice group), the frequencies (one or more frequencies) that support that slice and the frequency priority assigned to each frequency. An example of slice frequency information is shown in Figure 10.

[0054] In the example shown in Figure 10, three frequencies, F1, F2, and F4, are associated with slice #1 as the frequencies that support slice #1. Of these three frequencies, F1 has a frequency priority of "6", F2 has a frequency priority of "4", and F4 has a frequency priority of "2". In the example in Figure 10, a higher frequency priority number indicates a higher priority, but a lower number could also indicate a higher priority.

[0055] Furthermore, for slice #2, three frequencies, F1, F2, and F3, are associated as frequencies that support slice #2. Of these three frequencies, F1 has a frequency priority of "0", F2 has a frequency priority of "5", and F3 has a frequency priority of "7".

[0056] Furthermore, for slice #3, three frequencies, F1, F3, and F4, are associated as frequencies that support slice #3. Of these three frequencies, F1 has a frequency priority of "3", F3 has a frequency priority of "7", and F4 has a frequency priority of "2".

[0057] In the following, to distinguish it from the absolute priority in conventional cell reselection procedures, the frequency priority shown in the slice frequency information may be referred to as "slice intrinsic frequency priority."

[0058] Figure 11 shows the basic flow of the slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, UE100 is assumed to be in an RRC idle state or RRC inactive state and to have received and retained the slice frequency information described above.

[0059] In step S0, the NAS of UE100 determines the slice identifier of the desired slices of UE100 and the slice priority of each desired slice, and notifies the AS of UE100 of the slice information, including the determined slice priorities. "Desired slices" include slices that are likely to be used, candidate slices, desired slices, slices to communicate, requested slices, allowed slices, or intended slices. For example, slice #1 is determined to have a slice priority of "3", slice #2 has a slice priority of "2", and slice #3 has a slice priority of "1". A higher number indicates a higher priority, although a lower number may also indicate a higher priority.

[0060] In step S1, the AS of UE100 sorts the slices (slice identifiers) notified from the NAS in step S0 in order of slice priority. The list of slices sorted in this way is called the "slice list".

[0061] In step S2, the AS of UE100 selects one network slice in order of slice priority. The network slice selected in this way is called the "selected network slice".

[0062] In step S3, the AS of the UE100 assigns frequency priority to each frequency associated with the selected network slice. Specifically, the AS of the UE100 identifies the frequencies associated with the slice based on the slice frequency information and assigns frequency priority to the identified frequencies. For example, if the selected network slice selected in step S2 is slice #1, the AS of the UE100 assigns frequency priority "6" to frequency F1, frequency priority "4" to frequency F2, and frequency priority "2" to frequency F4 based on the slice frequency information (e.g., the information in Figure 10). The AS of the UE100 refers to the list of frequencies arranged in descending order of frequency priority as the "frequency list".

[0063] In step S4, the AS of UE100 selects one frequency from the selected network slice selected in step S2 in order of frequency priority, and performs measurement processing on the selected frequency. The frequency thus selected is called the "selected frequency". The AS of UE100 may also rank each cell measured within the selected frequency in order of wireless quality.

[0064] In step S5, the AS of UE100 identifies the highest-ranked cell based on the results of the measurement process in step S4 and determines whether the selected network slice is available in that cell. The method of determination will be explained in the operation examples below.

[0065] If the AS of UE100 determines that a selected network slice is available in the highest-ranked cell (step S5: YES), in step S5a, the AS of UE100 re-selects the highest-ranked cell and camps on to that cell.

[0066] On the other hand, if it is determined that a selected network slice is not available in the highest-ranked cell (step S5: NO), in step S6, the AS of UE100 determines whether there are any unmeasured frequencies in the frequency list created in step S3. If it is determined that there are any unmeasured frequencies (step S6: YES), the AS of UE100 resumes processing targeting the next highest frequency priority and performs measurement processing on that frequency as the selected frequency (returning to step S4).

[0067] If it is determined that there are no unmeasured frequencies in the frequency list created in step S3 (step S6: NO), then in step S7, the AS of UE100 may determine whether there are any unselected slices in the slice list created in step S1. If it is determined that there are unselected slices (step S7: YES), the AS of UE100 resumes processing targeting the next highest slice priority network slice and selects that network slice as the selected network slice (returning to step S2). Note that in the basic flow shown in Figure 11, the processing in step S7 may be omitted.

[0068] If it is determined that there are no unselected slices (step S7: NO), in step S8, the AS of UE100 performs the conventional cell reselection process. The conventional cell reselection process may refer to the entire general cell reselection procedure shown in Figure 7, or it may refer only to the cell reselection process shown in Figure 7 (step S30). In the latter case, UE100 may reuse the measurement results from step S4 without measuring the wireless quality of the cell again.

[0069] (Example of operation of the first embodiment) In the slice-specific cell reselection process described above, UE100 selects a cell belonging to the frequency that supports the desired slice as the serving cell. While the desired slice should be available in the cells belonging to the frequency that supports it, there may be cases where a cell temporarily does not provide the slice due to congestion or other reasons. In this case, UE100 may select a cell that does not provide the desired slice as the serving cell, potentially resulting in the inability to use the desired slice.

[0070] In the first embodiment, the UE 100 identifies cells belonging to frequencies that support the desired slice as candidate cells for cell reselection. The UE 100 receives slice availability information (predetermined information) from the network 50 to determine whether the desired slice is unavailable in the candidate cells.

[0071] Figure 12 shows an example of operation according to the first embodiment. Before starting the operation in this example, UE100 is assumed to be in an RRC idle state or an RRC inactive state, and to have received and retained the slice frequency information described above.

[0072] As shown in Figure 12, in step S101, UE100 initiates the procedure for re-selecting slice-specific cells.

[0073] In step S102, UE100 measures and ranks cells belonging to the frequencies that support the desired slice, based on the slice frequency priority information. For specific operation details, please refer to the operation of steps S1 to S8 in Figure 11.

[0074] In step S103, UE100 identifies candidate cells to camp on. Specifically, UE100 identifies the highest-ranked cell as a candidate cell to camp on. Here, UE100 identifies cell #2, which is adjacent to cell #1 (the current serving cell), as a candidate cell.

[0075] In step S104, UE100 receives slice availability information broadcast from the candidate cell (cell #2). Here, the slice availability information is broadcast from the candidate cell via the Master Information Block (MIB) or System Information Block (SIB).

[0076] Slice availability information includes slice identifiers of unavailable slices in the cell broadcasting the slice availability information. Slice availability information may further include slice identifiers of available slices in the cell. For each slice identifier, the slice availability information may include information indicating whether the slice identified by that slice identifier is available. If there are no unavailable slices in a cell, the slice availability information broadcast by that cell may indicate this fact. In the following, "unavailable slices in a cell" may be read as "slices that are temporarily not provided in the cell" or "slices that are temporarily not supported in the cell."

[0077] In step S105, UE100 determines whether the desired slice is unavailable in the candidate cell based on the slice availability information received in step S104. Specifically, UE100 determines that the desired slice is unavailable in the candidate cell if the slice identifier of the desired slice matches the slice identifier of an unavailable slice indicated by the slice availability information.

[0078] If UE100 determines that the desired slice is unavailable in a candidate cell (step S105: YES), it controls the system in step S107 to prevent camp-on to that cell. For example, UE100 may then perform the operations from step S6 onward in Figure 11. Alternatively, UE100 may lower the priority of the frequency to which the cell belongs. For example, it may be considered the lowest priority. Or, it may remove the frequency priority altogether (i.e., treat the frequency as if no frequency priority is assigned).

[0079] On the other hand, if UE100 determines that the desired slice is available in the candidate cell (i.e., the desired slice is available) (step S105: NO), in step S106, it re-selects the cell and camps on to it.

[0080] In the first embodiment, the UE100 may receive slice availability information via dedicated RRC messages. Such dedicated RRC messages include, for example, RRC Release messages, RRC Setup messages, RRC Reestablishment messages, RRC Resume messages, and new RRC messages.

[0081] (Example of modification of the first embodiment) Regarding the modifications to the first embodiment, the differences from the first embodiment will be explained primarily.

[0082] In the modified example, the slice availability information transmitted by the cell (gNB200) includes not only the slice identifiers of slices unavailable in that cell, but also the slice identifiers of slices unavailable in adjacent cells. This allows the UE100 to determine whether the desired slice is available in the candidate cell during cell reselection based on the slice availability information transmitted from the serving cell, eliminating the need to check the candidate cell's SIB.

[0083] In the example of the change, cell information indicating the correspondence between cell identifiers and slice identifiers of slices unavailable in the cell identified by the cell identifier is transmitted and received between adjacent cells (gNB200) (for example, transmitted and received via the Xn interface). This allows a cell (gNB200) to know the slice identifiers of slices unavailable in adjacent cells. The cell information may also be notified to each gNB200 from the OAM.

[0084] If adjacent cells are managed by different DUs belonging to the same gNB200, the CU may notify the DUs of cell information about the adjacent DUs via an F1 message.

[0085] Figure 13 shows an example of slice availability information in a modified example. In the example shown in Figure 13, the slice availability information indicates that slices #1 and #2 are unavailable in cell #1, slice #1 is unavailable in cell #2, and there are no unavailable slices in cell #3.

[0086] The slice availability information in the example change may further include slice identifiers for slices available in adjacent cells.

[0087] Figure 14 shows the operation of a modified example of the first embodiment.

[0088] In step S201, UE100 receives slice availability information from the current serving cell (cell #1). UE100 then stores the received slice availability information.

[0089] The operations in steps S202 to S204 are the same as the operations in steps S101 to S103 in Figure 12.

[0090] In step S205, UE100 determines whether the desired slice is unavailable in the candidate cell (cell #2) based on the slice availability information received and retained in step S201.

[0091] The operations in steps S206 and S207 are the same as those in steps S106 and S107 in Figure 12.

[0092] In a modified example of the first embodiment, the UE100 may receive slice availability information via a dedicated RRC message. Such dedicated RRC messages include, for example, an RRC Release message, an RRC Setup message, an RRC Reestablishment message, an RRC Resume message, and a new RRC message.

[0093] For example, gNB200 includes slice availability information in the RRCRelease message used to transition UE100, which is currently in an RRC connected state, to an RRC idle or RRC inactive state. UE100 receives the slice availability information via this RRCRelease message.

[0094] In a modified example of the first embodiment, UE100 may, before step S203, identify cells for which the desired slice is not possible based on slice availability information, and exclude the identified cells from the cells to be measured in step S203.

[0095] [Second Embodiment] The second embodiment will be described primarily in terms of its differences from the first embodiment.

[0096] In 5G (NR), the system information (SI) broadcast by a cell is divided into an MIB and multiple SIBs. The MIB is always broadcast. Of the multiple SIBs, SIB1 is always broadcast, but the other SIBs (hereinafter referred to as "other SIBs") may always be broadcast, or they may be broadcast only upon request from the UE100.

[0097] Since other SIBs are not always broadcast, it is preferable to transmit slice availability information via SIB1 so that UE100 can grasp the slice availability of candidate cells more quickly during cell reselection. However, SIB1 has a limited message size, making it difficult to include slice availability information, including each slice identifier, in SIB1. Therefore, in the second embodiment, gNB200 transmits a slice indicator (predetermined information) in SIB1 indicating whether or not there are unavailable slices in the cell, and transmits slice availability information, including the slice identifier of the unavailable slices, in an SIB belonging to other SIBs (hereinafter, such an SIB may be referred to as a slice SIB).

[0098] The slice indicator does not include the slice identifier. The slice indicator is, for example, 1 bit of information, where "0" indicates that there are no unavailable slices in the cell, and "1" indicates that there are unavailable slices in the cell.

[0099] Alternatively, the slice indicator may only indicate the presence of unavailable slices in a cell. In this case, gNB200 notifies UE100 that there are no unavailable slices in the cell by not including a slice indicator in SIB1.

[0100] Additionally, gNB200 may include a slice indicator in the MIB instead of SIB1.

[0101] The gNB200 sends a slice indicator to show that there are unavailable slices in any of the cells it manages.

[0102] Figure 15 shows an example of operation according to the second embodiment.

[0103] As shown in Figure 15, the operations in steps S301 to S303 are the same as the operations in steps S101 to S103 in Figure 12.

[0104] In step S304, UE100 receives a slice indicator from the candidate cell (cell #2) via SIB1 or MIB, indicating whether or not there are any unavailable slices in that cell.

[0105] In step S305, UE100 determines whether or not there are any unavailable slices in the candidate cell (cell #2) based on the slice indicator received in step S304.

[0106] If UE100 determines that there are no unavailable slices in the candidate cell (step S305: NO), in step S309, it re-selects the cell and camps on to it.

[0107] On the other hand, if UE100 determines that there are unavailable slices in the candidate cell (cell #2) (step S305: YES), in step S306, it sends a request message to the candidate cell (cell #2) to request a slice SIB including slice availability. Then, in step S307, UE100 receives the slice SIB including slice availability information from the candidate cell (cell #2). Note that if the slice SIB has already been broadcast in the candidate cell, the operation in step S306 may be omitted. Whether or not the slice SIB has already been broadcast in the candidate cell may be notified to UE100 by the SIB1 broadcast by the candidate cell.

[0108] The operation in step S308 is the same as the operation in step 105 in Figure 12.

[0109] If UE100 determines that the desired slice is unavailable in a candidate cell (step S308: YES), it does not camp on to that cell in step S310. On the other hand, if UE100 determines that the desired slice is available in a candidate cell (i.e., the desired slice is available) (step S308: NO), it re-selects that cell in step S309 and camps on to that cell.

[0110] (Example of modification of the second embodiment) Regarding the modifications to the second embodiment, the differences from the second embodiment will be explained primarily.

[0111] In this modified example, UE100 omits receiving slice availability information and controls whether or not to camp on to candidate cells based solely on the slice indicator. This allows UE100 to determine which cells to camp on more quickly during cell re-selection.

[0112] For example, if the frequencies that support the desired slice only support the desired slice (for example, in the frequency priority information, the frequencies that support the desired slice are mapped only to the desired slice), then UE100 can determine whether the desired slice is available in the candidate cell based solely on the slice indicator.

[0113] Furthermore, the reason for the existence of unavailable slices is primarily thought to be cell congestion. Therefore, if even one slice is unavailable in a cell, UE100 can assume that other slices in that cell are also unavailable (or will soon become unavailable due to congestion), and thus determine that the desired slice is unavailable in that cell.

[0114] Figure 16 shows an example of a modification of the second embodiment.

[0115] As shown in Figure 16, the operations in steps S401 to S405 are the same as the operations in steps S301 to S305 in Figure 15.

[0116] If UE100 determines that there are no unavailable slices in the candidate cell (step S405: NO), in step S406, it re-selects the cell and camps on to it.

[0117] On the other hand, if UE100 determines that there is an unavailable slice in the candidate cell (step S405: YES), it controls the system in step S407 to prevent camp-on to that cell.

[0118] [Other embodiments] Each of the above-described operation flows can be performed not only independently, but also in combination of two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0119] In the embodiments and examples described above, an example was described in which the base station is an NR base station (gNB), but the base station may also be an LTE base station (eNB) or a 6G base station. Furthermore, 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 an IAB node. Furthermore, the user equipment may be an MT (Mobile Termination) of an IAB node.

[0120] A program may be provided that causes a computer to perform each of the processes that UE100 or gNB200 performs. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded is non The recording medium may be transient. The non-transient recording medium is not particularly limited, but may be, for example, a CD-ROM or DVD-ROM. Alternatively, the circuits that perform each process carried out by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0121] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0122] The terms "based on" and "depending on" used in this disclosure do not mean "based solely on" or "depending solely on" unless otherwise specified. The term "based on" means both "based solely on" and "at least partially on." Similarly, the term "depending on" means both "at least partially on" and "at least partially on." Also, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from other nodes, or obtaining information by generating it. The terms "include," "comprise," and their variations do not mean to include only the listed items, but may include only the listed items, or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to mean exclusive OR. Furthermore, any reference to elements using designations such as "first," "second," etc., used in this disclosure does not limit the quantity or order of those elements in general. These designations may be used herein as a convenient way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be employed therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated otherwise by the context.

[0123] This application claims priority to Japanese Patent Application No. 2021-171717 (filed October 20, 2021), and all of its contents are incorporated into the specification of this application.

Claims

1. A communication method performed on a user device that is in an RRC idle state or an RRC inactive state, Identifying cells belonging to frequencies that support selected network slice groups, chosen according to the priority provided by the NAS layer, as candidate cells in cell re-selection, The process includes determining whether the candidate cell supports the selected network slice group, The aforementioned determination is, For each of the multiple network slice groups, the user device receives a system information block from the serving cell that includes information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group. This includes determining whether the candidate cell supports the selected network slice group based on the information described above, Receiving from the candidate cell another system information block indicating whether or not a system information block containing an identifier of an unavailable network slice group is broadcast in the candidate cell, If, based on the other system information blocks, it is determined that the system information block containing the identifier of the unavailable network slice group is not broadcast in the candidate cell, the system further includes sending a request message to the candidate cell to request the system information block containing the identifier of the unavailable network slice group. Communication method.

2. User device, A process to identify cells belonging to frequencies that support selected network slice groups, which are selected according to the priority provided by the NAS layer, as candidate cells in cell reselection, and The system includes a processor that performs a process to determine whether the candidate cell supports the selected network slice group, The process for making the aforementioned determination is: For each of the multiple network slice groups, a system information block containing information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group is received from the serving cell of the user device. The process includes determining whether the candidate cell supports the selected network slice group based on the aforementioned information, The process of receiving from the candidate cell another system information block indicating whether or not a system information block containing an identifier of a network slice group that is unavailable in the candidate cell is broadcast in the candidate cell, If, based on the other system information blocks, it is determined that the system information block containing the identifier of the unavailable network slice group is not broadcast in the candidate cell, the process further executes: sending a request message to the candidate cell to request the system information block containing the identifier of the unavailable network slice group. User device.

3. A processor that controls user devices, A process to identify cells belonging to frequencies that support selected network slice groups, which are selected according to the priority provided by the NAS layer, as candidate cells in cell reselection, and The process of determining whether the candidate cell supports the selected network slice group is performed, The process for making the aforementioned determination is: For each of the multiple network slice groups, a system information block containing information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group is received from the serving cell of the user device. The process includes determining whether the candidate cell supports the selected network slice group based on the aforementioned information, The process of receiving from the candidate cell another system information block indicating whether or not a system information block containing an identifier of a network slice group that is unavailable in the candidate cell is broadcast in the candidate cell, If, based on the other system information blocks, it is determined that the system information block containing the identifier of the unavailable network slice group is not broadcast in the candidate cell, the process further executes: sending a request message to the candidate cell to request the system information block containing the identifier of the unavailable network slice group. Processor.

4. A program for controlling user devices, A process to identify cells belonging to frequencies that support selected network slice groups, which are selected according to the priority provided by the NAS layer, as candidate cells in cell reselection, and The user device is instructed to perform a process to determine whether the candidate cell supports the selected network slice group, The process for making the aforementioned determination is: For each of the multiple network slice groups, a system information block containing information indicating the identifier of the network slice group and the cell identifier of a cell that does not support the network slice group is received from the serving cell of the user device. The process includes determining whether the candidate cell supports the selected network slice group based on the aforementioned information, The process of receiving from the candidate cell another system information block indicating whether or not a system information block containing an identifier of a network slice group that is unavailable in the candidate cell is broadcast in the candidate cell, If, based on the other system information blocks, it is determined that the system information block containing the identifier of the unavailable network slice group is not broadcast in the candidate cell, the user device is further instructed to send a request message to the candidate cell to request the system information block containing the identifier of the unavailable network slice group. program.

5. A system including the user device described in claim 2.

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