Cell reselection method and user device

Abstract

A cell reselection method according to a first aspect of the present invention is a cell reselection method in a mobile communication system. The cell reselection method includes a step of acquiring, by a user device, from a base station, slice frequency information indicating a correspondence among network slices, frequencies, and frequency priorities. The cell reselection method also includes a step of measuring, by the user device, the frequency. The cell reselection method further includes a step of excluding, when the cell ranked highest in the frequency as a result of measuring the frequency does not support a network slice, by the user device, excluding frequencies in that network slice from a target of slice-specific cell reselection. The cell reselection method further includes a step of executing, by the user device, the slice-specific cell reselection.

Description

Technical Field

[0001] The present disclosure relates to a cell reselection method in a mobile communication system.

Background Art

[0002] In the specifications of 3GPP (The 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 constructing network slices, which are virtual networks, by logically dividing the physical network constructed by a communication carrier.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] The cell reselection method according to the first aspect is a cell reselection method in a mobile communication system. The cell reselection method includes a step in which a user equipment acquires slice frequency information indicating a correspondence relationship between a network slice, a frequency, and a frequency priority from a base station. The cell reselection method also includes a step in which the user equipment measures a frequency. Further, the cell reselection method includes a step in which, as a result of the user equipment measuring a frequency, if a cell having the highest rank at the frequency does not support a network slice, the user equipment excludes the frequency in the network slice from targets for slice-specific cell reselection. Further, the cell reselection method includes a step in which the user equipment performs slice-specific cell reselection.

[0005] The cell reselection method according to the second embodiment is a cell reselection method in a mobile communication system. The cell reselection method includes the step of a base station transmitting slice non-support cell information indicating that there are cells that do not support the network slice at frequencies included in slice frequency information that shows the correspondence between network slices, frequencies, and frequency priority. The cell reselection method also includes the step of a user device performing slice-specific cell reselection based on the slice non-support cell information.

[0006] The third aspect of the cell reselection method is a cell reselection method in a mobile communication system. The cell reselection method includes the step of a base station transmitting slice support status information indicating whether or not all network slices supported by each cell are the same in a predetermined range larger than the cell range. The cell reselection method also includes the step of a user device performing slice-specific cell reselection based on the slice support status information. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a diagram showing an example configuration of a mobile communication system according to the first embodiment. [Figure 2] Figure 2 is a diagram showing an example configuration of a UE (User Equipment) according to the first embodiment. [Figure 3] Figure 3 is a diagram showing an example configuration of a gNB (base station) according to the first embodiment. [Figure 4] Figure 4 is a diagram showing an example of the configuration of a protocol stack related to the user plane according to the first embodiment. [Figure 5] Figure 5 is a diagram showing an example of the configuration of a protocol stack related to the control plane according to the first embodiment. [Figure 6] Figure 6 is a diagram illustrating the overview of the cell reselection procedure. [Figure 7] Figure 7 is a diagram illustrating the general flow of a typical cell reselection procedure. [Figure 8]Figure 8 shows an example of network slicing. [Figure 9] Figure 9 is a diagram illustrating the overview of the slice-specific cell reselection procedure. [Figure 10] Figure 10 shows an example of slice frequency information. [Figure 11] Figure 11 is a diagram illustrating the basic flow of the slice-specific cell reselection procedure. [Figure 12] Figure 12 is a diagram illustrating an example of operation according to the first embodiment. [Figure 13] Figure 13 is a diagram showing an example of slice priority information and slice frequency information according to the first embodiment. [Figure 14] Figures 14(A) and 14(B) are diagrams illustrating an example of priority according to the first embodiment. [Figure 15] Figures 15(A) and 15(B) are diagrams illustrating examples of slice non-supported cell information according to the second embodiment. [Figure 16] Figure 16 is a diagram illustrating an example of operation according to the second embodiment. [Figure 17] Figure 17(A) shows an example of a homogeneous organism according to the third embodiment, and Figure 17(B) shows an example of a heterogeneous organism according to the third embodiment. [Figure 18] Figures 18(A) and 18(B) are diagrams illustrating an example of operation according to the third embodiment. [Modes for carrying out the invention]

[0008] User devices in a Radio Resource Control (RRC) idle or RRC inactive state execute a cell reselection procedure. 3GPP is considering slice-specific cell reselection, a network slice-dependent cell reselection procedure.

[0009] One aspect aims to perform efficient slice-specific cell reselection. Another aspect aims to suppress the power consumption of the user equipment.

[0010] The mobile communication system according to the 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.

[0011] [First Embodiment]

[0012] (Configuration of Mobile Communication System) FIG. 1 is a diagram showing the configuration of a mobile communication system according to the first embodiment. The mobile communication system 1 complies with the 5th generation system (5GS) of the 3GPP standard. Hereinafter, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system. Also, the 6th generation (6G) system may be at least partially applied to the mobile communication 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] UE100 is a mobile wireless communication device. UE100 can be any device as long as it is used by a user. For example, UE100 can be a mobile phone terminal (including smartphones), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided for a sensor, a vehicle or a device provided for a vehicle (Vehicle UE), an aircraft or a device provided for an aircraft (Aerial UE).

[0015] NG-RAN10 includes base stations (referred to as "gNB" in the 5G system) 200. gNB200s are interconnected via the Xn interface which is an interface between base stations. gNB200 manages one or more cells. gNB200 performs wireless communication with UE100 that has established a connection with its cell. gNB200 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. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with UE100. 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 5GC. The base station of LTE and the gNB can also be connected via an interface between base stations.

[0017] The 5GC20 includes the AMF (Access and Mobility Management Function) and UPF (User Plane Function) 300. The AMF 300 performs various mobility controls for the UE 100. The AMF 300 manages the mobility of the UE 100 by communicating with it using NAS (Non-Access Stratum) signaling. The UPF controls data transfer. The AMF and UPF 300 are connected to the gNB 200 via the NG interface, which is the base station-core network interface.

[0018] Figure 2 is a diagram showing the configuration of UE100 (user device) according to the first embodiment. UE100 comprises 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 gNB200.

[0019] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 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 130.

[0020] The transmitting unit 120 performs various types of 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 (transmission 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 is a diagram showing 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 Automatic Repeat request (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 (Quality of Service) 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 is not required.

[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 AMF300'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. Alternatively, the current serving cell and the adjacent cell may be managed by different gNB200s.

[0040] Figure 7 is a schematic diagram illustrating a typical (or legacy) cell reselection procedure.

[0041] In step S11, 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 S12, 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 if the current serving cell's radio quality falls below a predetermined quality.

[0043] In step S13, 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 an adjacent cell if the frequency priority of an 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 an 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 an adjacent cell that has a higher rank than the current serving cell for a predetermined period. If the frequency priority of an 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 an 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 create slices tailored to the service requirements of different service types, such as eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable and Low Latency Communications), and mMTC (massive Machine Type Communications), 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 Slicing 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. Alternatively, the term "network slice (slice)" may mean a slice group, which is a group of one or more S-NSSAIs or NSSAIs.

[0051] Furthermore, the UE100 determines the desired slice it wishes to use. The desired slice is sometimes called an "intended slice". In the first embodiment, the UE100 determines the slice priority for each network slice (desired slice). For example, the NAS of the UE100 determines the slice priority based on the operating status of applications within the UE100 and / or user operations / settings, and notifies the AS of the slice priority information indicating the determined slice priority.

[0052] (Overview of the slice-specific cell reselection procedure) Figure 9 is a diagram illustrating the overview of the slice-specific cell reselection procedure.

[0053] 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).

[0054] 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.

[0055] 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.

[0056] 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".

[0057] 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".

[0058] 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."

[0059] As shown in Figure 9, UE100 may perform cell reselection processing based on slice support information provided from network 50. Slice support information may also be information indicating the correspondence between cells (e.g., serving cells and each adjacent cell) and network slices that the cell does not provide or does provide. For example, a cell may temporarily not provide some or all of a network slice due to congestion or other reasons. That is, even if a slice support frequency has the capability to provide a certain network slice, some cells within that frequency may not provide that network slice. Based on the slice support information, UE100 can identify the network slices that each cell does not provide. Such slice support information may be provided to UE100 from gNB200 via broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message).

[0060] Figure 11 shows the basic flow of the slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, it is assumed that UE100 is in an RRC idle or RRC inactive state and has received and is holding the slice frequency information described above. The procedure for "slice-specific cell reselection" is referred to as the "slice-specific cell reselection procedure." However, in the following, "slice-specific cell reselection" and "slice-specific cell reselection procedure" may be used interchangeably.

[0061] 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 priority information, including the determined slice priorities. "Desired slices" are "Intended slices" and 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 priority of slice #1 is determined to be "3", slice priority of slice #2 is determined to be "2", and slice priority of slice #3 is determined to be "1". A higher number indicates higher priority, although a lower number may also indicate higher priority.

[0062] 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".

[0063] 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".

[0064] 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".

[0065] 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. Among the cells measured within the selected frequency, those that meet a predetermined quality standard (i.e., the minimum required quality standard) are called "candidate cells".

[0066] 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, based on the slice support information, whether that cell provides the selected network slice. If it is determined that the highest-ranked cell provides the selected network slice (step S5: YES), in step S5a, the AS of UE100 re-selects the highest-ranked cell and camps on to that cell.

[0067] On the other hand, if it is determined that the highest-ranked cell does not provide a selected network slice (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. In other words, the AS of UE100 determines whether there are any frequencies in the selected network slice other than the selected frequencies that were assigned in step S3. If it is determined that there are 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).

[0068] 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 or not there are any unselected slices in the slice list created in step S1. In other words, the AS of UE100 may determine whether or not there are network slices other than the selected network slices in the slice list. 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.

[0069] 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 (or legacy) cell reselection procedure shown in Figure 7. Alternatively, the conventional cell reselection process 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.

[0070] (Method for reselecting cells according to the first embodiment) As described above, in the Slice-Specific Cell Reselection (or Slice-Aware Cell Reselection) procedure, UE100 performs a measurement process on the selected frequency in the selected network slice (step S4 in Figure 11). Then, based on the results of the measurement process, UE100 determines whether the highest-ranked cell (i.e., one of the adjacent cells to the serving cell) supports the selected network slice (step S5 in Figure 11). At this time, UE100 uses network slice information to determine whether the highest-ranked cell supports the selected network slice.

[0071] Network slice information is basically transmitted from the serving cell of UE100. That is, the serving cell transmits slice support information for neighboring cells (i.e., including the highest-ranked cell) via broadcast signaling or individual signaling. UE100 determines step S5 by acquiring this slice support information.

[0072] However, network slice information may not be transmitted from the serving cell. This is because, although 3GPP has agreed that network slice information should be transmitted from the serving cell, it is optional.

[0073] If network slice information is not sent from the serving cell, UE100 may perform an action in step S5 of the slice-specific cell reselection procedure, such as obtaining slice support information for adjacent cells.

[0074] However, performing the process of retrieving slice support information from adjacent cells while the slice-specific cell reselection procedure is running may affect the processing time of the slice-specific cell reselection procedure. It may also affect the power consumption of the UE100.

[0075] Therefore, the first embodiment aims to perform cell reselection efficiently. Furthermore, the first embodiment aims to suppress the power consumption of the UE100.

[0076] Therefore, in the first embodiment, UE100 measures the frequency (one or more frequencies) based on the slice frequency information before performing the slice-specific cell reselection procedure. Then, if the highest-ranked cell at that frequency does not support network slicing, UE100 excludes that frequency from the slice-specific cell reselection process. UE100 then executes the slice-specific cell reselection procedure with that frequency excluded.

[0077] Specifically, firstly, the user device (e.g., UE100) obtains network slice frequency information from the base station (e.g., gNB200) that shows the correspondence between network slices, frequencies, and frequency priority. Secondly, the user device measures the frequency. Thirdly, if the user device finds that the cell with the highest rank at that frequency does not support the network slice, it excludes that frequency in that network slice from the selection of slice-specific cells. Fourthly, the user device performs slice-specific cell selection.

[0078] As a result, for example, cells that do not support network slices at a given frequency are excluded from the slice-specific cell reselection process, so that all top-ranked cells support the selected network slice. Therefore, the slice-specific cell reselection procedure does not need to check whether the top-ranked cells support the selected network slice. This makes it possible to improve the efficiency of the cell reselection process. In addition, since the slice-specific cell reselection procedure does not need to check whether the top-ranked cells support the selected network slice, it is possible to reduce the power consumption of the UE100 during cell reselection compared to when this check is performed.

[0079] (Example of operation according to the first embodiment) Figure 12 is a diagram illustrating an example of operation according to the first embodiment.

[0080] As shown in Figure 12, in step S20, UE100 acquires slice priority information. For example, UE100 acquires slice priority information by outputting it to UE100's AS from UE100's NAS. As described above, slice priority information is information indicating the slice priority for each desired slice.

[0081] In step S21, UE100 obtains slice frequency information from gNB200. As described above, slice frequency information is information that shows the correspondence between network slices, frequencies, and frequency priorities.

[0082] Figure 13 shows an example of slice priority information and slice frequency information according to the first embodiment. In the example shown in Figure 13, the slice priority information indicates that slice #1 has a slice priority of "6" and slice #2 has a slice priority of "5". In addition, the slice frequency information associates three frequencies F1, F2, and F4 with slice #1. The slice frequency information indicates that the priority of F1 is "7", the priority of F2 is "4", and the priority of F3 is "2". Furthermore, the slice frequency information associates frequencies F1, F2, and F3 with slice #2. The slice frequency information indicates that the priority of F1 is "0", the priority of F2 is "5", and the priority of F3 is "6".

[0083] In Figure 12, the order of steps S20 and S21 may be reversed.

[0084] In step S22, UE100 measures the frequency. If DRX (Discontinuous Reception) control is being performed, UE100 may measure the frequency when DRX is off. The frequencies to be measured are those included in the slice frequency information. In the example in Figure 13, UE100 measures F1, F2, F3, and F4. However, UE100 does not have to measure all the frequencies included in the slice frequency information. The frequencies to be measured may be the same as the serving cell frequency (i.e., intra frequency). Alternatively, the frequencies to be measured may be different from the serving cell frequency (i.e., inter frequency). Furthermore, the frequencies to be measured may be those with a frequency priority greater than the first frequency priority threshold among the frequencies with the same frequency as the serving cell. Furthermore, the frequencies to be measured may be those with a frequency priority greater than the second frequency priority threshold among the frequencies different from the serving cell frequency. The first frequency priority threshold and the second frequency priority threshold may be the same value or different values. Furthermore, the frequency to be measured may be selected from the frequencies included in the slice frequency information based on the received power (e.g., RSRP (Reference Signal Received Power)) and received quality (e.g., RSRQ (Reference Signal Received Quality)) relative to the serving cell frequency. In the following, the frequency to be measured may be referred to as the "measured frequency."

[0085] Furthermore, UE100 may execute step S22 after a certain period of time has elapsed. This certain period of time may be set by gNB200. For example, if gNB200 sets it to 10 seconds, UE100 may start a timer set to that value (10 seconds) when executing step S22. When the timer expires, UE100 executes step S22 again.

[0086] Alternatively, UE100 may repeat step S22 in response to receiving an instruction from gNB200 to perform step S22. For example, gNB200 sends such instruction to UE100 when the slice support status of an adjacent cell changes. By UE100 repeating step S22, UE100 can follow the change in the slice support status of the adjacent cell.

[0087] In step S23, UE100 determines whether the highest-ranked cell supports network slices based on the measurement results at the measurement frequency. If the serving cell provides slice support information for neighboring cells, UE100 determines whether the highest-ranked cell supports network slices based on this slice support information. That is, UE100 receives slice support information for neighboring cells from the serving cell and determines whether support is available based on this slice support information. On the other hand, if the serving cell does not provide slice support information for neighboring cells, UE100 obtains slice support information for neighboring cells from the System Information Block (SIB) broadcast by the highest-ranked cell (i.e., one of the neighboring cells). That is, UE100 receives slice support information for neighboring slices from the highest-ranked cell and determines whether support is available based on this slice support information.

[0088] If UE100 determines that the highest-ranked cell at the measurement frequency does not support network slicing (NO in step S23), the process proceeds to step S24. On the other hand, if UE100 determines that the highest-ranked cell at the measurement frequency does support network slicing (YES in step S23), the process proceeds to step S25.

[0089] Alternatively, slice support determination information, which indicates the slice support determination result, can be stored in memory, and the slice support determination process during the execution of a separate slice-specific cell reselection procedure can be omitted by reading this slice support determination information from memory.

[0090] In step S24, UE100 excludes the measured frequency from the slice-specific cell reselection process. That is, if the cell with the highest rank at the measured frequency does not support the network slice, UE100 excludes the frequency in that network slice from the slice-specific cell reselection process. In the example in Figure 13, the cell with the highest rank at the measured frequency F1 does not support slice #1, so F1 in slice #1 is excluded from the slice-specific cell reselection process.

[0091] Returning to Figure 12, in step S25, UE100 executes the slice-specific cell reselection procedure. That is, if the highest-ranked cell at the measurement frequency does not support network slicing (NO in step S23), UE100 executes the slice-specific cell reselection procedure while excluding the measurement frequency. In the example in Figure 13, UE executes the slice-specific cell reselection procedure while excluding frequency F1 in slice #1. On the other hand, if the highest-ranked cell at the measurement frequency supports the desired slice (YES in step S23), UE100 executes the slice-specific cell reselection procedure without excluding the measurement frequency. In the example in Figure 13, UE100 executes the slice-specific cell reselection procedure without excluding frequencies other than frequency F1 in slice #1. Note that if network slicing is not supported at any frequency, UE100 performs general (legacy) cell reselection.

[0092] The slice support determination process (steps S20 to S24) and the slice-specific cell reselection procedure (step S25) may be performed at predetermined timings. For example, when the electric field strength of a serving cell does not require cell reselection, the UE100 checks for the presence or absence of slice support in adjacent cells (step S23) and stores the slice support determination result information in memory. Then, when the electric field strength of a serving cell reaches a stage where cell reselection is required, the UE100 uses the slice support determination result information stored in memory to execute the slice-specific cell reselection procedure (step S25).

[0093] Figure 14(A) is a diagram showing an example of priority according to the first embodiment. Figure 14(A) shows an example of priority after the exclusion process (step S24 in Figure 12). As shown in Figure 14(A), since frequency F1 in slice #1 has been excluded by the exclusion process, priority is shown for each frequency included in the other slice frequency information.

[0094] On the other hand, Figure 14(B) also shows an example of priority according to the first embodiment. Figure 14(B) shows an example of priority based on frequency priority included in slice frequency information. In order to enable the slice-specific cell reselection procedure to be executed with as little repetition as possible, for example, UE100 may execute the procedure based on priority based on frequency priority as shown in Figure 14(B). Alternatively, UE100 may execute the slice-specific cell reselection procedure while appropriately swapping the priority shown in Figure 14(A) and the priority shown in Figure 14(B).

[0095] In the example shown in Figure 14(A), UE100 may perform cell reselection for the highest-ranked cell at frequency F2. In the example shown in Figure 14(B), UE100 may also perform cell reselection for the highest-ranked cell at frequency F3.

[0096] Furthermore, if UE100 has excluded a measurement frequency in the desired slice (step S24 in Figure 12), it may release the exclusion of the measurement frequency. In this case, UE100 will execute the slice-specific cell reselection procedure without excluding the measurement frequency. This is because, for example, the wireless conditions may change as UE100 moves, causing the highest-ranking cell at the measurement frequency to change, and that cell may then support the network slice.

[0097] Firstly, UE100 may keep the exclusion process (step S24) active until the highest-ranked cell is replaced, at which point the exclusion is removed. However, the highest-ranked cell before the replacement does not support network slicing, but it may be re-selected by legacy cell re-selection. Therefore, UE100 may continue to measure the received power and received quality for the (original) highest-ranked cell even after removing the exclusion.

[0098] Secondly, UE100 may keep the exclusion in effect until the next slice-specific cell reselection procedure (step S25 in Figure 12), and then release the exclusion during the following slice-specific cell reselection procedure.

[0099] Thirdly, the UE100 may have a timer or similar device set to set a time limit for release. Fourthly, the release may be triggered by a change in the position of the UE100.

[0100] Fifth, UE100 may be configured to perform some number of operations before release. For example, this could be based on the paging cycle, or it could be configured to release after 2.56(s) × n operations (where n is a natural number). For example, if the presence or absence of slice support is checked for the highest-ranked cell, the above time may be used to allow for the check of slice support to be waived.

[0101] [Second Embodiment] Next, a second embodiment will be described.

[0102] In the first embodiment, an example was described in which, if the highest-ranked cell at a frequency included in the slice frequency information does not support network slicing, that frequency is excluded in slice-specific cell reselection. In that case, UE100 determined whether or not the highest-ranked cell at that frequency supports network slicing based on slice support information (step S23 in Figure 12).

[0103] In contrast, the second embodiment is an example in which gNB200 notifies UE100 if there are cells that do not support network slicing at frequencies included in the slice frequency information. That is, among the cells that support the frequency in question, there are cells that do not support a specific network slice, and gNB200 notifies UE100 that such cells exist at that frequency. Cells that do not support network slicing at such frequencies are sometimes referred to as "slice-unsupported cells." Information indicating the existence of cells that do not support network slicing at a given frequency is sometimes referred to as "slice-unsupported cell information." The second embodiment is an embodiment in which gNB200 notifies UE100 of slice-unsupported cell information.

[0104] Figure 15(A) is a diagram showing an example of slice-unsupported cell information according to the second embodiment. In the example in Figure 15(A), it is shown that there are slice-unsupported cells for frequencies F1 and F3 among the frequencies F1, F2, F3, and F4 included in the slice frequency information. That is, for F1, it indicates that there are cells that do not support at least one of slices #1 and slice #2. Also, for F3, it indicates that there are cells that do not support slice #2. In the example in Figure 15(A), the presence of slice-unsupported cells is indicated by a flag.

[0105] Conversely, for frequencies where the slice non-support cell flag is not set, such as F2 or F4, all cells supporting that frequency support the network slice indicated by the slice priority information. In the example in Figure 15(A), for F2, all cells supporting F2 support both slice #1 and slice #2. Similarly, for F4, all cells supporting F4 support slice #1. Therefore, when UE100 determines whether the highest-ranked cell supports the selected network slice in the slice-specific cell reselection procedure (step S5 in Figure 11), it does not need to check slice support information for frequencies where the slice non-support cell flag is not set. This is because, for those frequencies, all cells supporting that frequency (including the highest-ranked cell) support the network slice, so UE100 does not need to check slice support information. As explained in the first embodiment, there are cases where slice support information for adjacent cells is not transmitted from the serving cell. However, for frequencies not indicated by the slice non-support cell information, all cells support the network slice, so UE can proceed with the slice-specific cell reselection procedure even without that slice support information. This makes it possible to improve the efficiency of the cell re-selection process in the second embodiment. In addition, since UE100 does not always need to check slice support information, it is possible to reduce power consumption compared to when slice support information is always checked.

[0106] Figure 15(B) is also a diagram showing an example of slice non-support cell information according to the second embodiment. In the example in Figure 15(A), the slice non-support cell information was linked to multiple network slices, but in Figure 15(B), the slice non-support cell information is linked to a single network slice (or to each network slice). In the example in Figure 15(B), it is shown that for frequency F1, there are cells that do not support slice #1. Also, in the example in Figure 15(B), it is shown that for frequency F3, there are cells that do not support slice #2. On the other hand, even for the same frequency F1, it is shown that all cells support slice #2. In other words, in the case shown in Figure 15(B), as in the case shown in Figure 15(A), it is shown that for frequencies not indicated by the slice non-support cell information, all cells support the network slice. Therefore, in the slice-specific cell reselection procedure, UE100 does not need to check from the slice support information whether, for example, the highest-ranked cell for frequency F1 supports slice #1. This makes it possible to improve the efficiency of slice-specific cell reselection. Furthermore, it is possible to reduce the power consumption of the UE100.

[0107] In this second embodiment, specifically, firstly, a base station (e.g., gNB200) transmits slice non-support cell information indicating that there are cells that do not support the network slice at a given frequency, which is included in the slice frequency information that shows the correspondence between network slices, frequencies, and frequency priority. Secondly, a user device (e.g., UE100) executes a slice-specific cell reselection procedure based on the slice non-support cell information.

[0108] As a result, as mentioned above, it is not necessary to check the slice support information for frequencies not indicated by the slice non-support cell information, thus improving the efficiency of the cell re-selection process. Furthermore, since it is not necessary to check the slice support information for frequencies not indicated by the slice non-support cell information, it is also possible to reduce the power consumption of the UE100.

[0109] (Example of operation according to the second embodiment) Figure 16 is a diagram illustrating an example of operation according to the second embodiment. It is assumed that UE100 has received slice frequency information from gNB200 before performing the processing shown in Figure 16. It is also assumed that the AS of UE100 has received slice priority information from the NAS of UE100 before performing the processing shown in Figure 16.

[0110] As shown in Figure 16, in step S30, if a cell in gNB200 cannot support its own slice, it notifies gNB200 of this fact. For example, the DU of gNB200 notifies the CU of gNB200 of this fact. Reasons for inability to support include, for example, high load on the cell in question.

[0111] In step S31, the gNB200 transmits slice non-supported cell information. The slice non-supported cell information includes information indicating that there are cells that do not support the network slice for the frequencies included in the slice frequency information. The slice non-supported cell information may be included in the slice frequency information. Alternatively, the slice non-supported cell information may be transmitted together with the slice frequency information. The slice non-supported cell information may be associated with frequencies included in the slice frequency information. That is, as shown in Figure 15(A), slice non-supported cell information may be associated with multiple network slices. The slice non-supported cell information may be associated with network slices included in the slice priority information and frequencies included in the slice frequency information. That is, as shown in Figure 15(B), slice non-supported cell information may be associated with each network slice for each frequency. The slice non-supported cell information may be broadcast by broadcast signaling (e.g., SIB). Alternatively, the slice non-supported cell information may be transmitted by individual signaling (e.g., RRC release (RRCRelease) message).

[0112] Note that the information indicating cells that do not support a slice may also indicate the existence of cells that support network slices. For example, in the example in Figure 15(A), if the flag indicating the existence of cells that support network slices is set for F1, it means that cells that support F1 also support both slice #1 and slice #2. For F2, where the flag is not set, it means that among the cells that support F2, there are cells that do not support either slice #1 or slice #2. Also, for example in the example in Figure 15(B), since the flag is set for frequency F1 corresponding to slice #1, it means that all cells that support F1 also support slice #1. Also, since the flag is not set for frequency F1 corresponding to slice #2, it means that among the cells that support F1, there are cells that do not support slice #2.

[0113] Information on cells that do not support slicing may include information indicating that no cells support network slicing and information indicating that cells support network slicing exist.

[0114] Returning to Figure 16, in step S32, UE100 measures the frequency included in the slice frequency information. If DRX control is being performed, UE100 may measure the frequency when DRX is off. At this time, UE100 checks for the presence or absence of slice support based on the slice non-support cell information. That is, UE100 checks for the presence or absence of slice support for frequencies where slice non-support cells exist, but does not check for the presence or absence of slice support for frequencies other than those frequencies. This is because for frequencies other than those where slice non-support cells exist, all cells supporting that frequency support network slices, so it is not necessary to check the slice support information.

[0115] In step S33, UE100 re-selects the highest rank cell for the frequency for which the frequency was measured.

[0116] Step S32 is a process performed before the slice-specific cell reselection procedure, similar to the frequency measurement in the first embodiment (step S22 in Figure 12), and step S33 may be a process performed during the slice-specific cell reselection procedure. Furthermore, both steps S32 and S33 may be processes performed during the slice-specific cell reselection procedure.

[0117] [Third Embodiment] Next, a third embodiment will be described.

[0118] In the third embodiment, slice support information is notified over a predetermined range larger than the cell. Specifically, firstly, a base station (e.g., gNB200) transmits slice support status information indicating whether all network slices supported by each cell are the same within a predetermined range larger than the cell. Secondly, a user device executes a slice-specific cell reselection procedure based on the slice support status information.

[0119] As mentioned above, slice support information is transmitted by the serving cell. Therefore, slice support information can basically be considered valid only within the serving cell.

[0120] However, it is possible that slice support information may be the same across a large range that extends beyond a single cell. For example, it is possible that multiple cells may all support the same network slice.

[0121] In this way, when all the network slices supported by each cell within a given range are the same, it is sometimes referred to as "homogeneous."

[0122] Figure 17(A) is a diagram showing an example of Homogeneous according to the third embodiment. In the example shown in Figure 17(A), the network slices supported by cell #1 are slice #1, slice #2, and slice #3, and the network slices supported by cell #2 are also slice #1, slice #2, and slice #3, and the same applies to the other cells. Within a predetermined range, the network slices supported by each cell are all the same: slice #1, slice #2, and slice #3. Homogeneous may support the same network slices at all frequencies within a predetermined range. Alternatively, Homogeneous may have a uniform correspondence between the supported network slices and frequencies within a predetermined range. In the latter case, for example, if slices #1 and slice #2 are supported at frequency F1 and slice #3 is supported at frequency F2, and this correspondence is the same within the predetermined range, it is still considered Homogeneous.

[0123] Within the predetermined range indicated as homogeneous, all slice supports are identical, so UE100 does not need to re-check for the presence or absence of slice supports within the predetermined range after the initial check. This reduces the number of times UE100 checks for the presence or absence of slice supports in the slice-specific cell re-selection procedure (specifically, step S5 in Figure 11) compared to when all cells are checked. Therefore, the efficiency of the cell re-selection process can be improved. Furthermore, by reducing the number of times slice support is checked, it is also possible to reduce the power consumption of UE100.

[0124] Homogeneous means that within a given range, each cell supports the same network slice. However, within that range, each cell may support different network slices. When each cell supports different network slices within a given range, this is sometimes referred to as "heterogeneous."

[0125] Figure 17(B) is a diagram showing an example of Heterogeneous according to the third embodiment. In the example shown in Figure 17(B), the network slices supported by cell #1 are slices #1, #2, and #3; the network slices supported by cell #2 are slices #4, #5, and #6; and cell #3 supports slices #1 and #4. Thus, within a predetermined range, the network slices supported by each cell are not the same. That is, Heterogeneous may support different network slices at different frequencies within a predetermined range. Alternatively, Heterogeneous may have a non-uniform correspondence between frequencies and network slices within a predetermined range.

[0126] Homogeneous means that all cells within a specified range support the same network slice; if even one network slice is different, it can become heterogeneous. Information indicating whether a cell is homogeneous or heterogeneous within a specified range may be referred to as "slice support status information." Slice support status information may also indicate whether a cell is homogeneous or heterogeneous within a specified range. Alternatively, slice support status information may also indicate whether a cell is heterogeneous or heterogeneous within a specified range.

[0127] Firstly, the predetermined range may be a Tracking Area (TA). A TA includes one or more cells and indicates an area that a UE100 in an RRC idle state can move to without updating the MME. If the UE100 confirms that it is homogeneous within the TA using slice support status information, it does not need to check slice support information within the same TA. The predetermined range may also be indicated by a Tracking Area Identity (TAI) to show which TA constitutes the predetermined range. The predetermined range may consist of multiple TAs. In this case, the predetermined range may be indicated by the existence of multiple TAIs for each TA constituting the predetermined range.

[0128] Secondly, the specified range may be a Registration Area (RA). An RA includes one or more cells and is defined as a collection of Terminal Areas (TAs). Since an RA includes multiple TAs, the number of times registration update signaling is sent can be reduced compared to when registration update signaling is sent for each TA. If UE100 confirms that an RA is homogeneous based on slice support status information, it does not need to check slice support information within the same RA. Note that an RA can be distinguished from other RAs by a list of TA identification information (TAI) included in that RA. Therefore, which RA constitutes the specified range may be indicated by a list of TAIs. Note that the specified range may consist of multiple RAs. In this case, the specified range may be indicated by the existence of multiple TAI lists for each RA constituting the specified range.

[0129] Thirdly, the specified range may be a PLMN (Public Land Mobile Network). A PLMN indicates the range in which a telecommunications carrier can provide services. Within the PLMN, if UE100 confirms that it is homogeneous based on slice support status information, then it is the same PLMNIt is not necessary to check slice support information within the system. The predetermined range may be indicated by the PLMN ID, showing which PLMN falls within the predetermined range.

[0130] Fourth, the predetermined range may be RNA (RAN-based Notification Area). The RNA is a narrower range than the TA, but includes one or more cells. The RNA indicates an area that UE100 in an RRC inactive state can move to without notifying NG-RAN10. Within the RNA, if UE100 confirms that it is homogeneous based on slice support status information, it does not need to confirm slice support information within the same RNA. The predetermined range may be indicated by some method of distinguishing RNA from other RNA, indicating which RNA is within the predetermined range. In the case of RNA, the predetermined range may be composed of multiple RNAs. In this case, the predetermined range may be indicated by the existence of multiple identification information for each RNA constituting the predetermined range.

[0131] The specified range does not necessarily have to be TA, RA, PLMN, or RNA, as long as it is an area composed of multiple cells. For example, the specified range may be a gNB200 that manages multiple cells. Alternatively, the specified range may be indicated by, for example, a cell list containing multiple cells.

[0132] Slice support status information can be viewed from the serving cell, and also from adjacent cells.

[0133] Furthermore, the slice support status information may have an expiration date. The expiration date may be valid within the homogeneous range. The expiration date may also be valid within the heterogeneous range. The expiration date may also differ for each predetermined range. The expiration date may also be the same for all predetermined ranges. For example, the expiration date may differ for each TA, or it may be the same for all TAs.

[0134] (Example of operation of the third embodiment) Next, an example of operation of the third embodiment will be described.

[0135] Slice support status information may be transmitted from gNB200 to UE100. Alternatively, this slice support status information may be transmitted from AMF300 to UE100. Figure 18(A) shows an example of transmission from gNB200 to UE100, and Figure 18(B) shows an example of transmission from AMF300 to UE100. Both Figure 18(A) and Figure 18(B) are diagrams that represent operation examples according to the third embodiment.

[0136] First, let's explain Figure 18(A).

[0137] As shown in Figure 18(A), in step S40, the gNB200 collects slice support information. Examples of slice support information include the following:

[0138] Firstly, a cell may temporarily disable network slice support due to high load or other reasons. In this case, notification may be made by the DU of gNB200 sending an F1 message to the CU containing information indicating that the network slice will be temporarily disabled. Alternatively, gNB200 may notify neighboring gNBs of the temporary disabling of network slice support. For example, gNB200 may send an Xn message containing this information to neighboring gNBs.

[0139] Secondly, there are cases where a network slice is temporarily unsupported for deployment reasons. In this case, the operator may decide to temporarily unsupport the network slice for deployment reasons and specify that the network slice should be temporarily unsupported. For example, notification may be given by sending an NG message from AMF300 to gNB200 that contains information indicating that the network slice will be temporarily unsupported. For information that gNB200 does not have (for example, PLMN deployment information), AMF300 may notify gNB200 using an NG message in step S40.

[0140] Thirdly, the predetermined range is one of TA, RA, PLMN, and RNA. The predetermined range may also be a combination of TA, RA, PLMN, and RNA. For example, the predetermined range may be represented by RNA#1 and TA#1. The range information indicating the predetermined range may be transmitted from AMF300 to gNB200 (step S41). In this case, AMF300 may notify gNB200 by sending an NG message containing the range information. Alternatively, the range information may be transmitted directly from AMF300 to UE100 (step S42). In this case, AMF300 may send a NAS message containing the range information to the NAS of UE100, and the NAS of UE100 may notify the AS of UE100 of the range information.

[0141] In step S43, the gNB200 creates slice support status information based on the collected slice support status and transmits the slice support status information. The gNB200 may broadcast the slice support status information by broadcast signaling (e.g., SIB). Alternatively, the gNB200 may transmit the slice support status information by individual signaling (e.g., RRC release (RRCRelease) message). The slice support status information may include information indicating whether it is homogeneous or heterogeneous. As mentioned above, the slice support status information may include information indicating homogeneous and not include information indicating heterogeneous. Also, as mentioned above, the slice support status information may include information indicating heterogeneous and not include information indicating homogeneous. Furthermore, as mentioned above, the slice support status information may include information indicating a predetermined range (this may be information indicating TA, RA, PLMN, or RNA, or information indicating a combination of TA, RA, PLMN, and RNA). Furthermore, as mentioned above, the slice support status information may include an expiration date.

[0142] In the case of Figure 18(B), if gNB200 temporarily disables support for a network slice due to high load or other reasons, it sends temporary slice dissupport information to AMF300 indicating that the network slice is temporarily unsupported (step S50). The temporary slice dissupport information may also be sent included in an NG message. Similar to Figure 18(A), AMF300 may collect slice support status and obtain information it does not have from gNB200 via NG messages.

[0143] Then, in step S51, the AMF300 sends slice support status information to the UE100 using NAS messages. For example, the AMF300 may include slice support status information in a Registration Accept message, which is a NAS message during the NAS registration sequence, and send it.

[0144] In both Figure 18(A) and Figure 18(B), the UE100 receives slice support status information. Based on this information, the UE100 can determine whether the slice is homogeneous or heterogeneous within a predetermined range. If the slice is homogeneous within the range, the UE100 can execute the slice-specific cell reselection procedure without checking the slice support status information. Therefore, even if slice support status information for adjacent cells is not transmitted from the serving cell, the slice-specific cell reselection procedure can be executed without obtaining slice support status information from adjacent cells. Thus, the UE100 can efficiently perform slice-specific cell reselection. Furthermore, the UE100 can perform slice-specific cell reselection while suppressing power consumption.

[0145] [Other embodiments] 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 may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM.

[0146] Alternatively, the circuits that perform each process carried out by the UE100 or gNB200 may be integrated, and at least a portion of the UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC: System on a chip).

[0147] 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.

[0148] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the gist of the work. Furthermore, it is possible to combine all or part of each embodiment, each operation, each process, and each step, as long as they do not contradict each other.

[0149] This application claims priority to Japanese Patent Application No. 2022-018787 (filed on February 9, 2022), and all of its contents are incorporated into the specification of this application.

[0150] (Note) The features of the above-described embodiment are noted below.

[0151] (1) A cell reselection method in a mobile communication system, The user device obtains slice frequency information from the base station that shows the correspondence between network slices, frequencies, and frequency priority. The user device includes the step of measuring the frequency, If, as a result of measuring the frequency, the user device determines that the cell with the highest rank at the frequency does not support the network slice, the user device excludes the frequency in the network slice from the selection of slice-specific cells. The user device has the step of performing the slice-specific cell reselection. How to re-select a cell.

[0152] (2) The exclusion step includes the user device determining, based on slice support information indicating whether the cell provides the network slice, that the highest-ranked cell does not support the network slice. The cell reselection method described in (1) above.

[0153] (3) The User device is The slice support information is received from the serving cell, or The slice support information is received from the cell that has the highest rank. The cell reselection method described in (1) or (2) above.

[0154] (4) Furthermore, the user device has a step of undoing the exclusion of the frequency from the slice-specific cell reselection. The cell reselection method described in any of (1) to (3) above.

[0155] (5) A cell reselection method in a mobile communication system, The base station transmits slice non-support cell information indicating that there are cells that do not support the network slice at the frequencies included in slice frequency information showing the correspondence between network slices, frequencies, and frequency priority. The user device has the step of performing slice-specific cell reselection based on the slice non-supported cell information. How to re-select a cell.

[0156] (6) The steps described above include the user device performing slice-specific cell reselection without checking whether the highest-rank cell supports the network slice for frequencies other than those indicated in the slice non-supported cell information, The cell reselection method described in (5) above.

[0157] (7) A cell reselection method in a mobile communication system, The base station transmits slice support status information indicating whether all network slices supported by each cell are the same within a predetermined range larger than the cell range. The user device has the step of performing slice-specific cell reselection based on the slice support status information. How to re-select a cell.

[0158] (8) The slice support status information indicates that all network slices supported by each cell within the predetermined range are identical, or The slice support status information indicates that the network slices supported by each cell within the predetermined range are not the same. The cell reselection method described in (7) above.

[0159] (9) The aforementioned predetermined range is one of the following: per TA (Tracking Area), per RA (Registration Area), or per PLMN (Public Land Mobile Network). The cell reselection method described in (7) or (8) above. [Explanation of Symbols]

[0160] 1: Mobile communication systems 20:5GC 100 :UE 110: Receiving unit 120: Transmitter 130: Control Unit 200 :gNB 210: Transmitter 220: Receiving unit 230: Control Unit 300: AMF

Claims

1. A cell reselection method in a mobile communication system, The network node transmits slice non-support cell information for each frequency included in the slice frequency information that shows the correspondence between network slices, frequencies, and frequency priority, indicating that there are cells that do not support a predetermined network slice at that frequency that supports a predetermined network slice. The user device performs slice-specific cell reselection based on the slice non-supported cell information. How to re-select a cell.

2. The above execution includes the user device performing slice-specific cell reselection for frequencies other than those indicated in the slice non-supported cell information, without checking whether the highest-ranked cell supports the network slice. The cell reselection method according to claim 1.

3. User device, A receiving unit receives slice non-supported cell information from a network node, indicating that for each frequency included in slice frequency information showing the correspondence between network slices, frequencies, and frequency priority, there are cells that do not support a predetermined network slice at that frequency that supports a predetermined network slice. The system includes a control unit that performs slice-specific cell reselection based on the slice non-supported cell information. User device.

4. On the user device, For each frequency included in the slice frequency information that shows the correspondence between network slices, frequencies, and frequency priority, the process of receiving slice non-support cell information from a network node, indicating that there are cells that do not support a predetermined network slice at that frequency that supports a predetermined network slice, Based on the slice non-supported cell information, the process of re-selecting slice-specific cells is executed. program.

5. A chipset for a user device, For each frequency included in the slice frequency information that shows the correspondence between network slices, frequencies, and frequency priority, the process of receiving slice non-support cell information from a network node, indicating that there are cells that do not support a predetermined network slice at that frequency that supports a predetermined network slice, Based on the slice non-supported cell information, the process of performing slice-specific cell reselection is executed. Chipset.

6. The user device described in claim 3 and a network node are provided. Mobile communication system.

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