Cell reselection method and user device

Abstract

A cell re-selection method according to one embodiment of the present invention is a method for re-selecting a cell in a mobile communication system. This cell re-selection method has a step in which, when at least some network slices included in a first slice group are included in a second slice group, the first slice group being usable in a region of a base station and the second slice group being usable in an adjacent region that is adjacent to the aforementioned region, the base station transmits information pertaining to mapping of the first and second slice groups. The cell re-selection method also has a step in which a user device executes re-selection of a slice-specific cell by using the mapping information.

Description

【Technical Field】 【0001】 This 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】 3GPP TS 38.300 V16.8.0 (2021-12) 【Summary of the Invention】 【0004】 A cell reselection method according to one aspect is a cell reselection method in a mobile communication system. The cell reselection method includes a step in which a base station transmits mapping information between a first slice group available in the area of the base station and a second slice group available in an adjacent area adjacent to the area, when at least some of the network slices included in the first slice group are included in the second slice group. The cell reselection method also includes a step in which a user equipment executes slice-specific cell reselection using the mapping information. 【Brief Description of the Drawings】 【0005】 [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 the mapping relationship between slice groups and network slices according to the first embodiment. [Figure 13] Figure 13 is a diagram illustrating an example of the mapping relationship between slice groups and network slices according to the first embodiment. [Figure 14] Figure 14 is a diagram illustrating an example of the mapping relationship between slice groups and network slices according to the first embodiment. [Figure 15] Figure 15 is a diagram illustrating an example of the mapping relationship between slice groups and network slices according to the first embodiment. [Figure 16]Figure 16 is a diagram illustrating an example of operation according to the first embodiment. [Modes for carrying out the invention] 【0006】 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. 【0007】 One embodiment aims to appropriately perform cell reselection in user equipment. Another embodiment aims to improve transmission efficiency at base stations. Furthermore, another embodiment aims to mitigate security issues. 【0008】 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. 【0009】 [First Embodiment] (Configuration of mobile communication systems) Figure 1 is a diagram showing 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 applied to it. Furthermore, the mobile communication system may also have at least a portion of a 6th Generation (6G) system applied to it. 【0010】 The mobile communication system 1 comprises User Equipment (UE) 100, a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereafter, NG-RAN 10 may be simply referred to as RAN 10, and 5GC 20 may be simply referred to as core network (CN) 20. 【0011】 A UE100 is a mobile wireless communication device. A UE100 can be any device used by a user. For example, a UE100 can be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or chipset), a sensor or a device attached to a sensor, a vehicle or a device attached to a vehicle (Vehicle UE), or an aircraft or a device attached to an aircraft (Aerial UE). 【0012】 NG-RAN10 includes base stations (referred to as "gNBs" in 5G systems) 200. The gNBs 200 are interconnected via the Xn interface, which is an inter-base station interface. Each gNB 200 manages one or more cells. The gNB 200 performs wireless communication with UEs 100 that have established a connection with its own cell. The gNB 200 has radio resource management (RRM) functions, user data routing functions (hereinafter simply referred to as "data"), measurement and control functions for mobility control and scheduling, etc. "Cell" is used as a term to indicate the smallest unit of a wireless communication area. "Cell" is also used as a term to indicate a function or resource that performs wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency"). 【0013】 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. 【0014】 The 5GC 20 includes an AMF (Access and Mobility Management Function) and a 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 the UE 100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF 300 are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network. 【0015】 FIG. 2 is a diagram showing the configuration of the UE 100 (user device) 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. 【0016】 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. 【0017】 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. 【0018】 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. 【0019】 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. 【0020】 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. 【0021】 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. 【0022】 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. 【0023】 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. 【0024】 Figure 4 shows the configuration of the protocol stack for the user plane's wireless interface that handles data. 【0025】 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. 【0026】 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. 【0027】 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. 【0028】 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. 【0029】 The PDCP layer performs header compression / decompression, encryption / decryption, etc. 【0030】 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. 【0031】 Figure 5 shows the configuration of the protocol stack of the wireless interface of the control plane that handles signaling (control signals). 【0032】 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. 【0033】 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. 【0034】 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). 【0035】 (Overview of the cell reselection procedure) Figure 6 is a diagram illustrating the overview of the cell reselection procedure. 【0036】 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. 【0037】 Figure 7 is a schematic diagram illustrating a typical (or legacy) cell reselection procedure. 【0038】 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. 【0039】 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. 【0040】 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. 【0041】 (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." 【0042】 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. 【0043】 Figure 8 shows an example of network slicing. 【0044】 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. 【0045】 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). 【0046】 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. 【0047】 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. 【0048】 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. 【0049】 (Overview of the slice-specific cell reselection procedure) Figure 9 is a diagram illustrating the overview of the slice-specific cell reselection procedure. 【0050】 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). 【0051】 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. 【0052】 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. 【0053】 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". 【0054】 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". 【0055】 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." 【0056】 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). 【0057】 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. 【0058】 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. 【0059】 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". 【0060】 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". 【0061】 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". 【0062】 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". 【0063】 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. 【0064】 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). 【0065】 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. 【0066】 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. 【0067】 (Method for reselecting cells according to the first embodiment) As described above, in slice-specific cell reselection (or slice-aware cell reselection), UE100 selects the desired slice and processes it. In this case, UE100 may also select a slice group as the selected slice. For example, UE100 may select slice group #1, which contains the desired slice, slice #1. In this case, UE100 can reselect the cells that support slice group #1 during slice-specific cell reselection. 【0068】 A slice group contains one or more network slices. In 3GPP, it is agreed that slice groups should be homogeneous within the same Registration Area (RA). That is, all network slices included in a slice group within the same RA should be identical. 【0069】 Furthermore, an RA (Tracking Area) includes one or more cells and is defined as a collection of TAs (Tracking Areas). Because an RA includes multiple TAs, it is possible to reduce the number of times registration update signaling is sent compared to when registration update signaling is sent for each TA. 【0070】 On the other hand, different RAs may result in different network slices being included in the slice group. 【0071】 Figure 12 is a diagram illustrating an example of the mapping relationship between slice groups and network slices according to the first embodiment. In Figure 12, the boundary between the cell range of gNB200-1 and the cell range of gNB200-2 is shown as the boundary of the RA. That is, the cells of gNB200-1 belong to RA#1, and the cells of gNB200-2 belong to RA#2. In RA#1, which includes the cells of gNB200-1, slice group #1 includes slices #1 and #2. In RA#2, which includes the cells of gNB200-2, slice group #1 includes slices #3 and #4. Even though RA#1 and RA#2 are the same slice group #1, the network slices included in slice group #1 are different. 【0072】 In such an example, consider the following case: UE100 camps on to a cell supporting slice group #1 in RA#1 through cell reselection using a slice-specific cell reselection procedure. 【0073】 Subsequently, UE100 moves and performs cell reselection again using the slice-specific cell reselection procedure. At this point, we assume that UE100 has moved to an area where it can communicate with cells in gNB200-2 (i.e., cells in RA#2). In this case, since the desired slice is slice #1, UE100 may select slice group #1 in RA#2 and perform the slice-specific cell reselection procedure. Then, UE100 attempts to camp on to the cell supporting slice group #1 in RA#2. 【0074】 However, slice group #1 of RA#2 does not support slice #1, which is the desired slice. Therefore, in such a case, UE100 selecting slice group #1 of RA#2 results in the selection of the wrong cell group. In such cases, UE100 cannot be said to be performing cell reselection correctly. 【0075】 Therefore, it is conceivable that the gNB200 could solve this problem by having it communicate the slice groups supported in adjacent cells via SIB. For example, in the case of Figure 12, the gNB200-1 communicates the identification information of slice group #1 and the identification information of slices #3 and #4 as information about slice group #1 supported in its adjacent cell (i.e., RA#2). Since the UE100 can understand the mapping relationship between slice group #1 and slices (slice #3 and slice #4) in RA#2, it is possible to avoid selecting slice group #1 in RA#2 when re-selecting a slice-specific cell. 【0076】 However, the gNB200 notifying slice groups could lead to the following problems: 【0077】 Firstly, network slice identification information consists of 32 bits. Compared to slice groups, which are simply numbers, the data size of network slice identification information is large. Therefore, when the gNB200 transmits network slice identification information when transmitting slice groups, it is not necessarily more efficient than when transmitting slice group identification information alone. 【0078】 Secondly, the transmission of network slice identification information by the gNB200 can pose security problems. For example, a company other than the one managing the gNB200 could potentially obtain the network slice identification information. 【0079】 Therefore, the objective of the first embodiment is to appropriately perform cell reselection in UE100. Furthermore, the objective of the first embodiment is to improve the transmission efficiency in gNB200. In addition, the objective of the first embodiment is to suppress security issues. 【0080】 Therefore, in the first embodiment, gNB200-1 transmits mapping information representing the mapping relationship between the slice group of RA#1 and the slice group of RA#2 without transmitting network slice identification information. 【0081】 Specifically, firstly, a base station (e.g., gNB200-1) transmits mapping information between a first slice group (e.g., cell group #1) available in the base station's area (e.g., RA#1) and a second slice group (e.g., cell group #2) available in an adjacent area adjacent to the base station (e.g., RA#2), if at least some of the network slices included in the first slice group are included in the second slice group. Secondly, a user device (e.g., UE100) uses the mapping information to perform slice-specific cell reselection. 【0082】 This allows UE100 to obtain information about the slice group containing the desired slice in RA#2 from the mapping information received from gNB200-1. Therefore, even when UE100 moves to the boundary of the RA, it can prevent selecting the wrong slice group by re-selecting the cell supporting the desired slice. Thus, cell re-selection can be performed appropriately in UE100. 【0083】 Furthermore, the mapping information does not include network slice identification information. Therefore, compared to cases where network slice identification information is transmitted, the transmission efficiency of the gNB200 can be improved. In addition, since network slice identification information is not transmitted, security issues can be mitigated. 【0084】 The mapping information specifically includes the following: 【0085】 In other words, firstly, this is the case when a portion of the network slices included in the first slice group in the first RA are included in the second slice group in the second RA. 【0086】 Figure 13 is a diagram showing an example of the mapping relationship between slice groups and network slices according to the first embodiment. In Figure 13, slice #1 is the same in slice group #1 of RA#1 and slice group #2 of RA#2. Therefore, as mapping information, slice group #1 of RA#1 and slice group #2 of RA#2 can be mapped. Specifically, the identification information of RA#1 is mapped to the identification information of slice group #1, the identification information of RA#2 is mapped to the identification information of slice group #2, and furthermore, the information obtained by mapping these may be included in the mapping information. The identification information of RA may be represented by a list of TAs (TAI (Tracking Area Identity) list) included in RA. The same applies below. The mapping information may also include information indicating that it is a "partial match". The mapping information may also include the number of network slices included in each slice group. For example, in the example in Figure 13, the mapping information may include that slice group #1 of RA#1 is "2" (slice #1 and slice #2), and slice group #2 of RA#2 is "2" (slice #1 and slice #5). 【0087】 Secondly, this is the case when all network slices included in the first slice group in the first RA are included in the second slice group in the second RA. 【0088】 Figure 14 is a diagram showing an example of the mapping relationship between slice groups and network slices according to the first embodiment. In Figure 14, the network slices (slice #3 and slice #4) included in slice group #2 of RA#1 and the network slices (slice #3 and slice #4) included in slice group #1 of RA#2 are all identical. In this case, the mapping information may include the mapping of the identification information of RA#1 to the identification information of slice group #2, the mapping of the identification information of RA#2 to the identification information of slice group #1, and further, the information resulting from these mappings may be included in the mapping information. The mapping information may also include information indicating that it is an "exact match". In addition, the mapping information may include the number of network slices included in each slice group. For example, in the example of Figure 14, the mapping information includes information indicating that slice group #2 of RA#1 is "2" (slice #3 and slice #4) and slice group #1 of RA#2 is "2" (slice #3 and slice #4). 【0089】 Thirdly, this is the case when one network slice included in the first slice group in the first RA is the same as one network slice included in the second slice group in the second RA. 【0090】 Figure 15 is a diagram illustrating an example of the mapping relationship between slice groups and network slices according to the first embodiment. In Figure 15, one network slice (slice #6) included in slice group #3 of RA#1 and one network slice (slice #6) included in slice group #3 of RA#2 are identical. In this case, the mapping information may include the mapping of the identification information of RA#1 to the identification information of slice group #3, the mapping of the identification information of RA#2 to the identification information of slice group #3, and further, the information obtained by mapping these may be included in the mapping information. This type of mapping information is more effective when one slice group contains only one network slice. The mapping information may also include information indicating that it is an "exact match". The mapping information may also include the number of network slices included in the slice group. For example, in the example of Figure 15, the mapping information may include information indicating that slice group #3 of RA#1 is "1" (slice #6) and slice group #3 of RA#2 is "1" (slice #6). 【0091】 The three types of mapping information described above may be combined. In the example shown in Figure 14, slice group #1 of RA#1 is mapped to slice group #2 of RA#2, and slice group #2 of RA#1 is mapped to slice group #1 of RA#2, so that two mapping relationships may be included in one piece of mapping information. Also, in the example shown in Figure 15, slice group #1 of RA#1 is mapped to slice group #2 of RA#2, slice group #2 of RA#1 is mapped to slice group #1 of RA#2, and slice group #3 of RA#1 is mapped to slice group #3 of RA#2, so that three mapping relationships may be included in one piece of mapping information. The mapping information may also include information indicating the type of each mapping relationship ("partial match" or "exact match"). Furthermore, the mapping information may also include information indicating the number of network slices included in each slice group. 【0092】 The above example describes a case where the network slices included in the slice group differ for each RA, but it is not limited to this case. For example, the network slices included in the slice group may differ for each TA. For example, in Figure 15, if the part labeled "RA#1" is replaced with "TA#1" and the part labeled "RA#2" is replaced with "TA#2", the procedure can be carried out in the same way as in the case of RA. 【0093】 In other words, any region in which the mapping relationship between slice groups and network slices is homogeneous can be used, and if there is a possibility that the mapping relationship between slice groups and network slices may change between such regions, the implementation can be carried out at the boundaries of such regions. The example above shows that the region may be an RA or a TA. Furthermore, the region may be an RNA (RAN-based Notification Area) or a PLMN (Public Land Mobile Network). Moreover, the region may contain multiple cells. Furthermore, the region may be composed of multiple RAs, multiple TAs, or multiple RNAs. Moreover, the region may be a combination of TA, RA, RNA, PLMN, and multiple cells. For example, a gNB200 located at TA#1 may transmit mapping information for RA#2 adjacent to TA#1. 【0094】 (Example of operation according to the first embodiment) Figure 16 is a diagram illustrating an example of operation according to the first embodiment. In the following description, the region RA (or TA) will be used as an example. 【0095】 As shown in Figure 16, in step S20, gNB200 obtains the mapping relationship between slice groups and network slices in the adjacent RA (or adjacent TA). gNB200-1 may obtain information representing the mapping relationship between slice groups and network slices from the adjacent gNB200-2 located in the adjacent RA (or adjacent TA). In this case, gNB200-1 may obtain the information by receiving an Xn message containing the information. Alternatively, gNB200-1 may obtain the information by receiving an NG message containing the information from AMF300. 【0096】 In step S21, gNB200 generates mapping information based on the mapping relationships between slice groups and network slices in its own RA (or TA) and the mapping relationships between slice groups and network slices in neighboring RAs (or neighboring TAs). In the example in Figure 13, gNB200 manages the mapping relationships between slice group #1 and each slice (slice #1 and slice #2) in its own RA (RA#1). It is also assumed that gNB200 obtains the mapping relationships between slice groups and network slices (the mapping relationships between slice group #1 and each slice (slice #3 and slice #4), and the mapping relationships between slice group #2 and each slice (slice #1 and slice #5)) from neighboring RAs. In this case, since both slice group #1 of RA#1 and slice group #2 of RA#2 contain slice #1, gNB200 generates mapping information that maps slice group #1 of RA#1 to slice group #2 of RA#2. 【0097】 Furthermore, gNB200 may obtain mapping information from AMF300 without generating it itself. In this case, gNB200 may obtain the mapping information by receiving an NG message containing the mapping information. Alternatively, gNB200 may obtain mapping information from a neighboring gNB without generating it itself. In this case, gNB200 may obtain the mapping information by receiving an Xn message containing the mapping information. 【0098】 Returning to Figure 16, in step S22, gNB200 transmits mapping information. gNB200 may broadcast the mapping information via broadcast signaling (e.g., SIB). Alternatively, gNB200 may transmit the mapping information via individual signaling (e.g., RRC release (RRCRelease) message). In this case, gNB200 may include the mapping relationships between slice groups and network slices in the adjacent RA (or adjacent TA) in the mapping information. For example, in the example in Figure 13, gNB200-1 may include and transmit the mapping relationships between slice group #1 of RA#2 and each slice (slice #3 and slice #4), and between slice group #2 of RA#2 and each slice (slice #1 and slice #5) in the mapping information because security concerns are mitigated in RRC messages. However, regardless of RRC messages, even in the case of broadcast transmission, gNB200 may transmit the mapping relationships between slice groups and network slices in the adjacent RA (or adjacent TA) in certain cases. The specified cases include, for example, at least one of the following: when there is only a "partial match" with an adjacent RA (or adjacent TA), or when it is an RA (or TA) boundary. This is based on the idea that security concerns are not considered an issue under these limited conditions. 【0099】 Furthermore, the mapping information may include TAC (Tracking Area Code) and / or PCI (Physical Cell ID). 【0100】 Alternatively, the AMF300 may send mapping information to the UE100. In this case, the AMF300 may send a NAS message containing the mapping information to the UE100's NAS, and the UE100's NAS may notify the UE100's AS of the mapping information. In this case, if the gNB200 generates the mapping information, the gNB200 may send an NG message containing the mapping information to the AMF300. 【0101】 Subsequently, in step S23, UE100 uses the mapping information to execute the slice-specific cell reselection procedure. For example, consider the case where UE100 moves to the vicinity of the cells of gNB200-2 located in the adjacent RA (or adjacent TA), as shown in Figure 13, and executes the slice-specific cell reselection procedure. Even in this case, UE100 can use the mapping information to select slice group #2 in RA#2 as the selected slice, and reselect the cells that support slice group #2 in RA#2. 【0102】 The transmission of mapping information (step S22) and the execution of the slice-specific cell reselection procedure (step S23) may be performed at predetermined timings. For example, gNB200 transmits mapping information (step S22) when the electric field strength of the serving cell in UE100 (e.g., the serving cell of gNB200-1) does not require cell reselection. Then, when the electric field strength reaches a stage where cell reselection is required, UE100 may execute the slice-specific cell reselection procedure (step S23). 【0103】 [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. 【0104】 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). 【0105】 The terms “based on” and “depending on” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending on” means both “at least partially on” and “at least partially on.” Furthermore, the terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included; they may include only the listed items, or they 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. Moreover, any reference to elements using designations such as “first,” “second,” etc., used in this disclosure does not generally limit the quantity or order of those elements. 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 adopted 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 by the context that they are not. 【0106】 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. 【0107】 This application claims priority to Japanese Patent Application No. 2022-019037 (filed on February 9, 2022), the entirety of which is incorporated into the specification of this application. 【0108】 (Note) The features of the above-described embodiment are noted below. 【0109】 (1) A cell reselection method in a mobile communication system, The base station transmits mapping information between the first slice group and the second slice group if at least some of the network slices included in the first slice group are included in the second slice group, in the area of ​​the base station and an adjacent area adjacent to the area of ​​the base station. The user device has the step of performing slice-specific cell reselection using the mapping information. How to re-select a cell. 【0110】 (2) The aforementioned region is a Tracking Area (TA), and the adjacent region is an adjacent TA adjacent to the aforementioned TA, or The aforementioned region is a Registration Area (RA), and the adjacent region is an adjacent RA adjacent to the aforementioned RA. The cell reselection method described in (1) above. 【0111】 (3) The mapping information includes identification information for the first slice group and identification information for the second slice group. The cell reselection method described in (1) or (2) above. [Explanation of Symbols] 【0112】 1: Mobile communication systems 20:5GC 100 :UE 110: Receiver 120: Transmitter 130: Control Unit 200 :gNB 210: Transmitter 220: Receiving unit 230: Control Unit 300 :AMF

Claims

[Claim 1] A cell reselection method in a mobile communication system, A base station transmits mapping information between a first slice group and a second slice group, provided that at least some of the network slices included in the first slice group are included in the second slice group, within the area of ​​the base station and an adjacent area adjacent to the area of ​​the base station. The user device performs slice-specific cell reselection using the mapping information, The mapping information does not include identification information for network slices, but it does include type information indicating whether the network slices included in the first slice group and the second slice group are partial or exact matches. How to re-select a cell. [Claim 2] The aforementioned region is a Tracking Area (TA), and the adjacent region is an adjacent TA adjacent to the aforementioned TA, or The aforementioned region is a Registration Area (RA), and the adjacent region is an adjacent RA adjacent to the aforementioned RA. The cell reselection method according to claim 1. [Claim 3] The mapping information includes identification information for the first slice group and identification information for the second slice group. The cell reselection method according to claim 1. [Claim 4] A user device in a mobile communication system, A base station receives mapping information between a first slice group and a second slice group, where at least some of the network slices included in the first slice group are included in the second slice group, in the case where a first slice group is available in the area of ​​the base station and a second slice group is available in an adjacent area adjacent to the area of ​​the base station. The system includes a control unit that performs slice-specific cell reselection using the aforementioned mapping information, The mapping information does not include identification information for network slices, but it does include type information indicating whether the network slices included in the first slice group and the second slice group are partial or exact matches. User device.

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