Slice-specific cell reselection method

Abstract

A slice-specific cell reselection method according to one aspect is for a mobile communication system. The slice-specific cell reselection method comprises a step in which a user device receives, from a base station or an access management device, a slice priority indicating priority per network slice. The slice-specific cell reselection method also comprises a step in which, when wireless resource free space is equal to or greater than a threshold value, the base station transmits a slice-priority-ignore permission message indicating that it is permitted to ignore the slice priority. Furthermore, the slice-specific cell reselection method comprises a step in which the user device uses a network slice desired by the user device to perform slice-specific cell reselection without the using slice priority, in accordance with the reception of the slice-priority-ignore permission message.

Description

[Technical Field]

[0001] The present disclosure relates to a slice-specific cell reselection method in a mobile communication system. [Background technology]

[0002] Network slicing is defined in the specifications of the Third Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter), a standardization project for mobile communication systems. Network slicing is a technology that creates network slices, which are virtual networks, by logically dividing the physical networks built by telecommunications carriers.

[0003] A user equipment in a radio resource control (RRC) idle state or an RRC inactive state can perform a cell reselection procedure. 3GPP is considering slice-specific cell reselection, which is a network slice-dependent cell reselection procedure (see, for example, Non-Patent Document 1). By performing the slice-specific cell reselection procedure, the user equipment can, for example, camp on a neighboring cell that supports a desired network slice.

[0004] The slice-specific cell reselection procedure uses a slice priority that indicates the priority of each network slice. The user equipment performs the slice-specific cell reselection procedure in order from the network slice with the highest slice priority. In 3GPP, there is discussion on providing slice priority from a network to a user device (see, for example, Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] 3GPP TS 38.300 V16.8.0 (2021-12) [Non-patent document 2] “RP-220386”, “On RAN Slicing”, Ericsson, Deutsche Telekom, 3GPP TSG-RAN#95-e, 2022-03-17-2022-03-23 Summary of the Invention

[0006] A slice-specific cell reselection method according to one aspect is a slice-specific cell reselection method in a mobile communication system. The slice-specific cell reselection method includes a step in which a user equipment receives, from a base station or an access management device, slice priorities indicating priorities for each network slice. The slice-specific cell reselection method also includes a step in which the base station transmits a slice priority ignore permission message indicating that ignoring of the slice priority is permitted when available radio resources are equal to or greater than a threshold. The slice-specific cell reselection method further includes a step in which, in response to receiving the slice priority ignore permission message, the user equipment performs slice-specific cell reselection using a network slice desired by the user equipment without using slice priorities. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a mobile communication system according to the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a UE (user equipment) according to the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example configuration of a gNB (base station) according to the first embodiment. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a protocol stack related to a user plane according to the first embodiment. [Figure 5]FIG. 5 is a diagram illustrating an example of the configuration of a protocol stack related to the control plane according to the first embodiment. [Figure 6] FIG. 6 is a diagram for explaining an outline of the cell reselection procedure. [Figure 7] FIG. 7 is a diagram illustrating a general flow of a general cell reselection procedure. [Figure 8] FIG. 8 is a diagram illustrating an example of network slicing. [Figure 9] FIG. 9 is a diagram outlining a slice-specific cell reselection procedure. [Figure 10] FIG. 10 is a diagram illustrating an example of slice frequency information. [Figure 11] FIG. 11 is a diagram illustrating the basic flow of a slice-specific cell reselection procedure. [Figure 12] FIG. 12 is a diagram illustrating an example of operation according to the first embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of operation according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] One aspect of the present disclosure aims to provide a slice-specific cell reselection method that enables a user equipment to reselect a cell that supports its desired network slice.

[0009] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0010] [First embodiment] (Configuration of a mobile communication system) FIG. 1 is a diagram illustrating the configuration of a mobile communication system according to a first embodiment. The mobile communication system 1 conforms to the 3GPP standard 5th Generation System (5GS). In the following description, 5GS is used as an example, but the mobile communication system may also be at least partially based on an LTE (Long Term Evolution) system. Alternatively, the mobile communication system may also be at least partially based on a sixth generation (6G) system.

[0011] 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. The 5GC 20 may be simply referred to as the core network (CN) 20.

[0012] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone), a tablet terminal, a laptop PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0013] The NG-RAN 10 includes a base station (called "gNB" in the 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has 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. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] In addition, gNBs can also connect to the Evolved Packet Core (EPC), which is the LTE core network. LTE base stations can also connect to 5GC. LTE base stations and gNBs can also be connected via a base station-to-base station interface.

[0015] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0016] 2 is a diagram showing the configuration of a UE 100 (user equipment) according to the first embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0017] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0018] 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 a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0019] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes in each layer, which will be 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 in the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 130 may perform each process or operation in the UE 100 in each of the embodiments described below.

[0020] 3 is a diagram showing the configuration of a gNB200 (base station) according to the first embodiment. The gNB200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that performs communication with the CN20.

[0021] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0022] 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 a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0023] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes in each layer, which will be 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 in the processes by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals, etc. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 230 may perform each process or operation in the gNB 200 in each of the embodiments described below.

[0024] The backhaul communication unit 240 is connected to neighboring base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 may be configured (i.e., functionally divided) with a CU (Central Unit) and a DU (Distributed Unit), and both units may be connected via an F1 interface, which is a fronthaul interface.

[0025] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0026] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added.

[0028] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via transport channels. The MAC layer of gNB200 includes a scheduler, which determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0029] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via logical channels.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0031] The SDAP layer maps IP flows, which are the units for Quality of Service (QoS) control by the core network, to radio bearers, which are the units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP is not necessary.

[0032] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0033] The protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) instead of the SDAP layer shown in FIG.

[0034] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0035] The NAS, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of the UE 100 and the NAS of the AMF 300. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. The layer below the NAS is called an AS (Access Stratum).

[0036] (Overview of cell reselection procedure) FIG. 6 is a diagram for explaining an overview of a cell reselection procedure.

[0037] When the UE 100 is in an RRC idle state or an RRC inactive state, it performs a cell reselection procedure to transition from a current serving cell (cell #1) to a neighboring cell (any of cells #2 to #4) as it moves. Specifically, the UE 100 identifies a neighboring cell on which it should camp by the cell reselection procedure, and reselects the identified neighboring cell. When the current serving cell and the neighboring cell have the same frequency (carrier frequency), this is called intra-frequency, and when the current serving cell and the neighboring cell have different frequencies (carrier frequencies), this is called inter-frequency. The current serving cell and the neighboring cell may be managed by the same gNB 200 or different gNBs 200.

[0038] FIG. 7 is a diagram illustrating a general flow of a typical (or legacy) cell reselection procedure.

[0039] In step S11, the UE 100 performs a frequency prioritization process based on the priority (also referred to as "absolute priority") for each frequency specified by the gNB 200, for example, by a system information block or an RRC release message. Specifically, the UE 100 manages the frequency priority specified by the gNB 200 for each frequency.

[0040] In step S12, UE 100 performs a measurement process to measure radio quality for each of the serving cell and the neighboring cell. UE 100 measures the received power and received quality of reference signals transmitted by each of the serving cell and the neighboring cell, specifically, CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, UE 100 always measures radio quality for frequencies having a higher priority than the frequency priority of the current serving cell, and for frequencies having a priority equal to or lower than the frequency priority of the current serving cell, UE 100 measures the radio quality of the frequency having the same priority or lower priority when the radio quality of the current serving cell falls below a predetermined quality.

[0041] In step S13, UE 100 performs a cell reselection process to reselect a cell on which UE 100 will camp based on the measurement result in step S20. For example, if the frequency priority of a neighboring cell is higher than the priority of a current serving cell and the neighboring cell satisfies a predetermined quality standard (i.e., a minimum required quality standard) for a predetermined period, UE 100 may perform cell reselection to the neighboring cell. If the frequency priority of the neighboring cell is the same as the priority of the current serving cell, UE 100 may rank the radio qualities of the neighboring cells and perform cell reselection to the neighboring cell having a higher rank than the rank of the current serving cell for a predetermined period. If the frequency priority of the neighboring cell is lower than the priority of the current serving cell and the radio quality of the current serving cell is lower than a certain threshold and the radio quality of the neighboring cell is higher than another threshold, UE 100 may perform cell reselection to the neighboring cell.

[0042] (Network Slicing Overview) Network slicing is a technology that creates multiple virtual networks by virtually dividing a physical network constructed by a carrier (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."

[0043] Network slicing allows telecommunications operators to create slices that meet 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.

[0044] FIG. 8 is a diagram illustrating an example of network slicing.

[0045] Three slices (slice #1 to slice #3) are configured on a network 50 configured with an NG-RAN 10 and a 5GC 20. Slice #1 is associated with a service type called eMBB, slice #2 is associated with a service type called URLLC, and slice #3 is associated with a service type called mMTC. Note that three or more slices may be configured on the network 50. One service type may be associated with multiple slices.

[0046] Each slice is provided with a slice identifier that identifies the slice. 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 for differentiating multiple slices associated with the same service type. Information including multiple S-NSSAIs is called NSSAI (Network Slice Selection Assistance Information).

[0047] Furthermore, one or more slices may be grouped to form a slice group. A slice group is a group including one or more slices, and a slice group identifier is assigned to the slice group. The slice group may be configured by a core network (e.g., AMF 300) or a radio access network (e.g., gNB 200). The configured slice group may be notified to UE 100.

[0048] Hereinafter, the term "network slice (slice)" may refer to an S-NSSAI, which is an identifier of a single slice, or an NSSAI, which is a collection of S-NSSAIs. Alternatively, the term "network slice (slice)" may refer to a slice group, which is a group of one or more S-NSSAIs or NSSAIs.

[0049] Furthermore, UE 100 determines a desired slice that it wishes to use. A desired slice is sometimes called an "intended slice." In the first embodiment, UE 100 determines a slice priority for each network slice (desired slice). For example, the NAS of UE 100 determines the slice priority based on the operation status of an application in UE 100 and / or a user operation / setting, and notifies the AS of slice priority information indicating the determined slice priority.

[0050] (Overview of slice-specific cell reselection procedure) FIG. 9 is a diagram illustrating an overview of a slice-specific cell reselection (also referred to as slice-aware cell reselection or slice-based cell reselection) procedure.

[0051] In the slice-specific cell reselection procedure, the UE 100 performs a cell reselection process based on slice frequency information provided by the network 50. The slice frequency information may be provided to the UE 100 from the gNB 200 by broadcast signaling (e.g., a system information block) or dedicated signaling (e.g., an RRC release message).

[0052] The slice frequency information indicates the correspondence between network slices, frequencies, and frequency priorities. For example, for each slice (or slice group), the slice frequency information indicates the frequency (one or more frequencies) that supports the slice and the frequency priority assigned to each frequency. An example of the slice frequency information is shown in FIG. 10.

[0053] In the example shown in Fig. 10, three frequencies F1, F2, and F4 are associated with slice #1 as frequencies supporting 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 of Fig. 10, the larger the frequency priority number, the higher the priority; however, it may also be the case that the smaller the number, the higher the priority.

[0054] Furthermore, three frequencies F1, F2, and F3 are associated with slice #2 as frequencies supporting 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."

[0055] Furthermore, three frequencies F1, F3, and F4 are associated with slice #3 as frequencies supporting 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."

[0056] Hereinafter, the frequency priority indicated in the slice frequency information may be referred to as a "slice-specific frequency priority" to distinguish it from the absolute priority in the conventional cell reselection procedure.

[0057] As shown in FIG. 9, UE 100 may perform a cell reselection process based on slice support information provided by network 50. The slice support information may be information indicating a correspondence between a cell (e.g., a serving cell and each neighboring cell) and a network slice that the cell does not provide or provides. For example, a cell may temporarily not provide some or all network slices 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 the frequency may not provide the network slice. UE 100 can identify the network slices that each cell does not provide based on the slice support information. Such slice support information may be provided to UE 100 by broadcast signaling (e.g., a system information block) or dedicated signaling (e.g., an RRC release message) from gNB 200.

[0058] 11 is a diagram showing a basic flow of a slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, the UE 100 is in an RRC idle state or an RRC inactive state, and has received and stored the above-mentioned slice frequency information. Note that the procedure of "slice-specific cell reselection" is represented by a "slice-specific cell reselection procedure." However, hereinafter, "slice-specific cell reselection" and "slice-specific cell reselection procedure" may be used interchangeably.

[0059] In step S0, the NAS of UE 100 determines slice identifiers of desired slices of UE 100 and slice priorities of each desired slice, and notifies the AS of UE 100 of slice priority information including the determined slice priorities. A "desired slice" is an "intended slice" and includes a slice that is likely to be used, a candidate slice, a desired slice, a slice to be communicated, a requested slice, an allowed slice, or an intended slice. For example, the slice priority of slice #1 is determined to be "3," the slice priority of slice #2 is determined to be "2," and the slice priority of slice #3 is determined to be "1." A larger number for the slice priority indicates a higher priority, but a smaller number may also indicate a higher priority.

[0060] In step S1, the AS of the UE 100 sorts the slices (slice identifiers) notified from the NAS in step S0 in descending order of slice priority. The list of slices sorted in this way is called a "slice list."

[0061] In step S2, the AS of the UE 100 selects one network slice in descending order of slice priority. The network slice selected in this manner is called a "selected network slice."

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

[0063] In step S4, the AS of UE 100 selects one frequency in descending order of frequency priority for the selected network slice selected in step S2, and performs measurement processing on the selected frequency. The frequency selected in this manner is called a "selected frequency." The AS of UE 100 may rank the cells measured within the selected frequency in descending order of wireless quality. Among the cells measured within the selected frequency, a cell that satisfies a predetermined quality standard (i.e., a required minimum quality standard) is called a "candidate cell."

[0064] In step S5, the AS of UE100 identifies the highest-ranked cell based on the result of the measurement process in step S4, and determines whether the cell provides the selected network slice based on the slice support information. If it is determined that the highest-ranked cell provides the selected network slice (step S5: YES), in step S5a, the AS of UE100 reselects the highest-ranked cell and camps on the cell.

[0065] On the other hand, if it is determined that the highest-ranked cell does not provide the selected network slice (step S5: NO), in step S6, the AS of UE 100 determines whether or not there is an unmeasured frequency in the frequency list created in step S3. In other words, the AS of UE 100 determines whether or not there is a frequency assigned in step S3 other than the selected frequency in the selected network slice. If it is determined that there is an unmeasured frequency (step S6: YES), the AS of UE 100 resumes processing on the frequency with the next highest frequency priority and performs measurement processing with that frequency as the selected frequency (returning to step S4).

[0066] If it is determined that there are no unmeasured frequencies in the frequency list created in step S3 (step S6: NO), 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 any network slices other than the selected network slice in the slice list. If it is determined that there are any unselected slices (step S7: YES), the AS of UE100 resumes processing on the network slice with the next highest slice priority and selects that network slice as the selected network slice (returns processing to step S2). Note that in the basic flow shown in FIG. 11, the processing of step S7 may be omitted.

[0067] If it is determined that there is no unselected slice (step S7: NO), in step S8, the AS of UE 100 performs a conventional cell reselection process. The conventional cell reselection process may mean the entire general (or legacy) cell reselection procedure shown in Fig. 7. Alternatively, the conventional cell reselection process may mean only the cell reselection process (step S30) shown in Fig. 7. In the latter case, UE 100 may use the measurement result in step S4 without measuring the radio quality of the cell again.

[0068] The general cell reselection procedure shown in Fig. 7 may be referred to as a "legacy cell reselection procedure." Although the "legacy cell reselection procedure" represents the procedure for "legacy cell reselection," in the following, "legacy cell reselection" and "legacy cell reselection procedure" may be used interchangeably.

[0069] (Slice-specific cell reselection method according to the first embodiment) As described above, in the slice-specific cell reselection procedure, processing is performed in order from the network slice with the highest slice priority. The slice priority is notified from the NAS of UE 100 to the AS of UE 100, and the slice-specific cell reselection procedure using the slice priority is executed in the AS of UE 100.

[0070] Regarding this slice priority, 3GPP is discussing the network 50 providing the slice priority to the UE 100. This makes it possible, for example, to control (a part of) the slice-specific cell reselection procedure performed by the UE 100 on the network 50 side.

[0071] However, regarding the slice priority provided by the network 50 side, a network slice with a lower slice priority than others may be the network slice desired by the user (or UE 100). In such a case, even if the UE 100 executes a slice-specific cell reselection procedure, it may not be possible to reselect a cell that supports the desired network slice because the slice priority is lower than others. As a result, the UE 100 may not be able to execute an application desired by the user.

[0072] Therefore, the first embodiment aims to provide a slice-specific cell reselection method that enables UE 100 to reselect a cell that supports its desired network slice.

[0073] Therefore, in the first embodiment, when a predetermined condition is met, the gNB 200 transmits a slice priority ignore permission message indicating that ignoring of the slice priority transmitted from the network 50 is permitted. Then, in response to receiving the message, the UE 100 performs slice-specific cell reselection using a network slice desired by the UE 100 without using the slice priority received from the network 50.

[0074] Specifically, first, a user equipment (e.g., UE100) receives a slice priority indicating a priority for each network slice from a base station (e.g., gNB200) or an access management device (e.g., AMF300). Second, when the available capacity of radio resources is equal to or greater than a threshold, the base station transmits a slice priority ignore permission message indicating that ignoring of the slice priority is permitted. Third, in response to receiving the slice priority ignore permission message, the user equipment performs slice-specific cell reselection using a network slice desired by the user equipment without using slice priority.

[0075] As a result, for example, when UE 100 receives a slice priority ignore permission message, it becomes possible to execute a slice-specific cell reselection procedure, for example, with its desired network slice as the highest priority. Therefore, by executing this procedure, UE 100 becomes able to reselect a cell that supports its desired network slice.

[0076] The predetermined condition is that the available capacity of the radio resources used for radio communication between the gNB 200 and the UE 100 is equal to or greater than a threshold. The reason for this is, for example, as follows.

[0077] That is, it has been described that in 3GPP, discussions are being held regarding the network 50 controlling slice-specific cell reselection. One reason why the network 50 wants to control slice-specific cell reselection is load distribution of the UE 100. For example, when multiple UEs 100 perform a slice-specific cell reselection procedure at the same time, there is a case where specific radio resources are used intensively between the multiple UEs 100 and the gNB 200. The reason for controlling slice-specific cell reselection in the network 50 is to prevent such a situation as much as possible and to distribute the load of the UEs 100. Therefore, if there is free capacity in the radio resources equal to or greater than a threshold, the UE 100 can perform slice-specific cell reselection by prioritizing its desired network slice rather than following the control on the network 50 side. For this reason, in the first embodiment, a condition related to radio resources is set as the predetermined condition.

[0078] Note that frequency priority (i.e., slice-specific frequency priority) can be controlled on the network 50 side. As described above, the frequency priority is included in the slice frequency information and is notified from the network 50 to the UE 100. Therefore, the network 50 can also change the frequency priority.

[0079] However, a change in frequency priority may affect a large number of UEs 100, and may also affect deployment scenarios on the network 50 side.

[0080] Therefore, in the first embodiment, the control target will be described as slice priority rather than frequency priority.

[0081] (Operation example of the first embodiment) FIG. 12 is a diagram illustrating an example of operation according to the first embodiment.

[0082] As shown in FIG. 12, in step S20, UE100 receives slice priority information including slice priority. The NAS of UE100 may receive a NAS message (for example, a Registration Accept message) including the slice priority information from AMF300. The NAS of UE100 outputs the received slice priority information to the AS of UE100. The NAS of UE100 may also receive the slice priority information from a user application. The slice priority information that the NAS of UE100 receives from the user application may be slice priority information related to a network slice allowed by the Allowed NSSAI received from AMF300. The slice priority information that the NAS of UE100 receives from the user application may also be slice priority information specified by the user application, regardless of whether it is received from the network side such as AMF300. In this case, too, the NAS of UE100 outputs the received slice priority information to the AS of UE100. The AS of UE100 may receive an RRC message including the slice priority information from gNB200. The RRC message may be a System Information Block (SIB) or an RRC Release (RRCRelease) message.

[0083] In step S21, the gNB 200 transmits slice frequency information including frequency priority. As described above, the gNB 200 may transmit the slice frequency information using an RRC message including the slice frequency information.

[0084] In step S22, the application of the UE 100 selects a network slice with a lower priority than the others as a desired network slice, and then outputs information about the network slice to the AS of the UE 100 via the NAS of the UE 100.

[0085] Here, it is assumed that in step S20, the AS of UE100 receives slice priority information in which the slice priority of network slice #1 is "7" and the slice priority of network slice #2 is "1" (the larger the slice priority value, the higher the slice priority). Also, it is assumed that in step S22, the application of UE100 selects network slice #2 as the desired network slice. If the AS of UE100 continues to perform slice-specific cell reselection according to the slice priority received from network 50, it may reselect a cell that supports network slice #1 and not reselect a cell that supports network slice #2 that is desired by the application of UE100.

[0086] In step S23, when the available capacity of radio resources is equal to or greater than a threshold, the gNB 200 transmits a message indicating that ignoring of the slice priority transmitted from the network 50 is permitted. Such a message is called a slice priority ignore permission message. The gNB 200 may transmit the slice priority ignore permission message by an RRC message such as broadcast signaling (e.g., SIB) or dedicated signaling (e.g., an RRC release (RRCRelease) message).

[0087] In step S24, in response to receiving the slice priority ignore permission message, UE100 performs slice-specific cell reselection using the network slice desired by UE100 (step S22) without using the slice priority (step S20) received from network 50. In the above example, the AS of UE100 performs slice-specific cell reselection using network slice #2 desired by the application of UE100 without using network slice #1 with the highest slice priority.

[0088] In step S25, when the available capacity of radio resources falls below a threshold, the gNB 200 transmits a message indicating that it will revoke the permission to ignore the slice priority transmitted from the network 50. Such a message is called a slice priority ignore cancellation message. The gNB 200 may transmit the slice priority ignore cancellation message by an RRC message such as broadcast signaling (e.g., SIB) or dedicated signaling (e.g., an RRC release (RRCRelease) message).

[0089] In step S26, in response to receiving the slice priority ignore cancel message, the UE 100 performs slice-specific cell reselection using the slice priority received from the network 50 (step S20).

[0090] In this way, in the first embodiment, after receiving the slice priority ignore permission message, UE100 performs slice-specific cell reselection using the network slice desired by UE100 itself until receiving the slice priority ignore cancellation message. Therefore, UE100 can reselect to a cell that supports the network slice desired by UE100 itself, and can also execute a user application desired by UE100 itself, for example.

[0091] In the first embodiment, an example has been described in which the slice priority ignore permission message (step S23) and the slice priority ignore cancel message (step S25) are transmitted from the gNB 200, but this is not limiting. The slice priority ignore permission message and the slice priority ignore cancel message may be transmitted from the AMF 300 to the UE 100. In this case, the slice priority ignore permission message and the slice priority ignore cancel message are transmitted using a NAS message. For example, when the available capacity of radio resources is equal to or greater than a threshold, the gNB 200 may transmit a message indicating this (or a message indicating that the slice priority ignore permission message may be transmitted) to the AMF 300, and the AMF 300 may transmit the slice priority ignore permission message to the UE 100 in response to receiving the message. Furthermore, for example, when the available capacity of radio resources becomes less than a threshold, the gNB 200 may transmit a message indicating this (or a message indicating that the slice priority ignore cancel message may be transmitted) to the AMF 300, and the AMF 300 may transmit the slice priority ignore cancel message in response to receiving the message.

[0092] (Modification 1 of the first embodiment) Next, a first modification of the first embodiment will be described.

[0093] In the first embodiment, an example has been described in which UE100 performs slice-specific cell reselection using a network slice desired by UE100 upon receiving a slice priority ignore permission message, but this is not limited to this. For example, UE100 may perform slice-specific cell reselection using a network slice desired by UE100 when it has not received a slice priority (step S20) from gNB200 or AMF300. That is, UE100 performs slice-specific cell reselection using a network slice desired by UE100 when it has not received a slice priority from network 50. When network 50 does not transmit slice priority, it may instruct UE100 by signaling that 1) UE100 may ignore slice priority, or 2) follow existing cell reselection. For example, gNB200 may transmit an RRC message including information indicating the instruction to UE100. Alternatively, for example, AMF300 may transmit a NAS message including information indicating the instruction to UE100.

[0094] However, when UE100 receives the frequency priority (step S21), it performs slice-specific cell reselection according to the frequency priority. The slice frequency information indicates the relationship between the network slice, the frequency supported in the network slice, and the frequency priority of the frequency. Therefore, by following the frequency priority, UE100 performs slice-specific cell reselection in order, for example, starting from the network slice that supports the frequency with the highest frequency priority.

[0095] In addition, gNB200 may not transmit slice priority when the available capacity of radio resources is equal to or greater than a threshold, taking into consideration load balancing of UE100, and may transmit slice priority when the available capacity of radio resources becomes less than the threshold. If UE100 has not received slice priority, it performs slice-specific cell reselection using its desired network slice, and if it has received slice priority, it performs slice-specific cell reselection using the slice priority.

[0096] (Modification 2 of the first embodiment) Next, a second modification of the first embodiment will be described.

[0097] In the first embodiment, the gNB200 has been described as transmitting a slice priority ignore permission message indicating that ignoring of slice priority is permitted, but this is not limited thereto. For example, the gNB200 may transmit a message indicating that the network slice desired by the UE100 (or the slice priority desired by the UE100) is applied when the available capacity of radio resources is equal to or greater than a threshold. Alternatively, the gNB200 may transmit a message indicating that the network slice (or the slice priority) is to be followed by the desire (or preference) of the UE100 regarding the network slice (or the slice priority) when the available capacity of radio resources is equal to or greater than a threshold. In response to receiving these messages, the UE100 performs slice-specific cell reselection using the network slice desired by the UE100 (or the slice priority desired by the UE100), as in the first embodiment. Then, the gNB200 may transmit a message indicating that the application of the network slice desired by the UE100 (or the slice priority desired by the UE100) is canceled when the available capacity of radio resources falls below a threshold. Alternatively, the gNB 200 may transmit a message indicating that it will cancel the network slice (or slice priority) preference of the UE 100 when the available radio resource capacity falls below a threshold. In response to receiving these messages, the UE 100 performs slice-specific cell reselection using the slice priority received from the network 50.

[0098] (Modification 3 of the first embodiment) Next, a third modification of the first embodiment will be described.

[0099] In the first embodiment, an example has been described in which UE100 selects one network slice having a lower priority than the others, but this is not limited thereto. For example, UE100 may select multiple network slices having a lower priority than the others. In this case, UE100 may set slice priorities for the selected multiple network slices. In response to receiving a slice priority ignore permission message (step S23), UE100 performs slice-specific cell reselection using the slice priority set by itself. Then, in response to receiving a slice priority ignore cancel message (step S25), UE100 performs slice-specific cell reselection using the slice priority received from network 50.

[0100] In addition, UE 100 may set slice priority in the NAS of UE 100 or an application of UE 100. For example, multiple network slices may be selected in the application of UE 100, and slice priority may be set for the multiple network slices in the NAS of UE 100.

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

[0102] In the current specifications of 3GPP, there is no mechanism for UE 100 to transmit its desired slice priority to network 50. Furthermore, even if UE 100 changes its desired slice priority, there is no mechanism for UE 100 to transmit the changed slice priority to network 50. Therefore, in the current specifications, it may not be possible to perform slice-specific cell reselection that satisfies the desires of UE 100. Therefore, as in the first embodiment, there may be cases where UE 100 itself cannot reselect a cell that supports its desired network slice.

[0103] Therefore, in the second embodiment, when the slice priority transmitted by the network 50 differs from the slice priority desired by the UE 100, if the available capacity of radio resources is greater than or equal to a threshold, the gNB 200 or the AMF 300 transmits the slice priority desired by the UE 100.

[0104] Specifically, first, a user device (e.g., UE100) transmits a first slice priority, which represents a priority for each network slice and is desired by the user device, to a base station (e.g., gNB200) or an access management device (or AMF300). Second, when the second slice priority transmitted by the base station or access management device differs from the first slice priority, the base station or access management device transmits the first slice priority if the available capacity of radio resources is equal to or greater than a threshold. Third, in response to receiving the first slice priority, the user device performs slice-specific cell reselection using the first slice priority.

[0105] As a result, for example, UE 100 can perform slice-specific cell reselection using the slice priority desired by itself, and can perform slice-specific cell reselection that satisfies the desires of UE 100. Therefore, it is also possible for UE 100 to reselect a cell that supports the desired network slice.

[0106] (Operation example of the second embodiment) Fig. 13 is a diagram showing an example of operation according to the second embodiment. Note that it is assumed that the gNB200 or the AMF300 transmits slice priority information including slice priorities before performing the operation shown in Fig. 13. For example, the gNB200 may transmit the slice priority information using an RRC message. Alternatively, the gNB200 and the AMF300 may transmit the slice priority information using an NAS message. When the AMF300 transmits the slice priority information, it is assumed that the gNB200 has received the slice priority information from the AMF300. In other words, it is assumed that the gNB200 is aware of the slice priorities transmitted by the AMF300, even when the AMF300 transmits the slice priority information.

[0107] As shown in FIG. 13, in step S30, UE 100 determines its desired slice priority (e.g., first slice priority) and transmits slice priority information (e.g., first slice priority information) including the slice priority to network 50.

[0108] First, UE100 may transmit the slice priority information to AMF300. In this case, the NAS of UE100 may transmit its desired slice priority to AMF300 by transmitting a NAS message (for example, a Registration Request message) including the slice priority information. In this case, AMF300 may transmit an NG message including the slice priority information to gNB200. The gNB200 receives the slice priority desired by UE100 via AMF300. After transmitting the slice priority information to AMF300, the NAS of UE100 may output its desired slice priority to the AS of UE100.

[0109] Second, UE100 may transmit the slice priority information to gNB200. In this case, the NAS of UE100 outputs its desired slice priority to the AS of UE100. Then, the AS of UE100 transmits slice priority information including the desired slice priority to gNB200. The AS of UE100 may transmit the slice priority information by transmitting an RRC message (for example, an RRC Setup Request message) including the slice priority information to gNB200. In this case, gNB200 receives the slice priority desired by UE100 directly from UE100.

[0110] In the slice priority information, multiple network slices (desired by UE 100) may be in the form of a list, and the order of entries in the list may indicate the slice priority. For example, the first entry in the list represents the network slice with the highest priority, the next entry represents the network slice with the second highest priority, and so on. Also, for example, the order of entries in each S-NSSAI included in the Configured NSSAI (or Allowed NSSAI, or Requested NSSAI) may represent the slice priority. Since the Configured NSSAI includes a maximum of eight S-NSSAIs, for example, when eight S-NSSAIs are included, the first entry in the Configured NSSAI represents the network slice with the highest priority, the next entry represents the network slice with the second highest priority, and so on. In this case, a dummy S-NSSAI (for example, an S-NSSAI with all "1"s) may be included in the Configured NSSAI. For example, the first entry is the S-NSSAI (highest priority) of network slice #1, the next entry is a dummy S-NSSAI (second highest priority), and the next entry is the S-NSSAI of network slice #2, etc. The same applies to the Allowed NSSAI or the Requested NSSAI. Note that in the above example, the first entry has the highest priority and the last entry has the lowest priority, but the priority order may be reversed, with the first entry having the lowest priority and the last entry having the highest priority.

[0111] In step S32, when the slice priority (e.g., second slice priority) transmitted by the gNB200 or the AMF300 differs from the slice priority (e.g., first slice priority) desired by the UE100, if the available capacity of radio resources is equal to or greater than a threshold, the gNB200 transmits slice priority information including a new slice priority. The new slice priority is the slice priority desired by the UE100. The new slice priority may also mean the slice priority granted to the UE100. When the slice priority information includes a network slice in the form of a list, the order of entries in the list may represent the new slice priority, as in step S30.

[0112] First, for a specific UE 100, the gNB 200 may transmit slice priority information including new priority by using an RRC release (RRCRelease) message. That is, the gNB 200 notifies the specific UE 100 of the new priority by transmitting an RRC release (RRCRelease) message including the slice priority information. Furthermore, the AMF 300 may notify the specific UE 100 of the new priority by transmitting an NAS message including the slice priority information to the NAS of the specific UE 100 (step S34).

[0113] Secondly, the gNB 200 may notify multiple UEs 100 of the new priority by transmitting (or broadcasting) an SIB including the slice priority information.

[0114] Note that, instead of transmitting slice priority information including new slice priorities, the gNB200 or the AMF300 may transmit a message indicating that the slice priority desired by the UE100 may be prioritized over the slice priorities transmitted by the gNB200 or the AMF300. The gNB200 may transmit the message by using an RRC message. Alternatively, the AMF300 may transmit the message by using an NAS message.

[0115] In step S35, UE100 performs slice-specific cell reselection using the new slice priority in response to receiving slice priority information including the new slice priority. That is, UE100 performs slice-specific cell reselection using the slice priority in response to receiving the slice priority desired by UE100 itself. Since the slice priority is the slice priority desired by UE100 itself, by performing slice-specific cell reselection, it becomes possible to reselect a cell that supports the network slice desired by UE100.

[0116] [Other embodiments] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0117] In addition, circuits that execute each process performed by UE100 or gNB200 may be integrated, and at least a portion of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0118] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." Furthermore, the terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Furthermore, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0119] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made within the scope of the gist. Furthermore, it is also possible to combine all or part of each embodiment, each operation, each process, and each step within the scope of consistent combinations.

[0120] This application claims priority from Japanese Patent Application No. 2022-069720 (filed April 20, 2022), the entire contents of which are incorporated herein by reference.

[0121] (Addendum) In one embodiment, (1) a slice-specific cell reselection method in a mobile communication system, comprising: a step in which a user device receives a slice priority representing a priority for each network slice from a base station or an access management device; a step in which the base station transmits a slice priority ignore permission message representing permission to ignore the slice priority when the available capacity of radio resources is equal to or greater than a threshold; and a step in which the user device, in response to receiving the slice priority ignore permission message, performs slice-specific cell reselection using a network slice desired by the user device without using the slice priority.

[0122] (2) The slice-specific cell reselection method of (1) above may further include a step in which the base station transmits a slice priority ignore cancellation message indicating that permission to ignore the slice priority is revoked when the available capacity of the radio resources becomes less than a threshold after transmitting the slice priority ignore permission message, and a step in which the user equipment performs slice-specific cell reselection using the slice priority in response to receiving the slice priority ignore cancellation message.

[0123] (3) The slice-specific cell reselection method of (1) or (2) above may further include, in the performing step, a step of performing slice-specific cell reselection using the network slice desired by the user equipment when the user equipment does not receive the slice priority from the base station or the access management device.

[0124] Also, in one embodiment, (4) a slice-specific cell reselection method in a mobile communication system includes the steps of: a user device transmitting a first slice priority representing a priority for each network slice, the first slice priority desired by the user device, to a base station or an access management device; the base station or the access management device transmitting the first slice priority if the available capacity of radio resources is greater than or equal to a threshold when the second slice priority transmitted by the base station or the access management device differs from the first slice priority; and the user device performing slice-specific cell reselection using the first slice priority in response to receiving the first slice priority.

[0125] (5) The slice-specific cell reselection method of (4) above may further include a step in which the step of transmitting the first slice priority includes, instead of transmitting the first slice priority, transmitting a message indicating that the base station or the access management device may prioritize the first slice priority over the second slice priority. [Explanation of symbols]

[0126] 1: Mobile communication system 20 :CN 100:UE 110: Receiving unit 120: Transmitter 130: Control unit 200 :gNB 210: Transmission unit 220: Receiving unit 230: Control unit 300:AMF

Claims

1. A slice-specific cell reselection method in a mobile communication system, comprising: A user equipment receives, from a base station or an access management device, a slice priority indicating a priority for each network slice; When the available capacity of radio resources is equal to or greater than a threshold, the base station transmits a slice priority ignorance permission message indicating that ignoring of the slice priority is permitted; In response to receiving the slice priority ignore permission message, the user equipment performs slice-specific cell reselection using a network slice desired by the user equipment without using the slice priority. Slice-specific cell reselection method.

2. Furthermore, when the available capacity of the radio resources becomes less than a threshold after transmitting the slice priority ignore permission message, the base station transmits a slice priority ignore cancel message indicating that permission to ignore the slice priority is canceled; and performing slice-specific cell reselection using the slice priority in response to receiving the slice priority ignore cancellation message by the user equipment. The slice-specific cell reselection method of claim 1 .

3. The performing includes, when the user equipment does not receive the slice priority from the base station or the access management device, performing slice-specific cell reselection using the network slice desired by the user equipment. The slice-specific cell reselection method of claim 1 .

4. A slice-specific cell reselection method in a mobile communication system, comprising: A user device transmits a first slice priority indicating a priority for each network slice, the first slice priority being desired by the user device, to a base station or an access management device; When the second slice priority transmitted by the base station or the access management device is different from the first slice priority, if the available capacity of radio resources is equal to or greater than a threshold, the base station or the access management device transmits the first slice priority; and performing slice-specific cell reselection using the first slice priority, in response to receiving the first slice priority, by the user equipment. Slice-specific cell reselection method.

5. Transmitting the first slice priority includes, instead of transmitting the first slice priority, transmitting a message indicating that the base station or the access management device may prioritize the first slice priority over the second slice priority. The slice-specific cell reselection method of claim 4.

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