Cell reselection method, user equipment, chipset, program, and mobile communication system

Abstract

A cell reselection method according to a first aspect of the present invention is performed by a user device in a mobile communication system. The cell reselection method involves: receiving slice frequency information from a network, the slice frequency information indicating a plurality of frequencies and a network slice group supported by each of the plurality of frequencies; and, when a predetermined frequency that does not support a predetermined network slice group announced from an NAS layer of the user device is present in the slice frequency information, performing control that makes it more difficult to select a cell belonging to the predetermined frequency than a cell belonging to a frequency supporting the predetermined network slice group.

Description

Technical Field

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

Background Art

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

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

[0004] The cell reselection method according to the first aspect is a cell reselection method executed by a user equipment in a mobile communication system. The cell reselection method includes receiving, from a network, slice frequency information indicating a plurality of frequencies and a network slice group supported by each of the plurality of frequencies, and when a predetermined frequency that does not support a predetermined network slice group notified from the NAS layer of the user equipment exists in the slice frequency information, performing control to make it less likely to select a cell belonging to the predetermined frequency as a serving cell compared to a cell belonging to a frequency that supports the predetermined network slice group.

[0005] The user equipment according to the second aspect is a user equipment in a mobile communication system. The user equipment includes a processor. The processor performs a process of receiving, from a network, slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies, and a process of, when a predetermined frequency that does not support a predetermined network slice group notified from the NAS layer of the user equipment exists in the slice frequency information, performing control to make it less likely to select a cell belonging to the predetermined frequency as a serving cell than a cell belonging to a frequency that supports the predetermined network slice group.

[0006] The cell reselection method according to the third aspect is a method executed by a user equipment in a mobile communication system. The cell reselection method includes a step of receiving, from a network, slice frequency information indicating a correspondence relationship between a network slice, a frequency, and a frequency priority, a step of assigning the frequency priority indicated by the slice frequency information to a corresponding frequency for a selected network slice selected by the user equipment, and a step of reselecting a candidate cell that satisfies a predetermined quality criterion within a selected frequency selected by the user equipment according to the assigned frequency priority. The reselection step includes a step of reselecting a second candidate cell that is different from the first candidate cell and provides the selected network slice when the first candidate cell with the highest radio quality does not provide the selected network slice.

[0007] The cell reselection method according to the fourth aspect is a method executed by a user equipment in a mobile communication system. The cell reselection method includes the steps of receiving, from a network, slice frequency information indicating a correspondence relationship between a network slice, a frequency, and a frequency priority; for a selected network slice selected by the user equipment, allocating the frequency priority indicated by the slice frequency information to a corresponding frequency; determining, within a selected frequency selected by the user equipment according to the allocated frequency priority, whether a candidate cell satisfying a predetermined quality criterion provides the selected network slice; and when there is no cell providing the selected network slice at the selected frequency, performing cell reselection processing using only the selected frequency or the candidate cell as a reselection candidate.

[0008] The cell reselection method according to the fifth aspect is a method executed by a user equipment in a mobile communication system. The cell reselection method includes the steps of receiving, from a serving cell, a message indicating whether the serving cell provides adjacent cell information indicating a correspondence relationship between an adjacent cell and a network slice provided by the adjacent cell; determining, based on the message, whether the serving cell provides the adjacent cell information; and receiving, from the serving cell, the adjacent cell information in response to determining that the serving cell provides the adjacent cell information.

Brief Description of the Drawings

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BEST MODE FOR CARRYING OUT THE INVENTION

[0010] A user equipment in the radio resource control (RRC) idle state or RRC inactive state executes a cell reselection procedure. In 3GPP, slice-specific cell reselection, which is a cell reselection procedure dependent on a network slice, is under consideration.

[0011] In such slice-specific cell reselection, it is assumed that the user equipment preferentially reselects (i.e., camps on) a cell belonging to a frequency with a higher frequency priority associated with, for example, an intended slice that the user equipment desires to use. However, the specific method of slice-specific cell reselection is undetermined.

[0012] The present disclosure relates to a cell reselection method and a user equipment that smooth slice-specific cell reselection.

[0013] 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.

[0014] [First Embodiment]

[0015] (Configuration of Mobile Communication System) FIG. 1 is a diagram showing the configuration of a mobile communication system according to the first embodiment. The mobile communication system 1 complies with the 5th generation system (5GS) of the 3GPP standard. In the following, the 5GS will be described as an example, but the LTE (Long Term Evolution) system may be at least partially applied to the mobile communication system, or the 6th generation (6G) system may be at least partially applied.

[0016] The mobile communication system 1 includes a user equipment (UE), a 5G radio access network (NG-RAN) 10, and a 5G core network (5GC) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. Also, the 5GC 20 may be simply referred to as the core network (CN) 20.

[0017] The UE 100 is a movable wireless communication device. The UE 100 may be any device as long as it is a device used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in the sensor, a vehicle or a device provided in the vehicle (Vehicle UE), an aircraft or a device provided in the aircraft (Aerial UE).

[0018] The NG-RAN 10 includes base stations (referred to as "gNB" in the 5G system) 200. The gNBs 200 are interconnected via an Xn interface which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with the UE 100 that has established a connection with its own cell. The gNB 200 has functions such as a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), and a measurement control function for mobility control and scheduling. "Cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0019] 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.

[0020] The 5GC 20 includes an AMF (Access and Mobility Management Function) and a UPF (User Plane Function) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF performs data transfer control. The AMF and the UPF are connected to the gNB 200 via the NG interface, which is an interface between the base station and the core network.

[0021] FIG. 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.

[0022] 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 radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130.

[0023] 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 radio signal and transmits it from the antenna.

[0024] The control unit 130 performs various controls and processes in the UE 100. Such processes include the processes of 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 the processing 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, etc. The CPU executes programs stored in the memory to perform various processes.

[0025] FIG. 3 is a diagram showing the configuration of the gNB 200 (base station) according to the first embodiment. The gNB 200 includes a transmission unit 210, a reception unit 220, a control unit 230, and a backhaul communication unit 240. The transmission unit 210 and the reception unit 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 communicates with the CN 20.

[0026] 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 the baseband signal (transmission signal) output by the control unit 230 into a wireless signal and transmits it from the antenna.

[0027] The reception unit 220 performs various receptions under the control of the control unit 230. The reception unit 220 includes an antenna and a receiver. The receiver converts the wireless signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0028] The control unit 230 performs various controls and processes in the gNB 200. Such processes include the processes of each layer described below. 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 the processor's processing. 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.

[0029] The backhaul communication unit 240 is connected to an adjacent base station via the Xn interface which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via the NG interface which is an interface between the base station and the core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally split), and the two units may be connected by the F1 interface which is a fronthaul interface.

[0030] Figure 4 is a diagram showing the configuration of the protocol stack of the radio interface of the user plane that handles data.

[0031] The radio interface protocol of the user plane has 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.

[0032] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the PHY layer of UE100 and the PHY layer of gNB200, data and control information are transmitted via physical channels. Note that the PHY layer of UE100 receives downlink control information (DCI) transmitted on the physical downlink control channel (PDCCH) from gNB200. Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and obtains the successfully decoded DCI as the DCI destined for itself. The DCI transmitted from gNB200 has CRC parity bits scrambled by the RNTI added thereto.

[0033] The MAC layer performs priority control of data, retransmission processing by hybrid automatic repeat request (HARQ), and random access procedures, etc. Between the MAC layer of UE100 and the MAC layer of gNB200, data and control information are transmitted via transport channels. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport formats (transport block size, modulation and coding scheme (MCS)) and the resource blocks allocated to UE100.

[0034] The RLC layer transmits data to the RLC layer on the receiving side by utilizing the functions of the MAC layer and the PHY layer. Between the RLC layer of UE100 and the RLC layer of gNB200, data and control information are transmitted via logical channels.

[0035] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0036] The SDAP layer performs mapping between an IP flow, which is a unit for the core network to perform QoS control, and a radio bearer, which is a unit for the access stratum (AS) to perform QoS control. Note that when the RAN is connected to the EPC, the SDAP may not be necessary.

[0037] 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).

[0038] The protocol stack of the radio interface of the control plane has an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) instead of the SDAP layer shown in FIG. 4.

[0039] Between the RRC layer of UE100 and the RRC layer of gNB200, RRC signaling for various settings is transmitted. The RRC layer controls logical channels, transport channels, and physical channels in response 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 the RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in the RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in the RRC inactive state.

[0040] The NAS located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of UE100 and the NAS of AMF300A. Note that UE100 has an application layer, etc. in addition to the protocol of the radio interface. Also, the layer below the NAS is called the AS (Access Stratum).

[0041] (Overview of the cell reselection procedure) FIG. 6 is a diagram for explaining the overview of the cell reselection procedure.

[0042] UE100 in the RRC idle state or RRC inactive state performs a cell reselection procedure to move from the current serving cell (Cell #1) to an adjacent cell (any one of Cells #2 to #4) as it moves. Specifically, UE100 identifies an adjacent cell to camp on through the cell reselection procedure and reselects the identified adjacent cell. When the frequencies (carrier frequencies) are the same between the current serving cell and the adjacent cell, it is called intra-frequency, and when the frequencies (carrier frequencies) are different between the current serving cell and the adjacent cell, it is called inter-frequency. The current serving cell and the adjacent cells may be managed by the same gNB200 or may be managed by different gNB200s from each other.

[0043] Figure 7 is a diagram showing a schematic flow of a general cell reselection procedure.

[0044] In step S10, UE100 performs frequency prioritization processing based on the priority (also called "absolute priority") for each frequency specified by gNB200, for example, by a system information block or an RRC release message. Specifically, UE100 manages the frequency priorities specified by gNB200 for each frequency.

[0045] In step S20, UE100 performs measurement processing to measure the radio quality for each of the serving cell and the adjacent cells. UE100 measures the received power and received quality of the reference signals transmitted by each of the serving cell and the adjacent cells, specifically, CD-SSB (Cell Defining-Synchronization Signal and PBCH block). For example, UE100 always measures the radio quality for frequencies having a priority higher than the priority of the frequency of the current serving cell, and for frequencies having a priority equal to or lower than the priority of the frequency of the current serving cell, when the radio quality of the current serving cell falls below a predetermined quality, it measures the radio quality of the frequencies having an equal or lower priority.

[0046] In step S30, the UE 100 performs a cell reselection process of reselecting the cell on which it camps based on the measurement results in step S20. For example, when the priority of the frequency of an adjacent cell is higher than the priority of the current serving cell and the adjacent cell satisfies a predetermined quality criterion (i.e., the minimum required quality criterion) over a predetermined period, the UE 100 may perform cell reselection to the adjacent cell. When the priority of the frequency of an adjacent cell is the same as the priority of the current serving cell, the UE 100 ranks the radio quality of the adjacent cell and may perform cell reselection to an adjacent cell having a rank higher than the rank of the current serving cell over a predetermined period. When the priority of the frequency of an adjacent 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 adjacent cell is higher than another threshold continuously over a predetermined period, the UE 100 may perform cell reselection to the adjacent cell.

[0047] (Overview of Network Slicing) Network slicing is a technology for creating a plurality of virtual networks by virtually dividing a physical network (e.g., a network composed of NG-RAN 10 and 5GC 20) constructed by an operator. Each virtual network is called a network slice. Hereinafter, a network slice may be simply referred to as a "slice".

[0048] By means of network slicing, a communication operator can create slices according to service requirements of different service types such as eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable and Low Latency Communications), mMTC (massive Machine Type Communications), etc., and can optimize network resources.

[0049] FIG. 8 is a diagram showing an example of network slicing.

[0050] On the network 50 composed of NG-RAN 10 and 5GC 20, three slices (Slice #1 to Slice #3) are configured. Slice #1 is associated with the service type of eMBB, Slice #2 is associated with the service type of URLLC, and Slice #3 is associated with the service type of mMTC. Note that more than three slices may be configured on the network 50. One service type may be associated with a plurality of slices.

[0051] Each slice is provided with a slice identifier for identifying the slice. As an example of the slice identifier, S-NSSAI (Single Network Slicing Selection Assistance Information) can be mentioned. 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 with which the slice is associated. SD is information for differentiating a plurality of slices associated with the same service type. Information including a plurality of S-NSSAI is called NSSAI (Network Slice Selection Assistance Information).

[0052] In addition, one or more slices may be grouped to form a slice group. Also, 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 (for example, AMF 300), or may be configured by a radio access network (for example, gNB 200). The configured slice group may be notified to the UE 100.

[0053] Hereinafter, the term "network slice (slice)" may mean an S-NSSAI which is an identifier of a single slice or an NSSA which is a collection of S-NSSAIs, or may mean a slice group which is a group of one or more S-NSSAIs or NSAIs.

[0054] Also, the UE 100 determines a desired network slice that it desires to use. Such a desired slice may be referred to as an Intended slice. In the first embodiment, the UE 100 determines a slice priority for each network slice (desired network slice). For example, the NAS of the UE 100 determines the slice priority based on the operating status of applications in the UE 100 and / or user operations / settings, etc., and notifies the determined slice priority to the AS.

[0055] (Outline of slice-specific cell reselection procedure) FIG. 9 is a diagram showing an outline of the slice-specific cell reselection procedure.

[0056] In the slice-specific cell reselection procedure, the UE 100 performs cell reselection processing based on the slice frequency information provided from the network 50. The slice frequency information may be provided to the UE 100 by the gNB 200 via broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message).

[0057] The slice frequency information is information indicating the correspondence relationship between the network slice, the frequency, and the frequency priority. For example, the slice frequency information indicates, for each slice (or slice group), 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.

[0058] In the example shown in FIG. 10, for slice #1, three frequencies, i.e., frequencies F1, F2, and F4, are associated as the frequencies supporting slice #1. Among these three frequencies, the frequency priority of F1 is "6", the frequency priority of F2 is "4", and the frequency priority of F4 is "2". In the example of FIG. 10, it is assumed that the larger the number of the frequency priority, the higher the priority, but it may also be assumed that the smaller the number, the higher the priority.

[0059] Also, for slice #2, three frequencies, i.e., frequencies F1, F2, and F3, are associated as the frequencies supporting slice #2. Among these three frequencies, the frequency priority of F1 is "0", the frequency priority of F2 is "5", and the frequency priority of F3 is "7".

[0060] Also, for slice #3, three frequencies, i.e., frequencies F1, F3, and F4, are associated as the frequencies supporting slice #3. Among these three frequencies, the frequency priority of F1 is "3", the frequency priority of F3 is "7", and the frequency priority of F4 is "2".

[0061] In the following, in order to distinguish from the absolute priority in the conventional cell reselection procedure, the frequency priority shown in the slice frequency information may be referred to as "slice-specific frequency priority".

[0062] UE100 may perform cell reselection processing based on the cell information provided by network 50. The cell information may be information indicating the correspondence between cells (e.g., a serving cell and each neighboring cell) and network slices that the cell does not provide or provides. For example, there may be a case where a certain cell temporarily does not provide some or all network slices due to congestion or the like. That is, even for a slice support frequency having the ability to provide a certain network slice, some cells within the frequency may not provide the network slice. UE100 can grasp the network slices that each cell does not provide based on the cell information. Such cell information may be provided to UE100 by gNB200 through broadcast signaling (e.g., system information block) or dedicated signaling (e.g., RRC release message).

[0063] Figure 11 is a diagram showing the basic flow of a slice-specific cell reselection procedure. Before starting the slice-specific cell reselection procedure, it is assumed that UE100 is in the RRC idle state or the RRC inactive state and has received and held the above-described slice frequency information.

[0064] In step S0, the NAS of UE100 determines the slice identifier of the desired slice of UE100 and the slice priority of each desired slice, and notifies the AS of UE100 of the slice information including the determined slice priority. The "desired slice" includes a slice with potential use, a candidate slice, a desired slice, a slice to communicate with, 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". It is assumed that the larger the number of the slice priority, the higher the priority, but it may also be that the smaller the number, the higher the priority.

[0065] In step S1, the AS of UE100 rearranges the slices (slice identifiers) notified from the NAS in step S0 in descending order of slice priority. The list of slices arranged in this way is called the "slice list".

[0066] In step S2, the AS of UE100 selects one network slice in descending order of slice priority. The network slice selected in this way is called the "selected network slice".

[0067] In step S3, the AS of UE100 assigns frequency priorities to each frequency associated with the selected network slice for the selected network slice. Specifically, the AS of UE100 identifies the frequencies associated with the slice based on the 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 a frequency priority of "6" to frequency F1, a frequency priority of "4" to frequency F2, and a frequency priority of "2" to frequency F4 based on the slice frequency information (e.g., the information in FIG. 10). The AS of UE100 calls the list of frequencies arranged in descending order of frequency priority the "frequency list".

[0068] In step S4, the AS of UE100 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 way is called the "selected frequency". The AS of UE100 may rank each cell measured within the selected frequency in descending order of radio quality. A cell that satisfies a predetermined quality criterion (i.e., the minimum required quality criterion) among the cells measured within the selected frequency is called a "candidate cell".

[0069] In step S5, the AS of UE100 identifies the cell with the highest rank based on the result of the measurement process in step S4, and determines whether the cell provides the selected network slice based on the cell information. If it is determined that the cell with the highest rank provides the selected network slice (step S5: YES), in step S5a, the AS of UE100 reselects the cell with the highest rank and camps on the cell.

[0070] On the other hand, if it is determined that the cell with the highest rank does not provide the selected network slice (step S5: NO), in step S6, the AS of UE100 determines whether there is an unmeasured frequency in the frequency list created in step S3. If it is determined that there is an unmeasured frequency (step S6: YES), the AS of UE100 resumes the process targeting the frequency with the highest frequency priority and performs the measurement process using the frequency as the selected frequency (returns the process to step S4).

[0071] If it is determined that there is no unmeasured frequency in the frequency list created in step S3 (step S6: NO), in step S7, the AS of UE100 may determine whether there is an unselected slice in the slice list created in step S1. If it is determined that there is an unselected slice (step S7: YES), the AS of UE100 resumes the process targeting the network slice with the highest slice priority and selects the network slice as the selected network slice (returns the process to step S2). Note that in the basic flow shown in FIG. 11, the process of step S7 may be omitted.

[0072] When it is determined that there is no unselected slice (step S7: NO), in step S8, the AS of UE100 performs conventional cell reselection processing. The conventional cell reselection processing may mean the entire general cell reselection procedure shown in FIG. 7, or may mean only the cell reselection processing (step S30) shown in FIG. 7. In the latter case, UE100 may reuse the measurement results in step S4 without measuring the radio quality of the cell again.

[0073] (Slice-specific cell reselection procedure according to the first embodiment) In the basic flow of the above slice-specific cell reselection procedure, the AS of UE100 selects a slice in step S2 and assigns a frequency priority to each frequency that supports the slice in step S3.

[0074] Here, it is considered that the set value of the frequency priority (slice-specific frequency priority) is not provided in the slice frequency information for frequencies that do not support the slice. Since such frequencies have no frequency priority, they are considered to be frequencies outside the reselection candidates in the slice-specific cell reselection procedure. Therefore, in the slice-specific cell reselection procedure according to the first embodiment, frequencies for which the slice-specific frequency priority is not set are excluded from the reselection candidates.

[0075] In the first embodiment, UE100 receives slice frequency information indicating the correspondence between network slices, frequencies, and frequency priorities from network 50. For the selected network slice, when there are frequencies without frequency priority in the slice frequency information, UE100 excludes the frequencies without frequency priority from the candidate frequencies for cell reselection. Then, UE100 reselects candidate cells that meet a predetermined quality criterion within the selected frequencies selected from the candidate frequencies according to the frequency priority. This can smooth the slice-specific cell reselection procedure.

[0076] FIG. 12 is a diagram showing the flow of the slice-specific cell reselection procedure according to the first embodiment. Here, the differences from the basic flow of FIG. 11 will be described.

[0077] In step S100, the UE 100 excludes, from the candidates (specifically, the measurement targets) for slice-specific cell reselection, the frequencies for which the frequency priorities are not set in the selected network slice selected in step S2.

[0078] [Second Embodiment] The differences between the slice-specific cell reselection procedure according to the second embodiment and the first embodiment will be mainly described.

[0079] Before the UE 100 executes the slice-specific cell reselection procedure, for example, before the intended slice is notified from the NAS, it is considered that the UE 100 is executing a general cell reselection procedure (see FIG. 7). Also, it is conceivable that the intended slice changes during the execution of the slice-specific cell reselection procedure. Furthermore, it is conceivable that the selected slice moves from the slice with the highest slice priority to the slice with the second highest slice priority during the execution of the slice-specific cell reselection procedure (see steps S2 and S7 described above).

[0080] In these situations, since the frequency priorities of each frequency change, the AS of the UE 100 needs to execute the replacement (update) of the frequency priorities. Here, the handling of the frequency priorities that have already been applied becomes a problem. In particular, it is necessary to clarify how to process when there are already applied frequency priorities (absolute priority or slice-specific frequency priority) and there is no setting of the frequency priority (slice-specific frequency priority) in the new intended slice.

[0081] In the second embodiment, the UE 100 receives slice frequency information indicating the correspondence relationship between network slices, frequencies, and frequency priorities from the network 50. For the selected network slice selected by the UE 100, after removing the already set frequency priorities for each frequency, the UE 100 assigns the frequency priorities indicated by the slice frequency information to the corresponding frequencies. That is, before applying the slice-specific frequency priorities for the selected network slice, the UE 100 clears the already applied frequency priorities. Then, the UE 100 reselects candidate cells that meet a predetermined quality criterion within the selected frequencies according to the assigned frequency priorities.

[0082] In this way, in the second embodiment, the UE 100 clears the already applied frequency priorities, initializes to a state where no frequency priority is applied to any frequency, and then executes slice-specific cell reselection.

[0083] FIG. 13 is a diagram showing the flow of the slice-specific cell reselection procedure according to the second embodiment. Here, the differences from the basic flow of FIG. 11 will be described.

[0084] In step S200, before step S3, the UE 100 clears (removes) all the already applied frequency priorities for the selected network slice. For example, if there are already applied frequency priorities for the selected network slice, the UE 100 removes the already applied frequency priorities for the selected network slice.

[0085] Note that the frequency priorities cleared in step S200 may be the frequency priorities provided by broadcast signaling (e.g., SIB). Alternatively, when the frequency priorities are set by dedicated signaling (e.g., RRC Release message), after the UE 100 RRC Inactive State or RRC Idle State transitions, for a predetermined time (e.g., In the 3GPP standardDuring the period when the timer T320 is operating, the frequency priority may be prioritized (i.e., continuously applied), and the process of step S200 may be applied after T320 expires.

[0086] [Third Embodiment] Regarding the slice-specific cell reselection procedure according to the third embodiment, the differences from the first and second embodiments will be mainly described.

[0087] As described above, when the highest-rank cell does not provide the selected network slice in step S5, the UE100 does not reselect the cell. For example, it is considered that the gNB200 may temporarily not be able to support a specific slice depending on its own resource usage situation, etc.

[0088] In the example shown in FIG. 10, assuming that slice #1 is the selected network slice, the UE100 measures the frequency F1 in step S4. However, if the highest-rank cell of frequency F1 does not (temporarily) provide the selected network slice, it may be preferable for the UE100 to reselect another candidate cell (i.e., a cell of the second or lower rank) of the same frequency F1.

[0089] However, if the UE100 reselects a cell of the second or lower rank, for example, it may affect the interference to the highest-rank cell.

[0090] In a general cell reselection procedure, that is, a cell reselection procedure that does not depend on network slices, when the highest-rank cell is access-restricted, the network 50 (gNB200) specifies to the UE100 whether the UE100 may reselect another cell of the same frequency. Specifically, the gNB200 notifies the UE100 in the Intra Frequency Reselection Indicator (IFRI) in the Master Information Block (MIB) whether it is possible to reselect another cell of the same frequency.

[0091] On the other hand, it is considered preferable to apply control different from the general cell reselection procedure to slice-specific cell reselection. For example, due to reasons such as few UEs 100 supporting network slices, there may be little interference caused by reselection to another cell within the same frequency.

[0092] Therefore, in the third embodiment, a mechanism is introduced that allows reselection of cells other than the highest-ranked cell within the same frequency in the slice-specific cell reselection procedure.

[0093] In the third embodiment, the UE 100 that receives slice frequency information indicating the correspondence relationship between the network slice, frequency, and frequency priority from the network 50 assigns the frequency priority indicated by the slice frequency information to the corresponding frequency for the selected network slice, and reselects a candidate cell that satisfies a predetermined quality criterion within the selected frequency according to the assigned frequency priority. Here, when the first candidate cell (i.e., the highest-ranked cell) with the highest radio quality does not provide the selected network slice, the UE 100 reselects a second candidate cell (i.e., a cell ranked second or lower) that is different from the first candidate cell and provides the selected network slice.

[0094] Specifically, the UE 100 reselects the second candidate cell within the same frequency as the frequency to which the first candidate cell belongs. The UE 100 may receive control information from the network 50 (e.g., gNB 200) for controlling whether to permit reselection of the second candidate cell within the same frequency. The control information may be information dedicated to the slice-specific cell reselection procedure, which is a network slice-dependent cell reselection procedure. Thereby, the network 50 can specify whether to permit reselection of cells other than the highest-ranked cell within the same frequency in the slice-specific cell reselection procedure.

[0095] FIG. 14 is a diagram for explaining the control information according to the third embodiment.

[0096] In step S310, the network 50 (gNB200) transmits to the UE100 an IFRI (hereinafter, "slice IFRI") which is control information applied only to the slice-specific cell reselection procedure. The network 50 (gNB200) may notify the UE100 of the slice IFRI by broadcast signaling (e.g., SIB) or dedicated signaling (e.g., RRC Release message), or may notify the UE100 by MIB. When notified by MIB, the slice IFRI may be stored in a field different from the conventional IFRI (hereinafter, "non-slice IFRI").

[0097] The network 50 (gNB200) may transmit the slice IFRI in association with a slice identifier. For example, the network 50 (gNB200) may notify and set the UE100 such that slice #1 is "not allowed" and slice #2 is "allowed". Alternatively, the slice IFRI may be applied to all slices (i.e., collectively "allowed / not allowed").

[0098] The UE100 receives the slice IFRI and executes the slice-specific cell reselection procedure based on the slice IFRI. When the slice IFRI is notified ("allowed"), the UE100 may ignore the non-slice IFRI in the slice-specific cell reselection procedure. On the other hand, when the slice IFRI is not notified, the UE100 may also perform selection of other cells within the same frequency according to the non-slice IFRI in the slice-specific cell reselection procedure.

[0099] FIG. 15 is a diagram showing the flow of the slice-specific cell reselection procedure according to the third embodiment. Here, the differences from the basic flow of FIG. 11 will be described.

[0100] In step S5, assume that UE100 determines that the selected network slice selected in step S2 is not provided by the highest-ranked cell (first candidate cell) (step S5: NO).

[0101] In step S300, UE100 checks whether slice IFRI permits cell reselection of the second candidate cells within the same frequency for the selected network slice selected in step S2. If permitted (“allowed”), UE100 determines whether the second candidate cells within the same frequency as the first candidate cell provide the selected network slice. Here, UE100 makes the determination in the order of the second-ranked candidate cells, the third-ranked candidate cells, and so on. If it is determined that the second candidate cell provides the selected network slice, UE100 reselects and camps on the second candidate cell (step S5a).

[0102] On the other hand, if slice IFRI does not permit cell reselection of the second candidate cells within the same frequency (“not allowed”), or if all the second candidate cells do not provide the selected network slice in step S300 and / or all the second candidate cells do not meet the required minimum quality criteria in step S300, UE100 executes steps S6 and later.

[0103] [First Modification Example of the Third Embodiment] In the above-described third embodiment, when reselecting candidate cells of the second rank or lower (i.e., the second candidate cells), problems such as interference become prominent if reselection of cells with an arbitrarily low rank is permitted. Therefore, in this modification example, certain restrictions are imposed when reselecting candidate cells of the second rank or lower.

[0104] In this modification example, when reselecting the second candidate cell, UE100 may reselect the second candidate cell from among the candidate cells up to a predetermined number from the first candidate cell in descending order of the radio quality measured in step S4. The setting information indicating the predetermined number (i.e., the rank order limit value) may be set from network 50 to UE100.

[0105] In this modification example, UE 100 may camp on the second candidate cell until a predetermined time elapses after reselecting the second candidate cell. The setting information indicating the predetermined time (i.e., the time limit value) may be set from network 50 to UE 100.

[0106] FIG. 16 is a diagram for explaining the setting information according to this modification example.

[0107] In step S360, network 50 (e.g., gNB 200) transmits the setting information regarding the reselection of the next cell (the second and subsequent ranked cells) on the same frequency to UE 100. Network 50 (e.g., gNB 200) may transmit the setting information to UE 100 in the same message as slice IFRI, or may transmit the setting information to UE 100 in a message different from slice IFRI. Alternatively, the setting information may be a fixed value defined in the technical specification.

[0108] The setting information may include a rank order limit value. The rank order limit value may be, for example, the content of permitting up to the second-ranked cell on the same frequency. The setting information may include a time limit value. The time limit value may be, for example, the content of permitting camping on the next cell on the same frequency within 1 minute.

[0109] UE 100 receives the setting information and executes a slice-specific cell reselection procedure based on the setting information.

[0110] Here, the operation according to this modification example will be described with specific examples. As shown in FIG. 15, the UE 100 performs measurement processing in step S4. Assume that the measurement results shown in FIG. 17 are obtained as a result of this measurement. Specifically, assume that slice #1 with a slice priority of "6" is the selected network slice, and cells A to C are detected at frequency F1 with a frequency priority of "7". Cell A is the highest ranked cell and is a candidate cell that meets the minimum required quality criteria (suitable). Cell B is the second ranked cell and is a candidate cell that meets the minimum required quality criteria (suitable). Cell C is a cell that does not meet the minimum required quality criteria (not suitable). nd ranked) cell and is a candidate cell that meets the minimum required quality criteria (suitable). Cell C is a cell that does not meet the minimum required quality criteria (not suitable).

[0111] In such a case, if the highest ranked cell (cell A) does not provide the selected network slice in step S5, the UE 100 attempts to reselect to the next candidate cell (cell B) within the same frequency. Here, when selecting the next candidate cell, it follows the setting information.

[0112] The UE 100 may be allowed to reselect candidate cells within the same frequency up to the second ranked cell, for example, according to the rank order limit.

[0113] The UE 100 may be allowed, for example, to reselect candidate cells within the same frequency (the time to camp on and stay in the cell) only within 1 minute according to the time limit. In this case, when the UE 100 reselects the next cell, it starts a timer, and when the timer expires, it executes the slice-specific cell reselection procedure again.

[0114] [Second Modification Example of the Third Embodiment] In this modification example, if the first candidate cell (i.e., the highest ranked cell) does not provide the selected network slice at each of the multiple selected frequencies selected according to the frequency priority, the UE 100 reselects the second candidate cell (i.e., the cell ranked second or lower).

[0115] FIG. 18 is a diagram showing the flow of the slice-specific cell reselection procedure according to this modification example. Here, the differences from the basic flow of FIG. 11 will be described.

[0116] If the answer in step S6 is "NO", in step S350, UE 100 checks whether slice IFRI permits cell reselection to the second candidate cell within the same frequency for the selected network slice selected in step S2. If it is permitted ("allowed"), UE 100 determines whether the second candidate cell provides the selected network slice in descending order of frequency priority. If it is determined that the second candidate cell provides the selected network slice, the second candidate cell is reselected and camped on (step S5a).

[0117] The operation according to this modification example will be described with a specific example. As shown in FIG. 19, it is assumed that the processing for frequencies F1 and F3 has been completed when the answer in step S6 is "NO". Here, it is assumed that the highest-rank cells (i.e., cell A and cell C) of each selected frequency (frequencies F1 and F3) of the selected network slice have not been selected (not camped on). In this case, UE 100 attempts to camp on the second-rank cell (cell B) of frequency F1 with the highest frequency priority. If the cell cannot be selected (camped on), UE 100 attempts to camp on the second-rank cell (cell D) of frequency F3 with the second frequency priority.

[0118] [Fourth Embodiment] The slice-specific cell reselection procedure according to the fourth embodiment will be mainly described in terms of the differences from the first to third embodiments.

[0119] In the basic flow of the above slice-specific cell reselection procedure, if none of the candidate cells within all the selected frequencies for the selected network slice provide the selected network slice, the UE 100 performs conventional cell reselection in step S8. However, if these candidate cells temporarily do not provide the selected network slice, there is a possibility that they may provide the selected network slice at the time or after the time when conventional cell reselection is performed in step S8. Therefore, in the fourth embodiment, the UE 100 preferentially reselects the frequencies and / or candidate cells determined not to provide the selected network slice in step S8.

[0120] In the fourth embodiment, the UE 100 that receives slice frequency information indicating the correspondence relationship between the network slice, the frequency, and the frequency priority from the network 50 assigns the frequency priority indicated by the slice frequency information to the corresponding frequency for the selected network slice (step S3), and determines whether a candidate cell that satisfies a predetermined quality criterion within the selected frequencies selected according to the frequency priority provides the selected network slice (step S5). If there is no cell that provides the selected network slice at the selected frequency, the UE 100 performs cell reselection processing using only the selected frequency or the candidate cell as a reselection candidate.

[0121] FIG. 20 is a diagram showing the flow of the slice-specific cell reselection procedure according to the fourth embodiment. Here, the differences from the basic flow of FIG. 11 will be described.

[0122] If the result in step S5 is "NO", that is, if the first candidate cell within the selected frequency does not provide the selected network slice, in step S410, the UE 100 records the selected frequency and / or the first candidate cell.

[0123] For example, in step S410, if the highest-ranked cell (or all cells) at a certain frequency does not provide the selected network slice, the UE 100 puts the identifier of that frequency into the first list. The first list will have frequencies that the UE 100 tried to reselect but that did not (temporarily) provide the selected network slice added to it. Alternatively, if the highest-ranked cell (or all cells) at a certain frequency does not provide the selected network slice, the UE 100 puts the identifier of that cell into the second list. The second list will have candidate cells that the UE 100 tried to reselect but that did not (temporarily) provide the selected network slice added to it.

[0124] After that, in step S420, the UE 100 performs cell reselection processing based on step S410. For example, in step S420, the UE 100 may perform cell reselection processing by increasing the priority of the frequencies recorded in the first list. For example, a positive offset may be added to the frequency priority (absolute priority) of the frequency, or the frequency priority of the frequency may be set as the highest priority. In step S420, the UE 100 may perform cell reselection processing only on the cells recorded in the second list. Here, the UE 100 may attempt cell reselection in descending order of the frequency priority (slice-specific frequency priority) associated with the cell.

[0125] [Fifth Embodiment] In the above-described embodiment, an example of the UE 100 grasping the network slices provided or not provided by each cell based on the cell information provided from the network 50 has been described.

[0126] In the fifth embodiment, the serving cell (gNB200) may broadcast to the UE100 adjacent cell information indicating the correspondence between an adjacent cell and a network slice provided by the adjacent cell. For example, the serving cell (gNB200) broadcasts a system information block (SIB) including the adjacent cell information. Such an SIB may be other SI (OSI: Other SI) different from the minimum system information (Minimum SI) that each cell always broadcasts. Hereinafter, the OSI including such adjacent cell information is referred to as SIBx.

[0127] The adjacent cell information may include, for each adjacent cell, a set of the cell identifier of the adjacent cell and the identifier of the network slice provided by the adjacent cell. Alternatively, the adjacent cell information may include, for each adjacent cell, a set of the cell identifier of the adjacent cell and the identifier of the network slice not provided by the adjacent cell.

[0128] Here, when the adjacent cell information is an optional information element, the serving cell (gNB200) does not necessarily provide the adjacent cell information to the UE100. Even when the serving cell (gNB200) does not provide the adjacent cell information, the UE100 that does not know that the adjacent cell information is not provided may receive and analyze the SIBx to obtain the adjacent cell information. As a result, a wasteful operation occurs, which is not preferable from the viewpoints of power consumption and processing load of the UE100.

[0129] Therefore, in the fifth embodiment, the serving cell (gNB200) transmits to the UE100 a message indicating whether or not the serving cell (the serving cell) provides adjacent cell information indicating the correspondence between an adjacent cell and a network slice provided by the adjacent cell. Thereby, based on the message, the UE100 can grasp whether or not the serving cell provides the adjacent cell information, so that the above-described wasteful operation can be avoided.

[0130] The message may be a message that constitutes Minimum SI, i.e., System Information Block Type 1 (SIB1) or Master Information Block (MIB). For example, the serving cell (gNB200) may provide the UE100 with a flag (1-bit information) indicating whether to provide adjacent cell information in SIB1 or MIB. When providing adjacent cell information, the flag information may have "1" set, and when not providing adjacent cell information, "0" may be set.

[0131] Alternatively, the message may be an RRC Release message. For example, when transitioning the UE100 from the RRC connected state to the RRC idle state or the RRC inactive state, the serving cell (gNB200) may send the UE100 an RRC Release message including a flag (1-bit information) indicating whether to provide adjacent cell information.

[0132] Alternatively, the message may be a Non-Access Stratum (NAS) message. For example, the serving cell (gNB200) may send the UE100 a NAS message provided by the AMF, and the NAS message may include a flag (1-bit information) indicating whether to provide adjacent cell information. The NAS of the UE100 may notify the AS of the UE100 of the flag information.

[0133] The UE100 that receives the message from the serving cell determines whether the serving cell provides adjacent cell information based on the flag information. Then, in response to determining that the serving cell provides adjacent cell information, the UE100 receives SIBx from the serving cell and obtains the adjacent cell information in SIBx. The UE100 uses the obtained adjacent cell information for the determination in step S5 described above. For example, the UE100 determines whether the cell (adjacent cell) with the highest rank measured at the selected frequency provides the selected network slice based on the obtained adjacent cell information.

[0134] Note that when the UE 100 determines that the serving cell does not provide adjacent cell information, in step S5 described above, based on the cell information received from the cell with the highest rank measured at the selected frequency (adjacent cell), it may be determined whether the cell provides the selected network slice.

[0135] FIG. 21 is a diagram showing an operation according to the fifth embodiment. As a premise of this operation, the gNB 200 may acquire information on network slices (slice information) provided or not provided by each adjacent cell through signaling between gNB-gNB, CU-DU, DU-DU, and / or OAM-gNB. For example, the gNB 200 (CU) may acquire slice information from an adjacent gNB (CU) that manages adjacent cells by means of an Xn message. The gNB 200 (CU) may acquire information on the slices of the cells managed by its own DU by means of an F1 message. Also, the gNB 200 (CU) may set, by means of an F1 message, whether or not the self-cell (the cell managed by the DU) provides the adjacent cell information described below to the DU connected to itself.

[0136] In step S501, the gNB 200 (serving cell) transmits a message indicating whether or not the self-cell (serving cell) provides adjacent cell information indicating the correspondence between the adjacent cell and the network slice provided by the adjacent cell to the UE 100. The UE 100 receives the message.

[0137] In step S502, the UE 100 determines whether the serving cell provides adjacent cell information based on the message received in step S501. Also, the UE 100 may determine whether the gNB 200 (serving cell) broadcasts SIBx based on the SI scheduling information in SIB1 broadcast by the gNB 200 (serving cell). When SIBx is an on-demand SIB transmitted in response to a request from the UE 100, there may be a case where the gNB 200 (serving cell) that provides adjacent cell information has stopped broadcasting SIBx (not broadcasted). Since the SI scheduling information in SIB1 includes an information element indicating whether SIBx is being broadcasted (broadcasted) or the broadcast has been stopped (not broadcasted), the UE 100 may determine whether the gNB 200 (serving cell) broadcasts SIBx based on the said information element.

[0138] If it is determined that the serving cell provides adjacent cell information, in step S503, the UE 100 receives SIBx (OSI) from the serving cell to obtain adjacent cell information, and uses the adjacent cell information in the slice-specific cell reselection procedure (particularly, the determination in step S5). Here, when the 1-bit flag information indicates that the serving cell provides adjacent cell information and the SI scheduling information in SIB1 indicates that SIBx is being broadcasted, the UE 100 may receive SIBx. On the contrary, when the 1-bit flag information indicates that the serving cell provides adjacent cell information but the SI scheduling information in SIB1 indicates that SIBx is not being broadcasted, the UE 100 may request the serving cell to transmit SIBx and then receive SIBx from the serving cell. On the other hand, if it is determined that the serving cell does not provide adjacent cell information, the UE 100 does not have to receive and confirm SIBx (OSI) from the serving cell.

[0139] [Other Embodiments] Each of the above operation flows can be implemented not only separately and independently, but also by combining two or more operation flows. For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0140] In the above embodiments and examples, an example where the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. Also, the base station may be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may be the DU of the IAB node. Also, the user equipment may be the MT (Mobile Termination) of the IAB node.

[0141] A program may be provided to cause a computer to execute each process performed by UE100 or gNB200. The program may be recorded on a computer-readable medium. By 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-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Also, a circuit that executes each process performed by UE100 or gNB200 may be integrated, and at least a part of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0142] As described above, the embodiments have been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

[0143] As used in this disclosure, the terms "based on" and "depending on" do not mean "only based on" or "only depending on" unless otherwise specified. The term "based on" means both "only based on" and "at least partially based on". Similarly, the term "depending on" means both "only depending on" and "at least partially depending on". Also, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from other nodes, or obtaining the information by generating the information. The terms "include", "comprise", and their variants do not mean including only the listed items, and may include only the listed items or may include additional items in addition to the listed items. Also, the term "or" used in this disclosure is not intended to be an exclusive disjunction. Further, any reference to an element 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 in this specification as a convenient way to distinguish between two or more elements. Thus, a reference to a first and a second element does not mean that only two elements can be employed there or that the first element must precede the second element in some form. In this disclosure, for example, when articles are added by translation like a, an, and the in English, these articles are assumed to include a plurality if not otherwise indicated from the context.

[0144] This application claims priority to U.S. Provisional Application No. 63 / 257,659, filed Oct. 20, 2021, the entire content of which is incorporated herein by reference.

[0145] [Appendix] 1. Introduction Based on the discussions in RAN2#115e, the following procedure was agreed upon for slice-specific cell reselection. Agreed matters 2. The following is adopted as the baseline for solution option 4. Using both broadcast and dedicated signals, the "slice information" (single slice or slice group) agreed to be provided to the UE in the previous RAN2 is provided for serving and adjacent frequencies. The following procedures are used for slice-based cell (re)selection in the AS. Step 0: The NAS layer of the UE provides slice information including slice priorities to the AS layer of the UE. Step 1: The AS sorts in order from the slice with the highest priority. Step 2: Select in order from the slice with the highest priority. Step 3: Assign priorities to the frequencies received from the network for the selected slice. Step 4: Perform measurements in order from the frequency with the highest priority (the same as legacy). Step 5: If the cell with the highest rank is appropriate and supports the slice selected in Step 2, camp on the cell and end this operation sequence. Further consideration is required on how the UE determines whether the cell with the highest rank supports the selected slice. Step 6: If there are remaining frequencies, return to Step 4. Step 7: If not reaching the end of the slice list, return to Step 2 (matters requiring further consideration). Step 8: Perform legacy cell reselection.

[0146] 1: Select solution option 4 and proceed with further consideration, that is, resolve matters requiring further consideration, send the necessary LS, and thereby start the draft of the specification CR.

[0147] In this appendix, two matters requiring further consideration in Steps 5 and 7 are described.

[0148] 2. Consideration 2.1. Matters Requiring Further Consideration in Step 5 RAN2 leaves the following items that require further consideration in step 5 as follows. Step 5: If the highest-ranked cell is appropriate and supports the slice selected in step 2, camp on that cell and end this series of operations.

[0149] RAN2 #113bis-e agreed to be consistent with the assumptions of SA2 (homogeneous deployment in TA) as follows. Agreement items (RAN2 #113-bis-e)

[0150] 1: RAN2 is consistent with the SA2 assumption that the support of slices within TA is homogeneous even in Rel-17 (i.e., all cells within TA support the availability of the same slice). If SA2 determines support for heterogeneous deployment, RAN2 can re-examine this.

[0151] Homogeneous deployment means that the permitted slices are always available in all cells within TA. On the other hand, in TR38.832, many problems related to resource shortage have been identified. For example, it is stated that "Problem 4: If the serving cell cannot support the required slice, the serving cell may have to perform a handover to a cell that supports the required slice or release the RRC connection." Therefore, due to high load, the slice may become temporarily unavailable within the cell, which will be applied to homogeneous deployment.

[0152] Finding 1: Even assuming homogeneous deployment, the slice may be unavailable in the cell temporarily.

[0153] In light of Finding 1, a UE in idle / inactive state needs to know whether the highest-ranked cell supports the slice selected in the slice-specific cell reselection procedure, i.e., the items that require further consideration in step 5. At the research stage, it is captured as a conclusion that the UE may be provided with the slice information supported by neighboring cells from the current cell.

[0154] For slice-based cell reselection, the following solutions are recommended as standard operations. To support cell reselection, the RAN can broadcast, in the SI message, the supported slice information of the current cell and neighboring cells, and the cell reselection priority for each slice. Also, the RAN can include slice information (the same information as the agreed slice information in the SI message) in the RRC Release message.

[0155] When the supported slice information of neighboring cells is provided, the UE does not need to obtain the system information of neighboring cells to determine whether the slice supported by the highest-ranked cell is selected during the slice-specific cell reselection procedure. Therefore, it is beneficial in terms of power saving of the UE and rapid completion of cell reselection.

[0156] Finding 2: When the current cell broadcasts the supported slice information of neighboring cells, the UE can use it to determine whether the slice selected by the highest-ranked cell is supported without obtaining the system information of neighboring cells.

[0157] Therefore, similar to the conclusion of the above discussion, the supported slice information of neighboring cells should be broadcast as an option.

[0158] Proposal 1: RAN2 should agree to broadcast, in addition to the agreed slice information (i.e., the mapping of slices and frequency priorities), the supported slice information of neighboring cells by the current cell.

[0159] Proposal 2: RAN2 should agree that the UE determines whether the slice selected by the highest-ranked cell is supported according to the supported slice information as in Proposal 1.

[0160] If Proposal 1 is accepted, the information will be regarded as the PCI (Physical Cell ID) for each supported slice(s). On the other hand, as in Finding 1, considering the same type of deployment, there may be cases where a cell temporarily cannot support a slice(s). Therefore, it is more efficient to broadcast the PCI for each unsupported slice(s).

[0161] Proposal 3: RAN2 should agree that it can provide the UE with the cell ID for each unsupported slice via SIB or RRC Release.

[0162] 2.2. Additional 1-bit information in SIB1 If Proposal 3 is agreed upon, the cell ID(s) that do not support the slice, together with the mapping between the slice and the frequency priority, are provided to the UE from the current cell. As intended in TR38.832, since the neighboring cell information is provided as an option, it is not always broadcast. Also, the neighboring cell information may not follow the latest status, for example, when the non-corresponding slice of the neighboring cell is changed. In these cases, the UE may not be able to accurately determine whether the slice selected by the highest-ranked cell in Step 5 is supported. For example, the intended slice may not actually be supported by the highest-ranked cell. To avoid such situations, the UE may need to always obtain the SIB and check the current status of the highest-ranked cell in Step 5. However, obtaining the SIB takes a long time and consumes the UE's battery, so it is not beneficial. Also, since it takes time to obtain information from the SIB, it is beneficial to use SIB1 to notify whether the cell is broadcasting the information of neighboring cells.

[0163] Finding 3: The corresponding slice information of neighboring cells in Proposal 3 is not always broadcast, nor is it always up-to-date.

[0164] Proposal 4: RAN2 should discuss whether to introduce 1-bit information in SIB1 indicating whether this cell is currently broadcasting neighbor cell information.

[0165] In this case, it is beneficial to introduce broadcasting another 1-bit information in SIB1 to inform the UE whether there are any restrictions on at least one slice currently (e.g., whether the cell has unsupported slices). The UE can know whether the highest-ranked cell has any restrictions on slice support in step 5. Thus, the UE does not always need to obtain the SIB and only needs to receive the SIB when the cell has unsupported slices. Therefore, RAN2 should discuss the additional 1-bit information in SIB1.

[0166] Proposal 5: RAN2 should discuss whether to introduce 1-bit information in SIB1 indicating whether this cell is currently restricting the use of its own slice, e.g., having at least one unsupported slice.

[0167] 2.3. Matters Requiring Further Consideration in Step 7 RAN2 left the matters requiring further consideration in step 7 as follows. Step 7: Matters Requiring Further Consideration: If the end of the slice list has not been reached, return to step 2.

[0168] Similar to Finding 1, it is necessary to consider that the highest-ranked cell may not support the slice selected in step 5. In this case, the UE aims to reselect the cell at the next priority frequency if there are still frequencies remaining, similar to step 6. If the UE cannot reselect any cell for the selected slice, it proceeds to step 7. When step 7 is executed, the UE can select the next priority slice for slice-specific cell reselection.

[0169] Considering that the UE can access multiple slices simultaneously, the number of intended slices provided by the NAS may be one or more. Also, as a result of the legacy cell reselection procedure, it is preferable for the UE to reselect a cell that supports the intended slice compared to a cell that may not support the intended slice, even if the slice priority is not the highest rank. In this sense, it is straightforward that the UE is permitted to select a slice whose priority is not the highest rank.

[0170] Proposal 6: RAN2 should agree that the UE is permitted to select a slice that is not of the highest priority. Therefore, remove the items that require further consideration from Step 7.

Claims

1. A cell reselection method executed by a user device in a mobile communication system, comprising: receiving slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies from a network; assigning priorities to each of the plurality of frequencies based on a predetermined network slice group notified from the NAS layer of the user device; reselecting a candidate cell that meets a predetermined quality criterion based on the priority, wherein the assigning includes, when there is a predetermined frequency that does not support the predetermined network slice group in the slice frequency information, making it less likely to select a cell belonging to the predetermined frequency as a serving cell compared to a cell belonging to a frequency that supports the predetermined network slice group, and assigning the priority to each of the plurality of frequencies; A cell reselection method.

2. The reselection includes: identifying a first candidate cell with the highest radio quality as the candidate cell; when the first candidate cell does not provide the predetermined network slice group, re-identifying the candidate cell within the same frequency as the frequency to which the first candidate cell belongs, wherein a time-related limit is provided for the re-identification. The cell reselection method according to Claim 1.

3. A user device that performs cell reselection in a mobile communication system, comprising: a process of receiving slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies from a network; a process of assigning priorities to each of the plurality of frequencies based on a predetermined network slice group notified from the NAS layer of the user device; A processor that executes a process of reselecting a candidate cell that satisfies a predetermined quality standard based on the priority. The allocating process includes allocating the priority to each of the plurality of frequencies such that when a predetermined frequency that does not support the predetermined network slice group exists in the slice frequency information, it is less likely to select a cell belonging to the predetermined frequency as a serving cell than a cell belonging to a frequency that supports the predetermined network slice group. User equipment. **Claim 4** A chipset for a user equipment that performs cell reselection in a mobile communication system, a process of receiving from a network slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies, a process of allocating a priority to each of the plurality of frequencies based on a predetermined network slice group notified from the NAS layer of the user equipment, executing a process of reselecting a candidate cell that satisfies a predetermined quality standard based on the priority, The allocating process includes allocating the priority to each of the plurality of frequencies such that when a predetermined frequency that does not support the predetermined network slice group exists in the slice frequency information, it is less likely to select a cell belonging to the predetermined frequency as a serving cell than a cell belonging to a frequency that supports the predetermined network slice group. Chipset. **Claim 5** In a user equipment that performs cell reselection in a mobile communication system, a process of receiving from a network slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies, a process of allocating a priority to each of the plurality of frequencies based on a predetermined network slice group notified from the NAS layer of the user equipment, Execute a process of reselecting candidate cells that meet a predetermined quality standard based on the priority. The process of assignment includes, when there is a predetermined frequency that does not support the predetermined network slice group in the slice frequency information, assigning the priority to each of the plurality of frequencies so that it is less likely to select a cell belonging to the predetermined frequency as a serving cell compared to a cell belonging to a frequency that supports the predetermined network slice group. Program. Claim 6 A mobile communication system including a user equipment, wherein the user equipment, receives from a network slice frequency information indicating a plurality of frequencies and network slice groups supported by each of the plurality of frequencies, assigns a priority to each of the plurality of frequencies based on a predetermined network slice group notified from the NAS layer of the user equipment, reselects candidate cells that meet a predetermined quality standard based on the priority, and when there is a predetermined frequency that does not support the predetermined network slice group in the slice frequency information, the user equipment assigns the priority to each of the plurality of frequencies so that it is less likely to select a cell belonging to the predetermined frequency as a serving cell compared to a cell belonging to a frequency that supports the predetermined network slice group. Mobile communication system.

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